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Certified_RS_ApprovedAvana Ridge Drainage TIR U15008868_PR16000004.pdf
© 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report (TIR) for AVANA RIDGE PUD 10615 SE 172nd Street Renton, Washington ___________________________________________________________________________ DRS Project No. 15088 Renton File No. C15008868 Owner/Applicant Avana Ridge, LLC 9725 SE 36th Street, Suite 214 Mercer Island, Washington 98040 Report Prepared by D. R. STRONG Consulting Engineers, Inc. 620 7th Avenue Kirkland WA 98033 (425) 827-3063 Report Revision Date March 23, 2017 Report Issue Date October 28, 2016 2015 D. R. STRONG Consulting Engineers Inc. i Avana Ridge Technical Information Report Renton, Washington TECHNICAL INFORMATION REPORT AVANA RIDGE PUD TABLE OF CONTENTS SECTION I .............................................................................................................................................. 1 PROJECT OVERVIEW: ...................................................................................................................... 1 PREDEVELOPED SITE CONDITIONS:............................................................................................... 1 DEVELOPED SITE CONDITIONS: ...................................................................................................... 1 NATURAL DRAINAGE SYSTEM FUNCTIONS: ................................................................................... 3 FIGURE 1. TIR WORKSHEET ....................................................................................................... 4 FIGURE 2. VICINITY MAP ............................................................................................................. 9 FIGURE 3. DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERISTICS ........................ 10 FIGURE 4. SOILS ........................................................................................................................ 11 SECTION II ........................................................................................................................................... 14 CONDITIONS AND REQUIREMENTS SUMMARY ............................................................................ 14 SECTION III .......................................................................................................................................... 17 OFF-SITE ANALYSIS ....................................................................................................................... 17 SECTION IV.......................................................................................................................................... 18 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN................................ 18 EXISTING SITE HYDROLOGY ......................................................................................................... 18 FIGURE 5. PREDEVELOPMENT AREA MAP ............................................................................. 19 DEVELOPED SITE HYDROLOGY .................................................................................................... 20 FIGURE 6. POST DEVELOPMENT AREA MAP ................................................................................ 22 PERFORMANCE STANDARDS ........................................................................................................ 23 FLOW CONTROL SYSTEM .............................................................................................................. 23 FIGURE 7. DETENTION & WATER QUALITY FACILITY DETAILS ............................................. 30 SECTION V........................................................................................................................................... 31 CONVEYANCE SYSTEM ANALYSIS AND DESIGN .......................................................................... 31 BACKWATER ANALYSIS ................................................................................................................. 34 FIGURE 8. BACKWATER ANALYSIS MAP ................................................................................. 36 FIGURE 9. UPSTREAM BACKWATER ANALYSIS MAP ............................................................. 37 BACKWATER ANALYSIS RESULTS ................................................................................................ 38 UPSTREAM BACKWATER ANALYSIS RESULTS ............................................................................ 44 SECTION VI.......................................................................................................................................... 49 SPECIAL REPORTS AND STUDIES ................................................................................................. 49 SECTION VII......................................................................................................................................... 50 OTHER PERMITS, VARIANCES AND ADJUSTMENTS .................................................................... 50 SECTION VIII........................................................................................................................................ 51 SECTION IX.......................................................................................................................................... 53 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ...................... 53 STORMWATER FACILITY SUMMARY SHEET ................................................................................. 54 SECTION X........................................................................................................................................... 55 OPERATIONS AND MAINTENANCE MANUAL ................................................................................. 55 APPENDIX “A” OFFSITE ANALYSIS .................................................................................................. 65 APPENDIX “B” CSWPPP ..................................................................................................................... 66 2015 D. R. STRONG Consulting Engineers Inc. ii Avana Ridge Technical Information Report Renton, Washington APPENDIX “C” BOND QUANTITY WORKSHEET ............................................................................... 67 APPENDIX “D” COVENANTS .............................................................................................................. 68 2015 D. R. STRONG Consulting Engineers Inc. 1 Avana Ridge Technical Information Report Renton, Washington SECTION I PROJECT OVERVIEW: The applicant is seeking approval to construct 74 apartment units, surface parking, and amenities on 3.78 acres (Parcel Number 2923059009 ) (Project). The Project is located at 10615 SE 172nd Street in Renton, Washington. PREDEVELOPED SITE CONDITIONS: Total site area is approximately 164,827 s.f. (3.78 acres) (Site). The Parcel is currently undeveloped and is heavily forested with moderate underbrush. The predeveloped Site is contained within one Threshold Discharge Area (TDA). The TDA has two Natural Discharge Areas (NDAs), NDA 1 and NDA 2. Runoff from NDA 1 discharges at the Site’s western property line (south of NDA 2) and heads north through the conveyance system in Benson Drive S, where it meets NDA 2. NDA 2 discharges across the western property line (north of NDA1). Flow from both NDAs eventually crosses under Benson Road S in a westerly direction. Runoff outlets into a ditch between parcels 2923059150 and 2923059134, flowing west. Before reaching Cedar Ave S, flow is conveyed into a system of pipes and catch basins and continues west along S 36th Street. Runoff is conveyed south between parcels 1441000150 and 1441000170 before moving west – parallel to S 36th Street along the south side of the parcels. Runoff crosses under Wells Ave S and outfalls into parcel 144100TRCT – a tract for an adjacent development. Based on available topography, runoff sheet flows west through the tract into another tract (810630TRCT). Runoff appears to continue into a pond in parcel 8106301170. Overflow from the pond travels southwest to Morris Ave S, where it continues south. Runoff continues south, crossing under S 38th Ct and eventually outfalling into Panther Creek. Panther Creek flows north and eventually becomes a tributary for Black River and the Duwamish River. DEVELOPED SITE CONDITIONS: The applicant is seeking approval to construct a 74-unit apartment complex on 3.78 acres (Project). The developable area (Project Area) is approximately 159,574 s.f. (3.66 acres) (excludes right-of-way dedication area and area of the identified stream from the gross Site area). The total area of work is 177,211 s.f. (4.068 acres) which includes all work within the right-of-way (full overlay). The total disturbed area for the project is 150,138 s.f. (3.447 acres). This total disturbed area includes 19,795 s.f. of open space area that will be fully dispersed. Per Section 1.2.3.1.B of the City of Renton 2009 SWDM Amendment, new impervious and pervious surfaces that are not fully dispersed are considered a target surface. Therefore, this open space area has been excluded from the predeveloped area figure and areabreakdown. The total target area for the project equals 130,343 s.f. (2.99 acres). 2015 D. R. STRONG Consulting Engineers Inc. 2 Avana Ridge Technical Information Report Renton, Washington A total of 69,089 S.F. of impervious area is proposed for the Site – which is less than 75 percent of total Site Area (123,620 S.F.). The remainder of the Project Area will consist of residential landscaping and other pervious surfaces. Per Section 5.2.1 of the 2009 King County Surface Water Design Manual (Manual), projects are required to mitigate for impervious surface by use of Flow Control Best Management Practices (BMP’s). The Project falls within the “Large Lot High Impervious” category, as the proposed impervious is approximately 40% of the total Site area and the total project area is larger than 22,000 SF. However, to meet the intent of the Manual, we have analyzed the impervious surface percentage based upon the developable area as approximately one acre (44,646 s.f. of stream buffer) of the site is encumbered by sensitive areas. With 1.59 acres of the 2.64 acres of developable area categorized as impervious (60%), it would be prudent to analyze the Project as “Large Lot High Impervious”. For projects that will result in an impervious surface coverage of more than 45% up to 65%, flow control BMPs must be applied to an impervious area equal to at least 20% of the [developable] lot area or 40% of the proposed impervious area, whichever is less; 31,915 s.f. (0.2 x 159,574) and 27,636 s.f. (0.4 x 69,089), respectively. Projects are required to first analyze the feasibility of dispersal and infiltration before choosing another method. The soils investigation summarized by the project geotechnical report are confined to the upper layers (up to 12 feet deep) of Site soils. That report indicates the presence of glacial till not conducive to full infiltration. The Project proposes to utilize limited infiltration, by drywells, for both buildings (approximately 26,659 s.f.) as depicted on the storm drainage plans. The Project will also utilize full dispersion for the open space area (approximately 4,685 s.f. of impervious area) as depicted on the storm drainage plans. The Project is proposing to collect existing non-targeted impervious area as a mitigation trade for the uncollectable portion of the frontage improvements in Benson Drive and Benson Road. The mitigation trade area is within both SE 172nd Street and Benson Road as shown in the Post-Developed Area Figure. The Project is located within a Flow Control Duration Standard Matching Forested Site Conditions and Basic Water Quality Area. However due to the fact that the Project is a multifamily development, it shall be required to adhere to the Enhanced Water Quality Treatment criteria. Per Section 1.2.8.1.A of the City of Renton SWDM Amendments, the Enhanced Water Quality Treatment requirement may be reduced to the Basic Water Quality requirement for this Project because no leachable metals will be used in areas of the site exposed to the weather and a covenant will be recorded that prohibits the future use of leachable metals on the site. Runoff will be collected and conveyed to a detention vault at the west end of the Site. The vault will be followed by a media filtration system (StormFilter) to accommodate the Basic Water Quality Treatment requirements. 2015 D. R. STRONG Consulting Engineers Inc. 3 Avana Ridge Technical Information Report Renton, Washington NATURAL DRAINAGE SYSTEM FUNCTIONS: A portion of the Natural Resource Conservation Service (NRCS) soil survey of King County is included as Figure 4 and indicates the presence of Alderwood gravelly sandy loam with 8 to 15 percent slopes (AgC). Per the 2009 King County Surface Water Design Manual, this soil type is classified as “Till” material. The Natural Re Soil series descriptions follow Figure 4. The upstream basin area was evaluated by examining the King County topographic map, City of Renton Mapping Application and by conducting field reconnaissance on December 15, 2015 under overcast conditions. Upstream runoff enters the Site in two locations. Portions of SE 172nd St and 106th Ave SE direct upstream runoff across the northern property line. Runoff from 106th Ave SE and the north side of SE 172nd St. enters a Type 1 catch basin at the intersection of these two streets. An 18-inch diameter concrete pipe conveys runoff south under SE 172nd St. and outfalls onto the Site. Runoff from the southern portion of SE 172nd St is intercepted by a ditch along the south side of SE 172nd St. and enters the Site where the previously mentioned 18-inch diameter concrete pipe outlets. Upstream runoff from the west side of Benson Rd S flows west into a ditch along the east property line. This ditch conveys upstream runoff southwest along the east property line until it enters a stream about halfway down the property line. This stream conveys water through the Site. The Project proposes to construct a conveyance system to collect runoff from these two upstream tributary areas and bypass the detention facility on Site. See Section V for the upstream bypass conveyance analysis. 2015 D. R. STRONG Consulting Engineers Inc. 4 Avana Ridge Technical Information Report Renton, Washington FIGURE 1. TIR WORKSHEET King County Department of Development and Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner: Avana Ridge, LLC Phone: (425) 588-1147 Address: 9675 SE 36th Street, Suite 105 Mercer Island, WA 98040 Project Engineer: Maher Joudi, P.E. Company: D. R. STRONG Consulting Engineers Inc. Phone: (425) 827-3063 Project Name: Avana Ridge DDES Permit#: N/A Location: Township: 23 North Range: 05 East Section: 29 Site Address: 10615 SE 172nd Street Renton, Washington Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Landuse Services Subdivision/ Short Subd. PUD Building Services M/F / Commercial / SFR Clearing and Grading Right-of-Way Other: DFW HPA Shoreline Management COE 404 Structural DOE Dam Safety Rockery/Vault/Wall FEMA Floodplain ESA Section 7 COE Wetlands Other: Part 5 PLAN AND REPORT INFORMATION Technical Information Report Drainage Review Type Full / Targeted / Large (circle one): Site Date (include revision October 28, 2016 dates): Date of Final: Site Improvement Plan (Engr. Plans) Type Full / Targeted / Small (circle one): Site Date (include revision October 27, 2016 dates): Date of Final: Part 6 ADJUSTMENT APPROVALS Type (circle one): Standard / Complex / Preapplication / Experimental / Blanket Description: (include conditions in TIR Section 2) _____________________________________________________________________________________ _____________________________________________________________________________________ ____________________________________________________________________________________ Date of Approval: 2015 D. R. STRONG Consulting Engineers Inc. 5 Avana Ridge Technical Information Report Renton, Washington Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes/ No Start Date: Completion Date Describe: __________________________ ___________________________________ ___________________________________ ___________________________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: Soos Creek Special District Overlays: N/A Drainage Basin: Black River, Panther Creek Sub-Basin Stormwater Requirements: Flow Control Duration Standard Matching Forested Site Conditions, Enhanced WQ Treatment Menu reduced to Basic WQ Treatment Menu Part 9 ONSITE AND ADJACENT SENSITIVE AREAS River/ Stream Unnamed Type Ns stream Lake Wetlands: Closed Depression Floodplain Other Steep Slope Erosion Hazard Landslide Hazard Coal Mine Hazard (High) Seismic Hazard Habitat Protection Part 10 SOILS Soil Type _________AGC____ _________________ _________________ Slopes ________8-15%____ _________________ _________________ Erosion Potential Slight to Moderate _________________ _________________ High Groundwater Table (within 5 feet) Sole Source Aquifer other Low infiltration rate Seeps/Springs Additional Sheets Attached 2015 D. R. STRONG Consulting Engineers Inc. 6 Avana Ridge Technical Information Report Renton, Washington Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis Sensitive / Critical Area SEPA Other LIMITATION / SITE CONSTRAINT None Stream and associated buffers through Site None Additional Sheet attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: Site comprised of single, unnamed TDA (name or description) Core Requirements (all 8 apply) Discharge of Natural Location yes Number of Natural Discharge Locations: 2 Offsite Analysis Level: 1 / 2 / 3 dated: 12/15/2015 Flow Control Level: 1 / 2 / 3 or Exemption Number (incl. facility summary sheet Small Site BMPS N/A Conveyance System Spill containment located at: Detention facility Erosion and Sediment Control ESC Site Supervisor: T/B/D Contact Phone: T/B/D After Hours Phone: T/B/D Maintenance and Operation Responsibility: Private / Public (Both) If Private, Maintenance Log Required: Yes / No Financial Guarantees and Provided: Yes / No Liability Water Quality Type: Basic / Sens Lake / Enhanced Basic / Bog (include facility summary sheet) or exemption No. Landscape Management Plan: Yes / No Special Requirements (as applicable) Area Specific Drainage Type: CDA / SDO / MDP / BP / LMP / Shared / None Requirements Name: Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): Datum: Flood Protection Facilities Describe: N/A Source Control Describe Landuse: Multi Family (comm. / industrial landuse) Describe any structural controls: covered trash storage, Oil Control High-use Site: Yes / No Treatment BMP: Maintenance Agreement: Yes / No with whom? Other Drainage Structures Describe: N/A 2015 D. R. STRONG Consulting Engineers Inc. 7 Avana Ridge Technical Information Report Renton, Washington Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Clearing Limits Cover Measures Perimeter Protection Traffic Area Stabilization Sediment Retention Surface Water Collection Dewatering Control Dust control Flow Control MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize Exposed Surfaces Remove and Restore Temporary ESC Facilities Clean and Remove All Silt and Debris, Ensure Operations of Permanent Facilities Flag Limits of SAO and open space Preservation areas Other Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch Flow Control Type/Description Water Quality Type/Description Detention Infiltration Regional Facility Shared Facility Flow Control BMPs Other Vault Dispersion, Dry well Biofiltration Wetpool Media Filtration Oil Control Spill Control Flow Control BMPs Other Contech StormFilter See flow control Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS Drainage Easement Covenant Native Growth Protection Covenant Tract Other: Cast in Place Vault Retaining Wall Rockery > 4’ High Structural on Steep Slope Other: ” 2015 D. R. STRONG Consulting Engineers Inc. 8 Avana Ridge Technical Information Report Renton, Washington Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. Signed/Date 2015 D. R. STRONG Consulting Engineers Inc. 9 Avana Ridge Technical Information Report Renton, Washington FIGURE 2. VICINITY MAP SITE 2015 D. R. STRONG Consulting Engineers Inc. 10 Avana Ridge Technical Information Report Renton, Washington FIGURE 3. DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERISTICS GRAPHIC SCALE040801201 INCH = 80 FT. 2015 D. R. STRONG Consulting Engineers Inc. 11 Avana Ridge Technical Information Report Renton, Washington FIGURE 4. SOILS King County Area, Washington AgC—Alderwood gravelly sandy loam, 8 to 15 percent slopes Map Unit Setting • National map unit symbol: 2t626 • Elevation: 50 to 800 feet • Mean annual precipitation: 20 to 60 inches • Mean annual air temperature: 46 to 52 degrees F • Frost-free period: 160 to 240 days • Farmland classification: Prime farmland if irrigated Map Unit Composition • Alderwood and similar soils: 85 percent • Minor components: 15 percent • Estimates are based on observations, descriptions, and transects of the mapunit. SITE 2015 D. R. STRONG Consulting Engineers Inc. 12 Avana Ridge Technical Information Report Renton, Washington Description of Alderwood Setting • Landform: Ridges, hills • Landform position (two-dimensional): Shoulder • Landform position (three-dimensional): Nose slope, talf • Down-slope shape: Linear, convex • Across-slope shape: Convex • Parent material: Glacial drift and/or glacial outwash over dense glaciomarine deposits Typical profile • A - 0 to 7 inches: gravelly sandy loam • Bw1 - 7 to 21 inches: very gravelly sandy loam • Bw2 - 21 to 30 inches: very gravelly sandy loam • Bg - 30 to 35 inches: very gravelly sandy loam • 2Cd1 - 35 to 43 inches: very gravelly sandy loam • 2Cd2 - 43 to 59 inches: very gravelly sandy loam Properties and qualities • Slope: 8 to 15 percent • Depth to restrictive feature: 20 to 39 inches to densic material • Natural drainage class: Moderately well drained • Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) • Depth to water table: About 18 to 37 inches • Frequency of flooding: None • Frequency of ponding: None • Available water storage in profile: Very low (about 2.7 inches) Interpretive groups • Land capability classification (irrigated): None specified • Land capability classification (nonirrigated): 4s • Hydrologic Soil Group: B • Other vegetative classification: Limited Depth Soils (G002XN302WA), Limited Depth Soils (G002XS301WA), Limited Depth Soils (G002XF303WA) Minor Components Everett • Percent of map unit: 5 percent • Landform: Eskers, kames, moraines • Landform position (two-dimensional): Shoulder, footslope • Landform position (three-dimensional): Crest, base slope • Down-slope shape: Convex • Across-slope shape: Convex Indianola • Percent of map unit: 5 percent • Landform: Eskers, kames, terraces • Landform position (three-dimensional): Tread • Down-slope shape: Linear • Across-slope shape: Linear 2015 D. R. STRONG Consulting Engineers Inc. 13 Avana Ridge Technical Information Report Renton, Washington Shalcar • Percent of map unit: 3 percent • Landform: Depressions • Landform position (three-dimensional): Dip • Down-slope shape: Concave • Across-slope shape: Concave Norma • Percent of map unit: 2 percent • Landform: Depressions, drainageways • Landform position (three-dimensional): Dip • Down-slope shape: Concave, linear • Across-slope shape: Concave 2015 D. R. STRONG Consulting Engineers Inc. 14 Avana Ridge Technical Information Report Renton, Washington SECTION II CONDITIONS AND REQUIREMENTS SUMMARY The Project must comply with the following Core and Special Requirements: • C.R. #1 – Discharge at the Natural Location: Runoff from the Site will discharge at the natural location. • C.R. #2 – Offsite Analysis: An Offsite Analysis is included in Appendix A. The Analysis describes the Site’s runoff patterns in detail. • C.R. #3 – Flow Control: The Project is located in a Flow Control Duration Standard Matching Forested Site Conditions Area. A detention vault will provide flow control consistent with that standard. The Project is required to “match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the two-year peak flow up to the full 50-year peak flow. Also match developed peak discharge rates to predeveloped peak discharge rates for the 2- and the 10-year return periods. Assum(ing) historic conditions as the predeveloped condition.” (KCSWDM, Sec. 1.2) Final detention vault sizing is included in Section IV. Per Section 5.2.1 of the 2009 King County Surface Water Design Manual (Manual), projects are required to mitigate for impervious surface by use of Flow Control Best Management Practices (BMP’s). The Project falls within the “Large Lot High Impervious” category, as the proposed impervious is approximately 40% of the total Site area and the total project area is larger than 22,000 SF. However, to meet the intent of the Manual, we have analyzed the impervious surface percentage based upon the developable area as approximately one acre (44,646 s.f. of stream buffer) of the site is encumbered by sensitive areas. With 1.59 acres of the 2.64 acres of developable area categorized as impervious (60%), it would be prudent to analyze the Project as “Large Lot High Impervious”. For projects that will result in an impervious surface coverage of more than 45% up to 65%, flow control BMPs must be applied to an impervious area equal to at least 20% of the [developable] lot area or 40% of the proposed impervious area, whichever is less; 31,915 s.f. and 27,636 s.f., respectively. Projects are required to first analyze the feasibility of dispersal and infiltration before choosing another method. The soils investigation summarized by the project geotechnical report are confined to the upper layers (up to 12 feet deep) of Site soils. That report indicates the presence of glacial till not conducive to full infiltration. The Project proposes to utilize limited infiltration in gravelly sandy loam soil, by drywells, for both buildings (approximately 26,659 s.f.) as depicted on the storm drainage plans. See sizing information below. These drywells will be located underneath the parking lot and have a safe overall pipe routed to storm conveyance system as depicted on the storm drainage plans. The Project will also utilize full dispersion for the open space area (approximately 4,685 s.f. of impervious area) as depicted on the storm drainage plans. 2015 D. R. STRONG Consulting Engineers Inc. 15 Avana Ridge Technical Information Report Renton, Washington Drywell Building Served Tributary Area Top of Drywell Bottom of Drywell S.A. of Drywell Volume of Drywell D1 East 13659 374 370 1300 5200 D2 West 13000 368 364 1275 5100 Stormwater Flow Control BMP Drywell Table • C.R. #4 – Conveyance System: New pipe systems and ditches/channels are required to be designed with sufficient capacity to convey and contain (with minimum 6-inches of freeboard) the 25-year peak flow, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. Pipe system structures and ditches/channels may overtop for runoff events that exceed the 25-year design capacity, provided the overflow from a 100-year runoff event does not create or aggravate a “severe flooding problem” or “severe erosion problem” as defined in C.R. #2. Any overflow occurring onsite for runoff events up to and including the 100-year event must discharge at the natural location for the project site. In residential subdivisions, such overflow must be contained within an onsite drainage easement, tract, covenant or public right-of-way. The proposed conveyance system will be analyzed using the KCBW program to determine if the proposed conveyance system is capable of conveying the 100-year peak storm without overtopping any structures or channels. This analysis was performed and is included in Section V. • C.R. #5 – Erosion and Sediment Control: The Project provides the nine minimum ESC measures. • C.R. #6 – Maintenance and Operations: Maintenance of the proposed detention facility, StormFilter, and Flow Control BMPs will be the responsibility of the HOA. An Operation and Maintenance Manual is included in Section X. • C.R. #7 – Financial Guarantees: Prior to commencing construction, the Applicant must post a drainage facilities restoration and site stabilization financial guarantee. For any constructed or modified drainage facilities to be maintained and operated by the City, the Applicant must: 1) Post a drainage defect and maintenance financial guarantee for a period of two years, and 2) Maintain the drainage facilities during the two-year period following posting of the drainage defect and maintenance financial guarantee. • C.R. #8 - The Project is located in the Enhanced Water Quality Treatment area, but is able to reduce the requirement to Basic Water Quality as discussed above in Section I under Developed Site Conditions. A detention vault will be followed by a StormFilter media filtration system to meet water quality requirements. • S.R. #1 – Other Adopted Area-Specific Requirements: Not applicable for this Project. • S.R. #2 – Floodplain/Floodway Delineation: Not applicable for this Project. • S.R. #3 – Flood Protection Facilities: Not applicable for this Project. • S.R. #4 – Source Control: The project shall comply with the 2009 Stormwater Pollution Prevention Manual with such measures as cleaning of the storm drain 2015 D. R. STRONG Consulting Engineers Inc. 16 Avana Ridge Technical Information Report Renton, Washington system, prohibiting illicit connections to the storm drainage system and stenciling the site storm drains among other BMP’s. • S.R. #5 – Oil Control: Not applicable to this project. • S.R. #6 – Aquifer Protection Area: Not applicable for this project. 2015 D. R. STRONG Consulting Engineers Inc. 17 Avana Ridge Technical Information Report Renton, Washington SECTION III OFF-SITE ANALYSIS A Level One Downstream Analysis was prepared by D.R. STRONG Consulting Engineers Inc. and is included in Appendix A. 2015 D. R. STRONG Consulting Engineers Inc. 18 Avana Ridge Technical Information Report Renton, Washington SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN The continuous simulation model, the King County Runoff Time Series, KCRTS, was used to analyze the pre and post developed runoff rates. Per Table 3.2.2.b of the Manual, the soil type is modeled as “Till” for the Alderwood gravelly sandy loam SCS classification as shown in Figure 4. Soils. Results of the KCRTS analysis are included in this section. EXISTING SITE HYDROLOGY Modeling input Hourly Time Series Predev.tsf Impervious 0.000 Till Grass 0.000 Pre-Developed Conditions 2.990 Till Forest 2.990 Wetland 0.000 Time Step: Scale Factor:1.000 Rainfall Gage Seatac Total Area: Land cover Acres Data Type:Reduced Modeling results Flow Frequency Analysis Time Series File:predev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.188 2 2/09/01 18:00 0.241 1 100.00 0.990 0.051 7 1/06/02 3:00 0.188 2 25.00 0.960 0.140 4 2/28/03 3:00 0.145 3 10.00 0.900 0.005 8 3/24/04 20:00 0.140 4 5.00 0.800 0.083 6 1/05/05 8:00 0.122 5 3.00 0.667 0.145 3 1/18/06 21:00 0.083 6 2.00 0.500 0.122 5 11/24/06 4:00 0.051 7 1.30 0.231 0.241 1 1/09/08 9:00 0.005 8 1.10 0.091 Computed Peaks 0.223 50.00 0.980 Ex. 2yr Q = 0.083 cfs Ex. 10yr Q = 0.145 cfs 2015 D. R. STRONG Consulting Engineers Inc. 19 Avana Ridge Technical Information Report Renton, Washington FIGURE 5. PREDEVELOPMENT AREA MAP GRAPHIC SCALE040801601 INCH = 80 FT. 2015 D. R. STRONG Consulting Engineers Inc. 20 Avana Ridge Technical Information Report Renton, Washington DEVELOPED SITE HYDROLOGY Soil type The soil types are unchanged from pre-developed conditions. Land covers KCRTS was used to model the developed peak runoff from the Site. The portions of the Site within the proposed clearing limits tributary to the proposed detention vault were modeled as “Till Grass” and Impervious as appropriate. Results of the KCRTS analysis are included in this section. Modeling input Time Step:Hourly Time Series Rdin.tsf Impervious 1.722 2.695 Till Grass 0.973 Wetland 0.000 Till Forest 0.000 Reduced Post-Developed Conditions Scale Factor:1.000 Rainfall Gage Seatac Total Area: Land cover Acres Data Type: Modeling results Flow Frequency Analysis Time Series File:rdin.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.504 6 2/09/01 2:00 1.02 1 100.00 0.990 0.412 8 1/05/02 16:00 0.650 2 25.00 0.960 0.606 3 2/27/03 7:00 0.606 3 10.00 0.900 0.447 7 8/26/04 2:00 0.538 4 5.00 0.800 0.538 4 10/28/04 16:00 0.536 5 3.00 0.667 0.536 5 1/18/06 16:00 0.504 6 2.00 0.500 0.650 2 10/26/06 0:00 0.447 7 1.30 0.231 1.02 1 1/09/08 6:00 0.412 8 1.10 0.091 Computed Peaks 0.896 50.00 0.980 2015 D. R. STRONG Consulting Engineers Inc. 21 Avana Ridge Technical Information Report Renton, Washington BYPASS AREA HYDROLOGY Modeling input 0.294 Impervious 0.003 Data Type:Reduced Wetland 0.000 Till Grass 0.291 Bypass Area Time Step:Hourly Scale Factor:1.000 Rainfall Gage Seatac Time Series Bypass.tsf Total Area: Till Forest 0.000 Land cover Acres Modeling results Flow Frequency Analysis Time Series File:bypass.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.027 4 2/09/01 2:00 0.063 1 100.00 0.990 0.014 7 1/05/02 16:00 0.034 2 25.00 0.960 0.034 2 2/27/03 7:00 0.027 3 10.00 0.900 0.006 8 8/26/04 2:00 0.027 4 5.00 0.800 0.015 6 1/05/05 8:00 0.025 5 3.00 0.667 0.027 3 1/18/06 16:00 0.015 6 2.00 0.500 0.025 5 11/24/06 3:00 0.014 7 1.30 0.231 0.063 1 1/09/08 6:00 0.006 8 1.10 0.091 COMPUTED PEAKS 0.053 50.00 0.980 2015 D. R. STRONG Consulting Engineers Inc. 22 Avana Ridge Technical Information Report Renton, Washington FIGURE 6. POST DEVELOPMENT AREA MAP GRAPHIC SCALE040801601 INCH = 80 FT. 2015 D. R. STRONG Consulting Engineers Inc. 23 Avana Ridge Technical Information Report Renton, Washington PERFORMANCE STANDARDS The Project is located in a Flow Control Duration Standard Matching Forested Site Conditions Area and will therefore adhere to Level 2 Flow Control Standards, forested conditions. A detention vault will provide flow control as required. The Project is required to “match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the two-year peak flow up to the full 50-year peak flow. Also match developed peak discharge rates to predeveloped peak discharge rates for the 2 and the 10 year return periods. Assum(ing) historic conditions as the predeveloped condition.” (KCSWDM, Sec. 1.2). FLOW CONTROL SYSTEM Retention/Detention Facility Type of Facility: Detention Vault Facility Length: 188.00 ft Facility Width: 15.70 ft Facility Area: 2952. sq. ft Effective Storage Depth: 11.50 ft Stage 0 Elevation: 349.50 ft Storage Volume: 33943. cu. ft Riser Head: 11.50 ft Riser Diameter: 18.00 inches Number of orifices: 3 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 0.70 0.045 2 7.50 1.40 0.106 4.0 3 11.00 0.92 0.016 4.0 Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) 0.00 349.50 0. 0.000 0.000 0.00 0.01 349.51 30. 0.001 0.002 0.00 0.02 349.52 59. 0.001 0.002 0.00 0.03 349.53 89. 0.002 0.002 0.00 0.04 349.54 118. 0.003 0.003 0.00 0.05 349.55 148. 0.003 0.003 0.00 0.06 349.56 177. 0.004 0.003 0.00 0.28 349.78 826. 0.019 0.007 0.00 0.51 350.01 1505. 0.035 0.009 0.00 0.73 350.23 2155. 0.049 0.011 0.00 0.96 350.46 2834. 0.065 0.013 0.00 1.19 350.69 3512. 0.081 0.014 0.00 1.41 350.91 4162. 0.096 0.016 0.00 1.64 351.14 4841. 0.111 0.017 0.00 1.86 351.36 5490. 0.126 0.018 0.00 2.09 351.59 6169. 0.142 0.019 0.00 2.31 351.81 6818. 0.157 0.020 0.00 2.54 352.04 7497. 0.172 0.021 0.00 2.76 352.26 8146. 0.187 0.022 0.00 2015 D. R. STRONG Consulting Engineers Inc. 24 Avana Ridge Technical Information Report Renton, Washington 2.99 352.49 8825. 0.203 0.023 0.00 3.22 352.72 9504. 0.218 0.024 0.00 3.44 352.94 10154. 0.233 0.025 0.00 3.67 353.17 10832. 0.249 0.025 0.00 3.89 353.39 11482. 0.264 0.026 0.00 4.12 353.62 12161. 0.279 0.027 0.00 4.34 353.84 12810. 0.294 0.028 0.00 4.57 354.07 13489. 0.310 0.028 0.00 4.79 354.29 14138. 0.325 0.029 0.00 5.02 354.52 14817. 0.340 0.030 0.00 5.24 354.74 15466. 0.355 0.030 0.00 5.47 354.97 16145. 0.371 0.031 0.00 5.70 355.20 16824. 0.386 0.032 0.00 5.92 355.42 17473. 0.401 0.032 0.00 6.15 355.65 18152. 0.417 0.033 0.00 6.37 355.87 18802. 0.432 0.033 0.00 6.60 356.10 19481. 0.447 0.034 0.00 6.82 356.32 20130. 0.462 0.035 0.00 7.05 356.55 20809. 0.478 0.035 0.00 7.27 356.77 21458. 0.493 0.036 0.00 7.50 357.00 22137. 0.508 0.036 0.00 7.51 357.01 22167. 0.509 0.037 0.00 7.53 357.03 22226. 0.510 0.038 0.00 7.54 357.04 22255. 0.511 0.040 0.00 7.56 357.06 22314. 0.512 0.043 0.00 7.57 357.07 22344. 0.513 0.047 0.00 7.59 357.09 22403. 0.514 0.051 0.00 7.60 357.10 22432. 0.515 0.054 0.00 7.62 357.12 22491. 0.516 0.055 0.00 7.63 357.13 22521. 0.517 0.056 0.00 7.86 357.36 23200. 0.533 0.069 0.00 8.08 357.58 23849. 0.547 0.078 0.00 8.31 357.81 24528. 0.563 0.086 0.00 8.53 358.03 25177. 0.578 0.093 0.00 8.76 358.26 25856. 0.594 0.099 0.00 8.98 358.48 26505. 0.608 0.104 0.00 9.21 358.71 27184. 0.624 0.110 0.00 9.43 358.93 27834. 0.639 0.114 0.00 9.66 359.16 28512. 0.655 0.119 0.00 9.89 359.39 29191. 0.670 0.124 0.00 10.11 359.61 29841. 0.685 0.128 0.00 10.34 359.84 30520. 0.701 0.132 0.00 10.56 360.06 31169. 0.716 0.136 0.00 10.79 360.29 31848. 0.731 0.140 0.00 11.00 360.50 32468. 0.745 0.143 0.00 11.01 360.51 32497. 0.746 0.143 0.00 11.02 360.52 32527. 0.747 0.144 0.00 11.03 360.53 32556. 0.747 0.145 0.00 11.04 360.54 32586. 0.748 0.147 0.00 11.05 360.55 32615. 0.749 0.148 0.00 11.06 360.56 32645. 0.749 0.150 0.00 11.07 360.57 32674. 0.750 0.150 0.00 11.08 360.58 32704. 0.751 0.151 0.00 11.30 360.80 33353. 0.766 0.161 0.00 11.50 361.00 33943. 0.779 0.167 0.00 11.60 361.10 34239. 0.786 0.632 0.00 11.70 361.20 34534. 0.793 1.480 0.00 2015 D. R. STRONG Consulting Engineers Inc. 25 Avana Ridge Technical Information Report Renton, Washington 11.80 361.30 34829. 0.800 2.580 0.00 11.90 361.40 35124. 0.806 3.870 0.00 12.00 361.50 35419. 0.813 5.350 0.00 12.10 361.60 35714. 0.820 6.780 0.00 12.20 361.70 36010. 0.827 7.310 0.00 12.30 361.80 36305. 0.833 7.800 0.00 12.40 361.90 36600. 0.840 8.260 0.00 12.50 362.00 36895. 0.847 8.700 0.00 12.60 362.10 37190. 0.854 9.120 0.00 12.70 362.20 37485. 0.861 9.520 0.00 12.80 362.30 37780. 0.867 9.900 0.00 12.90 362.40 38076. 0.874 10.270 0.00 13.00 362.50 38371. 0.881 10.630 0.00 13.10 362.60 38666. 0.888 10.970 0.00 13.20 362.70 38961. 0.894 11.300 0.00 13.30 362.80 39256. 0.901 11.630 0.00 Hyd Inflow Outflow Peak Storage Stage Elev (Cu-Ft) (Ac-Ft) 1 1.02 0.59 11.59 361.09 34209. 0.785 2 0.50 0.17 11.50 361.00 33947. 0.779 3 0.61 0.13 10.05 359.55 29666. 0.681 4 0.65 0.12 9.90 359.40 29217. 0.671 5 0.54 0.08 8.11 357.61 23940. 0.550 6 0.54 0.04 7.32 356.82 21604. 0.496 7 0.41 0.04 6.94 356.44 20474. 0.470 8 0.45 0.03 4.49 353.99 13256. 0.304 Hyd R/D Facility Tributary Reservoir POC Outflow Outflow Inflow Inflow Target Calc 1 0.59 0.06 ******** ******* 0.61 2 0.17 0.03 ******** 0.19 0.19 3 0.13 0.03 ******** ******* 0.14 4 0.12 0.02 ******** ******* 0.14 5 0.08 0.03 ******** ******* 0.10 6 0.04 0.01 ******** ******* 0.05 7 0.04 0.01 ******** ******* 0.04 8 0.03 0.01 ******** ******* 0.03 ---------------------------------- Route Time Series through Facility Inflow Time Series File:rdin.tsf Outflow Time Series File:rdout POC Time Series File:dsout Inflow/Outflow Analysis Peak Inflow Discharge: 1.02 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.587 CFS at 10:00 on Jan 9 in Year 8 Peak Reservoir Stage: 11.59 Ft Peak Reservoir Elev: 361.09 Ft Peak Reservoir Storage: 34209. Cu-Ft : 0.785 Ac-Ft Add Time Series:bypass.tsf Peak Summed Discharge: 0.608 CFS at 10:00 on Jan 9 in Year 8 Point of Compliance File:dsout.tsf Flow Frequency Analysis 2015 D. R. STRONG Consulting Engineers Inc. 26 Avana Ridge Technical Information Report Renton, Washington Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) (ft) Period 0.174 2 2/09/01 20:00 0.587 11.59 1 100.00 0.990 0.035 7 1/07/02 4:00 0.174 11.50 2 25.00 0.960 0.127 3 3/06/03 22:00 0.127 10.05 3 10.00 0.900 0.028 8 8/26/04 8:00 0.124 9.90 4 5.00 0.800 0.036 6 1/08/05 5:00 0.079 8.11 5 3.00 0.667 0.079 5 1/19/06 0:00 0.036 7.32 6 2.00 0.500 0.124 4 11/24/06 8:00 0.035 6.94 7 1.30 0.231 0.587 1 1/09/08 10:00 0.028 4.49 8 1.10 0.091 Computed Peaks 0.450 11.56 50.00 0.980 Flow Frequency Analysis Time Series File:dsout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.194 2 2/09/01 20:00 0.608 1 100.00 0.990 0.043 7 1/05/02 16:00 0.194 2 25.00 0.960 0.141 3 3/06/03 21:00 0.141 3 10.00 0.900 0.031 8 8/26/04 2:00 0.141 4 5.00 0.800 0.045 6 1/05/05 8:00 0.095 5 3.00 0.667 0.095 5 1/19/06 0:00 0.045 6 2.00 0.500 0.141 4 11/24/06 7:00 0.043 7 1.30 0.231 0.608 1 1/09/08 10:00 0.031 8 1.10 0.091 Computed Peaks 0.470 50.00 0.980 Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.003 28646 46.716 46.716 53.284 0.533E+00 0.007 8629 14.072 60.788 39.212 0.392E+00 0.012 6932 11.305 72.092 27.908 0.279E+00 0.017 6107 9.959 82.052 17.948 0.179E+00 0.022 4844 7.900 89.951 10.049 0.100E+00 0.027 2491 4.062 94.013 5.987 0.599E-01 0.032 1880 3.066 97.079 2.921 0.292E-01 0.037 1451 2.366 99.446 0.554 0.554E-02 0.042 21 0.034 99.480 0.520 0.520E-02 0.046 8 0.013 99.493 0.507 0.507E-02 0.051 9 0.015 99.507 0.492 0.492E-02 0.056 15 0.024 99.532 0.468 0.468E-02 0.061 31 0.051 99.583 0.417 0.417E-02 0.066 24 0.039 99.622 0.378 0.378E-02 0.071 26 0.042 99.664 0.336 0.336E-02 0.076 28 0.046 99.710 0.290 0.290E-02 0.081 28 0.046 99.755 0.245 0.245E-02 0.086 19 0.031 99.786 0.214 0.214E-02 0.090 14 0.023 99.809 0.191 0.191E-02 0.095 11 0.018 99.827 0.173 0.173E-02 0.100 8 0.013 99.840 0.160 0.160E-02 0.105 15 0.024 99.865 0.135 0.135E-02 2015 D. R. STRONG Consulting Engineers Inc. 27 Avana Ridge Technical Information Report Renton, Washington 0.110 10 0.016 99.881 0.119 0.119E-02 0.115 12 0.020 99.901 0.099 0.995E-03 0.120 10 0.016 99.917 0.083 0.832E-03 0.125 15 0.024 99.941 0.059 0.587E-03 0.129 13 0.021 99.962 0.038 0.375E-03 0.134 6 0.010 99.972 0.028 0.277E-03 0.139 4 0.007 99.979 0.021 0.212E-03 0.144 4 0.007 99.985 0.015 0.147E-03 0.149 1 0.002 99.987 0.013 0.130E-03 0.154 1 0.002 99.989 0.011 0.114E-03 0.159 2 0.003 99.992 0.008 0.815E-04 0.164 1 0.002 99.993 0.007 0.652E-04 0.169 3 0.005 99.998 0.002 0.163E-04 0.173 0 0.000 99.998 0.002 0.163E-04 Flow Duration from Time Series File:dsout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.003 28725 46.844 46.844 53.156 0.532E+00 0.008 9862 16.083 62.927 37.073 0.371E+00 0.014 6897 11.248 74.175 25.825 0.258E+00 0.019 5800 9.459 83.633 16.367 0.164E+00 0.025 4449 7.255 90.889 9.111 0.911E-01 0.030 2378 3.878 94.767 5.233 0.523E-01 0.035 1715 2.797 97.564 2.436 0.244E-01 0.041 974 1.588 99.152 0.848 0.848E-02 0.046 176 0.287 99.439 0.561 0.561E-02 0.052 24 0.039 99.478 0.522 0.522E-02 0.057 12 0.020 99.498 0.502 0.502E-02 0.063 21 0.034 99.532 0.468 0.468E-02 0.068 36 0.059 99.591 0.409 0.409E-02 0.073 20 0.033 99.623 0.377 0.377E-02 0.079 28 0.046 99.669 0.331 0.331E-02 0.084 29 0.047 99.716 0.284 0.284E-02 0.090 14 0.023 99.739 0.261 0.261E-02 0.095 26 0.042 99.781 0.219 0.219E-02 0.101 16 0.026 99.808 0.192 0.192E-02 0.106 11 0.018 99.826 0.174 0.174E-02 0.112 10 0.016 99.842 0.158 0.158E-02 0.117 14 0.023 99.865 0.135 0.135E-02 0.122 10 0.016 99.881 0.119 0.119E-02 0.128 11 0.018 99.899 0.101 0.101E-02 0.133 9 0.015 99.914 0.086 0.864E-03 0.139 14 0.023 99.936 0.064 0.636E-03 0.144 18 0.029 99.966 0.034 0.342E-03 0.150 4 0.007 99.972 0.028 0.277E-03 0.155 2 0.003 99.976 0.024 0.245E-03 0.161 4 0.007 99.982 0.018 0.179E-03 0.166 2 0.003 99.985 0.015 0.147E-03 0.171 2 0.003 99.989 0.011 0.114E-03 0.177 1 0.002 99.990 0.010 0.978E-04 0.182 2 0.003 99.993 0.007 0.652E-04 0.188 3 0.005 99.998 0.002 0.163E-04 0.193 0 0.000 99.998 0.002 0.163E-04 Duration Comparison Anaylsis Base File: predev.tsf New File: dsout.tsf 2015 D. R. STRONG Consulting Engineers Inc. 28 Avana Ridge Technical Information Report Renton, Washington Cutoff Units: Discharge in CFS -----Fraction of Time----- ---------Check of Tolerance------- Cutoff Base New %Change Probability Base New %Change 0.041 | 0.97E-02 0.87E-02 -9.9 | 0.97E-02 0.041 0.040 -1.3 0.052 | 0.64E-02 0.52E-02 -19.1 | 0.64E-02 0.052 0.043 -16.9 0.063 | 0.50E-02 0.46E-02 -8.2 | 0.50E-02 0.063 0.058 -8.4 0.075 | 0.38E-02 0.37E-02 -2.6 | 0.38E-02 0.075 0.073 -1.9 0.086 | 0.29E-02 0.28E-02 -3.4 | 0.29E-02 0.086 0.084 -2.9 0.097 | 0.22E-02 0.21E-02 -7.4 | 0.22E-02 0.097 0.095 -2.7 0.109 | 0.15E-02 0.16E-02 9.8 | 0.15E-02 0.109 0.114 4.6 0.120 | 0.10E-02 0.13E-02 22.2 | 0.10E-02 0.120 0.128 6.3 0.132 | 0.62E-03 0.93E-03 50.0 | 0.62E-03 0.132 0.139 5.9 0.143 | 0.34E-03 0.38E-03 9.5 | 0.34E-03 0.143 0.145 1.2 0.154 | 0.23E-03 0.24E-03 7.1 | 0.23E-03 0.154 0.156 1.3 0.166 | 0.16E-03 0.15E-03 -10.0 | 0.16E-03 0.166 0.162 -2.4 0.177 | 0.11E-03 0.98E-04 -14.3 | 0.11E-03 0.177 0.175 -1.2 0.188 | 0.16E-04 0.16E-04 0.0 | 0.16E-04 0.188 0.194 3.0 Maximum positive excursion = 0.011 cfs ( 9.2%) occurring at 0.123 cfs on the Base Data:predev.tsf and at 0.134 cfs on the New Data:dsout.tsf Maximum negative excursion = 0.012 cfs (-20.4%) occurring at 0.058 cfs on the Base Data:predev.tsf and at 0.046 cfs on the New Data:dsout.tsf Evaluating Flow Control Performance (KCSWDM 3.3.2) 1. The post development flow duration curve lies strictly on or below the predevelopment curve at the lower limit of the range of control (between 50% of the 2-year and the 2 -year) • Duration comparison analysis shows a negative percent change up to 0.097 cfs which is beyond the required 0.083 cfs limit. 2. At any duration within the range of control, the post development flow is less than 1.1 times the predevelopment flow • At no duration is the flow exceeded by more than 10%; the maximum positive excursion is 9.2%. 3. The target duration curve may not be exceeded along more than 50% of the range of control • 8 out of 14 points show a negative excursion. 4. The peak flow at the upper end of the range of control (reduced, 25-year; historical, 50 year) may not exceed predeveloped levels by more than 10% • The predev 25-year peak is 0.188 cfs, the dsout 25 -year peak is 0.194 cfs which equates to a 3.1% exceedance and is therefore acceptable being less than the allowable 10%. Ex. 2yr Q = 0.083 cfs, Final Dsout 2yr Q = 0.045 cfs Ex. 10yr Q = 0.145 cfs, Final Dsout 10yr Q = 0.141 cfs 2015 D. R. STRONG Consulting Engineers Inc. 29 Avana Ridge Technical Information Report Renton, Washington Peak Plot Duration Analysis Water Quality Treatment The Project is required to meet Enhanced Water Quality Treatment requirements, but can reduce its requirements to Basic Water Quatilty Treatement. Per Section 1.2.8.1.A of the City of Renton SWDM Amendments, the Enhanced Water Quality Treatment requirement may be reduced to the Basic Water Quality requirement for this Project because no leachable metals will be used in areas of the site exposed to the weather and a covenant will be recorded that prohibits the future use of leachable metals on the site. A detention vault followed by a media filtration system will be utilized. A 60” Stormfilter manhole will be installed downstream of the detenti on facility with 4 ZPG cartridges. A total of 1.42 acres (approximately 61,850 s.f.) of PGIS will be routed to the StormFilter. See Figure 7 for details and cost estimate. 2015 D. R. STRONG Consulting Engineers Inc. 30 Avana Ridge Technical Information Report Renton, Washington FIGURE 7. DETENTION & WATER QUALITY FACILITY DETAILS www.contechES.comSTORMFILTER DESIGN NOTESCARTRIDGE HEIGHTSPECIFIC FLOW RATE (gpm/sf)CARTRIDGE FLOW RATE (gpm)RECOMMENDED HYDRAULIC DROP (H)27"18"LOW DROP3.05'2.3'1.8'2 gpm/ft²22.51 gpm/ft²2 gpm/ft²1 gpm/ft²2 gpm/ft²1 gpm/ft²11.25157.5105STORMFILTER TREATMENTCAPACITY IS A FUNCTION OF THE CARTRIDGE SELECTION AND THE NUMBER OF CARTRIDGES. THE STANDARD MANHOLESTYLE IS SHOWN WITH THE MAXIMUM NUMBER OF CARTRIDGES (7). VOLUME SYSTEM IS ALSO AVAILABLE WITH MAXIMUM 7 CARTRIDGES.