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Home My WebLink AboutTIR-3884 CONTACT phone: 253-301-4157 fax: 253-336-3950 beylerconsulting.com OFFICE 7602 Bridgeport Way W, Ste 3D Lakewood, WA 98499 Plan. Design. Manage. CIVIL & STRUCTURAL ENGINEERING | LAND SURVEYING | PLANNING PROJECT MANAGEMENT | FEASIBILITY | PERMIT EXPEDITING Prepared for: Prepared by: Reviewed by: Beyler Consulting 7602 Bridgeport Way W., Ste 3D Lakewood, WA 98499 253-301-4157 Page 2 Cedar River Station, Fueling Station TABLE OF CONTENTS I. PROJECT OVERVIEW ................................................................ 3 Project Description ....................................................................... 3 Figure 1. TIR Worksheet ............................................................. 4 Figure 2. Location Map ................................................................. 9 Figure 3. Drainage Basin Map ..................................................... 10 Figure 4. Soils Map .................................................................... 11 II. CONDITIONS AND REQUIREMENTS SUMMARY ....................... 12 III. OFFSITE ANALYSIS ................................................................ 14 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ................................................................................... 14 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ...................... 25 VI. SPECIAL REPORTS AND STUDIES ........................................... 26 VII. OTHER PERMITS ..................................................................... 26 VIII. CSWPPP ANALYSIS AND DESIGN ........................................... 26 IX. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ................................................................................. 26 X. OPERATION AND MAINTENANCE MANUAL .............................. 26 XI. Appendices ............................................................................. 27 APPENDIX A – CSWPPP APPENDIX B – CEDAR RIVER STATION TIR APPENDIX C – INFILTRATION LETTER Page 3 Cedar River Station, Fueling Station I. PROJECT OVERVIEW Project Description The Cedar River Station project is a commercial development consisting of 3 buildings, Lot A (previously permitted) and a fueling station on a separate parcel, Lot B. This drainage report accompanies the site construction drawings for the proposed fueling station. The project is located within the city of Renton, parcel 2323059211. The fueling station proposal is to construction a new retail store, fueling area, associated parking & utilities, and a future car wash tunnel, which will be a part of Phase 2. Phase 2 calculations have been included in this report. The site is accessed by an entrance off of SR 169 constructed as a part of the Cedar River Station project. The existing parcel is has been rough graded under a separate permit and nearly flat with the exception of the north, south, and east perimeter where the grade slopes down to the adjacent parcels and the conveyance system within SR 169. The proposed project is located in the Lower Cedar River King County Drainage Basin (WRIA #8) within the Cedar River-Lake Washington watershed. The developed basin is made up of the entire Cedar River Station project which includes the three commercial buildings and the fueling station on the project parcel. All parts of this development are managed by a shared stormwater detention and treatment system. The Cedar River Station (CRS) project has previously permitted and constructed a combined water quality and detention vault with associated pipes to convey water to this flow control facility. The proposed fueling station will install additional conveyance measures to collect and convey stormwater to this facility. Stormwater discharge from the flow control facility is directed to a catch basin within the SR- 169 ROW where stormwater is then released to a pipe/ditch system until runoff reach the Cedar River. A Dry Well is proposed for the retail store rooftop runoff to satisfy the Flow Control BMP requirement. This report is a supplement to the previously approved drainage report as prepared by ESM Consulting