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Bethany Corner TIR_16062_170410
2017 D. R. STRONG Consulting Engineers Inc. Bethany Corner Technical Information Report Renton, Washington TECHNICAL INFORMATION REPORT BETHANY CORNER SHORT PLAT TABLE OF CONTENTS SECTION I ...................................................................................................................... 4 Project Overview ......................................................................................................... 4 Predeveloped Site Conditions ..................................................................................... 4 Developed Site Conditions .......................................................................................... 4 King County Area, Washington .................................................................................. 14 AgC—Alderwood gravelly sandy loam, 8 to 15 percent slopes .............................. 14 SECTION II ................................................................................................................... 16 Conditions and Requirements Summary ................................................................... 16 Conditions of Approval............................................................................................... 18 SECTION III .................................................................................................................. 19 Off-Site Analysis ........................................................................................................ 19 Task 1: Define and Map Study Area ...................................................................... 19 Task 2: Resource Review ...................................................................................... 20 Task 3: Field Inspection ......................................................................................... 29 Task 4: Drainage System Description and Problem Descriptions .......................... 30 Task 5: Mitigation of Existing or Potential Problems .............................................. 31 SECTION IV .................................................................................................................. 37 Flow Control Analysis and Water Quality Design ...................................................... 37 Existing Site Hydrology .......................................................................................... 37 Developed Site Hydrology ...................................................................................... 39 Performance Standards ............................................................................................. 42 Flow Control System.................................................................................................. 43 Water Quality Treatment System ............................................................................... 50 SECTION V ................................................................................................................... 52 Conveyance System Analysis and Design ................................................................ 52 SECTION VI .................................................................................................................. 61 Special Reports and Studies ..................................................................................... 61 SECTION VII ................................................................................................................. 62 Other Permits, Variances and Adjustments ............................................................... 62 SECTION VIII ................................................................................................................ 63 CSWPPP Analysis and Design (Part A) .................................................................... 63 SWPPP Plan Design (Part B) .................................................................................... 63 SECTION IX .................................................................................................................. 65 Bond Quantities, Facility Summaries, and Declaration of Covenant .......................... 65 2017 D. R. STRONG Consulting Engineers Inc. Bethany Corner Technical Information Report Renton, Washington Stormwater Facility Summary Sheet.......................................................................... 66 SECTION X ................................................................................................................... 68 Operations and Maintenance Manual ........................................................................ 68 APPENDICES ............................................................................................................... 69 Appendix “A” Legal Description ................................................................................. 70 Appendix “B” CSWPPP ............................................................................................. 71 Appendix “C” Bond Quantity Worksheet .................................................................... 72 List of Figures Figure 1 TIR Worksheet .................................................................................................. 6 Figure 2 Vicinity Map ..................................................................................................... 11 Figure 3 Drainage Basins, Subbasins, and Site Characteristics ................................... 12 Figure 4 Soils ................................................................................................................ 13 Figure 5 City of Renton Topography Map ..................................................................... 21 Figure 6 City of Renton Coal Mine Hazard Areas Map.................................................. 22 Figure 7 City of Renton Flood Hazards Map ................................................................. 23 Figure 8 City of Renton Streams and Wetlands Map .................................................... 24 Figure 9 City of Renton Landslide Hazards Map ........................................................... 25 Figure 10 City of Renton Seismic Hazard Areas Map ................................................... 26 Figure 11 FEMA Map .................................................................................................... 27 Figure 12 King County iMap Drainage Complaints Map................................................ 28 Figure 13 Offsite Analysis Downstream Map ................................................................ 33 Figure 14 Offsite Analysis Downstream Table .............................................................. 34 Figure 15 Predeveloped Area Map................................................................................ 38 Figure 16 Developed Area Map .................................................................................... 41 Figure 17 Detention & Water Quality Facility Details ..................................................... 51 Figure 18 Backwater Analysis Map ............................................................................... 56 2017 D. R. STRONG Consulting Engineers Inc. Page 4 Bethany Corner Level One Downstream Analysis Renton, Washington SECTION I PROJECT OVERVIEW The Project is the proposed subdivision of two parcels into nine single-family residential lots, per the City of Renton’s (City) subdivision process. The Project is located at 16433 & 16451 111th Avenue SE, Renton, Washington (Site) also known as Tax Parcel Numbers 008800-0570 & -0560. The Project will meet the drainage requirements of the City of Renton Amendments to the 2009 King County Surface Water Design Manual (CORSWDMA). PREDEVELOPED SITE CONDITIONS The total existing Site area is approximately 79,710 s.f. (1.83 acres). The Site is currently developed with two single family homes, one trailer home, gravel driveways, one detached garage, a shed, a concrete foundation, and landscaping. The Site consists of a shallow grade to the southwest and is contains one Threshold Discharge Area (TDA). Runoff generated by the TDA gradually sheet flows east to southwest towards adjacent parcels to the west or is collected by a culvert in the southwest corner of the Site. Sheet flow over the west property line and culvert flow from the southwest corner of the Site form the two natural discharge locations for the Site. The two Natural Discharge Areas (NDAs) of the Site divide it roughly in half with the northern portion draining to the west and the southern portion draining to the cuvert. Sheet flow from the western property line is captured by Big Soos Creek on the adjacent parcels and is conveyed to the south. Runoff through the culvert in the the southwestern corner of the Site travels for approximately 55 feet in a westerly direction to a convergence point with Big Soos Creek. Flow from both NDAs converges within the ¼ mile and therefore the Site can be considered to be within one TDA. The Project frontage currently drains to a series of ditches and culverts along 111th Ave SE and converges with Big Soos Creek approximately 160 feet downstream. DEVELOPED SITE CONDITIONS The applicant is seeking approval to subdivide 1.83 acres into nine single–family residential lots (Project), with lot sizes ranging from approximately 5,508 s.f. to 8,379 s.f. All existing improvements located on the Site will be demolished or removed during plat construction. The project is required to meet the City’s Flow Control Duration Standard – Matching Forested and Basic Water Quality treatment. This standard matches the developed Site flow durations to the flow durations of pre-developed rates for forested (historical) site conditions. These standards will be met through the proposed combination detention and water quality vault. The proposed impervious surface areas are as follows: half street frontage improvements consisting of a 5’ sidewalk along 111th AVE SE, Road A, the nine new single-family residences and associated driveways, and Tract A, the storm water detention facility, will generate approximately 49,145 s.f. of impervious area (1.128 acres). The Project will implement the restricted footprint BMP and the allowable impervious of each lot will be reduced by 10%. 2017 D. R. STRONG Consulting Engineers Inc. Page 5 Bethany Corner Level One Downstream Analysis Renton, Washington A section of non-target impervious surface along the north side of 111th AVE SE will be collected by the proposed detention facility. The facility has been designed with this section being proposed as an offsite flow-through area. This area will be modeled as impervious in both the predeveloped and developed scenarios. Proposed Site cover and surfaces are show in Figure 16, Developed Site Conditions. (See Section IV). The Project proposes to combine runoff from both onsite NDAs and the target frontage into one detention system and to discharge to the road-side ditch system just upstream of the confluence with Big Soos Creek. The existing natural discharge locations for the Site are not suitable for concentrated. No drainage easements are available for discharge to Big Soos Creek to the west. Discharge to the road-side ditch connects to a manmade public conveyance system. The proposed discharge location is well within the ¼ mile of the natural discharge locations. 2017 D. R. STRONG Consulting Engineers Inc. Page 6 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 1 TIR WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner: Mark Seek and Mary Nguyen Phone: (206) 315-8130 Address: 15233 Manion Way NE, Duvall, WA 98019 9102 SE 41st Street, Mercer Island, WA 98040 Project Engineer: Jonathan S. Murray, P.E. Company: D. R. STRONG Consulting Engineers Inc. Phone: (425) 827-3063 Project Name: Bethany Corner City Permit#: PRE16-000651 Location: Township: 23 North Range: 05 East Section: 29 Site Address: 16433 & 16451 111th Avenue SE, Renton, WA Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Landuse Services Subdivision / Short Subdivision / UPD Building Services: M/F / Commercial / SFR Clearing and Grading Right-of-Way Other: DFW HPA Shoreline Mngmt COE 404 Structural DOE Dam Safety Rockery/Vault FEMA Floodplain ESA Section 7 COE Wetlands Other: Part 5 PLAN AND REPORT INFORMATION Technical Information Report Type of Drainage Review Full / Targeted / (circle): Large Site Date (include revision dates): April 10, 2017 Date of Final: Site Improvement Plan (Engr. Plans) Type (circle one): Full / Modified / : Small Site Date (include revision dates): Date of Final: Part 6 ADJUSTMENT APPROVALS 2017 D. R. STRONG Consulting Engineers Inc. Page 7 Bethany Corner Level One Downstream Analysis Renton, Washington Type (circle one): Standard / Complex / Preapplication / Experimental / Blanket Description: (include conditions in TIR Section 2) _____________________________________________________________________________________ _____________________________________________________________________________________ ____________________________________________________________________________________ Date of Approval: Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: TBD Completion Date Describe: Monitor discharge location during construction. Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: Benson Special District Overlays: N/A Drainage Basin: Green/Duwamish River Watershed Stormwater Requirements: Flow Control Duration Standard – Matching Forested and Basic WQ treatment Part 9 ONSITE AND ADJACENT SENSITIVE AREAS River/ Stream: Big Soos Creek Lake Wetlands Closed Depression Floodplain Other Steep Slope Erosion Hazard Landslide Hazard Coal Mine Hazard Seismic Hazard Habitat Protection Part 10 SOILS Soil Type AgC Slopes 8-15% Erosion Potential Moderate to Severe 2017 D. R. STRONG Consulting Engineers Inc. Page 8 Bethany Corner Level One Downstream Analysis Renton, Washington High Groundwater Table Sole Source Aquifer other Seeps/Springs Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core Requirement #2 – Offsite Analysis SEPA Sensitive Area Buffer _______ Additional Sheet Attached LIMITATION / SITE CONSTRAINT Part 12 TIR SUMMARY SHEET Threshold Discharge Area: Site comprised of one TDA (name or description) Core Requirements (all 8 apply) Discharge of Natural Location yes Number of Natural Discharge Locations: 1 Offsite Analysis Level: 1 / 2 / 3 dated: 09/28/2016 Flow Control Level: 1 / 2 / 3 or Exemption Number (incl. facility summary sheet Small Site BMPS Restricted Footprint Conveyance System Spill containment located at: TBD 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 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 2017 D. R. STRONG Consulting Engineers Inc. Page 9 Bethany Corner Level One Downstream Analysis Renton, Washington 100-year Base Flood Elevation (or range): Datum: Flood Protection Facilities Describe: N/A Source Control Describe Landuse: (comm. / industrial landuse) Describe any structural controls: Oil Control High-use Site: Yes / No Treatment BMP: Maintenance Agreement: Yes / No with whom? Other Drainage Structures Describe: Runoff will be collected and conveyed to the wet-vault detention facility located in Tract A. 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 2017 D. R. STRONG Consulting Engineers Inc. Page 11 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 2 VICINITY MAP The information included on this map has been compiled by King County staff from a variety of sources and is subject to change without notice. King County makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. King County shall not be liable for any general, special, indirect, incidental, or consequential damages including, but not limited to, lost revenues or lost profits resulting from the use or misuse of the information contained on this map. Any sale of this map or information on this map is prohibited except by written permission of King County. Site 2017 D. R. STRONG Consulting Engineers Inc. Page 12 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 3 DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERISTICS 0GRAPHIC SCALE6040201 INCH = 40 FT. 2017 D. R. STRONG Consulting Engineers Inc. Page 13 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 4 SOILS 2017 D. R. STRONG Consulting Engineers Inc. Page 14 Bethany Corner Level One Downstream Analysis Renton, Washington KING COUNTY AREA, WASHINGTON AGC—ALDERWOOD GRAVELLY SANDY LOAM, 8 TO 15 PERCENT SLOPES a) 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 b) Map Unit Composition • Alderwood and similar soils: 85 percent • Minor components: 15 percent • Estimates are based on observations, descriptions, and transects of the mapunit. c) Description of Alderwood (1) 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 (2) 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 (3) 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) (4) 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) • Hydric soil rating: No 2017 D. R. STRONG Consulting Engineers Inc. Page 15 Bethany Corner Level One Downstream Analysis Renton, Washington d) Minor Components (1) 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 • Hydric soil rating: No (2) Indianola • Percent of map unit: 5 percent • Landform: Eskers, kames, terraces • Landform position (three-dimensional): Tread • Down-slope shape: Linear • Across-slope shape: Linear • Hydric soil rating: No (3) Shalcar • Percent of map unit: 3 percent • Landform: Depressions • Landform position (three-dimensional): Dip • Down-slope shape: Concave • Across-slope shape: Concave • Hydric soil rating: Yes (4) Norma • Percent of map unit: 2 percent • Landform: Depressions, drainageways • Landform position (three-dimensional): Dip • Down-slope shape: Concave, linear • Across-slope shape: Concave • Hydric soil rating: Yes 2017 D. R. STRONG Consulting Engineers Inc. Page 16 Bethany Corner Level One Downstream Analysis 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: Existing drainage discharges the Site at one location, maintaining one TDA. The topography indicates that all stormwater runoff leaves the Site as sheet flow across the west property line. Runoff is collected by Big Soos Creek which is located on an adjacent property to the west. Developed runoff will require discharge to a conveyance system. Discharge from the project will be directed south to the existing conveyance system along 111th Ave SE. This discharge location converges with flow from the NDA within the ¼ mile. • C.R. #2 – Offsite Analysis: Analysis is included in Section III. The Analysis describes the Site’s runoff patterns in detail. • C.R. #3 – Flow Control: The Project is required to adhere to Flow Control Duration Standard – Matching Forested site conditions. One detention/wetvault will provide flow control as required for the new and replaced impervious and pervious surfaces. The Site is required to “match the flow duration of pre-developed rates for forested (historic) site conditions over the range of flows extending from 50% of 2-year up to the full 50-year flow,” (City of Renton 2009 Surface Water Design Manual Amendment, Sec. 1.2.3.1). A detention vault will accommodate this requirement. • C.R. #4 – Conveyance System: New pipe systems are required to be designed with sufficient capacity to convey and contain (at minimum) the 25-year peak flow, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. Pipe system structures 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. This analysis is shown in Section V. • C.R. #5 – Erosion and Sediment Control: The Project will provide the seven minimum ESC measures. A temporary erosion and sedimentation control plan is presented as part of the engineering construction plan set. • C.R. #6 – Maintenance and Operations: Maintenance of the proposed storm drainage facilities will be the responsibility of the City. An Operation and Maintenance Manual will be included in Section X at the time of construction plan preparation. • C.R. #7 – Financial Guarantees: Prior to commencing construction, the Applicant must post a drainage facilities restoration and site stabilization financial guarantee. 