Ø72" MANHOLE STORMFILTER PEAK HYDRAULIC CAPACITY IS 1.5 CFS. IF THE SITE CONDITIONS EXCEED 1.5 CFS AN UPSTREAM BYPASS STRUCTURE ISREQUIRED.CARTRIDGE SELECTIONGENERAL NOTES1.CONTECH TO PROVIDE ALL MATERIALS UNLESS NOTED OTHERWISE.2.DIMENSIONS MARKED WITH ( ) ARE REFERENCE DIMENSIONS. ACTUAL DIMENSIONS MAY VARY.3.FOR SITE SPECIFIC DRAWINGS WITH DETAILED VAULT DIMENSIONS AND WEIGHTS, PLEASE CONTACT YOUR CONTECH ENGINEERED SOLUTIONSLLC REPRESENTATIVE. www.contechES.com4.STORMFILTER WATER QUALITY STRUCTURE SHALL BE IN ACCORDANCE WITH ALL DESIGN DATA AND INFORMATION CONTAINED IN THISDRAWING.5.STRUCTURE SHALL MEET AASHTO HS20 LOAD RATING, ASSUMING EARTH COVER OF 0' - 5' AND GROUNDWATER ELEVATION AT, OR BELOW, THEOUTLET PIPE INVERT ELEVATION. ENGINEER OF RECORD TO CONFIRM ACTUAL GROUNDWATER ELEVATION. CASTINGS SHALL MEET AASHTOM306 AND BE CAST WITH THE CONTECH LOGO.6.FILTER CARTRIDGES SHALL BE MEDIA-FILLED, PASSIVE, SIPHON ACTUATED, RADIAL FLOW, AND SELF CLEANING. RADIAL MEDIA DEPTH SHALLBE 7-INCHES. FILTER MEDIA CONTACT TIME SHALL BE AT LEAST 39 SECONDS.7.SPECIFIC FLOW RATE IS EQUAL TO THE FILTER TREATMENT CAPACITY (gpm) DIVIDED BY THE FILTER CONTACT SURFACE AREA (sq ft).INSTALLATION NOTES1.ANY SUB-BASE, BACKFILL DEPTH, AND/OR ANTI-FLOTATION PROVISIONS ARE SITE-SPECIFIC DESIGN CONSIDERATIONS AND SHALL BESPECIFIED BY ENGINEER OF RECORD.2.CONTRACTOR TO PROVIDE EQUIPMENT WITH SUFFICIENT LIFTING AND REACH CAPACITY TO LIFT AND SET THE STORMFILTER STRUCTURE(LIFTING CLUTCHES PROVIDED).3.CONTRACTOR TO INSTALL JOINT SEALANT BETWEEN ALL STRUCTURE SECTIONS AND ASSEMBLE STRUCTURE.4.CONTRACTOR TO PROVIDE, INSTALL, AND GROUT INLET PIPE(S).5.CONTRACTOR TO PROVIDE AND INSTALL CONNECTOR TO THE OUTLET RISER STUB. STORMFILTER EQUIPPED WITH A DUAL DIAMETER HDPEOUTLET STUB AND SAND COLLAR. IF OUTLET PIPE IS LARGER THAN 8 INCHES, CONTRACTOR TO REMOVE THE 8 INCH OUTLET STUB AT MOLDEDIN CUT LINE. COUPLING BY FERNCO OR EQUAL AND PROVIDED BY CONTRACTOR.6.CONTRACTOR TO TAKE APPROPRIATE MEASURES TO PROTECT CARTRIDGES FROM CONSTRUCTION-RELATED EROSION RUNOFF.STRUCTURE IDWATER QUALITY FLOW RATE (cfs)PEAK FLOW RATE (cfs)RETURN PERIOD OF PEAK FLOW (yrs)# OF CARTRIDGES REQUIREDMEDIA TYPE (CSF, PERLITE, ZPG, GAC, PHS)PIPE DATA:I.E.MATERIALDIAMETERINLET PIPE #1INLET PIPE #2OUTLET PIPEWIDTHHEIGHTANTI-FLOTATION BALLASTNOTES/SPECIAL REQUIREMENTS:RIM ELEVATIONCARTRIDGE FLOW RATE* PER ENGINEER OF RECORDN/AN/A359.1418"LCPE347.64N/AN/AN/A18"LCPE349.44ZPG541000.6080.045CB 13 Size and Cost Estimate 11835 NE Glenn Widing Dr., Portland OR 97220 Toll-free: 800.548.4667 Fax: 800.561.1271 ©2012 Contech Engineered Solutions LLC www.ContechES.com Page 1 of 1 TS-P022 Prepared by Mike Gillette on October 3, 2016 Avana Ridge – Stormwater Treatment System Renton, WA Information provided: Total contributing area = 1.72 acres Pollution Generating Impervious area = 1.42 acres Detention release rate, Qtreat = 0.045 cfs Mitigated 100yr peak = 0.608 cfs Presiding agency = City of Renton Assumptions: Media = ZPG cartridges Per cartridge flow rate = 5 gpm Drop required from inlet to outlet = 1.8’ minimum Size and cost estimates: The StormFilter is a flow-based system, and therefore, is sized by calculating the peak water quality flow rate associated with the design storm. However, when the StormFilter is placed downstream of detention, the flow rate generated at the water quality storm is not always representative of the total volume of water that will go through the system or type of pollutant-loading the system may experience in one year. For this site, Contech Engineered Solutions LLC recommends using a 60” StormFilter manhole with (4) – Low drop cartridges with ZPG media (see attached detail). The estimated cost of this system is $19,000, complete and delivered to the job site. This estimate assumes that the vault is 6 feet deep. The final system cost will depend on the actual depth of the unit and whether extras like doors rather than castings are specified. The contractor is responsible for setting the StormFilter and all external plumbing. Typically, precast StormFilters have internal bypass capacities of 1.8 cfs. Since the peak discharge off the site is not expected to exceed this rate, a high-flow bypass upstream of the StormFilter system is not required. CONTECH Stormwater Solutions Inc. Engineer:MSG Date 10/3/2016 Site Information Project Name Avana Ridge Apartments Project State Washington Project Location Renton Drainage Area, Ad 1.72 ac Impervious Area, Ai 1.24 ac Pervious Area, Ap 0.48 % Impervious 72% Runoff Coefficient, Rc 0.70 Water quality flow 0.05 cfs Peak storm flow 0.61 cfs Filter System Filtration brand StormFilter Cartridge height 12 in Specific Flow Rate 1.00 gpm/ft2 Flow rate per cartridge 5.0 gpm SUMMARY Number of Cartridges 4 Determining Number of Cartridges for Flow Based Systems ©2006 CONTECH Stormwater Solutions contechstormwater.com 1 of 1 2015 D. R. STRONG Consulting Engineers Inc. 31 Avana Ridge Technical Information Report Renton, Washington SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN Per Core Requirement, #4 of the KCSWDM, the conveyance system must be analyzed and designed for existing tributary and developed onsite runoff from the proposed project. Pipe systems shall be designed to convey the 25-year storm with minimum 6- inches of freeboard and 100-year design storm. The Rational Method will be used to calculate the Q-Ratio for each pipe node. A conveyance system consisting primarily of pipes and catch basins has been designed for the Project. Onsite runoff from PGIS will be collected by the multiple catch basins. Pipes are typically twelve-inch diameter LCPE material. KCBW Calculations are included in this Section. The upstream bypass pipes are typically eighteen-inch and twelve-inch diameter LCPE material. Pipes (P17A, P18, P19 and P20) will be installed within the frontage improvements of Benson Road. These pipes are designed to convey the upstream flow currently discharging in that direction. Field reconnaissance and City GIS indicate that approximately 18.02 acres of runoff will be conveyed to CB 20. Fieldbrook Commons accounts for 3.84 acres of this. The 100-year peak outflow from the west vault at Fieldbrook Commons is 1.24 cfs. The tributary area for CB 17A is approximately 0.64 acres (assumed to be 100% impervious as a conservative measure). Table 3.2.2.D of the 2009 KCSWDM was utililze to determine the percent impervious coverage for existing residential areas. Please see below for an area breakdown of the upstream basins and the 15-minute KCRTS output for those basins. The tailwater for this system was assumed to be the high water mark of the stream (Elevation 387.20). SFR Gross Acres 8.83 Dwelling Units 26 DU/GA 2.94 Imp %34 MF/COMMERCIAL Gross Acres 5.35 Imp %85 FIELDBROOK COMMONS Gross Acres 3.84 Impervious Area 7.55 Pervious Area 6.63 Total 14.18 CB 20 Basin Area Gross Acres 0.64 Impervious %100 Impervious Area 0.64 Pervious Area 0 Total 0.64 CB 17A 2015 D. R. STRONG Consulting Engineers Inc. 32 Avana Ridge Technical Information Report Renton, Washington Flow Frequency Analysis Time Series File:cb20 upstream.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 3.60 6 8/27/01 18:00 12.27 1 100.00 0.990 2.67 8 1/05/02 15:00 8.26 2 25.00 0.960 8.26 2 12/08/02 17:15 5.16 3 10.00 0.900 2.90 7 8/23/04 14:30 5.10 4 5.00 0.800 5.16 3 11/17/04 5:00 4.46 5 3.00 0.667 4.46 5 10/27/05 10:45 3.60 6 2.00 0.500 5.10 4 10/25/06 22:45 2.90 7 1.30 0.231 12.27 1 1/09/08 6:30 2.67 8 1.10 0.091 Computed Peaks 10.93 50.00 0.980 Flow Frequency Analysis Time Series File:cb17a upstream.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.305 6 8/27/01 18:00 0.755 1 100.00 0.990 0.213 8 9/17/02 17:45 0.577 2 25.00 0.960 0.577 2 12/08/02 17:15 0.414 3 10.00 0.900 0.245 7 8/23/04 14:30 0.341 4 5.00 0.800 0.323 5 10/28/04 16:00 0.323 5 3.00 0.667 0.341 4 10/27/05 10:45 0.305 6 2.00 0.500 0.414 3 10/25/06 22:45 0.245 7 1.30 0.231 0.755 1 1/09/08 6:30 0.213 8 1.10 0.091 Computed Peaks 0.696 50.00 0.980 Pipes (P13, P14, P15, P16, P17 and P113) will be installed within the frontage improvements of SE 172nd Street and Benson Drive. These pipes are designed to convey the upstream flow currently discharging in that direction. Field reconnaissance and City GIS indicate that approximately 31.03 acres of runoff will be conveyed to CB 15. The tributary area for CB 17 is approximately 1.14 acres. Table 3.2.2.D of the 2009 KCSWDM was utililze to determine the percent impervious coverage for existing residential areas. Please see below for an area breakdown of the upstream basins and the 15-minute KCRTS output for those basins. Please see Figure 9 for an overall upstream backwater map. Please note that the upstream conveyance systems are designed with sufficient capacity to convey and contain (with minimum 6-inches of freeboard) the 100-year peak flow. The tailwater for this system was assumed to be elevation 348.40 which is assuming that the existing downstream system is flowing full. 2015 D. R. STRONG Consulting Engineers Inc. 33 Avana Ridge Technical Information Report Renton, Washington SFR Gross Acres 29.15 Dwelling Units 54 DU/GA 1.85 Imp %25 MF/COMMERCIAL Gross Acres 1.88 Imp %85 TILL FOREST Till Forest 4.92 Impervious Area 8.89 Till Grass 17.22 Till Forest 4.92 Total 31.03 CB 15 COMMERCIAL Gross Acres 1.14 Imp %85 Impervious Area 0.97 Pervious Area 0.17 Total 1.14 CB 17 Flow Frequency Analysis Time Series File:cb15 upstream.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 4.91 6 2/09/01 12:30 19.56 1 100.00 0.990 3.69 7 1/05/02 15:00 11.96 2 25.00 0.960 11.96 2 12/08/02 17:15 9.04 3 10.00 0.900 3.51 8 8/26/04 0:45 6.31 4 5.00 0.800 9.04 3 11/17/04 5:00 5.87 5 3.00 0.667 5.87 5 10/27/05 10:45 4.91 6 2.00 0.500 6.31 4 10/25/06 22:45 3.69 7 1.30 0.231 19.56 1 1/09/08 6:30 3.51 8 1.10 0.091 Computed Peaks 17.03 50.00 0.980 Flow Frequency Analysis Time Series File:cb17 upstream.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.462 6 8/27/01 18:00 1.23 1 100.00 0.990 0.323 8 9/17/02 17:45 0.911 2 25.00 0.960 0.911 2 12/08/02 17:15 0.633 3 10.00 0.900 0.372 7 8/23/04 14:30 0.528 4 5.00 0.800 0.500 5 10/28/04 16:00 0.500 5 3.00 0.667 0.528 4 10/27/05 10:45 0.462 6 2.00 0.500 0.633 3 10/25/06 22:45 0.372 7 1.30 0.231 1.23 1 1/09/08 6:30 0.323 8 1.10 0.091 Computed Peaks 1.12 50.00 0.980 2015 D. R. STRONG Consulting Engineers Inc. 34 Avana Ridge Technical Information Report Renton, Washington BACKWATER ANALYSIS Storm Water Runoff Variables: A=Total of Subasin and Tributary Areas C=Runoff Coefficient (the anticipated proportion of rainfall volume that runs off the area) see 2009 KCSWM Table 3.2.1A CC=Composite Runoff Coefficient CC=S(Cn*An)/ATotal T c=Time of Concentration (Typically 6.3 minutes which is the minimum value used in calculations) R=design return frequency iR=Unit peak rainfall intensity factor iR=(aR)(T c)^(-bR) aR,bR=coefficients from '98 KCSWM Table 3.2.1.B used to adjust the equation for the design storm IR=Peak rainfall intensity factor for a storm of return frequency 'R' IR=P R*iR P R=total precipitation (inches) for the 24-hour storm event for the given frequency. See Issopluvial Maps in 2009 KCSWM Figures 3.2.1.A - D QR=peak flow (cfs) for a storm of return frequency 'R' QR=CC*iR*A The Q-Ratio describes the ratio of the tributary flow to the main upstream flow. R=100 -year storm aR=2.61 bR=0.63 P R=3.9 inches Conveyance System Variables: d=pipe diameter n=Manning's Number l=length of pipe 2015 D. R. STRONG Consulting Engineers Inc. 35 Avana Ridge Technical Information Report Renton, Washington BASIN PIPE CB to CB A1 C1 A2 C2 Cc Tc iR IR Q-ratio d Mat'l n l Slope IE in IE out overflow Q Full V Full Bend CB sf ac.Basin Total in ft %ft ft ft cfs cfs degree Dia 9 9 9 8 7458 0.9 0 0.25 7458 0.17 0.90 6.3 0.82 3.19 0.49 0.49 0.00 12 LCPE 0.012 116 4.51 397.82 392.59 400.82 8.22 10.47 0 2 8 8 8 7 6497 0.9 722 0.25 7219 0.17 0.84 6.5 0.80 3.13 0.43 0.93 0.88 12 LCPE 0.012 93 7.22 392.59 385.88 395.59 10.40 13.24 2 2 7 7 7 6 5582 0.9 620 0.25 6202 0.14 0.84 6.6 0.79 3.10 0.37 1.29 0.40 12 LCPE 0.012 80 5.99 385.88 381.07 388.88 9.47 12.06 25 2 6 6 6 5 3641 0.9 405 0.25 4045 0.09 0.84 6.7 0.79 3.07 0.24 1.53 0.18 12 LCPE 0.012 32 8.04 381.07 378.52 384.07 10.97 13.97 7 2 5 5 5 4 2407 0.9 267 0.25 2674 0.06 0.84 6.8 0.78 3.06 0.16 1.69 0.10 12 LCPE 0.012 107 4.89 378.52 373.3 381.52 8.56 10.89 41 2 4 4 4 3 5394 0.9 0 0.25 5394 0.12 0.90 6.9 0.77 3.01 0.34 2.02 0.20 12 LCPE 0.012 60 3.52 373.30 371.18 376.30 7.26 9.25 4 2 14678 0.9 1093 0.25 15771 0.36 17923 0.9 5500 0.25 23423 0.54 3 3 2 32601 0.9 6593 0.25 39194 0.90 0.79 7.0 0.76 2.98 2.12 4.15 1.05 12 LCPE 0.012 101 5.54 371.18 365.6 374.96 9.11 11.60 5 2 2 2 2 1 4855 0.9 539 0.25 5394 0.12 0.84 7.2 0.75 2.94 0.30 4.45 0.07 12 LCPE 0.012 28 2.52 365.60 364.89 368.60 6.14 7.82 81 4 1800 0.9 0 0.25 1800 0.04 13096 0.9 1700 0.25 14796 0.34 1 1 INLET1 14896 0.9 1700 0.25 16596 0.38 0.83 7.2 0.75 2.93 0.93 5.38 0.21 12 LCPE 0.012 7.8 20.00 360.56 359 368.95 17.31 22.04 126 4 BASIN PIPE CB to CB A1 C1 A2 C2 Cc Tc iR IR Q-ratio d Mat'l n l Slope IE in IE out overflow Q Full V Full Bend CB sf ac.Basin Total in ft %ft ft ft cfs cfs degree Dia 101 101 101 1 1800 0.9 0 0.25 1800 0.04 0.90 6.3 0.82 3.19 0.12 0.12 0.00 12 LCPE 0.012 33 1.99 365.54 364.89 368.54 5.46 6.95 0 2 303 303 303 203 9836 0.9 1093 0.25 10929 0.25 0.84 6.3 0.82 3.19 0.67 0.67 0.00 12 LCPE 0.012 44 3.15 379.08 377.68 382.08 6.87 8.75 0 2 203 203 203 103 797 0.9 0 0.25 797 0.02 0.90 6.4 0.81 3.17 0.05 0.72 0.08 12 LCPE 0.012 96 5.74 377.68 372.16 380.78 9.28 11.81 44 2 103 103 103 3 4045 0.9 0 0.25 4045 0.09 0.90 6.5 0.80 3.12 0.26 0.98 0.36 12 LCPE 0.012 49 2.00 372.16 371.18 375.16 5.48 6.98 19 2 14678 0.9 1093 0.25 15771 0.36 0.85 11 11 11 10 5755 0.9 1016 0.25 6771 0.16 0.80 6.3 0.82 3.19 0.40 0.40 0.00 12 LCPE 0.012 63 2.02 360.34 359.07 363.34 5.50 7.01 0 2 10 10 10 INLET2 2217 0.9 2217 0.25 4433 0.10 0.58 6.4 0.81 3.15 0.18 0.58 0.46 12 LCPE 0.012 6 2.00 359.07 358.95 363.70 5.47 6.97 60 2 3 At 1 Run 101-1 Run 1-INLET 1 CB#303 TO CB#3 CB#11 TO INLET2 Qr (cfs) Run 303-3 CB#6 TO INLET 1 At Qr (cfs) CB#101 TO CB#1 Run 3-2 2015 D. R. STRONG Consulting Engineers Inc. 36 Avana Ridge Technical Information Report Renton, Washington FIGURE 8. BACKWATER ANALYSIS MAP GRAPHIC SCALE040801601 INCH = 80 FT. 2015 D. R. STRONG Consulting Engineers Inc. 37 Avana Ridge Technical Information Report Renton, Washington FIGURE 9. UPSTREAM BACKWATER ANALYSIS MAP 2015 D. R. STRONG Consulting Engineers Inc. 38 Avana Ridge Technical Information Report Renton, Washington BACKWATER ANALYSIS RESULTS BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB#9 TO INLET1.bwp Surcharge condition at intermediate junctions Tailwater Elevation:361. feet Discharge Range:0.49 to 5.38 Step of 0.489 [cfs] Overflow Elevation:400.82 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 7 LF - 12"CP @ 20.00% OUTLET: 359.00 INLET: 360.56 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 368.95 BEND: 90 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.21 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.49 0.30 360.86 * 0.012 0.30 0.12 2.00 2.00 0.30 ***** 0.30 0.98 0.50 361.06 * 0.012 0.42 0.17 2.00 2.0 0 0.42 ***** 0.50 1.47 0.67 361.23 * 0.012 0.52 0.20 2.00 2.00 0.52 ***** 0.67 1.96 0.84 361.40 * 0.012 0.60 0.23 2.00 2.00 0.60 ***** 0.84 2.45 1.01 361.57 * 0.012 0.67 0.26 2.00 2.00 0.67 ***** 1.01 2.93 1.19 361.75 * 0.012 0.74 0.28 2.00 2.00 0.74 ***** 1.19 3.42 1.42 361.98 * 0.012 0.80 0.31 2.00 2.00 0.80 ***** 1.42 3.91 1.68 362.24 * 0.012 0.84 0.33 2.00 2.00 0.84 ***** 1.68 4.40 1.98 362.54 * 0.012 0.88 0.35 2.00 2.00 0.88 ***** 1.98 4.89 2.31 362.87 * 0.012 0.92 0.37 2.00 2.00 0.92 ***** 2.31 5.38 2.68 363.24 * 0.012 0.94 0.39 2.00 2.00 0.94 ***** 2.68 5.87 3.08 363.64 * 0.012 0.96 0.41 2.00 2.00 0.96 ***** 3.08 Q25 = 4.60 cfs Q100 = 5.38 cfs PIPE NO. 2: 28 LF - 12"CP @ 2.52% OUTLET: 364.89 INLET: 365.60 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 368.60 BEND: 81 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.07 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.41 0.35 365.95 * 0.012 0.27 0.18 0.00 0.18 0.27 ***** 0.35 0.81 0.52 366.12 * 0.012 0.38 0.25 0.00 0.25 0.38 ***** 0.52 1.21 0.66 366.26 * 0.012 0.47 0.31 0.00 0.31 0.47 ***** 0.66 1.62 0.80 366.40 * 0.012 0.55 0.36 0.00 0.36 0.55 ***** 0.80 2.02 0.93 366.53 * 0.012 0.61 0.40 0.00 0.40 0.61 ***** 0.93 2.43 1.06 366.66 * 0.012 0.67 0.44 0.00 0.44 0.67 ***** 1.06 2.83 1.20 366.80 * 0.012 0.73 0.48 0.00 0.48 0.73 ***** 1.20 3.24 1.37 366.97 * 0.012 0.78 0.52 0.00 0.52 0.78 ***** 1.37 3.64 1.56 367.16 * 0.012 0.82 0.56 0.00 0.56 0.82 ***** 1.56 4.05 1.77 367.37 * 0.012 0.86 0.60 0.00 0.60 0.86 ***** 1.77 4.45 2.00 367.60 * 0.012 0.89 0.64 0.00 0.64 0.89 ***** 2.00 4.85 2.26 367.86 * 0.012 0.91 0.68 0.00 0.68 0.91 ***** 2.26 Q25 = 3.80 cfs Q100 = 4.45 cfs 2015 D. R. STRONG Consulting Engineers Inc. 39 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 3: 100 LF - 12"CP @ 5.54% OUTLET: 365.60 INLET: 371.18 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 374.96 BEND: 5 DEG DIA/WIDTH: 2.0 Q-RATIO: 1.05 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.38 0.32 371.50 * 0.012 0.26 0.14 0.35 0.35 0.26 ***** 0.32 0.75 0.48 371.66 * 0.012 0.37 0.20 0.52 0.52 0.37 ***** 0.48 1.13 0.61 371.79 * 0.012 0.45 0.24 0.66 0.66 0.45 ***** 0.61 1.51 0.73 371.91 * 0.012 0.53 0.28 0.80 0.80 0.53 ***** 0.73 1.88 0.85 372.03 * 0.012 0.59 0.31 0.93 0.93 0.59 ***** 0.85 2.26 0.96 372.14 * 0.012 0.65 0.35 1.06 1.06 0.65 ***** 0.96 2.64 1.08 372.26 * 0.012 0.70 0.37 1.20 1.20 0.70 ***** 1.08 3.02 1.20 372.38 * 0.012 0.75 0.40 1.37 1.37 0.75 ***** 1.20 3.39 1.36 372.54 * 0.012 0.79 0.43 1.56 1.56 0.79 ***** 1.36 3.77 1.53 372.71 * 0.012 0.83 0.45 1.77 1.77 0.83 ***** 1.53 4.15 1.71 372.89 * 0.012 0.86 0.48 2.00 2.00 0.86 ***** 1.71 4.52 1.91 373.09 * 0.012 0.89 0.50 2.26 2.26 0.89 ***** 1.91 Q25 = 3.54 cfs Q100 = 4.15 cfs PIPE NO. 4: 60 LF - 12"CP @ 3.52% OUTLET: 371.18 INLET: 373.30 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 376.30 BEND: 4 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.20 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.18 0.22 373.52 * 0.012 0.18 0.11 0.32 0.32 0.18 ***** 0.22 0.37 0.32 373.62 * 0.012 0.26 0.16 0.48 0.48 0.26 ***** 0.32 0.55 0.40 373.70 * 0.012 0.31 0.19 0.61 0.61 0.31 ***** 0.40 0.74 0.47 373.77 * 0.012 0.36 0.22 0.73 0.73 0.36 ***** 0.47 0.92 0.54 373.84 * 0.012 0.41 0.25 0.85 0.85 0.41 ***** 0.54 1.10 0.60 373.90 * 0.012 0.45 0.27 0.96 0.96 0.45 ***** 0.60 1.29 0.65 373.95 * 0.012 0.48 0.29 1.08 1.08 0.48 ***** 0.65 1.47 0.70 374.00 * 0.012 0.52 0.31 1.20 1.20 0.52 ***** 0.70 1.66 0.75 374.05 * 0.012 0.55 0.33 1.36 1.36 0.55 ***** 0.75 1.84 0.80 374.10 * 0.012 0.58 0.35 1.53 1.53 0.58 ***** 0.80 2.02 0.85 374.15 * 0.012 0.61 0.37 1.71 1.71 0.61 ***** 0.85 2.21 0.90 374.20 * 0.012 0.64 0.38 1.91 1.91 0.64 ***** 0.90 Q25 = 1.73 cfs Q100 = 2.02 cfs PIPE NO. 5: 106 LF - 12"CP @ 4.89% OUTLET: 373.30 INLET: 378.52 INTYP: 5 JUNC NO. 5: OVERFLOW-EL: 381.52 BEND: 41 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.10 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.15 0.19 378.71 * 0.012 0.17 0.10 0.22 0.22 0.17 ***** 0.19 0.31 0.28 378.80 * 0.012 0.23 0.13 0.32 0.32 0.23 ***** 0.28 0.46 0.36 378.88 * 0.012 0.29 0.16 0.40 0.40 0.29 ***** 0.36 0.61 0.42 378.94 * 0.012 0.33 0.19 0.47 0.47 0.33 ***** 0.42 0.77 0.48 379.00 * 0.012 0.37 0.21 0.54 0.54 0.37 ***** 0.48 0.92 0.53 379.05 * 0.012 0.41 0.23 0.60 0.60 0.41 ***** 0.53 1.07 0.58 379.10 * 0.012 0.44 0.24 0.65 0.65 0.44 ***** 0.58 1.23 0.63 379.15 * 0.012 0.47 0.26 0.70 0.70 0.47 ***** 0.63 1.38 0.68 379.20 * 0.012 0.50 0.28 0.75 0.75 0.50 ***** 0.68 1.54 0.72 379.24 * 0.012 0.53 0.29 0.80 0.80 0.53 ***** 0.72 1.69 0.76 379.28 * 0.012 0.56 0.31 0.85 0.85 0.56 ***** 0.76 1.84 0.80 379.32 * 0.012 0.58 0.32 0.90 0.90 0.58 ***** 0.80 Q25 = 1.45 cfs Q100 = 1.69 cfs 2015 D. R. STRONG Consulting Engineers Inc. 40 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 6: 31 LF - 12"CP @ 8.04% OUTLET: 378.52 INLET: 381.07 INTYP: 5 JUNC NO. 6: OVERFLOW-EL: 384.07 BEND: 7 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.18 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.14 0.17 381.24 * 0.012 0.16 0.08 0.19 0.19 0.16 ***** 0.17 0.28 0.25 381.32 * 0.012 0.22 0.11 0.28 0.28 0.22 ***** 0.25 0.42 0.32 381.39 * 0.012 0.27 0.14 0.36 0.36 0.27 ***** 0.32 0.56 0.38 381.45 * 0.012 0.32 0.16 0.42 0.42 0.32 ***** 0.38 0.70 0.44 381.51 * 0.012 0.35 0.18 0.48 0.48 0.35 ***** 0.44 0.84 0.49 381.56 * 0.012 0.39 0.19 0.53 0.53 0.39 ***** 0.49 0.98 0.53 381.60 * 0.012 0.42 0.21 0.58 0.58 0.42 ***** 0.53 1.11 0.58 381.65 * 0.012 0.45 0.22 0.63 0.63 0.45 ***** 0.58 1.25 0.62 381.69 * 0.012 0.48 0.23 0.68 0.68 0.48 ***** 0.62 1.39 0.66 381.73 * 0.012 0.50 0.25 0.72 0.72 0.50 ***** 0.66 1.53 0.70 381.77 * 0.012 0.53 0.26 0.76 0.76 0.53 ***** 0.70 1.67 0.73 381.80 * 0.012 0.55 0.27 0.80 0.80 0.55 ***** 0.73 Q25 = 1.31 cfs Q100 = 1.53 cfs PIPE NO. 7: 80 LF - 12"CP @ 5.99% OUTLET: 381.07 INLET: 385.88 INTYP: 5 JUNC NO. 7: OVERFLOW-EL: 388.88 BEND: 25 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.40 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.12 0.16 386.04 * 0.012 0.15 0.08 0.17 0.17 0.15 ***** 0.16 0.24 0.24 386.12 * 0.012 0.20 0.11 0.25 0.25 0.20 ***** 0.24 0.35 0.30 386.18 * 0.012 0.25 0.14 0.32 0.32 0.25 ***** 0.30 0.47 0.36 386.24 * 0.012 0.29 0.16 0.38 0.38 0.29 ***** 0.36 0.59 0.41 386.29 * 0.012 0.32 0.17 0.44 0.44 0.32 ***** 0.41 0.71 0.45 386.33 * 0.012 0.36 0.19 0.49 0.49 0.36 ***** 0.45 0.82 0.50 386.38 * 0.012 0.38 0.20 0.53 0.53 0.38 ***** 0.50 0.94 0.54 386.42 * 0.012 0.41 0.22 0.58 0.58 0.41 ***** 0.54 1.06 0.58 386.46 * 0.012 0.44 0.23 0.62 0.62 0.44 ***** 0.58 1.18 0.62 386.50 * 0.012 0.46 0.24 0.66 0.66 0.46 ***** 0.62 1.29 0.65 386.53 * 0.012 0.49 0.26 0.70 0.70 0.49 ***** 0.65 1.41 0.69 386.57 * 0.012 0.51 0.27 0.73 0.73 0.51 ***** 0.69 Q25 = 1.11 cfs Q100 = 1.29 cfs PIPE NO. 8: 93 LF - 12"CP @ 7.22% OUTLET: 385.88 INLET: 392.59 INTYP: 5 JUNC NO. 8: OVERFLOW-EL: 395.59 BEND: 2 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.88 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.08 0.12 392.71 * 0.012 0.12 0.07 0.16 0.16 0.12 ***** 0.12 0.17 0.19 392.78 * 0.012 0.17 0.09 0.24 0.24 0.17 ***** 0.19 0.25 0.24 392.83 * 0.012 0.21 0.11 0.30 0.30 0.21 ***** 0.24 0.34 0.29 392.88 * 0.012 0.24 0.13 0.36 0.36 0.24 ***** 0.29 0.42 0.33 392.92 * 0.012 0.27 0.14 0.41 0.41 0.27 ***** 0.33 0.51 0.37 392.96 * 0.012 0.30 0.16 0.45 0.45 0.30 ***** 0.37 0.59 0.40 392.99 * 0.012 0.32 0.17 0.50 0.50 0.32 ***** 0.40 0.67 0.44 393.03 * 0.012 0.35 0.18 0.54 0.54 0.35 ***** 0.44 0.76 0.47 393.06 * 0.012 0.37 0.19 0.58 0.58 0.37 ***** 0.47 0.84 0.50 393.09 * 0.012 0.39 0.20 0.62 0.62 0.39 ***** 0.50 0.93 0.53 393.12 * 0.012 0.41 0.21 0.65 0.65 0.41 ***** 0.53 1.01 0.56 393.15 * 0.012 0.43 0.22 0.69 0.69 0.43 ***** 0.56 Q25 = 0.79 cfs Q100 = 0.93 cfs 2015 D. R. STRONG Consulting Engineers Inc. 41 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 9: 115 LF - 12"CP @ 4.51% OUTLET: 392.59 INLET: 397.82 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.04 0.09 397.91 * 0.012 0.09 0.06 0.12 0.12 0.09 ***** 0.09 0.09 0.14 397.96 * 0.012 0.13 0.08 0.19 0.19 0.13 ***** 0.14 0.13 0.18 398.00 * 0.012 0.15 0.09 0.24 0.24 0.15 ***** 0.18 0.18 0.21 398.03 * 0.012 0.18 0.11 0.29 0.29 0.18 ***** 0.21 0.22 0.24 398.06 * 0.012 0.20 0.12 0.33 0.33 0.20 ***** 0.24 0.27 0.27 398.09 * 0.012 0.22 0.13 0.37 0.37 0.2 2 ***** 0.27 0.31 0.29 398.11 * 0.012 0.24 0.14 0.40 0.40 0.24 ***** 0.29 0.36 0.31 398.13 * 0.012 0.25 0.15 0.44 0.44 0.25 ***** 0.31 0.40 0.34 398.16 * 0.012 0.27 0.16 0.47 0.47 0.27 ***** 0.34 0.45 0.36 398.18 * 0.012 0.28 0.16 0.50 0.50 0.28 ***** 0.36 0.49 0.38 398.20 * 0.012 0.30 0.17 0.53 0.53 0.30 ***** 0.38 0.54 0.40 398.22 * 0.012 0.31 0.18 0.56 0.56 0.31 ***** 0.40 Q25 = 0.42 cfs Q100 = 0.49 cfs BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB#11 TO INLET2.bwp Surcharge condition at intermediate junctions Tailwater Elevation:361. feet Discharge Range:0.4 to 0.58 Step of 0.018 [cfs] Overflow Elevation:363.34 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 6 LF - 12"CP @ 2.00% OUTLET: 358.95 INLET: 359.07 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 363.70 BEND: 60 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.46 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.40 1.95 361.02 * 0.012 0.27 0.19 2.05 2.05 1.94 1.95 0.35 0.42 1.94 361.01 * 0.012 0.27 0.19 2.05 2.05 1.93 1.94 0.36 0.44 1.94 361.01 * 0.012 0.28 0.20 2.05 2.05 1.93 1.94 0.36 0.45 1.94 361.01 * 0.012 0.28 0.20 2.05 2.05 1.93 1.94 0.37 0.47 1.94 361.01 * 0.012 0.29 0.20 2.05 2.05 1.93 1.94 0.38 0.49 1.94 361.01 * 0.012 0.30 0.21 2.05 2.05 1.93 1.94 0.39 0.51 1.94 361.01 * 0.012 0.30 0.21 2.05 2.05 1.93 1.94 0.40 0.53 1.94 361.01 * 0.012 0.31 0.21 2.05 2.05 1.93 1.94 0.40 0.54 1.94 361.01 * 0.012 0.31 0.22 2.05 2.05 1.93 1.94 0.41 0.56 1.94 361.01 * 0.012 0.32 0.22 2.05 2.05 1.93 1.94 0.42 0.58 1.94 361.01 * 0.012 0.32 0.23 2.05 2.05 1.93 1.94 0.43 Q25 = 0.50 cfs Q100 = 0.58 cfs PIPE NO. 2: 62 LF - 12"CP @ 2.02% OUTLET: 359.07 INLET: 360.34 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.27 0.69 361.03 * 0.012 0.22 0.16 1.95 1.95 0.68 0.69 0.28 0.29 0.68 361.02 * 0.012 0.23 0.16 1.94 1.94 0.67 0.68 0.29 0.30 0.69 361.03 * 0.012 0.23 0.16 1.94 1.94 0.68 0.69 0.30 0.31 0.69 361.03 * 0.012 0.23 0.17 1.94 1.94 0.68 0.69 0.30 0.32 0.69 361.03 * 0.012 0.24 0.17 1.94 1.94 0.68 0.69 0.31 0.34 0.69 361.03 * 0.012 0.24 0.17 1.94 1.94 0.68 0.69 0.31 0.35 0.69 361.03 * 0.012 0.25 0.18 1.94 1.94 0.68 0.69 0.32 0.36 0.69 361.03 * 0.012 0.25 0.18 1.94 1.94 0.68 0.69 0.33 0.37 0.69 361.03 * 0.012 0.26 0.18 1.94 1.94 0.68 0.69 0.33 0.38 0.69 361.03 * 0.012 0.26 0.18 1.94 1.94 0.68 0.69 0.34 0.40 0.69 361.03 * 0.012 0.27 0.19 1.94 1.94 0.68 0.69 0.35 Q25 = 0.34 cfs 2015 D. R. STRONG Consulting Engineers Inc. 42 Avana Ridge Technical Information Report Renton, Washington Q100 = 0.40 cfs BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB#101 TO CB#1.bw p Surcharge condition at intermediate junctions Tailwater Elevation:363.24 feet Discharge Range:0.012 to 0.12 Step of 0.012 [cfs] Overflow Elevation:368.54 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 32 LF - 12"CP @ 1.99% OUTLET: 364.89 INLET: 365.54 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.01 0.05 365.59 * 0.012 0.05 0.04 0.00 0.04 0.05 ***** 0.05 0.02 0.08 365.62 * 0.012 0.07 0.05 0.00 0.05 0.07 ***** 0.08 0.04 0.09 365.63 * 0.012 0.08 0.06 0.00 0.06 0.08 ***** 0.09 0.05 0.11 365.65 * 0.012 0.09 0.07 0.00 0.07 0.09 ***** 0.11 0.06 0.12 365.66 * 0.012 0.10 0.08 0.00 0.08 0.10 ***** 0.12 0.07 0.14 365.68 * 0.012 0.11 0.09 0.00 0.09 0.11 ***** 0.14 0.08 0.15 365.69 * 0.012 0.12 0.09 0.00 0.09 0.12 ***** 0.15 0.10 0.16 365.70 * 0.012 0.13 0.10 0.00 0.10 0.13 ***** 0.16 0.11 0.17 365.71 * 0.012 0.14 0.10 0.00 0.10 0.14 ***** 0.17 0.12 0.18 365.72 * 0.012 0.15 0.11 0.00 0.11 0.15 ***** 0.18 Q25 = 0.10 cfs Q100 = 0.12 cfs BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB#303 TO CB#3.bwp Surcharge condition at intermediate junctions Tailwater Elevation:372.89 feet Discharge Range:0.67 to 0.98 Step of 0.031 [cfs] Overflow Elevation:382.08 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 48 LF - 12"CP @ 2.00% OUTLET: 371.18 INLET: 372.16 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 375.16 BEND: 19 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.36 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.67 0.76 372.92 * 0.012 0.35 0.24 1.71 1.71 0.74 0.76 0.46 0.70 0.77 372.93 * 0.012 0.35 0.25 1.71 1.71 0.75 0.77 0.47 0.73 0.78 372.94 * 0.012 0.36 0.25 1.71 1.71 0.75 0.78 0.48 0.76 0.78 372.94 * 0.012 0.37 0.26 1.71 1.71 0.75 0.7 8 0.49 0.79 0.78 372.94 * 0.012 0.38 0.26 1.71 1.71 0.75 0.78 0.51 0.83 0.78 372.94 * 0.012 0.39 0.27 1.71 1.71 0.75 0.78 0.52 0.86 0.79 372.95 * 0.012 0.39 0.27 1.71 1.71 0.75 0.79 0.53 0.89 0.79 372.95 * 0.012 0.40 0.28 1.71 1.71 0.75 0.79 0.54 0.92 0.79 372.95 * 0.012 0.41 0.28 1.71 1.71 0.75 0.79 0.55 0.95 0.80 372.96 * 0.012 0.41 0.29 1.71 1.71 0.76 0.80 0.56 0.98 0.81 372.97 * 0.012 0.42 0.29 1.71 1.71 0.76 0.81 0.57 Q25 = 0.84 cfs Q100 = 0.98 cfs 2015 D. R. STRONG Consulting Engineers Inc. 43 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 2: 96 LF - 12"CP @ 5.74% OUTLET: 372.16 INLET: 377.68 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 380.68 BEND: 44 DEG DIA/WIDTH: 2.0 Q -RATIO: 0.08 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.49 0.37 378.05 * 0.012 0.30 0.16 0.76 0.76 0.30 ***** 0.37 0.51 0.38 378.06 * 0.012 0.30 0.17 0.77 0.77 0.30 ***** 0.38 0.54 0.39 378.07 * 0.012 0.31 0.17 0.78 0.78 0.31 ***** 0.39 0.56 0.40 378.08 * 0.012 0.32 0.17 0.78 0.78 0.32 ***** 0.40 0.58 0.41 378.09 * 0.012 0.32 0.18 0.78 0.78 0.32 ***** 0.41 0.61 0.41 378.09 * 0.012 0.33 0.18 0.78 0.78 0.33 ***** 0.41 0.63 0.42 378.10 * 0.012 0.33 0.18 0.79 0.79 0.33 ***** 0.42 0.65 0.43 378.11 * 0.012 0.34 0.18 0.7 9 0.79 0.34 ***** 0.43 0.67 0.44 378.12 * 0.012 0.35 0.19 0.79 0.79 0.35 ***** 0.44 0.70 0.45 378.13 * 0.012 0.35 0.19 0.80 0.80 0.35 ***** 0.45 0.72 0.46 378.14 * 0.012 0.36 0.19 0.81 0.81 0.36 ***** 0.46 Q25 = 0.62 cfs Q100 = 0.72 cfs PIPE NO. 3: 44 LF - 12"CP @ 3.15% OUTLET: 377.68 INLET: 379.08 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.46 0.37 379.45 * 0.012 0.28 0.18 0.37 0.37 0.28 ***** 0.37 0.48 0.38 379.46 * 0.012 0.29 0.18 0.38 0.38 0.29 ***** 0.38 0.50 0.39 379.47 * 0.012 0.30 0.19 0.39 0.39 0.30 ***** 0.39 0.52 0.40 379.48 * 0.012 0.30 0.19 0.40 0.40 0.30 ***** 0.40 0.54 0.40 379.48 * 0.012 0.31 0.20 0.41 0.41 0.31 ***** 0.40 0.56 0.41 379.49 * 0.012 0.32 0.20 0.41 0.41 0.32 ***** 0.41 0.58 0.42 379.50 * 0.012 0.32 0.20 0.42 0.42 0.32 ***** 0.42 0.60 0.43 379.51 * 0.012 0.33 0.21 0.43 0.43 0.33 ***** 0.43 0.63 0.44 379.52 * 0.012 0.33 0.21 0.44 0.44 0.33 ***** 0.44 0.65 0.45 379.53 * 0.012 0.34 0.21 0.45 0.45 0.34 ***** 0.45 0.67 0.46 379.54 * 0.012 0.35 0.22 0.46 0.46 0.35 ***** 0.46 Q25 = 0.57 cfs Q100 = 0.67 cfs 2015 D. R. STRONG Consulting Engineers Inc. 44 Avana Ridge Technical Information Report Renton, Washington UPSTREAM BACKWATER ANALYSIS RESULTS BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB#20 TO Benson Rd Inlet.bwp Surcharge condition at intermediate junctions Tailwater Elevation:387.2 feet Discharge Range:13.51 to 14.27 Step of 0.076 [cfs] Overflow Elevation:408.85 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 83 LF - 18"CP @ 1.58% OUTLET: 390.39 INLET: 391.70 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 396.79 BEND: 34 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.06 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 13.51 2.75 394.45 * 0.012 1.37 1.17 0.00 1.17 1.37 ***** 2.75 13.59 2.77 394.47 * 0.012 1.37 1.17 0.00 1.17 1.37 ***** 2.77 13.66 2.79 394.49 * 0.012 1.38 1.18 0.00 1.18 1.38 ***** 2.79 13.74 2.81 394.51 * 0.012 1.38 1.19 0.00 1.19 1.38 ***** 2.81 13.81 2.83 394.53 * 0.012 1.38 1.19 0.00 1.19 1.38 ***** 2.83 13.89 2.85 394.55 * 0.012 1.38 1.20 0.00 1.20 1.38 ***** 2.85 13.97 2.87 394.57 * 0.012 1.39 1.21 0.00 1.21 1.39 ***** 2.87 14.04 2.89 394.59 * 0.012 1.39 1.21 0.00 1.21 1.39 ***** 2.89 14.12 2.91 394.61 * 0.012 1.39 1.22 0.00 1.22 1.39 ***** 2.91 14.19 2.93 394.63 * 0.012 1.39 1.23 0.00 1.23 1.39 ***** 2.93 14.27 2.95 394.65 * 0.012 1.39 1.23 0.00 1.23 1.39 ***** 2.95 Q100 = 14.27 cfs PIPE NO. 2: 123 LF - 18"CP @ 4.95% OUTLET: 391.70 INLET: 397.83 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 404.41 BEND: 3 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 12.79 2.26 400.09 * 0.012 1.35 0.76 2.75 2.75 1.35 ***** 2.26 12.87 2.28 400.11 * 0.012 1.35 0.76 2.77 2.77 1.35 ***** 2.28 12.94 2.29 400.12 * 0.012 1.35 0.76 2 .79 2.79 1.35 ***** 2.29 13.01 2.31 400.14 * 0.012 1.36 0.77 2.81 2.81 1.36 ***** 2.31 13.08 2.32 400.15 * 0.012 1.36 0.77 2.83 2.83 1.36 ***** 2.32 13.15 2.34 400.17 * 0.012 1.36 0.77 2.85 2.85 1.36 ***** 2.34 13.23 2.35 400.18 * 0.012 1.36 0.77 2.87 2.87 1.36 ***** 2.35 13.30 2.37 400.20 * 0.012 1.37 0.78 2.89 2.89 1.37 ***** 2.37 13.37 2.38 400.21 * 0.012 1.37 0.78 2.91 2.91 1.37 ***** 2.38 13.44 2.40 400.23 * 0.012 1.37 0.78 2.93 2.93 1.37 ***** 2.40 13.51 2.41 400.24 * 0.012 1.37 0.78 2.95 2.95 1.37 ***** 2.41 Q100 = 13.51 cfs PIPE NO. 3: 86 LF - 18"CP @ 1.00% OUTLET: 397.83 INLET: 398.69 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 407.66 BEND: 0 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 12.79 2.92 401.61 * 0.012 1.35 1.50 2.26 2.26 2.50 2.92 2.29 12.87 2.95 401.64 * 0.012 1.35 1.50 2.28 2.28 2.52 2.95 2.30 12.94 2.98 401.67 * 0.012 1.35 1.50 2.29 2.29 2.55 2.98 2.31 13.01 3.01 401.70 * 0.012 1.36 1.50 2.31 2.31 2.58 3.01 2.33 13.08 3.05 401.74 * 0.012 1.36 1.50 2.32 2.32 2.60 3.05 2.34 13.15 3.08 401.77 * 0.012 1.36 1.50 2.34 2.34 2.63 3.08 2.36 13.23 3.11 401.80 * 0.012 1.36 1.50 2.35 2.35 2.66 3.11 2.37 13.30 3.14 401.83 * 0.012 1.37 1.50 2.37 2.37 2.69 3.14 2.39 13.37 3.18 401.87 * 0.012 1.37 1.50 2.38 2.38 2.72 3.18 2.40 13.44 3.21 401.90 * 0.012 1.37 1.50 2.40 2.40 2.74 3.21 2.42 13.51 3.24 401.93 * 0.012 1.37 1.50 2.41 2.41 2.77 3.24 2.43 Q100 = 13.51 cfs 2015 D. R. STRONG Consulting Engineers Inc. 45 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 4: 15 LF - 18"CP @ 1.02% OUTLET: 398.69 INLET: 398.85 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 12.79 4.18 403.03 * 0.012 1.35 1.50 2.92 2.92 2.96 4.18 3.08 12.87 4.23 403.08 * 0.012 1.35 1.50 2.95 2.95 2.99 4.23 3.11 12.94 4.28 403.13 * 0.012 1.35 1.50 2.98 2.98 3.03 4.28 3.13 13.01 4.33 403.18 * 0.012 1.36 1.50 3.01 3.01 3.06 4.33 3.15 13.08 4.37 403.22 * 0.012 1.36 1.50 3.05 3.05 3.10 4.37 3.18 13.15 4.42 403.27 * 0.012 1.36 1.50 3.08 3.08 3.13 4.42 3.20 13.23 4.47 403.32 * 0.012 1.36 1.50 3.11 3.11 3.17 4.47 3.23 13.30 4.52 403.37 * 0.012 1.37 1.50 3.14 3.14 3.20 4.52 3.25 13.37 4.57 403.42 * 0.012 1.37 1.50 3.18 3.18 3.24 4.57 3.28 13.44 4.62 403.47 * 0.012 1.37 1.50 3.21 3.21 3.27 4.62 3.30 13.51 4.67 403.52 * 0.012 1.37 1.50 3.24 3.24 3.31 4.67 3.33 Q100 = 13.51 cfs BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:EX CB TO SR515 EX CB.bwp Surcharge condition at intermediate junctions Tailwater Elevation:348.4 feet Discharge Range:1.23 to 21.38 Step of 1.0075 [cfs] Overflow Elevation:395.96 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 44 LF - 18"CP @ 0.79% OUTLET: 347.10 INLET: 347.45 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 353.88 BEND: 12 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.03 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.23 0.97 348.42 * 0.012 0.42 0.36 1.30 1.30 0.95 0.97 0.56 2.24 1.01 348.46 * 0.012 0.57 0.48 1.30 1.30 0.95 1.01 0.76 3.25 1.08 348.53 * 0.012 0.69 0.59 1.30 1.30 0.95 1.08 0.93 4.25 1.17 348.62 * 0.012 0.80 0.68 1.30 1.30 0.94 1.17 1.08 5.26 1.30 348.75 * 0.012 0.89 0.77 1.30 1.30 0.93 1.30 1.21 6.27 1.34 348.79 * 0.012 0.97 0.86 1.30 1.30 0.97 ***** 1.34 7.28 1.45 348.90 * 0.012 1.05 0.94 1.30 1.30 1.05 ***** 1.45 8.28 1.57 349.02 * 0.012 1.12 1.04 1.30 1.30 1.12 ***** 1.57 9.29 1.73 349.18 * 0.012 1.18 1.13 1.30 1.30 1.18 ***** 1.73 10.30 1.89 349.34 * 0.012 1.24 1.26 1.30 1.30 1.26 1.79 1.89 11.31 2.08 349.53 * 0.012 1.29 1.50 1.30 1.30 1.42 1.86 2.08 12.31 2.28 349.73 * 0.012 1.33 1.50 1.30 1.33 1.58 2.06 2.28 13.32 2.50 349.95 * 0.012 1.37 1.50 1.30 1.37 1.67 2.23 2.50 14.33 2.73 350.18 * 0.012 1.40 1.50 1.30 1.40 1.77 2.42 2.73 15.33 2.98 350.43 * 0.012 1.42 1.50 1.30 1.42 1.87 2.61 2.98 16.34 3.25 350.70 * 0.012 1.44 1.50 1.30 1.44 1.98 2.82 3.25 17.35 3.54 350.99 * 0.012 1.45 1.50 1.30 1.45 2.10 3.05 3.54 18.36 3.84 351.29 * 0.012 1.46 1.50 1.30 1.46 2.22 3.29 3.84 19.36 4.16 351.61 * 0.012 1.47 1.50 1.30 1.47 2.35 3.54 4.16 20.37 4.50 351.95 * 0.012 1.47 1.50 1.30 1.47 2.48 3.79 4.50 21.38 4.86 352.31 * 0.012 1.48 1.50 1.30 1.48 2.63 4.08 4.86 21.38 4.86 352.31 * 0.012 1.48 1.50 1.30 1.48 2.63 4.08 4.86 Q100 = 21.38 cfs 2015 D. R. STRONG Consulting Engineers Inc. 46 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 2: 92 LF - 18"CP @ 5.97% OUTLET: 347.45 INLET: 353.00 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 360.32 BEND: 90 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.20 0.52 353.52 * 0.012 0.41 0.22 0.97 0.97 0.41 ***** 0.5 2 2.18 0.74 353.74 * 0.012 0.56 0.29 1.01 1.01 0.56 ***** 0.74 3.16 0.94 353.94 * 0.012 0.68 0.35 1.08 1.08 0.68 ***** 0.94 4.14 1.12 354.12 * 0.012 0.78 0.40 1.17 1.17 0.78 ***** 1.12 5.12 1.31 354.31 * 0.012 0.88 0.44 1.30 1.30 0.88 ***** 1.31 6.10 1.50 354.50 * 0.012 0.96 0.48 1.34 1.34 0.96 ***** 1.50 7.08 1.69 354.69 * 0.012 1.04 0.52 1.45 1.45 1.04 ***** 1.69 8.06 1.89 354.89 * 0.012 1.10 0.56 1.57 1.57 1.10 ***** 1.89 9.03 2.13 355.13 * 0.012 1.17 0.59 1.73 1.73 1.17 ***** 2.13 10.01 2.40 355.40 * 0.012 1.22 0.63 1.89 1.89 1.22 ***** 2.40 10.99 2.69 355.69 * 0.012 1.28 0.66 2.08 2.08 1.28 ***** 2.69 11.97 3.02 356.02 * 0.012 1.32 0.69 2.28 2.28 1.32 ***** 3.02 12.95 3.37 356.37 * 0.012 1.35 0.72 2.50 2.50 1.35 ***** 3.37 13.93 3.74 356.74 * 0.012 1.38 0.76 2.73 2.73 1 .38 ***** 3.74 14.91 4.15 357.15 * 0.012 1.41 0.79 2.98 2.98 1.41 ***** 4.15 15.89 4.58 357.58 * 0.012 1.43 0.82 3.25 3.25 1.43 ***** 4.58 16.87 5.04 358.04 * 0.012 1.44 0.85 3.54 3.54 1.44 ***** 5.0 4 17.85 5.53 358.53 * 0.012 1.45 0.88 3.84 3.84 1.45 ***** 5.53 18.83 6.05 359.05 * 0.012 1.46 0.91 4.16 4.16 1.46 ***** 6.05 19.81 6.59 359.59 * 0.012 1.47 0.94 4.50 4.50 1.47 ***** 6.59 20.79 7.16 360.16 * 0.012 1.48 0.97 4.86 4.86 2.42 6.34 7.16 20.79 7.16 360.16 * 0.012 1.48 0.97 4.86 4.86 2.41 6.33 7.16 Q100 = 20.79 cfs PIPE NO. 3: 227 LF - 18"CP @ 7.07% OUTLET: 353.00 INLET: 369.07 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 376.17 BEND: 3 DEG DIA/WIDTH: 4.0 Q -RATIO:15.90 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.20 0.51 369.58 * 0.012 0.41 0.21 0.52 0.52 0.41 ***** 0.51 2.18 0.73 369.80 * 0.012 0.56 0.28 0.74 0.74 0.56 ***** 0.73 3.16 0.91 369.98 * 0.012 0.68 0.33 0.94 0.94 0.68 ***** 0.91 4.14 1.09 370.16 * 0.012 0.78 0.38 1.12 1.12 0.78 ***** 1.09 5.12 1.26 370.33 * 0.012 0.88 0.42 1.31 1.31 0.88 ***** 1.26 6.10 1.43 370.50 * 0.012 0.96 0.46 1.50 1.50 0.96 ***** 1.43 7.08 1.60 370.67 * 0.012 1.04 0.50 1.69 1.69 1.04 ***** 1.60 8.06 1.78 370.85 * 0.012 1.10 0.53 1.89 1.89 1.10 ***** 1.78 9.03 2.00 371.07 * 0.012 1.17 0.57 2.13 2.13 1.17 ***** 2.00 10.01 2.23 371.30 * 0.012 1.22 0.60 2.40 2.40 1.22 ***** 2.23 10.99 2.50 371.57 * 0.012 1.28 0.63 2.69 2.69 1.28 ***** 2.50 11.97 2.79 371.86 * 0.012 1.32 0.66 3.02 3.02 1.32 ***** 2.79 12.95 3.10 372.17 * 0.012 1.35 0.69 3.37 3.37 1.35 ***** 3.10 13.93 3.43 372.50 * 0.012 1.38 0.72 3.74 3.74 1.38 ***** 3.43 14.91 3.80 372.87 * 0.012 1.41 0.75 4.15 4.15 1.41 ***** 3.80 15.89 4.18 373.25 * 0.012 1.43 0.78 4.58 4.58 1.43 ***** 4.18 16.87 4.59 373.66 * 0.012 1.44 0.81 5.04 5.04 1.44 ***** 4.59 17.85 5.03 374.10 * 0.012 1.45 0.83 5.53 5.53 1.45 ***** 5.03 18.83 5.49 374.56 * 0.012 1.46 0.86 6.05 6.05 1.46 ***** 5.49 19.81 5.97 375.04 * 0.012 1.47 0.89 6.59 6.59 1.47 ***** 5.97 20.79 6.48 375.55 * 0.012 1.48 0.92 7.16 7.16 1.48 ***** 6.48 20.79 6.48 375.55 * 0.012 1.48 0.92 7.16 7.16 1.48 ***** 6.48 Q100 = 20.79 cfs 2015 D. R. STRONG Consulting Engineers Inc. 47 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 4: 212 LF - 12"CP @ 8.72% OUTLET: 369.57 INLET: 388.06 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 391.20 BEND: 39 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.07 0.11 388.17 * 0.012 0.11 0.06 0.01 0.06 0.11 ***** 0.10 0.13 0.15 388.21 * 0.012 0.15 0.08 0.23 0.23 0.15 ***** 0.15 0.19 0.20 388.26 * 0.012 0.18 0.09 0.41 0.41 0.18 ***** 0.20 0.24 0.23 388.29 * 0.012 0.21 0.11 0.59 0.59 0.21 ***** 0.23 0.30 0.26 388.32 * 0.012 0.23 0.12 0.76 0.76 0.23 ***** 0.26 0.36 0.29 388.35 * 0.012 0.25 0.13 0.93 0.93 0.25 ***** 0.29 0.42 0.32 388.38 * 0.012 0.27 0.14 1.10 1.10 0.27 ***** 0.32 0.48 0.34 388.40 * 0.012 0.29 0.14 1.28 1.28 0.29 ***** 0.34 0.53 0.37 388.43 * 0.012 0.31 0.15 1.50 1.50 0.31 ***** 0.37 0.59 0.39 388.45 * 0.012 0.33 0.16 1.73 1.73 0.33 ***** 0.39 0.65 0.41 388.47 * 0.012 0.34 0.17 2.00 2.00 0.34 ***** 0.41 0.71 0.44 388.50 * 0.012 0.36 0.17 2.29 2.29 0.36 ***** 0.44 0.77 0.46 388.52 * 0.012 0.37 0.18 2.60 2.60 0.37 ***** 0.46 0.82 0.48 388.54 * 0.012 0.38 0.19 2.93 2.93 0.38 ***** 0.48 0.88 0.50 388.56 * 0.012 0.40 0.19 3.30 3.30 0.40 ***** 0.50 0.94 0.51 388.57 * 0.012 0.41 0.20 3.68 3.68 0.41 ***** 0.51 1.00 0.53 388.59 * 0.012 0.42 0.21 4.09 4.09 0.42 ***** 0.53 1.06 0.55 388.61 * 0.012 0.44 0.21 4.53 4.53 0.44 ***** 0.55 1.11 0.57 388.63 * 0.012 0.45 0.22 4.99 4.99 0.45 ***** 0.57 1.17 0.59 388.65 * 0.012 0.46 0.22 5.47 5.47 0.46 ***** 0.59 1.23 0.60 388.66 * 0.012 0.47 0.23 5.98 5.98 0.47 ***** 0.60 1.23 0.60 388.66 * 0.012 0.47 0.23 5.98 5.98 0.47 ***** 0.60 Q100 = 1.23 cfs PIPE NO. 5: 27 LF - 12"CP @ 1.59% OUTLET: 388.06 INLET: 388.50 INTYP: 5 JUNC NO. 5: OVERFLOW-EL: 392.00 BEND: 39 DEG DIA/WIDTH: 4.0 Q -RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.07 0.14 388.64 * 0.012 0.11 0.09 0.11 0.11 0.11 ***** 0.14 0.13 0.19 388.69 * 0.012 0.15 0.12 0.15 0.15 0.15 ***** 0.19 0.19 0.23 388.73 * 0.012 0.18 0.14 0.20 0.20 0.18 ***** 0.23 0.24 0.27 388.77 * 0.012 0.21 0.16 0.23 0.23 0.21 ***** 0.27 0.30 0.30 388.80 * 0.012 0.23 0.17 0.26 0.26 0.23 ***** 0.30 0.36 0.33 388.83 * 0.012 0.25 0.19 0.29 0.29 0.25 ***** 0.33 0.42 0.35 388.85 * 0.012 0.27 0.20 0.32 0.32 0.27 ***** 0.35 0.48 0.38 388.88 * 0.012 0.29 0.22 0.34 0.34 0.29 ***** 0.38 0.53 0.40 388.90 * 0.012 0.31 0.23 0.3 7 0.37 0.31 ***** 0.40 0.59 0.43 388.93 * 0.012 0.33 0.24 0.39 0.39 0.33 ***** 0.43 0.65 0.45 388.95 * 0.012 0.34 0.25 0.41 0.41 0.34 ***** 0.45 0.71 0.47 388.97 * 0.012 0.36 0.26 0.44 0.44 0.36 ***** 0.47 0.77 0.49 388.99 * 0.012 0.37 0.27 0.46 0.46 0.37 ***** 0.49 0.82 0.51 389.01 * 0.012 0.38 0.28 0.48 0.48 0.38 ***** 0.51 0.88 0.53 389.03 * 0.012 0.40 0.29 0.50 0.50 0.40 ***** 0.53 0.94 0.55 389.05 * 0.012 0.41 0.30 0.51 0.51 0.41 ***** 0.55 1.00 0.57 389.07 * 0.012 0.42 0.31 0.53 0.53 0.42 ***** 0.57 1.06 0.59 389.09 * 0.012 0.44 0.32 0.55 0.55 0.44 ***** 0.59 1.11 0.60 389.10 * 0.012 0.45 0.33 0.57 0.57 0.45 ***** 0.60 1.17 0.62 389.12 * 0.012 0.46 0.34 0.59 0.59 0.46 ***** 0.62 1.23 0.64 389.14 * 0.012 0.47 0.35 0.60 0.60 0.47 ***** 0.64 1.23 0.64 389.14 * 0.012 0.47 0.35 0.60 0.60 0.47 ***** 0.64 Q100 = 1.23 cfs 2015 D. R. STRONG Consulting Engineers Inc. 48 Avana Ridge Technical Information Report Renton, Washington PIPE NO. 6: 87 LF - 12"CP @ 2.68% OUTLET: 388.50 INLET: 390.84 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.07 0.13 390.97 * 0.012 0.11 0.08 0.14 0.14 0.11 ***** 0.13 0.13 0.18 391.02 * 0.012 0.15 0.10 0.19 0.19 0.15 ***** 0.18 0.19 0.23 391.07 * 0.012 0.18 0.12 0.23 0.23 0.18 ***** 0.23 0.24 0.26 391.10 * 0.012 0.21 0.14 0.27 0.27 0.21 ***** 0.26 0.30 0.29 391.13 * 0.012 0.23 0.15 0.30 0.30 0.23 ***** 0.29 0.36 0.32 391.16 * 0.012 0.25 0.17 0.33 0.33 0.2 5 ***** 0.32 0.42 0.35 391.19 * 0.012 0.27 0.18 0.35 0.35 0.27 ***** 0.35 0.48 0.38 391.22 * 0.012 0.29 0.19 0.38 0.38 0.29 ***** 0.38 0.53 0.40 391.24 * 0.012 0.31 0.20 0.40 0.40 0.31 ***** 0.40 0.59 0.43 391.27 * 0.012 0.33 0.21 0.43 0.43 0.33 ***** 0.43 0.65 0.45 391.29 * 0.012 0.34 0.22 0.45 0.45 0.34 ***** 0.45 0.71 0.48 391.32 * 0.012 0.36 0.23 0.47 0.47 0.36 ***** 0.48 0.77 0.50 391.34 * 0.012 0.37 0.24 0.49 0.49 0.37 ***** 0.50 0.82 0.52 391.36 * 0.012 0.38 0.25 0.51 0.51 0.38 ***** 0.52 0.88 0.54 391.38 * 0.012 0.40 0.26 0.53 0.53 0.40 ***** 0.54 0.94 0.56 391.40 * 0.012 0.41 0.27 0.55 0.55 0.41 ***** 0.56 1.00 0.58 391.42 * 0.012 0.42 0.27 0.57 0.57 0.42 ***** 0.58 1.06 0.60 391.44 * 0.012 0.44 0.28 0.59 0.59 0.44 ***** 0.60 1.11 0.62 391.46 * 0.012 0.45 0.29 0.60 0.60 0.45 ***** 0.62 1.17 0.64 391.48 * 0.012 0.46 0.30 0.62 0.62 0.46 ***** 0.64 1.23 0.66 391.50 * 0.012 0.47 0.30 0.64 0.64 0.47 ***** 0.66 1.23 0.66 391.50 * 0.012 0.47 0.30 0.64 0.64 0.4 7 ***** 0.66 Q100 = 1.23 cfs 2015 D. R. STRONG Consulting Engineers Inc. 49 Avana Ridge Technical Information Report Renton, Washington SECTION VI SPECIAL REPORTS AND STUDIES A number of reports have been prepared for the project as well as an earlier development proposal (Springbrook Ridge) on this parcel. These include: 1. Geological Engineering Services, Coal Mine Hazard Assessment, Cugini Property; Icicle Creek Engineers, Inc.; June 24, 1999. 2. Geological Engineering Services, Coal Mine Hazard Assessment, Cugini Property – Northwest Parcel; Icicle Creek Engineers, Inc.; March 22, 2004. 3. Geological Engineering Services, Proposed Property Development, Springbrook Ridge; Icicle Creek Engineers, Inc.; January 26, 2009. 4. Cugini Property wetland and stream delineation study – TWC Ref# 080109 , The Watershed Company, January 25, 2009. 5. Updated Coal Mine Hazard Assessment – Proposed Avana Ridge PUD; Earth Solutions NW, LLC; October 5, 2016. 6. Tree Inspection, Avana Ridge PPUD, Parcel Numbers 292305-9148, -9009, Renton, WA; Greenforest Incorporated; December 16, 2015 7. Wetland and Supplemental Stream Study – Avana Ridge PUD; Sewall Wetland Consulting, Inc.; December 22, 2015. 8. Habitat Data Report – Avana Ridge; Sewall Wetland Consulting, Inc.; December 22, 2015. 9. Avana Ridge Apartments, Traffic Impact Analysis; TraffEx; December 21, 2015. 10. Spring Brook Ridge, Transportation Impact Study; February 10, 2009. 11. Caldera Archaeology Repor t 1115B_Avana Ridge Development; January 26,2016 12. Hydraulic Study for Avana Ridge Apartments; Soos Creek Water & Sewer; March 22, 2016. 13. Phase I ESA - Two Undeveloped Parcels, Renton – Final; February 2, 2016 14. Tree Inspection, Avana Ridge PPUD, December 6, 2016 15. Avana Ridge Geotechnical Engineering Study; Earth Solutions NW LLC, December 21,2015 16. Memorandum - Revisions to TIA per Peer Review ; March 26, 2016 2015 D. R. STRONG Consulting Engineers Inc. 50 Avana Ridge Technical Information Report Renton, Washington SECTION VII OTHER PERMITS, VARIANCES AND ADJUSTMENTS • DOE Construction Stormwater General Permit – WAR304820 • Building Permit for Walls greater than 4-feet in height • Building Permit for Vault 2015 D. R. STRONG Consulting Engineers Inc. 51 Avana Ridge Technical Information Report Renton, Washington SECTION VIII ESC PLAN ANALYSIS AND DESIGN (PART A) The Erosion and Sedimentation Control Design meets the nine minimum requirements: 1. Clearing Limits – Areas to remain undisturbed shall be delineated with a high- visibility plastic fence prior to any site clearing or grading. 2. Cover Measures – Disturbed Site areas shall be covered with mulch and seeded, as appropriate, for temporary or permanent measures. 3. Perimeter protection – Perimeter protection shall consist of a silt fence down slope of any disturbed areas or stockpiles. 4. Traffic Area Stabilization – A stabilized construction entrance will be located at the point of ingress/egress. 5. Sediment Retention – Surface water collected from disturbed areas of the Site shall be routed through a sediment vault or sediment traps (baker tanks) prior to release from the Site. The sediment vault or traps will be installed prior to grading of any contributing area. 6. Surface Water Control –Interceptor berms or swales shall be installed to control and intercept all surface water from disturbed areas. Surface water controls shall be installed concurrently with and/or immediately following rough grading. 7. Dewatering Control – Will be provided as needed. 8. Dust Control – Dust control shall be provided by spraying exposed soils with water until wet. This is required when exposed soils are dry to the point that wind transport is possible which would impact roadways, drainage ways, surface waters, or neighboring residences. 9. Flow Control – Runoff collected in the sediment vault (baker tanks) will discharge to the permanent detention vault outfall system. 2015 D. R. STRONG Consulting Engineers Inc. 52 Avana Ridge Technical Information Report Renton, Washington SWPPS PLAN DESIGN (PART B) Construction activities that could contribute pollutants to surface and storm water include the following, with applicable BMP’s listed for each item: 1. Storage and use of chemicals: Utilize source control, and soil erosion and sedimentation control practices, such as using only recommended amounts of chemical materials applied in the proper manner; neutralizing concrete wash water, and disposing of excess concrete material only in areas prepared for concrete placement, or return to batch plant; disposing of wash-up waters from water-based paints in sanitary sewer; disposing of wastes from oil-based paints, solvents, thinners, and mineral spirits only through a licensed waste management firm, or treatment, storage, and disposal (TSD) facility. 2. Material delivery and storage: Locate temporary storage areas away from vehicular traffic, near the construction entrance, and away from storm drains. Material Safety Data Sheets (MSDS) should be supplied for all materials stored, and chemicals kept in their original labeled containers. Maintenance, fueling, and repair of heavy equipment and vehicles shall be conducted using spill prevention and control measures. Contaminated surfaces shall be cleaned immediately following any spill incident. Provide cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum products, and other potentially hazardous materials. 3. Building demolition: Protect stormwater drainage system from sediment-laden runoff and loose particles. To the extent possible, use dikes, berms, or other methods to protect overland discharge paths from runoff. Street gutter, sidewalks, driveways, and other paved surfaces in the immediate area of demolition must be swept daily to collect and properly dispose of loose debris and garbage. Spray the minimum amount of water to help control windblown fine particles such as concrete, dust, and paint chips. Avoid excessive spraying so that runoff from the site does not occur, yet dust control is achieved. Oils must never be used for dust control. 4. Sawcutting: Slurry and cuttings shall be vacuumed during the activity to prevent migration offsite and must not remain on permanent concrete or asphalt paving overnight. Collected slurry and cuttings shall be disposed of in a manner that does not violate ground water or surface water quality standards. The complete CSWPPP can be found in Appendix B. 2015 D. R. STRONG Consulting Engineers Inc. 53 Avana Ridge Technical Information Report Renton, Washington SECTION IX BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 1. Bond Quantity Worksheet – Appendix C 2. The Stormwater Facility Summary Sheet is included in this section. 3. Covenants – Draft Covenants have been provided in Appendix D. 2015 D. R. STRONG Consulting Engineers Inc. 54 Avana Ridge Technical Information Report Renton, Washington STORMWATER FACILITY SUMMARY SHEET Number 1 Detention Vault (Private Vault) Maintained by HOA (provide one Stormwater Facility Summary Sheet per Natural Discharge Location) Overview: Avana Ridge October 28, 2016 Project Name Date Downstream Drainage Basins Black River Panther Creek Major Basin Name Minor Basin Name Flow Control: Detention Vault Private Parking Lot Flow Control Facility Name/Number Facility Location If none, Flow control provided in regional/shared facility (give location) N/A No flow control required Exemption number General Facility Information: Type/Number of detention facilities Type/Number of infiltration facilities: Ponds Ponds 1 Vaults Tanks Tanks Trenches Control Structure Location Located inside proposed vault Type of Control Structure FROP-T Number of Orifices/Restrictions 3 Size of Orifice/Restriction: No. 1 0.70” No. 2 1.40” No. 3 0.92” No. 4 Flow Control Performance Standard: Level 2 Live Storage Volume 33,943 cf Depth 11.5 feet Volume Factor of Safety 1.0 Number of Acres Served 2.99 Number of Lots N/A Dam Safety Regulations (Washington State Department of Ecology) Reservoir Volume above natural grade N/A Depth of Reservoir above natural grade N/A Facility Summary Sheet Sketch All detention, infiltration and water quality facilities must include a detailed sketch. 2015 D. R. STRONG Consulting Engineers Inc. 55 Avana Ridge Technical Information Report Renton, Washington SECTION X OPERATIONS AND MAINTENANCE MANUAL The 50-foot dispersal trench, drywells, detention facility, and StormFilter will be privately maintained. Maintenance guidelines set forth in the 2009 KCSDWDM are included in this section. 2015 D. R. STRONG Consulting Engineers Inc. 56 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 57 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 58 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 59 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 60 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 61 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 62 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 63 Avana Ridge Technical Information Report Renton, Washington 2015 D. R. STRONG Consulting Engineers Inc. 64 Avana Ridge Technical Information Report Renton, Washington Dispersion Trench Dispersion devices must be inspected annually and after major storm events to identify and repair any physical defects. When native soil is exposed or erosion channels are present, the sources of the erosion or concentrated flow need to be identified and mitigated. Bare spots should be re-vegetated with native vegetation. Concentrated flow can be mitigated by leveling the edge of the pervious area and/or regarding or replenishing the rock in the dispersion device, such as in rock pads and gravel-filled trenches. Drywells Infiltration devices must be inspected annually and after major storm events to identify and repair any physical defects. Maintenance and operation of the system should focus on ensuring the system's viability by preventing sediment-laden flows from entering the device. Excessive sedimentation will result in a plugged or non-functioning facility. If the infiltration device has a catch basin, sediment accumulation must be removed on a yearly basis or more frequently if necessary. Prolonged ponding around or atop a device may indicate a plugged facility. If the device becomes plugged, it must be replaced. Keeping the areas that drain to infiltration devices well swept and clean will enhance the longevity of these devices. For roofs, frequent cleaning of gutters will reduce sediment loads to these devices. 