Engineers, Revised June 27, 2013. Although the previously approved report addressed the fueling station development, this report is a standalone document that provides further development, fueling station, details now that the an exact site plan is known. Impervious comparisons are made to check the assumptions of the Cedar River Station development Drainage report. Parts of this Drainage Report will refer to the CRS drainage report. Portions of CRS drainage report can be found in Appendix B. A full report can be found on record with the city. This project is subject to the 2009 King County Surface Water Design Manual (King Manual) and the City of Renton amendments to the Manual (Renton Manual). Per Figure 1.1.2.A of the Renton Manual, the project is subject to a Full drainage review. KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 1 Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner ________________________ Phone ______________________________ Address ____________________________ ____________________________________ Project Engineer ______________________ Company ___________________________ Phone ______________________________ Project Name _________________________ DDES Permit # ________________________ Location Township ______________ Range ________________ Section ________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Landuse Services Subdivison / Short Subd. / UPD Building Services M/F / Commerical / SFR Clearing and 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 (circle): Date (include revision dates): Date of Final: Full / Targeted / Large Site ___________________ ___________________ ___________________ Type (circle one): Date (include revision dates): Date of Final: Full / Modified / Small Site __________________ __________________ __________________ Part 6 ADJUSTMENT APPROVALS Type (circle one): Standard / Complex / Preapplication / Experimental / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Date of Approval: ______________________ KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 2 Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ _________________________________________ _________________________________________ 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 __________________ _________________________________ Part 10 SOILS Soil Type _________________ _________________ _________________ _________________ Slopes _________________ _________________ _________________ _________________ Erosion Potential _________________ _________________ _________________ _________________ High Groundwater Table (within 5 feet) Other ________________________ Sole Source Aquifer Seeps/Springs Additional Sheets Attached KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 3 Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis_________________ Sensitive/Critical Areas___________________ SEPA________________________________ 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 (incl. facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Small Site BMPs ___________________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control ESC Site Supervisor: Contact Phone: After Hours Phone: Maintenance and Operation Responsibility: Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type: Basic / Sens. Lake / Enhanced Basicm / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable) Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: Source Control (comm./industrial landuse) Describe landuse: Describe any structural controls: KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 4 Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Clearing Limits Cover Measures Perimeter Protection Traffic Area Stabilization Sediment Retention Surface Water Collection Dewatering Control Dust Control Flow Control MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize Exposed Surfaces Remove and Restore Temporary ESC Facilities Clean and Remove All Silt and Debris, Ensure Operation of Permanent Facilities Flag Limits of SAO and open space preservation areas Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description Detention Infiltration Regional Facility Shared Facility Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ Biofiltration Wetpool Media Filtration Oil Control Spill Control Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2009 Surface Water Design Manual 1/9/2009 5 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 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 Page 9 Cedar River Station, Fueling Station Figure 2. Location Map Page 10 Cedar River Station, Fueling Station Figure 3. Drainage Basin Map Page 11 Cedar River Station, Fueling Station Figure 4. Soils Map Please refer to the Geotechnical Report prepared by Earth Consulting Incorporated Dated October 1, 2007 for an accurate description of the onsite soils. Also refer to E3RA’s letter dated November 22, 2013. An infiltration letter has also been prepared by Migizi Group dated February 10, 2016 to address the feasibility of infiltration. This letter can be found in Appendix C of this Report. Page 12 Cedar River Station, Fueling Station II. CONDITIONS AND REQUIREMENTS SUMMARY Review of Eight Core Requirements and Five Special Requirements The following comments are a review of the Core and Special Requirements per the 2009 King County Surface Water Stormwater Manual. Core Requirement No. 1 Discharge at the Natural Location The project site will convey runoff to the previously permitted Cedar River Station (CRS) project. See the CRS Drainage report in Appendix B for a description of the discharge location. Core Requirement No 2 Offsite Analysis The project site will convey runoff to the previously permitted Cedar River Station (CRS) project. See the CRS Drainage report in Appendix B for the Offsite Analysis. Core Requirement No 3 Flow Control The project site will convey runoff to the previously permitted Cedar River Station (CRS) project. See the CRS Drainage report in Appendix B for the design of the flow control facility. In summary the flow control facility consists of a combined water quality and detention vault. The CRS drainage report made development assumptions for the fueling station phase, proposed project. See Section IV of this report for a detailed description of the pr oject areas as it compared to the assumed values of the CRS drainage report Flow Control BMPs: In addition to flow control facility requirements, flow control BMPs are also necessary per 1.2.3.3 of the Manual to provide additional mitigation of hydrologic impacts. Implementation of this requirement for this “non -subdivision” project will follow the individual lot BMP requirements in section 5.2.1.3 of the Manual, “Large Lot High Impervious BMP Requirements”. Based on a site evaluation, it has been determ ined that full dispersion or infiltration is not feasible. As a result, limited infiltration is proposed through the use of a Dry Well. See Part C of Section 5 of this report for the Large Lot High impervious BMP performance standards and analysis of the limited infiltration facility. Core Requirement No. 4 Conveyance System All new pipes systems will be designed with sufficient capacity to convey and contain at minimum the 25-year peak flow. See Section V of this report for the conveyance analysis. Core Requirement No. 5 Erosion and Sediment Control This development will be constructed in one phase. Please see Appendix E for the prepared CSWPPP, and sheets C2.0 - C3.0 in the prepared Construction Plans. Core Requirement No. 6 Maintenance and Operations The maintenance and Operations Manual can be provided upon request Core Requirement No. 7 Financial Guarantees and Liability Financial guarantees can be made available to the City upon request . Core Requirement No. 8 Water Quality The project site will convey runoff to the previously permitted Cedar River Station (CRS) project. See the CRS Drainage report in Appendix B for the design of the flow control facility. In summary the flow control facility consists of a combined water quality and detention vault. Page 13 Cedar River Station, Fueling Station The CRS Drainage report made development assumptions for the fueling station phase, proposed project. See Section IV of this report for a detailed description of the project areas as it compared to the assumed values of the CRS drainage report Special Requirement