2017 D. R. STRONG Consulting Engineers Inc. Page 17 Bethany Corner Level One Downstream Analysis Renton, Washington 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 – Water Quality: The Project is required to provide basic water quality treatment. A combined detention/wetvault will accommodate this requirement. • S.R. #1 – Other Adopted Area-Specific Requirements: Not applicable for this Project. • S.R. #2 – Flood Hazard Area Delineation: Not applicable for this Project. • S.R. #3 – Flood Protection Facilities: Not applicable for this Project. • S.R. #4 – Source Control: Not applicable for this Project. • S.R. #5 – Oil Control: Not applicable for this Project. • S.R. #6 – Aquifer Protection Area: Site not located within zones 1 and 2, therefore not applicable for this Project. 2017 D. R. STRONG Consulting Engineers Inc. Page 18 Bethany Corner Level One Downstream Analysis Renton, Washington CONDITIONS OF APPROVAL Bethany Corner PRE16-000651 TBD 2017 D. R. STRONG Consulting Engineers Inc. Page 19 Bethany Corner Level One Downstream Analysis Renton, Washington SECTION III OFF-SITE ANALYSIS LEVEL ONE DOWNSTREAM ANALYSIS DISCLAIMER: This report was prepared at the request of Mark Seek and Mary Nguyen for the 1.83 acre parcels known as a portion of the Northeast Quarter of Section 29, Township 23 North, Range 5 East, W.M., in King County, Tax Parcel Numbers 008800-0570, & -0560 (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 City Amendments as adopted by the City of Renton (Manual). The Site is located at 16433 & 16451 111th Avenue SE, Renton, Washington. The Project is the subdivision of two parcels into nine single-family lots. See Figures 5 through 12 for maps of the study area. 2017 D. R. STRONG Consulting Engineers Inc. Page 20 Bethany Corner Level One Downstream Analysis Renton, Washington TASK 2: RESOURCE REVIEW • Adopted Basin Plans: The City of Renton and King County Department of Permitting and Environmental Review (DPER) and Department of Natural Resources and Parks (DNRP) do not have a specific plan for the East Lake Washington Drainage Basin. • Finalized Drainage Studies: No available applicable drainage studies at this time. • Basin Reconnaissance Summary Reports: None available. • Comprehensive Plans: Renton’s Comprehensive Plan, adopted on June 22, 2015, effective July 1, 2015. • Floodplain/Floodway (FEMA) Map: No floodplains exist on site, See Figure 11. • Other Offsite Analysis Reports: None available within adjacent properties. • Sensitive Areas Map Folios, City of Renton GIS: See Figures 6-10. The City’s GIS system shows a wetland on Site. A Wetland Assessment dated June 2, 2016 was prepared by Mark Rigos, P.E. This assessment found that there were no areas on the Site which met the definitions of wetlands. • DNRP Drainage Complaints and Studies: Per King County Water and Land Resources Division, there is one complaint within the downstream paths, within approximately one mile from the Site within the last 10 years. See Figure 12. • USDA King County Soils Survey: See Figure 4 • King County Wetlands Inventory: Vol. 2 East (1990) – Wetland 5401 (category 2) identified within one mile of the downstream path. See Figure 8. • Migrating River Studies: The Site is not located near the channel migration zones of Cedar River, Tolt River, Raging River, Snoqualmie River, or Green River. • King County Designated Water Quality Problems: Per the Washington State Water Quality Assessment 303(d)/305(b) Integrated Report current as of 2012, there are no water quality problems within 1 mile downstream of the Site. 2017 D. R. STRONG Consulting Engineers Inc. Page 21 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 5 CITY OF RENTON TOPOGRAPHY MAP Site 2017 D. R. STRONG Consulting Engineers Inc. Page 22 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 6 CITY OF RENTON COAL MINE HAZARD AREAS MAP Site 2017 D. R. STRONG Consulting Engineers Inc. Page 23 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 7 CITY OF RENTON FLOOD HAZARDS MAP Site 2017 D. R. STRONG Consulting Engineers Inc. Page 24 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 8 CITY OF RENTON STREAMS AND WETLANDS MAP Site 2017 D. R. STRONG Consulting Engineers Inc. Page 25 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 9 CITY OF RENTON LANDSLIDE HAZARDS MAP Site 2017 D. R. STRONG Consulting Engineers Inc. Page 26 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 10 CITY OF RENTON SEISMIC HAZARD AREAS MAP Site 2017 D. R. STRONG Consulting Engineers Inc. Page 27 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 11 FEMA MAP Site (Approximate) 2017 D. R. STRONG Consulting Engineers Inc. Page 28 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 12 KING COUNTY IMAP DRAINAGE COMPLAINTS MAP Location Complaint Year Description A C 2007 Runoff from construction site Site A 2017 D. R. STRONG Consulting Engineers Inc. Page 29 Bethany Corner Level One Downstream Analysis Renton, Washington TASK 3: FIELD INSPECTION UPSTREAM TRIBUTARY AREA Upon evaluation of the upstream area through examining COR topographic map (see Figure 5) and by conducting field reconnaissance on March 21st 2016, the upstream tributary area for the Site is considered negligible. The parcels to the north and south sheet flow to the west, and a swale exists in the right of way of 111th AVE SE, conveying runoff to the south, away from the site. GENERAL ONSITE AND OFFSITE DRAINAGE DESCRIPTIONS The Site is contained within one Threshold Discharge Area (TDA). Runoff from the Site sheet flows over the west property line and is collected by Big Soos Creek, which is flowing in a southerly direction. There also exists a Natural Discharge Area (NDA) which consists of a 12 inch reinforced concrete pipe in the southeastern corner of the Site which conveys storm water approximately 55 feet before sheet flowing westerly and converging with Big Soos Creek. The convergence point for the two NDA’s is approximately 85 feet downstream from the Site. Big Soos Creek is conveyed through a series of culverts, swales, and as channel flow before discharging into an unnamed wetland approximately ½ mile downstream. 2017 D. R. STRONG Consulting Engineers Inc. Page 30 Bethany Corner Level One Downstream Analysis Renton, Washington TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS DRAINAGE SYSTEM DESCRIPTION The downstream analysis is further illustrated and detailed in the Downstream Map Figure 13 and Downstream Table Figure 14. The drainage area is located within the East Lake Washington - Renton Drainage Basin. The drainage area was evaluated by reviewing available resources described in task 2, and by conducting a field reconnaissance on October 28th, 2016 under overcast conditions. DOWNSTREAM PATH 1 “A1” is a Natural Discharge Area (NDA) for the Site. It is located along the western property line (±0). From Point “A1” to Point “B1”, runoff continues to flow west as sheet flow over till grass. No concentrated flow was observed (±0’-45’). Point “B1”, runoff is collected by Big Soos Creek. (±45’). From Point “B1” to Point “C1”, runoff is conveyed in a southerly direction as channel flow via Big Soos Creek. Moderate flow was observed (±45’-502’). Point “C1” is the inlet of a 12” diameter Reinforced Concrete Pipe (RCP). Did not observe. (±502’). From Point “C1” to Point “D1”, runoff is conveyed easterly as pipe flow via 12” RCP. Moderate flow observed (±502’-807’). Point “D1” is the outlet of a 12” diameter RCP. Moderate flow observed. (±807’). From Point “D1” to Point “E1”, runoff is conveyed southerly as channel flow via a 2’ tall and 3’ wide swale. Moderate flow observed (±807’-813’). Point “E1” is the inlet of a 12” diameter RCP. Moderate flow observed. (±813’). From Point “E1” to Point “F1”, runoff is conveyed in a southerly direction as pipe flow via 12” RCP culvert. Moderate flow was observed (±813’-835’). Point “F1” is the outlet of a 12” diameter RCP. Moderate flow observed. (±835’). From Point “F1” to Point “G1”, runoff is conveyed in a southerly direction as channel flow via a 2’ tall and 4’ wide swale. Moderate flow was observed. (±835’-925’). Point “G1” is the inlet of a 12” diameter RCP. Moderate flow observed. (±925’). From Point “G1” to Point “H1”, runoff is conveyed in a southerly direction as pipe flow via 12” diameter RCP culvert. Moderate flow was observed (±925’-968’). Point “H1” is the outlet of a 12” diameter RCP. Moderate flow observed. (±968’). From Point “H1” to Point “I1”, runoff is conveyed in a southerly direction as channel flow via a 2’ tall and 4’ wide swale. Moderate flow was observed (±968’-986’). Point “I1” is the inlet of a 12” diameter RCP. Inlet was partially submerged. (±986’). From Point “I1” to Point “J1”, runoff is conveyed in an easterly direction as pipe flow via 12” diameter RCP culvert. Heavy flow was observed (±986’-1,022’). Point “J1” is the outlet of a 12” RCP. Outlet was fully submerged. (±1,022’). 2017 D. R. STRONG Consulting Engineers Inc. Page 31 Bethany Corner Level One Downstream Analysis Renton, Washington From Point “J1” to Point “K1”, runoff is conveyed in a southerly direction as channel flow via a 2’ tall and 4’ wide swale. Heavy flow was observed (±1,022’-1,037’). Point “K1” is the inlet of a 24” diameter Corrugated Metal Pipe (CMP) (±1,037’). From Point “K1” to Point “L1”, runoff is conveyed in a southerly direction as pipe flow via 24” CMP. Moderate flow was observed (±1,037’-1,121’). Point “L1”, is a Type 1 CB with the outlet of a 24” diameter CMP pipe from the north and the inlet of a 12” CMP in a southeasterly direction. Facility ID No 180983. Standing water observed. (±1,121’). From Point “L1” to Point “M1”, runoff is conveyed in a southeasterly direction as pipe flow via a 12” diameter CMP. Inlet was observed to be fully submerged. (±1,121’- 1,180’). Point “M1” is the outlet of a 12” diameter CMP. Not observed. (±1,180’). From Point “M1” to Point “N1”, runoff is conveyed in a southeasterly direction as channel flow via Big Soos Creek. Moderate flow was observed. (±1,180’-1,599’). The downstream path crosses the ¼ mile point during this stretch. Point “N1” is the inlet of an 18” diameter Corrugated Plastic Pipe (CPP) with a metal debris barrier. Moderate flow observed (±1,599’). From Point “N1” to Point “O1”, runoff is conveyed in a southerly direction under SE 168th Street via an 18” CPP. Moderate flow was observed (±1,599’-1,675’). Point “O1” is the outlet of an 18” CPP discharging into Big Soos Creek. Moderate flow observed (±1,675’). The outlet could not be investigated in the field. This is the end of field investigation. DOWNSTREAM PATH 2 “A2” is a NDL for the Site. It is located in the southeastern corner of the Site. This NDL is the inlet of a 12” diameter reinforced concrete pipe conveying storm water in a southeasterly direction (±0). From Point “A2” to Point “B2”, runoff continues in a southwesterly direction as pipe flow. No concentrated flow was observed (±0’-55’). Point “B2” is the outlet of a 12” reinforced concrete. (±55’). From Point “B2” to point “C2,” runoff continues in a southwesterly direction as sheet flow. (±55’-85’). Point “C2” is Big Soos Creek which collects runoff and is the convergence point of Downstream Paths 1 and 2. (±85’). TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS A review of the King County Water and Land Resources Division – Drainage Services Section Documented Drainage Complaints within one mile of the downstream flow 2017 D. R. STRONG Consulting Engineers Inc. Page 32 Bethany Corner Level One Downstream Analysis Renton, Washington paths revealed one complaint within the last ten years and has since been closed. Several drainage complaints exist within the downstream path but are not within the last ten years and are not applicable for Level One Downstream Analysis. 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. A wetvault will provide flow control and basic water quality requirements for the entire 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. 2017 D. R. STRONG Consulting Engineers Inc. Page 33 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 13 OFFSITE ANALYSIS DOWNSTREAM MAP GRAPHIC SCALE 0 100 200 400 1 INCH = 200 FT. 2017 D. R. STRONG Consulting Engineers Inc. Page 34 Bethany Corner Level One Downstream Analysis Renton, Washington FIGURE 14 OFFSITE ANALYSIS DOWNSTREAM TABLE DOWNSTREAM PATH 1 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 mile = 1,320 feet 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 Natural discharge area Runoff exits at the NDA along the western property line of the Site. –0’ None Observed None Anticipated No concentrated flow observed A1-B1 West sheet flow Sheet flow over till grass None Observed None Anticipated No concentrated flow observed B1 Stream Big Soos Creek –45’ None Observed None Anticipated Moderate flow observed B1-C1 Southerly channel flow Big Soos Creek None Observed None Anticipated Moderate flow observed C1 Pipe inlet 12” diameter Reinforced Concrete Pipe (RCP) ±502’ Did not observe C1-D1 Easterly pipe flow 12” diameter RCP. None Observed None Anticipated Moderate flow observed D1 Pipe outlet 12” diameter RCP ±807’ None Observed None Anticipated Moderate flow observed D1-E1 Southerly channel flow 2’ tall 3’ wide swale None Observed None Anticipated Moderate flow observed E1 Pipe inlet 12” diameter RCP ±813’ None Observed None Anticipated Moderate flow observed E1-F1 Southerly pipe flow 12” diameter RCP None Observed None Anticipated Moderate flow observed F1 Pipe outlet 12” diameter RCP ±835’ None Observed None Anticipated Moderate flow observed F1-G1 Southerly channel flow 2’ tall and 4’ wide swale None Observed None Anticipated Moderate flow observed 2017 D. R. STRONG Consulting Engineers Inc. Page 35 Bethany Corner Level One Downstream Analysis Renton, Washington G1 Pipe inlet 12” diameter RCP ±925’ None Observed None Anticipated Moderate flow observed G1-H1 Southerly pipe flow 12” diameter RCP None Observed None Anticipated Moderate flow observed H1 Pipe outlet 12” diameter RCP ±968’ None Observed None Anticipated Moderate flow observed H1-I1 Southerly channel flow 2’ tall and 4’ wide swale None Observed None Anticipated Moderate flow observed I1 Pipe inlet 12” diameter RCP ±986’ Partially submerged None Anticipated Heavy flow observed I1-J1 Easterly pipe flow 12” diameter RCP None Observed None Anticipated Heavy flow observed J1 Pipe outlet 12” diameter RCP ±1,022’ Fully submerged None Anticipated Heavy flow observed J1-K1 Southerly channel flow 2’ tall 4’ wide swale None Observed None Anticipated Heavily vegetated - moderate flow observed K1 Pipe inlet 24” diameter Corrugated Metal Pipe (CMP) ±1,037’ None Observed None Anticipated Moderate flow observed K1-L1 Southerly pipe flow 24” diameter CMP None Observed None Anticipated Moderate flow observed L1 Type 1 CB Renton Facility No. 180983 ±1,121’ None Observed None Anticipated Standing water observed L1-M1 Southeasterly pipe 12” diameter CMP Fully submerged None Anticipated Heavy flow observed M1 Pipe outlet 12” diameter CMP ±1,180’ None Observed None Anticipated Moderate flow observed M1-N1 Southeasterly channel flow Big Soos Creek None Observed None Anticipated Moderate flow observed N1 Pipe inlet 18” diameter corrugated plastic pipe (CPP) under SE 168th Street ±1,599’ None Observed None Anticipated Moderate flow observed. Metal debris barrier covering inlet N1-O1 Southerly pipe flow 18” diameter CPP None Observed None Anticipated Moderate flow observed O1 Pipe outlet 18” diameter CPP. Discharging into Big Soos Creek ±1,675’ None Observed None Anticipated Discharge point not observed 2017 D. R. STRONG Consulting Engineers Inc. Page 36 Bethany Corner Level One Downstream Analysis Renton, Washington DOWNSTREAM PATH 2 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 mile = 1,320 feet 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 Natural discharge area – Pipe inlet 12” diameter RCP. –0’ None Observed None Anticipated No concentrated flow observed A2-B2 Southwesterly pipe flow 12” diameter RCP None Observed None Anticipated No concentrated flow observed B2 Pipe outlet 12” diameter RCP –55’ None Observed None Anticipated No concentrated flow observed B2-C2 Southwesterly sheet flow Sheet flow over moderately vegetated areas None Observed None Anticipated Moderate flow observed C2 Stream Big Soos Creek. Convergence point of Downstream Paths 1 and 2 ±85’ Did not observe 2017 D. R. STRONG Consulting Engineers Inc. Page 37 Bethany Corner Technical Information Report Renton, Washington SECTION IV FLOW CONTROL ANALYSIS AND WATER QUALITY DESIGN EXISTING SITE HYDROLOGY KCRTS was used to model runoff from the Site. The Site falls within the City’s Flow Control Duration Standard – Matching Forested area. The Site was modeled as predeveloped forested condtions for target surfaces and impervious for flow-through surfaces (see Figure 15). Results of the KCRTS analysis are included in this section. Modeling Input for the Pre-developed Site 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 0.128 2 2/09/01 18:00 0.179 1 100.00 0.990 0.046 7 1/05/02 16:00 0.128 2 25.00 0.960 0.105 3 2/28/03 3:00 0.105 3 10.00 0.900 0.019 8 8/26/04 2:00 0.103 4 5.00 0.800 0.063 6 1/05/05 8:00 0.093 5 3.00 0.667 0.103 4 1/18/06 20:00 0.063 6 2.00 0.500 0.093 5 11/24/06 4:00 0.046 7 1.30 0.231 0.179 1 1/09/08 9:00 0.019 8 1.10 0.091 Computed Peaks 0.162 50.00 0.980 2017 D. R. STRONG Consulting Engineers Inc. Page 38 Bethany Corner Technical Information Report Renton, Washington FIGURE 15 PREDEVELOPED AREA MAP GRAPHIC SCALE 0 20 40 60 1 INCH = 40 FT. 2017 D. R. STRONG Consulting Engineers Inc. Page 39 Bethany Corner Technical Information Report Renton, Washington DEVELOPED SITE HYDROLOGY Soil Type The soil types are unchanged from predeveloped conditions. Land Cover KCRTS was used to model the developed peak runoff from the Site. The portions of the Site within the developable area tributary to the proposed detention facility were modeled as “Till Grass”, and Impervious as appropriate. Results of the KCRTS analysis are included in this section. Modeling Input for RDIN Site 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 0.334 6 2/09/01 2:00 0.674 1 100.00 0.990 0.274 8 1/05/02 16:00 0.433 2 25.00 0.960 0.402 3 2/27/03 7:00 0.402 3 10.00 0.900 0.298 7 8/26/04 2:00 0.358 4 5.00 0.800 0.358 4 10/28/04 16:00 0.355 5 3.00 0.667 0.355 5 1/18/06 16:00 0.334 6 2.00 0.500 0.433 2 10/26/06 0:00 0.298 7 1.30 0.231 0.674 1 1/09/08 6:00 0.274 8 1.10 0.091 Computed Peaks 0.594 50.00 0.980 2017 D. R. STRONG Consulting Engineers Inc. Page 40 Bethany Corner Technical Information Report Renton, Washington Modeling Input for the Bypass . Modeling Results Flow Frequency Analysis Time Series File:byp.