2015 D. R. STRONG Consulting Engineers Inc. 65 Avana Ridge Technical Information Report Renton, Washington APPENDIX “A” OFFSITE ANALYSIS ____________________________________________________________________________ LEVEL ONE DOWNSTREAM ANALYSIS AVANA RIDGE 17249 Benson Road S and 10615 SE 172nd Street Renton, Washington ____________________________________________________________________________ DRS Project No. 15088 City Of Renton File No. XXXX Owner/Applicant Avana Ridge, LLC 9675 SE 36th Street, Suite 105 Mercer Island, Washington 98040 Report Prepared by D. R. STRONG Consulting Engineers, Inc. 620 7th Avenue Kirkland, WA 98033 (425) 827-3063 Report Issue Date December 28, 2015 2015 D. R. STRONG Consulting Engineers Inc. Avana Ridge Level One Downstream Analysis Renton, Washington AVANA RIDGE LEVEL ONE DOWNSTREAM ANALYSIS DISCLAIMER: ........................................................................................................................... 1 TASK 1: DEFINE AND MAP STUDY AREA ........................................................................ 1 TASK 2: RESOURCE REVIEW ............................................................................................. 1 FIGURE 1. Vicinity Map................................................................................. 2 FIGURE 2: Site Map ....................................................................................... 3 FIGURE 3. King County iMap Topography .............................................. 4 FIGURE 4. King County Sensitive Area Map .......................................... 5 FIGURE 5. City of Renton Erosion Hazards Map ................................... 6 FIGURE 6. City of Renton Landslide Hazards Map ............................... 7 FIGURE 7. City of Renton Coal Mine Hazards Map ............................... 8 FIGURE 8. City of Renton Steep Slopes .................................................. 9 FIGURE 9. City of Renton Flood Hazard ................................................ 10 FIGURE 10. City of Renton Seismic Hazards ....................................... 11 FIGURE 11. City of Renton Liquefaction Hazards ............................... 12 FIGURE 12. City of Renton Aquifer Protection Zones........................ 13 FIGURE 13. USDA King County Soils Survey Map ............................. 14 FIGURE 14. FEMA Map ............................................................................... 17 TASK 3: FIELD INSPECTION ............................................................................................. 18 Upstream Tributary Area ........................................................................................... 18 General Onsite and Offsite Drainage Description ................................................ 18 TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS ........................................................................................................ 18 Drainage System Description ................................................................................... 18 TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS .......................... 20 APPENDIX A. OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE & DOWNSTREAM MAP ............................................................................................... 21 2015 D. R. STRONG Consulting Engineers Inc 1 Avana Ridge Level One Downstream Analysis Renton, Washington LEVEL ONE DOWNSTREAM ANALYSIS DISCLAIMER: THIS REPORT WAS PREPARED AT THE REQUEST OF PNW HOLDINGS, LLC FOR THE 3.78 ACRE PARCELS KNOWN AS A PORTION OF THE SOUTHEAST QUARTER OF SECTION 29, TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M., IN KING COUNTY, TAX PARCEL NUMBERS 292305900 AND 292309148 (SITE). D. R. STRONG CONSULTING ENGINEERS INC. (DRS) HAS PREPARED THIS REPORT FOR THE EXCLUSIVE USE OF DRS, THE OWNER, AND THEIR AGENTS, FOR SPECIFIC APPLICATION TO THE DEVELOPMENT PROJECT AS DESCRIBED HEREIN. USE OR RELIANCE ON THIS REPORT, OR ANY OF ITS CONTENTS FOR ANY REVISIONS OF THIS PROJECT, OR ANY OTHER PROJECT, OR BY OTHERS NOT DESCRIBED ABOVE, IS FORBIDDEN WITHOUT THE EXPRESSED PERMISSION BY DRS. TASK 1: DEFINE AND MAP STUDY AREA This Offsite Analysis was prepared in accordance with Core Requirement #2, Section 1.2.2 of the 2009 King County Surface Water Design Manual and Section 2.3 of the 2010 City of Renton Amendments to the King County Surface Water Design Manual (Manual). The Site is located at 17249 Benson Road S and 10615 SE 172 nd Street Renton, Washington. The Project is the development of two parcels into a 74 unit apartment complex. See Figures 1, 2 and 3 for maps of the study area. TASK 2: RESOURCE REVIEW Adopted Basin Plans: None at this time Finalized Drainage Studies: None available Basin Reconnaissance Summary Reports: The Green-Duwamish and Puget Sound Water Resource Inventory Area 9 Habitat Limiting Factors And Reconnaissance Assessment Report is available for the Basin. Floodplain/Floodway (FEMA) Map: No floodplains exist on site, See Figure 14 Other Offsite Analysis Reports: Technical Information Report (TIR) for Fieldbrook Commons, dated December 2nd, 2013 by D.R. Strong Consulting Engineers Sensitive Areas Map: See Figures 4-12 DNRP Drainage Complaints and Studies: Per King County Water and Land Resources Division, there are no complaints within the downstream path, 1 mile from the Site within the last 10 years. USDA King County Soils Survey: See Figure 13 Wetlands Inventory: Vol. 2 East (1990) – The wetland inventory revealed no additional wetlands within one mile along the downstream path, see Appendix C. Migrating River Studies: None Applicable King County Designated Water Quality Problems: None at this time 2015 D. R. STRONG Consulting Engineers Inc 2 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 1 - Vicinity Map SITE 2015 D. R. STRONG Consulting Engineers Inc 3 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 2 - Site Map GRAPHIC SCALE 0 40 80 120 1 INCH = 80 FT. 2015 D. R. STRONG Consulting Engineers Inc 4 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 3 - King County iMap Topography SITE 2015 D. R. STRONG Consulting Engineers Inc 5 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 4 - King County Sensitive Area Map SITE 2015 D. R. STRONG Consulting Engineers Inc 6 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 5 - City of Renton Erosion Hazards Map NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 7 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 6 - City of Renton Landslide Hazards Map NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 8 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 7 - City of Renton Coal Mine Hazards Map NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 9 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 8 - City of Renton Steep Slopes NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 10 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 9 - City of Renton Flood Hazard NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 11 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 10 - City of Renton Seismic Hazards NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 12 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 11 - City of Renton Liquefaction Hazards NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 13 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 12 - City of Renton Aquifer Protection Zones NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 14 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 13 - USDA King County Soils Survey Map King County Area, Washington AgC—Alderwood gravelly sandy loam, 8 to 15 percent slopes Map Unit Setting National map unit symbol: 2t626 Elevation: 50 to 800 feet Mean annual precipitation: 20 to 60 inches Mean annual air temperature: 46 to 52 degrees F Frost-free period: 160 to 240 days Farmland classification: Prime farmland if irrigated Map Unit Composition Alderwood and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood SITE 2015 D. R. STRONG Consulting Engineers Inc 15 Avana Ridge Level One Downstream Analysis Renton, Washington Setting Landform: Ridges, hills Landform position (two-dimensional): Shoulder Landform position (three-dimensional): Nose slope, talf Down-slope shape: Linear, convex Across-slope shape: Convex Parent material: Glacial drift and/or glacial outwash over dense glaciomarine deposits Typical profile A - 0 to 7 inches: gravelly sandy loam Bw1 - 7 to 21 inches: very gravelly sandy loam Bw2 - 21 to 30 inches: very gravelly sandy loam Bg - 30 to 35 inches: very gravelly sandy loam 2Cd1 - 35 to 43 inches: very gravelly sandy loam 2Cd2 - 43 to 59 inches: very gravelly sandy loam Properties and qualities Slope: 8 to 15 percent Depth to restrictive feature: 20 to 39 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 37 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Other vegetative classification: Limited Depth Soils (G002XN302WA), Limited Depth Soils (G002XS301WA), Limited Depth Soils (G002XF303WA) Minor Components Everett Percent of map unit: 5 percent Landform: Eskers, kames, moraines Landform position (two-dimensional): Shoulder, footslope Landform position (three-dimensional): Crest, base slope Down-slope shape: Convex Across-slope shape: Convex Indianola Percent of map unit: 5 percent Landform: Eskers, kames, terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Shalcar 2015 D. R. STRONG Consulting Engineers Inc 16 Avana Ridge Level One Downstream Analysis Renton, Washington Percent of map unit: 3 percent Landform: Depressions Landform position (three-dimensional): Dip Down-slope shape: Concave Across-slope shape: Concave Norma Percent of map unit: 2 percent Landform: Depressions, drainageways Landform position (three-dimensional): Dip Down-slope shape: Concave, linear Across-slope shape: Concave 2015 D. R. STRONG Consulting Engineers Inc 17 Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 14 - FEMA Map NTS SITE 2015 D. R. STRONG Consulting Engineers Inc 18 Avana Ridge Level One Downstream Analysis Renton, Washington TASK 3: FIELD INSPECTION Upstream Tributary Area The upstream basin area was evaluated by examining the King County topographic map (see Figure 3), City of Renton Mapping Application and by conducting field reconnaissance on December 15, 2015 under overcast conditions. Upstream runoff enters the Site in two locations. Portions of SE 172nd St and 106th Ave SE direct upstream runoff across the northern property line. Runoff from 106th Ave SE and the north side of SE 172nd St. enters a Type 1 catch basin at the intersection of these two streets. An 18-inch diameter concrete pipe conveys runoff south under SE 172nd St. and outfalls onto the Site. Runoff from the southern portion of SE 172nd St is intercepted by a ditch along the south side of SE 172nd St. and enters the Site where the previously mentioned 18-inch diameter concrete pipe outlets. Upstream runoff from the west side of Benson Rd S flows west into a ditch along the east property line. This ditch conveys upstream runoff southwest along the east property line until it enters a stream about halfway down the property line. This stream conveys water through the Site. The Project proposes to construct a conveyance system to collect runoff from these two upstream tributary areas and bypass the infiltration facility on Site. General Onsite and Offsite Drainage Description The Site is contained within one Threshold Discharge Area (TDA) but is divided into two distinct Natural Discharge Areas (NDA’s), NDA 1 and NDA 2. See Downstream Analysis Map for the location of each NDA. Natural Discharge Point 1 (NDP 1) is located at approximately the midpoint of the southwestern property line. NDP 2 is northwest of NDP 1. See Appendix A for a map of the NDAs and downstream paths. Runoff exits the Site via an onsite ditch from both NDAs. NDA 1 is approximately 2.65 acres (115,449 SF) and NDA 2 is approximately 1.13 acres (49,378 SF). The flow paths were observed and appear to converge at points D1 and C2. TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS Drainage System Description The downstream area was evaluated b y reviewing available resources and by conducting a field reconnaissance on December 15, 2015 under overcast conditions. The analysis is illustrated and detailed in the Downstream Map and Downstream Table located in Appendix A. The downstream path is located within the Black River Drainage Basin; more specifically the Panther Creek Subbasin. For point-to-point descriptions of downstream flow, see Appendix A. Runoff exits the Site via channel flow from an onsite ditch in two locations – NDP 1 and NDP 2. Both NDPs are located along the western property line. Runoff enters box culverts on the northeast side of SR 515, eventually crossing under the road to the southwe st. Flows from each NDA converge at a Type 2 catch basin on the southwest side of SR 515, just east of parcel 2015 D. R. STRONG Consulting Engineers Inc 19 Avana Ridge Level One Downstream Analysis Renton, Washington 2923059150. Runoff continues west through a ditch between parcels 2923059150 and 2923059134 and is conveyed west through a series of catch basins and PVC pipes. Runoff outlets west of Wells Ave S and continues west , eventually outfalling into Panther Creek. A review of the King County Water and Land Resources Division – Drainage Services Section Documented Drainage Complaints within one mile of the downstream flow paths revealed no complaints within the last ten years along all downstream paths for the Site. ª 2015 D. R. STRONG Consulting Engineers Inc 20 Avana Ridge Level One Downstream Analysis Renton, Washington TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS No drainage complaints were found in Task 4, and therefore no mitigation is required by this Project. All potential maintenance issues should be resolved by either City Maintenance (public systems) or the respective property owners (private systems). No further analysis should be required of this Project. The Project should not create any problems as specified in Section 1.2.2.1 of the Manual and therefore is not required to provide Drainage Problem Impact Mitigation subject to the requirements of Section 1.2.2.2. Project runoff will be collected and released per the Manual’s requirements to accommodate Flow Control Duration Standard – Matching Forested Site Conditions (Level 2 Flow Control). The Project is located within a Basic Water Quality Area, but since the Project is a multifamily development, it shall adhere to Enhanced Basic Water Quality requirements. Per Section 1.2.8.1.A of the City of Renton SWDM Amendments, the Enhanced Water Quality Treatment requirement may be reduced to the Basic Water Quality requirement for this Project because no leachable metals will be used in areas of the site exposed to the weather and a covenant will be recorded that prohibits the future use of leachable metals on the site. During construction, standard sediment and erosion control methods will be utilized. This will include the use of a stabilized construction entrance, perimeter silt fencing, and other necessary measures to minimize soil erosion during construction. 2015 D. R. STRONG Consulting Engineers Inc. 21 Avana Ridge Level One Downstream Analysis Renton, Washington APPENDIX A. OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE & DOWNSTREAM MAP OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 TDA 1: NDA 1 Basin: Black River Subbasin Name: Panther Creek Subbasin Number: N/A Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance From site Discharge Existing Problems Potential Problems Observations of field inspector resource reviewer, or resident See map Type: sheet flow, swale, Stream, channel, pipe, Pond; Size: diameter Surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume % 1/4 mi=1,320 ft Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts. A1 2’ x 4’ Concrete Box Culvert Northeast side of SR 515, approximate midpoint of western property line. 0’ None Observed Slight potential for blockage from debris/foliage Light flow observed A1-B1 Southwesterly Pipe Flow 18” Concrete Pipe 0’-19’ None Observed None Anticipated B1 Type 2 Catch Basin Slightly southwest of box culvert on the northeast side of SR 515. 18” Conc. (NE,SW) 19’ None Observed None Anticipated Light flow observed B1-C1 Southwesterly Pipe Flow 18” Concrete Pipe, travels southwest under SR515 19’-74’ None Observed None Anticipated C1 Type 2 Catch Basin On the southwest side of SR 515, across the street from CB at point B1. 12” Conc. (SE), 18” Conc. (NE, NW) 74’ None Observed None Anticipated Light flow observed C1-D1 Northwesterly Pipe Flow 18” Concrete Pipe, travels northwest along the southwestern side of SR 515. 74’-358’ None Observed None Anticipated D1 Type 2 Catch Basin Southwestern side of SR 515, just east of parcel 2923059150. 18” Conc. (NE,SE), 24” Conc. (SW) 358’ None Observed None Anticipated Moderate flow observed D1-E1 Southwesterly Pipe Flow 24” Concrete Pipe, travels southwest under the sidewalk and outfalls into ditch. 358’-378’ None Observed None Anticipated 2015 D. R. STRONG Consulting Engineers Inc. 22 Avana Ridge Level One Downstream Analysis Renton, Washington E1 Pipe Outlet 24” Concrete Pipe outfalls into ditch on the southwest side of SR 515, heading southwest between parcels 2923059150 and 2923059134 378’ None Observed None Anticipated Moderate flow observed E1-F1 Channel Flow Runoff flows southwesterly between the parcels through a moderately vegetated ditch, approximately 2’ wide 378’-791’ None Observed General maintenance and clearing may be necessary in the future F1 Culvert Inlet Runoff flows into 30” CMP with trash rack. Flow is separated from the sidewalk by a ~2’ high concrete wall and chainlink fence. Inlet is custom designed and transitions from 30” to 18” pipe. 791’ None Observed Heavy flow may erode subgrade of wooden fence near inlet and cause problems Moderate flow observed F1-G1 Southwesterly Pipe Flow 18” PVC Pipe 791’-856’ None Observed None Anticipated G1 Type 1 Catch Basin South side of S 36th St. 18” (NE, SE, W) 856’ None Observed None Anticipated Moderate flow observed G1-H1 Westerly Pipe Flow 18” PVC Pipe 856’-954’ None Observed None Anticipated H1 Type 2 Catch Basin Solid lid in south side of S 36th St. 18” PVC (E, NW) 954’ None Observed None Anticipated Moderate flow observed H1-I1 Northwesterly Pipe Flow 18” PVC Pipe 954’-1127’ None Observed None Anticipated I1 Type 2 Catch Basin Solid lid in south side of S 36th St. 18” PVC (SE, W) 1127’’ None Observed None Anticipated Moderate flow observed I1-J1 Westerly Pipe Flow 18” PVC Pipe 1127’-1264’ None Observed None Anticipated J1 Type 2 Catch Basin Solid lid in south side of S 36th St. 18” PVC (E, SW) 1264’ None Observed None Anticipated Moderate flow observed J1-K1 Southwesterly Pipe Flow 18” PVC Pipe 1264’-1377’ None Observed None Anticipated 2015 D. R. STRONG Consulting Engineers Inc. 23 Avana Ridge Level One Downstream Analysis Renton, Washington K1 Type 2 Catch Basin Solid lid in south side of S 36th St. 18” PVC (NE, S). Over ¼ mile downstream - end of field reconnaissance. Runoff continues south between parcels 1441000150 and 1441000160. According to record drawings from the City of Renton, flow enters a CB at the back of parcel 1441000150, moves to another CB at the back of parcel 8106300980, and then moves west towards a CB at the front of parcel 8106300890, 1866’ along the downstream path. This Type 2 CB was observed during field reconnaissance. Moderate flow was observed. 18” pipe (E,W). Runoff outlets to the west. 1377’ None Observed None Anticipated Moderate flow observed 2015 D. R. STRONG Consulting Engineers Inc. 24 Avana Ridge Level One Downstream Analysis Renton, Washington OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 TDA 1: NDA 2 Basin: Black River Subbasin Name: Panther Creek Subbasin Number: N/A Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance From site Discharge Existing Problems Potential Problems Observations of field inspector resource reviewer, or resident See map Type: sheet flow, swale, Stream, channel, pipe, Pond; Size: diameter Surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume % 1/4 mi=1,320 ft Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts. A2 2’ x 4’ Concrete Box Culvert Northeast side of SR 515, just southeast of the northwest property corner. 0’ None Observed Slight potential for blockage from debris/foliage Light Flow Observed A2-B2 Southwesterly Pipe Flow 18” Concrete Pipe 0’-16’ None Observed None Anticipated B2 Type 2 Catch Basin Slightly southwest of box culvert on the northeast side of SR 515. 18” Conc. (NE,W) 16’ None Observed None Anticipated Light Flow Observed B2-C2 Westerly Pipe Flow 18” Concrete Pipe, travels west under SR515 16’-84’ None Observed None Anticipated C2 (D1) Type 1 CB Southwestern side of SR 515, just east of parcel 2923059150. 18” Conc. (NE,SE), 24” Conc. (SW). Flow combines at point D1 and continues along path for NDA 1 84’ None Observed None Anticipated Moderate Flow Observed GRAPHIC SCALE 0 75 150 225 1 INCH =150 FT. 2015 D. R. STRONG Consulting Engineers Inc. 66 Avana Ridge Technical Information Report Renton, Washington APPENDIX “B” CSWPPP D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Construction Stormwater General Permit Stormwater Pollution Prevention Plan (SWPPP) for Avana Ridge Prepared for: The Washington State Department of Ecology Northwest Regional Office 3190 16th Avenue SE Bellevue, WA 98008-5452 Permittee / Owner Developer Operator / Contractor Avana Ridge, LLC 9675 SE 36th Street, Suite 105 Mercer Island, WA 98040 Avana Ridge, LLC 9675 SE 36th Street, Suite 105 Mercer Island, WA 98040 TBD 10615 SE 172nd Street, Renton, Washington Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number TBD Earth Solutions NW, LLC 425.284.3300 SWPPP Prepared By Name Organization Contact Phone Number Maher A. Joudi, PE DR Strong Consulting Engineers, Inc. (425) 827-3063 SWPPP Preparation Date October 28, 2016 Project Construction Dates Activity / Phase Start Date End Date Site Development TBD TBD D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page i Table of Contents 1 Project Information ...............................................................................................................2 1.1 Existing Conditions .......................................................................................................2 1.2 Proposed Construction Activities ...................................................................................2 2 Construction Stormwater Best Management Practices (BMPs) ............................................4 2.1 The 12 Elements ...........................................................................................................4 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits .........................................4 2.1.2 Element 2: Establish Construction Access .............................................................5 2.1.3 Element 3: Control Flow Rates...............................................................................6 2.1.4 Element 4: Install Sediment Controls .....................................................................7 2.1.5 Element 5: Stabilize Soils.......................................................................................9 2.1.6 Element 6: Protect Slopes....................................................................................10 2.1.7 Element 7: Protect Drain Inlets.............................................................................11 2.1.8 Element 8: Stabilize Channels and Outlets ..........................................................12 2.1.9 Element 9: Control Pollutants ...............................................................................13 2.1.10 Element 10: Control Dewatering ..........................................................................16 2.1.11 Element 11: Maintain BMPs .................................................................................17 2.1.12 Element 12: Manage the Project ..........................................................................18 3 Pollution Prevention Team .................................................................................................20 4 Monitoring and Sampling Requirements ............................................................................21 4.1 Site Inspection ............................................................................................................21 4.2 Stormwater Quality Sampling ......................................................................................21 4.2.1 Turbidity Sampling ...............................................................................................22 4.2.2 pH Sampling ........................................................................................................23 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies .........................24 5.1 303(d) Listed Waterbodies ..........................................................................................24 5.2 TMDL Waterbodies .....................................................................................................24 6 Reporting and Record Keeping ..........................................................................................25 6.1 Record Keeping ..........................................................................................................25 6.1.1 Site Log Book ......................................................................................................25 6.1.2 Records Retention ...............................................................................................25 6.1.3 Updating the SWPPP ...........................................................................................25 6.2 Reporting ....................................................................................................................25 6.2.1 Discharge Monitoring Reports ..............................................................................25 6.2.2 Notification of Noncompliance ..............................................................................26 D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page ii List of Tables Table 1 – Summary of Site Pollutant Constituents .................................................................2 Table 3 – pH-Modifying Sources ............................................................................................15 Table 5 – Management ............................................................................................................18 Table 7 – Team Information ....................................................................................................20 Table 8 – Turbidity Sampling Method ....................................................................................22 Table 9 – pH Sampling Method ..............................................................................................23 List of Appendices A. Site Map B. BMP Detail C. Correspondence D. Site Inspection Form E. Construction Stormwater General Permit (CSWGP) F. Engineering Calculations D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 1 List of Acronyms and Abbreviations Acronym / Abbreviation Explanation 303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies BFO Bellingham Field Office of the Department of Ecology BMP(s) Best Management Practice(s) CESCL Certified Erosion and Sediment Control Lead CO2 Carbon Dioxide CRO Central Regional Office of the Department of Ecology CSWGP Construction Stormwater General Permit CWA Clean Water Act DMR Discharge Monitoring Report DO Dissolved Oxygen Ecology Washington State Department of Ecology EPA United States Environmental Protection Agency ERO Eastern Regional Office of the Department of Ecology ERTS Environmental Report Tracking System ESC Erosion and Sediment Control GULD General Use Level Designation NPDES National Pollutant Discharge Elimination System NTU Nephelometric Turbidity Units NWRO Northwest Regional Office of the Department of Ecology pH Power of Hydrogen RCW Revised Code of Washington SPCC Spill Prevention, Control, and Countermeasure su Standard Units SWMMEW Stormwater Management Manual for Eastern Washington SWMMWW Stormwater Management Manual for Western Washington SWPPP Stormwater Pollution Prevention Plan TESC Temporary Erosion and Sediment Control SWRO Southwest Regional Office of the Department of Ecology TMDL Total Maximum Daily Load VFO Vancouver Field Office of the Department of Ecology WAC Washington Administrative Code WSDOT Washington Department of Transportation WWHM Western Washington Hydrology Model D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 2 1 Project Information Project/Site Name: Avana Ridge Street/Location: 10615 SE 172nd Street City: Renton State: WA Zip code: 98059 Subdivision: N/A Receiving waterbody: Black River and Duwamish River 1.1 Existing Conditions Total acreage (including support activities such as off-site equipment staging yards, material storage areas, borrow areas). Total acreage: 3.78 Disturbed acreage: 3.64 Existing structures: 0.00 Landscape topography: 3.64 (estimate) Drainage patterns: 0.00 Existing Vegetation: 3.64 (estimate) Critical Areas (wetlands, streams, high erosion risk, steep or difficult to stabilize slopes): 0.09 Stream and adjacent wetland List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: Black River – Dissolved Oxygen, Bacteria, Bioassessment Duwamish River – Temperature, pH Table 1 includes a list of suspected and/or known contaminants associated with the construction activity. Table 1 – Summary of Site Pollutant Constituents Constituent (Pollutant) Location Depth Concentration No known contaminants exist on the Site 1.2 Proposed Construction Activities The applicant has gained approval to construct a 74-unit apartment complex on 3.78 acres (Project). The developable area (Project Area) is approximately 159,574 s.f. (3.64 acres) (excludes right-of-way dedication area and area of the identified stream from the gross Site area). A total of 66,438 s.f. of impervious area is proposed for the Site – which is less than 75 percent of total Site Area (123,620 s.f.). The remainder of the Project Area will consist of residential landscaping and other pervious surfaces. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 3 The proposed impervious surface includes an internal plat road, Road ‘North-South’, which will have a proposed 25-foot right of way and will be improved with 24 feet of pavement and vertical curb. The internal plat road, Road “East-West”, will have a proposed 66-foot right of way and will be improved with up to 65 feet of pavement, vertical curb, catch basins, and parking sections. Frontage improvements will be made to SE 172nd Street, Benson Road, and SR 515 (Benson Drive), including catch basins, vertical gutter, replacement of asphalt paths, and 8 foot sidewalk. The total proposed impervious area for the Site is 66,438 s.f. The majority of the southern section of the Site is a proposed open space and recreation area to provide a buffer for the existing stream running through the Site. Construction work will be completed under the Site Development permit. Activities will include installation of sewer, water and dry utilities; installation of storm sewer; construction of stormwater detention vault; road and sidewalks; and landscaping including enhancement planting of stream buffer. Runoff will be collected and conveyed to the proposed detention vault or dry wells. Appendix A shows the Site Plan with T.E.S.C. measures. Final stabilization of the disturbed land will include: • Asphalt roadway • Concrete sidewalks • Formal landscape planting • Stream buffer landscape planting • Keystone and precast retaining walls Contaminated Site Information: Proposed activities regarding contaminated soils or groundwater (example: on-site treatment system, authorized sanitary sewer discharge): The Project is located in the Enhanced Water Quality Treatment area. A combined detention/wet vault will be followed by a StormFilter media filtration system to meet water quality requirements. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 4 2 Construction Stormwater Best Management Practices (BMPs) The SWPPP is a living document reflecting current conditions and changes throughout the life of the project. These changes may be informal (i.e., hand-written notes and deletions). Update the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design. 2.1 The 12 Elements 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits To protect adjacent properties and reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land-disturbing activities begin. Trees that are to be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in the field and on the plans. In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. The BMPs relevant to marking the clearing limits that will be applied for this project include: The plastic or metal fence will be placed around the perimeter of the developable area of the Site. BMP will be implemented at the start of construction. Alternate BMPs for marking clearing limits are included in Appendix B as a quick reference tool for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the CESCL will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. List and describe BMPs: High Visibility Plastic or Metal Fence (BMP C103) Silt Fence (BMP C223) Installation Schedules: Installation will occur before all other activity. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 5 2.1.2 Element 2: Establish Construction Access Construction access or activities occurring on unpaved areas will be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads, and wheel washing, street sweeping, and street cleaning shall be employed to prevent sediment from entering state waters. All wash wastewater shall be controlled on site. Construction entrances will be installed in the location of the proposed access entrances, located on SE 172nd Street and Benson Road, and the proposed vault access road entrance along SE 172nd Street. Construction road and parking area stabilization will occur along these entrances. List and describe BMPs: Stabilized Construction Entrance (BMP C105) Construction Road/Parking Area Stabilization (BMP C107) Installation Schedules: Installation will occur after the clearing limits are marked. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 6 2.1.3 Element 3: Control Flow Rates In order to protect the properties and waterways downstream of the project site, stormwater discharges from the site will be controlled. Once the detention vault is constructed, it will be utilized during construction as a flow control and sedimentation device. Before the detention vault is completed, Baker Tanks will be used in its place as a flow control and sedimentation device. Discharge from the vault will be conveyed southwest to the existing storm conveyance system located in SR 515 (Benson Drive). Alternate flow control BMPs are included in Appendix B as a quick reference tool for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. The project site is located west of the Cascade Mountain Crest. As such, the project must comply with Minimum Requirement 7 (Ecology 2005). In general, discharge rates of stormwater from the site will be controlled where increases in impervious area or soil compaction during construction could lead to downstream erosion, or where necessary to meet local agency stormwater discharge requirements (e.g. discharge to combined sewer systems). Will you construct stormwater retention and/or detention facilities? Yes No Will you use permanent infiltration ponds or other low impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? Yes No List and describe BMPs: Baker Tanks (As necessary) Installation Schedules: Installation will occur before any grading occurs. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 7 2.1.4 Element 4: Install Sediment Controls Silt fence will be installed around the perimeter of the Site in areas where runoff could sheet- flow offsite. This BMP will be installed at the start of construction. The interceptor swales will be installed during site grading. The interceptor swales will be directed towards the Baker Tanks located at the northwest corner of the Site. Alternate sediment control BMPs are included in Appendix B as a quick reference tool for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. In addition, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on vehicle tires away from the site and to minimize washoff of sediments from adjacent streets in runoff. Whenever possible, sediment laden water shall be discharged into onsite, relatively level, vegetated areas (BMP C240 paragraph 5, page 4-102). In some cases, sediment discharge in concentrated runoff can be controlled using permanent stormwater BMPs (e.g., infiltration swales, ponds, trenches). Sediment loads can limit the effectiveness of some permanent stormwater BMPs, such as those used for infiltration or biofiltration; however, those BMPs designed to remove solids by settling (wet ponds or detention ponds) can be used during the construction phase. When permanent stormwater BMPs will be used to control sediment discharge during construction, the structure will be protected from excessive sedimentation with adequate erosion and sediment control BMPs. Any accumulated sediment shall be removed after construction is complete and the permanent stormwater BMP will be restabilized with vegetation per applicable design requirements once the remainder of the site has been stabilized. The following BMPs will be implemented as end-of-pipe sediment controls as required to meet permitted turbidity limits in the site discharge(s). Prior to the implementation of these technologies, sediment sources and erosion control and soil stabilization BMP efforts will be maximized to reduce the need for end-of-pipe sedimentation controls. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 8 List and describe BMPs: Baker Tank (As necessary) Silt Fence (BMP C233) Interceptor Swale (BMP C200) Installation Schedules: These will all be installed before any grading occurs. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 9 2.1.5 Element 5: Stabilize Soils Temporary seeding and cover measures may be required for interim grading activity and at soil stockpiles. Permanent Seeding will occur as grading is completed. All stabilized sections will be seeded and vegetated. Nets and Blankets along with Plastic Covering will be used on all slopes of 2:1 as shown on the plan. Dust Control will occur throughout the site as deemed necessary by the contractor and CESCL. Alternate soil stabilization BMPs are included in Appendix B as a quick reference tool for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be temporarily covered with plastic sheeting. All stockpiled soils shall be stabilized from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways, and drainage channels. West of the Cascade Mountains Crest Season Dates Number of Days Soils Can be Left Exposed During the Dry Season May 1 – September 30 7 days During the Wet Season October 1 – April 30 2 days Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Anticipated project dates: Start date: TBD End date: TBD Will you construct during the wet season? Yes No List and describe BMPs: Temporary and Permanent Seeding (BMP C120) Nets and Blankets (BMP C122) Plastic Covering (BMP C123) Dust Control (BMP C140) Installation Schedules: These will all be installed before any grading occurs. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 10 2.1.6 Element 6: Protect Slopes Temporary slope protection measures may be required for interim grading activity and at soil stockpiles. Permanent Seeding will occur throughout the site as slopes are stabilized. Nets and Blankets along with Plastic Covering will be used on all slopes of 2:1 Checks Dams will be installed every 50’ as shown on the plan. Alternate slope protection BMPs are included in Appendix B as a quick reference tool for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. Will steep slopes be present at the site during construction? Yes No List and describe BMPs: Temporary and Permanent Seeding (BMP C120) Nets and Blankets (BMP C122) Plastic Covering (BMP C123) Check Dams (BMP C207) Installation Schedules: In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be temporarily covered with plastic sheeting. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 11 2.1.7 Element 7: Protect Drain Inlets All storm drain inlets and culverts made operable during construction shall be protected to prevent unfiltered or untreated water from entering the drainage conveyance system. However, the first priority is to keep all access roads clean of sediment and keep street wash water separate from entering storm drains until treatment can be provided. Storm Drain Inlet Protection (BMP C220) will be implemented for all drainage inlets and culverts that could potentially be impacted by sediment-laden runoff on and near the project site. The following inlet protection measures will be applied on this project: • Catch Basin Filters (BMP C220) There are several existing catch basins which will require filters. If the BMP options listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D), or if no BMPs are listed above but deemed necessary during construction, the Certified Erosion and Sediment Control Lead shall implement one or more of the alternative BMP inlet protection options listed in Appendix B. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 12 2.1.8 Element 8: Stabilize Channels and Outlets Rip Rap (BMP C209) will be provided at all outlets. Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all conveyance systems. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 13 2.1.9 Element 9: Control Pollutants All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well-organized, and free of debris. If required, BMPs to be implemented to control specific sources of pollutants are discussed below. Vehicles, construction equipment, and/or petroleum product storage/dispensing: • All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. • On-site fueling tanks and petroleum product storage containers shall include secondary containment. • Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. • Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Demolition: • Dust released from demolished sidewalks, buildings, or structures will be controlled using Dust Control measures (BMP C140). • Storm drain inlets vulnerable to stormwater discharge carrying dust, soil, or debris will be protected using Storm Drain Inlet Protection (BMP C220 as described above for Element 7). • Process water and slurry resulting from sawcutting and surfacing operations will be prevented from entering the waters of the State by implementing Sawcutting and Surfacing Pollution Prevention measures (BMP C152). Concrete and grout: • Process water and slurry resulting from concrete work will be prevented from entering the waters of the State by implementing Concrete Handling measures (BMP C151). Sanitary wastewater: • Portable sanitation facilities will be firmly secured, regularly maintained, and emptied when necessary. Solid Waste: • Solid waste will be stored in secure, clearly marked containers. Other: • Other BMPs will be administered as necessary to address any additional pollutant sources on site. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 14 The project is not expected to exceed the 1,320 gallon stored-fuel threshold that requires developing a Spill Prevention, Control, and Countermeasure (SPCC) Plan under the Federal regulations of the Clean Water Act (CWA). List and describe BMPs: Dust Control measures (BMP C140) Concrete Handling measures (BMP C151) Sawcutting and Surfacing Pollution Prevention measures (BMP C152) Storm Drain Inlet Protection (BMP C220) Installation Schedules: Immediately following or in conjunction with activities. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site? Yes No List and describe BMPs: N/A Installation Schedules: N/A Inspection and Maintenance plan: Weekly Responsible Staff: CESCL Will wheel wash or tire bath system BMPs be used during construction? Yes No List and describe BMPs: Presently not anticipated . SWPPP to be amended if wheel wash proves necessary. Installation Schedules: TBD Inspection and Maintenance plan: Weekly Responsible Staff: CESCL Will pH-modifying sources be present on-site? D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 15 Yes No Table 3 – pH-Modifying Sources None Bulk cement Cement kiln dust Fly ash Other cementitious materials New concrete washing or curing waters Waste streams generated from concrete grinding and sawing Exposed aggregate processes Dewatering concrete vaults Concrete pumping and mixer washout waters Recycled concrete Other (i.e., calcium lignosulfate) [please describe: ] List and describe BMPs: Wash water to be contained and routed to Baker Tank. Specific pH treatment measures to be determined by contractor and CECSL. Presently, CO2 sparging or dry ice anticipated approach if pH must be altered. Installation Schedules: prior to placement of concrete Inspection and Maintenance plan: Monitoring will occur at the time of concrete wash operations. Responsible Staff: CESCL Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches, streets, or streams. Excess concrete must not be dumped on-site, except in designated concrete washout areas with appropriate BMPs installed. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 16 2.1.10 Element 10: Control Dewatering There will be no dewatering as part of this construction project. If excavation results in the requirement of dewatering, this SWPPP can be modified to include dewatering measures including control of discharge waters. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 17 2.1.11 Element 11: Maintain BMPs All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained and repaired as needed to ensure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP specification (see Volume II of the SWMMWW or Chapter 7 of the SWMMEW). Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to once every calendar month. All temporary ESC BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal of either BMPs or vegetation shall be permanently stabilized. Additionally, protection must be provided for all BMPs installed for the permanent control of stormwater from sediment and compaction. BMPs that are to remain in place following completion of construction shall be examined and restored to full operating condition. If sediment enters these BMPs during construction, the sediment shall be removed and the facility shall be returned to conditions specified in the construction documents. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 18 2.1.12 Element 12: Manage the Project Project management will incorporate the key components listed below: Table 5 – Management Design the project to fit the existing topography, soils, and drainage patterns Emphasize erosion control rather than sediment control Minimize the extent and duration of the area exposed Keep runoff velocities low Retain sediment on-site Thoroughly monitor site and maintain all ESC measures Schedule major earthwork during the dry season Other (please describe) As this project site is located west of the Cascade Mountain Crest, the project will be managed according to the following key project components: Phasing of Construction • The construction project is being phased to the extent practicable in order to prevent soil erosion, and, to the maximum extent possible, the transport of sediment from the site during construction. • Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the clearing activities during each phase of construction, per the Scheduling BMP (C 162). Seasonal Work Limitations • From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if shown to the satisfaction of the local permitting authority that silt-laden runoff will be prevented from leaving the site through a combination of the following: o Site conditions including existing vegetative coverage, slope, soil type, and proximity to receiving waters; and o Limitations on activities and the extent of disturbed areas; and o Proposed erosion and sediment control measures. • Based on the information provided and/or local weather conditions, the local permitting authority may expand or restrict the seasonal limitation on site disturbance. • The following activities are exempt from the seasonal clearing and grading limitations: o Routine maintenance and necessary repair of erosion and sediment control BMPs; o Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil; and o Activities where there is 100 percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 19 Coordination with Utilities and Other Jurisdictions • Care has been taken to coordinate with utilities, other construction projects, and the local jurisdiction in preparing this SWPPP and scheduling the construction work. Inspection and Monitoring • All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Site inspections shall be conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. This person has the necessary skills to: o Assess the site conditions and construction activities that could impact the quality of stormwater, and o Assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. • A Certified Erosion and Sediment Control Lead shall be on-site or on-call at all times. • Whenever inspection and/or monitoring reveals that the BMPs identified in this SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible. Maintaining an Updated Construction SWPPP • This SWPPP shall be retained on-site or within reasonable access to the site. • The SWPPP shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. • The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection. • If BMP(s) are deemed do not satisfy the requirements set forth in the General NPDES Permit (Appendix D), the CESCL will promptly implement one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. • Site inspections and monitoring will be conducted in accordance with Special Condition S4 of the CSWGP. Sampling will occur at the baker tank discharge piping. • The SWPPP will be updated, maintained, and implemented in accordance with Special Conditions S3, S4, and S9 of the CSWGP. • As site work progresses the SWPPP will be modified routinely to reflect changing site conditions. The SWPPP will be reviewed monthly to ensure the content is current. • Upon request, contractor shall provide the DOE and City of Sammamish with current SWPPP. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 20 3 Pollution Prevention Team Table 7 – Team Information Title Name(s) Phone Number Certified Erosion and Sediment Control Lead (CESCL) Earth Solutions NW, LLC 425.284.3300 Resident Engineer Maher A. Joudi, PE 425-827-3063 Emergency Ecology Contact Howard Zorzi 425-649-7130 Emergency Permittee/ Owner Contact Justin Lagers 206-588-1147 Non-Emergency Owner Contact Justin Lagers 206-588-1147 Monitoring Personnel Earth Solutions NW, LLC 425.284.3300 Ecology Regional Office Northwest Regional Office 425-649-7000 City Spill Hotline (8:00 am to 5:00 pm) 425-295-0500 King County Spill Hotline (After Hours) 206-296-8100 D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 21 4 Monitoring and Sampling Requirements Monitoring includes visual inspection, sampling for water quality parameters of concern, and documentation of the inspection and sampling findings in a site log book. A site log book will be maintained for all on-site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Stormwater sampling data File a blank form under Appendix D. The site log book must be maintained on-site within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See CSWGP Special Condition S8 and Section 5 of this template. 