No. 1 Other Adopted Area-Specific Requirements The project lies within the Lower Cedar River Drainage Basin. No other adopted area specific requirements pertain to this property. Special Requirement No. 2 Flood Hazard Area Delineation The project does not contain or is not adjacent to a flood hazard area for a river, stream, lake, wetland, closed depression, or marine shoreline that is within the 100 -year floodplain according to King County and FEMA. Special Requirement No. 3 Flood Protection Facilities This project does not rely on any flood protection facility such as a levee or revetment nor will construct a new flood protection facility. Special Requirement No. 4 Source Control This project does provide source control in the area of the proposed fueling area. The fueling area will be covered. The covered fueling area will be hydraulically isolated to prevent any fuel spills from coming into contact with the proposed stormwater system. Any fuel spill will be directed to a trench drain and conveyed to an oil/water separator before discharging into the sanitary sewer system. Special Requirement No. 5 Oil Control This project is not defined as a high-use site nor is a redevelopment project proposing $100,000 or more of improvements to an exi sting high-use site. This special requirement is not applicable to stormwater management. Page 14 Cedar River Station, Fueling Station III. OFFSITE ANALYSIS See the previously approved downstream analysis prepared as a part of the Cedar River Station Project. IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN The fueling station project is located within the Conservation flow control area. All exposed impervious areas from Lot B will be collected and tightlined with new conveyance pipes. The new pipes will connect to the proposed storm syst em of the Cedar River project as designed by ESM. These pipes lead to the underground combined water quality and detention vault as approved by Renton. This vault will detain stormwater to required flow control standards and provide Basic treatment to stormwater before releasing runoff downstream. The vault has been designed by ESM and is designed to manage stormwater for the entire Cedar River Station project, Lot A and B. The flow control and water quality sizing calculation are included in Appendix B of this report. The CRS project accounted for the fueling station project in the calculations. Existing Site Hydrology (Part A) Existing conditions on the project site consists of a previously rough graded 0.80 acre property. As a part of the CRS project, the fueling station parcel was assumed to forested in nature, Till Forest, to determine a Predeveloped flow rate. Developed Site Hydrology (Part B) The entire CRS project contains three proposed buildings and the fueling station area with respective parking. The fueling station project will consist of two phases. The first phase consists of the fueling area and the retail store. The second phase will include additional asphalt and a car wash tunnel. Table 4.1 provides the area for both phases. The assumed impervious area of the fueling station per the CRS site construction plans is 22,590 sf (0.52 ac). Tables 4.1 breaks down the proposed areas for phase 1 and 2 of the fueling station and compares it with the previously assumed area assumed impervious area of the fueling station per the CRS site construction plans. Page 15 Cedar River Station, Fueling Station TABLE 4.1a – Fueling station Phase 1 & Phase 2 Conditions Sub-basin Impervious sf (ac) Till Grass sf (ac) Phase 1 (fueling area, parking, and retail store) 19,558 (0.445) 12,973 (0.30) Phase 1+2 (additional paving and Carwash tunnel) 24,830 (0.57) 7,201 (0.17) CRS Assumption for facility sizing 22,590 (0.52) 9,441 (0.22) Difference +2,240 (0.05) -2,240 TABLE 4.1b – Fueling station Phase 1 & Phase 2 Conditions W/Flow Control BMP Credits* Sub-basin Impervious sf (ac) Till Grass sf (ac) Phase 1 (fueling area, parking, and retail store) 17,753 (0.41) 14,779 (0.34) Phase 1+2 (additional paving and Carwash tunnel) 23,024 (0.53) 9,007 (0.21) CRS Assumption for facility sizing 22,590 (0.52) 9,441 (0.22) Difference +434 (0.01) -434 *3,612 sf (0.08ac) of