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 0.016 4 2/09/01 2:00 0.037 1 100.00 0.990 0.009 6 1/05/02 16:00 0.020 2 25.00 0.960 0.020 2 2/27/03 7:00 0.017 3 10.00 0.900 0.006 8 8/26/04 2:00 0.016 4 5.00 0.800 0.009 7 1/05/05 8:00 0.015 5 3.00 0.667 0.017 3 1/18/06 16:00 0.009 6 2.00 0.500 0.015 5 11/24/06 3:00 0.009 7 1.30 0.231 0.037 1 1/09/08 6:00 0.006 8 1.10 0.091 Computed Peaks 0.031 50.00 0.980 2017 D. R. STRONG Consulting Engineers Inc. Page 41 Bethany Corner Technical Information Report Renton, Washington FIGURE 16 DEVELOPED AREA MAP GRAPHIC SCALE 0 20 40 60 1 INCH = 40 FT. 2017 D. R. STRONG Consulting Engineers Inc. Page 42 Bethany Corner Technical Information Report Renton, Washington PERFORMANCE STANDARDS The Site is required to adhere to Flow Control Duration Standard – Matching Forested site conditions of the existing site (reference 11-A of COR 2009 Surface Water Design Manual Amendment). A wet-vault will provide flow control and basic water quality treatment. The Project is required to “match the flow duration of pre-developed rates for forested (historic) site conditions over the range of flows extending from 50% of 2-year up to the full 50-year flow.” (2009 Surface Water Design Manual Amendment, Sec. 1.2.3.1). 2017 D. R. STRONG Consulting Engineers Inc. Page 43 Bethany Corner Technical Information Report Renton, Washington FLOW CONTROL SYSTEM The Project will utilize an detention facility designed to control site runoff. The King County Runoff Time Series (KCRTS) software was used to size the facility. The detention pond design information is included in this section. Retention/Detention Facility Type of Facility: Detention Vault Facility Length: 96.00 ft Facility Width: 45.00 ft Facility Area: 4320. sq. ft Effective Storage Depth: 5.00 ft Stage 0 Elevation: 0.00 ft Storage Volume: 21600. cu. ft Riser Head: 5.00 ft Riser Diameter: 12.00 inches Number of orifices: 2 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 0.75 0.034 2 3.15 1.38 0.070 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 0.00 0. 0.000 0.000 0.00 0.01 0.01 43. 0.001 0.001 0.00 0.02 0.02 86. 0.002 0.002 0.00 0.03 0.03 130. 0.003 0.003 0.00 0.04 0.04 173. 0.004 0.003 0.00 0.05 0.05 216. 0.005 0.004 0.00 0.06 0.06 259. 0.006 0.004 0.00 0.16 0.16 691. 0.016 0.006 0.00 0.26 0.26 1123. 0.026 0.008 0.00 0.36 0.36 1555. 0.036 0.009 0.00 0.46 0.46 1987. 0.046 0.010 0.00 0.56 0.56 2419. 0.056 0.011 0.00 0.66 0.66 2851. 0.065 0.012 0.00 0.76 0.76 3283. 0.075 0.013 0.00 0.86 0.86 3715. 0.085 0.014 0.00 0.96 0.96 4147. 0.095 0.015 0.00 1.06 1.06 4579. 0.105 0.016 0.00 1.16 1.16 5011. 0.115 0.016 0.00 1.26 1.26 5443. 0.125 0.017 0.00 1.36 1.36 5875. 0.135 0.018 0.00 1.46 1.46 6307. 0.145 0.018 0.00 1.56 1.56 6739. 0.155 0.019 0.00 2017 D. 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Page 44 Bethany Corner Technical Information Report Renton, Washington 1.66 1.66 7171. 0.165 0.020 0.00 1.76 1.76 7603. 0.175 0.020 0.00 1.86 1.86 8035. 0.184 0.021 0.00 1.96 1.96 8467. 0.194 0.021 0.00 2.06 2.06 8899. 0.204 0.022 0.00 2.16 2.16 9331. 0.214 0.022 0.00 2.26 2.26 9763. 0.224 0.023 0.00 2.36 2.36 10195. 0.234 0.023 0.00 2.46 2.46 10627. 0.244 0.024 0.00 2.56 2.56 11059. 0.254 0.024 0.00 2.66 2.66 11491. 0.264 0.025 0.00 2.76 2.76 11923. 0.274 0.025 0.00 2.86 2.86 12355. 0.284 0.026 0.00 2.96 2.96 12787. 0.294 0.026 0.00 3.06 3.06 13219. 0.303 0.027 0.00 3.15 3.15 13608. 0.312 0.027 0.00 3.16 3.16 13651. 0.313 0.027 0.00 3.18 3.18 13738. 0.315 0.029 0.00 3.19 3.19 13781. 0.316 0.031 0.00 3.21 3.21 13867. 0.318 0.033 0.00 3.22 3.22 13910. 0.319 0.037 0.00 3.24 3.24 13997. 0.321 0.041 0.00 3.25 3.25 14040. 0.322 0.044 0.00 3.26 3.26 14083. 0.323 0.045 0.00 3.36 3.36 14515. 0.333 0.052 0.00 3.46 3.46 14947. 0.343 0.057 0.00 3.56 3.56 15379. 0.353 0.062 0.00 3.66 3.66 15811. 0.363 0.066 0.00 3.76 3.76 16243. 0.373 0.070 0.00 3.86 3.86 16675. 0.383 0.073 0.00 3.96 3.96 17107. 0.393 0.077 0.00 4.06 4.06 17539. 0.403 0.080 0.00 4.16 4.16 17971. 0.413 0.083 0.00 4.26 4.26 18403. 0.422 0.086 0.00 4.36 4.36 18835. 0.432 0.088 0.00 4.46 4.46 19267. 0.442 0.091 0.00 4.56 4.56 19699. 0.452 0.094 0.00 4.66 4.66 20131. 0.462 0.096 0.00 4.76 4.76 20563. 0.472 0.098 0.00 4.86 4.86 20995. 0.482 0.101 0.00 4.96 4.96 21427. 0.492 0.103 0.00 5.00 5.00 21600. 0.496 0.104 0.00 5.10 5.10 22032. 0.506 0.414 0.00 5.20 5.20 22464. 0.516 0.979 0.00 5.30 5.30 22896. 0.526 1.710 0.00 5.40 5.40 23328. 0.536 2.500 0.00 5.50 5.50 23760. 0.545 2.790 0.00 5.60 5.60 24192. 0.555 3.050 0.00 5.70 5.70 24624. 0.565 3.280 0.00 5.80 5.80 25056. 0.575 3.500 0.00 5.90 5.90 25488. 0.585 3.710 0.00 6.00 6.00 25920. 0.595 3.910 0.00 6.10 6.10 26352. 0.605 4.090 0.00 6.20 6.20 26784. 0.615 4.270 0.00 2017 D. 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Page 45 Bethany Corner Technical Information Report Renton, Washington 6.30 6.30 27216. 0.625 4.440 0.00 6.40 6.40 27648. 0.635 4.610 0.00 6.50 6.50 28080. 0.645 4.760 0.00 6.60 6.60 28512. 0.655 4.920 0.00 6.70 6.70 28944. 0.664 5.070 0.00 6.80 6.80 29376. 0.674 5.210 0.00 6.90 6.90 29808. 0.684 5.350 0.00 7.00 7.00 30240. 0.694 5.490 0.00 Hyd Inflow Outflow Peak Storage Stage Elev (Cu-Ft) (Ac-Ft) 1 0.67 0.42 5.10 5.10 22034. 0.506 2 0.33 0.10 4.87 4.87 21055. 0.483 3 0.43 0.09 4.26 4.26 18397. 0.422 4 0.40 0.08 4.17 4.17 18003. 0.413 5 0.35 0.06 3.54 3.54 15293. 0.351 6 0.36 0.03 3.04 3.04 13153. 0.302 7 0.27 0.03 2.67 2.67 11541. 0.265 8 0.30 0.02 1.93 1.93 8357. 0.192 Hyd R/D Facility Tributary Reservoir POC Outflow Outflow Inflow Inflow Target Calc 1 0.42 0.04 ******** ******* 0.43 2 0.10 0.02 ******** 0.13 0.11 3 0.09 0.02 ******** ******* 0.09 4 0.08 0.02 ******** ******* 0.09 5 0.06 0.02 ******** ******* 0.07 6 0.03 0.01 ******** ******* 0.03 7 0.03 0.01 ******** ******* 0.03 8 0.02 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: 0.674 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.416 CFS at 10:00 on Jan 9 in Year 8 Peak Reservoir Stage: 5.10 Ft Peak Reservoir Elev: 5.10 Ft Peak Reservoir Storage: 22034. Cu-Ft : 0.506 Ac-Ft Add Time Series:byp.tsf Peak Summed Discharge: 0.428 CFS at 10:00 on Jan 9 in Year 8 Point of Compliance File:dsout.tsf Flow Frequency Analysis Time Series File:rdout.tsf Project Location:Sea-Tac 2017 D. R. STRONG Consulting Engineers Inc. Page 46 Bethany Corner Technical Information Report Renton, Washington ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) (ft) Period 0.101 2 2/09/01 20:00 0.416 5.10 1 100.00 0.990 0.025 7 1/07/02 4:00 0.101 4.87 2 25.00 0.960 0.083 4 3/06/03 22:00 0.086 4.26 3 10.00 0.900 0.021 8 8/26/04 7:00 0.083 4.17 4 5.00 0.800 0.027 6 1/08/05 5:00 0.061 3.54 5 3.00 0.667 0.061 5 1/19/06 0:00 0.027 3.04 6 2.00 0.500 0.086 3 11/24/06 8:00 0.025 2.67 7 1.30 0.231 0.416 1 1/09/08 10:00 0.021 1.93 8 1.10 0.091 Computed Peaks 0.311 5.07 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 0.112 2 2/09/01 19:00 0.428 1 100.00 0.990 0.029 7 1/05/02 16:00 0.112 2 25.00 0.960 0.091 4 3/06/03 21:00 0.095 3 10.00 0.900 0.025 8 8/26/04 2:00 0.091 4 5.00 0.800 0.032 6 1/05/05 8:00 0.069 5 3.00 0.667 0.069 5 1/18/06 23:00 0.032 6 2.00 0.500 0.095 3 11/24/06 7:00 0.029 7 1.30 0.231 0.428 1 1/09/08 10:00 0.025 8 1.10 0.091 Computed Peaks 0.323 50.00 0.980 Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.002 31693 51.685 51.685 48.315 0.483E+00 0.004 4992 8.141 59.826 40.174 0.402E+00 0.007 5705 9.304 69.129 30.871 0.309E+00 0.010 5562 9.070 78.200 21.800 0.218E+00 0.013 4378 7.140 85.339 14.661 0.147E+00 0.016 3113 5.077 90.416 9.584 0.958E-01 0.018 2161 3.524 93.940 6.060 0.606E-01 0.021 1460 2.381 96.321 3.679 0.368E-01 0.024 1178 1.921 98.242 1.758 0.176E-01 0.027 687 1.120 99.362 0.638 0.638E-02 0.030 118 0.192 99.555 0.445 0.445E-02 0.033 18 0.029 99.584 0.416 0.416E-02 0.035 8 0.013 99.597 0.403 0.403E-02 0.038 7 0.011 99.609 0.391 0.391E-02 0.041 8 0.013 99.622 0.378 0.378E-02 0.044 5 0.008 99.630 0.370 0.370E-02 0.047 15 0.024 99.654 0.346 0.346E-02 0.050 18 0.029 99.684 0.316 0.316E-02 0.052 22 0.036 99.720 0.280 0.280E-02 0.055 18 0.029 99.749 0.251 0.251E-02 0.058 20 0.033 99.781 0.219 0.219E-02 0.061 16 0.026 99.808 0.192 0.192E-02 2017 D. 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Page 47 Bethany Corner Technical Information Report Renton, Washington 0.064 13 0.021 99.829 0.171 0.171E-02 0.066 10 0.016 99.845 0.155 0.155E-02 0.069 11 0.018 99.863 0.137 0.137E-02 0.072 9 0.015 99.878 0.122 0.122E-02 0.075 8 0.013 99.891 0.109 0.109E-02 0.078 7 0.011 99.902 0.098 0.978E-03 0.081 10 0.016 99.918 0.082 0.815E-03 0.083 14 0.023 99.941 0.059 0.587E-03 0.086 13 0.021 99.962 0.038 0.375E-03 0.089 6 0.010 99.972 0.028 0.277E-03 0.092 2 0.003 99.976 0.024 0.245E-03 0.095 4 0.007 99.982 0.018 0.179E-03 0.097 5 0.008 99.990 0.010 0.978E-04 0.100 3 0.005 99.995 0.005 0.489E-04 Flow Duration from Time Series File:dsout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.002 31567 51.479 51.479 48.521 0.485E+00 0.005 5752 9.380 60.859 39.141 0.391E+00 0.008 5741 9.362 70.222 29.778 0.298E+00 0.011 5683 9.268 79.490 20.510 0.205E+00 0.014 4234 6.905 86.394 13.606 0.136E+00 0.017 3083 5.028 91.422 8.578 0.858E-01 0.020 1796 2.929 94.351 5.649 0.565E-01 0.023 1447 2.360 96.711 3.289 0.329E-01 0.027 953 1.554 98.265 1.735 0.174E-01 0.030 640 1.044 99.309 0.691 0.691E-02 0.033 128 0.209 99.517 0.483 0.483E-02 0.036 29 0.047 99.565 0.435 0.435E-02 0.039 16 0.026 99.591 0.409 0.409E-02 0.042 11 0.018 99.609 0.391 0.391E-02 0.045 8 0.013 99.622 0.378 0.378E-02 0.048 9 0.015 99.636 0.364 0.364E-02 0.052 17 0.028 99.664 0.336 0.336E-02 0.055 21 0.034 99.698 0.302 0.302E-02 0.058 16 0.026 99.724 0.276 0.276E-02 0.061 15 0.024 99.749 0.251 0.251E-02 0.064 18 0.029 99.778 0.222 0.222E-02 0.067 17 0.028 99.806 0.194 0.194E-02 0.070 19 0.031 99.837 0.163 0.163E-02 0.073 10 0.016 99.853 0.147 0.147E-02 0.076 9 0.015 99.868 0.132 0.132E-02 0.080 8 0.013 99.881 0.119 0.119E-02 0.083 8 0.013 99.894 0.106 0.106E-02 0.086 8 0.013 99.907 0.093 0.930E-03 0.089 9 0.015 99.922 0.078 0.783E-03 0.092 15 0.024 99.946 0.054 0.538E-03 0.095 13 0.021 99.967 0.033 0.326E-03 0.098 3 0.005 99.972 0.028 0.277E-03 0.101 2 0.003 99.976 0.024 0.245E-03 0.105 3 0.005 99.980 0.020 0.196E-03 0.108 5 0.008 99.989 0.011 0.114E-03 0.111 3 0.005 99.993 0.007 0.652E-04 2017 D. 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Page 48 Bethany Corner Technical Information Report Renton, Washington Duration Comparison Anaylsis Base File: predev.tsf New File: dsout.tsf Cutoff Units: Discharge in CFS -----Fraction of Time----- ---------Check of Tolerance------- Cutoff Base New %Change Probability Base New %Change 0.031 | 0.76E-02 0.53E-02 -31.2 | 0.76E-02 0.031 0.029 -6.3 0.039 | 0.56E-02 0.41E-02 -26.8 | 0.56E-02 0.039 0.031 -20.6 0.046 | 0.43E-02 0.38E-02 -13.5 | 0.43E-02 0.046 0.036 -22.4 0.054 | 0.32E-02 0.31E-02 -2.0 | 0.32E-02 0.054 0.053 -1.0 0.061 | 0.25E-02 0.24E-02 -0.7 | 0.25E-02 0.061 0.061 -0.1 0.069 | 0.17E-02 0.17E-02 -0.9 | 0.17E-02 0.069 0.069 -0.1 0.076 | 0.12E-02 0.14E-02 12.2 | 0.12E-02 0.076 0.079 3.8 0.084 | 0.90E-03 0.10E-02 16.4 | 0.90E-03 0.084 0.087 3.8 0.091 | 0.62E-03 0.59E-03 -5.3 | 0.62E-03 0.091 0.091 -0.1 0.098 | 0.34E-03 0.28E-03 -19.0 | 0.34E-03 0.098 0.095 -3.8 0.106 | 0.16E-03 0.13E-03 -20.0 | 0.16E-03 0.106 0.105 -0.4 0.113 | 0.11E-03 0.00E+00 -100.0 | 0.11E-03 0.113 0.108 -4.9 0.121 | 0.82E-04 0.00E+00 -100.0 | 0.82E-04 0.121 0.110 -9.1 0.128 | 0.16E-04 0.00E+00 -100.0 | 0.16E-04 0.128 0.112 -12.9 Maximum positive excursion = 0.005 cfs ( 5.9%) occurring at 0.079 cfs on the Base Data:predev.tsf and at 0.084 cfs on the New Data:dsout.tsf Maximum negative excursion = 0.011 cfs (-24.7%) occurring at 0.043 cfs on the Base Data:predev.tsf and at 0.033 cfs on the New Data:dsout.tsf 2017 D. R. STRONG Consulting Engineers Inc. Page 49 Bethany Corner Technical Information Report Renton, Washington Flow Frequency Duration Analysis 2017 D. R. STRONG Consulting Engineers Inc. Page 50 Bethany Corner Technical Information Report Renton, Washington WATER QUALITY TREATMENT SYSTEM The Project is required to adhere to the City of Renton’s Basic Water Quality treatment criteria. A combined detention/water quality vault located within Tract A is proposed to accommodate this requirement. Sizing for a wetvault was calculated from the formula provided by Section 6.4.1.1 Methods of Analysis of the Manual. The minimum wetpool volume required is 6,262 cubic feet. The Project will provide 11,333 cubic feet of dead storage. The wetvault will occupy the eastern half of the detention vault. The vault geometry provides a length to width ratio of 4.33 : 1 so a removable baffle will be provided as shown on the plans. BASIC WETVAULT ANALYSIS As required per Section 6.4.1.1 2009 King County Step 1: Identify required water quality facility volume factor ("f") f=3 (basic wetpond volume factor) Step 2: Determine rainfall (R) for the mean annual storm per Fig. 6.4.1.A R=0.47 in. Step 3: Calculate runoff from the mean annual storm (Vr) for the developed site. Vr =(0.9Ai + 0.25Atg + 0.10Atf + 0.01Ao) x R/12 where . . . Vr =volume of runoff from mean annual storm (c.f.) Ai=area of impervious surface (s.f.) Atg=area of till soil covered with grass (s.f.) Atf=area of till soil covered with till forest (s.f.) Ao=area of outwash soil covered with grass or forest (s.f.) R=rainfall from mean annual storm (in.) Ai=50,896 s.f. Atg=29,953 s.f. Atf=- s.f. Ao=0 s.f. R =0.47 in. Vr =2,087 c.f. Step 4: Calculate water quality volume (Vb). Vb=f x Vr where . . . Vb=water quality volume (cf) f=volume factor from Step 1 Vr =runoff volume from Step 3 Vb=6,262 c.f. (minimum wetpool volume required) 2017 D. R. STRONG Consulting Engineers Inc. Page 51 Bethany Corner Technical Information Report Renton, Washington FIGURE 17 DETENTION & WATER QUALITY FACILITY DETAILS BY:Date: RECOMMENDED FOR APPOVAL BY: BY: BY: Date: Date: Date: 2017 D. R. STRONG Consulting Engineers Inc. Page 52 Bethany Corner 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 the existing tributary and developed onsite runoff. Pipe systems shall be designed to convey the 25-year storm with a minimum of 6-inches of freeboard between the design water surface and structure grate. Any overflow from the 100-year design storm must not create or aggravate a severe flooding problem. 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 will be designed for the Project. Onsite runoff will be collected by the multiple catch basins. Pipes are typically six-inch to twelve-inch diameter LCPE material. Per Figures 3.2.1.C and 3.2.1.D in the 2009 Manual the 24-hour precipitation in inches is 3.4 and 3.9 for the 25-year and 100-year storms respectively. In all cases the 25-year storm was conveyed with at least 6-inches of freeboard. There were no overflows as a result of the 100-year storm. 