4.1 Site Inspection All BMPs will be inspected, maintained, and repaired as needed to assure continued performance of their intended function. The inspector will be a Certified Erosion and Sediment Control Lead (CESCL) per BMP C160. The name and contact information for the CESCL is provided in Section 3 of this SWPPP. Site inspection will occur in all areas disturbed by construction activities and at all stormwater discharge points. Stormwater will be examined for the presence of suspended sediment, turbidity, discoloration, and oily sheen. The site inspector will evaluate and document the effectiveness of the installed BMPs and determine if it is necessary to repair or replace any of the BMPs to improve the quality of stormwater discharges. All maintenance and repairs will be documented in the site log book or forms provided in this document. All new BMPs or design changes will be documented in the SWPPP as soon as possible. Site inspections will be conducted at least once every calendar week and within 24 hours following any discharge from the site. For sites that are temporarily stabilized and inactive, the required frequency is reduced to once per calendar month. The site inspector will record each site inspection using the site log inspection forms provided in Appendix E. The site inspection log forms may be separated from this SWPPP document, but will be maintained on-site or within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. 4.2 Stormwater Quality Sampling Runoff will be collected and conveyed to the proposed vault, followed by a StormFilter media filtration system to meet Enhanced Water Quality requirements. Testing will occur as deemed necessary by the CESCL. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 22 4.2.1 Turbidity Sampling Requirements include calibrated turbidity meter or transparency tube to sample site discharges for compliance with the CSWGP. Sampling will be conducted at all discharge points at least once per calendar week. Method for sampling turbidity: Table 8 – Turbidity Sampling Method Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size) Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size) The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency less than 33 centimeters. If the discharge’s turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to or greater than 6 cm, the following steps will be conducted: 1. Review the SWPPP for compliance with Special Condition S9. Make appropriate revisions within 7 days of the date the discharge exceeded the benchmark. 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period. 3. Document BMP implementation and maintenance in the site log book. If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following steps will be conducted: 1. Telephone the applicable Ecology Region’s Environmental Report Tracking System (ERTS) number within 24 hours. • Central Region (Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, Yakima): (509) 575-2490 • Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman): (509) 329-3400 • Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish, Whatcom): (425) 649-7000 • Southwest Region (Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, Wahkiakum,): (360) 407-6300 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period 3. Document BMP implementation and maintenance in the site log book. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 23 4. Continue to sample discharges daily until one of the following is true: • Turbidity is 25 NTU (or lower). • Transparency is 33 cm (or greater). • Compliance with the water quality limit for turbidity is achieved. o 1 - 5 NTU over background turbidity, if background is less than 50 NTU o 1% - 10% over background turbidity, if background is 50 NTU or greater • The discharge stops or is eliminated. 4.2.2 pH Sampling pH monitoring is required for “Significant concrete work” (i.e., greater than 1000 cubic yards poured or recycled concrete over the life of the project). The use of engineered soils (soil amendments including but not limited to Portland cement-treated base [CTB], cement kiln dust [CKD] or fly ash) also requires pH monitoring. For significant concrete work, pH sampling will start the first day concrete is poured and continue until it is cured, typically three (3) weeks after the last pour. For engineered soils, pH sampling begins when engineered soils are first exposed to precipitation and continues until the area is fully stabilized. If the measured pH is 8.5 or greater, the following measures will be taken: 1. Prevent high pH water from entering storm sewer systems or surface water. 2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate technology such as carbon dioxide (CO2) sparging (liquid or dry ice). 3. Written approval will be obtained from Ecology prior to the use of chemical treatment other than CO2 sparging or dry ice. Method for sampling pH: Table 9 – pH Sampling Method pH meter pH test kit Wide range pH indicator paper Not: pH monitoring equipment unknown at this time; to be determined by CESCL D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 24 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies 5.1 303(d) Listed Waterbodies Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH? Yes No List the impairment(s): 5.2 TMDL Waterbodies Waste Load Allocation for CWSGP discharges: List and describe BMPs: Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point of discharge. The Construction Stormwater General Permit Proposed New Discharge to an Impaired Water Body form is included in Appendix F. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 25 6 Reporting and Record Keeping 6.1 Record Keeping 6.1.1 Site Log Book A site log book will be maintained for all on-site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Sample logs 6.1.2 Records Retention Records will be retained during the life of the project and for a minimum of three (3) years following the termination of permit coverage in accordance with Special Condition S5.C of the CSWGP. Permit documentation to be retained on-site: • CSWGP • Permit Coverage Letter • SWPPP • Site Log Book Permit documentation will be provided within 14 days of receipt of a written request from Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP. 6.1.3 Updating the SWPPP The SWPPP will be modified if: • Found ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. • There is a change in design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the State. The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine additional or modified BMPs are necessary for compliance. An updated timeline for BMP implementation will be prepared. 6.2 Reporting 6.2.1 Discharge Monitoring Reports Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page 26 monitoring period the DMR will be submitted as required, reporting “No Discharge”. The DMR due date is fifteen (15) days following the end of each calendar month. DMRs will be reported online through Ecology’s WQWebDMR System. 6.2.2 Notification of Noncompliance If any of the terms and conditions of the permit is not met, and the resulting noncompliance may cause a threat to human health or the environment, the following actions will be taken: 1. Ecology will be immediately notified of the failure to comply by calling the applicable Regional office ERTS phone number (Regional office numbers listed below). 2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or correct the noncompliance. If applicable, sampling and analysis of any noncompliance will be repeated immediately and the results submitted to Ecology within five (5) days of becoming aware of the violation. 3. A detailed written report describing the noncompliance will be submitted to Ecology within five (5) days, unless requested earlier by Ecology. Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6 cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as required by Special Condition S5.A of the CSWGP. • Central Region at (509) 575-2490 for Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, or Yakima County • Eastern Region at (509) 329-3400 for Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, or Whitman County • Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit, Snohomish, or Whatcom County • Southwest Region at (360) 407-6300 for Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, or Wahkiakum Include the following information: 1. Your name and / Phone number 2. Permit number 3. City / County of project 4. Sample results 5. Date / Time of call 6. Date / Time of sample 7. Project name In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH water. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page A-1 Appendix A Site Map SDSDGRAPHIC SCALE02040801 INCH = 40 FT. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page B-1 Appendix B BMP Details Volume II – Construction Stormwater Pollution Prevention - August 2012 4-3 BMP C101: Preserving Natural Vegetation Purpose The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site disturbance is the single most effective method for reducing erosion. For example, conifers can hold up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the tree can be released slowly to the ground after the storm. Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent watercourses or swales, and on building sites in wooded areas. • As required by local governments. • Phase construction to preserve natural vegetation on the project site for as long as possible during the construction period. Design and Installation Specifications Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines. The preservation of individual plants is more difficult because heavy equipment is generally used to remove unwanted vegetation. The points to remember when attempting to save individual plants are: • Is the plant worth saving? Consider the location, species, size, age, vigor, and the work involved. Local governments may also have ordinances to save natural vegetation and trees. • Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground disturbance away from the trees at least as far out as the dripline. Plants need protection from three kinds of injuries: • Construction Equipment - This injury can be above or below the ground level. Damage results from scarring, cutting of roots, and compaction of the soil. Placing a fenced buffer zone around plants to be saved prior to construction can prevent construction equipment injuries. • Grade Changes - Changing the natural ground level will alter grades, which affects the plant's ability to obtain the necessary air, water, and minerals. Minor fills usually do not cause problems although sensitivity between species does vary and should be checked. Trees can typically tolerate fill of 6 inches or less. For shrubs and other plants, the fill should be less. When there are major changes in grade, it may become necessary to supply air to the roots of plants. This can be done by placing a layer of gravel and a tile system over the roots before the fill is made. A tile system protects a tree from a raised grade. The tile system should be Volume II – Construction Stormwater Pollution Prevention - August 2012 4-4 laid out on the original grade leading from a dry well around the tree trunk. The system should then be covered with small stones to allow air to circulate over the root area. Lowering the natural ground level can seriously damage trees and shrubs. The highest percentage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can cause serious injury. To protect the roots it may be necessary to terrace the immediate area around the plants to be saved. If roots are exposed, construction of retaining walls may be needed to keep the soil in place. Plants can also be preserved by leaving them on an undisturbed, gently sloping mound. To increase the chances for survival, it is best to limit grade changes and other soil disturbances to areas outside the dripline of the plant. • Excavations - Protect trees and other plants when excavating for drainfields, power, water, and sewer lines. Where possible, the trenches should be routed around trees and large shrubs. When this is not possible, it is best to tunnel under them. This can be done with hand tools or with power augers. If it is not possible to route the trench around plants to be saved, then the following should be observed: Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a wood dressing like asphalt base paint if roots will be exposed for more than 24-hours. Backfill the trench as soon as possible. Tunnel beneath root systems as close to the center of the main trunk to preserve most of the important feeder roots. Some problems that can be encountered with a few specific trees are: • Maple, Dogwood, Red alder, Western hemlock, Western red cedar, and Douglas fir do not readily adjust to changes in environment and special care should be taken to protect these trees. • The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock is moderate. The danger of windthrow increases where dense stands have been thinned. Other species (unless they are on shallow, wet soils less than 20 inches deep) have a low windthrow hazard. • Cottonwoods, maples, and willows have water-seeking roots. These can cause trouble in sewer lines and infiltration fields. On the other hand, they thrive in high moisture conditions that other trees would not. • Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause serious disease problems. Disease can become established through damaged limbs, trunks, roots, Volume II – Construction Stormwater Pollution Prevention - August 2012 4-5 and freshly cut stumps. Diseased and weakened trees are also susceptible to insect attack. Maintenance Standards Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. • If tree roots have been exposed or injured, “prune” cleanly with an appropriate pruning saw or lopers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. BMP C102: Buffer Zones Purpose Creation of an undisturbed area or strip of natural vegetation or an established suitable planting that will provide a living filter to reduce soil erosion and runoff velocities. Conditions of Use Natural buffer zones are used along streams, wetlands and other bodies of water that need protection from erosion and sedimentation. Vegetative buffer zones can be used to protect natural swales and can be incorporated into the natural landscaping of an area. Critical-areas buffer zones should not be used as sediment treatment areas. These areas shall remain completely undisturbed. The local permitting authority may expand the buffer widths temporarily to allow the use of the expanded area for removal of sediment. Design and Installation Specifications • Preserving natural vegetation or plantings in clumps, blocks, or strips is generally the easiest and most successful method. • Leave all unstable steep slopes in natural vegetation. • Mark clearing limits and keep all equipment and construction debris out of the natural areas and buffer zones. Steel construction fencing is the most effective method in protecting sensitive areas and buffers. Alternatively, wire-backed silt fence on steel posts is marginally effective. Flagging alone is typically not effective. • Keep all excavations outside the dripline of trees and shrubs. • Do not push debris or extra soil into the buffer zone area because it will cause damage from burying and smothering. • Vegetative buffer zones for streams, lakes or other waterways shall be established by the local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undisturbed. Replace all damaged flagging immediately. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-6 BMP C103: High Visibility Fence Purpose Fencing is intended to: 1. Restrict clearing to approved limits. 2. Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undisturbed. 3. Limit construction traffic to designated construction entrances, exits, or internal roads. 4. Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used: • At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. • As necessary to control vehicle access to and on the site. Design and Installation Specifications High visibility plastic fence shall be composed of a high-density polyethylene material and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high visibility orange. The fence tensile strength shall be 360 lbs./ft. using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233 to act as high visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-7 BMP C105: Stabilized Construction Entrance / Exit Purpose Stabilized Construction entrances are established to reduce the amount of sediment transported onto paved roads by vehicles or equipment. This is done by constructing a stabilized pad of quarry spalls at entrances and exits for construction sites. Conditions of Use Construction entrances shall be stabilized wherever traffic will be entering or leaving a construction site if paved roads or other paved areas are within 1,000 feet of the site. For residential construction provide stabilized construction entrances for each residence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size/configuration. On large commercial, highway, and road projects, the designer should include enough extra materials in the contract to allow for additional stabilized entrances not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed. Design and Installation Specifications See Figure 4.1.1 for details. Note: the 100’ minimum length of the entrance shall be reduced to the maximum practicable size when the size or configuration of the site does not allow the full length (100’). Construct stabilized construction entrances with a 12-inch thick pad of 4- inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed concrete, cement, or calcium chloride for construction entrance stabilization because these products raise pH levels in stormwater and concrete discharge to surface waters of the State is prohibited. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the following standards: Grab Tensile Strength (ASTM D4751) 200 psi min. Grab Tensile Elongation (ASTM D4632) 30% max. Mullen Burst Strength (ASTM D3786-80a) 400 psi min. AOS (ASTM D4751) 20-45 (U.S. standard sieve size) • Consider early installation of the first lift of asphalt in areas that will paved; this can be used as a stabilized entrance. Also consider the installation of excess concrete as a stabilized entrance. During large concrete pours, excess concrete is often available for this purpose. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-8 • Fencing (see BMP C103) shall be installed as necessary to restrict traffic to the construction entrance. • Whenever possible, the entrance shall be constructed on a firm, compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance. • Construction entrances should avoid crossing existing sidewalks and back of walk drains if at all possible. If a construction entrance must cross a sidewalk or back of walk drain, the full length of the sidewalk and back of walk drain must be covered and protected from sediment leaving the site. Maintenance Standards Quarry spalls shall be added if the pad is no longer in accordance with the specifications. • If the entrance is not preventing sediment from being tracked onto pavement, then alternative measures to keep the streets free of sediment shall be used. This may include replacement/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of the entrance, or the installation of a wheel wash. • Any sediment that is tracked onto pavement shall be removed by shoveling or street sweeping. The sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be cleaned by washing down the street, except when high efficiency sweeping is ineffective and there is a threat to public safety. If it is necessary to wash the streets, the construction of a small sump to contain the wash water shall be considered. The sediment would then be washed into the sump where it can be controlled. • Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high efficiency mechanical sweeper because this creates dust and throws soils into storm systems or conveyance ditches. • Any quarry spalls that are loosened from the pad, which end up on the roadway shall be removed immediately. • If vehicles are entering or exiting the site at points other than the construction entrance(s), fencing (see BMP C103) shall be installed to control traffic. • Upon project completion and site stabilization, all construction accesses intended as permanent access for maintenance shall be permanently stabilized. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-9 Figure 4.1.1 – Stabilized Construction Entrance Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C105. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html BMP C106: Wheel Wash Purpose Wheel washes reduce the amount of sediment transported onto paved roads by motor vehicles. Conditions of Use When a stabilized construction entrance (see BMP C105) is not preventing sediment from being tracked onto pavement. • Wheel washing is generally an effective BMP when installed with careful attention to topography. For example, a wheel wash can be detrimental if installed at the top of a slope abutting a right-of-way where the water from the dripping truck can run unimpeded into the street. Driveway shall meet the requirements of the permitting agency It is recommended that the entrance be crowned so that runoff drains off the pad Provide full width of ingress/egress area 12” min. thickness Geotextile 4’ – 8” quarry spalls Install driveway culvert if there is a roadside ditch present Volume II – Construction Stormwater Pollution Prevention - August 2012 4-10 • Pressure washing combined with an adequately sized and surfaced pad with direct drainage to a large 10-foot x 10-foot sump can be very effective. • Discharge wheel wash or tire bath wastewater to a separate on-site treatment system that prevents discharge to surface water, such as closed-loop recirculation or upland land application, or to the sanitary sewer with local sewer district approval. • Wheel wash or tire bath wastewater should not include wastewater from concrete washout areas. Design and Installation Specifications Suggested details are shown in Figure 4.1.2. The Local Permitting Authority may allow other designs. A minimum of 6 inches of asphalt treated base (ATB) over crushed base material or 8 inches over a good subgrade is recommended to pave the wheel wash. Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy will work well to test clearance. Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck tongues with water. Midpoint spray nozzles are only needed in extremely muddy conditions. Wheel wash systems should be designed with a small grade change, 6- to 1-inches for a 10-foot-wide pond, to allow sediment to flow to the low side of pond to help prevent re-suspension of sediment. A drainpipe with a 2- to 3-foot riser should be installed on the low side of the pond to allow for easy cleaning and refilling. Polymers may be used to promote coagulation and flocculation in a closed-loop system. Polyacrylamide (PAM) added to the wheel wash water at a rate of 0.25 - 0.5 pounds per 1,000 gallons of water increases effectiveness and reduces cleanup time. If PAM is already being used for dust or erosion control and is being applied by a water truck, the same truck can be used to change the wash water. Maintenance Standards The wheel wash should start out the day with fresh water. The wash water should be changed a minimum of once per day. On large earthwork jobs where more than 10-20 trucks per hour are expected, the wash water will need to be changed more often. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-11 Figure 4.1.2 – Wheel Wash Notes: 1. Asphalt construction entrance 6 in. asphalt treated base (ATB). 2. 3-inch trash pump with floats on the suction hose. 3. Midpoint spray nozzles, if needed. 4. 6-inch sewer pipe with butterfly valves. Bottom one is a drain. Locate top pipe’s invert 1 foot above bottom of wheel wash. 5. 8 foot x 8 foot sump with 5 feet of catch. Build so the sump can be cleaned with a trackhoe. 6. Asphalt curb on the low road side to direct water back to pond. 7. 6-inch sleeve under road. 8. Ball valves. 9. 15 foot. ATB apron to protect ground from splashing water. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-12 BMP C107: Construction Road/Parking Area Stabilization Purpose Stabilizing subdivision roads, parking areas, and other on-site vehicle transportation routes immediately after grading reduces erosion caused by construction traffic or runoff. Conditions of Use Roads or parking areas shall be stabilized wherever they are constructed, whether permanent or temporary, for use by construction traffic. • High Visibility Fencing (see BMP C103) shall be installed, if necessary, to limit the access of vehicles to only those roads and parking areas that are stabilized. Design and Installation Specifications • On areas that will receive asphalt as part of the project, install the first lift as soon as possible. • A 6-inch depth of 2- to 4-inch crushed rock, gravel base, or crushed surfacing base course shall be applied immediately after grading or utility installation. A 4-inch course of asphalt treated base (ATB) may also be used, or the road/parking area may be paved. It may also be possible to use cement or calcium chloride for soil stabilization. If cement or cement kiln dust is used for roadbase stabilization, pH monitoring and BMPs (BMPs C252 and C253) are necessary to evaluate and minimize the effects on stormwater. If the area will not be used for permanent roads, parking areas, or structures, a 6-inch depth of hog fuel may also be used, but this is likely to require more maintenance. Whenever possible, construction roads and parking areas shall be placed on a firm, compacted subgrade. • Temporary road gradients shall not exceed 15 percent. Roadways shall be carefully graded to drain. Drainage ditches shall be provided on each side of the roadway in the case of a crowned section, or on one side in the case of a super-elevated section. Drainage ditches shall be directed to a sediment control BMP. • Rather than relying on ditches, it may also be possible to grade the road so that runoff sheet-flows into a heavily vegetated area with a well-developed topsoil. Landscaped areas are not adequate. If this area has at least 50 feet of vegetation that water can flow through, then it is generally preferable to use the vegetation to treat runoff, rather than a sediment pond or trap. The 50 feet shall not include wetlands or their buffers. If runoff is allowed to sheetflow through adjacent vegetated areas, it is vital to design the roadways and parking areas so that no concentrated runoff is created. • Storm drain inlets shall be protected to prevent sediment-laden water entering the storm drain system (see BMP C220). Maintenance Standards Inspect stabilized areas regularly, especially after large storm events. Crushed rock, gravel base, etc. shall be added as required to maintain a Volume II – Construction Stormwater Pollution Prevention - August 2012 4-13 stable driving surface and to stabilize any areas that have eroded. Following construction, these areas shall be restored to pre-construction condition or better to prevent future erosion. Perform street cleaning at the end of each day or more often if necessary. BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch with straw or an erosion control blanket until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of September. Otherwise, vegetation will not establish itself enough to provide more than average protection. • Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding. See BMP C121: Mulching for specifications. • Seed and mulch, all disturbed areas not otherwise vegetated at final site stabilization. Final stabilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement, riprap, gabions or geotextiles) which will prevent erosion. Design and Installation Specifications Seed retention/detention ponds as required. Install channels intended for vegetation before starting major earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control blankets over hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed before water flow; install sod in the channel bottom—over hydromulch and erosion control blankets. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-14 • Confirm the installation of all required surface water control measures to prevent seed from washing away. • Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 percent tackifier. See BMP C121: Mulching for specifications. • Areas that will have seeding only and not landscaping may need compost or meal-based mulch included in the hydroseed in order to establish vegetation. Re-install native topsoil on the disturbed soil surface before application. • When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this, consider increasing seed quantities by up to 50 percent. • Enhance vegetation establishment by dividing the hydromulch operation into two phases: 1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift. 2. Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by: 1. Installing the mulch, seed, fertilizer, and tackifier in one lift. 2. Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre. 3. Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for: • Irrigation. • Reapplication of mulch. • Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum) and BFM/MBFMs (3,000 pounds per acre minimum). • Seed may be installed by hand if: • Temporary and covered by straw, mulch, or topsoil. • Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or erosion blankets. • The seed mixes listed in the tables below include recommended mixes for both temporary and permanent seeding. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-15 • Apply these mixes, with the exception of the wetland mix, at a rate of 120 pounds per acre. This rate can be reduced if soil amendments or slow-release fertilizers are used. • Consult the local suppliers or the local conservation district for their recommendations because the appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the local authority may be used. • Other mixes may be appropriate, depending on the soil type and hydrology of the area. • Table 4.1.2 lists the standard mix for areas requiring a temporary vegetative cover. Table 4.1.2 Temporary Erosion Control Seed Mix % Weight % Purity % Germination Chewings or annual blue grass Festuca rubra var. commutata or Poa anna 40 98 90 Perennial rye - Lolium perenne 50 98 90 Redtop or colonial bentgrass Agrostis alba or Agrostis tenuis 5 92 85 White dutch clover Trifolium repens 5 98 90 • Table 4.1.3 lists a recommended mix for landscaping seed. Table 4.1.3 Landscaping Seed Mix % Weight % Purity % Germination Perennial rye blend Lolium perenne 70 98 90 Chewings and red fescue blend Festuca rubra var. commutata or Festuca rubra 30 98 90 Volume II – Construction Stormwater Pollution Prevention - August 2012 4-16 • Table 4.1.4 lists a turf seed mix for dry situations where there is no need for watering. This mix requires very little maintenance. Table 4.1.4 Low -Growing Turf Seed Mix % Weight % Purity % Germination Dwarf tall fescue (several varieties) Festuca arundinacea var. 45 98 90 Dwarf perennial rye (Barclay) Lolium perenne var. barclay 30 98 90 Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 • Table 4.1.5 lists a mix for bioswales and other intermittently wet areas. Table 4.1.5 Bioswale Seed Mix* % Weight % Purity % Germination Tall or meadow fescue Festuca arundinacea or Festuca elatior 75-80 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 92 85 Redtop bentgrass Agrostis alba or Agrostis gigantea 5-10 90 80 * Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix Volume II – Construction Stormwater Pollution Prevention - August 2012 4-17 • Table 4.1.6 lists a low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands. Apply this mixture at a rate of 60 pounds per acre. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Table 4.1.6 Wet Area Seed Mix* % Weight % Purity % Germination Tall or meadow fescue Festuca arundinacea or Festuca elatior 60-70 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 98 85 Meadow foxtail Alepocurus pratensis 10-15 90 80 Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 * Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix • Table 4.1.7 lists a recommended meadow seed mix for infrequently maintained areas or non-maintained areas where colonization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending the soil can reduce the need for clover. Table 4.1.7 Meadow Seed Mix % Weight % Purity % Germination Redtop or Oregon bentgrass Agrostis alba or Agrostis oregonensis 20 92 85 Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Volume II – Construction Stormwater Pollution Prevention - August 2012 4-18 • Roughening and Rototilling: • The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk slopes before seeding if engineering purposes require compaction. Backblading or smoothing of slopes greater than 4H:1V is not allowed if they are to be seeded. • Restoration-based landscape practices require deeper incorporation than that provided by a simple single-pass rototilling treatment. Wherever practical, initially rip the subgrade to improve long-term permeability, infiltration, and water inflow qualities. At a minimum, permanent areas shall use soil amendments to achieve organic matter and permeability performance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches complete the rototilling process in multiple lifts, or prepare the engineered soil system per specifications and place to achieve the specified depth. • Fertilizers: • Conducting soil tests to determine the exact type and quantity of fertilizer is recommended. This will prevent the over-application of fertilizer. • Organic matter is the most appropriate form of fertilizer because it provides nutrients (including nitrogen, phosphorus, and potassium) in the least water-soluble form. • In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium) fertilizer at a rate of 90 pounds per acre. Always use slow-release fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agitate, more than 20 minutes before use. Too much agitation destroys the slow-release coating. • There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal provides a good source of long-term, slow-release, available nitrogen. • Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix: • On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre of mulch with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Installed products per manufacturer’s instructions. Most products require 24-36 hours to cure before rainfall and cannot be installed on wet or saturated soils. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-19 Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. • BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation establishment. Advantages over blankets include: • BFM and MBFMs do not require surface preparation. • Helicopters can assist in installing BFM and MBFMs in remote areas. • On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses for safety. • Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. Maintenance Standards Reseed any seeded areas that fail to establish at least 80 percent cover (100 percent cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such as sodding, mulching, or nets/blankets. If winter weather prevents adequate grass growth, this time limit may be relaxed at the discretion of the local authority when sensitive areas would otherwise be protected. • Reseed and protect by mulch any areas that experience erosion after achieving adequate cover. Reseed and protect by mulch any eroded area. • Supply seeded areas with adequate moisture, but do not water to the extent that it causes runoff. Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C120. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html BMP C121: Mulching Purpose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There is an enormous variety of mulches that can be used. This section discusses only the most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used: • For less than 30 days on disturbed areas that require cover. • At all times for seeded areas, especially during the wet season and Volume II – Construction Stormwater Pollution Prevention - August 2012 4-20 during the hot summer months. • During the wet season on slopes steeper than 3H:1V with more than 10 feet of vertical relief. Mulch may be applied at any time of the year and must be refreshed periodically. • For seeded areas mulch may be made up of 100 percent: cottonseed meal; fibers made of wood, recycled cellulose, hemp, kenaf; compost; or blends of these. Tackifier shall be plant-based, such as guar or alpha plantago, or chemical-based such as polyacrylamide or polymers. Any mulch or tackifier product used shall be installed per manufacturer’s instructions. Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. Design and Installation Specifications For mulch materials, application rates, and specifications, see Table 4.1.8. Always use a 2-inch minimum mulch thickness; increase the thickness until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or other areas highly susceptible to erosion. Mulch used within the ordinary high-water mark of surface waters should be selected to minimize potential flotation of organic matter. Composted organic materials have higher specific gravities (densities) than straw, wood, or chipped material. Consult Hydraulic Permit Authority (HPA) for mulch mixes if applicable. Maintenance Standards • The thickness of the cover must be maintained. • Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-21 Table 4.1.8 Mulch Standards and Guidelines Mulch Material Quality Standards Application Rates Remarks Straw Air-dried; free from undesirable seed and coarse material. 2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per acre Cost-effective protection when applied with adequate thickness. Hand-application generally requires greater thickness than blown straw. The thickness of straw may be reduced by half when used in conjunction with seeding. In windy areas straw must be held in place by crimping, using a tackifier, or covering with netting. Blown straw always has to be held in place with a tackifier as even light winds will blow it away. Straw, however, has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long- term benefits. It should also not be used within the ordinary high-water elevation of surface waters (due to flotation). Hydromulch No growth inhibiting factors. Approx. 25-30 lbs per 1,000 sf or 1,500 - 2,000 lbs per acre Shall be applied with hydromulcher. Shall not be used without seed and tackifier unless the application rate is at least doubled. Fibers longer than about ¾-1 inch clog hydromulch equipment. Fibers should be kept to less than ¾ inch. Composted Mulch and Compost No visible water or dust during handling. Must be produced in accordance with WAC 173-350, Solid Waste Handling Standards. . 2" thick min.; approx. 100 tons per acre (approx. 800 lbs per yard) More effective control can be obtained by increasing thickness to 3". Excellent mulch for protecting final grades until landscaping because it can be directly seeded or tilled into soil as an amendment. Composted mulch has a coarser size gradation than compost. It is more stable and practical to use in wet areas and during rainy weather conditions. Do not use composted mulch near wetlands or near phosphorous impaired water bodies. Chipped Site Vegetation Average size shall be several inches. Gradations from fines to 6 inches in length for texture, variation, and interlocking properties. 2" thick min.; This is a cost-effective way to dispose of debris from clearing and grubbing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above approx. 10% because of its tendency to be transported by runoff. It is not recommended within 200 feet of surface waters. If seeding is expected shortly after mulch, the decomposition of the chipped vegetation may tie up nutrients important to grass establishment. Wood-based Mulch or Wood Straw No visible water or dust during handling. Must be purchased from a supplier with a Solid Waste Handling Permit or one exempt from solid waste regulations. 2” thick min.; approx. 100 tons per acre (approx. 800 lbs. per cubic yard) This material is often called “hog or hogged fuel.” The use of mulch ultimately improves the organic matter in the soil. Special caution is advised regarding the source and composition of wood-based mulches. Its preparation typically does not provide any weed seed control, so evidence of residual vegetation in its composition or known inclusion of weed plants or seeds should be monitored and prevented (or minimized). Wood Strand Mulch A blend of loose, long, thin wood pieces derived from native conifer or deciduous trees with high length-to-width ratio. 2” thick min. Cost-effective protection when applied with adequate thickness. A minimum of 95-percent of the wood strand shall have lengths between 2 and 10-inches, with a width and thickness between 1/16 and ⅜-inches. The mulch shall not contain resin, tannin, or other compounds in quantities that would be detrimental to plant life. Sawdust or wood shavings shall not be used as mulch. (WSDOT specification (9-14.4(4)) Volume II – Construction Stormwater Pollution Prevention - August 2012 4-22 BMP C122: Nets and Blankets Purpose Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on steep slopes and in channels so that vegetation can become well established. In addition, some nets and blankets can be used to permanently reinforce turf to protect drainage ways during high flows. Nets (commonly called matting) are strands of material woven into an open, but high-tensile strength net (for example, coconut fiber matting). Blankets are strands of material that are not tightly woven, but instead form a layer of interlocking fibers, typically held together by a biodegradable or photodegradable netting (for example, excelsior or straw blankets). They generally have lower tensile strength than nets, but cover the ground more completely. Coir (coconut fiber) fabric comes as both nets and blankets. Conditions of Use Erosion control nets and blankets should be used: • To aid permanent vegetated stabilization of slopes 2H:1V or greater and with more than 10 feet of vertical relief. • For drainage ditches and swales (highly recommended). The application of appropriate netting or blanket to drainage ditches and swales can protect bare soil from channelized runoff while vegetation is established. Nets and blankets also can capture a great deal of sediment due to their open, porous structure. Nets and blankets can be used to permanently stabilize channels and may provide a cost- effective, environmentally preferable alternative to riprap. 100 percent synthetic blankets manufactured for use in ditches may be easily reused as temporary ditch liners. Disadvantages of blankets include: • Surface preparation required. • On slopes steeper than 2.5H:1V, blanket installers may need to be roped and harnessed for safety. • They cost at least $4,000-6,000 per acre installed. Advantages of blankets include: • Installation without mobilizing special equipment. • Installation by anyone with minimal training • Installation in stages or phases as the project progresses. • Installers can hand place seed and fertilizer as they progress down the slope. • Installation in any weather. • There are numerous types of blankets that can be designed with various parameters in mind. Those parameters include: fiber blend, mesh strength, longevity, biodegradability, cost, and availability. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-23 Design and Installation Specifications • See Figure 4.1.3 and Figure 4.1.4 for typical orientation and installation of blankets used in channels and as slope protection. Note: these are typical only; all blankets must be installed per manufacturer’s installation instructions. • Installation is critical to the effectiveness of these products. If good ground contact is not achieved, runoff can concentrate under the product, resulting in significant erosion. • Installation of Blankets on Slopes: 1. Complete final grade and track walk up and down the slope. 2. Install hydromulch with seed and fertilizer. 3. Dig a small trench, approximately 12 inches wide by 6 inches deep along the top of the slope. 4. Install the leading edge of the blanket into the small trench and staple approximately every 18 inches. NOTE: Staples are metal, “U”-shaped, and a minimum of 6 inches long. Longer staples are used in sandy soils. Biodegradable stakes are also available. 5. Roll the blanket slowly down the slope as installer walks backwards. NOTE: The blanket rests against the installer’s legs. Staples are installed as the blanket is unrolled. It is critical that the proper staple pattern is used for the blanket being installed. The blanket is not to be allowed to roll down the slope on its own as this stretches the blanket making it impossible to maintain soil contact. In addition, no one is allowed to walk on the blanket after it is in place. 6. If the blanket is not long enough to cover the entire slope length, the trailing edge of the upper blanket should overlap the leading edge of the lower blanket and be stapled. On steeper slopes, this overlap should be installed in a small trench, stapled, and covered with soil. • With the variety of products available, it is impossible to cover all the details of appropriate use and installation. Therefore, it is critical that the design engineer consult the manufacturer's information and that a site visit takes place in order to ensure that the product specified is appropriate. Information is also available at the following web sites: 1. WSDOT (Section 3.2.4): http://www.wsdot.wa.gov/NR/rdonlyres/3B41E087-FA86-4717- 932D-D7A8556CCD57/0/ErosionTrainingManual.pdf 2. Texas Transportation Institute: http://www.txdot.gov/business/doing_business/product_evaluation/ erosion_control.htm Volume II – Construction Stormwater Pollution Prevention - August 2012 4-24 • Use jute matting in conjunction with mulch (BMP C121). Excelsior, woven straw blankets and coir (coconut fiber) blankets may be installed without mulch. There are many other types of erosion control nets and blankets on the market that may be appropriate in certain circumstances. • In general, most nets (e.g., jute matting) require mulch in order to prevent erosion because they have a fairly open structure. Blankets typically do not require mulch because they usually provide complete protection of the surface. • Extremely steep, unstable, wet, or rocky slopes are often appropriate candidates for use of synthetic blankets, as are riverbanks, beaches and other high-energy environments. If synthetic blankets are used, the soil should be hydromulched first. • 100-percent biodegradable blankets are available for use in sensitive areas. These organic blankets are usually held together with a paper or fiber mesh and stitching which may last up to a year. • Most netting used with blankets is photodegradable, meaning they break down under sunlight (not UV stabilized). However, this process can take months or years even under bright sun. Once vegetation is established, sunlight does not reach the mesh. It is not uncommon to find non-degraded netting still in place several years after installation. This can be a problem if maintenance requires the use of mowers or ditch cleaning equipment. In addition, birds and small animals can become trapped in the netting. Maintenance Standards • Maintain good contact with the ground. Erosion must not occur beneath the net or blanket. • Repair and staple any areas of the net or blanket that are damaged or not in close contact with the ground. • Fix and protect eroded areas if erosion occurs due to poorly controlled drainage. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-25 Min. 2“Overlap Slope surface shall be smooth beforeplacement for proper soil contact. Stapling pattern as permanufacturer’s recommendations. Do not stretch blankets/mattings tight -allow the rolls to mold to any irregularities. For slopes less than 3H:1V, rollsmay be placed in horizontal strips. If there is a berm at thetop of slope, anchorupslope of the berm. Anchor in 6"x6" min. Trenchand staple at 12" intervals. Min. 6" overlap. Staple overlapsmax. 5" spacing. Bring material down to a level area, turnthe end under 4" and staple at 12" intervals. Lime, fertilize, and seed before installation.Planting of shrubs, trees, etc. Should occurafter installation. Figure 4.1.3 – Channel Installation Figure 4.1.4 – Slope Installation Volume II – Construction Stormwater Pollution Prevention - August 2012 4-26 BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30 days, except as stated below. • Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively rapid breakdown of most polyethylene sheeting makes it unsuitable for long-term (greater than six months) applications. • Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. • Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on-site measures to counteract the increases. Creating a trough with wattles or other material can convey clean water away from these areas. • To prevent undercutting, trench and backfill rolled plastic covering products. • While plastic is inexpensive to purchase, the added cost of installation, maintenance, removal, and disposal make this an expensive material, up to $1.50-2.00 per square yard. • Whenever plastic is used to protect slopes install water collection measures at the base of the slope. These measures include plastic- covered berms, channels, and pipes used to covey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project. • Other uses for plastic include: 1. Temporary ditch liner. 2. Pond liner in temporary sediment pond. 3. Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored. 4. Emergency slope protection during heavy rains. 5. Temporary drainpipe (“elephant trunk”) used to direct water. Design and Installation Specifications • Plastic slope cover must be installed as follows: 1. Run plastic up and down slope, not across slope. 2. Plastic may be installed perpendicular to a slope if the slope length is less than 10 feet. 3. Minimum of 8-inch overlap at seams. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-27 4. On long or wide slopes, or slopes subject to wind, tape all seams. 5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope and backfill with soil to keep water from flowing underneath. 6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them together with twine to hold them in place. 7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This prevents high velocity runoff from contacting bare soil which causes extreme erosion. 