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HomeMy WebLinkAboutRS_TIR_221209_v3 Castro Short Plat SITE ADDRESS: 12727 SE Petrovitsky Rd, Renton, WA 98058 SECTION 28, TOWNSHIP 23 N, RANGE 05 E, W.M. Technical Information Report Prepared For: Alex Castro 110 Aspen Ln S Pacific, WA, 98047 206-478-3045 Date Prepared: January 28, 2019 (Revised November, 2022) Prepared By: Vincent Clifton, EIT Reviewed By: Jim Cook, P.E. Beyler Consulting LLC 5920 100th St. SW, #25 Lakewood, WA 98499 253-984-2900 CONTACT (253) 984-2900 info@beylerconsulting.com beylerconsulting.com CORPORATE OFFICE 5920 100th St. SW, #25 Lakewood, WA 98499 Plan. Design. Manage. CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING Page 2 of 22 Castro Short Plat Table Of Contents I. Technical Information Report ................................................... 3 Section 1 – Project Overview ......................................................... 3 TIR Worksheet ......................................................................... 4 Section 2 – Conditions And Requirements Summary ....................... 12 Section 3 – Off-Site Analysis ........................................................ 13 Section 4 – Flow Control/Water Quality Facility Analysis And Design . 16 Section 5 – Conveyance Systems Analysis And Design .................... 22 Section 6 – Special Reports And Studies ....................................... 22 Section 7 – Other Permits ........................................................... 22 Section 8 – CSWPPP Analysis And Design ...................................... 22 Section 9 – Bonds, Facilities, And Declaration Of Covenant .............. 22 Section 10 – Maintenance & Operations Manual ............................. 22 II. Appendices ............................................................................. 23 Appendix A – Additional Figures Appendix B – CSWPPP Appendix C – Soils Report Appendix D – Bond Quantities Appendix E – WWHM2012 Reports Appendix F – Maintenance & Operations Page 3 of 22 Castro Short Plat I. Technical Information Report Section 1 – Project Overview This project will create a new 3-lot short plat including driveways, utilities, stormwater facilities, and associated grading and landscaping. Frontage improvements will be created for SE Petrovitsky Rd and 128th Ave SE consisting of landscape buffers and sidewalk. The curb radius and ramp at the intersection of the 2 str eets will also be shifted. A half street extension will be done for SE 176th St to connect to a new public access road that will provide access to the short plat. The new access road and SE 176th St will have curb/gutter, landscape buffers, and a sidewalk. The property is located at 12727 SE Petrovitsky Rd, Renton, WA 98058, in the City of Renton, with parcel number 0739000085. The site is 49,389 sf (1.134 ac), has a zoning classification of Rural 4 (R4), and is found within the Residential Low Density comprehensive plan. The lot is partially developed with an existing structure, overgrown dirt driveway, and overhead power. Roughly 50-75% of the site is undisturbed forest, with the remaining areas taken up by the building, dirt road, and pasture. The grades are fairly flat (3%-6%) for most of the mid-section of the property. Steeper slopes exist along the entire west and east property lines. These slopes range from 30%-80%, and typically stretch over only 5’-20’ of horizonal space. The site’s soil is made up of Alderwood gravelly sandy loam. Soos Creek Park is located 30’ south of the property. Stormwater in the predeveloped condition sheet flows southwest about 1,000’ over forest and pasture to Big Soos Creek. The project will add 24,300 sf of new impervious surfaces, and 11,350 sf of new pollution generating surfaces. According to the 2017 City of Renton Surface Water Design Manual (Manual), a Full Drainage Review is needed. Core Requirements #1-9 and Special Requirements #1-6 will be addressed. The project will utilize stormwater BMPs to mitigate runoff generated by new surfaces. The new streets, driveways, and sidewalks will be constructed with permeable pavement. The houses will use downspout infiltration trenches. Cleared and landscaped areas will receive amended soils. The project will meet flow control standards, and the soil treatment exemption for water quality. CITY OF RENTON SURFACE WATER DESIGN MANUAL 2017 City of Renton Surface Water Design Manual 12/12/2016 8-A-1 REFERENCE 8-A TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner _____________________________ Phone ___________________________________ Address __________________________________ _________________________________________ Project Engineer ___________________________ Company _________________________________ Phone ___________________________________ Project Name __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS  Land Use (e.g., Subdivision / Short Subd.)  Building (e.g., M/F / Commercial / SFR)  Grading  Right-of-Way Use  Other _______________________  DFW HPA  COE 404  DOE Dam Safety  FEMA Floodplain  COE Wetlands  Other ________  Shoreline Management  Structural Rockery/Vault/_____  ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (check one): Date (include revision dates): Date of Final:  Full  Targeted  Simplified  Large Project  Directed __________________ __________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final:  Full  Modified  Simplified __________________ __________________ __________________ X X X X X X Alex Castro 206-478-3045 110 Aspen Ln S, Pacific, WA 98047 Jim Cook Beyler Consulting 253-301-4157 Castro Short Plat 23 N 05 E 28 12727 SE Petrovitsky Rd Renton, WA 98058 11/1/19 11/1/19 Page 5 of 22 Castro Short Plat TIR Page 2 REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: _____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS  River/Stream ________________________  Lake ______________________________  Wetlands ____________________________  Closed Depression ____________________  Floodplain ___________________________  Other _______________________________ _______________________________  Steep Slope __________________________  Erosion Hazard _______________________  Landslide Hazard ______________________  Coal Mine Hazard ______________________  Seismic Hazard _______________________  Habitat Protection ______________________  _____________________________________ X X Renton Soos Creek Flow Control, Water Quality Adjacent Page 6 of 22 Castro Short Plat TIR Page 3 REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ On-site BMPs: _______________________________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Alderwood gravelly sandy loam Mostly 2%-10% Steeper Areas 30%-80% Low High Flow Control Duration Standard 2 TBD TBD TBD Sub-Basin 1 - Project Site 1 Page 7 of 22 Castro Short Plat TIR Page 4 REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): _______________ Datum: Flood Protection Facilities Describe: Source Control (commercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-Use Site: Yes / No Treatment BMP: _________________________________ Maintenance Agreement: Yes / No with whom? _____________________________________ Other Drainage Structures Describe: 4 Page 8 of 22 Castro Short Plat TIR Page 5 REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-5 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  Control Pollutants  Protect Existing and Proposed BMPs/Facilities  Maintain Protective BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent BMPs/Facilities, restore operation of BMPs/Facilities as necessary  Flag limits of sensitive areas and open space preservation areas  Other _______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description  Detention  Infiltration  Regional Facility  Shared Facility  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS  Drainage Easement  Covenant  Native Growth Protection Covenant  Tract  Other ____________________________  Cast in Place Vault  Retaining Wall  Rockery > 4′ High  Structural on Steep Slope  Other _______________________________ X X X X X X X X X X X X X X X X Trench, Pavement Trench, Pavement Soil Treatment Right-of-Way Dedication REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-6 Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. ____________________________________________________________________________________ Signed/Date 7/14/2022 Page 9 of 22 Castro Short Plat Figure 1: Vicinity Map Page 10 of 22 Castro Short Plat Figure 2: Site Characteristics #1 Page 11 of 22 Castro Short Plat Figure 3: Site Characteristics #2 Page 12 of 22 Castro Short Plat Section 2 – Conditions And Requirements Summary Projects triggering a Full Drainage Review must meet Core Requirements #1-9 from Section 1.2, and Special Requirements #1-6 from Section 1.3. Core Requirement #1: Discharge at the Natural Location The project will use infiltration BMPs to allow runoff to enter back into the ground. The site will be graded to match the existing topography where possible. All generated runoff will remain on site. Core Requirement #2: Offsite Analysis An offsite analysis and Level 1 downstream analysis can be found in Section 3. Core Requirement #3: Flow Control The site is classified as a Flow Control Duration Standard (Forested Conditions). According to Section 1.2.3 of the Manual, projects that produce 5,000 sf or more of impervious surfaces, 0.75 ac of pervious surfaces, or cause a 0.15 cfs increase in the 100-year peak flows require construction of flow control facilities and/or land use management BMPs . The project will generate more than 5,000 sf of new impervious surfaces, and increase more than 0.15 cfs in 100-year peak flows, so flow control facilities are required. See Section 4.D. for more details on flow control. Core Requirement #4: Conveyance System The storm systems have been designed/analyzed to prevent overtopping, flooding, or erosion to the site and neighboring properties. See Section 5 for more details on conveyance systems. Core Requirement #5: Construction Stormwater Pollution Prevention A Construction Stormwater Pollution Prevention Plan is in Appendix B. Core Requirement #6: Operations and Maintenance An Operations and Maintenance manual is in Appendix F. Core Requirement #7: Financial Guarantees and Liability Before starting construction, a drainage facilities restoration and site stabilization financial guarantee will be posted. This guarantee will be sufficient to cover the cost of corrective work performed on the project. Core Requirement #8: Water Quality The site is classified as a Basic Water Quality Treatment Area. According to Section 1.2.8 of the Manual, projects that produce 5,000 sf or more of pollution-generating impervious surfaces (PGIS) in a threshold discharge area require water quality facilities. The site will include more than 5,000 square feet of PGHS, so treatment facilities are required . The site will meet the Soil Treatment Exemption. The existing soil will be tested to ensure it will provide the necessary basic treatment for the pollution generating surfaces. If it does not meet these requirements, a 6” sand layer will be placed under the permeable pavement. See Section 4.E. for more details on water quality. Core Requirement #9 On-Site BMPs The project is on a lot that is more than 22,000 sf, which gives it a large lot classification. Flow control BMPs must be applied as specified in the requirements list 1.2.9.2.2, or the LID Performance Standard must be achieved. The project will provide onsite flow control BMPs using the list. See Section 4.C. for more details on flow control BMPs. Page 13 of 22 Castro Short Plat Special Requirement #1: Other Adopted Area-Specific Requirements There are no adopted area-specific requirements for the site. Special Requirement #2: Floodplain/Floodway Delineation This site is not within a 100-year floodplain. Special Requirement #3: Flood Protection Facilities This requirement is not applicable. Special Requirement #4: Source Control This requirement is not applicable for residential projects. Special Requirement #5: Oil Control This requirement is not applicable for residential projects. Special Requirement #6: Aquifer Protection Area This site is not within an aquifer protection area. Section 3 – Offsite Analysis Task 1: Study Area Maps King County iMap and City of Renton GIS were reviewed to determine critical areas, drainage problems, basin features, and general information about the site and surrounding areas. See Appendix A for additional Figures for this section. Figure 3: Downstream Analysis Figure 6: Special Flood Areas Figure 7: Basin Condition Figure 8: Drainage Complaints Figure 9: Groundwater Contamination Figure 10: Seismic Hazard Figure 11: Wetlands Task 2: Resource Review Section 2.3.1.1 of the Manual outlines the resource requirements for off -site analysis: • Adopted Basin Plans The property is found in the Soos Creek drainage basin and Duwamish – Green River watershed. The WRIA classification is Duwamish-Green (9). • Floodplain/Floodway (FEMA) Maps Panel 53033C0983F of the Federal Emergency Management Agency maps shows that the site is categorized in Zone X, an area to be outside of the 500-year floodplain. • Other Offsite Analysis Reports in the Sub-Basin No other reports were found. • Sensitive Areas Page 14 of 22 Castro Short Plat