roof top to be managed by limited Infiltration. Impervious area managed by limited infiltration Is considered 50% till grass and 50 % impervious Per Table 5.2.2.A of the King Manual. Table 4.1b reflects This credit. As indicated in Table 4.1b, the addition of phase 2 increases the proposed impervious surface to a larger amount than initially assumed in the CRS Drainage Report by 434 sf. With this being the case the CRS drainage report was reviewed to determine by how much the constructed water quality and detention system is oversized. See Part D and E. Performance Standards (Part C) Flow Control Facility Per the CRS drainage report, the site required Level 2 conservation flow control. This requires that the develop site discharge match Predeveloped discharge rates from 50% of the 2 -year peak flow up to the full 50-year peak flow. Stormwater Conveyance The conveyance system capacity standards require that new c onveyance systems contain the 25-year peak flow and ensure that the 100-year event does not create a severe flooding or Page 16 Cedar River Station, Fueling Station erosion problem. See Section V of this report for the conveyance analysis per Core Requirement #4. Flow Control BMPs In addition to flow control facility requirements, flow control BMPs are also necessary per 1.2.3.3 of the Manual. Implementation of this requirement for this “non-subdivision” project will follow the individual lot BMP requirements in section 5.2.1.3 of the Manual, “La rge Lot High Impervious BMP Requirements”. Based on a site evaluation, it has been determined that full dispersion and infiltration is not feasible. As a result, limited infiltration utilizing a Dry Well is proposed. Per Section 5.2.1.3.2, flow control BMPs must be applied to an impervious area equal to at least 10% of the site/lot or 20% of the target impervious surface, whichever is less. Target impervious surface is defined as new impervious surface not fully dispersed and replaced impervious surface that is not fully dispersed on a parcel redevelopment project in which the total of new plus replaced impervious surface is 5,000 sf AND whose valuation of proposed improvements exceeds 50% of the assessed value of the existing site improvements. The project parcel is 35,031 sf. Ten percent of the site is 3,503 sf. The new impervious area is approximately 19,558 sf on the existing site and expansion site. Twenty percent of the target impervious surfaces is 3,911 sf. Ten percent of the site surfaces is less than 20% of the target impervious surfaces. At a minimum, 3,503 sf of impervious will be managed by a flow control BMP. See part D below for BMP sizing. Flow Control Systems (Part D) The constructed detention vault built for the CRS project prov ided 44,938 cf of storage according to the CRS construction drawings. This is approximately 642 cf more than the modeled 44,296 cf per the CRS drainage report. Due to the additional impervious area being conveyed to the vault , the following analysis determines if the vault has adequate storage to meet the flow control performance standards. In summary, after taking into considering the constructed vault volume of 44,938 cf, the detention facility is still within the Flow Control Standards per the evaluation on the next page. This is taking into considering the additional impervious surfaces within the vault basin than initially assumed for the CRS project. To determine if the existing vault can provide the necessary storage, KCRTS was used with modified basin numbers. The input parameters remained the same as previously modeled with the CRS project with the additional impervious surface over the amount initially assumed. The following table provides the information input into KCRTS. Page 17 Cedar River Station, Fueling Station TABLE 4.2 – KCRTS Input Basin Condition Impervious* (ac) Till Grass (ac) Till Forest (ac) Predeveloped 3.02 CRS Developed w/assumed fueling station areas* 2.48 0.16 Additional from Fueling Station per Table 4.1b +0.01 +0.04* *50% of retail rooftop, Retail rooftop (3,612 sf) considered 50% grass 50% impervious per Table 5.2.2.A of the King Manual. See table 4.1b. *KCRTS Input from approved CRS Drainage Report