2017 D. R. STRONG Consulting Engineers Inc. Page 53 Bethany Corner Technical Information Report Renton, Washington 2017 D. R. STRONG Consulting Engineers Inc. Page 54 Bethany Corner Technical Information Report Renton, Washington 2017 D. R. STRONG Consulting Engineers Inc. Page 55 Bethany Corner Technical Information Report Renton, Washington BACKWATER ANALYSIS 2017 D. R. STRONG Consulting Engineers Inc. Page 56 Bethany Corner Technical Information Report Renton, Washington FIGURE 18 BACKWATER ANALYSIS MAP 2017 D. R. STRONG Consulting Engineers Inc. Page 57 Bethany Corner Technical Information Report Renton, Washington BACKWATER ANALYSIS RESULTS BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB-6 TO INLET 1.bwp Surcharge condition at intermediate junctions Tailwater Elevation:423.61 feet Discharge Range:2.11 to 2.61 Step of 0.1 [cfs] Overflow Elevation:424.91 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 25 LF - 12"CP @ 15.40% OUTLET: 416.50 INLET: 420.35 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 426.64 BEND: 0 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.02 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 2.11 3.40 423.75 * 0.012 0.63 0.26 7.11 7.11 3.34 3.40 0.77 2.21 3.41 423.76 * 0.012 0.64 0.26 7.11 7.11 3.34 3.41 0.80 2.31 3.43 423.78 * 0.012 0.66 0.27 7.11 7.11 3.35 3.43 0.82 2.41 3.44 423.79 * 0.012 0.67 0.27 7.11 7.11 3.36 3.44 0.84 2.51 3.46 423.81 * 0.012 0.68 0.28 7.11 7.11 3.37 3.46 0.86 2.61 3.47 423.82 * 0.012 0.70 0.29 7.11 7.11 3.37 3.47 0.88 2.61 3.47 423.82 * 0.012 0.70 0.29 7.11 7.11 3.37 3.47 0.88 PIPE NO. 2: 106 LF - 12"CP @ 1.00% OUTLET: 420.35 INLET: 421.41 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 424.91 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.48 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 2.07 2.84 424.25 * 0.012 0.62 0.53 3.40 3.40 2.65 2.84 0.97 2.17 2.90 424.31 * 0.012 0.63 0.54 3.41 3.41 2.69 2.90 1.00 2.27 2.96 424.37 * 0.012 0.65 0.56 3.43 3.43 2.73 2.96 1.04 2.36 3.03 424.44 * 0.012 0.66 0.57 3.44 3.44 2.78 3.03 1.07 2.46 3.10 424.51 * 0.012 0.68 0.59 3.46 3.46 2.83 3.10 1.11 2.56 3.17 424.58 * 0.012 0.69 0.60 3.47 3.47 2.88 3.17 1.14 2.56 3.17 424.58 * 0.012 0.69 0.60 3.47 3.47 2.88 3.17 1.14 PIPE NO. 3: 25 LF - 12"CP @ 1.00% OUTLET: 421.41 INLET: 421.66 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.40 2.70 424.36 * 0.012 0.51 0.42 2.84 2.84 2.63 2.70 0.72 1.46 2.77 424.43 * 0.012 0.52 0.43 2.90 2.90 2.68 2.77 0.74 1.53 2.84 424.50 * 0.012 0.53 0.44 2.96 2.96 2.75 2.84 0.77 1.60 2.92 424.58 * 0.012 0.54 0.45 3.03 3.03 2.82 2.92 0.79 1.66 3.00 424.66 * 0.012 0.55 0.46 3.10 3.10 2.90 3.00 0.81 1.73 3.09 424.75 * 0.012 0.56 0.47 3.17 3.17 2.98 3.09 0.83 1.73 3.09 424.75 * 0.012 0.56 0.47 3.17 3.17 2.98 3.09 0.83 BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB-8 TO INLET 2.bwp Surcharge condition at intermediate junctions Tailwater Elevation:423.61 feet Discharge Range:0.11 to 0.61 Step of 0.1 [cfs] Overflow Elevation:428.4 feet Weir:NONE Upstream Velocity:0. feet/sec 2017 D. 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Page 58 Bethany Corner Technical Information Report Renton, Washington PIPE NO. 1: 24 LF - 12"CP @ 12.08% OUTLET: 416.50 INLET: 419.40 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 426.65 BEND: 0 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.30 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.11 4.22 423.62 * 0.012 0.14 0.07 7.11 7.11 4.22 4.22 0.12 0.21 4.21 423.61 * 0.012 0.19 0.09 7.11 7.11 4.21 4.21 0.19 0.31 4.21 423.61 * 0.012 0.23 0.11 7.11 7.11 4.21 4.21 0.25 0.41 4.22 423.62 * 0.012 0.27 0.12 7.11 7.11 4.21 4.22 0.30 0.51 4.22 423.62 * 0.012 0.30 0.14 7.11 7.11 4.21 4.22 0.34 0.61 4.23 423.63 * 0.012 0.33 0.15 7.11 7.11 4.22 4.23 0.38 PIPE NO. 2: 82 LF - 12"CP @ 7.01% OUTLET: 419.40 INLET: 425.15 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.08 0.12 425.27 * 0.012 0.12 0.07 4.22 4.22 0.12 ***** 0.12 0.16 0.19 425.34 * 0.012 0.17 0.09 4.21 4.21 0.17 ***** 0.19 0.24 0.24 425.39 * 0.012 0.21 0.11 4.21 4.21 0.21 ***** 0.24 0.32 0.28 425.43 * 0.012 0.24 0.13 4.22 4.22 0.24 ***** 0.28 0.39 0.32 425.47 * 0.012 0.26 0.14 4.22 4.22 0.26 ***** 0.32 0.47 0.35 425.50 * 0.012 0.29 0.15 4.23 4.23 0.29 ***** 0.35 BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB-9 TO CB-7.bwp Surcharge condition at intermediate junctions Tailwater Elevation:423.63 feet Discharge Range:0.02 to 0.13 Step of 0.02 [cfs] Overflow Elevation:424.9 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 73 LF - 12"CP @ 3.42% OUTLET: 419.40 INLET: 421.90 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.02 1.74 423.64 * 0.012 0.06 0.04 4.23 4.23 1.74 1.74 0.06 0.04 1.73 423.63 * 0.012 0.09 0.06 4.23 4.23 1.73 1.73 0.09 0.06 1.73 423.63 * 0.012 0.10 0.07 4.23 4.23 1.73 1.73 0.12 0.08 1.73 423.63 * 0.012 0.12 0.08 4.23 4.23 1.73 1.73 0.14 0.10 1.73 423.63 * 0.012 0.13 0.09 4.23 4.23 1.73 1.73 0.16 0.12 1.73 423.63 * 0.012 0.15 0.10 4.23 4.23 1.73 1.73 0.17 0.14 1.73 423.63 * 0.012 0.16 0.10 4.23 4.23 1.73 1.73 0.19 BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:CB-11 TO CB-1.bwp Surcharge condition at intermediate junctions Tailwater Elevation:418.18 feet Discharge Range:0.11 to 0.91 Step of 0.1 [cfs] Overflow Elevation:433.42 feet Weir:NONE Upstream Velocity:0. feet/sec PIPE NO. 1: 8 LF - 12"CP @ 1.00% OUTLET: 417.18 INLET: 417.26 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 419.88 BEND: 68 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.00 2017 D. 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Page 59 Bethany Corner Technical Information Report Renton, Washington Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.11 0.93 418.19 * 0.012 0.14 0.12 1.00 1.00 0.93 0.93 0.18 0.21 0.93 418.19 * 0.012 0.19 0.16 1.00 1.00 0.93 0.93 0.25 0.31 0.93 418.19 * 0.012 0.23 0.20 1.00 1.00 0.93 0.93 0.31 0.41 0.94 418.20 * 0.012 0.27 0.23 1.00 1.00 0.93 0.94 0.36 0.51 0.94 418.20 * 0.012 0.30 0.25 1.00 1.00 0.93 0.94 0.40 0.61 0.94 418.20 * 0.012 0.33 0.27 1.00 1.00 0.93 0.94 0.44 0.71 0.95 418.21 * 0.012 0.36 0.30 1.00 1.00 0.93 0.95 0.48 0.81 0.95 418.21 * 0.012 0.38 0.32 1.00 1.00 0.93 0.95 0.52 0.91 0.96 418.22 * 0.012 0.40 0.34 1.00 1.00 0.93 0.96 0.55 PIPE NO. 2: 134 LF - 12"CP @ 0.80% OUTLET: 417.26 INLET: 418.33 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 424.41 BEND: 64 DEG DIA/WIDTH: 4.0 Q-RATIO: 1.10 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.11 0.18 418.51 * 0.012 0.14 0.13 0.93 0.93 0.14 ***** 0.18 0.21 0.25 418.58 * 0.012 0.19 0.17 0.93 0.93 0.19 ***** 0.25 0.31 0.31 418.64 * 0.012 0.23 0.21 0.93 0.93 0.23 ***** 0.31 0.41 0.36 418.69 * 0.012 0.27 0.24 0.94 0.94 0.27 ***** 0.36 0.51 0.40 418.73 * 0.012 0.30 0.26 0.94 0.94 0.30 ***** 0.40 0.61 0.45 418.78 * 0.012 0.33 0.29 0.94 0.94 0.33 ***** 0.45 0.71 0.49 418.82 * 0.012 0.36 0.31 0.95 0.95 0.36 ***** 0.49 0.81 0.52 418.85 * 0.012 0.38 0.33 0.95 0.95 0.38 ***** 0.52 0.91 0.56 418.89 * 0.012 0.40 0.36 0.96 0.96 0.40 ***** 0.56 PIPE NO. 3: 11 LF - 12"CP @ 17.73% OUTLET: 418.33 INLET: 420.28 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 425.28 BEND: 49 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.05 0.10 420.38 * 0.012 0.10 0.05 0.18 0.18 0.10 ***** 0.05 0.10 0.13 420.41 * 0.012 0.13 0.06 0.25 0.25 0.13 ***** 0.08 0.15 0.16 420.44 * 0.012 0.16 0.07 0.31 0.31 0.16 ***** 0.12 0.20 0.19 420.47 * 0.012 0.19 0.08 0.36 0.36 0.19 ***** 0.16 0.24 0.21 420.49 * 0.012 0.21 0.09 0.40 0.40 0.21 ***** 0.19 0.29 0.23 420.51 * 0.012 0.23 0.10 0.45 0.45 0.23 ***** 0.21 0.34 0.25 420.53 * 0.012 0.25 0.10 0.49 0.49 0.25 ***** 0.24 0.39 0.26 420.54 * 0.012 0.26 0.11 0.52 0.52 0.26 ***** 0.26 0.43 0.28 420.56 * 0.012 0.28 0.12 0.56 0.56 0.28 ***** 0.28 PIPE NO. 4: 151 LF - 12"CP @ 2.93% OUTLET: 420.28 INLET: 424.70 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 428.40 BEND: 49 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.05 0.11 424.81 * 0.012 0.10 0.07 0.10 0.10 0.10 ***** 0.11 0.10 0.16 424.86 * 0.012 0.13 0.09 0.13 0.13 0.13 ***** 0.16 0.15 0.20 424.90 * 0.012 0.16 0.11 0.16 0.16 0.16 ***** 0.20 0.20 0.23 424.93 * 0.012 0.19 0.12 0.19 0.19 0.19 ***** 0.23 0.24 0.26 424.96 * 0.012 0.21 0.14 0.21 0.21 0.21 ***** 0.26 0.29 0.29 424.99 * 0.012 0.23 0.15 0.23 0.23 0.23 ***** 0.29 0.34 0.31 425.01 * 0.012 0.25 0.16 0.25 0.25 0.25 ***** 0.31 0.39 0.33 425.03 * 0.012 0.26 0.17 0.26 0.26 0.26 ***** 0.33 0.43 0.36 425.06 * 0.012 0.28 0.18 0.28 0.28 0.28 ***** 0.36 PIPE NO. 5: 132 LF - 12"CP @ 4.46% OUTLET: 424.70 INLET: 430.59 INTYP: 5 2017 D. R. STRONG Consulting Engineers Inc. Page 60 Bethany Corner Technical Information Report Renton, Washington Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.05 0.10 430.69 * 0.012 0.10 0.06 0.11 0.11 0.10 ***** 0.10 0.10 0.15 430.74 * 0.012 0.13 0.08 0.16 0.16 0.13 ***** 0.15 0.15 0.19 430.78 * 0.012 0.16 0.10 0.20 0.20 0.16 ***** 0.19 0.20 0.22 430.81 * 0.012 0.19 0.11 0.23 0.23 0.19 ***** 0.22 0.24 0.25 430.84 * 0.012 0.21 0.12 0.26 0.26 0.21 ***** 0.25 0.29 0.28 430.87 * 0.012 0.23 0.13 0.29 0.29 0.23 ***** 0.28 0.34 0.31 430.90 * 0.012 0.25 0.14 0.31 0.31 0.25 ***** 0.31 0.39 0.33 430.92 * 0.012 0.26 0.15 0.33 0.33 0.26 ***** 0.33 0.43 0.35 430.94 * 0.012 0.28 0.16 0.36 0.36 0.28 ***** 0.35 2017 D. R. STRONG Consulting Engineers Inc. Page 61 Bethany Corner Technical Information Report Renton, Washington SECTION VI SPECIAL REPORTS AND STUDIES The following report and studies are provided with this submittal. Critical Areas Study: Mark Rigos, P.E. – December 10st, 2016, Revised: March 26th, 2017 Stream Buffer Mitigation Plan: Mark Rigos, P.E. – March 30th, 2016 Subsurface Exploration and Geotechnical Engineering Report: Associated Earth Sciences Incorporated – December 16, 2016 Arborist Report: Tree Harmony Arborists, LLC – December 12, 2016 Kirkland Office | 911 Fifth Avenue | Kirkland, WA 98033 P | 425.827.7701 F| 425.827.5424 Everett Office | 2911 ½ Hewitt Avenue, Suite 2 | Everett, WA 98201 P | 425.259.0522 F | 425.827.5424 Tacoma Office | 1552 Commerce Street, Suite 102 | Tacoma, WA 98402 P | 253.722.2992 F | 253.722.2993 www.aesgeo.com December 16, 2016 Project No. EE160674A Mark Seek 15233 Manion Way NE Duvall, Washington 98019 Subject: Subsurface Exploration and Geotechnical Engineering Report Bethany Corner 16451 111th Avenue SE Renton, Washington Dear Mr. Seek: As requested, this letter-report presents the results of our subsurface exploration and geotechnical engineering services for the above-referenced project. Our understanding of the project is based on our discussions with you and a review of the proposed site plan prepared by DR Strong Consulting Engineers Inc. dated November 29, 2016. Written authorization to proceed with this study was granted by Mark Seek. Our study was accomplished in general accordance with our scope of work as presented in a signed contract dated December 8, 2016. This letter-report has been prepared for the exclusive use of Mr. Mark Seek and his agents for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect, in this area at the time our letter-report was prepared. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. No other warranty, express or implied, is made. SITE AND PROJECT DESCRIPTION The project site is located on two currently developed parcels with addresses of 16433 and 16451 111th Avenue Northwest in Renton, Washington. The parcels are combined for the project and create a fairly square property with a total area of about 1.8 acres. The site location is shown on the “Vicinity Map,” Figure 1. The parcel is currently developed with residential construction and is vegetated typical residential landscaping. Site topography generally slopes downward towards the west from 111th Avenue NW to the homes and is relatively level for the remainder of the lot area Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 2 to the west. The north side of the site gradually slopes up to the adjacent lot. The total topographic difference on the site is about 6 to 8 feet We understand, the project will consist of the construction of nine single-family residential lots and a drainage tract. Access to the lots will be from the east by a single road with five lots on the north side and four on the south. Within the drainage tract at the southeast corner of the plat we understand there will be a storm water vault. Preliminary planning indicates that the bottom of the vault will be about 12 to 14 feet below the existing grade. SUBSURFACE EXPLORATION AND CONDITIONS Our subsurface exploration completed for this project included the excavation of five exploration pits dug on December 14, 2016. The conclusions and recommendations presented in this letter-report are based on the explorations completed for this study. The locations and depths of the explorations were completed within site and budget constraints. The approximate locations of explorations completed for this study are presented on the “Site and Exploration Plan,” Figure 2. Copies of the subsurface exploration logs are also attached with this letter-report in the Appendix. The exploration pits were excavated using a tracked mini excavator provided by the client. The pits permitted direct, visual observation of subsurface conditions. Materials encountered in the exploration pits were studied and classified in the field by an experienced geotechnical engineer from our firm. All exploration pits were backfilled after examination and logging. Selected samples were then transported to our laboratory for further visual classification. Our explorations generally encountered shallow, native lodgement till soils and fill placed over the lodgement till, for the full depth of the exploration to a depth of about 6 to 8 feet. The encountered lodgement till was weathered near the surface consisting of medium dense, moist, tan, silty sand with gravel and was unsorted. At depths of 2 to 3 feet below the surface the lodgement till graded to unweathered till that consisted of dense, gray, silty fine sand with gravel and was unsorted. In the vicinity of the vault we extended a pit to a depth of 14 feet. At this depth the till was underlain by a hard silt described as pre Vashon silt. On the central to west end of the site we encountered fill soils (soil not naturally placed) to a maximum depth of about 6 feet. The fill consisted of a mixture of sand silt and gravel mixed with trace amounts of debris and pockets of organics. Lodgement till was deposited at the base of an active continental glacier during the Vashon Stade of the Fraser Glaciation approximately 12,500 to 15,000 years ago. The till was compacted by the weight of about 3,000 feet of overlying ice. Lodgement till typically has high-strength and Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 3 low-compressibility attributes that are favorable for structural support with proper preparation. Lodgement till is typically silty, moisture-sensitive, and easily disturbed under wet site or weather conditions. Excavated lodgement till is suitable for reuse in structural fill applications under dry site and weather conditions when it can be moisture-conditioned to allow compaction to a firm and unyielding condition at the specified level for the intended purpose. Lodgement till is considered suitable for foundation support but is not considered a suitable infiltration receptor. The geologic units identified on the subject property closely match those units identified within the site area on the Geologic Map of Surficial Deposits in the Seattle 30’ by 60’ Quadrangle, Washington, by J.C. Yount and others, 1993. Hydrology Minor to abundant seepage was observed in all of our explorations. We anticipate that shallow ground water will be limited to interflow. Interflow commonly occurs in areas underlain by glacially consolidated sediments and originates as surface water that percolates down through the near-surface, relatively permeable surface soils, such as weathered lodgement till, and becomes trapped or “perched” atop the underlying, relatively impermeable, glacial sediments. Interflow is often a seasonal phenomenon. It should be noted that the presence and depth of seepage at the site may vary in response to such factors as changes in season, precipitation, and site use. Infiltration Feasibility The site is underlain at shallow depths by medium dense to very dense lodgement till and fill soils. Lodgement till generally consisted of silty fine sand with gravel and has been consolidated by the weight of an overriding ice sheet during the most recent ice age. As a result, the lodgement till has a low permeability due to its relative high density and high silt content and is not a suitable receptor for infiltration. In addition, the till layer commonly creates a perched ground water layer described in the previous section that will not allow adequate separation from high winter ground water for a proposed infiltration facility, if present. Therefore, we do not recommend the use of infiltration as a method for storm water disposal. DESIGN RECOMMENDATIONS Introduction Our explorations indicate that, from a geotechnical standpoint, the proposed project is feasible provided the recommendations contained herein are properly followed. The bearing stratum is generally shallow on the east end and conventional shallow foundations should perform well with proper subgrade preparation. The west end of the site will require that the unsuitable fill be removed to a depth of about 6 feet prior to the placement of additional structural fill or Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 4 foundations. We recommend that building foundations are founded on the dense native, glacial till soils or structural fill placed on top of the native glacial till. Site Preparation Site preparation of the construction area should include removal of all previously placed fill, grass, brush, debris, and any other deleterious materials. Erosion and surface water control should be established around the clearing limits to satisfy local requirements. We recommend existing fill, be removed from below areas of shallow foundations. When structural fill is required for restoration of the planned foundation grade, our recommendations detailed in the “Structural Fill” section should be followed. Removal of unsuitable soil should extend laterally beyond the building footprint by a distance equal to the depth of overexcavation. For example, when existing fill is removed to a depth of 2 feet below a planned footing area, the excavation should also extend laterally 2 feet beyond the building footprint in that area. Where existing fill is removed and replaced with structural fill, conventional shallow foundations may be used for structure support. The required depth of removal should be determined in the field based on actual conditions encountered during excavation. Below planned on-site paving or under building slabs-on-grade, the stripped subgrade should be proof-rolled with heavy, rubber-tired construction equipment, such as a fully loaded tandem-axle dump truck. Proof-rolling should be performed prior to structural fill placement. The proof-roll should be monitored by the geotechnical engineer so that any soft or yielding subgrade soils can be identified. Any soft or loose, yielding soils should be removed to a stable subgrade. Proof-rolling should only be attempted if soil moisture contents are at or near optimum moisture content. Proof-rolling of wet subgrades could result in further degradation. Temporary Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, however, temporary, unsupported cut slopes can be planned at 1.5H:1V (Horizontal:Vertical) or flatter in the existing fill and underlying weathered glacial deposits, provided they are not saturated. Temporary slopes in unsaturated, unweathered lodgement till may be planned at 1H:1V. These slope angles are for areas where ground water seepage is not encountered, and assume that surface water is not allowed to flow across the temporary slope faces. If ground or surface water is present when the temporary excavation slopes are exposed, flatter slope angles will be required. As is typical with earthwork operations, some sloughing and raveling may occur and cut slopes may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 5 Site Disturbance The on-site soils contain a high percentage of fine-grained material, which makes them easy to disturb during wet weather. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened during wet weather conditions. Structural Fill All references to structural fill in this letter-report refer to subgrade preparation, fill type and placement, and compaction of materials, as discussed in this section. If a percentage of compaction is specified under another section of this letter-report, the value given in that section should be used. After stripping, planned excavation, and any required overexcavation have been performed to the satisfaction of the geotechnical engineer, the upper 12 inches of exposed ground in areas to receive fill should be recompacted to a firm and unyielding condition. If the subgrade contains silty soils and too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt migration from below. After recompaction of the exposed ground is approved, or a free-draining rock course is laid, structural fill may be placed to attain desired grades. Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to 95 percent of the modified Proctor maximum density using American Society for Testing and Materials (ASTM) D-1557 as the standard. Use of soils from the site in structural fill applications is acceptable if the material meets the project specifications for the intended use, and if specifically allowed by project specifications. In the case of roadway and utility trench filling, structural fill should be placed and compacted in accordance with current City of Renton codes and standards. The top of the compacted fill should extend horizontally outward a minimum distance of 3 feet beyond the locations of the roadway edges before sloping down at an angle of 2H:1V. Structural fills with sloping faces that cannot be compacted directly by a vibratory roller should be compacted by overbuilding, then cutting back to a compacted slope core. The contractor should note that any proposed fill soils must be evaluated by Associated Earth Sciences, Inc. (AESI) prior to their use in fills. This would require that we have a sample of the material 72 hours in advance to perform a Proctor test and determine its field compaction standard. Soils in which the amount of fine-grained material (smaller than the No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive soil in structural fills should be limited to Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 6 favorable dry weather conditions, and is only permitted if specifically allowed by project plans and specifications. The native soils present onsite contained significant amounts of silt and are considered highly moisture-sensitive. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses, and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing program. Ground Motion Structural design of the project should be in accordance with the 2015 International Building Code (IBC) using Site Class D. Foundations Spread footings that are supported on dense native lodgement till sediments or a combination of structural fill and dense native lodgement till sediments may be designed with an allowable foundation soil bearing pressure of 2,500 pounds per square foot (psf), including both dead and live loads. For the storm water vault located at the southeast corner of the site, a higher allowable bearing capacity of 3,000 psf can be used due to the increased depth of the excavation. An increase of one-third may be used for short-term wind or seismic loading for all foundations. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection. However, all footings must penetrate to the prescribed bearing stratum, and no footing should be founded in or above organic or loose soils. It should be noted that the area bound by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM D-1557. In addition, a 1.5H:1V line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. Anticipated settlement of footings founded as described above should be on the order of ½ inch or less. However, disturbed soil not removed from footing excavations prior to footing placement Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 7 could result in increased settlements. All footing areas should be inspected by AESI prior to placing concrete to verify that the design bearing capacity of the soils has been attained and that construction conforms to the recommendations contained in this letter-report. Such inspections may be required by the governing municipality. Perimeter footing drains should be provided, as discussed under the “Drainage Considerations” section of this letter-report. Lateral loads can be resisted by friction between the foundation and the natural glacial soils or supporting structural fill soils, and by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with structural fill and compacted to at least 95 percent of the maximum dry density to achieve the passive resistance provided below. We recommend the following allowable design parameters: • Passive equivalent fluid = 350 pounds per cubic foot (pcf) • Coefficient of friction = 0.35 Drainage Considerations Foundations should be provided with foundation drains. Drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed pea gravel. The drains should be constructed with sufficient gradient to allow gravity discharge away from the proposed building. Roof and surface runoff should not discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. In planning, exterior grades adjacent to walls should be sloped downward away from the proposed building to achieve surface drainage. Lateral Wall Pressures All backfill behind foundation walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the letter-report. Horizontally backfilled walls, which are drained and free to yield laterally at least 0.1 percent of their height, may be designed to resist active lateral earth pressure represented by an equivalent fluid equal to 35 pcf. Fully restrained, drained, horizontally backfilled, rigid walls that cannot yield such as the storm water vault should be designed for an at-rest equivalent fluid of 50 pcf. If parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. Walls with sloping backfill are not expected; however, if walls with sloping backfill are planned, we should be contacted to offer situation-specific surcharge recommendations. As required by the 2015 IBC, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. Considering the site soils and the recommended wall backfill materials, we recommend a seismic surcharge pressure of 8H and 11H psf, where H is the wall height in feet, for the “active” and “at-rest” loading conditions, Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 8 respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the midpoint of the walls. The lateral pressures presented above are based on the conditions of a uniform backfill consisting of excavated on-site soils, or imported structural fill compacted to 90 percent of ASTM D-1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in settlement of slab-on-grade floors or other structures supported above the walls. Thus, the compaction level is critical and must be tested by our firm during placement. Surcharges from adjacent footings or heavy construction equipment must be added to the above values. Perimeter footing drains should be provided for all retaining walls, as discussed under the “Drainage Considerations” section of this letter-report. It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain to within 1 foot of finish grade for the full wall height using imported, washed gravel against the walls. Pavement Recommendations Pavement areas should be prepared in accordance with the “Site Preparation” section of this letter-report. If the stripped native soil subgrade can be compacted to 95 percent of ASTM D-1557 and is firm and unyielding, no additional preparation is required. Soft or yielding areas should be overexcavated to provide a suitable subgrade and backfilled with structural fill. The pavement sections included in this letter-report section are for driveway and parking areas onsite, and are not applicable to right-of-way improvements. If any new paving of public streets is required, we should be allowed to offer situation-specific recommendations. The exposed ground should be recompacted to a firm and unyielding condition. If required, structural fill may then be placed to achieve desired subbase grades. Upon completion of the recompaction and structural fill, a pavement section consisting of 3 inches of asphaltic concrete pavement (ACP) underlain by 4 inches of 1¼-inch crushed surfacing base course is the recommended minimum in areas of planned passenger car driving and parking. In driveway areas subjected to heavier loads, such as that from school buses or fire trucks, a minimum pavement section consisting of 4 inches of ACP underlain by 2 inches of 5/8-inch crushed surfacing top course and 4 inches of 1¼-inch crushed surfacing base course is recommended. The crushed rock course must be compacted to 95 percent of the maximum density, as determined by ASTM D-1557. All paving materials should meet gradation criteria contained in the current Washington State Department of Transportation (WSDOT) Standard Specifications. Bethany Corner Subsurface Exploration Renton, Washington and Geotechnical Engineering Report December 16, 2016 ASSOCIATED EARTH SCIENCES, INC. MM/pc - EE160525A4 - Projects\20160525\EE\WP Page 9 PROJECT DESIGN AND CONSTRUCTION MONITORING We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this letter-report is based. If the reviewing agency requires the Engineer of Record to review the project during final design and construction, we are available. In this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design and construction of the project. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the building foundations depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of the current scope of work. If these services are desired, please let us know and we will prepare a cost proposal. We have enjoyed working with you on this study and are confident that these recommendations will aid in the successful completion of your project. If you should have any questions, or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Everett, Washington Matthew A. Miller, P.E. Principal Engineer Attachments: Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Appendix: Exploration Logs Copyright:© 2013 National Geographic Society, i-cubed 0 20001000 FEET ± NOTE: BLACK AND WHITEREPRODUCTION OF THIS COLORORIGINAL MAY REDUCE ITSEFFECTIVENESS AND LEAD TOINCORRECT INTERPRETATION VICINITY MAP PROJ NO. DATE: FIGURE:EE160674A 12/16 1 Document Path: G:\GIS_Projects\aTemplatesNTRP\aVM_Template\VM_MXD\160674 Fig1 ProjectVicinity_Bethany.mxdDATA SOURCES / REFERENCES:USGS: 24K SERIES TOPOGRAPHIC MAPSKING CO: STREETS, CITY LIMITS, PARCELS 2016 LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE KitsapCounty Snohomish County Pierce County King County SE 164th St 111thAveSE109thAveSE!( SITE¬«167 ¥405 ¬«515 BETHANY CORNERRENTON, WASHINGTON NOTES: 1. BASE MAP REFERENCE: D. L. STRONG CONSULTING ENGINEERS, BETHANY CORNER PRELIMINARY PLAY, PRELIMINARY PLAT PLAN, UNDATED.160674 Bethany Corner \ 160674 F2 Site-Explr.cdrBETHANY CORNER RENTON, WASHINGTON SITE AND EXPLORATION PLAN PROJ NO.DATE:FIGURE: KE160674A 12/16 2 BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. a s s o c i a t e d e a r t h s c i e n c e s i n c o r p o r a t e d FEET 20 400 N CONTOUR INTERVAL = 2’ LEGEND: EXPLORATION PITEP NOTE: LOCATION AND DISTANCES SHOWN ARE APPROXIMATE. EP-3 EP-2 EP-1 EP-5 EP-4 APPENDIX Grass / Topsoil Vashon Lodgement Till Loose to medium dense, tannish gray, silty, fine SAND, some gravel; mottled (SM). Medium dense to dense, moist, tannish gray, silty, fine SAND, some gravel; unsorted (SM). Pre-Vashon Fine-Grained Stiff, moist to very moist, olive gray, fine sandy SILT, trace gravel (ML). As above. Bottom of exploration pit at depth 13.5 feet No seepage. No caving. DESCRIPTION Renton, WA Bethany Corner 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: AWR Approved by: ????12/14/16 Project No. EE160674A LOG OF EXPLORATION PIT NO. EP-1 Depth (ft)KCTP3 160674.GPJ December 15, 2016 Grass / Topsoil Fill Loose, very moist, tan and dark gray, fine to medium SAND, some silt (SP-SM). Pockets of organic soil and debris. Operator notes harder digging. Vashon Lodgement Till Medium dense, wet, gray, silty, fine SAND; mottled (SM). As above. Bottom of exploration pit at depth 8 feetModerate seepage at 3 feet. Heavy caving from 2 to 6 feet. DESCRIPTION Renton, WA Bethany Corner 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: AWR Approved by: ????12/14/16 Project No. EE160674A LOG OF EXPLORATION PIT NO. EP-2 Depth (ft)KCTP3 160674.GPJ December 15, 2016 Grass / Topsoil Fill Loose, moist, tannish brown, silty, fine SAND, some gravel; contains pockets of organics (SM). Operator notes harder digging. Vashon Lodgement Till Medium dense, wet, grayish tan, silty, fine SAND; mottled (SM). Dense, moist, tan, silty, fine SAND, some gravel; mottled (SM). Bottom of exploration pit at depth 8.5 feet Moderate seepage from 3 to 5 feet. Moderate caving from 2 to 5 feet. DESCRIPTION Renton, WA Bethany Corner 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: AWR Approved by: ????12/14/16 Project No. EE160674A LOG OF EXPLORATION PIT NO. EP-3 Depth (ft)KCTP3 160674.GPJ December 15, 2016 Grass / Topsoil Fill Loose to medium dense, very moist, tannish brown, silty, fine SAND, some gravel; contains organics soil and debris (SM). Pre-Vashon Fine-Grained Medium stiff, very moist to wet, olive gray, fine sandy SILT (ML). Tukwila Formation Weathered SAND / SILT STONE. Bottom of exploration pit at depth 10 feetMinor seepage from 2 to 3 feet. Minor caving from 1 to 5 feet. DESCRIPTION Renton, WA Bethany Corner 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: AWR Approved by: ????12/14/16 Project No. EE160674A LOG OF EXPLORATION PIT NO. EP-4 Depth (ft)KCTP3 160674.GPJ December 15, 2016 Grass / Topsoil Fill Loose, very moist, tannish brown, silty, fine SAND, some gravel, trace organic debris (SM). Vashon Lodgement Till Medium dense, wet, tan, silty, fine SAND, some gravel (SM). Dense, moist, tannish gray, silty, fine SAND, some gravel; unsorted (SM). Bottom of exploration pit at depth 7.5 feetModerate seepage at 4 feet. Minor caving from 2 to 5 feet. DESCRIPTION Renton, WA Bethany Corner 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: AWR Approved by: ????12/14/16 Project No. EE160674A LOG OF EXPLORATION PIT NO. EP-5 Depth (ft)KCTP3 160674.GPJ December 15, 2016 2017 D. R. STRONG Consulting Engineers Inc. Page 62 Bethany Corner Technical Information Report Renton, Washington SECTION VII OTHER PERMITS, VARIANCES AND ADJUSTMENTS None at this time. 2017 D. R. STRONG Consulting Engineers Inc. Page 63 Bethany Corner Technical Information Report Renton, Washington SECTION VIII CSWPPP ANALYSIS AND DESIGN (PART A) The Erosion and Sedimentation Control Design will meet the seven minimum King County requirements: 1. Areas to remain undisturbed shall be delineated with a high visibility plastic fence prior to any site clearing or grading. 2. Site disturbed areas shall be covered with mulch and seeded, as appropriate, for temporary or permanent measures. 3. Perimeter protection shall consist of a silt fence down slope of any disturbed areas or stockpiles. 4. A stabilized construction entrance will be located at the point of ingress/egress (i.e. onsite access road). 5. The detention pond will act as a sediment pond for sediment retention. Perimeter silt fences will provide sediment retention within the bypass areas. 6. Surface water from disturbed areas will sheet flow to the sediment pond for treatment. 7. 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. SWPPP 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. 