8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place. • Plastic sheeting shall have a minimum thickness of 0.06 millimeters. • If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance Standards • Torn sheets must be replaced and open seams repaired. • Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radiation. • Completely remove plastic when no longer needed. • Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C123. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html BMP C124: Sodding Purpose The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize drainage ways where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas: • Disturbed areas that require short-term or long-term cover. • Disturbed areas that require immediate vegetative cover. • All waterways that require vegetative lining. Waterways may also be seeded rather than sodded, and protected with a net or blanket. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-28 Design and Installation Specifications Sod shall be free of weeds, of uniform thickness (approximately 1-inch thick), and shall have a dense root mat for mechanical strength. The following steps are recommended for sod installation: • Shape and smooth the surface to final grade in accordance with the approved grading plan. The swale needs to be overexcavated 4 to 6 inches below design elevation to allow room for placing soil amendment and sod. • Amend 4 inches (minimum) of compost into the top 8 inches of the soil if the organic content of the soil is less than ten percent or the permeability is less than 0.6 inches per hour. See http://www.ecy.wa.gov/programs/swfa/organics/soil.html for further information. • Fertilize according to the supplier's recommendations. • Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface. • Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V. Staple the upstream edge of each sod strip. • Roll the sodded area and irrigate. • When sodding is carried out in alternating strips or other patterns, seed the areas between the sod immediately after sodding. Maintenance Standards If the grass is unhealthy, the cause shall be determined and appropriate action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability, or some other cause, the sod shall be removed, the area seeded with an appropriate mix, and protected with a net or blanket. BMP C125: Topsoiling / Composting Purpose Topsoiling and composting provide a suitable growth medium for final site stabilization with vegetation. While not a permanent cover practice in itself, topsoiling and composting are an integral component of providing permanent cover in those areas where there is an unsuitable soil surface for plant growth. Use this BMP in conjunction with other BMPs such as seeding, mulching, or sodding. Native soils and disturbed soils that have been organically amended not only retain much more stormwater, but they also serve as effective biofilters for urban pollutants and, by supporting more vigorous plant growth, reduce the water, fertilizer and pesticides needed to support Volume II – Construction Stormwater Pollution Prevention - August 2012 4-29 installed landscapes. Topsoil does not include any subsoils but only the material from the top several inches including organic debris. Conditions of Use • Permanent landscaped areas shall contain healthy topsoil that reduces the need for fertilizers, improves overall topsoil quality, provides for better vegetal health and vitality, improves hydrologic characteristics, and reduces the need for irrigation. • Leave native soils and the duff layer undisturbed to the maximum extent practicable. Stripping of existing, properly functioning soil system and vegetation for the purpose of topsoiling during construction is not acceptable. Preserve existing soil systems in undisturbed and uncompacted conditions if functioning properly. • Areas that already have good topsoil, such as undisturbed areas, do not require soil amendments. • Restore, to the maximum extent practical, native soils disturbed during clearing and grading to a condition equal to or better than the original site condition’s moisture-holding capacity. Use on-site native topsoil, incorporate amendments into on-site soil, or import blended topsoil to meet this requirement. • Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils of critically low pH (high acid) levels. • Beware of where the topsoil comes from, and what vegetation was on site before disturbance, invasive plant seeds may be included and could cause problems for establishing native plants, landscaped areas, or grasses. • Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root growth and nutrient transfer. These native mycorrhiza are acclimated to the site and will provide optimum conditions for establishing grasses. Use commercially available mycorrhiza products when using off-site topsoil. Design and Installation Specifications Meet the following requirements for areas requiring disruption and topsoiling: • Maximize the depth of the topsoil wherever possible to provide the maximum possible infiltration capacity and beneficial growth medium. Topsoil shall have: • A minimum depth of 8-inches. Scarify subsoils below the topsoil layer at least 4-inches with some incorporation of the upper material to avoid stratified layers, where feasible. Ripping or re- structuring the subgrade may also provide additional benefits regarding the overall infiltration and interflow dynamics of the soil system. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-30 • A minimum organic content of 10% dry weight, and 5% organic matter content in turf areas. Incorporate organic amendments to a minimum 8-inch depth except where tree roots or other natural features limit the depth of incorporation. • A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil. • If blended topsoil is imported, then fines should be limited to 25 percent passing through a 200 sieve. • Accomplish the required organic content and pH by either returning native topsoil to the site and/or incorporating organic amendments. • To meet the organic content use compost that meets the definition of “composted materials” in WAC 173-350-220. This code is available online at: http://apps.leg.wa.gov/WAC/default.aspx?cite=173-350-220. The compost must also have an organic matter content of 35% to 65%, and a carbon to nitrogen ratio below 25H:1V. The carbon to nitrogen ratio may be as high as 35H:1V for plantings composed entirely of plants native to the Puget Sound Lowlands region. • For till soils use a mixture of approximately two parts soil to one part compost. This equates to 4 inches of compost mixed to a depth of 12 inches in till soils. Increasing the concentration of compost beyond this level can have negative effects on vegetal health, while decreasing the concentrations can reduce the benefits of amended soils. • Gravel or cobble outwash soils, may require different approaches. Organics and fines easily migrate through the loose structure of these soils. Therefore, the importation of at least 6 inches of quality topsoil, underlain by some type of filter fabric to prevent the migration of fines, may be more appropriate for these soils. • The final composition and construction of the soil system will result in a natural selection or favoring of certain plant species over time. For example, incorporation of topsoil may favor grasses, while layering with mildly acidic, high-carbon amendments may favor more woody vegetation. • Allow sufficient time in scheduling for topsoil spreading prior to seeding, sodding, or planting. • Take care when applying top soil to subsoils with contrasting textures. Sandy topsoil over clayey subsoil is a particularly poor combination, as water creeps along the junction between the soil layers and causes the topsoil to slough. If topsoil and subsoil are not properly bonded, water will not infiltrate the soil profile evenly and it will be difficult to Volume II – Construction Stormwater Pollution Prevention - August 2012 4-31 establish vegetation. The best method to prevent a lack of bonding is to actually work the topsoil into the layer below for a depth of at least 6 inches. • Field exploration of the site shall be made to determine if there is surface soil of sufficient quantity and quality to justify stripping. Topsoil shall be friable and loamy (loam, sandy loam, silt loam, sandy clay loam, and clay loam). Avoid areas of natural ground water recharge. • Stripping shall be confined to the immediate construction area. A 4- inch to 6-inch stripping depth is common, but depth may vary depending on the particular soil. All surface runoff control structures shall be in place prior to stripping. • Do not place topsoil while in a frozen or muddy condition, when the subgrade is excessively wet, or when conditions exist that may otherwise be detrimental to proper grading or proposed sodding or seeding. • In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas. Stockpiled topsoil is to be reapplied to other portions of the site where feasible. • Locate the topsoil stockpile so that it meets specifications and does not interfere with work on the site. It may be possible to locate more than one pile in proximity to areas where topsoil will be used. Stockpiling of topsoil shall occur in the following manner: • Side slopes of the stockpile shall not exceed 2H:1V. • Between October 1 and April 30: • An interceptor dike with gravel outlet and silt fence shall surround all topsoil. • Within 2 days complete erosion control seeding, or covering stockpiles with clear plastic, or other mulching materials. • Between May 1 and September 30: • An interceptor dike with gravel outlet and silt fence shall surround all topsoil if the stockpile will remain in place for a longer period of time than active construction grading. • Within 7 days complete erosion control seeding, or covering stockpiles with clear plastic, or other mulching materials. • When native topsoil is to be stockpiled and reused the following should apply to ensure that the mycorrhizal bacterial, earthworms, and other beneficial organisms will not be destroyed: 1. Re-install topsoil within 4 to 6 weeks. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-32 2. Do not allow the saturation of topsoil with water. 3. Do not use plastic covering. Maintenance Standards • Inspect stockpiles regularly, especially after large storm events. Stabilize any areas that have eroded. • Establish soil quality and depth toward the end of construction and once established, protect from compaction, such as from large machinery use, and from erosion. • Plant and mulch soil after installation. • Leave plant debris or its equivalent on the soil surface to replenish organic matter. • Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesticides, rather than continuing to implement formerly established practices. BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection Purpose Polyacrylamide (PAM) is used on construction sites to prevent soil erosion. Applying PAM to bare soil in advance of a rain event significantly reduces erosion and controls sediment in two ways. First, PAM increases the soil’s available pore volume, thus increasing infiltration through flocculation and reducing the quantity of stormwater runoff. Second, it increases flocculation of suspended particles and aids in their deposition, thus reducing stormwater runoff turbidity and improving water quality. Conditions of Use PAM shall not be directly applied to water or allowed to enter a water body. In areas that drain to a sediment pond, PAM can be applied to bare soil under the following conditions: • During rough grading operations. • In Staging areas. • Balanced cut and fill earthwork. • Haul roads prior to placement of crushed rock surfacing. • Compacted soil roadbase. • Stockpiles. • After final grade and before paving or final seeding and planting. • Pit sites. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-33 • Sites having a winter shut down. In the case of winter shut down, or where soil will remain unworked for several months, PAM should be used together with mulch. Design and Installation Specifications PAM may be applied with water in dissolved form. The preferred application method is the dissolved form. PAM is to be applied at a maximum rate of 2/3 pound PAM per 1,000 gallons water (80 mg/L) per 1 acre of bare soil. Table 4.1.9 can be used to determine the PAM and water application rate for a disturbed soil area. Higher concentrations of PAM do not provide any additional effectiveness. Table 4.1.9 PAM and Water Application Rates Disturbed Area (ac) PAM (lbs) Water (gal) 0.50 0.33 500 1.00 0.66 1,000 1.50 1.00 1,500 2.00 1.32 2,000 2.50 1.65 2,500 3.00 2.00 3,000 3.50 2.33 3,500 4.00 2.65 4,000 4.50 3.00 4,500 5.00 3.33 5,000 The Preferred Method: • Pre-measure the area where PAM is to be applied and calculate the amount of product and water necessary to provide coverage at the specified application rate (2/3 pound PAM/1000 gallons/acre). • PAM has infinite solubility in water, but dissolves very slowly. Dissolve pre-measured dry granular PAM with a known quantity of clean water in a bucket several hours or overnight. Mechanical mixing will help dissolve the PAM. Always add PAM to water - not water to PAM. • Pre-fill the water truck about 1/8 full with water. The water does not have to be potable, but it must have relatively low turbidity – in the range of 20 NTU or less. • Add PAM /Water mixture to the truck • Completely fill the water truck to specified volume. • Spray PAM/Water mixture onto dry soil until the soil surface is uniformly and completely wetted. An Alternate Method: Volume II – Construction Stormwater Pollution Prevention - August 2012 4-34 PAM may also be applied as a powder at the rate of 5 lbs. per acre. This must be applied on a day that is dry. For areas less than 5-10 acres, a hand- held “organ grinder” fertilizer spreader set to the smallest setting will work. Tractor-mounted spreaders will work for larger areas. The following shall be used for application of powdered PAM: • Powered PAM shall be used in conjunction with other BMPs and not in place of other BMPs. • Do not use PAM on a slope that flows directly into a stream or wetland. The stormwater runoff shall pass through a sediment control BMP prior to discharging to surface waters. • Do not add PAM to water discharging from site. • When the total drainage area is greater than or equal to 5 acres, PAM treated areas shall drain to a sediment pond. • Areas less than 5 acres shall drain to sediment control BMPs, such as a minimum of 3 check dams per acre. The total number of check dams used shall be maximized to achieve the greatest amount of settlement of sediment prior to discharging from the site. Each check dam shall be spaced evenly in the drainage channel through which stormwater flows are discharged off-site. • On all sites, the use of silt fence shall be maximized to limit the discharges of sediment from the site. • All areas not being actively worked shall be covered and protected from rainfall. PAM shall not be the only cover BMP used. • PAM can be applied to wet soil, but dry soil is preferred due to less sediment loss. • PAM will work when applied to saturated soil but is not as effective as applications to dry or damp soil. • Keep the granular PAM supply out of the sun. Granular PAM loses its effectiveness in three months after exposure to sunlight and air. • Proper application and re-application plans are necessary to ensure total effectiveness of PAM usage. • PAM, combined with water, is very slippery and can be a safety hazard. Care must be taken to prevent spills of PAM powder onto paved surfaces. During an application of PAM, prevent over-spray from reaching pavement as pavement will become slippery. If PAM powder gets on skin or clothing, wipe it off with a rough towel rather than washing with water-this only makes cleanup messier and take longer. • Some PAMs are more toxic and carcinogenic than others. Only the most environmentally safe PAM products should be used. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-35 The specific PAM copolymer formulation must be anionic. Cationic PAM shall not be used in any application because of known aquatic toxicity problems. Only the highest drinking water grade PAM, certified for compliance with ANSI/NSF Standard 60 for drinking water treatment, will be used for soil applications. Recent media attention and high interest in PAM has resulted in some entrepreneurial exploitation of the term "polymer." All PAM are polymers, but not all polymers are PAM, and not all PAM products comply with ANSI/NSF Standard 60. PAM use shall be reviewed and approved by the local permitting authority. • PAM designated for these uses should be "water soluble" or "linear" or "non-crosslinked". Cross-linked or water absorbent PAM, polymerized in highly acidic (pH<2) conditions, are used to maintain soil moisture content. • The PAM anionic charge density may vary from 2-30 percent; a value of 18 percent is typical. Studies conducted by the United States Department of Agriculture (USDA)/ARS demonstrated that soil stabilization was optimized by using very high molecular weight (12- 15 mg/mole), highly anionic (>20% hydrolysis) PAM. • PAM tackifiers are available and being used in place of guar and alpha plantago. Typically, PAM tackifiers should be used at a rate of no more than 0.5-1 lb. per 1000 gallons of water in a hydromulch machine. Some tackifier product instructions say to use at a rate of 3 –5 lbs. per acre, which can be too much. In addition, pump problems can occur at higher rates due to increased viscosity. Maintenance Standards • PAM may be reapplied on actively worked areas after a 48-hour period. • Reapplication is not required unless PAM treated soil is disturbed or unless turbidity levels show the need for an additional application. If PAM treated soil is left undisturbed a reapplication may be necessary after two months. More PAM applications may be required for steep slopes, silty and clayey soils (USDA Classification Type "C" and "D" soils), long grades, and high precipitation areas. When PAM is applied first to bare soil and then covered with straw, a reapplication may not be necessary for several months. • Loss of sediment and PAM may be a basis for penalties per RCW 90.48.080. BMP C130: Surface Roughening Purpose Surface roughening aids in the establishment of vegetative cover, reduces runoff velocity, increases infiltration, and provides for sediment trapping through the provision of a rough soil surface. Horizontal depressions are Volume II – Construction Stormwater Pollution Prevention - August 2012 4-36 created by operating a tiller or other suitable equipment on the contour or by leaving slopes in a roughened condition by not fine grading them. Use this BMP in conjunction with other BMPs such as seeding, mulching, or sodding. Conditions for Use • All slopes steeper than 3H:1V and greater than 5 vertical feet require surface roughening to a depth of 2 to 4 inches prior to seeding.. • Areas that will not be stabilized immediately may be roughened to reduce runoff velocity until seeding takes place. • Slopes with a stable rock face do not require roughening. • Slopes where mowing is planned should not be excessively roughened. Design and Installation Specifications There are different methods for achieving a roughened soil surface on a slope, and the selection of an appropriate method depends upon the type of slope. Roughening methods include stair-step grading, grooving, contour furrows, and tracking. See Figure 4.1.5 for tracking and contour furrows. Factors to be considered in choosing a method are slope steepness, mowing requirements, and whether the slope is formed by cutting or filling. • Disturbed areas that will not require mowing may be stair-step graded, grooved, or left rough after filling. • Stair-step grading is particularly appropriate in soils containing large amounts of soft rock. Each "step" catches material that sloughs from above, and provides a level site where vegetation can become established. Stairs should be wide enough to work with standard earth moving equipment. Stair steps must be on contour or gullies will form on the slope. • Areas that will be mowed (these areas should have slopes less steep than 3H:1V) may have small furrows left by disking, harrowing, raking, or seed-planting machinery operated on the contour. • Graded areas with slopes steeper than 3H:1V but less than 2H:1V should be roughened before seeding. This can be accomplished in a variety of ways, including "track walking," or driving a crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel to slope contours. • Tracking is done by operating equipment up and down the slope to leave horizontal depressions in the soil. Maintenance Standards • Areas that are graded in this manner should be seeded as quickly as possible. • Regular inspections should be made of the area. If rills appear, they should be re-graded and re-seeded immediately. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-37 Figure 4.1.5 – Surface Roughening by Tracking and Contour Furrows Volume II – Construction Stormwater Pollution Prevention - August 2012 4-38 BMP C131: Gradient Terraces Purpose Gradient terraces reduce erosion damage by intercepting surface runoff and conducting it to a stable outlet at a non-erosive velocity. Conditions of Use • Gradient terraces normally are limited to denuded land having a water erosion problem. They should not be constructed on deep sands or on soils that are too stony, steep, or shallow to permit practical and economical installation and maintenance. Gradient terraces may be used only where suitable outlets are or will be made available. See Figure 4.1.6 for gradient terraces. Design and Installation Specifications • The maximum vertical spacing of gradient terraces should be determined by the following method: VI = (0.8)s + y Where: VI = vertical interval in feet s = land rise per 100 feet, expressed in feet y = a soil and cover variable with values from 1.0 to 4.0 Values of “y” are influenced by soil erodibility and cover practices. The lower values are applicable to erosive soils where little to no residue is left on the surface. The higher value is applicable only to erosion-resistant soils where a large amount of residue (1½ tons of straw/acre equivalent) is on the surface. • The minimum constructed cross-section should meet the design dimensions. • The top of the constructed ridge should not be lower at any point than the design elevation plus the specified overfill for settlement. The opening at the outlet end of the terrace should have a cross section equal to that specified for the terrace channel. • Channel grades may be either uniform or variable with a maximum grade of 0.6 feet per 100 feet length (0.6%). For short distances, terrace grades may be increased to improve alignment. The channel velocity should not exceed that which is nonerosive for the soil type. • All gradient terraces should have adequate outlets. Such an outlet may be a grassed waterway, vegetated area, or tile outlet. In all cases the outlet must convey runoff from the terrace or terrace system to a point where the outflow will not cause damage. Vegetative cover should be used in the outlet channel. • The design elevation of the water surface of the terrace should not be lower than the design elevation of the water surface in the outlet at their junction, when both are operating at design flow. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-39 Slope to adequate outlet. 10' min. • Vertical spacing determined by the above methods may be increased as much as 0.5 feet or 10 percent, whichever is greater, to provide better alignment or location, to avoid obstacles, to adjust for equipment size, or to reach a satisfactory outlet. The drainage area above the terrace should not exceed the area that would be drained by a terrace with normal spacing. • The terrace should have enough capacity to handle the peak runoff expected from a 2-year, 24-hour design storm without overtopping. • The terrace cross-section should be proportioned to fit the land slope. The ridge height should include a reasonable settlement factor. The ridge should have a minimum top width of 3 feet at the design height. The minimum cross-sectional area of the terrace channel should be 8 square feet for land slopes of 5 percent or less, 7 square feet for slopes from 5 to 8 percent, and 6 square feet for slopes steeper than 8 percent. The terrace can be constructed wide enough to be maintained using a small vehicle. Maintenance Standards • Maintenance should be performed as needed. Terraces should be inspected regularly; at least once a year, and after large storm events. Figure 4.1.6 – Gradient Terraces Volume II – Construction Stormwater Pollution Prevention - August 2012 4-40 BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, drainage ways, and surface waters. Conditions of Use • In areas (including roadways) subject to surface and air movement of dust where on-site and off-site impacts to roadways, drainage ways, or surface waters are likely. Design and Installation Specifications • Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching, or paving is impractical, apply gravel or landscaping rock. • Limit dust generation by clearing only those areas where immediate activity will take place, leaving the remaining area(s) in the original condition. Maintain the original ground cover as long as practical. • Construct natural or artificial windbreaks or windscreens. These may be designed as enclosures for small dust sources. • Sprinkle the site with water until surface is wet. Repeat as needed. To prevent carryout of mud onto street, refer to Stabilized Construction Entrance (BMP C105). • Irrigation water can be used for dust control. Irrigation systems should be installed as a first step on sites where dust control is a concern. • Spray exposed soil areas with a dust palliative, following the manufacturer’s instructions and cautions regarding handling and application. Used oil is prohibited from use as a dust suppressant. Local governments may approve other dust palliatives such as calcium chloride or PAM. • PAM (BMP C126) added to water at a rate of 0.5 lbs. per 1,000 gallons of water per acre and applied from a water truck is more effective than water alone. This is due to increased infiltration of water into the soil and reduced evaporation. In addition, small soil particles are bonded together and are not as easily transported by wind. Adding PAM may actually reduce the quantity of water needed for dust control. Use of PAM could be a cost-effective dust control method. Techniques that can be used for unpaved roads and lots include: • Lower speed limits. High vehicle speed increases the amount of dust stirred up from unpaved roads and lots. • Upgrade the road surface strength by improving particle size, shape, and mineral types that make up the surface and base materials. • Add surface gravel to reduce the source of dust emission. Limit the amount of fine particles (those smaller than .075 mm) to 10 to 20 percent. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-41 • Use geotextile fabrics to increase the strength of new roads or roads undergoing reconstruction. • Encourage the use of alternate, paved routes, if available. • Restrict use of paved roadways by tracked vehicles and heavy trucks to prevent damage to road surface and base. • Apply chemical dust suppressants using the admix method, blending the product with the top few inches of surface material. Suppressants may also be applied as surface treatments. • Pave unpaved permanent roads and other trafficked areas. • Use vacuum street sweepers. • Remove mud and other dirt promptly so it does not dry and then turn into dust. • Limit dust-causing work on windy days. • Contact your local Air Pollution Control Authority for guidance and training on other dust control measures. Compliance with the local Air Pollution Control Authority constitutes compliance with this BMP. Maintenance Standards Respray area as necessary to keep dust to a minimum. BMP C150: Materials on Hand Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and emergency situations such as unexpected heavy summer rains. Having these materials on-site reduces the time needed to implement BMPs when inspections indicate that existing BMPs are not meeting the Construction SWPPP requirements. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard. Conditions of Use • Construction projects of any size or type can benefit from having materials on hand. A small commercial development project could have a roll of plastic and some gravel available for immediate protection of bare soil and temporary berm construction. A large earthwork project, such as highway construction, might have several tons of straw, several rolls of plastic, flexible pipe, sandbags, geotextile fabric and steel “T” posts. • Materials are stockpiled and readily available before any site clearing, grubbing, or earthwork begins. A large contractor or developer could keep a stockpile of materials that are available for use on several projects. • If storage space at the project site is at a premium, the contractor could maintain the materials at their office or yard. The office or yard must be less than an hour from the project site. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-42 Design and Installation Specifications Depending on project type, size, complexity, and length, materials and quantities will vary. A good minimum list of items that will cover numerous situations includes: Material Clear Plastic, 6 mil Drainpipe, 6 or 8 inch diameter Sandbags, filled Straw Bales for mulching, Quarry Spalls Washed Gravel Geotextile Fabric Catch Basin Inserts Steel “T” Posts Silt fence material Straw Wattles Maintenance Standards • All materials with the exception of the quarry spalls, steel “T” posts, and gravel should be kept covered and out of both sun and rain. • Re-stock materials used as needed. BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete process water, and concrete slurry from entering waters of the state. Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction projects include, but are not limited to, the following: • Curbs • Sidewalks • Roads • Bridges • Foundations • Floors • Runways Design and Installation • Wash out concrete truck chutes, pumps, and internals into formed areas only. Assure that washout of concrete trucks is performed off- Volume II – Construction Stormwater Pollution Prevention - August 2012 4-43 Specifications site or in designated concrete washout areas. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. Refer to BMP C154 for information on concrete washout areas. • Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas. • Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels into formed areas only. • Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances. • Do not allow washdown from areas, such as concrete aggregate driveways, to drain directly to natural or constructed stormwater conveyances. • Contain washwater and leftover product in a lined container when no formed areas are available,. Dispose of contained concrete in a manner that does not violate ground water or surface water quality standards. • Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. • Refer to BMPs C252 and C253 for pH adjustment requirements. • Refer to the Construction Stormwater General Permit for pH monitoring requirements if the project involves one of the following activities: • Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project). • The use of engineered soils amended with (but not limited to) Portland cement-treated base, cement kiln dust or fly ash. • Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-44 BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Sawcutting and surfacing operations include, but are not limited to, the following: • Sawing • Coring • Grinding • Roughening • Hydro-demolition • Bridge and road surfacing Design and Installation Specifications • Vacuum slurry and cuttings during cutting and surfacing operations. • Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight. • Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including stormwater systems. This may require temporarily blocking catch basins. • Dispose of collected slurry and cuttings in a manner that does not violate ground water or surface water quality standards. • Do not allow process water generated during hydro-demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose process water in a manner that does not violate ground water or surface water quality standards. • Handle and dispose cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and vacuum trucks. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-45 BMP C153: Material Delivery, Storage and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a designated area, and install secondary containment. Conditions of Use These procedures are suitable for use at all construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g. Polyacrylamide) • Fertilizers, pesticides and herbicides • Detergents • Asphalt and concrete compounds • Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds • Any other material that may be detrimental if released to the environment Design and Installation Specifications The following steps should be taken to minimize risk: • Temporary storage area should be located away from vehicular traffic, near the construction entrance(s), and away from waterways or storm drains. • Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. • Hazardous material storage on-site should be minimized. • Hazardous materials should be handled as infrequently as possible. • During the wet weather season (Oct 1 – April 30), consider storing materials in a covered area. • Materials should be stored in secondary containments, such as earthen dike, horse trough, or even a children’s wading pool for non-reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in “bus boy” trays or concrete mixing trays. • Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, and within secondary containment. • If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-46 Material Storage Areas and Secondary Containment Practices: • Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. • Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater. • Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. • Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non-hazardous. • Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. • During the wet weather season (Oct 1 – April 30), each secondary containment facility shall be covered during non-working days, prior to and during rain events. • Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material (spill kit). • The spill kit should include, at a minimum: • 1-Water Resistant Nylon Bag • 3-Oil Absorbent Socks 3”x 4’ • 2-Oil Absorbent Socks 3”x 10’ • 12-Oil Absorbent Pads 17”x19” • 1-Pair Splash Resistant Goggles • 3-Pair Nitrile Gloves • 10-Disposable Bags with Ties • Instructions Volume II – Construction Stormwater Pollution Prevention - August 2012 4-47 BMP C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants to stormwater from concrete waste by conducting washout off-site, or performing on-site washout in a designated area to prevent pollutants from entering surface waters or ground water. Conditions of Use Concrete washout area best management practices are implemented on construction projects where: • Concrete is used as a construction material • It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant, etc.). • Concrete trucks, pumpers, or other concrete coated equipment are washed on-site. • Note: If less than 10 concrete trucks or pumpers need to be washed out on-site, the washwater may be disposed of in a formed area awaiting concrete or an upland disposal site where it will not contaminate surface or ground water. The upland disposal site shall be at least 50 feet from sensitive areas such as storm drains, open ditches, or water bodies, including wetlands. Design and Installation Specifications Implementation The following steps will help reduce stormwater pollution from concrete wastes: • Perform washout of concrete trucks off-site or in designated concrete washout areas only. • Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. • Do not allow excess concrete to be dumped on-site, except in designated concrete washout areas. • Concrete washout areas may be prefabricated concrete washout containers, or self-installed structures (above-grade or below-grade). • Prefabricated containers are most resistant to damage and protect against spills and leaks. Companies may offer delivery service and provide regular maintenance and disposal of solid and liquid waste. • If self-installed concrete washout areas are used, below-grade structures are preferred over above-grade structures because they are less prone to spills and leaks. • Self-installed above-grade structures should only be used if excavation is not practical. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-48 Education • Discuss the concrete management techniques described in this BMP with the ready-mix concrete supplier before any deliveries are made. • Educate employees and subcontractors on the concrete waste management techniques described in this BMP. • Arrange for contractor’s superintendent or Certified Erosion and Sediment Control Lead (CESCL) to oversee and enforce concrete waste management procedures. • A sign should be installed adjacent to each temporary concrete washout facility to inform concrete equipment operators to utilize the proper facilities. Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor agreements. Location and Placement • Locate washout area at least 50 feet from sensitive areas such as storm drains, open ditches, or water bodies, including wetlands. • Allow convenient access for concrete trucks, preferably near the area where the concrete is being poured. • If trucks need to leave a paved area to access washout, prevent track- out with a pad of rock or quarry spalls (see BMP C105). These areas should be far enough away from other construction traffic to reduce the likelihood of accidental damage and spills. • The number of facilities you install should depend on the expected demand for storage capacity. • On large sites with extensive concrete work, washouts should be placed in multiple locations for ease of use by concrete truck drivers. On-site Temporary Concrete Washout Facility, Transit Truck Washout Procedures: • Temporary concrete washout facilities shall be located a minimum of 50 ft from sensitive areas including storm drain inlets, open drainage facilities, and watercourses. See Figures 4.1.7 and 4.1.8. • Concrete washout facilities shall be constructed and maintained in sufficient quantity and size to contain all liquid and concrete waste generated by washout operations. • Approximately 7 gallons of wash water are used to wash one truck chute. • Approximately 50 gallons are used to wash out the hopper of a concrete pump truck. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-49 • Washout of concrete trucks shall be performed in designated areas only. • Concrete washout from concrete pumper bins can be washed into concrete pumper trucks and discharged into designated washout area or properly disposed of off-site. • Once concrete wastes are washed into the designated area and allowed to harden, the concrete should be broken up, removed, and disposed of per applicable solid waste regulations. Dispose of hardened concrete on a regular basis. • Temporary Above-Grade Concrete Washout Facility • Temporary concrete washout facility (type above grade) should be constructed as shown on the details below, with a recommended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to contain all liquid and concrete waste generated by washout operations. • Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other defects that compromise the impermeability of the material. • Temporary Below-Grade Concrete Washout Facility • Temporary concrete washout facilities (type below grade) should be constructed as shown on the details below, with a recommended minimum length and minimum width of 10 ft. The quantity and volume should be sufficient to contain all liquid and concrete waste generated by washout operations. • Lath and flagging should be commercial type. • Plastic lining material shall be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other defects that compromise the impermeability of the material. • Liner seams shall be installed in accordance with manufacturers’ recommendations. • Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the plastic lining material. Maintenance Standards Inspection and Maintenance • Inspect and verify that concrete washout BMPs are in place prior to the commencement of concrete work. • During periods of concrete work, inspect daily to verify continued performance. • Check overall condition and performance. • Check remaining capacity (% full). Volume II – Construction Stormwater Pollution Prevention - August 2012 4-50 • If using self-installed washout facilities, verify plastic liners are intact and sidewalls are not damaged. • If using prefabricated containers, check for leaks. • Washout facilities shall be maintained to provide adequate holding capacity with a minimum freeboard of 12 inches. • Washout facilities must be cleaned, or new facilities must be constructed and ready for use once the washout is 75% full. • If the washout is nearing capacity, vacuum and dispose of the waste material in an approved manner. • Do not discharge liquid or slurry to waterways, storm drains or directly onto ground. • Do not use sanitary sewer without local approval. • Place a secure, non-collapsing, non-water collecting cover over the concrete washout facility prior to predicted wet weather to prevent accumulation and overflow of precipitation. • Remove and dispose of hardened concrete and return the structure to a functional condition. Concrete may be reused on-site or hauled away for disposal or recycling. • When you remove materials from the self-installed concrete washout, build a new structure; or, if the previous structure is still intact, inspect for signs of weakening or damage, and make any necessary repairs. Re-line the structure with new plastic after each cleaning. Removal of Temporary Concrete Washout Facilities • When temporary concrete washout facilities are no longer required for the work, the hardened concrete, slurries and liquids shall be removed and properly disposed of. • Materials used to construct temporary concrete washout facilities shall be removed from the site of the work and disposed of or recycled. • Holes, depressions or other ground disturbance caused by the removal of the temporary concrete washout facilities shall be backfilled, repaired, and stabilized to prevent erosion. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-51 Figure 4.1.7a – Concrete Washout Area Volume II – Construction Stormwater Pollution Prevention - August 2012 4-52 Figure 4.1.7b – Concrete Washout Area Figure 4.1.8 – Prefabricated Concrete Washout Container w/Ramp Volume II – Construction Stormwater Pollution Prevention - August 2012 4-53 BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge of erosion and sediment control (ESC), and water quality protection. The designated person shall be the Certified Erosion and Sediment Control Lead (CESCL) who is responsible for ensuring compliance with all local, state, and federal erosion and sediment control and water quality requirements. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to surface waters of the state. Sites less than one acre may have a person without CESCL certification conduct inspections; sampling is not required on sites that disturb less than an acre. • The CESCL shall: • Have a current certificate proving attendance in an erosion and sediment control training course that meets the minimum ESC training and certification requirements established by Ecology (see details below). Ecology will maintain a list of ESC training and certification providers at: http://www.ecy.wa.gov/programs/wq/stormwater/cescl.html OR • Be a Certified Professional in Erosion and Sediment Control (CPESC); for additional information go to: www.cpesc.net Specifications • Certification shall remain valid for three years. • The CESCL shall have authority to act on behalf of the contractor or developer and shall be available, or on-call, 24 hours per day throughout the period of construction. • The Construction SWPPP shall include the name, telephone number, fax number, and address of the designated CESCL. • A CESCL may provide inspection and compliance services for multiple construction projects in the same geographic region. Duties and responsibilities of the CESCL shall include, but are not limited to the following: • Maintaining permit file on site at all times which includes the Construction SWPPP and any associated permits and plans. • Directing BMP installation, inspection, maintenance, modification, and removal. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-54 • Updating all project drawings and the Construction SWPPP with changes made. • Completing any sampling requirements including reporting results using WebDMR. • Keeping daily logs, and inspection reports. Inspection reports should include: • Inspection date/time. • Weather information; general conditions during inspection and approximate amount of precipitation since the last inspection. • A summary or list of all BMPs implemented, including observations of all erosion/sediment control structures or practices. The following shall be noted: 1. Locations of BMPs inspected. 2. Locations of BMPs that need maintenance. 3. Locations of BMPs that failed to operate as designed or intended. 4. Locations of where additional or different BMPs are required. • Visual monitoring results, including a description of discharged stormwater. The presence of suspended sediment, turbid water, discoloration, and oil sheen shall be noted, as applicable. • Any water quality monitoring performed during inspection. • General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. • Facilitate, participate in, and take corrective actions resulting from inspections performed by outside agencies or the owner. BMP C162: Scheduling Purpose Sequencing a construction project reduces the amount and duration of soil exposed to erosion by wind, rain, runoff, and vehicle tracking. Conditions of Use The construction sequence schedule is an orderly listing of all major land- disturbing activities together with the necessary erosion and sedimentation control measures planned for the project. This type of schedule guides the contractor on work to be done before other work is started so that serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land- disturbing activities and the installation of control measures is perhaps the most cost-effective way of controlling erosion during construction. The removal of surface ground cover leaves a site vulnerable to accelerated Volume II – Construction Stormwater Pollution Prevention - August 2012 4-55 erosion. Construction procedures that limit land clearing provide timely installation of erosion and sedimentation controls, and restore protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations • Minimize construction during rainy periods. • Schedule projects to disturb only small portions of the site at any one time. Complete grading as soon as possible. Immediately stabilize the disturbed portion before grading the next portion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-56 4.2 Runoff Conveyance and Treatment BMPs This section contains the standards and specifications for Runoff Conveyance and Treatment BMPs. Table 4.2.1, below, shows the relationship of the BMPs in Section 4.2 to the Construction Stormwater Pollution Prevention Plan (SWPPP) Elements described in Section 3.3.3. Table 4.2.1 Runoff Conveyance and Treatment BMPs by SWPPP Element Volume II – Construction Stormwater Pollution Prevention - August 2012 4-57 BMP C200: Interceptor Dike and Swale Purpose Provide a ridge of compacted soil, or a ridge with an upslope swale, at the top or base of a disturbed slope or along the perimeter of a disturbed construction area to convey stormwater. Use the dike and/or swale to intercept the runoff from unprotected areas and direct it to areas where erosion can be controlled. This can prevent storm runoff from entering the work area or sediment-laden runoff from leaving the construction site. Conditions of Use Where the runoff from an exposed site or disturbed slope must be conveyed to an erosion control facility which can safely convey the stormwater. • Locate upslope of a construction site to prevent runoff from entering disturbed area. • When placed horizontally across a disturbed slope, it reduces the amount and velocity of runoff flowing down the slope. • Locate downslope to collect runoff from a disturbed area and direct water to a sediment basin. Design and Installation Specifications • Dike and/or swale and channel must be stabilized with temporary or permanent vegetation or other channel protection during construction. • Channel requires a positive grade for drainage; steeper grades require channel protection and check dams. • Review construction for areas where overtopping may occur. • Can be used at top of new fill before vegetation is established. • May be used as a permanent diversion channel to carry the runoff. • Sub-basin tributary area should be one acre or less. • Design capacity for the peak flow from a 10-year, 24-hour storm, assuming a Type 1A rainfall distribution, for temporary facilities. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model. For facilities that will also serve on a permanent basis, consult the local government’s drainage requirements. Interceptor dikes shall meet the following criteria: Top Width 2 feet minimum. Height 1.5 feet minimum on berm. Side Slope 2H:1V or flatter. Grade Depends on topography, however, dike system minimum is 0.5%, and maximum is 1%. Compaction Minimum of 90 percent ASTM D698 standard proctor. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-58 Horizontal Spacing of Interceptor Dikes: Average Slope Slope Percent Flowpath Length 20H:1V or less 3-5% 300 feet (10 to 20)H:1V 5-10% 200 feet (4 to 10)H:1V 10-25% 100 feet (2 to 4)H:1V 25-50% 50 feet Stabilization depends on velocity and reach Slopes <5% Seed and mulch applied within 5 days of dike construction (see BMP C121, Mulching). Slopes 5 - 40% Dependent on runoff velocities and dike materials. Stabilization should be done immediately using either sod or riprap or other measures to avoid erosion. • The upslope side of the dike shall provide positive drainage to the dike outlet. No erosion shall occur at the outlet. Provide energy dissipation measures as necessary. Sediment-laden runoff must be released through a sediment trapping facility. • Minimize construction traffic over temporary dikes. Use temporary cross culverts for channel crossing. Interceptor swales shall meet the following criteria: Bottom Width 2 feet minimum; the cross-section bottom shall be level. Depth 1-foot minimum. Side Slope 2H:1V or flatter. Grade Maximum 5 percent, with positive drainage to a suitable outlet (such as a sediment pond). Stabilization Seed as per BMP C120, Temporary and Permanent Seeding, or BMP C202, Channel Lining, 12 inches thick riprap pressed into the bank and extending at least 8 inches vertical from the bottom. • Inspect diversion dikes and interceptor swales once a week and after every rainfall. Immediately remove sediment from the flow area. • Damage caused by construction traffic or other activity must be repaired before the end of each working day. Check outlets and make timely repairs as needed to avoid gully formation. When the area below the temporary diversion dike is permanently stabilized, remove the dike and fill and stabilize the channel to blend with the natural surface. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-59 BMP C201: Grass-Lined Channels Purpose To provide a channel with a vegetative lining for conveyance of runoff. See Figure 4.2.1 for typical grass-lined channels. Conditions of Use This practice applies to construction sites where concentrated runoff needs to be contained to prevent erosion or flooding. • When a vegetative lining can provide sufficient stability for the channel cross section and at lower velocities of water (normally dependent on grade). This means that the channel slopes are generally less than 5 percent and space is available for a relatively large cross section. • Typical uses include roadside ditches, channels at property boundaries, outlets for diversions, and other channels and drainage ditches in low areas. • Channels that will be vegetated should be installed before major earthwork and hydroseeded with a bonded fiber matrix (BFM). The vegetation should be well established (i.e., 75 percent cover) before water is allowed to flow in the ditch. With channels that will have high flows, erosion control blankets should be installed over the hydroseed. If vegetation cannot be established from seed before water is allowed in the ditch, sod should be installed in the bottom of the ditch in lieu of hydromulch and blankets. Design and Installation Specifications Locate the channel where it can conform to the topography and other features such as roads. • Locate them to use natural drainage systems to the greatest extent possible. • Avoid sharp changes in alignment or bends and changes in grade. • Do not reshape the landscape to fit the drainage channel. • The maximum design velocity shall be based on soil conditions, type of vegetation, and method of revegetation, but at no times shall velocity exceed 5 feet/second. The channel shall not be overtopped by the peak runoff from a 10-year, 24-hour storm, assuming a Type 1A rainfall distribution." Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model to determine a flow rate which the channel must contain. • Where the grass-lined channel will also function as a permanent stormwater conveyance facility, consult the drainage conveyance requirements of the local government with jurisdiction. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-60 • An established grass or vegetated lining is required before the channel can be used to convey stormwater, unless stabilized with nets or blankets. • If design velocity of a channel to be vegetated by seeding exceeds 2 ft/sec, a temporary channel liner is required. Geotextile or special mulch protection such as fiberglass roving or straw and netting provides stability until the vegetation is fully established. See Figure 4.2.2. • Check dams shall be removed when the grass has matured sufficiently to protect the ditch or swale unless the slope of the swale is greater than 4 percent. The area beneath the check dams shall be seeded and mulched immediately after dam removal. • If vegetation is established by sodding, the permissible velocity for established vegetation may be used and no temporary liner is needed. • Do not subject grass-lined channel to sedimentation from disturbed areas. Use sediment-trapping BMPs upstream of the channel. • V-shaped grass channels generally apply where the quantity of water is small, such as in short reaches along roadsides. The V-shaped cross section is least desirable because it is difficult to stabilize the bottom where velocities may be high. • Trapezoidal grass channels are used where runoff volumes are large and slope is low so that velocities are nonerosive to vegetated linings. (Note: it is difficult to construct small parabolic shaped channels.) • Subsurface drainage, or riprap channel bottoms, may be necessary on sites that are subject to prolonged wet conditions due to long duration flows or a high water table. • Provide outlet protection at culvert ends and at channel intersections. • Grass channels, at a minimum, should carry peak runoff for temporary construction drainage facilities from the 10-year, 24-hour storm without eroding. Where flood hazard exists, increase the capacity according to the potential damage. • Grassed channel side slopes generally are constructed 3H:1V or flatter to aid in the establishment of vegetation and for maintenance. • Construct channels a minimum of 0.2 foot larger around the periphery to allow for soil bulking during seedbed preparations and sod buildup. Maintenance Standards During the establishment period, check grass-lined channels after every rainfall. • After grass is established, periodically check the channel; check it after every heavy rainfall event. Immediately make repairs. • It is particularly important to check the channel outlet and all road crossings for bank stability and evidence of piping or scour holes. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-61 • Remove all significant sediment accumulations to maintain the designed carrying capacity. Keep the grass in a healthy, vigorous condition at all times, since it is the primary erosion protection for the channel. Figure 4.2.1 – Typical Grass-Lined Channels Volume II – Construction Stormwater Pollution Prevention - August 2012 4-62 OVERCUTCHANNEL 2'(50mm) TOALLOW BULKING DURING SEEDBED PREPARATION TYPICAL INSTALLATION WITH EROSION CONTROL BLANKETS OR TURF REINFORCEMENT MATS Intermittent Check Slot Longitudinal Anchor Trench Shingle-lap spliced ends or begin new roll in an intermittent check slot Prepare soil and apply seed before installing blankets, mats or other temporary channel liner system / NOTES: 1 Design velocities exceeding 2 ft/sec (0.5m/sec) require temporary blankets, mats or similar liners to protect seed and soil until vegetation becomes established. 2 Grass-lined channels with design velocities exceeding 6 ft/sec (2m/sec) should include turf reinforcement mats. Fig ure 4.2 .2 – Temporary Channel Liners Volume II – Construction Stormwater Pollution Prevention - August 2012 4-63 BMP C202: Channel Lining Purpose To protect channels by providing a channel liner using either blankets or riprap. Conditions of Use When natural soils or vegetated stabilized soils in a channel are not adequate to prevent channel erosion. • When a permanent ditch or pipe system is to be installed and a temporary measure is needed. • In almost all cases, synthetic and organic coconut blankets are more effective than riprap for protecting channels from erosion. Blankets can be used with and without vegetation. Blanketed channels can be designed to handle any expected flow and longevity requirement. Some synthetic blankets have a predicted life span of 50 years or more, even in sunlight. • Other reasons why blankets are better than rock include the availability of blankets over rock. In many areas of the state, rock is not easily obtainable or is very expensive to haul to a site. Blankets can be delivered anywhere. Rock requires the use of dump trucks to haul and heavy equipment to place. Blankets usually only require laborers with hand tools, and sometimes a backhoe. • The Federal Highway Administration recommends not using flexible liners whenever the slope exceeds 10 percent or the shear stress exceeds 8 lbs/ft2. Design and Installation Specifications See BMP C122 for information on blankets. Since riprap is used where erosion potential is high, construction must be sequenced so that the riprap is put in place with the minimum possible delay. • Disturbance of areas where riprap is to be placed should be undertaken only when final preparation and placement of the riprap can follow immediately behind the initial disturbance. Where riprap is used for outlet protection, the riprap should be placed before or in conjunction with the construction of the pipe or channel so that it is in place when the pipe or channel begins to operate. • The designer, after determining the riprap size that will be stable under the flow conditions, shall consider that size to be a minimum size and then, based on riprap gradations actually available in the area, select the size or sizes that equal or exceed the minimum size. The possibility of drainage structure damage by children shall be considered in selecting a riprap size, especially if there is nearby water or a gully in which to toss the stones. • Stone for riprap shall consist of field stone or quarry stone of approximately rectangular shape. The stone shall be hard and angular Volume II – Construction Stormwater Pollution Prevention - August 2012 4-64 and of such quality that it will not disintegrate on exposure to water or weathering and it shall be suitable in all respects for the purpose intended. • A lining of engineering filter fabric (geotextile) shall be placed between the riprap and the underlying soil surface to prevent soil movement into or through the riprap. The geotextile should be keyed in at the top of the bank. • Filter fabric shall not be used on slopes greater than 1-1/2H:1V as slippage may occur. It should be used in conjunction with a layer of coarse aggregate (granular filter blanket) when the riprap to be placed is 12 inches and larger. BMP C203: Water Bars Purpose A small ditch or ridge of material is constructed diagonally across a road or right-of-way to divert stormwater runoff from the road surface, wheel tracks, or a shallow road ditch. See Figure 4.2.3. Conditions of use Clearing right-of-way and construction of access for power lines, pipelines, and other similar installations often require long narrow right-of-ways over sloping terrain. Disturbance and compaction promotes gully formation in these cleared strips by increasing the volume and velocity of runoff. Gully formation may be especially severe in tire tracks and ruts. To prevent gullying, runoff can often be diverted across the width of the right-of-way to undisturbed areas by using small predesigned diversions. • Give special consideration to each individual outlet area, as well as to the cumulative effect of added diversions. Use gravel to stabilize the diversion where significant vehicular traffic is anticipated. Design and Installation Specifications Height: 8-inch minimum measured from the channel bottom to the ridge top. • Side slope of channel: 2H:1V maximum; 3H:1V or flatter when vehicles will cross. • Base width of ridge: 6-inch minimum. • Locate them to use natural drainage systems and to discharge into well vegetated stable areas. • Guideline for Spacing: Slope % Spacing (ft) < 5 125 5 - 10 100 10 - 20 75 20 - 35 50 > 35 Use rock lined ditch Volume II – Construction Stormwater Pollution Prevention - August 2012 4-65 • Grade of water bar and angle: Select angle that results in ditch slope less than 2 percent. • Install as soon as the clearing and grading is complete. Reconstruct when construction is complete on a section when utilities are being installed. • Compact the ridge when installed. • Stabilize, seed and mulch the portions that are not subject to traffic. Gravel the areas crossed by vehicles. Maintenance Standards Periodically inspect right-of-way diversions for wear and after every heavy rainfall for erosion damage. • Immediately remove sediment from the flow area and repair the dike. • Check outlet areas and make timely repairs as needed. • When permanent road drainage is established and the area above the temporary right-of-way diversion is permanently stabilized, remove the dikes and fill the channel to blend with the natural ground, and appropriately stabilize the disturbed area. Figure 4.2.3 – Water Bar Volume II – Construction Stormwater Pollution Prevention - August 2012 4-66 BMP C204: Pipe Slope Drains Purpose To use a pipe to convey stormwater anytime water needs to be diverted away from or over bare soil to prevent gullies, channel erosion, and saturation of slide-prone soils. Conditions of Use Pipe slope drains should be used when a temporary or permanent stormwater conveyance is needed to move the water down a steep slope to avoid erosion (Figure 4.2.4). On highway projects, pipe slope drains should be used at bridge ends to collect runoff and pipe it to the base of the fill slopes along bridge approaches. These can be designed into a project and included as bid items. Another use on road projects is to collect runoff from pavement and pipe it away from side slopes. These are useful because there is generally a time lag between having the first lift of asphalt installed and the curbs, gutters, and permanent drainage installed. Used in conjunction with sand bags, or other temporary diversion devices, these will prevent massive amounts of sediment from leaving a project. Water can be collected, channeled with sand bags, Triangular Silt Dikes, berms, or other material, and piped to temporary sediment ponds. Pipe slope drains can be: • Connected to new catch basins and used temporarily until all permanent piping is installed; • Used to drain water collected from aquifers exposed on cut slopes and take it to the base of the slope; • Used to collect clean runoff from plastic sheeting and direct it away from exposed soil; • Installed in conjunction with silt fence to drain collected water to a controlled area; • Used to divert small seasonal streams away from construction. They have been used successfully on culvert replacement and extension jobs. Large flex pipe can be used on larger streams during culvert removal, repair, or replacement; and, • Connected to existing down spouts and roof drains and used to divert water away from work areas during building renovation, demolition, and construction projects. There are now several commercially available collectors that are attached to the pipe inlet and help prevent erosion at the inlet. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-67 Design and Installation Specifications Size the pipe to convey the flow. The capacity for temporary drains shall be sufficient to handle the peak flow from a 10-year, 24-hour storm event, assuming a Type 1A rainfall distribution. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model. Consult local drainage requirements for sizing permanent pipe slope drains. • Use care in clearing vegetated slopes for installation. • Re-establish cover immediately on areas disturbed by installation. • Use temporary drains on new cut or fill slopes. • Use diversion dikes or swales to collect water at the top of the slope. • Ensure that the entrance area is stable and large enough to direct flow into the pipe. • Piping of water through the berm at the entrance area is a common failure mode. • The entrance shall consist of a standard flared end section for culverts 12 inches and larger with a minimum 6-inch metal toe plate to prevent runoff from undercutting the pipe inlet. The slope of the entrance shall be at least 3 percent. Sand bags may also be used at pipe entrances as a temporary measure. • The soil around and under the pipe and entrance section shall be thoroughly compacted to prevent undercutting. • The flared inlet section shall be securely connected to the slope drain and have watertight connecting bands. • Slope drain sections shall be securely fastened together, fused or have gasketed watertight fittings, and shall be securely anchored into the soil. • Thrust blocks should be installed anytime 90 degree bends are utilized. Depending on size of pipe and flow, these can be constructed with sand bags, straw bales staked in place, “t” posts and wire, or ecology blocks. • Pipe needs to be secured along its full length to prevent movement. This can be done with steel “t” posts and wire. A post is installed on each side of the pipe and the pipe is wired to them. This should be done every 10-20 feet of pipe length or so, depending on the size of the pipe and quantity of water to divert. • Interceptor dikes shall be used to direct runoff into a slope drain. The height of the dike shall be at least 1 foot higher at all points than the top of the inlet pipe. • The area below the outlet must be stabilized with a riprap apron (see BMP C209 Outlet Protection, for the appropriate outlet material). Volume II – Construction Stormwater Pollution Prevention - August 2012 4-68 Dike material compacted 90% modified proctor CPEP or equivalent pipe Discharge to a stabilizedwatercourse, sediment retentionfacility, or stabilized outlet Inlet and all sections must besecurely fastened togetherwith gasketed watertight fittings Provide riprap pador equivalent energydissipation Interceptor Dike Standard flaredend section • If the pipe slope drain is conveying sediment-laden water, direct all flows into the sediment trapping facility. • Materials specifications for any permanent piped system shall be set by the local government. Maintenance Standards Check inlet and outlet points regularly, especially after storms. The inlet should be free of undercutting, and no water should be going around the point of entry. If there are problems, the headwall should be reinforced with compacted earth or sand bags. • The outlet point should be free of erosion and installed with appropriate outlet protection. • For permanent installations, inspect pipe periodically for vandalism and physical distress such as slides and wind-throw. • Normally the pipe slope is so steep that clogging is not a problem with smooth wall pipe, however, debris may become lodged in the pipe. Figure 4.2.4 – Pipe Slope Drain Volume II – Construction Stormwater Pollution Prevention - August 2012 4-69 BMP C205: Subsurface Drains Purpose To intercept, collect, and convey ground water to a satisfactory outlet, using a perforated pipe or conduit below the ground surface. Subsurface drains are also known as “french drains.” The perforated pipe provides a dewatering mechanism to drain excessively wet soils, provide a stable base for construction, improve stability of structures with shallow foundations, or to reduce hydrostatic pressure to improve slope stability. Conditions of Use Use when excessive water must be removed from the soil. The soil permeability, depth to water table and impervious layers are all factors which may govern the use of subsurface drains. Design and Installation Specifications Relief drains are used either to lower the water table in large, relatively flat areas, improve the growth of vegetation, or to remove surface water. Relief drains are installed along a slope and drain in the direction of the slope. They can be installed in a grid pattern, a herringbone pattern, or a random pattern. • Interceptor drains are used to remove excess ground water from a slope, stabilize steep slopes, and lower the water table immediately below a slope to prevent the soil from becoming saturated. Interceptor drains are installed perpendicular to a slope and drain to the side of the slope. They usually consist of a single pipe or series of single pipes instead of a patterned layout. • Depth and spacing of interceptor drains --The depth of an interceptor drain is determined primarily by the depth to which the water table is to be lowered or the depth to a confining layer. For practical reasons, the maximum depth is usually limited to 6 feet, with a minimum cover of 2 feet to protect the conduit. • The soil should have depth and sufficient permeability to permit installation of an effective drainage system at a depth of 2 to 6 feet. • An adequate outlet for the drainage system must be available either by gravity or by pumping. • The quantity and quality of discharge needs to be accounted for in the receiving stream (additional detention may be required). • This standard does not apply to subsurface drains for building foundations or deep excavations. • The capacity of an interceptor drain is determined by calculating the maximum rate of ground water flow to be intercepted. Therefore, it is Volume II – Construction Stormwater Pollution Prevention - August 2012 4-70 good practice to make complete subsurface investigations, including hydraulic conductivity of the soil, before designing a subsurface drainage system. • Size of drain--Size subsurface drains to carry the required capacity without pressure flow. Minimum diameter for a subsurface drain is 4 inches. • The minimum velocity required to prevent silting is 1.4 ft./sec. The line shall be graded to achieve this velocity at a minimum. The maximum allowable velocity using a sand-gravel filter or envelope is 9 ft/sec. • Filter material and fabric shall be used around all drains for proper bedding and filtration of fine materials. Envelopes and filters should surround the drain to a minimum of 3-inch thickness. • The outlet of the subsurface drain shall empty into a sediment pond through a catch basin. If free of sediment, it can then empty into a receiving channel, swale, or stable vegetated area adequately protected from erosion and undermining. • The trench shall be constructed on a continuous grade with no reverse grades or low spots. • Soft or yielding soils under the drain shall be stabilized with gravel or other suitable material. • Backfilling shall be done immediately after placement of the pipe. No sections of pipe shall remain uncovered overnight or during a rainstorm. Backfill material shall be placed in the trench in such a manner that the drain pipe is not displaced or damaged. • Do not install permanent drains near trees to avoid the tree roots that tend to clog the line. Use solid pipe with watertight connections where it is necessary to pass a subsurface drainage system through a stand of trees. • Outlet--Ensure that the outlet of a drain empties into a channel or other watercourse above the normal water level. • Secure an animal guard to the outlet end of the pipe to keep out rodents. • Use outlet pipe of corrugated metal, cast iron, or heavy-duty plastic without perforations and at least 10 feet long. Do not use an envelope or filter material around the outlet pipe, and bury at least two-thirds of the pipe length. • When outlet velocities exceed those allowable for the receiving stream, outlet protection must be provided. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-71 Maintenance Standards Subsurface drains shall be checked periodically to ensure that they are free-flowing and not clogged with sediment or roots. • The outlet shall be kept clean and free of debris. • Surface inlets shall be kept open and free of sediment and other debris. • Trees located too close to a subsurface drain often clog the system with their roots. If a drain becomes clogged, relocate the drain or remove the trees as a last resort. Drain placement should be planned to minimize this problem. • Where drains are crossed by heavy vehicles, the line shall be checked to ensure that it is not crushed. BMP C206: Level Spreader Purpose To provide a temporary outlet for dikes and diversions consisting of an excavated depression constructed at zero grade across a slope. To convert concentrated runoff to sheet flow and release it onto areas stabilized by existing vegetation or an engineered filter strip. Conditions of Use Used when a concentrated flow of water needs to be dispersed over a large area with existing stable vegetation. • Items to consider are: 1. What is the risk of erosion or damage if the flow may become concentrated? 2. Is an easement required if discharged to adjoining property? 3. Most of the flow should be as ground water and not as surface flow. 4. Is there an unstable area downstream that cannot accept additional ground water? • Use only where the slopes are gentle, the water volume is relatively low, and the soil will adsorb most of the low flow events. Design and Installation Specifications Use above undisturbed areas that are stabilized by existing vegetation. If the level spreader has any low points, flow will concentrate, create channels and may cause erosion. • Discharge area below the outlet must be uniform with a slope flatter than 5H:1V. • Outlet to be constructed level in a stable, undisturbed soil profile (not on fill). • The runoff shall not re-concentrate after release unless intercepted by another downstream measure. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-72 Densely vegetated for aMin. of 100' and slopeless than 5:1 Pressure-Treated 2"x10" 1' Min.2:1 Max.3' Min. • The grade of the channel for the last 20 feet of the dike or interceptor entering the level spreader shall be less than or equal to 1 percent. The grade of the level spreader shall be 0 percent to ensure uniform spreading of storm runoff. • A 6-inch high gravel berm placed across the level lip shall consist of washed crushed rock, 2- to 4-inch or 3/4-inch to 1½-inch size. • The spreader length shall be determined by estimating the peak flow expected from the 10-year, 24-hour design storm. The length of the spreader shall be a minimum of 15 feet for 0.1 cfs and shall increase by 10 feet for each 0.1 cfs thereafter to a maximum of 0.5 cfs per spreader. Use multiple spreaders for higher flows. • The width of the spreader should be at least 6 feet. • The depth of the spreader as measured from the lip should be at least 6 inches and it should be uniform across the entire length. • Level spreaders shall be setback from the property line unless there is an easement for flow. • Level spreaders, when installed every so often in grassy swales, keep the flows from concentrating. Materials that can be used include sand bags, lumber, logs, concrete, and pipe. To function properly, the material needs to be installed level and on contour. Figures 4.2.5Figure425 and 4.2.6 provide a cross-section and a detail of a level spreader. A capped perforated pipe could also be used as a spreader. Maintenance Standards The spreader should be inspected after every runoff event to ensure that it is functioning correctly. • The contractor should avoid the placement of any material on the structure and should prevent construction traffic from crossing over the structure. • If the spreader is damaged by construction traffic, it shall be immediately repaired. Figure 4.2.5 – Cross Section of Level Spreader Volume II – Construction Stormwater Pollution Prevention - August 2012 4-73 Figure 4.2.6 – Detail of Level Spreader BMP C207: Check Dams Purpose Construction of small dams across a swale or ditch reduces the velocity of concentrated flow and dissipates energy at the check dam. Conditions of Use Where temporary channels or permanent channels are not yet vegetated, channel lining is infeasible, and/or velocity checks are required. • Check dams may not be placed in streams unless approved by the State Department of Fish and Wildlife. Check dams may not be placed in wetlands without approval from a permitting agency. • Do not place check dams below the expected backwater from any salmonid bearing water between October 1 and May 31 to ensure that there is no loss of high flow refuge habitat for overwintering juvenile salmonids and emergent salmonid fry. • Construct rock check dams from appropriately sized rock. The rock used must be large enough to stay in place given the expected design flow through the channel. The rock must be placed by hand or by mechanical means (no dumping of rock to form dam) to achieve complete coverage of the ditch or swale and to ensure that the center of the dam is lower than the edges. • Check dams may also be constructed of either rock or pea-gravel filled bags. Numerous new products are also available for this purpose. They tend to be re-usable, quick and easy to install, effective, and cost efficient. • Place check dams perpendicular to the flow of water. • The dam should form a triangle when viewed from the side. This prevents undercutting as water flows over the face of the dam rather than falling directly onto the ditch bottom. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-74 • Before installing check dams impound and bypass upstream water flow away from the work area. Options for bypassing include pumps, siphons, or temporary channels. • Check dams in association with sumps work more effectively at slowing flow and retaining sediment than just a check dam alone. A deep sump should be provided immediately upstream of the check dam. • In some cases, if carefully located and designed, check dams can remain as permanent installations with very minor regrading. They may be left as either spillways, in which case accumulated sediment would be graded and seeded, or as check dams to prevent further sediment from leaving the site. • The maximum spacing between the dams shall be such that the toe of the upstream dam is at the same elevation as the top of the downstream dam. • Keep the maximum height at 2 feet at the center of the dam. • Keep the center of the check dam at least 12 inches lower than the outer edges at natural ground elevation. • Keep the side slopes of the check dam at 2H:1V or flatter. • Key the stone into the ditch banks and extend it beyond the abutments a minimum of 18 inches to avoid washouts from overflow around the dam. • Use filter fabric foundation under a rock or sand bag check dam. If a blanket ditch liner is used, filter fabric is not necessary. A piece of organic or synthetic blanket cut to fit will also work for this purpose. • In the case of grass-lined ditches and swales, all check dams and accumulated sediment shall be removed when the grass has matured sufficiently to protect the ditch or swale - unless the slope of the swale is greater than 4 percent. The area beneath the check dams shall be seeded and mulched immediately after dam removal. • Ensure that channel appurtenances, such as culvert entrances below check dams, are not subject to damage or blockage from displaced stones. Figure 4.2.7 depicts a typical rock check dam. Maintenance Standards Check dams shall be monitored for performance and sediment accumulation during and after each runoff producing rainfall. Sediment shall be removed when it reaches one half the sump depth. • Anticipate submergence and deposition above the check dam and erosion from high flows around the edges of the dam. • If significant erosion occurs between dams, install a protective riprap liner in that portion of the channel. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-75 Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C207. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html Volume II – Construction Stormwater Pollution Prevention - August 2012 4-76 Figure 4.2.7 – Rock Check Dam Volume II – Construction Stormwater Pollution Prevention - August 2012 4-77 BMP C208: Triangular Silt Dike (TSD) (Geotextile-Encased Check Dam) Purpose Triangular silt dikes may be used as check dams, for perimeter protection, for temporary soil stockpile protection, for drop inlet protection, or as a temporary interceptor dike. Conditions of use • May be used on soil or pavement with adhesive or staples. • TSDs have been used to build temporary: 1. sediment ponds; 2. diversion ditches; 3. concrete wash out facilities; 4. curbing; 5. water bars; 6. level spreaders; and, 7. berms. Design and Installation Specifications Made of urethane foam sewn into a woven geosynthetic fabric. It is triangular, 10 inches to 14 inches high in the center, with a 20-inch to 28-inch base. A 2–foot apron extends beyond both sides of the triangle along its standard section of 7 feet. A sleeve at one end allows attachment of additional sections as needed. • Install with ends curved up to prevent water from flowing around the ends. • The fabric flaps and check dam units are attached to the ground with wire staples. Wire staples should be No. 11 gauge wire and should be 200 mm to 300 mm in length. • When multiple units are installed, the sleeve of fabric at the end of the unit shall overlap the abutting unit and be stapled. • Check dams should be located and installed as soon as construction will allow. • Check dams should be placed perpendicular to the flow of water. • When used as check dams, the leading edge must be secured with rocks, sandbags, or a small key slot and staples. • In the case of grass-lined ditches and swales, check dams and accumulated sediment shall be removed when the grass has matured sufficiently to protect the ditch or swale unless the slope of the swale is greater than 4 percent. The area beneath the check dams shall be seeded and mulched immediately after dam removal. Maintenance • Triangular silt dams shall be inspected for performance and sediment Volume II – Construction Stormwater Pollution Prevention - August 2012 4-78 Standards accumulation during and after each runoff producing rainfall. Sediment shall be removed when it reaches one half the height of the dam. • Anticipate submergence and deposition above the triangular silt dam and erosion from high flows around the edges of the dam. Immediately repair any damage or any undercutting of the dam. BMP C209: Outlet Protection Purpose Outlet protection prevents scour at conveyance outlets and minimizes the potential for downstream erosion by reducing the velocity of concentrated stormwater flows. Conditions of use Outlet protection is required at the outlets of all ponds, pipes, ditches, or other conveyances, and where runoff is conveyed to a natural or manmade drainage feature such as a stream, wetland, lake, or ditch. Design and Installation Specifications The receiving channel at the outlet of a culvert shall be protected from erosion by rock lining a minimum of 6 feet downstream and extending up the channel sides a minimum of 1–foot above the maximum tailwater elevation or 1-foot above the crown, whichever is higher. For large pipes (more than 18 inches in diameter), the outlet protection lining of the channel is lengthened to four times the diameter of the culvert. • Standard wingwalls, and tapered outlets and paved channels should also be considered when appropriate for permanent culvert outlet protection. (See WSDOT Hydraulic Manual, available through WSDOT Engineering Publications). • Organic or synthetic erosion blankets, with or without vegetation, are usually more effective than rock, cheaper, and easier to install. Materials can be chosen using manufacturer product specifications. ASTM test results are available for most products and the designer can choose the correct material for the expected flow. • With low flows, vegetation (including sod) can be effective. • The following guidelines shall be used for riprap outlet protection: 1. If the discharge velocity at the outlet is less than 5 fps (pipe slope less than 1 percent), use 2-inch to 8-inch riprap. Minimum thickness is 1-foot. 2. For 5 to 10 fps discharge velocity at the outlet (pipe slope less than 3 percent), use 24-inch to 48-inch riprap. Minimum thickness is 2 feet. 3. For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), an engineered energy dissipater shall be used. • Filter fabric or erosion control blankets should always be used under riprap to prevent scour and channel erosion. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-79 • New pipe outfalls can provide an opportunity for low-cost fish habitat improvements. For example, an alcove of low-velocity water can be created by constructing the pipe outfall and associated energy dissipater back from the stream edge and digging a channel, over- widened to the upstream side, from the outfall. Overwintering juvenile and migrating adult salmonids may use the alcove as shelter during high flows. Bank stabilization, bioengineering, and habitat features may be required for disturbed areas. This work may require a HPA. See Volume V for more information on outfall system design. Maintenance Standards • Inspect and repair as needed. • Add rock as needed to maintain the intended function. • Clean energy dissipater if sediment builds up. BMP C220: Storm Drain Inlet Protection Purpose Storm drain inlet protection prevents coarse sediment from entering drainage systems prior to permanent stabilization of the disturbed area. Conditions of Use Use storm drain inlet protection at inlets that are operational before permanent stabilization of the disturbed drainage area. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless conveying runoff entering catch basins to a sediment pond or trap. Also consider inlet protection for lawn and yard drains on new home construction. These small and numerous drains coupled with lack of gutters in new home construction can add significant amounts of sediment into the roof drain system. If possible delay installing lawn and yard drains until just before landscaping or cap these drains to prevent sediment from entering the system until completion of landscaping. Provide 18-inches of sod around each finished lawn and yard drain. Table 4.2.2 lists several options for inlet protection. All of the methods for storm drain inlet protection tend to plug and require a high frequency of maintenance. Limit drainage areas to one acre or less. Possibly provide emergency overflows with additional end-of-pipe treatment where stormwater ponding would cause a hazard. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-80 Table 4.2.2 Storm Drain Inlet Protection Type of Inlet Protection Emergency Overflow Applicable for Paved/ Earthen Surfaces Conditions of Use Drop Inlet Protection Excavated drop inlet protection Yes, temporary flooding will occur Earthen Applicable for heavy flows. Easy to maintain. Large area Requirement: 30’ X 30’/acre Block and gravel drop inlet protection Yes Paved or Earthen Applicable for heavy concentrated flows. Will not pond. Gravel and wire drop inlet protection No Applicable for heavy concentrated flows. Will pond. Can withstand traffic. Catch basin filters Yes Paved or Earthen Frequent maintenance required. Curb Inlet Protection Curb inlet protection with a wooden weir Small capacity overflow Paved Used for sturdy, more compact installation. Block and gravel curb inlet protection Yes Paved Sturdy, but limited filtration. Culvert Inlet Protection Culvert inlet sediment trap 18 month expected life. Design and Installation Specifications Excavated Drop Inlet Protection - An excavated impoundment around the storm drain. Sediment settles out of the stormwater prior to entering the storm drain. • Provide a depth of 1-2 ft as measured from the crest of the inlet structure. • Slope sides of excavation no steeper than 2H:1V. • Minimum volume of excavation 35 cubic yards. • Shape basin to fit site with longest dimension oriented toward the longest inflow area. • Install provisions for draining to prevent standing water problems. • Clear the area of all debris. • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. • Protect weep holes with screen wire and washed aggregate. • Seal weep holes when removing structure and stabilizing area. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-81 • Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter - A barrier formed around the storm drain inlet with standard concrete blocks and gravel. See Figure 4.2.8. • Provide a height of 1 to 2 feet above inlet. • Recess the first row 2-inches into the ground for stability. • Support subsequent courses by placing a 2x4 through the block opening. • Do not use mortar. • Lay some blocks in the bottom row on their side for dewatering the pool. • Place hardware cloth or comparable wire mesh with ½-inch openings over all block openings. • Place gravel just below the top of blocks on slopes of 2H:1V or flatter. • An alternative design is a gravel donut. • Provide an inlet slope of 3H:1V. • Provide an outlet slope of 2H:1V. • Provide a1-foot wide level stone area between the structure and the inlet. • Use inlet slope stones 3 inches in diameter or larger. • Use gravel ½- to ¾-inch at a minimum thickness of 1-foot for the outlet slope. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-82 Figure 4.2.8 – Block and Gravel Filter Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the inlet. This structure does not provide an overflow. • Use a hardware cloth or comparable wire mesh with ½-inch openings. • Use coarse aggregate. • Provide a height 1-foot or more, 18-inches wider than inlet on all sides. • Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot beyond each side of the inlet structure. • Overlap the strips if more than one strip of mesh is necessary. Ponding Height Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-83 • Place coarse aggregate over the wire mesh. • Provide at least a 12-inch depth of gravel over the entire inlet opening and extend at least 18-inches on all sides. Catchbasin Filters – Use inserts designed by manufacturers for construction sites. The limited sediment storage capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. To reduce maintenance requirements combine a catchbasin filter with another type of inlet protection. This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights-of-way. • Provides 5 cubic feet of storage. • Requires dewatering provisions. • Provides a high-flow bypass that will not clog under normal use at a construction site. • Insert the catchbasin filter in the catchbasin just below the grating. Curb Inlet Protection with Wooden Weir – Barrier formed around a curb inlet with a wooden frame and gravel. • Use wire mesh with ½-inch openings. • Use extra strength filter cloth. • Construct a frame. • Attach the wire and filter fabric to the frame. • Pile coarse washed aggregate against wire/fabric. • Place weight on frame anchors. Block and Gravel Curb Inlet Protection – Barrier formed around a curb inlet with concrete blocks and gravel. See Figure 4.2.9. • Use wire mesh with ½-inch openings. • Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. • Place a 2x4 stud through the outer holes of each spacer block to align the front blocks. • Place blocks on their sides across the front of the inlet and abutting the spacer blocks. • Place wire mesh over the outside vertical face. • Pile coarse aggregate against the wire to the top of the barrier. Curb and Gutter Sediment Barrier – Sandbag or rock berm (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure 4.2.10. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-84 • Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. • Construct a horseshoe shaped sedimentation trap on the outside of the berm sized to sediment trap standards for protecting a culvert inlet. Maintenance Standards • Inspect catch basin filters frequently, especially after storm events. Clean and replace clogged inserts. For systems with clogged stone filters: pull away the stones from the inlet and clean or replace. An alternative approach would be to use the clogged stone as fill and put fresh stone around the inlet. • Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate. Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C220. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html Volume II – Construction Stormwater Pollution Prevention - August 2012 4-85 Figure 4.2.9 – Block and Gravel Curb Inlet Protection A Plan View Wire Screen or Filter Fabric Catch Basin Curb Inlet Concrete Block Ponding Height Overflow 2x4 Wood Stud (100x50 Timber Stud) Concrete Block Wire Screen or Filter Fabric Curb Inlet ¾" Drain Gravel (20mm) ¾" Drain Gravel (20mm)Section A - A Back of Curb Concrete Block 2x4 Wood Stud Catch BasinBack of Sidewalk NOTES: 1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff. 2. Barrier shall allow for overflow from severe storm event. 3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-86 Figure 4.2.10 – Curb and Gutter Barrier Volume II – Construction Stormwater Pollution Prevention - August 2012 4-87 If required, drape filter fabricover brush and secure in 4"x4"min. trench with compactedbackfill. Min. 5' wide brush barrier withmax. 6" diameter woody debris.Alternatively topsoil strippingsmay be used to form the barrier. Anchor downhill edge offilter fabric with stakes,sandbags, or equivalent. 2' Min. Height BMP C231: Brush Barrier Purpose The purpose of brush barriers is to reduce the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use • Brush barriers may be used downslope of all disturbed areas of less than one-quarter acre. • Brush barriers are not intended to treat concentrated flows, nor are they intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment pond. The only circumstance in which overland flow can be treated solely by a brush barrier, rather than by a sediment pond, is when the area draining to the barrier is small. • Brush barriers should only be installed on contours. Design and Installation Specifications • Height 2 feet (minimum) to 5 feet (maximum). • Width 5 feet at base (minimum) to 15 feet (maximum). • Filter fabric (geotextile) may be anchored over the brush berm to enhance the filtration ability of the barrier. Ten-ounce burlap is an adequate alternative to filter fabric. • Chipped site vegetation, composted mulch, or wood-based mulch (hog fuel) can be used to construct brush barriers. • A 100 percent biodegradable installation can be constructed using 10- ounce burlap held in place by wooden stakes. Figure 4.2.11 depicts a typical brush barrier. Maintenance Standards • There shall be no signs of erosion or concentrated runoff under or around the barrier. If concentrated flows are bypassing the barrier, it must be expanded or augmented by toed-in filter fabric. • The dimensions of the barrier must be maintained. Figure 4.2.11 – Brush Barrier Volume II – Construction Stormwater Pollution Prevention - August 2012 4-88 BMP C232: Gravel Filter Berm Purpose A gravel filter berm is constructed on rights-of-way or traffic areas within a construction site to retain sediment by using a filter berm of gravel or crushed rock. Conditions of Use Where a temporary measure is needed to retain sediment from rights-of- way or in traffic areas on construction sites. Design and Installation Specifications • Berm material shall be ¾ to 3 inches in size, washed well-grade gravel or crushed rock with less than 5 percent fines. • Spacing of berms: − Every 300 feet on slopes less than 5 percent − Every 200 feet on slopes between 5 percent and 10 percent − Every 100 feet on slopes greater than 10 percent • Berm dimensions: − 1 foot high with 3H:1V side slopes − 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design storm Maintenance Standards • Regular inspection is required. Sediment shall be removed and filter material replaced as needed. BMP C233: Silt Fence Purpose Use of a silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. See Figure 4.2.12 for details on silt fence construction. Conditions of Use Silt fence may be used downslope of all disturbed areas. • Silt fence shall prevent soil carried by runoff water from going beneath, through, or over the top of the silt fence, but shall allow the water to pass through the fence. • Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Convey any concentrated flows through the drainage system to a sediment pond. • Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything deeper than sheet or overland flow. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-89 Figure 4.2.12 – Silt Fence Design and Installation Specifications • Use in combination with sediment basins or other BMPs. • Maximum slope steepness (normal (perpendicular) to fence line) 1H:1V. • Maximum sheet or overland flow path length to the fence of 100 feet. • Do not allow flows greater than 0.5 cfs. • The geotextile used shall meet the following standards. All geotextile properties listed below are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 4.2.3): Table 4.2.3 Geotextile Standards Polymeric Mesh AOS (ASTM D4751) 0.60 mm maximum for slit film woven (#30 sieve). 0.30 mm maximum for all other geotextile types (#50 sieve). 0.15 mm minimum for all fabric types (#100 sieve). Water Permittivity (ASTM D4491) 0.02 sec-1 minimum Grab Tensile Strength (ASTM D4632) 180 lbs. Minimum for extra strength fabric. 100 lbs minimum for standard strength fabric. Grab Tensile Strength (ASTM D4632) 30% maximum Ultraviolet Resistance (ASTM D4355) 70% minimum • Support standard strength fabrics with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the Volume II – Construction Stormwater Pollution Prevention - August 2012 4-90 fabric. Silt fence materials are available that have synthetic mesh backing attached. • Filter fabric material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F. to 120°F. • One-hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by local regulations. • Refer to Figure 4.2.12 for standard silt fence details. Include the following standard Notes for silt fence on construction plans and specifications: 1. The contractor shall install and maintain temporary silt fences at the locations shown in the Plans. 2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those activities. 3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the original ground surface. 4. The filter fabric shall be sewn together at the point of manufacture to form filter fabric lengths as required. Locate all sewn seams at support posts. Alternatively, two sections of silt fence can be overlapped, provided the Contractor can demonstrate, to the satisfaction of the Engineer, that the overlap is long enough and that the adjacent fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. 5. Attach the filter fabric on the up-slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's recommendations. Attach the filter fabric to the posts in a manner that reduces the potential for tearing. 6. Support the filter fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely to the up-slope side of the posts with the filter fabric up-slope of the mesh. 7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2-inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh must be as resistant to the same level of ultraviolet radiation as the filter fabric it supports. 8. Bury the bottom of the filter fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of the filter fabric, so that no flow can pass beneath the fence and Volume II – Construction Stormwater Pollution Prevention - August 2012 4-91 scouring cannot occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches min. 9. Drive or place the fence posts into the ground 18-inches min. A 12–inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H:1V or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained, the posts shall be adequately secured by bracing or guying to prevent overturning of the fence due to sediment loading. 