The geotechnical report outlines the critical areas found on the site. The potential for future shallow failures of the onsite slopes is moderate to high for the east and west areas. • King County Soils Survey The Geologic Map of King County classifies the soils as Alderwood gravelly sandy loam . See the soils report found in Appendix C for additional soils information. • Wetlands Inventory Maps According to the wetland report, there are no wetlands on site, but there is a wetland associated with Big Soos Creek approximately 165’ southwest of the property. • Clean Water Act Section 303d List of Polluted Waters No polluted waters were found. • City of Renton Erosion and Landslide Maps There are no erosion or landslide hazards on or near the site. Task 3: Field Inspection The upstream and downstream corridor was inspected utilizing available maps. Task 4: Drainage System Description and Problem Descriptions A. Upstream Analysis: The site is situated near the division of 2 drainage basins. This places it at a relative high point for the area. With the slopes going east to west, the site would potentially receive runoff from the neighboring lots to the east. However, 128th Ave SE has frontage improvements including curbs and a storm system, which prevents stormwater from continuing west. There are 3 small lots (totaling about 12,000 sf) at the southeast corner of the site which could contribute runoff. Two of the lots are developed and are likely connected to the existing storm system in 128th Ave SE. The third lot remains vegetated with trees and lawn. B. Downstream Analysis: The following is a discussion of the 0.25 mile downstream corridor from the discharge location of the project. See the list below for a summary of each reach, including form of conveyance, length, and a map of each reach’s location. Reach 0 0’ Runoff flows to the west of the site over vegetation. Reach 1 0’-1,000’ Stormwater flows southwest from the site over forest and wetland into Big Soos Creek . Reach 2 Page 15 of 22 Castro Short Plat 1,000’-1,350’ Runoff flows south down Big Soos Creek for the extend of the ¼ mile analysis. The creek eventually makes its way to Green River in Auburn. Task 5: Mitigation of Existing or Potential Problems The analysis did not produce any observed or documented concerns regarding the downstream system. The mitigation measures as described in Section 4 will not create or exacerbate any existing problems within the downstream drainage corridor. Figure 4: Downstream Analysis Map Page 16 of 22 Castro Short Plat Section 4 – Flow Control And Water Quality Facility Analysis And Design A. Existing Site Hydrology The site is 49,389 sf (1.134 ac) and is largely undeveloped with an existing structure, overgrown dirt driveway, and overhead power. The property is surrounded by developed single-family lots on the north, west, and south, and the undeveloped Soos Creek Park to the south. Average grades between 3%-6% run east to west across the mid-section of the property. Steeper slopes exist along the entire west and east property lines. These slopes range from 30%-80%, and typically stretch over only 5’-20’ of horizonal space. Roughly 50- 75% of the site is undisturbed forest, with the remaining areas taken up by the building, dirt road, and pasture. The Geologic Map of King County shows the site as having Alderwood gravelly sandy loam. Soos Creek Park is located 30’ south of the property; the majority of the area being classified as a wetland. Stormwater in the predeveloped condition sheet flows southwest about 1,000’ over undisturbed forest and pasture to Big Soos Creek. B. Developed Site Hydrology The development for this project will include 3 houses and driveways, a new road and road extension with curb/gutter, and frontage improvements for 2 existing roads . The new roads and frontage improvements will each have new landscape buffers and sidewalks. Roof runoff will be collected in roof drains and piped to infiltration trenches. Road and driveway runoff will infiltrate through the permeable pavement and into the ground . Sidewalks will also be constructed with permeable pavement. Cleared and landscaped areas will have the soils protected/amended. Table 1 – Existing Project Areas Surface Area (sf) Area (ac) Project Area 55,447 1.273 Building 1,655 0.038 Asphalt Driveway 555 0.013 Petrovitsky & 128th Sidewalk 1,724 0.040 Vegetation 51,513 1.183 Total Impervious 3,934 0.090 Total PGIS 555 0.013 Total Pervious 51,513 1.183 Page 17 of 22 Castro Short Plat Table 2 - Developed Project Areas Surface Area (sf) Offsite (ac) Project Area 51,950 1.193 176th & Access Road Pavement 9,970 0.229 176th & Access Road Curb & Gutter 190 0.004 176th & Access Road Sidewalk 1,750 0.040 Petrovitsky & 128th Sidewalk 1,790 0.041 Petrovitsky & 128th Curb 130 0.003 3 Houses (Buildable area) 10,100 0.232 3 Driveways 1,380 0.032 Lawn 16,560 0.380 Total Impervious 25,310 0.581 Total PGIS 11,350 0.261 Total Pervious 16,560 0.380 C. Performance Standards The project is on a lot that is more than 22,000 sf, which gives it a large lot classification. Flow control BMPs must be applied as specified in the requirements list 1.2.9.2.2, or the LID Performance Standard must be achieved. The project will provide onsite flow control BMPs using the list. Large Lot BMP Requirements (List 1.2.9.2.2) 1. The feasibility and applicability of full dispersion as detailed in Appendix C, Section C.2.1 must be evaluated for all target impervious surfaces. If feasible and applicable for any such surface, then full dispersion must be applied to that surface and implemented as part of the proposed project. Typically, full dispersion will be applicable only on the largest sites/lots where there may be enough forest area available within a threshold discharge area to meet the 15% ratio of fully dispersed impervious area to native vegetated surface. 2. Where full dispersion of target impervious roof areas is not feasible or applicable, or will cause flooding or erosion impacts, the feasibility and applicability of full infiltration of roof runoff must be evaluated in accordance with Appendix C, Section C.2.2, or Section 5.2, whichever is applicable based on the type of project. If feasible and applicable, full infiltration of roof runoff must be implemented as part of the proposed project. 3. All target impervious surfaces not mitigated by Requirements 1 and 2 above, must be mitigated to the maximum extent feasible using one or more BMPs from the following list. Use of a given BMP is subject to evaluation of its feasibility and applicability as detailed in Appendix C. Feasible BMPs are required to be implemented. The BMPs listed below may be located anywhere on the site/lot subject to the limitations and design Page 18 of 22 Castro Short Plat specifications for each BMP. These BMPs must be implemented as part of the proposed project. • Full Infiltration per Appendix C, Section C.2.2, or per Section 5.2, whichever is applicable • Limited Infiltration per Appendix C, Section C.2.3, • Bioretention per Appendix C, Section C.2.6, sized as follows: o Inside the UGA (Rainfall region SeaTac 1.0 and less): In till soils, provide bioretention volume based on 0.6 inches of equivalent storage depth; in outwash soils provide bioretention volume based on 0.1 inches of equivalent storage depth, o Inside the UGA (Rainfall regions greater than SeaTac 1.0): In till soils, provide bioretention volume based on 0.8 inches of equivalen t storage depth; in outwash soils, provide bioretention volume based on 0.4 inches of equivalent storage depth, o Outside the UGA: In till soils, provide bioretention volume based on 1.9 inches of equivalent storage depth; in outwash soils provide bioretention volume based on 1.0 inches of equivalent storage depth, • Permeable Pavement per Appendix C, Section C.2.7, 4. All target impervious surfaces not mitigated by Requirements 1,2 and 3 above, must be mitigated to the maximum extent feasible using the Basic Dispersion BMP described below. Use of Basic Dispersion is subject to evaluation of its feasibility and applicability as detailed in Appendix C. Feasible BMPs are required to be implemented. Basic Dispersion BMPs may be located anywhere on the site/lot subject to the limitations and design specifications cited in Appendix C. The BMP must be implemented as part of the proposed project. • Basic Dispersion per Appendix C, Section C.2.4, 5. BMPs must be implemented, at minimum, for impervious area amounts defined as follows. • For projects that will result in an impervious surface coverage on the buildable portion of the site/lot of less than 45%, on-site BMPs must be applied to 50% of target impervious surfaces. • For projects that will result in an impervious surface coverage 45-65% on the buildable portion of the site/lot, on-site BMPs must be applied to 50% of target impervious surfaces reduced by 1.5% for each 1% of impervious surface coverage above 45% (e.g., impervious coverage of 55% results in a requirement of on-site BMPs applied to 35% of target impervious surfaces). • For projects that will result in an impervious surface coverage greater than 65% on the buildable portion of the site/lot, on-site BMPs must be applied to 20% of the target impervious surfaces or to an impervious area equal to at least 10% of the site/lot, whichever is less. The buildable portion of the site/lot is the total area of the site/lot minus any critical areas and minus 200 ft. buffer areas from a steep slope hazard, landslide hazard, or erosion hazard area. If these minimum areas are not mitigated using feasible BMPs from Requirements 1, 2, 3, and 4 above, one or more BMPs from the following list are required to be implemented to achieve compliance. These BMPs must be implemented as part of the proposed project. • Reduced Impervious Surface Credit per Appendix C, Section C.2.9, • Native Growth Retention Credit per Appendix C, Section C.2.10, • Tree Retention Credit per Appendix C, Section C.2.14. 6. The soil moisture holding capacity of new pervious surfaces (target pervious surfaces) must be protected in accordance with the soil amendment BMP as detailed in Appendix C, Section C.2.13. 7. Any proposed connection of roof downspouts to the local drainage system must be via a perforated pipe connection as detailed in Appendix C, Section C.2.11. Page 19 of 22 Castro Short Plat Amended Soils Any areas disturbed during construction, or that will become lawn/landscaping will receive amended soils according to Section C.2.13 of the Manual. The design requirements are listed below. • Soil Retention: Retain, in an undisturbed state, the duff layer and native topsoil to the maximum extent practicable. In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. • Soil Quality: All areas subject to clearing and grading that have not been covered by impervious surface, incorporated into a drainage facility or engineered as structural f ill or slope shall, at project completion, demonstrate the following: 1. A topsoil layer with a minimum organic matter content of 10% dry weight in beds, and 5% organic matter content in turf areas, and a pH from 6.0 to 8.0 or matching the pH of the undisturbed soil. The topsoil layer shall have a minimum depth of eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where feasible. 2. Mulch planting beds with 2 inches of organic material 3. Use compost and other materials that meet these organic content requirements: a) The organic content for “pre-approved” amendment rates can be met only using compost meeting the compost specification for Bioretention (Refer to Section C.2.6) with the exception that the compost may have up to 35% biosolids or manure. The compost must also have an organic matter content of 40% to 65%, and a carbon to nitrogen ratio below 25:1. The carbon to nitrogen ratio may be as high as 35:1 for plantings composed entirely of plants native to the Puget Sound Lowlands region. b) Calculated amendment rates may be met through use of composted material meeting “a)” above; or other organic materials amended to meet the carbon to nitrogen ratio requirements, and not exceeding the limits identified in Table 220- B, Testing Parameters, in WAC 173-350-220. 4. The resulting soil should be conducive to the type of vegetation to be established. • Implementation Options: The soil quality design guidelines listed above can be met by using one of the methods listed below: 1. Leave undisturbed native vegetation and soil, and protect from compaction during construction. 2. Amend existing site topsoil or subsoil either at default “pre-approved” rates, or at custom calculated rates based on tests of the soil and amendment. 3. Stockpile existing topsoil during grading, and replace it p rior to planting. 