2017 D. R. STRONG Consulting Engineers Inc. Page 64 Bethany Corner Technical Information Report Renton, Washington 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. December 12, 2016 Project: Pre-construction assessment for lot development at 16433 and 16451 111th Avenue SE, Renton, WA. Parcel numbers 0088000570 and -560. Contact: Jonathan Murray - D. R. Strong Consulting Engineers, Inc 620 7th Avenue, Kirkland, WA 98033 Phone – 425 827 3063 Email – jonathan.murray@drstrong.com Objectives: Evaluate health of existing trees and establish criteria for their preservation. Description: This is a pair of midsized parcels, each close to 40,000 square feet, tucked in the middle of a row larger lots in the Renton Higlands (Figures 1-3). Each property has an existing home on the east end, the 16433 home was built in 1952, and the 16451 home in 1966. The 16433 parcel is lightly treed and no significant changes have occurred on it over the last twenty years. The 16451 parcel was fairly well covered with trees until 2009 when it was partially cleared. It was totally cleared by 2012. There is a wire fence running between the 16433 property and the 16411 property to the north. Another wire fence runs along the west end of 16433 and ties into a wood fence at the west end of the 16451 property. The wood fence runs nearly the entire width of the property, stopping about 5’ short of what appeared to be the SW corner of the 16451 parcel. Another wire fence runs east from that corner to about even with the back of the house. Both existing homes will be razed. According to the proposed development plans each parcel will be subdivided into five lots. A new home will be built on each save the east end of the 16451 parcel which will have a water retention area (Figures 4 and 5). The following itemized list begins at the SE corner of the 16433 property and runs roughly counter clockwise through the two parcels. Each tree was tagged and their numerical designations are reflected in Figures 3-5. Diameters were measured at the standard height of 54” above grade (DSH) during the December 2016 site visit. Heights were estimated. The majority of the trees described are shown on the November 2016 Short Plat. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 1) Weeping Willow (Salix babylonica) 26.5” DSH, 22’ tall, 14’ spread standing just to the right side of the south entrance to the 16433 property. The tree is in weak condition. It has been topped repeatedly and has multiple atrophied and decayed areas. 2) Scots Pine (Pinus sylvestris) 18” DSH, 30’ tall in fair condition with average new growth and color. Standing at east end of line at south end of the house. 3) Scots Pine 16” DSH, 32’ tall in fair condition with average new growth and color. Next tree west of #2. 4) Scots Pine 16” DSH, 35’ tall in fair condition with average new growth and color. Next tree west of #3. 5) Scots Pine 10.5” DSH, 25’ tall in weak condition with below average new growth, poor color, and signs of needle blight. Next tree west of #4. 6) Douglas Fir (Pseudotsuga menziesii) 10.5” DSH, 20’ tall standing just north of the end of the line of pines. Tree is dead. 7) Douglas Fir 12.5” DSH, 22’ tall standing at the SW corner of the 16433 house. Tree is dead. 8) Ash (Fraxinus sp) 19” DSH, 30’ tall, 14’ spread standing in line with and north of the #7 tree. It is in poor condition with a significant decay column running from the base to where it was topped near the 12’ level. 9) Douglas Fir 15” DSH, 26’ tall standing north of #8. It is in fair health but bifurcates at the 9’ mark and has an active fracture plane. May have been topped. 10) Douglas Fir 14” DSH, 28’ tall standing north of #9. It bifurcates at the 6’ mark and has an active fracture plane. May have been topped. Upper canopy is stunted and discolored. 11) Douglas Fir 12.5” DSH, 26’ tall standing at the NW corner of the 16433 house. It is in fair health but bifurcates at the 10’ mark and the codominant stems twine. May have been topped. 12) Big Leaf Maple (Acer macrophyllum) clump standing 15’ north of #11 and on the north fenceline. There are 10 stem in the stand varying from 3-6” DSH and they average 20’ tall. Most likely stump sprouts. 13) White Ash (Fraxinus Americana) 10” DSH, 26’ tall 9’ spread standing 20’ west of the #12 tree and in the fence line area. Fair condition. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 14) Excelsa Cedar (Thuja plicata ‘Excelsa’) 20” DSH, 25’ tall standing 10’ west of #11. Tree is in good condition. 15) Redwood (Sequoia sempervirens) 26” and 24” DSH, 50’ tall standing 17 west of #14 and 8’north of the fence. Separates at base. Good condition. 16) White Ash 5.5” and 8.5” DSH, 37’ tall, 16’ one sided spread standing 10’ SSW of #15. Fair condition. Tree separates at 3’ level. 17) Redwood 28” DSH, 48’ tall standing 20’ west of the #15 tree and 8’ north of the fence. Good condition. 18) White Ash 5” and 10” DSH, 39’ tall, 10’ spread standing 15’ SW of #15. Fair condition. Tree separates at 40” level. 19) Redwood 27” DSH, 46’ tall standing 20’ west of the #17 tree and 8’ north of the fence. Good condition. 20) White Ash 13” DSH, 26’ tall, 8’ spread standing 22’ W of #18. Fair condition. Tree bifurcates at 5’ mark. 21) White Ash 6.5” and 10.5” DSH, 25’ tall, 8’ spread standing 21’ east of the NW corner of the property. Fair condition. Tree separates at 13” level. 22) Weeping Willow 17.5” DSH, 20’ tall, standing 17’ south of the north line and 14’ east of the west line. The tree leans east near 20 degrees and extends 24’ and about 14’ wide. 23) Cottonwood (Populus trichocarpa) 25” DSH, 65’ tall, 18’ spread standing 6’ west of the west fence line and 20’ south of the north line. Tree has a significant structural fault near the 30’ level. Decay may be present. 24) Red Alder (Alnus rubra) 13” and 15” DSH, 45’ tall, 8’ spreads standing 5’ west of the west line and 15’ south of #23. Both stems have less than 15% viable canopies and both lean lightly to the southeast. 25) Western Red Cedar (Thuja plicata) 13.5” DSH, 35’ tall standing 5’ east of the west line and 8’ south of the #24 tree. There is a tree fort fastened between this tree and the #26 tree which has been in place at least 8 years based on how much the tree has grown around the boards and bolts. Tree is in poor condition with little to no new growth and weak color. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 26) Western Red Cedar 11.5” DSH and 14” DSH, 35’ tall standing 10’ south of #25 and holding the other end of the fort. Stems separate from the base. Tree is in poor condition. 27) Western Red Cedar 12” and 14” DSH, 31’ tall standing 9’ south of #26. The stems separate from the base and the larger is on the east side. Tree is in weak condition. 28) Western Red Cedar 15” DSH, 30’ tall standing 42’ north of the SE corner of the 16433 property and 6’ east of the west line. It is in weak condition. 29) Western Red Cedar 18” DSH, 26’ tall standing 6’ south of the #28 tree. It is in weak condition. 30) Cottonwood 16” DSH, 52’ tall, 16’ spread standing 5’ west of the four way corner at the NW corner of the 16451 parcel and in the property due west of it. Tree is in fair condition. 31) Cottonwood tree 12” DSH, 65’ tall, 9’ spread standing as part of a clump 15’ south and 15’ east of the NW corner of the 16451 property. It is in fair condition. 32) Cottonwood tree 12.5” DSH, 42’ tall, 9’ spread standing just south of the #31 tree. It is in fair condition. 33) Cottonwood tree 22.5” DSH, 75’ tall, 18’ spread standing in between and just west of the #31 and #32 trees. It is in fair condition. There are two subordinate saplings, 4” and 6” caliper, standing below this tree and closer to the west fence. 34) Cottonwood tree 10” DSH, 35’ tall and 14” DSH, 45’ tall, 9’ overall spread standing 28’ south of the #31-33 clump. It is in the west fence line and in weak condition. 35) Cottonwood tree 13” DSH, 32’ tall, 8’ spread standing 35’ south of the #34 tree and against the fence. It is in fair condition. 36) Big Leaf Maple 10” DSH, 33’ tall, 10’ spread standing 5’ north of the SW corner of the 16451 property. It is in fair condition. 37) Grove of at least twelve cottonwood saplings, all less than 6” DSH, standing at about the center point of the south side of the property and on the southern neighbor’s side of the line. Fair conditions. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Methods: Tree assessment is both an art and a science. To properly perform, an arborist must have an extensive background in biology, tree mechanics, and tree structure that is equal parts academic and field knowledge. It takes years of study to recognize and correctly diagnose the subtle signs trees exhibit before their failure, whether it be partial or total. The process begins with a visual inspection (visual tree assessment, VTA) which is followed up as necessary with soundings, core testing, and/or other detection means. Each tree is examined and evaluated according to several factors including species type, size, vigor, injuries present, root and grade disturbance, deadwood, location and extent of decay, stem taper, exposure, and targets that are at risk. Discussion: There are two levels of concern at this site, primary and secondary. The primary construction impact zone includes the environs immediately within the boundaries of the new home base areas (see Figures 4 and 5), those in the area of the new road improvements, the areas expected for the driveway access to each home site, and the regions within ten feet of those boundaries. Trees #1-11, #28, and #31-33 clearly stand in the primary impact zones. They will be removed at the time of clearing and grading The secondary impact area includes the trees which have root systems extending within the construction area. This region, the Critical Root Zone (CRZ), is defined as a circle with a radius of one foot per inch of tree diameter. For example the #13 White Ash, with a 10” DSH, has a 10’ radial CRZ. Typically intrusion within the CRZ is strongly discouraged by the tree care industry. However trenching type incursion, that is excavation that will occur along only one sector of a tree’s CRZ, can reach significantly into the root growth area without having a detrimental long term effect. What does have to be absolutely protected is a tree’s Structural Root Plate (SRP). This radial area is again related to the diameter inches of the tree in question but not quite in a direct proportion as in the CRZ. Figure 6 below illustrates the relationship. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 6. Size of the Structural Root Plate in relation to tree stem diameter. Note that the SRP levels off at 10’ for any tree over 24” in diameter. In the case of the #10 White Ash mentioned above, the #2 house base area will be 20’ back from the north property line so will not interfere with tree. But if other grading is required along the edges of the parcel then the #10 tree, as seen in Figure 6, has a 5’ Structural Root Plate, and excavating will have to stay outside of that area. Looking at the entire row of trees along the north fence line the redwoods have the largest diameters and will require the full 10’ set back. They are already 8’ north of the line so only 2’ of their SRP extends into the parcel. The Ash standing on the property line have diameters which indicate no greater than 6’ SRPs. The #22 willow has a 17.5” DSH and means it has somewhere around an 8’ SRP. The area shown on the short plat as set aside for the #5 house will be just at 8’ from the base of the tree. The largest of the cedars standing on the west end of the 16433 parcel has an 18” DSH which indicates an 8’ SRP. The cottonwoods and maple standing on the west end of the 16451 parcel range between 10” DSH and 13” DSH which indicate SRPs between 6’ and 7’ radial spread. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner The chart shown in Figure 7 below is used to determine what percentage of a tree’s Critical Root Zone will be affected by trenching type incursion. In general trees can sustain losses of up to 30% of the overall area within their CRZ without having long term detrimental results. Figure 7. Chart giving the loss in critical root area as a function of the radial distance to the CRZ disturbance. For the trees along the north border, the CRZs of the redwoods (26-28’ radial spread) overlap those of the ash (10-12’ radial spreads) in the fence line. From the chart in Figure 7 the redwoods require a 19’ setback to prevent detrimental impact. As they are 8’ north of the fence line an 11’ non-intrusion zone along the length of the north line should be adequate for all the trees. The #22 willow requires a 13’ set back which appears to overlap with the graded area at the NW corner of the #5 home site. The cedars #25-27 are in an region set aside as a sensitive area. But there appears to be step down grading which will occur in their vicinity. Their CRZ should not be disturbed within 10’ of the base of the trees. If fill is being brought in it can be no deeper than 4” within 10’ of the trees. The #29 cedar is close to the SW corner of the graded site for the #5 home. It requires a 13’ set back. The cottonwoods and maple on the west end of 16451 all have 10’ maximum setbacks. They also appear to be in regions of stepped down grading. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Recommendations: Nearly all the trees present on site in this case will have to be removed. The majority stand in the primary impact zone for the development. Of these only the #2-4 Scots pines are in at least average condition. The others are dead, in weak to poor condition, and/or have structural issues making them undesirable to retain. Removal and replacement with young, healthy trees is the most viable option for these spaces. The #22 willow and # 29 cedar stand in the center of grade transition zones. Neither is in good condition and both require CRZ protection at 18’ out from their bases. If it is not possible, or practical, to maintain these protection circles then the trees should be removed. Note that burying the CRZs of trees with more than 4” of soil interferes with their biological functions and for all intents and purposes is no different from cutting the roots. Raising grade within the CRZ of a retained tree is not allowed. Typically protection fencing such as 6’ chain link is set at the CRZ limits for retained trees. For the north side border stand the simplest thing is to just run the fence 11’ south of the property line for the length of the row. If the #22 willow is to be kept than it will require a circular enclosure at 17.5’ radial distance. Obviously the tree itself will extend beyond the fence line and may require clearance pruning. The protection fence for the #25-27 cedars can be set at their 10’ one-sided encroachment limit on the east and then tapered around both ends at 14’ distance. The #29 cedar, if it is to be kept, will have to be circled at 18’ radial distance. The two cottonwoods and maple at the west end of 16451 should be fenced at their CRZ extent and the fence tied back to the existing wood one. All the retained trees should be covered with 6-8” of arbormulch within the region of their CRZs. Excelsior cedars, Deodar cedar, Alaska Weeping Cedar, and even Sequoia are great options for evergreen replacements. Columnar maples, hornbeams, beech, Katsura, Crimson King maple, and certain oak varieties are options for larger deciduous. Japanese Snowbell, Stewartia, redbuds, vine maples, and columnar magnolias can work for color and more mid-sized options. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Waiver of Liability Because the science of tree risk assessment is constantly broadening its understanding, it cannot be said to be an exact science. Every tree is different and performing tree risk assessment is a continual learning process. Many variables beyond the control, or immediate knowledge, of the arborist involved may adversely affect a tree and cause its premature failure. Internal cracks and faults, undetectable root rot, unexposed construction damage, interior decay, and even nutrient deficiencies can be debilitating factors. Changes in circumstance and condition can also lead to a tree’s rapid deterioration and resulting instability. All trees have a risk of failure. As they increase in stature and mass their risk of breakdown also increases, eventual failure is inevitable. While every effort has been taken to provide the most thorough and accurate snapshot of the trees’ health, it is just that, a snapshot, a frozen moment in time. These findings do not guarantee future safety nor are they predictions of imminent events. It is the responsibility of the property owner to adequately care for the tree(s) in question by utilizing the proper professionals and to schedule future assessments in a timely fashion. This report and all attachments, enclosures, and references, are confidential and are for the use of D.R. Strong Consulting Engineers and their representatives only. They may not be reproduced, used in any way, or disseminated in any form without the prior consent of the client concerned. Anthony Moran Certified Arborist Qualified Tree Risk Assessor ISA #PN-5847A ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 1. Aerial overview of the two property. The subject trees are labeled in red. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 2. Close up aerial view of the 16433 property. Not that the faint red lines designating the boundaries appear to be shifted to the south. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 3. Close up aerial view of the 16451 property. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 4. Excerpt from plot plan showing location of proposed new lots and road improvements for the 16433 parcel. Note the step down grading notation at the west (left) side of the image. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 5. Excerpt from plot plan showing location of proposed new lots and road improvements for the 16451 parcel. Note the stepped grading at the west end of the property. 