10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a maximum of 6-feet. Posts shall consist of either: • Wood with dimensions of 2-inches by 2-inches wide min. and a 3-feet min. length. Wood posts shall be free of defects such as knots, splits, or gouges. • No. 6 steel rebar or larger. • ASTM A 120 steel pipe with a minimum diameter of 1-inch. • U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. • Other steel posts having equivalent strength and bending resistance to the post sizes listed above. 11. Locate silt fences on contour as much as possible, except at the ends of the fence, where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. 12. If the fence must cross contours, with the exception of the ends of the fence, place gravel check dams perpendicular to the back of the fence to minimize concentrated flow and erosion. The slope of the fence line where contours must be crossed shall not be steeper than 3H:1V. • Gravel check dams shall be approximately 1-foot deep at the back of the fence. Gravel check dams shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. • Gravel check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Gravel check dams shall be located every 10 feet along the fence where the fence must cross contours. • Refer to Figure 4.2.13 for slicing method details. Silt fence installation using the slicing method specifications: Volume II – Construction Stormwater Pollution Prevention - August 2012 4-92 1. The base of both end posts must be at least 2- to 4-inches above the top of the filter fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary, to mark base points before installation. 2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7- feet apart in standard applications. 3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as possible to the filter fabric, enabling posts to support the filter fabric from upstream water pressure. 4. Install posts with the nipples facing away from the filter fabric. 5. Attach the filter fabric to each post with three ties, all spaced within the top 8-inches of the filter fabric. Attach each tie diagonally 45 degrees through the filter fabric, with each puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging. 6. Wrap approximately 6-inches of fabric around the end posts and secure with 3 ties. 7. No more than 24-inches of a 36-inch filter fabric is allowed above ground level. Compact the soil immediately next to the filter fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. Check and correct the silt fence installation for any deviation before compaction. Use a flat-bladed shovel to tuck fabric deeper into the ground if necessary. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-93 Figure 4.2.13 – Silt Fence Installation by Slicing Method Maintenance Standards • Repair any damage immediately. • Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment pond. • Check the uphill side of the fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence or remove the trapped sediment. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-94 • Remove sediment deposits when the deposit reaches approximately one-third the height of the silt fence, or install a second silt fence. • Replace filter fabric that has deteriorated due to ultraviolet breakdown. BMP C234: Vegetated Strip Purpose Vegetated strips reduce the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use • Vegetated strips may be used downslope of all disturbed areas. • Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment pond. The only circumstance in which overland flow can be treated solely by a strip, rather than by a sediment pond, is when the following criteria are met (see Table 4.2.4): Table 4.2.4 Contributing Drainage Area for Vegetated Strips Average Contributing area Slope Average Contributing area Percent Slope Max Contributing area Flowpath Length 1.5H:1V or flatter 67% or flatter 100 feet 2H:1V or flatter 50% or flatter 115 feet 4H:1V or flatter 25% or flatter 150 feet 6H:1V or flatter 16.7% or flatter 200 feet 10H:1V or flatter 10% or flatter 250 feet Design and Installation Specifications • The vegetated strip shall consist of a minimum of a 25-foot flowpath length continuous strip of dense vegetation with topsoil. Grass- covered, landscaped areas are generally not adequate because the volume of sediment overwhelms the grass. Ideally, vegetated strips shall consist of undisturbed native growth with a well-developed soil that allows for infiltration of runoff. • The slope within the strip shall not exceed 4H:1V. • The uphill boundary of the vegetated strip shall be delineated with clearing limits. Maintenance Standards • Any areas damaged by erosion or construction activity shall be seeded immediately and protected by mulch. • If more than 5 feet of the original vegetated strip width has had vegetation removed or is being eroded, sod must be installed. • If there are indications that concentrated flows are traveling across the buffer, surface water controls must be installed to reduce the flows Volume II – Construction Stormwater Pollution Prevention - August 2012 4-95 entering the buffer, or additional perimeter protection must be installed. BMP C235: Wattles Purpose Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or other material that is wrapped in biodegradable tubular plastic or similar encasing material. They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sediment. Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. Wattles are placed in shallow trenches and staked along the contour of disturbed or newly constructed slopes. See Figure 4.2.14 for typical construction details. WSDOT Standard Plan I-30.30-00 also provides information on Wattles (http://www.wsdot.wa.gov/Design/Standards/Plans.htm#SectionI) Conditions of Use • Use wattles: • In disturbed areas that require immediate erosion protection. • On exposed soils during the period of short construction delays, or over winter months. • On slopes requiring stabilization until permanent vegetation can be established. • The material used dictates the effectiveness period of the wattle. Generally, Wattles are typically effective for one to two seasons. • Prevent rilling beneath wattles by properly entrenching and abutting wattles together to prevent water from passing between them. Design Criteria • Install wattles perpendicular to the flow direction and parallel to the slope contour. • Narrow trenches should be dug across the slope on contour to a depth of 3- to 5-inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, the trenches should be dug to a depth of 5- to 7- inches, or 1/2 to 2/3 of the thickness of the wattle. • Start building trenches and installing wattles from the base of the slope and work up. Spread excavated material evenly along the uphill slope and compacted using hand tamping or other methods. • Construct trenches at intervals of 10- to 25-feet depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches. • Install the wattles snugly into the trenches and abut tightly end to end. Do not overlap the ends. • Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-96 • If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. • Wooden stakes should be approximately 3/4 x 3/4 x 24 inches min. Willow cuttings or 3/8-inch rebar can also be used for stakes. • Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake protruding above the wattle. Maintenance Standards • Wattles may require maintenance to ensure they are in contact with soil and thoroughly entrenched, especially after significant rainfall on steep sandy soils. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-97 Figure 4.2.14 – Wattles Volume II – Construction Stormwater Pollution Prevention - August 2012 4-98 • Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted or water has scoured beneath the wattles. Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C235. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html BMP C236: Vegetative Filtration Purpose Vegetative Filtration may be used in conjunction with BMP C241 Temporary Sediment Ponds, BMP C206 Level Spreader and a pumping system with surface intake to improve turbidity levels of stormwater discharges by filtering through existing vegetation where undisturbed forest floor duff layer or established lawn with thatch layer are present. Vegetative Filtration can also be used to infiltrate dewatering waste from foundations, vaults, and trenches as long as runoff does not occur. Conditions of Use • For every five acre of disturbed soil use one acre of grass field, farm pasture, or wooded area. Reduce or increase this area depending on project size, ground water table height, and other site conditions. • Wetlands shall not be used for filtration. • Do not use this BMP in areas with a high ground water table, or in areas that will have a high seasonal ground water table during the use of this BMP. • This BMP may be less effective on soils that prevent the infiltration of the water, such as hard till. • Using other effective source control measures throughout a construction site will prevent the generation of additional highly turbid water and may reduce the time period or area need for this BMP. • Stop distributing water into the vegetated area if standing water or erosion results. Design Criteria • Find land adjacent to the project that has a vegetated field, preferably a farm field, or wooded area. • If the project site does not contain enough vegetated field area consider obtaining permission from adjacent landowners (especially for farm fields). • Install a pump and downstream distribution manifold depending on the project size. Generally, the main distribution line should reach 100 to 200-feet long (many large projects, or projects on tight soil, will Volume II – Construction Stormwater Pollution Prevention - August 2012 4-99 require systems that reach several thousand feet long with numerous branch lines off of the main distribution line). • The manifold should have several valves, allowing for control over the distribution area in the field. • Install several branches of 4” schedule 20, swaged-fit common septic tight-lined sewer line, or 6” fire hose, which can convey the turbid water out to various sections of the field. See Figure 4.2.15. • Determine the branch length based on the field area geography and number of branches. Typically, branches stretch from 200-feet to several thousand feet. Always, lay branches on contour with the slope. • On uneven ground, sprinklers perform well. Space sprinkler heads so that spray patterns do not overlap. • On relatively even surfaces, a level spreader using 4-inch perforated pipe may be used as an alternative option to the sprinkler head setup. Install drain pipe at the highest point on the field and at various lower elevations to ensure full coverage of the filtration area. Pipe should be place with the holes up to allow for a gentle weeping of stormwater evenly out all holes. Leveling the pipe by staking and using sandbags may be required. • To prevent the over saturation of the field area, rotate the use of branches or spray heads. Do this as needed based on monitoring the spray field. • Monitor the spray field on a daily basis to ensure that over saturation of any portion of the field doesn’t occur at any time. The presence of standing puddles of water or creation of concentrated flows visually signify that over saturation of the field has occurred. • Since the operator is handling contaminated water, physically monitor the vegetated spray field all the way down to the nearest surface water, or furthest spray area, to ensure that the water has not caused overland or concentrated flows, and has not created erosion around the spray nozzle. • Monitoring usually needs to take place 3-5 times per day to ensure sheet-flow into state waters. Do not exceed water quality standards for turbidity. • Ecology strongly recommends that a separate inspection log be developed, maintained and kept with the existing site logbook to aid the operator conducting inspections. This separate “Field Filtration Logbook” can also aid the facility in demonstrating compliance with permit conditions. Maintenance Standards • Inspect the spray nozzles daily, at a minimum, for leaks and plugging from sediment particles. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-100 • If erosion, concentrated flows, or over saturation of the field occurs, rotate the use of branches or spray heads or move the branches to a new field location. • Check all branches and the manifold for unintended leaks. Flowpath Guidelines for Vegetative Filtration Average Slope Average Area % Slope Estimated Flowpath Length (ft) 1.5H:1V 67% 250 2H:1V 50% 200 4H:1V 25% 150 6H:1V 16.7% 115 10H:1V 10% 100 Figure 4.2.15 – Manifold and Braches in a wooded, vegetated spray field Volume II – Construction Stormwater Pollution Prevention - August 2012 4-101 BMP C240: Sediment Trap Purpose A sediment trap is a small temporary ponding area with a gravel outlet used to collect and store sediment from sites cleared and/or graded during construction. Sediment traps, along with other perimeter controls, shall be installed before any land disturbance takes place in the drainage area. Conditions of Use Prior to leaving a construction site, stormwater runoff must pass through a sediment pond or trap or other appropriate sediment removal best management practice. Non-engineered sediment traps may be used on-site prior to an engineered sediment trap or sediment pond to provide additional sediment removal capacity. It is intended for use on sites where the tributary drainage area is less than 3 acres, with no unusual drainage features, and a projected build-out time of six months or less. The sediment trap is a temporary measure (with a design life of approximately 6 months) and shall be maintained until the site area is permanently protected against erosion by vegetation and/or structures. Sediment traps and ponds are only effective in removing sediment down to about the medium silt size fraction. Runoff with sediment of finer grades (fine silt and clay) will pass through untreated, emphasizing the need to control erosion to the maximum extent first. Whenever possible, sediment-laden water shall be discharged into on-site, relatively level, vegetated areas (see BMP C234 – Vegetated Strip). This is the only way to effectively remove fine particles from runoff unless chemical treatment or filtration is used. This can be particularly useful after initial treatment in a sediment trap or pond. The areas of release must be evaluated on a site-by-site basis in order to determine appropriate locations for and methods of releasing runoff. Vegetated wetlands shall not be used for this purpose. Frequently, it may be possible to pump water from the collection point at the downhill end of the site to an upslope vegetated area. Pumping shall only augment the treatment system, not replace it, because of the possibility of pump failure or runoff volume in excess of pump capacity. All projects that are constructing permanent facilities for runoff quantity control should use the rough-graded or final-graded permanent facilities for traps and ponds. This includes combined facilities and infiltration facilities. When permanent facilities are used as temporary sedimentation facilities, the surface area requirement of a sediment trap or pond must be met. If the surface area requirements are larger than the surface area of the permanent facility, then the trap or pond shall be enlarged to comply with the surface area requirement. The permanent pond shall also be divided into two cells as required for sediment ponds. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-102 Either a permanent control structure or the temporary control structure (described in BMP C241, Temporary Sediment Pond) can be used. If a permanent control structure is used, it may be advisable to partially restrict the lower orifice with gravel to increase residence time while still allowing dewatering of the pond. A shut-off valve may be added to the control structure to allow complete retention of stormwater in emergency situations. In this case, an emergency overflow weir must be added. A skimmer may be used for the sediment trap outlet if approved by the Local Permitting Authority. Design and Installation Specifications • See Figures 4.2.16 and 4.2.17 for details. • If permanent runoff control facilities are part of the project, they should be used for sediment retention. • To determine the sediment trap geometry, first calculate the design surface area (SA) of the trap, measured at the invert of the weir. Use the following equation: SA = FS(Q2/Vs) where Q2 = Design inflow based on the peak discharge from the developed 2-year runoff event from the contributing drainage area as computed in the hydrologic analysis. The 10-year peak flow shall be used if the project size, expected timing and duration of construction, or downstream conditions warrant a higher level of protection. If no hydrologic analysis is required, the Rational Method may be used. Vs = The settling velocity of the soil particle of interest. The 0.02 mm (medium silt) particle with an assumed density of 2.65 g/cm3 has been selected as the particle of interest and has a settling velocity (Vs) of 0.00096 ft/sec. FS = A safety factor of 2 to account for non-ideal settling. Therefore, the equation for computing surface area becomes: SA = 2 x Q2/0.00096 or 2080 square feet per cfs of inflow Note: Even if permanent facilities are used, they must still have a surface area that is at least as large as that derived from the above formula. If they do not, the pond must be enlarged. • To aid in determining sediment depth, all sediment traps shall have a staff gauge with a prominent mark 1-foot above the bottom of the trap. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-103 Surface area determinedat top of weir Note: Trap may be formed by berm or bypartial or complete excavation Discharge to stabilizedconveyance, outlet, orlevel spreader ¾" - 1.5"Washed gravel Geotextile Flat Bottom 1' Min. Overflow 1' Min. 4' Min. RipRap2"-4" Rock 1' Min. 1.5' Min. 3.5'-5' 3H : 1 V M a x . • Sediment traps may not be feasible on utility projects due to the limited work space or the short-term nature of the work. Portable tanks may be used in place of sediment traps for utility projects. Maintenance Standards • Sediment shall be removed from the trap when it reaches 1-foot in depth. • Any damage to the pond embankments or slopes shall be repaired. Figure 4.2.16 – Cross Section of Sediment Trap Figure 4.2.17 – Sediment Trap Outlet Native soil or compacted backfill Geotextile Min. 1' depth 2"-4"' rock Min. 1' depth 3/4"-1.5" washed gravel 6' Min. 1' Min. depth overflow spillway Volume II – Construction Stormwater Pollution Prevention - August 2012 4-104 BMP C241: Temporary Sediment Pond Purpose Sediment ponds remove sediment from runoff originating from disturbed areas of the site. Sediment ponds are typically designed to remove sediment no smaller than medium silt (0.02 mm). Consequently, they usually reduce turbidity only slightly. Conditions of Use Prior to leaving a construction site, stormwater runoff must pass through a sediment pond or other appropriate sediment removal best management practice. A sediment pond shall be used where the contributing drainage area is 3 acres or more. Ponds must be used in conjunction with erosion control practices to reduce the amount of sediment flowing into the basin. Design and Installation Specifications • Sediment basins must be installed only on sites where failure of the structure would not result in loss of life, damage to homes or buildings, or interruption of use or service of public roads or utilities. Also, sediment traps and ponds are attractive to children and can be very dangerous. Compliance with local ordinances regarding health and safety must be addressed. If fencing of the pond is required, the type of fence and its location shall be shown on the ESC plan. • Structures having a maximum storage capacity at the top of the dam of 10 acre-ft (435,600 ft3) or more are subject to the Washington Dam Safety Regulations (Chapter 173-175 WAC). • See Figures 4.2.18, 4.2.19, and 4.2.20 for details. • If permanent runoff control facilities are part of the project, they should be used for sediment retention. The surface area requirements of the sediment basin must be met. This may require temporarily enlarging the permanent basin to comply with the surface area requirements. The permanent control structure must be temporarily replaced with a control structure that only allows water to leave the pond from the surface or by pumping. The permanent control structure must be installed after the site is fully stabilized. . • Use of infiltration facilities for sedimentation basins during construction tends to clog the soils and reduce their capacity to infiltrate. If infiltration facilities are to be used, the sides and bottom of the facility must only be rough excavated to a minimum of 2 feet above final grade. Final grading of the infiltration facility shall occur only when all contributing drainage areas are fully stabilized. The infiltration pretreatment facility should be fully constructed and used with the sedimentation basin to help prevent clogging. • Determining Pond Geometry Obtain the discharge from the hydrologic calculations of the peak flow for the 2-year runoff event (Q2). The 10-year peak flow shall be used if Volume II – Construction Stormwater Pollution Prevention - August 2012 4-105 the project size, expected timing and duration of construction, or downstream conditions warrant a higher level of protection. If no hydrologic analysis is required, the Rational Method may be used. Determine the required surface area at the top of the riser pipe with the equation: SA = 2 x Q2/0.00096 or 2080 square feet per cfs of inflow See BMP C240 for more information on the derivation of the surface area calculation. The basic geometry of the pond can now be determined using the following design criteria: • Required surface area SA (from Step 2 above) at top of riser. • Minimum 3.5-foot depth from top of riser to bottom of pond. • Maximum 3H:1V interior side slopes and maximum 2H:1V exterior slopes. The interior slopes can be increased to a maximum of 2H:1V if fencing is provided at or above the maximum water surface. • One foot of freeboard between the top of the riser and the crest of the emergency spillway. • Flat bottom. • Minimum 1-foot deep spillway. • Length-to-width ratio between 3:1 and 6:1. • Sizing of Discharge Mechanisms. The outlet for the basin consists of a combination of principal and emergency spillways. These outlets must pass the peak runoff expected from the contributing drainage area for a 100-year storm. If, due to site conditions and basin geometry, a separate emergency spill- way is not feasible, the principal spillway must pass the entire peak runoff expected from the 100-year storm. However, an attempt to provide a separate emergency spillway should always be made. The runoff calculations should be based on the site conditions during construction. The flow through the dewatering orifice cannot be utilized when calculating the 100-year storm elevation because of its potential to become clogged; therefore, available spillway storage must begin at the principal spillway riser crest. The principal spillway designed by the procedures contained in this standard will result in some reduction in the peak rate of runoff. However, the riser outlet design will not adequately control the basin discharge to the predevelopment discharge limitations as stated in Minimum Requirement #7: Flow Control. However, if the basin for a permanent stormwater detention pond is used for a temporary Volume II – Construction Stormwater Pollution Prevention - August 2012 4-106 Riser pipe(principal spillway)open at top withtrash rackper Fig 4.4.4E Dewatering device (see riser detail) Wire-backed silt fencestaked haybales wrappedwith filter fabric, orequivalent divider Dewatering orifice Concrete base (see riser detail) Discharge to stabilized conveyance outlet or level spreader Embankment compacted 95% pervious materials such as gravel or clean sand shall not be used 6' min. WidthCrest of emergency spillway Key divider into slopeto prevent flowaround sides The pond length shall be 3 to 6 times the maximum pond width Emergency overflow spillway Discharge to stabilizedconveyance, outlet, orlevel spreader Note: Pond may be formed by berm or by partial or complete excavation Inflow Pond length Silt fence or equivalent divider Riser pipe sedimentation basin, the control structure for the permanent pond can be used to maintain predevelopment discharge limitations. The size of the basin, the expected life of the construction project, the anticipated downstream effects and the anticipated weather conditions during construction, should be considered to determine the need of additional discharge control. See Figure 4.2.21 for riser inflow curves. Figure 4.2.18 – Sediment Pond Plan View Figure 4.2.19 – Sediment Pond Cross Section Volume II – Construction Stormwater Pollution Prevention - August 2012 4-107 Perforated polyethylene drainage tubing, diameter min. 2" larger than dewatering orifice. Tubing shall comply with ASTM F667 and AASHTO M294 Polyethylene cap Provide adequate strapping Dewatering orifice, schedule, 40 steel stub min. Diameter as per calculations Alternatively, metal stakes and wire may be used to prevent flotation 2X riser dia. Min. Concrete base Corrugated metal riser Watertight coupling 18" min. 6" min. Tack weld 3.5" min. Figure 4.2.20 – Sediment Pond Riser Detail Volume II – Construction Stormwater Pollution Prevention - August 2012 4-108 Figure 4.2.21 – Riser Inflow Curves Volume II – Construction Stormwater Pollution Prevention - August 2012 4-109 Principal Spillway: Determine the required diameter for the principal spillway (riser pipe). The diameter shall be the minimum necessary to pass the site’s 15-minute, 10-year flowrate. If using the Western Washington Hydrology Model (WWHM), Version 2 or 3, design flow is the 10-year (1 hour) flow for the developed (unmitigated) site, multiplied by a factor of 1.6. Use Figure 4.2.21 to determine this diameter (h = 1-foot). Note: A permanent control structure may be used instead of a temporary riser. Emergency Overflow Spillway: Determine the required size and design of the emergency overflow spillway for the developed 100-year peak flow using the method contained in Volume III. Dewatering Orifice: Determine the size of the dewatering orifice(s) (minimum 1-inch diameter) using a modified version of the discharge equation for a vertical orifice and a basic equation for the area of a circular orifice. Determine the required area of the orifice with the following equation: 5.0 5.0 3600x6.0 )2( Tg hAAs o = where Ao = orifice area (square feet) As = pond surface area (square feet) h = head of water above orifice (height of riser in feet) T = dewatering time (24 hours) g = acceleration of gravity (32.2 feet/second2) Convert the required surface area to the required diameter D of the orifice: o o AADx54.13x24==π The vertical, perforated tubing connected to the dewatering orifice must be at least 2 inches larger in diameter than the orifice to improve flow characteristics. The size and number of perforations in the tubing should be large enough so that the tubing does not restrict flow. The orifice should control the flow rate. • Additional Design Specifications The pond shall be divided into two roughly equal volume cells by a permeable divider that will reduce turbulence while allowing movement of water between cells. The divider shall be at least one- half the height of the riser and a minimum of one foot below the top of the riser. Wire-backed, 2- to 3-foot high, extra strength filter fabric supported by treated 4"x4"s can be used as a divider. Alternatively, staked straw bales wrapped with filter fabric (geotextile) may be used. If the pond is more than 6 feet deep, a different mechanism must be proposed. A riprap embankment is one acceptable method of Volume II – Construction Stormwater Pollution Prevention - August 2012 4-110 separation for deeper ponds. Other designs that satisfy the intent of this provision are allowed as long as the divider is permeable, structurally sound, and designed to prevent erosion under or around the barrier. To aid in determining sediment depth, one-foot intervals shall be prominently marked on the riser. If an embankment of more than 6 feet is proposed, the pond must comply with the criteria contained in Volume III regarding dam safety for detention BMPs. • The most common structural failure of sedimentation basins is caused by piping. Piping refers to two phenomena: (1) water seeping through fine-grained soil, eroding the soil grain by grain and forming pipes or tunnels; and, (2) water under pressure flowing upward through a granular soil with a head of sufficient magnitude to cause soil grains to lose contact and capability for support. The most critical construction sequences to prevent piping will be: 1. Tight connections between riser and barrel and other pipe connections. 2. Adequate anchoring of riser. 3. Proper soil compaction of the embankment and riser footing. 4. Proper construction of anti-seep devices. Maintenance Standards • Sediment shall be removed from the pond when it reaches 1–foot in depth. • Any damage to the pond embankments or slopes shall be repaired. BMP C250: Construction Stormwater Chemical Treatment Purpose This BMP applies when using stormwater chemicals in batch treatment or flow-through treatment. Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a construction site. Sedimentation ponds are effective at removing larger particulate matter by gravity settling, but are ineffective at removing smaller particulates such as clay and fine silt. Traditional erosion and sediment control BMPs may not be adequate to ensure compliance with the water quality standards for turbidity in receiving water. Chemical treatment can reliably provide exceptional reductions of turbidity and associated pollutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when construction is to proceed through the wet season. Conditions of Use Formal written approval from Ecology is required for the use of chemical treatment regardless of site size. The Local Permitting Authority may also Volume II – Construction Stormwater Pollution Prevention - August 2012 4-111 require review and approval. When approved, the chemical treatment systems must be included in the Construction Stormwater Pollution Prevention Plan (SWPPP). Design and Installation Specifications See Appendix II-B for background information on chemical treatment. Criteria for Chemical Treatment Product Use: Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organisms. The Chemical Technology Assessment Protocol (CTAPE) must be used to evaluate chemicals proposed for stormwater treatment. Only chemicals approved by Ecology under the CTAPE may be used for stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or flow-through treatment), allowable application rates, and conditions of use can be found at the Department of Ecology Emerging Technologies website: http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.ht ml. Treatment System Design Considerations: The design and operation of a chemical treatment system should take into consideration the factors that determine optimum, cost-effective performance. It is important to recognize the following: • Only Ecology approved chemicals may be used and must follow approved dose rate. • The pH of the stormwater must be in the proper range for the polymers to be effective, which is typically 6.5 to 8.5 • The coagulant must be mixed rapidly into the water to ensure proper dispersion. • A flocculation step is important to increase the rate of settling, to produce the lowest turbidity, and to keep the dosage rate as low as possible. • Too little energy input into the water during the flocculation phase results in flocs that are too small and/or insufficiently dense. Too much energy can rapidly destroy floc as it is formed. • Care must be taken in the design of the withdrawal system to minimize outflow velocities and to prevent floc discharge. Discharge from a batch treatment system should be directed through a physical filter such as a vegetated swale that would catch any unintended floc discharge. Currently, flow-through systems always discharge through the chemically enhanced sand filtration system. • System discharge rates must take into account downstream conveyance integrity. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-112 Polymer Batch Treatment Process Description: A batch chemical treatment system consists of the stormwater collection system (either temporary diversion or the permanent site drainage system), a storage pond, pumps, a chemical feed system, treatment cells, and interconnecting piping. The batch treatment system shall use a minimum of two lined treatment cells in addition to an untreated stormwater storage pond. Multiple treatment cells allow for clarification of treated water while other cells are being filled or emptied. Treatment cells may be ponds or tanks. Ponds with constructed earthen embankments greater than six feet high or which impound more than 10 acre-feet require special engineering analyses. The Ecology Dam Safety Section has specific design criteria for dams in Washington State (see http://www.ecy.wa.gov/programs/wr/dams/GuidanceDocs.html ). Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage. The first step in the treatment sequence is to check the pH of the stormwater in the untreated stormwater storage pond. The pH is adjusted by the application of carbon dioxide or a base until the stormwater in the storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon dioxide is added immediately downstream of the transfer pump. Typically sodium bicarbonate (baking soda) is used as a base, although other bases may be used. When needed, base is added directly to the untreated stormwater storage pond. The stormwater is recirculated with the treatment pump to provide mixing in the storage pond. Initial pH adjustments should be based on daily bench tests. Further pH adjustments can be made at any point in the process. Once the stormwater is within the desired pH range (dependant on polymer being used), the stormwater is pumped from the untreated stormwater storage pond to a treatment cell as polymer is added. The polymer is added upstream of the pump to facilitate rapid mixing. After polymer addition, the water is kept in a lined treatment cell for clarification of the sediment-floc. In a batch mode process, clarification typically takes from 30 minutes to several hours. Prior to discharge samples are withdrawn for analysis of pH, flocculent chemical concentration, and turbidity. If both are acceptable, the treated water is discharged. Several configurations have been developed to withdraw treated water from the treatment cell. The original configuration is a device that withdraws the treated water from just beneath the water surface using a Volume II – Construction Stormwater Pollution Prevention - August 2012 4-113 float with adjustable struts that prevent the float from settling on the cell bottom. This reduces the possibility of picking up sediment-floc from the bottom of the pond. The struts are usually set at a minimum clearance of about 12 inches; that is, the float will come within 12 inches of the bottom of the cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up and down with the water level. More recent designs have an H-shaped array of pipes, set on the horizontal. This scheme provides for withdrawal from four points rather than one. This configuration reduces the likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vortex to form. Inlet diffusers, a long floating or fixed pipe with many small holes in it, are also an option. Safety is a primary concern. Design should consider the hazards associated with operations, such as sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds should have life rings, ladders, or steps extending from the bottom to the top. Polymer Batch Treatment Process Description: At a minimum, a flow-through chemical treatment system consists of the stormwater collection system (either temporary diversion or the permanent site drainage system), an untreated stormwater storage pond, and the chemically enhanced sand filtration system. Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage. Stormwater is then pumped from the untreated stormwater storage pond to the chemically enhanced sand filtration system where polymer is added. Adjustments to pH may be necessary before chemical addition. The sand filtration system continually monitors the stormwater for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the water is recycled to the untreated stormwater pond where it can be retreated. For batch treatment and flow-through treatment, the following equipment should be located in a lockable shed: • The chemical injector. • Secondary containment for acid, caustic, buffering compound, and treatment chemical. • Emergency shower and eyewash. • Monitoring equipment which consists of a pH meter and a turbidimeter. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-114 System Sizing: Certain sites are required to implement flow control for the developed sites. These sites must also control stormwater release rates during construction. Generally, these are sites that discharge stormwater directly, or indirectly, through a conveyance system, into a fresh water. System sizing is dependent on flow control requirements. Sizing Criteria for Batch Treatment Systems for Flow Control Exempt Water Bodies: The total volume of the untreated stormwater storage pond and treatment ponds or tanks must be large enough to treat stormwater that is produced during multiple day storm events. It is recommended that at a minimum the untreated stormwater storage pond be sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event. Bypass should be provided around the chemical treatment system to accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping). Primary settling should be encouraged in the untreated stormwater storage pond. A forebay with access for maintenance may be beneficial. There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a larger volume of water each time a batch is processed. However, the larger the cell the longer the time required to empty the cell. A larger cell may also be less effective at flocculation and therefore require a longer settling time. The simplest approach to sizing the treatment cell is to multiply the allowable discharge flow rate times the desired drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour work period, given 1 hour of flocculation followed by two hours of settling. If the discharge is directly to a flow control exempt receiving water listed in Appendix I-E of Volume I or to an infiltration system, there is no discharge flow limit. Ponds sized for flow control water bodies must at a minimum meet the sizing criteria for flow control exempt waters. Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies: When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies, the treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system flowrate for an 8-hour period. For a chitosan- enhanced sand filtration system, the treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic Volume II – Construction Stormwater Pollution Prevention - August 2012 4-115 loading rates may be more appropriate for other systems. Bypass should be provided around the chemical treatment system to accommodate extreme storms. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping). Sizing Criteria for Flow Control Water Bodies: Sites that must implement flow control for the developed site condition must also control stormwater release rates during construction. Construction site stormwater discharges shall not exceed the discharge durations of the pre-developed condition for the range of pre-developed discharge rates from ½ of the 2-year flow through the 10-year flow as predicted by an approved continuous runoff model. The pre-developed condition to be matched shall be the land cover condition immediately prior to the development project. This restriction on release rates can affect the size of the storage pond and treatment cells. The following is how WWHM can be used to determine the release rates from the chemical treatment systems: 1. Determine the pre-developed flow durations to be matched by entering the existing land use area under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the 10-year flow. 2. Enter the post developed land use area in the “Developed Unmitigated” scenario in WWHM. 3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario. 4. While in the “Developed Mitigated” scenario, add a pond element under the basin element containing the post-developed land use areas. This pond element represents information on the available untreated stormwater storage and discharge from the chemical treatment system. In cases where the discharge from the chemical treatment system is controlled by a pump, a stage/storage/discharge (SSD) table representing the pond must be generated outside WWHM and imported into WWHM. WWHM can route the runoff from the post- developed condition through this SSD table (the pond) and determine compliance with the flow duration standard. This would be an iterative design procedure where if the initial SSD table proved to be inadequate, the designer would have to modify the SSD table outside WWHM and re-import in WWHM and route the runoff through it again. The iteration will continue until a pond that complies with the flow duration standard is correctly sized. Notes on SSD table characteristics: Volume II – Construction Stormwater Pollution Prevention - August 2012 4-116 • The pump discharge rate would likely be initially set at just below ½ of the 2-year flow from the pre-developed condition. As runoff coming into the untreated stormwater storage pond increases and the available untreated stormwater storage volume gets used up, it would be necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year must be such that they provide some relief to the untreated stormwater storage needs but at the same time will not cause violations of the flow duration standard at the higher flows. The final design SSD table will identify the appropriate pumping rates and the corresponding stage and storages. • When building such a flow control system, the design must ensure that any automatic adjustments to the pumping rates will be as a result of changes to the available storage in accordance with the final design SSD table. 5. It should be noted that the above procedures would be used to meet the flow control requirements. The chemical treatment system must be able to meet the runoff treatment requirements. It is likely that the discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the case, the untreated stormwater discharge rate(s) (i.e., influent to the treatment system) must be reduced to allow proper treatment. Any reduction in the flows would likely result in the need for a larger untreated stormwater storage volume. If the discharge is to a municipal storm drainage system, the allowable discharge rate may be limited by the capacity of the public system. It may be necessary to clean the municipal storm drainage system prior to the start of the discharge to prevent scouring solids from the drainage system. If the municipal storm drainage system discharges to a water body not on the flow control exempt list, the project site is subject to flow control requirements. Obtain permission from the owner of the collection system before discharging to it. If system design does not allow you to discharge at the slower rates as described above and if the site has a retention or detention pond that will serve the planned development, the discharge from the treatment system may be directed to the permanent retention/detention pond to comply with the flow control requirement. In this case, the untreated stormwater storage pond and treatment system will be sized according to the sizing criteria for flow- through treatment systems for flow control exempt water bodies described earlier except all discharge (water passing through the treatment system and stormwater bypassing the treatment system) will be directed into the permanent retention/detention pond. If site constraints make locating the untreated stormwater storage pond difficult, the permanent retention/detention pond may be divided to serve as the untreated stormwater storage pond and the post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated Volume II – Construction Stormwater Pollution Prevention - August 2012 4-117 water. Both untreated stormwater storage requirements, and adequate post- treatment flow control must be achieved. The post-treatment flow control pond’s revised dimensions must be entered into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement. Maintenance Standards Monitoring: At a minimum, the following monitoring shall be conducted. Test results shall be recorded on a daily log kept on site. Additional testing may be required by the NPDES permit based on site conditions. Operational Monitoring: • Total volume treated and discharged. • Flow must be continuously monitored and recorded at not greater than 15-minute intervals. • Type and amount of chemical used for pH adjustment. • Amount of polymer used for treatment. • Settling time. Compliance Monitoring: • Influent and effluent pH, flocculent chemical concentration, and turbidity must be continuously monitored and recorded at not greater than 15-minute intervals. pH and turbidity of the receiving water. Biomonitoring: Treated stormwater must be non-toxic to aquatic organisms. Treated stormwater must be tested for aquatic toxicity or residual chemicals. Frequency of biomonitoring will be determined by Ecology. Residual chemical tests must be approved by Ecology prior to their use. If testing treated stormwater for aquatic toxicity, you must test for acute (lethal) toxicity. Bioassays shall be conducted by a laboratory accredited by Ecology, unless otherwise approved by Ecology. Acute toxicity tests shall be conducted per the CTAPE protocol. Discharge Compliance: Prior to discharge, treated stormwater must be sampled and tested for compliance with pH, flocculent chemical concentration, and turbidity limits. These limits may be established by the Construction Stormwater General Permit or a site-specific discharge permit. Sampling and testing for other pollutants may also be necessary at some sites. pH must be within the range of 6.5 to 8.5 standard units and not cause a change in the pH of the receiving water of more than 0.2 standard units. Treated stormwater samples and measurements shall be taken from the discharge pipe or another location representative of the nature of the treated stormwater discharge. Samples used for determining compliance with the water quality standards in the receiving water shall not be taken from the treatment pond prior to decanting. Compliance with the water quality standards is determined in the receiving water. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-118 Operator Training: Each contractor who intends to use chemical treatment shall be trained by an experienced contractor . Each site using chemical treatment must have an operator trained and certified by an organization approved by Ecology. Standard BMPs: Surface stabilization BMPs should be implemented on site to prevent significant erosion. All sites shall use a truck wheel wash to prevent tracking of sediment off site. Sediment Removal and Disposal: • Sediment shall be removed from the storage or treatment cells as necessary. Typically, sediment removal is required at least once during a wet season and at the decommissioning of the cells. Sediment remaining in the cells between batches may enhance the settling process and reduce the required chemical dosage. • Sediment that is known to be non-toxic may be incorporated into the site away from drainages. BMP C251: Construction Stormwater Filtration Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Background Information: Filtration with sand media has been used for over a century to treat water and wastewater. The use of sand filtration for treatment of stormwater has developed recently, generally to treat runoff from streets, parking lots, and residential areas. The application of filtration to construction stormwater treatment is currently under development. Conditions of Use Traditional BMPs used to control soil erosion and sediment loss from sites under development may not be adequate to ensure compliance with the water quality standard for turbidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5 µm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the stormwater. In some circumstances, sedimentation and filtration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treatment chemicals are not used. Filtration in conjunction with polymer treatment requires testing under the Chemical Technology Assessment Protocol – Ecology (CTAPE) before it can be initiated. Approval from the appropriate regional Ecology office must be obtained at each site where polymers use is proposed prior to use. For more guidance on stormwater chemical treatment see BMP C250. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-119 Design and Installation Specifications Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow. Rapid sand filters are the typical system used for water and wastewater treatment. They can achieve relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have automatic backwash systems to remove accumulated solids. In contrast, slow sand filters have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do not have backwash systems. Slow sand filtration has generally been used to treat stormwater. Slow sand filtration is mechanically simple in comparison to rapid sand filtration but requires a much larger filter area. Filtration Equipment. Sand media filters are available with automatic backwashing features that can filter to 50 µm particle size. Screen or bag filters can filter down to 5 µm. Fiber wound filters can remove particles down to 0.5 µm. Filters should be sequenced from the largest to the smallest pore opening. Sediment removal efficiency will be related to particle size distribution in the stormwater. Treatment Process Description. Stormwater is collected at interception point(s) on the site and is diverted to an untreated stormwater sediment pond or tank for removal of large sediment and storage of the stormwater before it is treated by the filtration system. The untreated stormwater is pumped from the trap, pond, or tank through the filtration system in a rapid sand filtration system. Slow sand filtration systems are designed as flow through systems using gravity. Maintenance Standards Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set pressure drop across the filter. If the backwash water volume is not large or substantially more turbid than the untreated stormwater stored in the holding pond or tank, backwash return to the untreated stormwater pond or tank may be appropriate. However, other means of treatment and disposal may be necessary. • Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged. • Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically, sediment removal is required once or twice during a wet season and at the decommissioning of the ponds. Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies: When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies the treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system flowrate for an 8-hour period. For a chitosan- enhanced sand filtration system, the treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic Volume II – Construction Stormwater Pollution Prevention - August 2012 4-120 loading rates may be more appropriate for other systems. Bypass should be provided around the chemical treatment system to accommodate extreme storms. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2. Worst-case conditions (i.e., producing the most runoff) should be used for analyses (most likely conditions present prior to final landscaping). Sizing Criteria for Flow Control Water Bodies: Sites that must implement flow control for the developed site condition must also control stormwater release rates during construction. Construction site stormwater discharges shall not exceed the discharge durations of the pre-developed condition for the range of pre-developed discharge rates from 1/2 of the 2-year flow through the 10-year flow as predicted by an approved continuous runoff model. The pre-developed condition to be matched shall be the land cover condition immediately prior to the development project. This restriction on release rates can affect the size of the storage pond, the filtration system, and the flow rate through the filter system. The following is how WWHM can be used to determine the release rates from the filtration systems: 1. Determine the pre-developed flow durations to be matched by entering the land use area under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the 10-year flow. 2. Enter the post developed land use area in the “Developed Unmitigated” scenario in WWHM. 3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario. 4. There are two possible ways to model stormwater filtration systems: a. The stormwater filtration system uses an untreated stormwater storage pond/tank and the discharge from this pond/tank is pumped to one or more filters. In-line filtration chemicals would be added to the flow right after the pond/tank and before the filter(s). Because the discharge is pumped, WWHM can’t generate a stage/storage /discharge (SSD) table for this system. This system is modeled the same way as described in BMP C250 and is as follows: While in the “Developed Mitigated” scenario, add a pond element under the basin element containing the post-developed land use areas. This pond element represents information on the available untreated stormwater storage and discharge from the filtration system. In cases where the discharge from the filtration system is controlled by a pump, a stage/storage/discharge (SSD) table representing the pond must be generated outside WWHM and Volume II – Construction Stormwater Pollution Prevention - August 2012 4-121 imported into WWHM. WWHM can route the runoff from the post-developed condition through this SSD table (the pond) and determine compliance with the flow duration standard. This would be an iterative design procedure where if the initial SSD table proved to be out of compliance, the designer would have to modify the SSD table outside WWHM and re-import in WWHM and route the runoff through it again. The iteration will continue until a pond that enables compliance with the flow duration standard is designed. Notes on SSD table characteristics: • The pump discharge rate would likely be initially set at just below ½ if the 2-year flow from the pre-developed condition. As runoff coming into the untreated stormwater storage pond increases and the available untreated stormwater storage volume gets used up, it would be necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year must be such that they provide some relief to the untreated stormwater storage needs but at the same time they will not cause violations of the flow duration standard at the higher flows. The final design SSD table will identify the appropriate pumping rates and the corresponding stage and storages. • When building such a flow control system, the design must ensure that any automatic adjustments to the pumping rates will be as a result of changes to the available storage in accordance with the final design SSD table. b. The stormwater filtration system uses a storage pond/tank and the discharge from this pond/tank gravity flows to the filter. This is usually a slow sand filter system and it is possible to model it in WWHM as a Filter element or as a combination of Pond and Filter element placed in series. The stage/storage/discharge table(s) may then be generated within WWHM as follows: (i) While in the “Developed Mitigated” scenario, add a Filter element under the basin element containing the post-developed land use areas. The length and width of this filter element would have to be the same as the bottom length and width of the upstream untreated stormwater storage pond/tank. (ii) In cases where the length and width of the filter is not the same as those for the bottom of the upstream untreated stormwater storage tank/pond, the treatment system may be modeled as a Pond element followed by a Filter element. By having these two elements, WWHM would then generate a SSD table for the storage pond which then gravity flows to the Filter element. The Filter element downstream of the untreated stormwater Volume II – Construction Stormwater Pollution Prevention - August 2012 4-122 storage pond would have a storage component through the media, and an overflow component for when the filtration capacity is exceeded. WWHM can route the runoff from the post-developed condition through the treatment systems in 4b and determine compliance with the flow duration standard. This would be an iterative design procedure where if the initial sizing estimates for the treatment system proved to be inadequate, the designer would have to modify the system and route the runoff through it again. The iteration would continue until compliance with the flow duration standard is achieved. 5. It should be noted that the above procedures would be used to meet the flow control requirements. The filtration system must be able to meet the runoff treatment requirements. It is likely that the discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the case, the untreated stormwater discharge rate(s) (i.e., influent to the treatment system) must be reduced to allow proper treatment. Any reduction in the flows would likely result in the need for a larger untreated stormwater storage volume. If system design does not allow you to discharge at the slower rates as described above and if the site has a retention or detention pond that will serve the planned development, the discharge from the treatment system may be directed to the permanent retention/detention pond to comply with the flow control requirements. In this case, the untreated stormwater storage pond and treatment system will be sized according to the sizing criteria for flow- through treatment systems for flow control exempt waterbodies described earlier except all discharges (water passing through the treatment system and stormwater bypassing the treatment system) will be directed into the permanent retention/detention pond. If site constraints make locating the untreated stormwater storage pond difficult, the permanent retention/detention pond may be divided to serve as the untreated stormwater discharge pond and the post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post- treatment flow control must be achieved. The post-treatment flow control pond’s revised dimensions must be entered into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-123 BMP C252: High pH Neutralization Using CO2 Purpose When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5, this process is called pH neutralization. pH neutralization involves the use of solid or compressed carbon dioxide gas in water requiring neutralization. Neutralized stormwater may be discharged to surface waters under the General Construction NPDES permit. Neutralized process water such as concrete truck wash-out, hydro- demolition, or saw-cutting slurry must be managed to prevent discharge to surface waters. Any stormwater contaminated during concrete work is considered process wastewater and must not be discharged to surface waters. Reason for pH Neutralization: A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this neutral pH is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Calcium hardness can contribute to high pH values and cause toxicity that is associated with high pH conditions. A high level of calcium hardness in waters of the state is not allowed. The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Ground water standard for calcium and other dissolved solids in Washington State is less than 500 mg/l. Conditions of Use Causes of High pH: High pH at construction sites is most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP C151: Concrete Handling for more information on concrete handling procedures). The principal caustic agent in cement is calcium hydroxide (free lime). Advantages of CO2 Sparging: • Rapidly neutralizes high pH water. • Cost effective and safer to handle than acid compounds. • CO2 is self-buffering. It is difficult to overdose and create harmfully low pH levels. • Material is readily available. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-124 The Chemical Process: When carbon dioxide (CO2) is added to water (H2O), carbonic acid (H2CO3) is formed which can further dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reaction as well. The colder the water temperature is the slower the reaction occurs and the warmer the water temperature is the quicker the reaction occurs. Most construction applications in Washington State have water temperatures in the 50°F or higher range so the reaction is almost simultaneous. Design and Installation Specifications Treatment Process: High pH water may be treated using continuous treatment, continuous discharge systems. These manufactured systems continuously monitor influent and effluent pH to ensure that pH values are within an acceptable range before being discharged. All systems must have fail safe automatic shut off switches in the event that pH is not within the acceptable discharge range. Only trained operators may operate manufactured systems. System manufacturers often provide trained operators or training on their devices. The following procedure may be used when not using a continuous discharge system: 1. Prior to treatment, the appropriate jurisdiction should be notified in accordance with the regulations set by the jurisdiction. 2. Every effort should be made to isolate the potential high pH water in order to treat it separately from other stormwater on-site. 3. Water should be stored in an acceptable storage facility, detention pond, or containment cell prior to treatment. 4. Transfer water to be treated to the treatment structure. Ensure that treatment structure size is sufficient to hold the amount of water that is to be treated. Do not fill tank completely, allow at least 2 feet of freeboard. 5. The operator samples the water for pH and notes the clarity of the water. As a rule of thumb, less CO2 is necessary for clearer water. This information should be recorded. 6. In the pH adjustment structure, add CO2 until the pH falls in the range of 6.9-7.1. Remember that pH water quality standards apply so adjusting pH to within 0.2 pH units of receiving water (background pH) is recommended. It is unlikely that pH can be adjusted to within 0.2 pH units using dry ice. Compressed carbon dioxide gas should be introduced to the water using a carbon dioxide diffuser located near Volume II – Construction Stormwater Pollution Prevention - August 2012 4-125 the bottom of the tank, this will allow carbon dioxide to bubble up through the water and diffuse more evenly. 7. Slowly discharge the water making sure water does not get stirred up in the process. Release about 80% of the water from the structure leaving any sludge behind. 8. Discharge treated water through a pond or drainage system. 9. Excess sludge needs to be disposed of properly as concrete waste. If several batches of water are undergoing pH treatment, sludge can be left in treatment structure for the next batch treatment. Dispose of sludge when it fills 50% of tank volume. Sites that must implement flow control for the developed site must also control stormwater release rates during construction. All treated stormwater must go through a flow control facility before being released to surface waters which require flow control. Maintenance Standards Safety and Materials Handling: • All equipment should be handled in accordance with OSHA rules and regulations. • Follow manufacturer guidelines for materials handling. Operator Records: Each operator should provide: • A diagram of the monitoring and treatment equipment. • A description of the pumping rates and capacity the treatment equipment is capable of treating. Each operator should keep a written record of the following: • Client name and phone number. • Date of treatment. • Weather conditions. • Project name and location. • Volume of water treated. • pH of untreated water. • Amount of CO2 needed to adjust water to a pH range of 6.9-7.1. • pH of treated water. • Discharge point location and description. A copy of this record should be given to the client/contractor who should retain the record for three years. Volume II – Construction Stormwater Pollution Prevention - August 2012 4-126 BMP C253: pH Control for High pH Water Purpose When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5, this process is called pH neutralization. Stormwater with pH levels exceeding water quality standards may be treated by infiltration, dispersion in vegetation or compost, pumping to a sanitary sewer, disposal at a permitted concrete batch plant with pH neutralization capabilities, or carbon dioxide sparging. BMP C252 gives guidelines for carbon dioxide sparging. Reason for pH Neutralization: A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this pH range is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Conditions of Use Causes of High pH: High pH levels at construction sites are most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP C151: Concrete Handling for more information on concrete handling procedures). The principal caustic agent in cement is calcium hydroxide (free lime). Design and Installation Specifications Disposal Methods: Infiltration • Infiltration is only allowed if soil type allows all water to infiltrate (no surface runoff) without causing or contributing to a violation of surface or ground water quality standards. • Infiltration techniques should be consistent with Volume V, Chapter 7 Dispersion Use BMP T5.30 Full Dispersion Sanitary Sewer Disposal • Local sewer authority approval is required prior to disposal via the sanitary sewer. Concrete Batch Plant Disposal • Only permitted facilities may accept high pH water. • Facility should be contacted before treatment to ensure they can accept the high pH water. Stormwater Discharge Any pH treatment options that generate treated water that must be discharged off site are subject to flow control requirements. Sites that must implement flow control for the developed site must also control Volume II – Construction Stormwater Pollution Prevention - August 2012 4-127 stormwater release rates during construction. All treated stormwater must go through a flow control facility before being released to surface waters which require flow control. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page C-1 Appendix C Correspondence None at this time. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page D-1 Appendix D Site Inspection Form The results of each inspection shall be summarized in an inspection report or checklist that is entered into or attached to the site log book. It is suggested that the inspection report or checklist be included in this appendix to keep monitoring and inspection information in one document, but this is optional. However, it is mandatory that this SWPPP and the site inspection forms be kept onsite at all times during construction, and that inspections be performed and documented as outlined below. At a minimum, each inspection report or checklist shall include: Inspection date/times Weather information: general conditions during inspection, approximate amount of precipitation since the last inspection, and approximate amount of precipitation within the last 24 hours. A summary or list of all BMPs that have been implemented, including observations of all erosion/sediment control structures or practices. The following shall be noted: locations of BMPs inspected, locations of BMPs that need maintenance, the reason maintenance is needed, locations of BMPs that failed to operate as designed or intended, and locations where additional or different BMPs are needed, and the reason(s) why A description of stormwater discharged from the site. The presence of suspended sediment, turbid water, discoloration, and/or oil sheen shall be noted, as applicable. A description of any water quality monitoring performed during inspection, and the results of that monitoring. General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. A statement that, in the judgment of the person conducting the site inspection, the site is either in compliance or out of compliance with the terms and conditions of the SWPPP and the NPDES permit. If the site inspection indicates that the site is out of compliance, the inspection report shall include a summary of the remedial actions required to bring the site back into compliance, as well as a schedule of implementation. D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page D-2 Name, title, and signature of person conducting the site inspection; and the following statement: “I certify under penalty of law that this report is true, accurate, and complete, to the best of my knowledge and belief”. When the site inspection indicates that the site is not in compliance with any terms and conditions of the NPDES permit, the Permittee shall take immediate action(s) to: stop, contain, and clean up the unauthorized discharges, or otherwise stop the noncompliance; correct the problem(s); implement appropriate Best Management Practices (BMPs), and/or conduct maintenance of existing BMPs; and achieve compliance with all applicable standards and permit conditions. In addition, if the noncompliance causes a threat to human health or the environment, the Permittee shall comply with the Noncompliance Notification requirements in Special Condition S5.F of the permit. Construction Stormwater Site Inspection Form D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page D-3 Project Name Permit #: Date: Time: Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre Print Name: Approximate rainfall amount since the last inspection (in inches): Approximate rainfall amount in the last 24 hours (in inches): Current Weather Clear Cloudy Mist Rain Wind Fog A. Type of inspection: Weekly Post Storm Event Other B. Phase of Active Construction (check all that apply): Pre Construction/installation of erosion/sediment controls Clearing/Demo/Grading Infrastructure/storm/roads Concrete pours Vertical Construction/buildings Utilities Offsite improvements Site temporary stabilized Final stabilization C. Questions: 1. Were all areas of construction and discharge points inspected? Yes No 2. Did you observe the presence of suspended sediment, turbidity, discoloration, or oil sheen Yes No 3. Was a water quality sample taken during inspection? (refer to permit conditions S4 & S5) Yes No 4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No 5. If yes to #4 was it reported to Ecology? Yes No 6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken, and when. *If answering yes to # 4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/ transparency is 33 cm or greater. Sampling Results: Date: Parameter Method (circle one) Result Other/Note NTU cm pH Turbidity tube, meter, laboratory pH Paper, kit, meter Construction Stormwater Site Inspection Form D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page D-4 D. Check the observed status of all items. Provide “Action Required “details and dates. Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 1 Clearing Limits Before beginning land disturbing activities are all clearing limits, natural resource areas (streams, wetlands, buffers, trees) protected with barriers or similar BMPs? (high visibility recommended) 2 Construction Access Construction access is stabilized with quarry spalls or equivalent BMP to prevent sediment from being tracked onto roads? Sediment tracked onto the road way was cleaned thoroughly at the end of the day or more frequent as necessary. 3 Control Flow Rates Are flow control measures installed to control stormwater volumes and velocity during construction and do they protect downstream properties and waterways from erosion? If permanent infiltration ponds are used for flow control during construction, are they protected from siltation? 4 Sediment Controls All perimeter sediment controls (e.g. silt fence, wattles, compost socks, berms, etc.) installed, and maintained in accordance with the Stormwater Pollution Prevention Plan (SWPPP). Sediment control BMPs (sediment ponds, traps, filters etc.) have been constructed and functional as the first step of grading. Stormwater runoff from disturbed areas is directed to sediment removal BMP. 5 Stabilize Soils Have exposed un-worked soils been stabilized with effective BMP to prevent erosion and sediment deposition? Are stockpiles stabilized from erosion, protected with sediment trapping measures and located away from drain inlet, waterways, and drainage channels? Have soils been stabilized at the end of the shift, before a holiday or weekend if needed based on the weather forecast? Construction Stormwater Site Inspection Form D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page D-5 Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 6 Protect Slopes Has stormwater and ground water been diverted away from slopes and disturbed areas with interceptor dikes, pipes and or swales? Is off-site storm water managed separately from stormwater generated on the site? Is excavated material placed on uphill side of trenches consistent with safety and space considerations? Have check dams been placed at regular intervals within constructed channels that are cut down a slope? 7 Drain Inlets Storm drain inlets made operable during construction are protected. Are existing storm drains within the influence of the project protected? 8 Stabilize Channel and Outlets Have all on-site conveyance channels been designed, constructed and stabilized to prevent erosion from expected peak flows? Is stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes and downstream conveyance systems? 9 Control Pollutants Are waste materials and demolition debris handled and disposed of to prevent contamination of stormwater? Has cover been provided for all chemicals, liquid products, petroleum products, and other material? Has secondary containment been provided capable of containing 110% of the volume? Were contaminated surfaces cleaned immediately after a spill incident? Were BMPs used to prevent contamination of stormwater by a pH modifying sources? Wheel wash wastewater is handled and disposed of properly. 10 Control Dewatering Concrete washout in designated areas. No washout or excess concrete on the ground. Dewatering has been done to an approved source and in compliance with the SWPPP. Were there any clean non turbid dewatering discharges? Construction Stormwater Site Inspection Form D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page D-6 Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 11 Maintain BMP Are all temporary and permanent erosion and sediment control BMPs maintained to perform as intended? 12 Manage the Project Has the project been phased to the maximum degree practicable? Has regular inspection, monitoring and maintenance been performed as required by the permit? Has the SWPPP been updated, implemented and records maintained? E. Check all areas that have been inspected. All in place BMPs All discharge locations All concrete wash out areas All construction entrances/exits All disturbed soils All material storage areas All equipment storage areas F. Elements checked “Action Required” (section D) describe corrective action to be taken. List the element number; be specific on location and work needed. Document, initial, and date when the corrective action has been completed and inspected. Element # Description and Location Action Required Completion Date Initials Attach additional page if needed Sign the following certification: “I certify that this report is true, accurate, and complete, to the best of my knowledge and belief” Inspected by: Print Signature Title/Qualification of Inspector Date D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page E-1 Appendix E Construction Stormwater General Permit (CSWGP) D.R. STRONG Consulting Engineers, Inc. Avana Ridge Stormwater Pollution Prevention Plan Page F-1 Appendix F Engineering Calculations Existing Site Hydrology KCRTS was used to model the peak runoff from the Site. Per Table 3.2.2.b of the Manual the soil type is modeled as “Till” for the Alderwood gravelly sandy loam SCS classification. The entire Site is modeled as “Forest.” Results of the KCRTS analysis are included in this section. Flow Frequency Analysis Time Series File:predev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.188 2 2/09/01 18:00 0.241 1 100.00 0.990 0.051 7 1/06/02 3:00 0.188 2 25.00 0.960 0.140 4 2/28/03 3:00 0.145 3 10.00 0.900 0.005 8 3/24/04 20:00 0.140 4 5.00 0.800 0.083 6 1/05/05 8:00 0.122 5 3.00 0.667 0.145 3 1/18/06 21:00 0.083 6 2.00 0.500 0.122 5 11/24/06 4:00 0.051 7 1.30 0.231 0.241 1 1/09/08 9:00 0.005 8 1.10 0.091 Computed Peaks 0.223 50.00 0.980 The maximum discharge of the construction stormwater will not exceed 50% of the 2-year predeveloped peak flow rate of 0.83 cfs. Therefore the max discharge from the Site during construction will not exceed 0.415 cfs. 2015 D. R. STRONG Consulting Engineers Inc. 67 Avana Ridge Technical Information Report Renton, Washington APPENDIX “C” BOND QUANTITY WORKSHEET Planning Division |1055 South Grady Way – 6 th Floor | Renton, WA 98057 (425) 430-7200 • • Section I: Project Information • • • Section II: Bond Quantities Worksheets • •Section II.a EROSION CONTROL (Stabilization/Erosion Sediment Control (ESC)) •Section II.b TRANSPORTATION (Street and Site Improvements) •Section II.c DRAINAGE (Drainage and Stormwater Facilities): •Section II.d WATER - ONLY APPLICABLE IF WATER SERVICE IS PROVIDED BY CITY OF RENTON •Section II.e SANITARY SEWER - ONLY APPLICABLE IF SEWER SERVICE IS PROVIDED BY CITY OF RENTON • • • • • • Section III. Bond Worksheet • BOND QUANTITY WORKSHEET INSTRUCTIONS This worksheet is intended to be a "working" copy of the bond quantity worksheet, which will be used throughout all phases of the project, from initial submittal to project close-out approval. Submit this workbook, in its entirety, as follows: The following forms are to be completed by the engineer/developer/applicant as applicable to the project: The Bond Worksheet form will auto-calculate and auto-populate from the information provided in Section I and Section II. This section includes all pertinent information for the project Section II contains a separate spreadsheet TAB for each of the following specialties: (1) electronic copy (.xlsx format) and (1) hard copy of the entire workbook for civil construction permit submittal. Hard copies are to be included as part of the Technical Information Report (TIR). (1) electronic copy (.xlsx format) and (1) hard copy of the entire workbook for final close-out submittal. This section must be completed in its entirety Information from this section auto-populates to all other relevant areas of the workbook This section calculates the required Permit Bond for construction permit issuance as well as the required Maintenance Bond for project close-out submittals to release the permit bond on a project. All unit prices include labor, equipment, materials, overhead and profit. Complete the 'Quantity' columns for each of the appropriate section(s). Include existing Right-of-Way (ROW), Future Public Improvements and Private Improvements. The 'Quantity Remaining' column is only to be used when a project is under construction. The City allows one (1) bond reduction during the life of the project with the exception of the maintenance period reduction. Excel will auto-calculate and auto-populate the relevant fields and subtotals throughout the document. Only the 'Quantity' columns should need completing. Additional items not included in the lists can be added under the "write-in" sections. Provide a complete description, cost estimate and unit of measure for each write-in item. Note: Private improvements, with the exception of stormwater facilities, are not included in the bond amount calculation, but must be entered on the form. Stormwater facilities (public and private) are required to be included in the bond amount. Page 1 of 14 Ref 8-H Bond Quantity Worksheet INSTRUCTIONS Unit Prices Updated: 03/2016 Version: 06/2016 Printed 3/30/2017 Planning Division |1055 South Grady Way – 6 th Floor | Renton, WA 98057 (425) 430-7200 Date Prepared: Name: PE Registration No: Firm Name: Firm Address: Phone No. Email Address: Project Name: Project Owner: CED Plan # (LUA):Phone: CED Permit # (U):Address: Site Address: Street Intersection:Addt'l Project Owner: Parcel #(s):Phone: Address: Clearing and grading greater than or equal to 5,000 board feet of timber? Yes/No:Water Service Provided by: If Yes, Provide Forest Practice Permit #:Sewer Service Provided by: Abbreviated Legal Description: Lots 1 and 2 of City of Renton Lot Line Adjustment No. LUA-09-024-LLA LND-30-0349, recored December 16, 2011 under Recording No. 20111216900001, in King County, Washington. 17249 Benson Rd S & 10615 SE 172nd St 9675 SE 36th Street, Suite 105U15008868 206-588-1147 3/30/2017 Prepared by: FOR APPROVALProject Phase 1 maher.joudi@drstrong.com Maher A. Joudi 45232 D.R. Strong Consulting Engineers 620 7th Avenue Kirkland WA 98033 425-827-3063 SITE IMPROVEMENT BOND QUANTITY WORKSHEET PROJECT INFORMATION SOOS CREEK WATER & SEWER SOOS CREEK WATER & SEWER 1 Select the current project status/phase from the following options: For Approval - Preliminary Data Enclosed, pending approval from the City; For Construction - Estimated Data Enclosed, Plans have been approved for contruction by the City; Project Closeout - Final Costs and Quantities Enclosed for Project Close-out Submittal Engineer Stamp Required (all cost estimates must have original wet stamp and signature) Clearing and Grading Utility Providers N/A Project Location and Description Project Owner Information Avana Ridge Mercer Island, WA 98040 292305-9148 and -9009 Avana Ridge, LLC LUA15-000894 Page 2 of 14 Ref 8-H Bond Quantity Worksheet SECTION I PROJECT INFORMATION Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Unit Reference #Price Unit Quantity Cost Backfill & compaction-embankment ESC-1 6.50$ CY Check dams, 4" minus rock ESC-2 SWDM 5.4.6.3 80.00$ Each 14 1,120.00 Catch Basin Protection ESC-3 35.50$ Each 21 745.50 Crushed surfacing 1 1/4" minus ESC-4 WSDOT 9-03.9(3)95.00$ CY Ditching ESC-5 9.00$ CY 150 1,350.00 Excavation-bulk ESC-6 2.00$ CY Fence, silt ESC-7 SWDM 5.4.3.1 1.50$ LF 1150 1,725.00 Fence, Temporary (NGPE)ESC-8 1.50$ LF Geotextile Fabric ESC-9 2.50$ SY Hay Bale Silt Trap ESC-10 0.50$ Each Hydroseeding ESC-11 SWDM 5.4.2.4 0.80$ SY 8000 6,400.00 Interceptor Swale / Dike ESC-12 1.00$ LF 870 870.00 Jute Mesh ESC-13 SWDM 5.4.2.2 3.50$ SY Level Spreader ESC-14 1.75$ LF Mulch, by hand, straw, 3" deep ESC-15 SWDM 5.4.2.1 2.50$ SY Mulch, by machine, straw, 2" deep ESC-16 SWDM 5.4.2.1 2.00$ SY 4000 8,000.00 Piping, temporary, CPP, 6"ESC-17 12.00$ LF Piping, temporary, CPP, 8"ESC-18 14.00$ LF Piping, temporary, CPP, 12"ESC-19 18.00$ LF 60 1,080.00 Plastic covering, 6mm thick, sandbagged ESC-20 SWDM 5.4.2.3 4.00$ SY Rip Rap, machine placed; slopes ESC-21 WSDOT 9-13.1(2)45.00$ CY Rock Construction Entrance, 50'x15'x1'ESC-22 SWDM 5.4.4.1 1,800.00$ Each 2 3,600.00 Rock Construction Entrance, 100'x15'x1'ESC-23 SWDM 5.4.4.1 3,200.00$ Each Sediment pond riser assembly ESC-24 SWDM 5.4.5.2 2,200.00$ Each Sediment trap, 5' high berm ESC-25 SWDM 5.4.5.1 19.00$ LF Sed. trap, 5' high, riprapped spillway berm section ESC-26 SWDM 5.4.5.1 70.00$ LF Seeding, by hand ESC-27 SWDM 5.4.2.4 1.00$ SY Sodding, 1" deep, level ground ESC-28 SWDM 5.4.2.5 8.00$ SY Sodding, 1" deep, sloped ground ESC-29 SWDM 5.4.2.5 10.00$ SY TESC Supervisor ESC-30 110.00$ HR 160 17,600.00 Water truck, dust control ESC-31 SWDM 5.4.7 140.00$ HR 120 16,800.00 Unit Reference #Price Unit Quantity Cost 500.00$ Each 1 500.00 1,500.00$ Each 24 36,000.00 EROSION/SEDIMENT SUBTOTAL:95,790.50 SALES TAX @ 9.5%9,100.10 EROSION/SEDIMENT TOTAL:104,890.60 (A) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR EROSION & SEDIMENT CONTROL Description No. (A) Sump Pump Baker Tank (month) WRITE-IN-ITEMS Page 3 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.a EROSION_CONTROL Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost GENERAL ITEMS Backfill & Compaction- embankment GI-1 6.00$ CY 3500 21,000.00 Backfill & Compaction- trench GI-2 9.00$ CY 500 4,500.00 500 4,500.00 Clear/Remove Brush, by hand (SY)GI-3 1.00$ SY Bollards - fixed GI-4 240.74$ Each Bollards - removable GI-5 452.34$ Each Clearing/Grubbing/Tree Removal GI-6 10,000.00$ Acre 0.25 2,500.00 2.5 25,000.00 Excavation - bulk GI-7 2.00$ CY 5000 10,000.00 Excavation - Trench GI-8 5.00$ CY 500 2,500.00 500 2,500.00 Fencing, cedar, 6' high GI-9 20.00$ LF Fencing, chain link, 4'GI-10 38.31$ LF 440 16,856.40 240 9,194.40 Fencing, chain link, vinyl coated, 6' high GI-11 20.00$ LF Fencing, chain link, gate, vinyl coated, 20' GI-12 1,400.00$ Each Fill & compact - common barrow GI-13 25.00$ CY Fill & compact - gravel base GI-14 27.00$ CY Fill & compact - screened topsoil GI-15 39.00$ CY Gabion, 12" deep, stone filled mesh GI-16 65.00$ SY Gabion, 18" deep, stone filled mesh GI-17 90.00$ SY Gabion, 36" deep, stone filled mesh GI-18 150.00$ SY Grading, fine, by hand GI-19 2.50$ SY Grading, fine, with grader GI-20 2.00$ SY Monuments, 3' Long GI-21 250.00$ Each Sensitive Areas Sign GI-22 7.00$ Each Sodding, 1" deep, sloped ground GI-23 8.00$ SY Surveying, line & grade GI-24 850.00$ Day 5 4,250.00 15 12,750.00 Surveying, lot location/lines GI-25 1,800.00$ Acre 0.25 450.00 2.5 4,500.00 Topsoil Type A (imported)GI-26 28.50$ CY Traffic control crew ( 2 flaggers )GI-27 120.00$ HR 32 3,840.00 Trail, 4" chipped wood GI-28 8.00$ SY 250 2,000.00 Trail, 4" crushed cinder GI-29 9.00$ SY Trail, 4" top course GI-30 12.00$ SY 75 900.00 Conduit, 2"GI-31 5.00$ LF Wall, retaining, concrete GI-32 55.00$ SF Wall, rockery GI-33 15.00$ SF 2170 32,550.00 1450 21,750.00 SUBTOTAL THIS PAGE:67,446.40 114,094.40 (B)(C)(D)(E) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR STREET AND SITE IMPROVEMENTS Quantity Remaining (Bond Reduction) (B)(C) Page 4 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.b TRANSPORTATION Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR STREET AND SITE IMPROVEMENTS Quantity Remaining (Bond Reduction) (B)(C) ROAD IMPROVEMENT/PAVEMENT/SURFACING AC Grinding, 4' wide machine < 1000sy RI-1 30.00$ SY 1000 30,000.00 AC Grinding, 4' wide machine 1000-2000sy RI-2 16.00$ SY 700 11,200.00 AC Grinding, 4' wide machine > 2000sy RI-3 10.00$ SY AC Removal/Disposal RI-4 35.00$ SY Barricade, Type III ( Permanent )RI-5 56.00$ LF Guard Rail RI-6 30.00$ LF Curb & Gutter, rolled RI-7 17.00$ LF Curb & Gutter, vertical RI-8 12.50$ LF 1175 14,687.50 1800 22,500.00 Curb and Gutter, demolition and disposal RI-9 18.00$ LF Curb, extruded asphalt RI-10 5.50$ LF Curb, extruded concrete RI-11 7.00$ LF Sawcut, asphalt, 3" depth RI-12 1.85$ LF Sawcut, concrete, per 1" depth RI-13 3.00$ LF 1300 3,900.00 Sealant, asphalt RI-14 2.00$ LF Shoulder, gravel, 4" thick RI-15 15.00$ SY Sidewalk, 4" thick RI-16 38.00$ SY 1330 50,540.00 Sidewalk, 4" thick, demolition and disposal RI-17 32.00$ SY 350 11,200.00 Sidewalk, 5" thick RI-18 41.00$ SY Sidewalk, 5" thick, demolition and disposal RI-19 40.00$ SY Sign, Handicap RI-20 85.00$ Each 4 340.00 Striping, per stall RI-21 7.00$ Each 20 140.00 94 658.00 Striping, thermoplastic, ( for crosswalk )RI-22 3.00$ SF 130 390.00 Striping, 4" reflectorized line RI-23 0.50$ LF 215 107.50 Additional 2.5" Crushed Surfacing RI-24 3.60$ SY HMA 1/2" Overlay 1.5" RI-25 14.00$ SY HMA 1/2" Overlay 2"RI-26 18.00$ SY 1700 30,600.00 HMA Road, 2", 4" rock, First 2500 SY RI-27 28.00$ SY HMA Road, 2", 4" rock, Qty. over 2500SY RI-28 21.00$ SY HMA Road, 4", 6" rock, First 2500 SY RI-29 45.00$ SY HMA Road, 4", 6" rock, Qty. over 2500 SY RI-30 37.00$ SY HMA Road, 4", 4.5" ATB RI-31 38.00$ SY 875 33,250.00 325 12,350.00 Gravel Road, 4" rock, First 2500 SY RI-32 15.00$ SY Gravel Road, 4" rock, Qty. over 2500 SY RI-33 10.00$ SY Thickened Edge RI-34 8.60$ LF SUBTOTAL THIS PAGE:185,625.00 36,238.00 (B)(C)(D)(E) Page 5 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.b TRANSPORTATION Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR STREET AND SITE IMPROVEMENTS Quantity Remaining (Bond Reduction) (B)(C) PARKING LOT SURFACING No. 2" AC, 2" top course rock & 4" borrow PL-1 21.00$ SY 2" AC, 1.5" top course & 2.5" base course PL-2 28.00$ SY 3450 96,600.00 4" select borrow PL-3 5.00$ SY 1.5" top course rock & 2.5" base course PL-4 14.00$ SY SUBTOTAL PARKING LOT SURFACING:96,600.00 (B)(C)(D)(E) LANDSCAPING & VEGETATION No. Street Trees LA-1 250.00$ Each 50 12,500.00 100 25,000.00 Median Landscaping LA-2 Right-of-Way Landscaping LA-3 Wetland Landscaping LA-4 25,000.00$ 1 25,000.00 SUBTOTAL LANDSCAPING & VEGETATION:12,500.00 50,000.00 (B)(C)(D)(E) TRAFFIC & LIGHTING No. Signs TR-1 200.00$ Each 1 200.00 Street Light System ( # of Poles)TR-2 3,000.00$ Each 17 51,000.00 Traffic Signal TR-3 3,000.00$ 1 3,000.00 Traffic Signal Modification TR-4 SUBTOTAL TRAFFIC & LIGHTING:54,200.00 (B)(C)(D)(E) WRITE-IN-ITEMS Pedestrian Bridge WI-1 25,000.00$ Each 1 25,000.00 Traffic Logix Solar Speed Radar Sign (SafePace 650)2,600.00$ Each 2 5,200.00 Pedestrian Pushbutton 1,000.00$ Each 3 3,000.00 SUBTOTAL WRITE-IN ITEMS:8,200.00 25,000.00 STREET AND SITE IMPROVEMENTS SUBTOTAL:327,971.40 225,332.40 SALES TAX @ 9.5%31,157.28 21,406.58 STREET AND SITE IMPROVEMENTS TOTAL:359,128.68 246,738.98 (B)(C)(D)(E) Page 6 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.b TRANSPORTATION Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost DRAINAGE (CPE = Corrugated Polyethylene Pipe, N12 or Equivalent) For Culvert prices, Average of 4' cover was assumed. Assume perforated PVC is same price as solid pipe.) Access Road, R/D D-1 26.00$ SY 10 260.00 90 2,340.00 * (CBs include frame and lid) Beehive D-2 90.00$ Each Through-curb Inlet Framework D-3 400.00$ Each CB Type I D-4 1,500.00$ Each 3 4,500.00 8 12,000.00 CB Type IL D-5 1,750.00$ Each CB Type II, 48" diameter D-6 2,300.00$ Each 9 20,700.00 2 4,600.00 for additional depth over 4' D-7 480.00$ FT 14 6,720.00 5 2,400.00 CB Type II, 54" diameter D-8 2,500.00$ Each for additional depth over 4'D-9 495.00$ FT CB Type II, 60" diameter D-10 2,800.00$ Each for additional depth over 4'D-11 600.00$ FT CB Type II, 72" diameter D-12 6,000.00$ Each for additional depth over 4'D-13 850.00$ FT CB Type II, 96" diameter D-14 14,000.00$ Each for additional depth over 4'D-15 925.00$ FT Trash Rack, 12"D-16 350.00$ Each Trash Rack, 15"D-17 410.00$ Each Trash Rack, 18"D-18 480.00$ Each Trash Rack, 21"D-19 550.00$ Each Cleanout, PVC, 4"D-20 150.00$ Each Cleanout, PVC, 6"D-21 170.00$ Each Cleanout, PVC, 8"D-22 200.00$ Each Culvert, PVC, 4" (Not allowed in ROW)D-23 10.00$ LF Culvert, PVC, 6" (Not allowed in ROW)D-24 13.00$ LF Culvert, PVC, 8" (Not allowed in ROW)D-25 15.00$ LF Culvert, PVC, 12" (Not allowed in ROW)D-26 23.00$ LF Culvert, PVC, 15" (Not allowed in ROW)D-27 35.00$ LF Culvert, PVC, 18" (Not allowed in ROW)D-28 41.00$ LF Culvert, PVC, 24" (Not allowed in ROW)D-29 56.00$ LF Culvert, PVC, 30" (Not allowed in ROW)D-30 78.00$ LF Culvert, PVC, 36" (Not allowed in ROW)D-31 130.00$ LF Culvert, CMP, 8"D-32 19.00$ LF Culvert, CMP, 12"D-33 29.00$ LF SUBTOTAL THIS PAGE:32,180.00 21,340.00 (B)(C)(D)(E) Quantity Remaining (Bond Reduction) (B)(C) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR DRAINAGE AND STORMWATER FACILITIES Page 7 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost Quantity Remaining (Bond Reduction) (B)(C) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR DRAINAGE AND STORMWATER FACILITIES DRAINAGE (Continued) Culvert, CMP, 15"D-34 35.00$ LF Culvert, CMP, 18"D-35 41.00$ LF Culvert, CMP, 24"D-36 56.00$ LF Culvert, CMP, 30"D-37 78.00$ LF Culvert, CMP, 36"D-38 130.00$ LF Culvert, CMP, 48"D-39 190.00$ LF Culvert, CMP, 60"D-40 270.00$ LF Culvert, CMP, 72"D-41 350.00$ LF Culvert, Concrete, 8"D-42 42.00$ LF Culvert, Concrete, 12"D-43 48.00$ LF Culvert, Concrete, 15"D-44 78.00$ LF Culvert, Concrete, 18"D-45 48.00$ LF Culvert, Concrete, 24"D-46 78.00$ LF Culvert, Concrete, 30"D-47 125.00$ LF Culvert, Concrete, 36"D-48 150.00$ LF Culvert, Concrete, 42"D-49 175.00$ LF Culvert, Concrete, 48"D-50 205.00$ LF Culvert, CPE, 6" (Not allowed in ROW)D-51 14.00$ LF Culvert, CPE, 8" (Not allowed in ROW)D-52 16.00$ LF Culvert, CPE, 12" (Not allowed in ROW)D-53 24.00$ LF Culvert, CPE, 15" (Not allowed in ROW)D-54 35.00$ LF Culvert, CPE, 18" (Not allowed in ROW)D-55 41.00$ LF Culvert, CPE, 24" (Not allowed in ROW)D-56 56.00$ LF Culvert, CPE, 30" (Not allowed in ROW)D-57 78.00$ LF Culvert, CPE, 36" (Not allowed in ROW)D-58 130.00$ LF Culvert, LCPE, 6"D-59 60.00$ LF Culvert, LCPE, 8"D-60 72.00$ LF Culvert, LCPE, 12"D-61 84.00$ LF 372 31,248.00 932 78,288.00 Culvert, LCPE, 15"D-62 96.00$ LF Culvert, LCPE, 18"D-63 108.00$ LF 629 67,932.00 8 864.00 Culvert, LCPE, 24"D-64 120.00$ LF Culvert, LCPE, 30"D-65 132.00$ LF Culvert, LCPE, 36"D-66 144.00$ LF Culvert, LCPE, 48"D-67 156.00$ LF Culvert, LCPE, 54"D-68 168.00$ LF SUBTOTAL THIS PAGE:99,180.00 79,152.00 (B)(C)(D)(E) Page 8 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost Quantity Remaining (Bond Reduction) (B)(C) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR DRAINAGE AND STORMWATER FACILITIES DRAINAGE (Continued) Culvert, LCPE, 60"D-69 180.00$ LF Culvert, LCPE, 72"D-70 192.00$ LF Culvert, HDPE, 6"D-71 42.00$ LF Culvert, HDPE, 8"D-72 42.00$ LF Culvert, HDPE, 12"D-73 74.00$ LF Culvert, HDPE, 15"D-74 106.00$ LF Culvert, HDPE, 18"D-75 138.00$ LF Culvert, HDPE, 24"D-76 221.00$ LF Culvert, HDPE, 30"D-77 276.00$ LF Culvert, HDPE, 36"D-78 331.00$ LF Culvert, HDPE, 48"D-79 386.00$ LF Culvert, HDPE, 54"D-80 441.00$ LF Culvert, HDPE, 60"D-81 496.00$ LF Culvert, HDPE, 72"D-82 551.00$ LF Pipe, Polypropylene, 6"D-83 84.00$ LF Pipe, Polypropylene, 8"D-84 89.00$ LF Pipe, Polypropylene, 12"D-85 95.00$ LF Pipe, Polypropylene, 15"D-86 100.00$ LF Pipe, Polypropylene, 18"D-87 106.00$ LF Pipe, Polypropylene, 24"D-88 111.00$ LF Pipe, Polypropylene, 30"D-89 119.00$ LF Pipe, Polypropylene, 36"D-90 154.00$ LF Pipe, Polypropylene, 48"D-91 226.00$ LF Pipe, Polypropylene, 54"D-92 332.00$ LF Pipe, Polypropylene, 60"D-93 439.00$ LF Pipe, Polypropylene, 72"D-94 545.00$ LF Culvert, DI, 6"D-95 61.00$ LF Culvert, DI, 8"D-96 84.00$ LF Culvert, DI, 12"D-97 106.00$ LF Culvert, DI, 15"D-98 129.00$ LF Culvert, DI, 18"D-99 152.00$ LF Culvert, DI, 24"D-100 175.00$ LF Culvert, DI, 30"D-101 198.00$ LF Culvert, DI, 36"D-102 220.00$ LF Culvert, DI, 48"D-103 243.00$ LF Culvert, DI, 54"D-104 266.00$ LF Culvert, DI, 60"D-105 289.00$ LF Culvert, DI, 72"D-106 311.00$ LF SUBTOTAL THIS PAGE: (B)(C)(D)(E) Page 9 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost Quantity Remaining (Bond Reduction) (B)(C) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR DRAINAGE AND STORMWATER FACILITIES Specialty Drainage Items Ditching SD-1 9.50$ CY Flow Dispersal Trench (1,436 base+)SD-3 28.00$ LF 50 2,836.00 French Drain (3' depth)SD-4 26.00$ LF Geotextile, laid in trench, polypropylene SD-5 3.00$ SY 20 60.00 Mid-tank Access Riser, 48" dia, 6' deep SD-6 2,000.00$ Each 1 2,000.00 Pond Overflow Spillway SD-7 16.00$ SY Restrictor/Oil Separator, 12"SD-8 1,150.00$ Each Restrictor/Oil Separator, 15"SD-9 1,350.00$ Each Restrictor/Oil Separator, 18"SD-10 1,700.00$ Each Riprap, placed SD-11 42.00$ CY Tank End Reducer (36" diameter)SD-12 1,200.00$ Each Infiltration pond testing SD-13 125.00$ HR Permeable Pavement SD-14 Permeable Concrete Sidewalk SD-15 Culvert, Box __ ft x __ ft SD-16 SUBTOTAL SPECIALTY DRAINAGE ITEMS:4,896.00 (B)(C)(D)(E) STORMWATER FACILITIES (Include Flow Control and Water Quality Facility Summary Sheet and Sketch) Detention Pond SF-1 Each Detention Tank SF-2 Each Detention Vault SF-3 200,000.00$ Each 1 200,000.00 Infiltration Pond SF-4 Each Infiltration Tank SF-5 Each Infiltration Vault SF-6 Each Infiltration Trenches SF-7 Each Basic Biofiltration Swale SF-8 Each Wet Biofiltration Swale SF-9 Each Wetpond SF-10 Each Wetvault SF-11 Each Sand Filter SF-12 Each Sand Filter Vault SF-13 Each Linear Sand Filter SF-14 Each StormFilter SF-15 19,000.00$ Each 1 19,000.00 Rain Garden SF-16 Each SUBTOTAL STORMWATER FACILITIES:219,000.00 (B)(C)(D)(E) Page 10 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost Quantity Remaining (Bond Reduction) (B)(C) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR DRAINAGE AND STORMWATER FACILITIES WRITE-IN-ITEMS Dry Well WI-1 5.00$ CF 10300 51,500.00 WI-2 WI-3 WI-4 WI-5 WI-6 WI-7 WI-8 WI-9 WI-10 WI-11 WI-12 WI-13 WI-14 WI-15 SUBTOTAL WRITE-IN ITEMS:51,500.00 DRAINAGE AND STORMWATER FACILITIES SUBTOTAL:131,360.00 375,888.00 SALES TAX @ 9.5%12,479.20 35,709.36 DRAINAGE AND STORMWATER FACILITIES TOTAL:143,839.20 411,597.36 (B)(C)(D)(E) Page 11 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost Connection to Existing Watermain W-1 2,000.00$ Each Ductile Iron Watermain, CL 52, 4 Inch Diameter W-2 50.00$ LF Ductile Iron Watermain, CL 52, 6 Inch Diameter W-3 56.00$ LF Ductile Iron Watermain, CL 52, 8 Inch Diameter W-4 60.00$ LF Ductile Iron Watermain, CL 52, 10 Inch Diameter W-5 70.00$ LF Ductile Iron Watermain, CL 52, 12 Inch Diameter W-6 80.00$ LF Gate Valve, 4 inch Diameter W-7 500.00$ Each Gate Valve, 6 inch Diameter W-8 700.00$ Each Gate Valve, 8 Inch Diameter W-9 800.00$ Each Gate Valve, 10 Inch Diameter W-10 1,000.00$ Each Gate Valve, 12 Inch Diameter W-11 1,200.00$ Each Fire Hydrant Assembly W-12 4,000.00$ Each Permanent Blow-Off Assembly W-13 1,800.00$ Each Air-Vac Assembly, 2-Inch Diameter W-14 2,000.00$ Each Air-Vac Assembly, 1-Inch Diameter W-15 1,500.00$ Each Compound Meter Assembly 3-inch Diameter W-16 8,000.00$ Each Compound Meter Assembly 4-inch Diameter W-17 9,000.00$ Each Compound Meter Assembly 6-inch Diameter W-18 10,000.00$ Each Pressure Reducing Valve Station 8-inch to 10-inch W-19 20,000.00$ Each WATER SUBTOTAL: SALES TAX @ 9.5% WATER TOTAL: (B)(C)(D)(E) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR WATER Quantity Remaining (Bond Reduction) (B)(C) Page 12 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.d WATER Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 CED Permit #:U15008868 Existing Future Public Private Right-of-Way Improvements Improvements (D) (E) Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost Clean Outs SS-1 1,000.00$ Each Grease Interceptor, 500 gallon SS-2 8,000.00$ Each Grease Interceptor, 1000 gallon SS-3 10,000.00$ Each Grease Interceptor, 1500 gallon SS-4 15,000.00$ Each Side Sewer Pipe, PVC. 4 Inch Diameter SS-5 80.00$ LF Side Sewer Pipe, PVC. 6 Inch Diameter SS-6 95.00$ LF Sewer Pipe, PVC, 8 inch Diameter SS-7 105.00$ LF Sewer Pipe, PVC, 12 Inch Diameter SS-8 120.00$ LF Sewer Pipe, DI, 8 inch Diameter SS-9 115.00$ LF Sewer Pipe, DI, 12 Inch Diameter SS-10 130.00$ LF Manhole, 48 Inch Diameter SS-11 6,000.00$ Each Manhole, 54 Inch Diameter SS-13 6,500.00$ Each Manhole, 60 Inch Diameter SS-15 7,500.00$ Each Manhole, 72 Inch Diameter SS-17 8,500.00$ Each Manhole, 96 Inch Diameter SS-19 14,000.00$ Each Pipe, C-900, 12 Inch Diameter SS-21 180.00$ LF Outside Drop SS-24 1,500.00$ LS Inside Drop SS-25 1,000.00$ LS Sewer Pipe, PVC, ____ Inch Diameter SS-26 Lift Station (Entire System)SS-27 LS SANITARY SEWER SUBTOTAL: SALES TAX @ 9.5% SANITARY SEWER TOTAL: (B)(C)(D)(E) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR SANITARY SEWER Quantity Remaining (Bond Reduction) (B)(C) Page 13 of 14 Ref 8-H Bond Quantity Worksheet SECTION II.e SANITARY SEWER Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 Planning Division |1055 South Grady Way – 6 th Floor | Renton, WA 98057 (425) 430-7200 Date: Name:Project Name: PE Registration No:CED Plan # (LUA): Firm Name:CED Permit # (U): Firm Address:Site Address: Phone No.Parcel #(s): Email Address:Project Phase: Site Restoration/Erosion Sediment Control Subtotal (a)(a)104,890.60$ Existing Right-of-Way Improvements Subtotal (b)(b)359,128.68$ Future Public Improvements Subtotal (c)(c)-$ Stormwater & Drainage Facilities Subtotal (d)(d)555,436.56$ Bond Reduction (Quantity Remaining)2 (e)(e)-$ Site Restoration Civil Construction Permit Maintenance Bond 182,913.05$ Bond Reduction 2 Construction Permit Bond Amount 3 Minimum Bond Amount is $10,000.00 1 Estimate Only - May involve multiple and variable components, which will be established on an individual basis by Development Engineering. 2 The City of Renton allows one request only for bond reduction prior to the maintenance period. Reduction of not more than 70% of the original bond amount, provided that the remaining 30% will cover all remaining items to be constructed. 3 Required Bond Amounts are subject to review and modification by Development Engineering. * Note: The word BOND as used in this document means any financial guarantee acceptable to the City of Renton. ** Note: All prices include labor, equipment, materials, overhead and profit. R ((b)+(c)+(d)) x 150% EST1 ((b) + (c) + (d)) x 20% -$ MAINTENANCE BOND */** (after final acceptance of construction) 104,890.60$ 359,128.68$ 1,371,847.86$ 157,335.90$ -$ -$ 555,436.56$ S (e) x 150% SITE IMPROVEMENT BOND QUANTITY WORKSHEET BOND CALCULATIONS 3/30/2017 Maher A. Joudi 45232 D.R. Strong Consulting Engineers T (P +R - S) Prepared by:Project Information CONSTRUCTION BOND AMOUNT */** (prior to permit issuance) 425-827-3063 maher.joudi@drstrong.com Avana Ridge LUA15-000894 17249 Benson Rd S & 10615 SE 172nd St 292305-9148 and -9009 FOR APPROVAL U15008868 620 7th Avenue Kirkland WA 98033 1,529,183.76$ P (a) x 150% Page 14 of 14 Ref 8-H Bond Quantity Worksheet SECTION III. BOND WORKSHEET Unit Prices Updated: 06/14/2016 Version: 06/14/2016 Printed 3/30/2017 2015 D. R. STRONG Consulting Engineers Inc. 68 Avana Ridge Technical Information Report Renton, Washington APPENDIX “D” COVENANTS