4. Stockpiled topsoil must also be amended if needed to meet the organic matter or depth requirements, either at a default “pre-approved” rate or at a custom calculated rate. 5. Import topsoil mix of sufficient organic content and depth to meet the requirements. More than one method may be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards, and is not compacted does not need to be amended. Permeable Pavement The roads, driveways, and sidewalks will use the permeable pavement BMP to mitigate stormwater. The pavement was designed using Section C.2.7 of the Manual. The streets will consist of 6” of porous asphalt, 2” of choker course, and 10” of gravel base/reservoir Page 20 of 22 Castro Short Plat course, resulting in a total depth of 18”. The driveways will consist of 6” of pervious concrete and 12” of gravel base/reservoir course, resulting in a total depth of 18”. The sidewalks will consist of 5” of pervious concrete and 6” of gravel base/reservoir course, resulting in a total depth of 11”. A 6” sand layer below the reservoir layer may be necessary for treatment if the existing soils do not meet treatment requirements (see Section 4.E. for details). The sand layer will not be required under the sidewalks. The SE 176th St extension will have a slope of 10%, so check dams will be installed in both the road and sidewalk . The west-east section of the new access road will also require check dams due to the 10% slope. All check dams will be spaced at 4’ on center, and be 9” high for the roads and 6” high for the sidewalk. The heights of the check dams includes a 3” key extended into the subgrade. The permeable pavement areas were modeled in WWHM2012 to ensure they could fully infiltrate 100% of the 100-year storm event. The minimum infiltration rate of 0.3 in/hr was used in the model to be conservative. See below for the permeable pavement information from WWHM and Appendix E for the WWHM report. WWHM Permeable Pavement Information Page 21 of 22 Castro Short Plat Limited Infiltration Trenches The houses are currently preliminary, so roof areas are assumed equal to the building setback for design purposes. The assumed roof runoff will be sent to gravel infiltration trenches. The trenches were designed and sized using Section C.2.3 of the Manual. The site is in rainfall region SeaTac 1.0 or less. The geotechnical engineer determined that for every 1,000 sf of roof area, lot 1 should have 90 ft of trench length and lots 2 and 3 should have 122 ft of trench length. The fill material present on site will be removed before construction which will allow lot 3 to use limited infiltration as well. These length ratios are assuming a 2 ft wide trench. In order to reduce the trench length by 50%, the widths will be increase d to retain the same infiltration area (see below for final lot trench dimensions). The trenches are sized to infiltrate 100% of the stormwater they receive. A sediment control structure will be placed before each trench to provide pre-treatment. Lot 1 Trench: 22’ long, 8’ wide, 2.5’ deep Lot 2 & 3 Trench (Shared): 48’ long, 5’ wide, 2.5’ deep D. Flow Control System The site is classified as a Conservation Flow Control Area (Level 2). According to Section 1.2.3 of the Manual, projects that produce 5,000 sf or more of impervious surfaces, 0.75 ac of pervious surfaces, or cause a 0.15 cfs increase (15-minute time steps) in the 100-year peak flows require construction of flow control facilities and/or land use management BMPs . The project will generate 25,310 sf of new impervious surfaces. To achieve flow control control standard, developed discharge durations shall not exceed predeveloped durations for the range of predeveloped discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow. Also, peak discharge rates shall not exceed predeveloped peak discharge rates for the 2- and 10-year return periods. The predeveloped and developed project areas were modeled in WWHM2012 to compare the flow rates, and were shown to achieve the flow control standard . Landscape that receives the soil amendment BMP can be modeled as pasture. Table 3 – WWHM2012 Input/Output Surface C, Forest, Mod C, Pasture, Mod Impervious, Mod Subtracted From Basin Existing 1.273 ac - - - Developed - 0.652 ac 0.007 ac 0.614 ac Table 4 - Flow Frequency Return Period (15-Minute) Predeveloped Flow (cfs) Developed Flow (cfs) 2-Year 0.0379 0.0266 5-Year 0.0621 0.0461 10-Year 0.0777 0.0623 25-Year 0.0962 0.0867 50-Year 0.1090 0.1079 100-Year 0.1210 0.1318 Page 22 of 22 Castro Short Plat See the WWHM flow frequency report in Appendix E. E. Water Quality System The site is classified as a Basic Water Quality Treatment Area. According to Section 1.2.8 of the Manual, projects that produce more than 5,000 sf of pollution-generating impervious surfaces (PGIS) in a threshold discharge area require water quality facilities. The site will include 11,350 square feet of PGIS, so treatment facilities are required. The site will meet the Soil Treatment Exemption. To achieve this exemption, stormwater must be infiltrated in a facility designed using the Manual, and the native soil needs to meet the groundwater protection criteria. For projects located outside groundwater protection areas, the first 2’ of soil beneath the infiltration facility must have a cation exchange capacity greater than 5 and an organic content of 0.5% or more. The soil also needs an infiltration rate of less than 9 in/hr. If the soil is tested and does not meet this criteria, a 6” sand layer will be placed under the permeable pavement. Section 5 – Conveyance Systems Analysis And Design The only conveyance systems proposed for the project will be the roof drains/pipes for the 4 infiltration trenches. These pipes will have sufficient capacity to handle their tributary runoff. Section 6 – Special Reports And Studies A wetland report was created for the site. Section 7 – Other Permits There are currently no other permits associated with this TIR. Section 8 – CSWPPP Analysis And Design A Construction Stormwater Pollution Prevention Plan is included in Appendix B. Section 9 – Declaration Of Covenant, Facility Summaries, & Bond Quantities Declaration of Covenant: Covenants will be completed at final submittal of this TIR. Bond Quantities: A bond worksheet will be completed at final submittal of this TIR. Section 10 – Operations And Maintenance Manual An Operations and Maintenance manual is included in Appendix F. II. Appendices Appendix A - Additional Figures Figure 6: Special Flood Areas Figure 7: Basin Condition Figure 8: Drainage Complaints Figure 9: Groundwater Contamination Figure 10: Seismic Hazards Figure 11: Wetlands Appendix B - Construction Stormwater Pollution Prevention Plan Castro Short Plat SITE ADDRESS: 12727 SE Petrovitsky Rd, Renton, WA 98058 SECTION 28, TOWNSHIP 23 N, RANGE 05 E, W.M. Construction Stormwater Pollution Prevention Plan Prepared For: Alex Castro 110 Aspen Ln S Pacific, WA, 98047 206-478-3045 Date Prepared: November 1, 2019 Prepared By: Brian Lewis Reviewed By: Jim Cook, P.E. Beyler Consulting LLC 5920 100th St. SW, #25 Lakewood, WA 98499 253-984-2900 CONTACT (253) 984-2900 info@beylerconsulting.com beylerconsulting.com CORPORATE OFFICE 5920 100th St. SW, #25 Lakewood, WA 98499 Plan. Design. Manage. CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING Page 2 of 21 Table Of Contents I. Construction Stormwater Pollution Prevention Plan ................. 3 Section 1 – Project Overview ......................................................... 3 Section 2 – Erosion Control Specialist ............................................. 4 Section 3 – Existing Site Conditions ................................................ 4 Section 4 – Adjacent Areas ............................................................ 4 Section 5 – Critical Areas .............................................................. 4 Section 6 – Soils .......................................................................... 4 Section 7 – Potential Erosion Problems............................................ 4 Section 8 – Construction Stormwater Pollution Prevention Elements ... 5 Section 9 – SWPPS Measures ....................................................... 13 Section 10 – Construction Sequence ............................................. 18 Section 11 – Construction Schedule .............................................. 19 Section 12 – Financial/Ownership Responsibilities .......................... 19 Section 13 – Engineering Calculations ........................................... 19 Page 3 of 19 I. Construction Pollution Prevention Plan Section 1 – Project Overview This project will create a new 3-lot short plat including driveways, utilities, stormwater facilities, and associated grading and landscaping. Frontage improvements will be created for SE Petrovitsky Rd and 128th Ave SE consisting of landscape buffers and sidewalk. The curb radius and ramp at the intersection of the 2 streets will also be shifted. A half street extension will be done for SE 176th St to connect to a new public access road that will provide access to the short plat. The new access road and SE 176th St will have curb/gutter, landscape buffers, and a sidewalk. The property is located at 12727 SE Petrovitsky Rd, Renton, WA 98058, in the City of Renton, with parcel number 0739000085. The site is 49,389 sf (1.134 ac), has a zoning classification of Rural 4 (R4), and is found within the Residential Low Density comprehensive plan. The lot is partially developed with an existing structure, overgrown dirt driveway, and overhead power. Roughly 50-75% of the site is undisturbed forest, with the remaining areas taken up by the building, dirt road, and pasture. The grades are fairly flat (3%-6%) for most of the mid-section of the property. Steeper slopes exist along the entire west and east property lines. These slopes range from 30%-80%, and typically stretch over only 5’-20’ of horizonal space. The site’s soil is made up of Alderwood gravelly sandy loam. Soos Creek Park is located 30’ south of the property. Stormwater in the predeveloped condition sheet flows southwest about 1,000’ over forest and pasture to Big Soos Creek. The project will add 24,300 sf of new impervious surfaces, and 11,350 sf of new pollution generating surfaces. According to the 2022 City of Renton Surface Water Design Manual (Manual), a Full Drainage Review is needed. Core Requirements #1-9 and Special Requirements #1-6 will be addressed. The project will utilize stormwater BMPs to mitigate runoff generated by new surfaces. The new streets, driveways, and sidewalks will be constructed with permeable pavement. The houses will use downspout infiltration trenches. Cleared and landscaped areas will receive amended soils. The project will meet the 0.15 cfs increase exception for flow control, and the soil treatment exemption for water quality. Page 4 of 19 Section 2 – Erosion Control Specialist It will be responsibility of the owner and/or the contractor to regularly inspect and maintain the proposed erosion control BMPs, and will take additional measures, as necessary, to respond to changing site conditions. Should it become necessary, the engineer (or geotechnical engineer) can be made available in providing recommendations for additional erosion measures to the site. Section 3 – Existing Site Conditions The site is 49,389 sf (1.134 ac) and is largely undeveloped with an existing structure, overgrown dirt driveway, and overhead power. The property is surrounded by developed single-family lots on the north, west, and south, and the undeveloped Soos Creek Park to the south. Average grades between 3%-6% run east to west across the mid-section of the property. Steeper slopes exist along the entire west and east property lines. These slopes range from 30%-80%, and typically stretch over only 5’-20’ of horizonal space. Roughly 50- 75% of the site is undisturbed forest, with the remaining areas taken up by the building, dirt road, and pasture. The Geologic Map of King County shows the site as having Alderwood gravelly sandy loam. Soos Creek Park is located 30’ south of the property; the majority of the area being classified as a wetland. Stormwater in the predeveloped condition sheet flows southwest about 1,000’ over undisturbed forest and pasture to Big Soos Creek. Section 4 – Adjacent Areas The site is situated near the division of 2 drainage basins. This places it at a relative high point for the area. With the slopes going east to west, the site would potentially receive runoff from the neighboring lots to the east. However, 128th Ave SE has frontage improvements including curbs and a storm system, which prevents stormwater from continuing west. There are 3 small lots (totaling about 12,000 sf) at the southeast corner of the site which could contribute runoff. Two of the lots are developed and are likely connected to the existing storm system in 128th Ave SE. The third lot remains vegetated with trees and lawn. See Section 3, Task 4 for the full downstream analysis. Section 5 – Critical Areas The site has a low erosion hazard, but was determined to be high at the west and east slopes. There is a wetland located about 165’ southwest of the property. Section 6 – Soils See the geotechnical report in Appendix C. Section 7 – Potential Erosion Problems The site has a high potential for erosion in the west and east slope areas, as mentioned by the geotechnical engineer. The measures listed in this CSWPPP, also suggested by the geotechnical engineer, should prevent the possibility of erosion on the site. Page 5 of 19 Section 8 – Construction Stormwater Pollution Prevention Elements There are 13 categories of erosion and sediment control measures that must be considered for application to the project. Details on each BMP can be found in Appendix D, Section D.2 of the Manual. Element 1: Clearing Limits Prior to any site clearing or grading, those areas that