Scale Factor: 1.0 Project Location: Sea-Tac Data Type: Historic Orifice #1: Height: 0.00ft, Dia: 0.95in Orifice #2: Height: 2.05ft, Dia: 1.50in Orifice #3: Height: 2.70ft, Dia: 1.75in Flow Control Performance Evaluation (Per Section 3.2.2) 1. The post-developed flow duration curve lies strictly below the predevelopment curve at the lower limit of the range of control (between 50% of the 2-year and the 2- year). Requirement Satisfied - The rdout duration curve lies strictly below the target duration curve 2. At any duration within the range of control, the post-development flow is less than 1.1 times the predevelopment flow. Requirement Satisfied – After running a flow durations comparison analysis, a maximum positive excursion found among the range of control was 8.5% (1.085 times) 3. The target duration curve may not be exceeded along more than 50% of the range of control. Requirement Almost Satisfied - After running a flow durations comparison analysis, 6 of the 14 flow duration cutoff values (<50%) were exceeded. 4. The peak flow at the upper end of the range of control (historical 50-year) may not exceed predeveloped levels by more than 10%. Requirement Satisfied – Peak flows at the upper end of the range of control do not exceed predeveloped flow levels by 10% ========================================================================== Page 18 Cedar River Station, Fueling Station Retention/Detention Facility Type of Facility: Detention Vault Facility Length: 180.00 ft Facility Width: 71.33 ft Facility Area: 12839. sq. ft Effective Storage Depth: 3.50 ft Stage 0 Elevation: 0.00 ft Storage Volume: 44938. cu. ft Riser Head: 3.50 ft Riser Diameter: 12.00 inches Number of orifices: 3 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 0.95 0.046 2 2.05 1.50 0.073 4.0 3 2.70 1.75 0.074 4.0 Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) 0.00 0.00 0. 0.000 0.000 0.00 0.01 0.01 128. 0.003 0.002 0.00 0.02 0.02 257. 0.006 0.003 0.00 0.03 0.03 385. 0.009 0.004 0.00 0.04 0.04 514. 0.012 0.005 0.00 0.05 0.05 642. 0.015 0.005 0.00 0.06 0.06 770. 0.018 0.006 0.00 0.07 0.07 899. 0.021 0.006 0.00 0.08 0.08 1027. 0.024 0.007 0.00 0.09 0.09 1156. 0.027 0.007 0.00 0.19 0.19 2440. 0.056 0.011 0.00 0.29 0.29 3723. 0.085 0.013 0.00 0.39 0.39 5007. 0.115 0.015 0.00 0.49 0.49 6291. 0.144 0.017 0.00 0.59 0.59 7575. 0.174 0.019 0.00 0.69 0.69 8859. 0.203 0.020 0.00 0.79 0.79 10143. 0.233 0.022 0.00 0.89 0.89 11427. 0.262 0.023 0.00 0.99 0.99 12711. 0.292 0.024 0.00 1.09 1.09 13995. 0.321 0.026 0.00 1.19 1.19 15279. 0.351 0.027 0.00 1.29 1.29 16563. 0.380 0.028 0.00 1.39 1.39 17847. 0.410 0.029 0.00 1.49 1.49 19131. 0.439 0.030 0.00 1.59 1.59 20415. 0.469 0.031 0.00 1.69 1.69 21699. 0.498 0.032 0.00 1.79 1.79 22983. 0.528 0.033 0.00 Page 19 Cedar River Station, Fueling Station 1.89 1.89 24266. 0.557 0.034 0.00 1.99 1.99 25550. 0.587 0.035 0.00 2.05 2.05 26321. 0.604 0.035 0.00 2.07 2.07 26578. 0.610 0.036 0.00 2.08 2.08 26706. 0.613 0.037 0.00 2.10 2.10 26963. 0.619 0.040 0.00 2.11 2.11 27091. 0.622 0.043 0.00 2.13 2.13 27348. 0.628 0.047 0.00 2.14 2.14 27476. 0.631 0.052 0.00 2.16 2.16 27733. 0.637 0.056 0.00 2.18 2.18 27990. 0.643 0.058 0.00 2.27 2.27 29145. 0.669 0.066 0.00 2.37 2.37 30429. 0.699 0.073 0.00 2.47 2.47 31713. 0.728 0.078 0.00 2.57 2.57 32997. 0.758 0.084 0.00 2.67 2.67 34281. 0.787 0.088 0.00 2.70 2.70 34666. 0.796 0.089 0.00 2.72 2.72 34923. 0.802 0.091 0.00 2.74 2.74 35180. 0.808 0.094 0.00 2.75 2.75 35308. 0.811 0.097 0.00 2.77 2.77 35565. 0.816 0.103 0.00 2.79 2.79 35822. 0.822 0.109 0.00 2.81 2.81 36079. 0.828 0.117 0.00 2.83 2.83 36336. 0.834 0.125 0.00 2.85 2.85 36592. 0.840 0.127 0.00 2.95 2.95 37876. 0.870 0.141 0.00 3.05 3.05 39160. 0.899 0.152 0.00 3.15 3.15 40444. 0.928 0.163 0.00 3.25 3.25 41728. 0.958 0.172 0.00 3.35 3.35 43012. 0.987 0.181 0.00 3.45 3.45 44296. 1.017 0.189 0.00 3.50 3.50 44938. 1.032 0.194 0.00 3.60 3.60 46222. 1.061 0.509 0.00 3.70 3.70 47506. 1.091 1.080 0.00 3.80 3.80 48790. 1.120 1.820 0.00 3.90 3.90 50074. 1.150 2.610 0.00 4.00 4.00 51358. 1.179 2.900 0.00 4.10 4.10 52642. 1.208 3.160 0.00 4.20 4.20 53925. 1.238 3.410 0.00 4.30 4.30 55209. 1.267 3.630 0.00 4.40 4.40 56493. 