2017 D. R. STRONG Consulting Engineers Inc. Page 65 Bethany Corner Technical Information Report Renton, Washington SECTION IX BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 1. Bond Quantity Worksheet – is located in Appendix C 2. The Stormwater Facility Summary Sheet is included in this section 2017 D. R. STRONG Consulting Engineers Inc. Page 66 Bethany Corner Technical Information Report Renton, Washington STORMWATER FACILITY SUMMARY SHEET Development Bethany Corner Date April 10, 2017 Location: 16433 & 16451 111th Avenue SE, Renton, Washington ENGINEER DEVELOPER Name Jonathan S. Murray, P.E. Name Mark Seek Firm D. R. STRONG Consulting Engineers, Inc. Firm Address 620 7th Avenue Address… 15233 Manion Way NE Kirkland, WA 98033 Duvall, WA 98019 Phone (425) 827-3063 Phone (425) 919-4062 Developed Site: 1.942 acres Number of lots: 9 Number of detention facilities on site: Number of infiltration facilities on site: ___1__ vaults ______ vaults ______ pond ______ ponds ______ tanks ______ tanks Flow control provided in regional facility (give location)___________________________ No flow control required_____ Exemption number ______________________________ Downstream Drainage Basins Immediate Major Basin Basin Benson Green/Duwamish River Watershed Number & type of water quality facilities on site: biofiltration swale (regular/wet/ or continuous inflow?) ______ sand filter (basic or large?) ______ sand filter, linear (basic or large?) ______ CONTECH Stormfilter __1___ combined detention/WQ vault ______ sand filter vault (basic or large?) ______ combined detention/wetpond ______ stormwater wetland ______ compost filter ______ wetvault (basic or large?) ______ filter strip ______ Wetvault ______ flow dispersion ______ pre-settling pond ______ farm management plan ______ flow-splitter catchbasin ______ landscape management plan ______ oil/water separator (baffle or coalescing plate?) ______ catch basin inserts: Manufacturer____________________________________________ 2017 D. R. STRONG Consulting Engineers Inc. Page 67 Bethany Corner Technical Information Report Renton, Washington ______ pre-settling structure: Manufacturer__________________________________________ DESIGN INFORMATION INDIVIDUAL BASIN Water Quality design flow Water Quality treated volume Drainage basin(s) 1 Onsite area (includes frontage) 1.942 Offsite area 0.0 Type of Storage Facility Detention Vault Live Storage Volume (required) 22,080 Predev Runoff Rate 2-year 0.061 10-year 0.103 100-year 0.176 Developed Runoff Rate 2-year 0.032 (includes bypass) 10-year 0.095 100-year 0.456 Type of Restrictor Size of orifice/restriction No. 1 0.75” Ø 0.00’ No. 2 1.375” Ø 3.23’ No. 3 2017 D. R. STRONG Consulting Engineers Inc. Page 68 Bethany Corner Technical Information Report Renton, Washington SECTION X OPERATIONS AND MAINTENANCE MANUAL The Home Owners Association will be responsible for maintenance of several private catch basins on various lots as depicted on the plans. Maintenance guidelines set forth in the 2009 KCSWDM are included in this section. All other drainage elements are to be publicly maintained. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-5 NO. 3 – DETENTION TANKS AND VAULTS Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Trash and debris Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to County personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Site Grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Trash and debris Any trash and debris accumulated in vault or tank (includes floatables and non-floatables). No trash or debris in vault. Tank or Vault Storage Area Sediment accumulation Accumulated sediment depth exceeds 10% of the diameter of the storage area for ½ length of storage vault or any point depth exceeds 15% of diameter. Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than ½ length of tank. All sediment removed from storage area. Plugged air vent Any blockage of the vent. Tank or vault freely vents. Tank bent out of shape Any part of tank/pipe is bent out of shape more than 10% of its design shape. Tank repaired or replaced to design. Tank Structure Gaps between sections, damaged joints or cracks or tears in wall A gap wider than ½-inch at the joint of any tank sections or any evidence of soil particles entering the tank at a joint or through a wall. No water or soil entering tank through joints or walls. Vault Structure Damage to wall, frame, bottom, and/or top slab Cracks wider than ½-inch, any evidence of soil entering the structure through cracks or qualified inspection personnel determines that the vault is not structurally sound. Vault is sealed and structurally sound. Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Inlet/Outlet Pipes Damaged Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-6 NO. 3 – DETENTION TANKS AND VAULTS Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Cover/lid not in place Cover/lid is missing or only partially in place. Any open manhole requires immediate maintenance. Manhole access covered. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs of lift. Cover/lid can be removed and reinstalled by one maintenance person. Access Manhole Ladder rungs unsafe Missing rungs, misalignment, rust, or cracks. Ladder meets design standards. Allows maintenance person safe access. Damaged or difficult to open Large access doors or plates cannot be opened/removed using normal equipment. Replace or repair access door so it can opened as designed. Gaps, doesn't cover completely Large access doors not flat and/or access opening not completely covered. Doors close flat and covers access opening completely. Large access doors/plate Lifting Rings missing, rusted Lifting rings not capable of lifting weight of door or plate. Lifting rings sufficient to lift or remove door or plate. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-7 NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Trash or debris of more than ½ cubic foot which is located immediately in front of the structure opening or is blocking capacity of the structure by more than 10%. No Trash or debris blocking or potentially blocking entrance to structure. Trash or debris in the structure that exceeds 1/3the depth from the bottom of basin to invert the lowest pipe into or out of the basin. No trash or debris in the structure. Trash and debris Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Sediment Sediment exceeds 60% of the depth from the bottom of the structure to the invert of the lowest pipe into or out of the structure or the bottom of the FROP-T section or is within 6 inches of the invert of the lowest pipe into or out of the structure or the bottom of the FROP-T section. Sump of structure contains no sediment. Corner of frame extends more than ¾ inch past curb face into the street (If applicable). Frame is even with curb. Top slab has holes larger than 2 square inches or cracks wider than ¼ inch. Top slab is free of holes and cracks. Damage to frame and/or top slab Frame not sitting flush on top slab, i.e., separation of more than ¾ inch of the frame from the top slab. Frame is sitting flush on top slab. Cracks wider than ½ inch and longer than 3 feet, any evidence of soil particles entering structure through cracks, or maintenance person judges that structure is unsound. Structure is sealed and structurally sound. Cracks in walls or bottom Cracks wider than ½ inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering structure through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Structure has settled more than 1 inch or has rotated more than 2 inches out of alignment. Basin replaced or repaired to design standards. Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the structure at the joint of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of inlet/outlet pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Structure Ladder rungs missing or unsafe Ladder is unsafe due to missing rungs, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows maintenance person safe access. T section is not securely attached to structure wall and outlet pipe structure should support at least 1,000 lbs of up or down pressure. T section securely attached to wall and outlet pipe. Structure is not in upright position (allow up to 10% from plumb). Structure in correct position. Connections to outlet pipe are not watertight or show signs of deteriorated grout. Connections to outlet pipe are water tight; structure repaired or replaced and works as designed. FROP-T Section Damage Any holes—other than designed holes—in the structure. Structure has no holes other than designed holes. Cleanout Gate Damaged or missing Cleanout gate is missing. Replace cleanout gate. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-8 NO. 4 – CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Cleanout gate is not watertight. Gate is watertight and works as designed. Gate cannot be moved up and down by one maintenance person. Gate moves up and down easily and is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Damaged or missing Control device is not working properly due to missing, out of place, or bent orifice plate. Plate is in place and works as designed. Orifice Plate Obstructions Any trash, debris, sediment, or vegetation blocking the plate. Plate is free of all obstructions and works as designed. Obstructions Any trash or debris blocking (or having the potential of blocking) the overflow pipe. Pipe is free of all obstructions and works as designed. Overflow Pipe Deformed or damaged lip Lip of overflow pipe is bent or deformed. Overflow pipe does not allow overflow at an elevation lower than design Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Inlet/Outlet Pipe Damaged Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and debris Trash and debris that is blocking more than 20% of grate surface. Grate free of trash and debris. footnote to guidelines for disposal Metal Grates (If Applicable) Damaged or missing Grate missing or broken member(s) of the grate. Grate is in place and meets design standards. Cover/lid not in place Cover/lid is missing or only partially in place. Any open structure requires urgent maintenance. Cover/lid protects opening to structure. Locking mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Manhole Cover/Lid Cover/lid difficult to Remove One maintenance person cannot remove cover/lid after applying 80 lbs. of lift. Cover/lid can be removed and reinstalled by one maintenance person. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-9 NO. 5 – CATCH BASINS AND MANHOLES Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Sediment Sediment exceeds 60% of the depth from the bottom of the catch basin to the invert of the lowest pipe into or out of the catch basin or is within 6 inches of the invert of the lowest pipe into or out of the catch basin. Sump of catch basin contains no sediment. Trash or debris of more than ½ cubic foot which is located immediately in front of the catch basin opening or is blocking capacity of the catch basin by more than 10%. No Trash or debris blocking or potentially blocking entrance to catch basin. Trash or debris in the catch basin that exceeds 1/3 the depth from the bottom of basin to invert the lowest pipe into or out of the basin. No trash or debris in the catch basin. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within catch basin. Trash and debris Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Corner of frame extends more than ¾ inch past curb face into the street (If applicable). Frame is even with curb. Top slab has holes larger than 2 square inches or cracks wider than ¼ inch. Top slab is free of holes and cracks. Damage to frame and/or top slab Frame not sitting flush on top slab, i.e., separation of more than ¾ inch of the frame from the top slab. Frame is sitting flush on top slab. Cracks wider than ½ inch and longer than 3 feet, any evidence of soil particles entering catch basin through cracks, or maintenance person judges that catch basin is unsound. Catch basin is sealed and structurally sound. Cracks in walls or bottom Cracks wider than ½ inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Catch basin has settled more than 1 inch or has rotated more than 2 inches out of alignment. Basin replaced or repaired to design standards. Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the catch basin at the joint of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of inlet/outlet pipes. Structure Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Inlet/Outlet Pipe Damaged Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-10 NO. 5 – CATCH BASINS AND MANHOLES Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and debris Trash and debris that is blocking more than 20% of grate surface. Grate free of trash and debris. footnote to guidelines for disposal Metal Grates (Catch Basins) Damaged or missing Grate missing or broken member(s) of the grate. Any open structure requires urgent maintenance. Grate is in place and meets design standards. Cover/lid not in place Cover/lid is missing or only partially in place. Any open structure requires urgent maintenance. Cover/lid protects opening to structure. Locking mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Manhole Cover/Lid Cover/lid difficult to Remove One maintenance person cannot remove cover/lid after applying 80 lbs. of lift. Cover/lid can be removed and reinstalled by one maintenance person. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-11 NO. 6 – CONVEYANCE PIPES AND DITCHES Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Sediment & debris accumulation Accumulated sediment or debris that exceeds 20% of the diameter of the pipe. Water flows freely through pipes. Vegetation/roots Vegetation/roots that reduce free movement of water through pipes. Water flows freely through pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to protective coating or corrosion Protective coating is damaged; rust or corrosion is weakening the structural integrity of any part of pipe. Pipe repaired or replaced. Pipes Damaged Any dent that decreases the cross section area of pipe by more than 20% or is determined to have weakened structural integrity of the pipe. Pipe repaired or replaced. Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 square feet of ditch and slopes. Trash and debris cleared from ditches. Sediment accumulation Accumulated sediment that exceeds 20% of the design depth. Ditch cleaned/flushed of all sediment and debris so that it matches design. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to County personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Vegetation Vegetation that reduces free movement of water through ditches. Water flows freely through ditches. Erosion damage to slopes Any erosion observed on a ditch slope. Slopes are not eroding. Ditches Rock lining out of place or missing (If Applicable) One layer or less of rock exists above native soil area 5 square feet or more, any exposed native soil. Replace rocks to design standards. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-12 NO. 7 – DEBRIS BARRIERS (E.G., TRASH RACKS) Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed. Trash and debris Trash or debris plugging more than 20% of the area of the barrier. Barrier clear to receive capacity flow. Site Sediment accumulation Sediment accumulation of greater than 20% of the area of the barrier Barrier clear to receive capacity flow. Structure Cracked broken or loose Structure which bars attached to is damaged - pipe is loose or cracked or concrete structure is cracked, broken of loose. Structure barrier attached to is sound. Bar spacing Bar spacing exceeds 6 inches. Bars have at most 6 inche spacing. Bars are bent out of shape more than 3 inches. Bars in place with no bends more than ¾ inch. Bars are missing or entire barrier missing. Bars in place according to design. Bars Damaged or missing bars Bars are loose and rust is causing 50% deterioration to any part of barrier. Repair or replace barrier to design standards. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-13 NO. 8 – ENERGY DISSIPATERS Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed. Trash and debris Trash and/or debris accumulation. Dissipater clear of trash and/or debris. Site Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Rock Pad Missing or moved Rock Only one layer of rock exists above native soil in area five square feet or larger or any exposure of native soil. Rock pad prevents erosion. Pipe plugged with sediment Accumulated sediment that exceeds 20% of the design depth. Pipe cleaned/flushed so that it matches design. Not discharging water properly Visual evidence of water discharging at concentrated points along trench (normal condition is a “sheet flow” of water along trench). Water discharges from feature by sheet flow. Perforations plugged. Over 1/4 of perforations in pipe are plugged with debris or sediment. Perforations freely discharge flow. Water flows out top of “distributor” catch basin. Water flows out of distributor catch basin during any storm less than the design storm. No flow discharges from distributor catch basin. Dispersion Trench Receiving area over- saturated Water in receiving area is causing or has potential of causing landslide problems. No danger of landslides. Damaged mesh Mesh of gabion broken, twisted or deformed so structure is weakened or rock may fall out. Mesh is intact, no rock missing. Corrosion Gabion mesh shows corrosion through more than ¼ of its gage. All gabion mesh capable of containing rock and retaining designed form. Collapsed or deformed baskets Gabion basket shape deformed due to any cause. All gabion baskets intact, structure stands as designed. Gabions Missing rock Any rock missing that could cause gabion to loose structural integrity. No rock missing. Worn or damaged post, baffles or side of chamber Structure dissipating flow deteriorates to ½ or original size or any concentrated worn spot exceeding one square foot which would make structure unsound. Structure is in no danger of failing. Damage to wall, frame, bottom, and/or top slab Cracks wider than ½-inch or any evidence of soil entering the structure through cracks, or maintenance inspection personnel determines that the structure is not structurally sound. Manhole/chamber is sealed and structurally sound. Manhole/Chamber Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the structure at the joint of the inlet/outlet pipes. No soil or water enters and no water discharges at the joint of inlet/outlet pipes. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-14 NO. 9 – FENCING Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Site Erosion or holes under fence Erosion or holes more than 4 inches high and 12- 18 inches wide permitting access through an opening under a fence. No access under the fence. Missing or damaged parts Missing or broken boards, post out of plumb by more than 6 inches or cross members broken No gaps on fence due to missing or broken boards, post plumb to within 1½ inches, cross members sound. Weakened by rotting or insects Any part showing structural deterioration due to rotting or insect damage All parts of fence are structurally sound. Wood Posts, Boards and Cross Members Damaged or failed post foundation Concrete or metal attachments deteriorated or unable to support posts. Post foundation capable of supporting posts even in strong wind. Post out of plumb more than 6 inches. Post plumb to within 1½ inches. Top rails bent more than 6 inches. Top rail free of bends greater than 1 inch. Any part of fence (including post, top rails, and fabric) more than 1 foot out of design alignment. Fence is aligned and meets design standards. Damaged parts Missing or loose tension wire. Tension wire in place and holding fabric. Deteriorated paint or protective coating Part or parts that have a rusting or scaling condition that has affected structural adequacy. Structurally adequate posts or parts with a uniform protective coating. Metal Posts, Rails and Fabric Openings in fabric Openings in fabric are such that an 8-inch diameter ball could fit through. Fabric mesh openings within 50% of grid size. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-15 NO. 10 – GATES/BOLLARDS/ACCESS BARRIERS Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Missing gate. Gates in place. Broken or missing hinges such that gate cannot be easily opened and closed by a maintenance person. Hinges intact and lubed. Gate is working freely. Gate is out of plumb more than 6 inches and more than 1 foot out of design alignment. Gate is aligned and vertical. Damaged or missing members Missing stretcher bar, stretcher bands, and ties. Stretcher bar, bands, and ties in place. Locking mechanism does not lock gate Locking device missing, no-functioning or does not link to all parts. Locking mechanism prevents opening of gate. Chain Link Fencing Gate Openings in fabric Openings in fabric are such that an 8-inch diameter ball could fit through. Fabric mesh openings within 50% of grid size. Damaged or missing cross bar Cross bar does not swing open or closed, is missing or is bent to where it does not prevent vehicle access. Cross bar swings fully open and closed and prevents vehicle access. Locking mechanism does not lock gate Locking device missing, no-functioning or does not link to all parts. Locking mechanism prevents opening of gate. Bar Gate Support post damaged Support post does not hold cross bar up. Cross bar held up preventing vehicle access into facility. Damaged or missing Bollard broken, missing, does not fit into support hole or hinge broken or missing. No access for motorized vehicles to get into facility. Bollards Does not lock Locking assembly or lock missing or cannot be attached to lock bollard in place. No access for motorized vehicles to get into facility. Dislodged Boulders not located to prevent motorized vehicle access. No access for motorized vehicles to get into facility. Boulders Circumvented Motorized vehicles going around or between boulders. No access for motorized vehicles to get into facility. APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 1/9/2009 2009 Surface Water Design Manual – Appendix A A-16 NO. 11 – GROUNDS (LANDSCAPING) Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Trash or litter Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to County personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Site Grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Hazard Any tree or limb of a tree identified as having a potential to fall and cause property damage or threaten human life.A hazard tree identified by a qualified arborist must be removed as soon as possible. No hazard trees in facility. Limbs or parts of trees or shrubs that are split or broken which affect more than 25% of the total foliage of the tree or shrub. Trees and shrubs with less than 5% of total foliage with split or broken limbs. Trees or shrubs that have been blown down or knocked over. No blown down vegetation or knocked over vegetation. Trees or shrubs free of injury. Trees and Shrubs Damaged Trees or shrubs which are not adequately supported or are leaning over, causing exposure of the roots. Tree or shrub in place and adequately supported; dead or diseased trees removed. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-17 NO. 12 – ACCESS ROADS Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Trash and debris exceeds 1 cubic foot per 1,000 square feet (i.e., trash and debris would fill up one standards size garbage can). Roadway drivable by maintenance vehicles. Trash and debris Debris which could damage vehicle tires or prohibit use of road. Roadway drivable by maintenance vehicles. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Any obstruction which reduces clearance above road surface to less than 14 feet. Roadway overhead clear to 14 feet high. Site Blocked roadway Any obstruction restricting the access to a 10- to 12 foot width for a distance of more than 12 feet or any point restricting access to less than a 10 foot width. At least 12-foot of width on access road. Erosion, settlement, potholes, soft spots, ruts Any surface defect which hinders or prevents maintenance access. Road drivable by maintenance vehicles. Road Surface Vegetation on road surface Trees or other vegetation prevent access to facility by maintenance vehicles. Maintenance vehicles can access facility. Erosion Erosion within 1 foot of the roadway more than 8 inches wide and 6 inches deep. Shoulder free of erosion and matching the surrounding road. Shoulders and Ditches Weeds and brush Weeds and brush exceed 18 inches in height or hinder maintenance access. Weeds and brush cut to 2 inches in height or cleared in such a way as to allow maintenance access. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Modular Grid Pavement Damaged or missing Access surface compacted because of broken on missing modular block. Access road surface restored so road infiltrates. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-23 NO. 17 – WETVAULT Maintenance Component Defect or Problem Condition When Maintenance is Needed Results Expected When Maintenance is Performed Site Trash and debris Trash and debris accumulated on facility site. Trash and debris removed from facility site. Trash and debris Any trash and debris accumulated in vault (includes floatables and non-floatables). No trash or debris in vault. Sediment accumulation Sediment accumulation in vault bottom exceeds the depth of the sediment zone plus 6 inches. No sediment in vault. Treatment Area Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to wall, frame, bottom, and/or top slab Cracks wider than ½-inch, any evidence of soil entering the structure through cracks, vault does not retain water or qualified inspection personnel determines that the vault is not structurally sound. Vault is sealed and structurally sound. Baffles damaged Baffles corroding, cracking, warping and/or showing signs of failure or baffle cannot be removed. Repair or replace baffles or walls to specifications. Vault Structure Ventilation Ventilation area blocked or plugged. No reduction of ventilation area exists. Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Inlet/Outlet Pipe Damaged Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Inoperable valve Valve will not open and close. Valve opens and closes normally. Gravity Drain Valve won’t seal Valve does not seal completely. Valve completely seals closed. Access cover/lid damaged or difficult to open Access cover/lid cannot be easily opened by one person. Corrosion/deformation of cover/lid. Access cover/lid can be opened by one person. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs of lift. Cover/lid can be removed and reinstalled by one maintenance person. Access doors/plate has gaps, doesn't cover completely Large access doors not flat and/or access opening not completely covered. Doors close flat and covers access opening completely. Lifting Rings missing, rusted Lifting rings not capable of lifting weight of door or plate. Lifting rings sufficient to lift or remove door or plate. Access Manhole Ladder rungs unsafe Missing rungs, misalignment, rust, or cracks. Ladder meets design standards. Allows maintenance person safe access. APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES 2009 Surface Water Design Manual – Appendix A 1/9/2009 A-35 NO. 24 – CATCH BASIN INSERT Maintenance Component Defect or Problem Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Visible Oil Visible oil sheen passing through media Media inset replaced. Insert does not fit catch basin properly Flow gets into catch basin without going through media. All flow goes through media. Filter media plugged Filter media plugged. Flow through filter media is normal. Oil absorbent media saturated Media oil saturated. Oil absorbent media replaced. Water saturated Catch basin insert is saturated with water, which no longer has the capacity to absorb. Insert replaced. Service life exceeded Regular interval replacement due to typical average life of media insert product, typically one month. Media replaced at manufacturer’s recommended interval. Media Insert Seasonal maintenance When storms occur and during the wet season. Remove, clean and replace or install new insert after major storms, monthly during the wet season or at manufacturer’s recommended interval. 2017 D. R. STRONG Consulting Engineers Inc. Page 69 Bethany Corner Technical Information Report Renton, Washington APPENDICES 2017 D. R. STRONG Consulting Engineers Inc. Page 70 Bethany Corner Technical Information Report Renton, Washington APPENDIX “A” LEGAL DESCRIPTION LOT 11, BLOCK 7, AKER'S FARMS NO. 6, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 42 OF PLATS, PAGE 15, RECORDS OF KING COUNTY, WASHINGTON; SITUATE IN THE COUNTY OF KING, STATE OF WASHINGTON. LOT 12, BLOCK 7, AKER'S FARMS NO. 6 ACCORDING TO PLAT RECORDED IN VOLUME 42 OF PLATS, PAGE 15, RECORDS OF KING COUNTY WASHINGTON. SITUATE IN THE COUNTY OF KING, STATE OF WASHINGTON. 2017 D. R. STRONG Consulting Engineers Inc. Page 71 Bethany Corner Technical Information Report Renton, Washington APPENDIX “B” CSWPPP D.R. STRONG Consulting Engineers, Inc. Bethany Corner Stormwater Pollution Prevention Plan Construction Stormwater General Permit Stormwater Pollution Prevention Plan (SWPPP) for Bethany Corner Prepared for: The Washington State Department of Ecology Northwest Regional Office 3190 16th Avenue SE Bellevue, WA 98008-5452 Permittee / Owner Developer Operator / Contractor Mark Seek 15233 Manion Way NE Duvall, WA 98019 TBD TBD 16433 & 16451 111th Avenue SE, Renton, Washington Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number TBD Associated Earth Sciences, Inc 425.827.7701 SWPPP Prepared By Name Organization Contact Phone Number Jonathan S. Murray, PE DR Strong Consulting Engineers, Inc. (425) 827-3063 SWPPP Preparation Date December 15, 2016 Project Construction Dates Activity / Phase Start Date End Date Site Development 4/2017 10/2018 D.R. STRONG Consulting Engineers, Inc. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner Stormwater Pollution Prevention Plan Page 2 1 Project Information Project/Site Name: Bethany Corner Street/Location: 16433 & 16451 111th Avenue SE City: Renton State: WA Zip code: 98055 Subdivision: N/A Receiving waterbody: Green/Duwamish River watershed 1.1 Existing Conditions Total acreage (including support activities such as off-site equipment staging yards, material storage areas, borrow areas). Total acreage: 1.96 Disturbed acreage: 1.96 Existing structures: 0.15 Landscape topography: 1.68 (estimate) Drainage patterns: 0.00 Existing Vegetation: 0.00 (estimate) Critical Areas (wetlands, streams, high erosion risk, steep or difficult to stabilize slopes): 0.01 Stream and adjacent wetland List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: Green River – Dissolved Oxygen, Temperature, Bioassessment, 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 is seeking approval to subdivide 1.83 acres into nine single–family residential lots (Project), with lot sizes ranging from approximately 5,948 s.f. to 7,118 s.f. All existing improvements located on the Site will be demolished or removed during plat construction. The proposed impervious surface includes an internal plat road, Road A, which will have a proposed 53-foot right of way and will be improved with 26 feet of pavement ,vertical curbs, 8’ planter strip and 5’ sidewalks. Frontage improvements will be made to 111th AVE SE, including catch basins, vertical gutter, and 5 foot sidewalk. Lot improvements will include single family residential houses and associated driveways. The total proposed impervious area for the Site is 50,896 s.f. D.R. STRONG Consulting Engineers, Inc. Bethany Corner Stormwater Pollution Prevention Plan Page 3 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. Runoff will be collected and conveyed to the proposed detention vault. 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 Contaminated Site Information: No known contamination exists on Site. Proposed activities regarding contaminated soils or groundwater (example: on-site treatment system, authorized sanitary sewer discharge): Not applicable as no known contamination. D.R. STRONG Consulting Engineers, Inc. Bethany Corner 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. Bethany Corner 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 entrance, located on 111th Avenue SE. Construction road and parking area stabilization will occur along this entrance. 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. Bethany Corner 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. Discharge from the vault will be conveyed south to the existing storm conveyance system located in 111th Avenue SE. 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: Sediment Trap (BMP C240) Installation Schedules: Installation will occur before any grading occurs. Inspection and Maintenance plan: Weekly Responsible Staff: CESCL D.R. STRONG Consulting Engineers, Inc. Bethany Corner 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. 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. Bethany Corner Stormwater Pollution Prevention Plan Page 8 List and describe BMPs: Silt Fence (BMP C233) Interceptor Swale (BMP C200) Storm Drain Inlet Protection (BMP C220) Sediment Trap (BMP C240) 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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: • Storm Drain Inlet Protection (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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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: 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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) Associated Earth Sciences, Inc. 425.827.7701 Resident Engineer Jonathan S. Murray, PE 425-827-3063 Emergency Ecology Contact Howard Zorzi 425-649-7130 Emergency Permittee/ Owner Contact Mark Seek 206-315-8130 Non-Emergency Owner Contact Mark Seek 206-315-8130 Monitoring Personnel Associated Earth Sciences, Inc. 425.827.7701 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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. Bethany Corner 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): Green River - pH 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. Bethany Corner 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. Bethany Corner 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. Alpine Nursery Stormwater Pollution Prevention Plan Page A-1 Appendix A Site Map GRAPHIC SCALE02040 80 1 INCH = 40 FT. BY:Date: RECOMMENDED FOR APPOVAL BY: BY: BY: Date: Date: Date: BY:Date: RECOMMENDED FOR APPOVAL BY: BY: BY: Date: Date: Date: GRAPHIC SCALE 0 15 30 60 1 INCH = 30 FT. BY:Date: RECOMMENDED FOR APPOVAL BY: BY: BY: Date: Date: Date: D.R. STRONG Consulting Engineers, Inc. Alpine Nursery Stormwater Pollution Prevention Plan Page B-1 Appendix B BMP Details D.R. STRONG Consulting Engineers, Inc. Alpine Nursery Stormwater Pollution Prevention Plan Page C-1 Appendix C Correspondence None at this time. D.R. STRONG Consulting Engineers, Inc. Alpine Nursery 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. Alpine Nursery 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. Alpine Nursery 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. Alpine Nursery 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. Alpine Nursery 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. Alpine Nursery 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. Alpine Nursery Stormwater Pollution Prevention Plan Page F-2 Appendix E Construction Stormwater General Permit (CSWGP) D.R. STRONG Consulting Engineers, Inc. Alpine Nursery Stormwater Pollution Prevention Plan Page F-2 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 0.131 2 2/09/01 18:00 0.176 1 100.00 0.990 0.042 7 1/05/02 16:00 0.131 2 25.00 0.960 0.103 3 2/28/03 3:00 0.103 3 10.00 0.900 0.012 8 8/26/04 2:00 0.103 4 5.00 0.800 0.061 6 1/05/05 8:00 0.091 5 3.00 0.667 0.103 4 1/18/06 20:00 0.061 6 2.00 0.500 0.091 5 11/24/06 4:00 0.042 7 1.30 0.231 0.176 1 1/09/08 9:00 0.012 8 1.10 0.091 Computed Peaks 0.161 50.00 0.980 The maximum discharge of the construction stormwater will not exceed 50% of the 2-year predeveloped peak flow rate of 0.061 cfs. Therefore the max discharge from the Site during construction will not exceed 0.0305 cfs. D.R. STRONG Consulting Engineers, Inc. Alpine Nursery Stormwater Pollution Prevention Plan Page F-2 Flow Frequency Analysis Time Series File:rdin_15.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 0.557 6 8/27/01 18:00 1.72 1 100.00 0.990 0.396 8 1/05/02 15:00 1.20 2 25.00 0.960 1.20 2 12/08/02 17:15 0.778 3 10.00 0.900 0.449 7 8/23/04 14:30 0.690 4 5.00 0.800 0.690 4 11/17/04 5:00 0.668 5 3.00 0.667 0.668 5 10/27/05 10:45 0.557 6 2.00 0.500 0.778 3 10/25/06 22:45 0.449 7 1.30 0.231 1.72 1 1/09/08 6:30 0.396 8 1.10 0.091 Computed Peaks 1.55 50.00 0.980 Sediment Trap Facility Sizing The Site will utilize one sediment trap for sediment control. The maximum discharge rate for the site is 0.031 cfs (50% of the 2-year predeveloped peak). The sediment traps will discharge to the collection system on 111th AVE SE. Below is sizing summary: Sediment Trap basin: 1.85 acres 2-year peak flow rate: 0.557 cfs Required Surface Area: 1,159 s.f. Provided Surface Area: 1,700 s.f. 2017 D. R. STRONG Consulting Engineers Inc. Page 72 Bethany Corner Technical Information Report Renton, Washington APPENDIX “C” BOND QUANTITY WORKSHEET