are to remain undisturbed during project construction shall be delineated. At a minimum, clearing limits shall be installed at the edges of all critical area buffers and any other areas required to be left uncleared such as portions of the site subject to clearing limits under KCC 16.82.150, areas around significant trees identified to be retained, flow control BMP areas to be protected, and other areas identified to be left undisturbed to protect sensitive features. Purpose: The purpose of clearing limits is to prevent disturbance of those areas of the project site that are not designated for clearing or grading. This is important because limiting site disturbance is the single most effective method for reducing erosion. Clearing limits may also be used to control construction traffic, thus reducing the disturbance of soil and limiting the amount of sediment tracked off site. When to Install: Clearing limits shall be installed prior to the clearing and/or grading of the site. Measures to Use: Marking clearing limits by delineating the site with a continuous length of brightly colored survey tape is sometimes sufficient. The tape may be supported by vegetation or stakes, and it shall be 3 to 6 feet high and highly visible. Critical areas and their buffers require more substantial protection and shall be delineated with plastic or metal safety fences or stake and wire fences. Fencing may be required at the County's discretion to control construction traffic or at any location where greater protection is warranted. Permanent fencing may also be used if desired by the applicant. Silt fence, in combination with survey flagging, is also an acceptable method of marking critical areas and their buffers. ESC Measures: D.2.1.1.1 Plastic or Metal Covering Element 2: Cover Measures Temporary and permanent cover measures shall be provided to protect all disturbed areas, including the faces of cut and fill slopes. Temporary cover shall be installed if an area is to remain unworked for more than seven days during the dry season (May 1 to September 30) or for more than two consecutive working days during the wet season (October 1 to April 30). These time limits may be relaxed if an area poses a low risk of erosion due to soil type, slope gradient, anticipated weather conditions, or other factors. Conversely, the County may reduce these time limits if site conditions warrant greater protection (e.g., adjacent to significant aquatic resources or highly erosive soils) or if significant precipitation (see Section D.2.4.2) is expected. Any area to remain unworked for more than 30 days shall be seeded or sodded, unless the County determines that winter weather makes vegetation establishment infeasible. During the wet season, slopes and stockpiles at 3H:1V or steeper and with more than ten feet of vertical relief shall be covered if they are to remain unworked for more than 12 hours. Also during the wet season, the material necessary to cover all disturbed areas must be stockpiled Page 6 of 19 on site. The intent of these cover requirements is to have as much area as possible covered during any period of precipitation. Purpose: The purpose of covering exposed soils is to prevent erosion, thus reducing reliance on less effective methods that remove sediment after it is entrained in runoff. Cover is the only practical method of reducing turbidity in runoff. Structural measures, such as silt fences and sediment ponds, are only capable of removing coarse particles and, in most circumstances, have little to no effect on turbidity. When to Install: Any exposed soils that will remain unworked for more than the time limit set above shall be covered by the end of the working day. If the exposed area is to remain unworked for more than 30 days, the area shall be seeded with the temporary seed mix or an equivalent mix that will provide rapid protection (see Section D.2.1.2.6). If the disturbed area is to remain unworked for a year or more or if the area has reached final grade, permanent seed mix or an equivalent mix shall be applied. Measures to Use: Cover methods include the use of surface roughening, mulch, erosion control nets and blankets, plastic covering, seeding, and sodding. Mulch and plastic sheeting are primarily intended to protect disturbed areas for a short period of time, typically days to a few months. Seeding and sodding are measures for areas that are to remain unworked for months. Erosion nets and blankets are to be used in conjunction with seeding steep slopes. The choice of measures is left to the designer; however, there are restrictions on the use of these methods, which are listed in the "Conditions of Use" and the "Design and Installation Specifications" sections for each measure. The methods listed are by no means exhaustive. Variations on the standards presented here are encouraged if other cost-effective products or methods provide substantially equivalent or superior performance. Also, the details of installation can, and should, vary with the site conditions. A useful reference on the application of cover measures in the Puget Sound area is Improving the Cost Effectiveness of Highway Construction Site Erosion and Pollution Control, Horner, Guedry, and Kortenhof (1990). ESC Measures: D.2.1.2.2 Mulching D.2.1.2.4 Plastic Covering D.2.1.2.6 Temporary and Permanent Seeding D.2.1.2.7 Sodding Element 3: Perimeter Protection Perimeter protection to filter sediment from sheetwash shall be located downslope of all disturbed areas and shall be installed prior to upslope grading. Perimeter protection includes the use of vegetated strips as well as, constructed measures, such as silt fences, fiber rolls, sand/gravel barriers, brush or rock filters, triangular silt dikes and other methods. During the wet season, 50 linear feet of silt fence (and the necessary stakes) per acre of disturbed area must be stockpiled on site. Purpose: The purpose of perimeter protection is to reduce the amount of sediment transported beyond the disturbed areas of the construction site. Perimeter protection is primarily a backup means of sediment control. Most, if not all, sediment-laden water is to be treated in a sediment trap or pond. The only circumstances in which perimeter control is to be used as a primary means of sediment removal is when the catchment is very small (see below). Page 7 of 19 When to Install: Perimeter protection is to be installed prior to any upslope clearing and grading. Measures to Use: The above measures may be used interchangeably and are not the only perimeter protection measures available. If surface water is collected by an interceptor dike or swale and routed to a sediment pond or trap, there may be no need for the perimeter protection measures specified in this section. Criteria for Use as Primary Treatment: At the boundary of a site, perimeter protection may be used as the sole form of treatment when the flowpath meets the criteria listed below. If these criteria are not met, perimeter protection shall only be used as a backup to a sediment trap or pond. Average Slope Slope Percent Flowpath Length 1.5H:1V or less 67% or less 100 feet 2H:1V or less 50% or less 115 feet 4H:1V or less 25% or less 150 feet 6H:1V or less 16.7% or less 200 feet 10H:1V or less 10% or less 250 feet ESC Measures: D.2.1.3.1 Silt Fence Element 4: Traffic Area Stabilization Unsurfaced entrances, roads, and parking areas used by construction traffic shall be stabilized to minimize erosion and tracking of sediment off site. Stabilized construction entrances shall be installed as the first step in clearing and grading. At the County's discretion, road and parking area stabilization is not required during the dry season (unless dust is a concern) or if the site is underlain by coarse-grained soils. Roads and parking areas shall be stabilized immediately after initial grading. Purpose: The purpose of traffic area stabilization is to reduce the amount of sediment transported off site by construction vehicles and to reduce the erosion of areas disturbed by vehicle traffic. Sediment transported off site onto paved streets is a significant problem because it is difficult to effectively remove, and any sediment not removed ends up in the drainage system. Additionally, sediment on public right-of-way can pose a serious traffic hazard. Construction road and parking area stabilization is important because the combination of wet soil and heavy equipment traffic typically forms a slurry of easily erodible mud. Finally, stabilization also is an excellent form of dust control in the summer months. When to Install: The construction entrance is to be installed as the first step in clearing and grading. Construction road stabilization shall occur immediately after initial grading of the construction roads and parking areas. Measures to Use: There are two types of traffic area stabilization: (1) a stabilized construction entrance and (2) construction road/parking area stabilization. Both measures must be used as specified under "Conditions of Use" for each measure. ESC Measures: D.2.1.4.1 Stabilized Construction Entrance Page 8 of 19 Element 5: Sediment Retention Surface water collected from disturbed areas of the site shall be routed through a sediment pond or trap prior to release from the site. An exception is for areas at the perimeter of the site with drainage areas small enough to be treated solely with perimeter protection (see Section D.2.1.3, p. D-33). Also, if the soils and topography are such that no offsite discharge of surface water is anticipated up to and including the developed 2-year runoff event, sediment ponds and traps are not required. A 10-year peak flow using the approved model with 15-minute time steps shall be used for sediment pond/trap sizing if the project size, expected timing and duration of construction, or downstream conditions warrant a higher level of protection (see below). At the County's discretion, sites may be worked during the dry season without sediment ponds and traps if there is some other form of protection of surface waters, such as a 100-foot forested buffer between the disturbed areas and adjacent surface waters. For small sites, use the criteria defined in Section D.2.1.3, Perimeter Protection to determine minimum flow path length. If the site work has to be extended into the wet season, a back-up plan must be identified in the CSWPP plan and implemented. Protection of catch basins is required for inlets that are likely to be impacted by sediment generated by the project and that do not drain to an onsite sediment pond or trap. Sediment retention facilities shall be installed prior to grading of any contributing area and shall be located so as to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages. Purpose: The purpose of sediment retention facilities is to remove sediment from runoff generated from disturbed areas. The site should not require any BMPs from this Element as the perimeter protection will be sufficient for the project. ESC Measures: D.2.1.3.1 Silt Fence Element 6: Surface Water Collection All surface water from disturbed areas shall be intercepted, conveyed to a sediment pond or trap, and discharged downslope of any disturbed areas. An exception is for areas at the perimeter of the site with drainage areas small enough to be treated solely with perimeter protection (see Section D.2.1.3). Also, if the soils and topography are such that no offsite discharge of surface water is anticipated up to and including the developed 2-year runoff event, surface water controls are not required. A 10-year approved model 15-minute peak flow shall be used for sizing surface water controls if the project size, expected timing and duration of construction, or downstream conditions warrant a higher level of protection (see the introduction to Section D.2.1.5). At the County's discretion, sites may be worked during the dry season without surface water controls, if there is some other form of protection of surface waters, such as a 100-foot forested buffer between the disturbed areas and adjacent surface waters. Significant sources of upslope surface water that drain onto disturbed areas shall be intercepted and conveyed to a stabilized discharge point downslope of the disturbed areas. Surface water controls shall be installed concurrently with rough grading. Purpose: The purpose of surface water control is to collect and convey surface water so that erosion is minimized, and runoff from disturbed areas is treated by a sediment pond or trap. Surface water control essentially consists of three elements: Page 9 of 19 1. Interception of runoff on and above slopes 2. Conveyance of the runoff to a sediment pond or trap (if the runoff was collected from a disturbed area) 3. Release of the runoff downslope of any disturbed areas. The site should not require any BMPs from this Element as the perimeter protection will be sufficient for the project. ESC Measures: D.2.1.3.1 Silt Fence Element 7: Dewatering Control Any runoff generated by dewatering shall be treated through construction of a sediment trap (Section D.2.1.5.1) when there is sufficient space or by releasing the water to a well vegetated, gently sloping area. Since pumps are used for dewatering, it may be possible to pump the sediment-laden water well away from the surface water so that