1.297 3.840 0.00 4.50 4.50 57777. 1.326 4.040 0.00 4.60 4.60 59061. 1.356 4.230 0.00 4.70 4.70 60345. 1.385 4.410 0.00 4.80 4.80 61629. 1.415 4.590 0.00 4.90 4.90 62913. 1.444 4.760 0.00 5.00 5.00 64197. 1.474 4.920 0.00 5.10 5.10 65481. 1.503 5.070 0.00 5.20 5.20 66765. 1.533 5.230 0.00 5.30 5.30 68049. 1.562 5.370 0.00 5.40 5.40 69333. 1.592 5.520 0.00 5.50 5.50 70617. 1.621 5.660 0.00 Hyd Inflow Outflow Peak Storage Page 20 Cedar River Station, Fueling Station Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 1.22 ******* 0.39 3.56 3.56 45737. 1.050 2 0.91 0.92 0.04 2.01 2.01 25777. 0.592 3 0.75 ******* 0.03 1.24 1.24 15977. 0.367 4 0.74 ******* 0.03 1.05 1.05 13537. 0.311 5 0.66 ******* 0.08 2.44 2.44 31300. 0.719 6 0.62 ******* 0.03 1.59 1.59 20473. 0.470 7 0.62 ******* 0.18 3.31 3.31 42465. 0.975 8 0.54 ******* 0.05 2.15 2.15 27596. 0.634 ---------------------------------- Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:rdout Inflow/Outflow Analysis Peak Inflow Discharge: 1.22 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.391 CFS at 11:00 on Jan 9 in Year 8 Peak Reservoir Stage: 3.56 Ft Peak Reservoir Elev: 3.56 Ft Peak Reservoir Storage: 45738. Cu-Ft : 1.050 Ac-Ft Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS % % % 0.003 25925 42.278 42.278 57.722 0.577E+00 0.008 8309 13.550 55.828 44.172 0.442E+00 0.013 8043 13.116 68.945 31.055 0.311E+00 0.019 6968 11.363 80.308 19.692 0.197E+00 0.024 5982 9.755 90.064 9.936 0.994E-01 0.029 2747 4.480 94.543 5.457 0.546E-01 0.035 2447 3.991 98.534 1.466 0.147E-01 0.040 426 0.695 99.229 0.771 0.771E-02 0.045 45 0.073 99.302 0.698 0.698E-02 0.050 26 0.042 99.344 0.656 0.656E-02 0.056 34 0.055 99.400 0.600 0.600E-02 0.061 62 0.101 99.501 0.499 0.499E-02 0.066 63 0.103 99.604 0.396 0.396E-02 0.072 51 0.083 99.687 0.313 0.313E-02 0.077 46 0.075 99.762 0.238 0.238E-02 0.082 34 0.055 99.817 0.183 0.183E-02 0.088 23 0.038 99.855 0.145 0.145E-02 0.093 15 0.024 99.879 0.121 0.121E-02 0.098 3 0.005 99.884 0.116 0.116E-02 0.103 3 0.005 99.889 0.111 0.111E-02 0.109 1 0.002 99.891 0.109 0.109E-02 0.114 3 0.005 99.896 0.104 0.104E-02 0.119 1 0.002 99.897 0.103 0.103E-02 0.125 5 0.008 99.905 0.095 0.946E-03 0.130 8 0.013 99.918 0.082 0.815E-03 0.135 7 0.011 99.930 0.070 0.701E-03 0.141 8 0.013 99.943 0.057 0.571E-03 Page 21 Cedar River Station, Fueling Station 0.146 5 0.008 99.951 0.049 0.489E-03 0.151 9 0.015 99.966 0.034 0.342E-03 0.156 5 0.008 99.974 0.026 0.261E-03 0.162 2 0.003 99.977 0.023 0.228E-03 0.167 1 0.002 99.979 0.021 0.212E-03 0.172 3 0.005 99.984 0.016 0.163E-03 0.178 2 0.003 99.987 0.013 0.130E-03 0.183 3 0.005 99.992 0.008 0.815E-04 0.188 4 0.007 99.998 0.002 0.163E-04 Duration Comparison Anaylsis Base File: predev.tsf New File: rdout.tsf Cutoff Units: Discharge in CFS -----Fraction of Time----- ---------Check of Tolerance------- Cutoff Base New %Change Probability Base New %Change 0.042 | 0.95E-02 0.75E-02 -21.4 | 0.95E-02 0.042 0.035 -15.4 0.053 | 0.63E-02 0.63E-02 0.5 | 0.63E-02 0.053 0.053 0.4 0.065 | 0.50E-02 0.43E-02 -13.2 | 0.50E-02 0.065 0.061 -5.2 0.076 | 0.37E-02 0.26E-02 -30.4 | 0.37E-02 0.076 0.068 -10.6 0.087 | 0.29E-02 0.15E-02 -49.1 | 0.29E-02 0.087 0.074 -15.1 0.099 | 0.22E-02 0.11E-02 -48.5 | 0.22E-02 0.099 0.078 -21.3 0.110 | 0.15E-02 0.11E-02 -27.5 | 0.15E-02 0.110 0.087 -20.9 0.122 | 0.10E-02 0.98E-03 -3.2 | 0.10E-02 0.122 0.121 -0.7 0.133 | 0.62E-03 0.75E-03 21.1 | 0.62E-03 0.133 0.138 3.8 0.144 | 0.34E-03 0.52E-03 52.4 | 0.34E-03 0.144 0.151 4.7 0.156 | 0.21E-03 0.26E-03 23.1 | 0.21E-03 0.156 0.168 7.6 0.167 | 0.16E-03 0.21E-03 30.0 | 0.16E-03 0.167 0.175 4.7 0.179 | 0.11E-03 0.13E-03 14.3 | 0.11E-03 0.179 0.179 0.4 0.190 | 0.16E-04 0.00E+00 -100.0 | 0.16E-04 0.190 0.189 -0.6 Maximum positive excursion = 0.012 cfs ( 7.6%) occurring at 0.156 cfs on the Base Data:predev.tsf and at 0.168 cfs on the New Data:rdout.tsf Maximum negative excursion = 0.022 cfs (-22.0%) occurring at 0.102 cfs on the Base Data:predev.tsf and at 0.080 cfs on the New Data:rdout.tsf Page 22 Cedar River Station, Fueling Station Page 23 Cedar River Station, Fueling Station Flow Control BMPs As discussed in Part C of Section 4, to satisfy the flow control BMP requirement, flow control