vegetation can be more effectively utilized for treatment. Discharge of sediment-laden water from dewatering activities to surface and storm waters is prohibited. If dewatering occurs from areas where the water has come in contact with new concrete, such as tanks, vaults, or foundations, the pH of the water must be monitored and must be neutralized prior to discharge. Clean non- turbid dewatering water, such as well point ground water can be discharged to systems tributary to, or directly to surface waters provided the flows are controlled so no erosion or flooding occurs. Clean water must not be routed through a stormwater sediment pond. Highly turbid or contaminated dewatering water must be handled separately from stormwater. Purpose: To prevent the untreated discharge of sediment-laden water from dewatering of utilities, excavated areas, foundations, etc. The project will not require dewatering control. Element 8: Dust Control Preventative measures to minimize the wind transport of soil shall be taken when a traffic hazard may be created or when sediment transported by wind is likely to be deposited in water resources or adjacent properties. Purpose: To prevent wind transport of dust from exposed soil surfaces onto roadways, drainage ways, and surface waters. When to Install: Dust control shall be implemented when exposed soils are dry to the point that wind transport is possible and roadways, drainage ways, or surface waters are likely to be impacted. Dust control measures may consist of chemical, structural, or mechanical methods. Measures to Install: Water is the most common dust control (or palliative) used in the area. When using water for dust control, the exposed soils shall be sprayed until wet, but runoff shall not be generated by spraying. Calcium chloride, Magnesium chloride, Lignin derivatives, Tree Resin Emulsions, and Synthetic Polymer Emulsions may also be used for dust control. Exposed areas shall be re-sprayed as needed. Oil shall not be used for dust control. The following table lists many common dust control measures. Some of the Page 10 of 19 measures are not recommended for use in King County and must have prior approval prior to use from the DPER inspector assigned to specific projects. Element 9: Flow Control Surface water from disturbed areas must be routed through the project's onsite flow control facility or other provisions must made to prevent increases in the existing site conditions 2- year and 10-year runoff peaks discharging from the project site during construction. Purpose: The purpose of surface water flow control is to mitigate increases in runoff peaks that occur during construction as a result of clearing vegetation, compacting the soil, and adding impervious surface. Such increases can cause or aggravate downstream flooding and erosion. When to Install: Surface water flow control shall be installed or otherwise provided prior to any clearing and/or grading of the site, except that required to construct the surface water flow control facilities. Measures to Use: The project's onsite flow control facility or other equivalent storage facility that meets the peak-matching performance criteria stated above. Element 10: Protect Existing and Proposed Flow Control BMPs Protection measures shall be applied/installed and maintained so as to prevent adverse impacts to existing flow control BMPs and areas of proposed flow control BMPs for the project. Adverse impacts can prompt the requirement to restore or replace affected BMPs. Purpose: The purpose of protecting existing and proposed flow control BMP areas is to avoid sedimentation and soil compaction that would adversely affect infiltration, and also avoid contamination by other pollutants. When to Install: Flow control BMP area protection shall be installed or otherwise provided prior to any clearing and/or grading of the site, except that required to construct flow control BMPs. Measures to Use: 1. Protect all flow control BMPs and proposed BMP footprints from sedimentation through installation and maintenance of erosion and sediment control BMPs on portions of the site that drain into the flow control BMPs. 2. BMPs shall be restored to their fully functioning condition if they accumulate sediment during construction. Restoring the BMP shall include, at a minimum, removal of sediment and any sediment-laden bioretention soils, and replacing the removed soils with soils meeting the design specification. Replacement with a new fully-functioning BMP may be required if restoration to the fully-functioning condition can’t be accomplished. 3. Prevent compacting Bioretention BMPs by excluding construction equipment and foot traffic. Protect completed lawn and landscaped areas from compaction due to construction equipment. 4. Control erosion and avoid introducing sediment from surrounding land uses onto permeable pavements. Do not allow muddy construction equipment on the base material or pavement. Do not allow sediment-laden runoff onto permeable pavements. Page 11 of 19 5. Pavements fouled with sediments or no longer passing an initial infiltration text must be cleaned using procedures from the local stormwater manual or the manufacturer’s procedures. 6. Keep all heavy equipment off existing soils under flow control BMPs that have been excavated to final grade to retain the infiltration rate of the soils. Additional Guidance See Chapter 5: Precision Site Preparation and Construction in the LID Technical Guidance Manual for Puget Sound for more detail on protecting LID integrated management practices. Note that the LID Technical Guidance Manual for Puget Sound (2012) is for additional informational purposes only. The guidance within this manual must be followed if there are any discrepancies between this manual and the LID Technical Guidance Manual for Puget Sound (2012). Element 11: Maintain Protective BMPs Protection measures shall be maintained to assure continued performance of their intended function, to prevent adverse impacts to existing flow control BMPs and areas of proposed flow control BMPs, and protect other disturbed areas of the project. Purpose: The purpose of maintaining protective BMPs is to provide continuous erosion and sediment control protection throughout the life of the project, and avoid sedimentation, soil compaction and contamination by other pollutants that would adversely affect infiltration and surface runoff. When to Maintain: Protection measures shall be monitored per Section D.2.4.4 at a minimum, and promptly maintained to fully functioning condition as necessary to assure continued performance of their intended function. Measures to Use: 1. Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. 2. Remove all temporary erosion and sediment control BMPs prior to final construction approval, or within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. 3. Provide protection to all BMPs installed for the permanent control of stormwater from sediment and compaction. All BMPs that are to remain in place following completion of construction shall be examined and placed in full operating conditions. If sediment enters the BMPs during construction, it shall be removed and the BMP shall be returned to the conditions specified in the construction documents or as required for full BMP replacement. 4. Remove or stabilize trapped sediment on site. Permanently stabilize disturbed soil resulting from removal of BMPs or vegetation. Element 12: Manage the Project Coordination and timing of site development activities relative to ESC concerns (Section D.2.4), and timely inspection, maintenance and update of protective measures (Section D.2.3) are necessary to effectively manage the project and assure the success of protective ESC and SWPPS design and implementation. Projects shall assign a qualified CSWPP Page 12 of 19 Supervisor (Section D.2.3.1) to be the primary contact for ESC and SWPPP issues and reporting, coordination with subcontractors and implementation of the CSWPP plan as a whole. Measures to Use: 1. Phase development projects to the maximum degree practicable and take into account seasonal work limits. 2. Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit and King County requirements. 3. Maintaining an updated construction SWPPP – Maintain, update, and implement the SWPPP in accordance with the Construction Stormwater General Permit and King County requirements. 4. Projects that disturb one or more acres must have, site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL) (see Section D.2.3.1). Project sites less than one acre (not part of a larger common plan of development or sale) may have a person without CESCL certification conduct inspections. By the initiation of construction, the SWPPP must identify the CESCL or inspector, who shall be present on-site or on-call at all times. The CESCL or inspector (project sites less than one acre) must have the skills to assess the:  Site conditions and construction activities that could impact the quality of stormwater.  Effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges.  The CESCL or inspector must examine stormwater visually for the presence of suspended sediment, turbidity, discoloration, and oil sheen. They must evaluate the effectiveness of BMPs and determine if it is necessary to install, maintain, or repair BMPs to improve the quality of stormwater discharges. Based on the results of the inspection, construction site operators must correct the problems identified by:  Reviewing the SWPPP for compliance with all construction SWPPP elements and making appropriate revisions within 7 days of the inspection.  Immediately beginning the process of fully implementing and maintaining appropriate source control and/or treatment BMPs as soon as possible, addressing the problems not later than within 10 days of the inspection. If installation of necessary treatment BMPs is not feasible within 10 days, the construction site operator may request an extension within the initial 10-day response period.  Documenting BMP implementation and maintenance in the site log book (applies only to sites that have coverage under the Construction Stormwater General Permit).  The CESCL or inspector must inspect all areas disturbed by construction activities, all BMPs, and all stormwater discharge points at least once every calendar week and within 24 hours of any discharge from the site. (For purposes of this condition, individual discharge events that last more than one day do not require daily inspections. For example, if a stormwater pond discharges continuously over the course of a week, only one inspection is required that week.) The CESCL or inspector may reduce the inspection frequency for temporary stabilized, inactive sites to once every calendar month. Page 13 of 19 Section 9 – SWPPS Measures Concrete Handling Purpose: Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete process water, and concrete slurry from entering waters of the state. Conditions of Use: Any time concrete is used, utilize these management practices. Concrete construction projects include, but are not limited to, curbs, sidewalks, roads, bridges, foundations, floors, stormwater vaults, retaining walls, driveways and runways. Concrete Washout Area Purpose: Prevent or reduce the discharge of pollutants to stormwater from concrete waste by conducting washout off-site, or performing on-site washout in a designated area to prevent pollutants from entering surface waters or ground water. Conditions of Use: Concrete washout area best management practices are implemented on construction projects where:  Concrete is used as a construction material  It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant, etc.).  Concrete trucks, pumpers, or other concrete coated equipment are washed on-site. Note: If less than 10 concrete trucks or pumpers need to be washed out on-site, the washwater may be disposed of in a formed area awaiting concrete or an upland disposal site where it will not contaminate surface or ground water. The upland disposal site shall be at least 50 feet from sensitive areas such as storm drains, open ditches, or water bodies, including wetlands. Sawcutting and Surfacing Pollution Prevention Purpose: Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State. Conditions of Use: Utilize these management practices anytime sawcutting or surfacing operations take place. Sawcutting and surfacing operations include, but are not limited to, sawing, coring, grinding, roughening, hydrodemolition, bridge and road surfacing Material Delivery, Storage and Containment Purpose: Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a designated area, and install secondary containment. Page 14 of 19 Conditions of Use: These procedures are suitable for use at all construction sites with delivery and storage of the following materials:  Petroleum products such as fuel, oil and grease  Soil stabilizers and binders (e.g. Polyacrylamide)  Fertilizers, pesticides and herbicides  Detergents  Asphalt and concrete compounds  Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds  Any other material that may be detrimental if released to the environment Construction Stormwater Chemical Treatment Purpose: This BMP applies when using stormwater chemicals in batch treatment or flow- through treatment. Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a construction site. Sedimentation ponds are effective at removing larger particulate matter by gravity settling, but are ineffective at removing smaller particulates such as clay and fine silt. Traditional erosion and sediment control BMPs may not be adequate to ensure compliance with the water quality standards for turbidity in receiving water. Chemical treatment can reliably provide exceptional reductions of turbidity and associated pollutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when construction is to proceed through the wet season. Conditions of Use: Formal written approval from Ecology is required for the use of chemical treatment regardless of site size. Accordingly, the requirements herein reflect Ecology’s review and approval process, including references to the Stormwater Management Manual for Western Washington (SMMWW). The Local Permitting Authority may also require review and approval. When approved, the chemical treatment systems must be included in the SWPPS portion of the project’s Construction Stormwater Pollution Prevention plan (CSWPP). Construction Stormwater Filtration Purpose: Filtration removes sediment from runoff originating from disturbed areas of the site. Background Information: Filtration with sand media has been used for over a century to treat water and wastewater. The use of sand filtration for treatment of stormwater has developed recently, generally to treat runoff from streets, parking lots, and residential areas. The application of filtration to construction stormwater treatment is currently under development. Conditions of Use: Traditional BMPs used to control soil erosion and sediment loss from sites under development may not be adequate to ensure compliance with the water quality standard for turbidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5 μm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the stormwater. In some circumstances, sedimentation and filtration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treatment chemicals are not used. Filtration in conjunction with polymer treatment requires testing under the Chemical Technology Assessment Protocol – Ecology (CTAPE) before it can be initiated. Approval from the appropriate regional Page 15 of 19 Ecology office must be obtained at each site where polymers use is proposed prior to use. For more guidance on stormwater chemical treatment see BMP D.2.2.5. High pH Neutralization Using CO2 Purpose: When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5, this process is called pH neutralization. pH neutralization involves the use of solid or compressed carbon dioxide gas in water requiring neutralization. Neutralized stormwater may be discharged to surface waters under the General Construction NPDES permit. Neutralized process water such as concrete truck wash-out, hydro-demolition, or saw-cutting slurry must be managed to prevent discharge to surface waters. Any stormwater contaminated during concrete work is considered process wastewater and must not be discharged to surface waters. Reason for pH Neutralization: A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this neutral pH is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Calcium hardness can contribute to high pH values and cause toxicity that is associated with high pH conditions. A high level of calcium hardness in waters of the state is not allowed. The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Ground water standard for calcium and other dissolved solids in Washington State is less than 500 mg/l. Conditions of Use: Causes of High pH: High pH at construction sites is most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP D.2.2.1, Concrete Handling for more information on concrete handling procedures). The principal caustic agent in cement is calcium hydroxide (free lime). Advantages of CO2 Sparging:  Rapidly neutralizes high pH water.  Cost effective and safer to handle than acid compounds.  CO2 is self-buffering. It is difficult to overdose and create harmfully low pH levels.  Material is readily available. The Chemical Process: When carbon dioxide (CO2) is added to water (H2O), carbonic acid (H2CO3) is formed which can further dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reaction as well. The colder the water temperature is the slower the reaction occurs and the warmer the water temperature is the quicker the reaction occurs. Most construction applications in Washington State have water temperatures in the 50°F or higher range so the reaction is almost simultaneous. pH Control for High pH Water Purpose: When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5, this process is called pH neutralization. Page 16 of 19 Stormwater with pH levels exceeding water quality standards may be treated by infiltration, dispersion in vegetation or compost, pumping to a sanitary sewer, disposal at a permitted concrete batch plant with pH neutralization capabilities, or carbon dioxide sparging. BMP D.2.2.7, High pH Neutralization Using CO2 gives guidelines for carbon dioxide sparging. Reason for pH Neutralization: A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this pH range is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Conditions of Use: Causes of High pH: High pH levels at construction sites are most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP D.2.2.1, Concrete Handling for more information on concrete handling procedures). The principal caustic agent in cement is calcium hydroxide (free lime). Use of High pH Soil Amendments on Construction Sites The use of soil amendments (including cement treated base (CTB) and cement kiln dust (CKD)) on development sites must be approved by King County. The approval process is described in "Processing Requirements for Use of Soil Amendments on Construction Sites" below. Use of Soil Amendments: It is sometimes a construction practice to add soil amendments to the surfaces of some construction areas in order to stabilize the ground for building. This practice includes placing an additive on the ground then mixing with the soil to a specified depth and finally compacting the mix. When mixed with the soil, the moisture in the ground may allow these additives to create a chemical reaction that cures similar to concrete and may absorb excessive moisture to allow soils to be compacted. The end result is a stable site for constructing a road or building pad. Because soil amendments may be rich in lime content and other material, water runoff from these areas can be affected. If not controlled and treated, this could result in a degradation of water quality and natural drainage systems. Because these additives come in a fine powder form, the actual application can create fugitive dust. When mixed with water, some additives can become corrosive. Definitions: The following are definitions of soil amendment products that are allowed for use under these procedures: 1. Cement Kiln Dust (CKD) is a by-product in the manufacturing of cement9. 2. Cement Treated Base (CTB) utilizes Portland Cement Type II as the soil additive. CTB/CKD Soil Amendment BMPs: Table D.2.2.9.A on the following pages lists twelve BMP categories of action and specific BMPs for each category to be applied when proposing CTB/CKD soil amendments or using soil amendments onsite. Note: Additional BMPs may be required to prevent adverse impacts to the public and/or the environment. It is the responsibility of the permit holder to remain in compliance with all other applicable local, state, and federal regulations. Purpose: This section establishes procedures for implementing BMPs when using high pH soil amendments on construction sites. See Table D.2.2.9.A for a description of the BMPs. This section outlines an expedited review process and typical approval conditions that will Page 17 of 19 allow contractors and builders to use soil amendments without impacting water quality. Additional BMPs may be required based upon site specific conditions that may warrant more protection. This policy is limited to those amendments, defined below, commonly known to add stability to sloppy soil conditions but which can alter water runoff quality. 10 Excerpted from the King County Stormwater Pollution Prevention Manual (SPPM), BMP Info Sheet #11 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-103 SECTION D.2.2 SWPPS MEASURES Authority: KCC 9.12.025 prohibits discharges of polluted or contaminated water into surface or storm water drainage systems. The purpose of this statute is to protect surface and ground water by regulating the discharge of potentially contaminated surface water. If soil amendments are proposed with an initial application, an environmental review is required, under SEPA, which assesses impacts, provides public input and mitigated conditions for its use. King County Road Design and Construction Standards, Sections 4.04 and 4.05 also require an engineered design for use of a soil amendment on road surfaces or around drainage systems. The design may incorporate a thorough assessment of soil composition and laboratory analysis. The Surface Water Design Manual authorizes DPER to adopt BMPs for the control and protection of surface water. Currently, for all sites, the BMPs established in this policy are the minimum standards that shall be applied. Maintain Protective BMPs Pollutant protection measures shall be maintained to assure continued performance of their intended function. Reporting and documentation shall be kept current and made available to DPER as indicated. Purpose: The purpose of maintaining protective BMPs is to provide effective pollutant protection when and where required by the plan and the project, and to provide timely and relevant project information. When to Maintain: Protection measures shall be monitored per Section D.2.4.4 at a minimum, continuously during operation, and promptly maintained to fully functioning condition as necessary to assure continued performance of their intended function. Documentation shall be kept current per specific BMP requirements. Measures to Use: 1. Maintain and repair all pollutant control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. 2. Maintain and repair storage locations for equipment and materials associated with BMP processes. Conduct materials disposal in compliance with County regulatory requirements. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-106 D.2.2.11 MANAGE THE PROJECT 3. As required, provide current reporting and performance documentation at an accessible location for the site inspector and other DPER staff. 4. Remove all temporary pollutant control BMPs prior to final construction approval, or within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. Page 18 of 19 Manage the Project SWPPP requirements shall be implemented and managed as part of the overall CSWPP plan. Concrete construction and its impacts are primary among pollutant concerns on site development projects. Fueling operations and materials containment of treatment chemicals and other project materials are also typical pollutant concerns. Operations that produce these and other pollutants are often conducted by subcontractors and their laborers, yet may require specific protective measures, documentation and reporting. Protective measures and BMPs need to be made available prior to construction and suitable oversight provided to assure inspection, monitoring and documentation requirements are met. Projects shall assign a qualified CSWPP Supervisor (Section D.2.3.1) to be the primary contact for SWPPP and ESC issues and reporting, coordination with subcontractors and implementation of the CSWPP plan as a whole. Measures to Use: 1. Phase development projects to the maximum degree practicable and take into account seasonal work limits. 2. Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit and King County requirements. Coordinate with subcontractors and laborers to assure the SWPPP measures are followed. 3. Documentation and reporting: – Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Document site inspections and monitoring in accordance with the Construction Stormwater General Permit, specific BMP conditions and King County requirements. Log sheets provided in Reference Section 8 may be used if appropriate. Follow reporting requirements and provide documentation as requested to DPER staff. 4. Maintaining an updated construction SWPPP – Maintain, update, and implement the SWPPP in accordance with the Construction Stormwater General Permit and King County requirements. Obtain approval for specific SWPPP measures (e.g., chemical treatments of stormwater) well in advance of need. Coordinate SWPPP plan updates with the site inspector (see Section D.2.4.1). Section 10 – Construction Sequence General Construction Sequence: 1. Pre-construction meeting. 2. Post sign with name and phone number of CSWPP/ESC supervisor (may be consolidated with the required notice of construction sign). 3. Flag or fence clearing limits. 4. Install catch basin protection and flow control BMP area protection as required. 5. Grade and install construction entrance(s). 6. Install perimeter protection (silt fence, brush barrier, etc.). 7. Construct sediment ponds and traps. 8. Grade and stabilize construction roads. 9. Construct surface water controls (interceptor dikes, pipe slope drains, etc.) simultaneously with clearing and grading for project development. Construct SWPPS controls in anticipation of scheduled construction activity (e.g., concrete-related pH measures for utility, vault or roadway construction) Page 19 of 19 10. Maintain erosion control and SWPPS measures in accordance with King County standards and manufacturer's recommendations. 11. Relocate erosion control and SWPPS measures or install new measures so that as site conditions change the erosion and sediment control and pollutant protection is always in accordance with the King County Construction Stormwater Pollution Prevention Standards. 12. Cover all areas that will be unworked for more than seven days during the dry season or two days during the wet season with straw, wood fiber mulch, compost, or equivalent. 13. Stabilize all areas that reach final grade within seven days. 14. Seed or sod any areas to remain unworked for more than 30 days. 15. Upon completion of the project, all disturbed areas must be stabilized and BMPs removed if appropriate. All storm drainage facilities shall be protected in place from construction activity via brightly flagged stakes or, if necessary, temporary construction fencing. Section 11 – Construction Schedule Special consideration is necessary for erosion and source control during the wet season (Oct. 1 – April 30). This may include re-ordering construction phases, having materials available for immediate stabilization of disturbed areas, and diligent examination of the site for possible erosion concerns. Additional expenses and delays should be expected. It is recommended that construction take place during the dry season if possible. Section 12 – Financial/Ownership Responsibilities The property owner will be responsible for ensuring proper erosion and sediment control, bonds, and other required securities for this project. Section 13 – Engineering Calculations No calculations were required during the construction of this SWPPP plan. Appendix C - Soils Report Appendix D - Bond Quantities (Will Be Provided Upon Final TIR Submittal) Appendix E - WWHM2012 Reports WWHM2012 PROJECT REPORT 18.00392 Castro 7/14/2022 9:40:39 AM Page 2 General Model Information Project Name:18.00392 Castro Site Name: Site Address: City: Report Date:7/14/2022 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2021/08/18 Version:4.2.18 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 18.00392 Castro 7/14/2022 9:40:39 AM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 1.273 Pervious Total 1.273 Impervious Land Use acre Impervious Total 0 Basin Total 1.273 Element Flows To: Surface Interflow Groundwater 18.00392 Castro 7/14/2022 9:40:39 AM Page 4 Mitigated Land Use Basin 1 Bypass:Yes GroundWater:No Pervious Land Use acre C, Pasture, Mod 0.728 Pervious Total 0.728 Impervious Land Use acre Impervious Total 0 Basin Total 0.728 Element Flows To: Surface Interflow Groundwater 18.00392 Castro 7/14/2022 9:40:39 AM Page 5 Routing Elements Predeveloped Routing 18.00392 Castro 7/14/2022 9:40:39 AM Page 6 Mitigated Routing Permeable Pavement 1 Pavement Area:0.3572 acre.Pavement Length: 778.00 ft. Pavement Width: 20.00 ft. Pavement slope 1:0.05 To 1 Pavement thickness: 0.4167 Pour Space of Pavement: 0.4 Material thickness of second layer: 0.5 Pour Space of material for second layer: 0.33 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate:0.3 Infiltration safety factor:1 Total Volume Infiltrated (ac-ft.):52.435 Total Volume Through Riser (ac-ft.):0 Total Volume Through Facility (ac-ft.):52.435 Percent Infiltrated:100 Total Precip Applied to Facility:0 Total Evap From Facility:3.684 Element Flows To: Outlet 1 Outlet 2 Permeable Pavement Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.357 0.000 0.000 0.000 0.0113 0.357 0.001 0.000 0.108 0.0226 0.357 0.002 0.000 0.108 0.0339 0.357 0.004 0.000 0.108 0.0452 0.358 0.005 0.000 0.108 0.0565 0.358 0.006 0.000 0.108 0.0678 0.358 0.008 0.000 0.108 0.0791 0.358 0.009 0.000 0.108 0.0904 0.358 0.010 0.000 0.108 0.1017 0.359 0.012 0.000 0.108 0.1130 0.359 0.013 0.000 0.108 0.1243 0.359 0.014 0.000 0.108 0.1356 0.359 0.016 0.000 0.108 0.1469 0.359 0.017 0.000 0.108 0.1582 0.360 0.018 0.000 0.108 0.1695 0.360 0.020 0.000 0.108 0.1807 0.360 0.021 0.000 0.108 0.1920 0.360 0.022 0.000 0.108 0.2033 0.360 0.024 0.000 0.108 0.2146 0.361 0.025 0.000 0.108 0.2259 0.361 0.026 0.000 0.108 0.2372 0.361 0.028 0.000 0.108 0.2485 0.361 0.029 0.000 0.108 0.2598 0.361 0.030 0.000 0.108 0.2711 0.362 0.032 0.000 0.108 0.2824 0.362 0.033 0.000 0.108 0.2937 0.362 0.034 0.000 0.108 0.3050 0.362 0.036 0.000 0.108 0.3163 0.362 0.037 0.000 0.108 18.00392 Castro 7/14/2022 9:40:39 AM Page 7 0.3276 0.363 0.038 0.000 0.108 0.3389 0.363 0.040 0.000 0.108 0.3502 0.363 0.041 0.000 0.108 0.3615 0.363 0.043 0.000 0.108 0.3728 0.363 0.044 0.000 0.108 0.3841 0.364 0.045 0.000 0.108 0.3954 0.364 0.047 0.000 0.108 0.4067 0.364 0.048 0.000 0.108 0.4180 0.364 0.049 0.000 0.108 0.4293 0.364 0.051 0.000 0.108 0.4406 0.365 0.052 0.000 0.108 0.4519 0.365 0.053 0.000 0.108 0.4632 0.365 0.055 0.000 0.108 0.4745 0.365 0.056 0.000 0.108 0.4858 0.365 0.058 0.000 0.108 0.4971 0.366 0.059 0.000 0.108 0.5084 0.366 0.061 0.000 0.108 0.5196 0.366 0.062 0.000 0.108 0.5309 0.366 0.064 0.000 0.108 0.5422 0.366 0.065 0.000 0.108 0.5535 0.367 0.067 0.000 0.108 0.5648 0.367 0.069 0.000 0.108 0.5761 0.367 0.070 0.000 0.108 0.5874 0.367 0.072 0.000 0.108 0.5987 0.367 0.074 0.000 0.108 0.6100 0.368 0.075 0.000 0.108 0.6213 0.368 0.077 0.000 0.108 0.6326 0.368 0.079 0.000 0.108 0.6439 0.368 0.080 0.000 0.108 0.6552 0.368 0.082 0.000 0.108 0.6665 0.369 0.084 0.000 0.108 0.6778 0.369 0.085 0.000 0.108 0.6891 0.369 0.087 0.000 0.108 0.7004 0.369 0.089 0.000 0.108 0.7117 0.370 0.090 0.000 0.108 0.7230 0.370 0.092 0.000 0.108 0.7343 0.370 0.094 0.000 0.108 0.7456 0.370 0.095 0.000 0.108 0.7569 0.370 0.097 0.000 0.108 0.7682 0.371 0.099 0.000 0.108 0.7795 0.371 0.101 0.000 0.108 0.7908 0.371 0.102 0.000 0.108 0.8021 0.371 0.104 0.000 0.108 0.8134 0.371 0.106 0.000 0.108 0.8247 0.372 0.107 0.000 0.108 0.8360 0.372 0.109 0.000 0.108 0.8473 0.372 0.111 0.000 0.108 0.8585 0.372 0.112 0.000 0.108 0.8698 0.372 0.114 0.000 0.108 0.8811 0.373 0.116 0.000 0.108 0.8924 0.373 0.117 0.000 0.108 0.9037 0.373 0.119 0.000 0.108 0.9150 0.373 0.121 0.000 0.108 0.9263 0.373 0.125 0.000 0.108 0.9376 0.374 0.129 0.000 0.108 0.9489 0.374 0.133 0.000 0.108 0.9602 0.374 0.138 0.000 0.108 0.9715 0.374 0.142 0.000 0.108 18.00392 Castro 7/14/2022 9:40:39 AM Page 8 0.9828 0.374 0.146 0.000 0.108 0.9941 0.375 0.150 0.000 0.108 1.0054 0.375 0.155 0.000 0.108 1.0167 0.375 0.159 0.000 0.108 18.00392 Castro 7/14/2022 9:40:39 AM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.273 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.728 Total Impervious Area:0.357208 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.037904 5 year 0.062109 10 year 0.077672 25 year 0.096185 50 year 0.109009 100 year 0.120987 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.027509 5 year 0.048452 10 year 0.065547 25 year 0.090905 50 year 0.112587 100 year 0.136719 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.044 0.044 1950 0.052 0.047 1951 0.083 0.051 1952 0.026 0.017 1953 0.021 0.014 1954 0.032 0.021 1955 0.052 0.032 1956 0.042 0.033 1957 0.033 0.027 1958 0.037 0.024 18.00392 Castro 7/14/2022 9:41:15 AM Page 10 1959 0.032 0.020 1960 0.057 0.043 1961 0.031 0.020 1962 0.020 0.013 1963 0.027 0.020 1964 0.038 0.028 1965 0.025 0.023 1966 0.024 0.016 1967 0.058 0.050 1968 0.033 0.027 1969 0.032 0.024 1970 0.026 0.020 1971 0.029 0.026 1972 0.063 0.041 1973 0.028 0.019 1974 0.031 0.027 1975 0.043 0.033 1976 0.031 0.024 1977 0.005 0.008 1978 0.026 0.019 1979 0.016 0.011 1980 0.074 0.083 1981 0.023 0.017 1982 0.048 0.047 1983 0.041 0.028 1984 0.025 0.016 1985 0.015 0.010 1986 0.065 0.041 1987 0.057 0.039 1988 0.023 0.016 1989 0.015 0.011 1990 0.137 0.145 1991 0.073 0.060 1992 0.030 0.023 1993 0.029 0.019 1994 0.010 0.009 1995 0.042 0.026 1996 0.096 0.074 1997 0.074 0.049 1998 0.018 0.022 1999 0.081 0.093 2000 0.029 0.018 2001 0.005 0.005 2002 0.033 0.030 2003 0.050 0.050 2004 0.053 0.042 2005 0.040 0.030 2006 0.045 0.029 2007 0.104 0.122 2008 0.126 0.102 2009 0.059 0.043 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1373 0.1451 2 0.1265 0.1225 3 0.1037 0.1018 18.00392 Castro 7/14/2022 9:41:15 AM Page 11 4 0.0961 0.0926 5 0.0828 0.0830 6 0.0813 0.0745 7 0.0742 0.0601 8 0.0740 0.0511 9 0.0728 0.0504 10 0.0650 0.0503 11 0.0629 0.0491 12 0.0590 0.0474 13 0.0582 0.0472 14 0.0573 0.0443 15 0.0571 0.0431 16 0.0534 0.0429 17 0.0518 0.0416 18 0.0515 0.0414 19 0.0500 0.0409 20 0.0480 0.0390 21 0.0446 0.0331 22 0.0436 0.0329 23 0.0430 0.0322 24 0.0416 0.0299 25 0.0415 0.0298 26 0.0411 0.0287 27 0.0397 0.0284 28 0.0381 0.0277 29 0.0372 0.0274 30 0.0335 0.0270 31 0.0335 0.0270 32 0.0328 0.0264 33 0.0322 0.0256 34 0.0319 0.0245 35 0.0319 0.0245 36 0.0314 0.0238 37 0.0309 0.0233 38 0.0307 0.0228 39 0.0297 0.0223 40 0.0290 0.0208 41 0.0289 0.0204 42 0.0289 0.0202 43 0.0279 0.0198 44 0.0268 0.0196 45 0.0260 0.0192 46 0.0260 0.0191 47 0.0256 0.0186 48 0.0253 0.0184 49 0.0247 0.0170 50 0.0243 0.0165 51 0.0232 0.0164 52 0.0226 0.0162 53 0.0210 0.0160 54 0.0196 0.0142 55 0.0182 0.0133 56 0.0157 0.0113 57 0.0150 0.0107 58 0.0147 0.0099 59 0.0097 0.0085 60 0.0052 0.0083 61 0.0045 0.0049 18.00392 Castro 7/14/2022 9:41:15 AM Page 12 18.00392 Castro 7/14/2022 9:41:15 AM Page 13 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0190 17079 6239 36 Pass 0.0199 15483 5467 35 Pass 0.0208 14067 4827 34 Pass 0.0217 12797 4301 33 Pass 0.0226 11567 3833 33 Pass 0.0235 10515 3382 32 Pass 0.0244 9561 2979 31 Pass 0.0253 8759 2644 30 Pass 0.0262 8040 2363 29 Pass 0.0271 7349 2064 28 Pass 0.0280 6737 1856 27 Pass 0.0290 6192 1679 27 Pass 0.0299 5730 1472 25 Pass 0.0308 5309 1289 24 Pass 0.0317 4924 1162 23 Pass 0.0326 4569 1062 23 Pass 0.0335 4237 961 22 Pass 0.0344 3951 874 22 Pass 0.0353 3645 786 21 Pass 0.0362 3388 708 20 Pass 0.0371 3133 622 19 Pass 0.0381 2915 499 17 Pass 0.0390 2706 428 15 Pass 0.0399 2490 379 15 Pass 0.0408 2314 328 14 Pass 0.0417 2136 282 13 Pass 0.0426 1972 237 12 Pass 0.0435 1824 189 10 Pass 0.0444 1702 166 9 Pass 0.0453 1577 138 8 Pass 0.0462 1442 122 8 Pass 0.0472 1325 104 7 Pass 0.0481 1232 84 6 Pass 0.0490 1147 74 6 Pass 0.0499 1083 63 5 Pass 0.0508 1020 52 5 Pass 0.0517 946 46 4 Pass 0.0526 886 42 4 Pass 0.0535 824 36 4 Pass 0.0544 760 33 4 Pass 0.0553 725 30 4 Pass 0.0562 674 24 3 Pass 0.0572 623 19 3 Pass 0.0581 589 17 2 Pass 0.0590 549 17 3 Pass 0.0599 506 16 3 Pass 0.0608 469 13 2 Pass 0.0617 427 13 3 Pass 0.0626 388 12 3 Pass 0.0635 356 12 3 Pass 0.0644 328 12 3 Pass 0.0653 297 12 4 Pass 0.0663 270 11 4 Pass 18.00392 Castro 7/14/2022 9:41:15 AM Page 14 0.0672 241 11 4 Pass 0.0681 218 10 4 Pass 0.0690 197 10 5 Pass 0.0699 173 9 5 Pass 0.0708 152 9 5 Pass 0.0717 130 9 6 Pass 0.0726 119 9 7 Pass 0.0735 104 9 8 Pass 0.0744 95 9 9 Pass 0.0754 83 8 9 Pass 0.0763 74 8 10 Pass 0.0772 69 8 11 Pass 0.0781 61 7 11 Pass 0.0790 53 7 13 Pass 0.0799 46 7 15 Pass 0.0808 39 7 17 Pass 0.0817 29 7 24 Pass 0.0826 25 7 28 Pass 0.0835 22 6 27 Pass 0.0844 20 6 30 Pass 0.0854 17 6 35 Pass 0.0863 14 6 42 Pass 0.0872 12 6 50 Pass 0.0881 8 6 75 Pass 0.0890 7 6 85 Pass 0.0899 7 6 85 Pass 0.0908 7 6 85 Pass 0.0917 6 6 100 Pass 0.0926 6 5 83 Pass 0.0935 6 5 83 Pass 0.0945 6 5 83 Pass 0.0954 6 5 83 Pass 0.0963 5 5 100 Pass 0.0972 5 5 100 Pass 0.0981 5 4 80 Pass 0.0990 5 4 80 Pass 0.0999 5 4 80 Pass 0.1008 5 4 80 Pass 0.1017 5 4 80 Pass 0.1026 4 3 75 Pass 0.1036 4 2 50 Pass 0.1045 3 2 66 Pass 0.1054 3 2 66 Pass 0.1063 3 2 66 Pass 0.1072 3 2 66 Pass 0.1081 3 2 66 Pass 0.1090 3 2 66 Pass 18.00392 Castro 7/14/2022 9:41:15 AM Page 15 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.0346 acre-feet On-line facility target flow:0.0189 cfs. Adjusted for 15 min:0.0189 cfs. Off-line facility target flow:0.0103 cfs. Adjusted for 15 min:0.0103 cfs. 18.00392 Castro 7/14/2022 9:41:15 AM Page 16 LID Report 18.00392 Castro 7/14/2022 9:41:40 AM Page 17 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. 18.00392 Castro 7/14/2022 9:41:40 AM Page 18 Appendix Predeveloped Schematic 18.00392 Castro 7/14/2022 9:41:40 AM Page 19 Mitigated Schematic 18.00392 Castro 7/14/2022 9:41:41 AM Page 20 Predeveloped UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 18.00392 Castro.wdm MESSU 25 Pre18.00392 Castro.MES 27 Pre18.00392 Castro.L61 28 Pre18.00392 Castro.L62 30 POC18.00392 Castro1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 11 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Basin 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 11 C, Forest, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 11 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 11 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO 18.00392 Castro 7/14/2022 9:41:41 AM Page 21 PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 11 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 11 0 4.5 0.08 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 11 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 11 0.2 0.5 0.35 6 0.5 0.7 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 11 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATE1 18.00392 Castro 7/14/2022 9:41:41 AM Page 22 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 1*** PERLND 11 1.273 COPY 501 12 PERLND 11 1.273 COPY 501 13 ******Routing****** END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC 18.00392 Castro 7/14/2022 9:41:41 AM Page 23 WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 END MASS-LINK END RUN 18.00392 Castro 7/14/2022 9:41:41 AM Page 24 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 18.00392 Castro.wdm MESSU 25 Mit18.00392 Castro.MES 27 Mit18.00392 Castro.L61 28 Mit18.00392 Castro.L62 30 POC18.00392 Castro1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 14 IMPLND 16 RCHRES 1 COPY 1 COPY 501 COPY 601 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Permeable Pavement 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 601 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 14 C, Pasture, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 14 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO 18.00392 Castro 7/14/2022 9:41:41 AM Page 25 <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 14 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 14 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 14 0 4.5 0.06 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 14 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 14 0.15 0.4 0.3 6 0.5 0.4 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 14 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 16 Porous Pavement 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 16 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 16 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 16 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 16 400 0.01 0.1 0.1 END IWAT-PARM2 18.00392 Castro 7/14/2022 9:41:41 AM Page 26 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 16 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 16 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** IMPLND 16 0.3572 RCHRES 1 5 Basin 1*** PERLND 14 0.728 COPY 501 12 PERLND 14 0.728 COPY 601 12 PERLND 14 0.728 COPY 501 13 PERLND 14 0.728 COPY 601 13 ******Routing****** RCHRES 1 1 COPY 501 17 END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** 1 Permeable Paveme-007 2 1 1 1 28 0 1 END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 5 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** 18.00392 Castro 7/14/2022 9:41:41 AM Page 27 <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.15 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES FTABLE 1 91 5 Depth Area Volume Outflow1 Outflow2 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.357208 0.000000 0.000000 0.000000 0.011297 0.357208 0.001332 0.000000 0.108056 0.022593 0.357208 0.002663 0.000000 0.108056 0.033890 0.357208 0.003995 0.000000 0.108056 0.045187 0.357208 0.005327 0.000000 0.108056 0.056483 0.357208 0.006658 0.000000 0.108056 0.067780 0.357208 0.007990 0.000000 0.108056 0.079077 0.357208 0.009321 0.000000 0.108056 0.090373 0.357208 0.010653 0.000000 0.108056 0.101670 0.357208 0.011985 0.000000 0.108056 0.112967 0.357208 0.013316 0.000000 0.108056 0.124263 0.357208 0.014648 0.000000 0.108056 0.135560 0.357208 0.015980 0.000000 0.108056 0.146857 0.357208 0.017311 0.000000 0.108056 0.158153 0.357208 0.018643 0.000000 0.108056 0.169450 0.357208 0.019975 0.000000 0.108056 0.180747 0.357208 0.021306 0.000000 0.108056 0.192043 0.357208 0.022638 0.000000 0.108056 0.203340 0.357208 0.023969 0.000000 0.108056 0.214637 0.357208 0.025301 0.000000 0.108056 0.225933 0.357208 0.026633 0.000000 0.108056 0.237230 0.357208 0.027964 0.000000 0.108056 0.248527 0.357208 0.029296 0.000000 0.108056 0.259823 0.357208 0.030628 0.000000 0.108056 0.271120 0.357208 0.031959 0.000000 0.108056 0.282417 0.357208 0.033291 0.000000 0.108056 0.293713 0.357208 0.034623 0.000000 0.108056 0.305010 0.357208 0.035954 0.000000 0.108056 0.316307 0.357208 0.037286 0.000000 0.108056 0.327603 0.357208 0.038617 0.000000 0.108056 0.338900 0.357208 0.039949 0.000000 0.108056 0.350197 0.357208 0.041281 0.000000 0.108056 0.361493 0.357208 0.042612 0.000000 0.108056 0.372790 0.357208 0.043944 0.000000 0.108056 0.384087 0.357208 0.045276 0.000000 0.108056 0.395383 0.357208 0.046607 0.000000 0.108056 0.406680 0.357208 0.047939 0.000000 0.108056 0.417977 0.357208 0.049271 0.000000 0.108056 0.429273 0.357208 0.050602 0.000000 0.108056 0.440570 0.357208 0.051934 0.000000 0.108056 0.451867 0.357208 0.053265 0.000000 0.108056 0.463163 0.357208 0.054597 0.000000 0.108056 0.474460 0.357208 0.055929 0.000000 0.108056 0.485757 0.357208 0.057260 0.000000 0.108056 0.497053 0.357208 0.058592 0.000000 0.108056 0.508350 0.357208 0.060206 0.000000 0.108056 0.519647 0.357208 0.061820 0.000000 0.108056 0.530943 0.357208 0.063434 0.000000 0.108056 0.542240 0.357208 0.065048 0.000000 0.108056 0.553537 0.357208 0.066663 0.000000 0.108056 0.564833 0.357208 0.068277 0.000000 0.108056 18.00392 Castro 7/14/2022 9:41:41 AM Page 28 0.576130 0.357208 0.069891 0.000000 0.108056 0.587427 0.357208 0.071505 0.000000 0.108056 0.598723 0.357208 0.073119 0.000000 0.108056 0.610020 0.357208 0.074733 0.000000 0.108056 0.621317 0.357208 0.076347 0.000000 0.108056 0.632613 0.357208 0.077961 0.000000 0.108056 0.643910 0.357208 0.079575 0.000000 0.108056 0.655207 0.357208 0.081190 0.000000 0.108056 0.666503 0.357208 0.082804 0.000000 0.108056 0.677800 0.357208 0.084418 0.000000 0.108056 0.689097 0.357208 0.086032 0.000000 0.108056 0.700393 0.357208 0.087646 0.000000 0.108056 0.711690 0.357208 0.089260 0.000000 0.108056 0.722987 0.357208 0.090874 0.000000 0.108056 0.734283 0.357208 0.092488 0.000000 0.108056 0.745580 0.357208 0.094102 0.000000 0.108056 0.756877 0.357208 0.095716 0.000000 0.108056 0.768173 0.357208 0.097331 0.000000 0.108056 0.779470 0.357208 0.098945 0.000000 0.108056 0.790767 0.357208 0.100559 0.000000 0.108056 0.802063 0.357208 0.102173 0.000000 0.108056 0.813360 0.357208 0.103787 0.000000 0.108056 0.824657 0.357208 0.105401 0.000000 0.108056 0.835953 0.357208 0.107015 0.000000 0.108056 0.847250 0.357208 0.108629 0.000000 0.108056 0.858547 0.357208 0.110243 0.000000 0.108056 0.869843 0.357208 0.111858 0.000000 0.108056 0.881140 0.357208 0.113472 0.000000 0.108056 0.892437 0.357208 0.115086 0.000000 0.108056 0.903733 0.357208 0.116700 0.000000 0.108056 0.915030 0.357208 0.118314 0.000000 0.108056 0.926327 0.357208 0.122349 0.000000 0.108056 0.937623 0.357208 0.126384 0.000000 0.108056 0.948920 0.357208 0.130420 0.000000 0.108056 0.960217 0.357208 0.134455 0.000000 0.108056 0.971513 0.357208 0.138490 0.000000 0.108056 0.982810 0.357208 0.142526 0.000000 0.108056 0.994107 0.357208 0.146561 0.000000 0.108056 1.005403 0.357208 0.150596 0.000000 0.108056 1.016700 0.357208 0.154631 0.000000 0.108056 END FTABLE 1 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 RCHRES 1 EXTNL POTEV END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL COPY 601 OUTPUT MEAN 1 1 48.4 WDM 901 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 5 MASS-LINK 12 18.00392 Castro 7/14/2022 9:41:41 AM Page 29 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 17 RCHRES OFLOW OVOL 1 COPY INPUT MEAN END MASS-LINK 17 END MASS-LINK END RUN 18.00392 Castro 7/14/2022 9:41:41 AM Page 30 Predeveloped HSPF Message File 18.00392 Castro 7/14/2022 9:41:41 AM Page 31 Mitigated HSPF Message File 18.00392 Castro 7/14/2022 9:41:41 AM Page 32 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2022; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Appendix F – Maintenance & Operations Manual Castro Short Plat SITE ADDRESS: 12727 SE Petrovitsky Rd, Renton, WA 98058 SECTION 28, TOWNSHIP 23 N, RANGE 05 E, W.M. Maintenance & Operations Manual Prepared For: Alex Castro 110 Aspen Ln S Pacific, WA, 98047 206-478-3045 Date Prepared: November 1, 2019 Prepared By: Brian Lewis Reviewed By: Jim Cook, P.E. Beyler Consulting LLC 5920 100th St. SW, #25 Lakewood, WA 98499 253-984-2900 CONTACT (253) 984-2900 info@beylerconsulting.com beylerconsulting.com CORPORATE OFFICE 5920 100th St. SW, #25 Lakewood, WA 98499 Plan. Design. Manage. CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING Page 2 of 14 Table Of Contents I. Operation & Maintenance ......................................................... 3 Section 1 – Project Description ...................................................... 3 Section 2 – Maintenance Importance and Intent .............................. 3 Section 3 – Responsible Parties ...................................................... 3 Section 4 – Facilities Requiring Maintenance .................................... 4 Section 5 – Maintenance Instructions .............................................. 4 II. Appendices ............................................................................... 8 Appendix A – Maintenance Checklists Page 3 of 14 I. Operation & Maintenance Section 1 – Project Description This project will create a new 3-lot short plat including driveways, utilities, stormwater facilities, and associated grading and landscaping. Frontage improvements will be created for SE Petrovitsky Rd and 128th Ave SE consisting of landscape buffers and sidewalk. The curb radius and ramp at the intersection of the 2 streets will also be shifted. A half street extension will be done for SE 176th St to connect to a new public access road that will provide access to the short plat. The new access road and SE 176th St will have curb/gutter, landscape buffers, and a sidewalk. The property is located at 12727 SE Petrovitsky Rd, Renton, WA 98058, in the City of Renton, with parcel number 0739000085. The site is 49,389 sf (1.134 ac), has a zoning classification of Rural 4 (R4), and is found within the Residential Low Density comprehensive plan. The project will utilize stormwater BMPs to mitigate runoff generated by new surfaces. The new streets, driveways, and sidewalks will be constructed with permeable pavement. The houses will use downspout infiltration trenches. Cleared and landscaped areas will receive amended soils. The project will meet the 0.15 cfs increase exception for flow control, and the soil treatment exemption for water quality. Section 2 – Maintenance Importance and Intent The importance of maintenance for the proper functioning of stormwater control facilities cannot be over-emphasized. A substantial portion of failures (clogging of filters, resuspension of sediments, loss of storage capacity, etc.) are due to inadequate maintenance. Stormwater BMP maintenance is essential to ensure that BMPs function as intended throughout their full life cycle. The fundamental goals of maintenance activities are to insure the entire flow regime and treatment train designed for this site continue to fully function. These may include:  Maintain designed stormwater infiltration capacity  Maintain designed stormwater detention/retention volume  Maintain ability of storm facility to attenuate flow rates  Maintain ability to safely convey design stormwater flows  Maintain ability to treat stormwater runoff quality  Preserve soil and plant health, as well as stormwater flow contact with plant and soil systems  Clearly identify systems so they can be protected  Keep maintenance costs low  Prevent large-scale or expensive stormwater system failures  Prevent water quality violations or damage to downstream properties The intent of this section and manual is to pass on to the responsible party(s) all the information critical to understand the design of the system, risks and considerations for proper use, suggestions for maintenance frequencies, and cost so that realistic budgets can be established. Section 3 – Responsible Parties The property owners are responsible for the maintenance and operation of private stormwater facilities and associated conveyance systems constructed for this project. The Page 4 of 14 City of Renton will be responsible for the improvements of SE 176th St, SE Petrovitsky Rd, 128th Ave SE, and the new road to the west. Section 4 – Facilities Requiring Maintenance Structures and BMPs requiring maintenance for the project: infiltration trenches, sediment control structures, pipes, landscaping, permeable concrete and asphalt. Section 5 – Maintenance Instructions The parties responsible for maintenance must review and apply the maintenance requirements contained herein. These maintenance instructions outline conditions for determining if maintenance actions are required, as identified through inspection. However, they are not intended to be measures of the facility's required condition at all times between inspections. Exceedance of these conditions at any time between inspections or maintenance activity does not automatically constitute a violation of these standards. However, based upon inspection observations, the inspection and maintenance presented in the checklists shall be adjusted to minimize the length of time that a facility is in a condition that requires a maintenance action. For facilities not owned and maintained by the City, a log of maintenance activity that indicates what actions were taken must be kept on site and be available for inspection by the City. The following pages describe maintenance instructions for all applicable storm components and facilities found on site. Appendix A includes maintenance checklists for all relevant structures and BMPs found on the site. Page 5 of 14 Page 6 of 14 Page 7 of 14 II. Appendices Appendix A – Maintenance Checklists