BMPs need to manage a minimum of 3,503 sf of impervious surface. Approximately 3,612 sf of retail area is proposed. The rooftop of retail area is porposed to be tightlined to a Drywell per Section C.2.3.4 of the King Manual. The geotechnical letter prepared by Migizi Group, found in Appendix C, recommends 230 cubic feet per 1,000 sf of impervious surface in the area of Test Pit #2. The proposed Dry Well is located at the Test Pit #2 location. The Dry Well will be proceeded by a Type 1 catch basin with a downt urned elbow to provide pretreatment. NOTE: runoff from a couple small awnings are also tightlined to the dry well. Drywell Sizing Rooftop Area: 3,612 sf Drywell Sizing Critera: 230 cf/1000 sf of rooftop Required Volume: (3,612sf/1000 sf)(230)=831 cf Drywell Diameter: 12 feet Drywell Surface Area: 𝐴=𝜋62 = 113 sf Drywell Depth: 831 cf/ 113 sf = 7.35 feet A 12-foot diameter, 7.5-foot-deep dry well is proposed. See Civil drawings for location and detail. Water Quality System (Part E) A similar exercise was performed to determine of the wetvault portion of the vault has enough storage volume to manage the additional 2,240 sf of impervious surface. The constructed water quality system built for the CRS project provided 11,983 cf of volume. This is approximately 350 cf more than the required 11,633 cf at the time. The proposed water quality wetvault for the site was sized to obtain adequate particulate removal efficiency per section 6.4.1.1 of the Manual. This is based on the volume of th e wetvault in relation to the volume of stormwater runoff from the mean annual storm, V B/VR. For basic water quality vaults, this ratio, vault volume/mean annual storm, shall equal at least 3. The sizing of the wetvault is accomplished by first determi ning the acreage of pervious and impervious areas. These values are used to calculate the treatment runoff volumes by multiplying the acreage of each surface type by the mean annual storm (0.039 feet, per Figure 6.4.1.A of the Manual). Runoff factors are also applied to each surface type, 0.25 for grass and 0.90 for impervious. The sum of the grass and impervious runoff volumes is the total Page 24 Cedar River Station, Fueling Station runoff volume, VR. The additional 2,240 sf of impervious was used in the below calculations to determine what additional wetvault volume is necessary to confirm the extra storage constructed exceeds this. Impervious runoff = (2,240 sf)(0.039’)(0.90) = 78.62 cf Total runoff volume, VR = 79 Total basin volume, VB = 79 cf x 3 = 237 cf An additional 237 cf is necessary. The constructed wetvault has an additional 350 cf of storage as discuss above per the CRS Drainage Report. Page 25 Cedar River Station, Fueling Station V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN For this proposed development, the new stormwater conveyance system will connect to the CRS conveyance system in two places. The entire proposed conveyance system being installed consists of 8” PVC pipes with exception to the 6” roof connections for the retail store and car wash. For the purpose of this report, an analysis has been prepared for the downstream 8” PVC pipe connecting to the existing catch basin. The basis area used, encompasses the largest area to any one 8” pipe on the project. See the basin map located on the follow sheet. Including both phase 1 and 2, phase 2 being the car wash, t he total impervious area is 12,550 sf. This also assumes the Dry Well managing the rooftop runoff from the retail area has failed. To analyze the proposed systems, the Rational Method was used based on:  QR = CIRA  King county I.D.F. Family (2009 Manual)  25 and 100-year 24 storm event flow  Runoff coefficients  Appropriate Manning’s number  Total Impervious Area = 12,550 sf = 0.29 ac The Rational Method was used per section 3.2.1. of the Manual. The runoff coefficients, ‘C’ values were taken from Table 3.2.1.A. A C value of 0.9 was used for the roofed surface and a conservative time of concentration value of 6.3 minutes was used. This is a low travel time, but will provide relatively higher flow rate. Croof/pavement = 0.90 Tc = 6.3 (minimum) IR – (PR)(iR) iR = (aR)(Tc)(-bR) a25 = 2.66, a100 = 2.61 (Table 3.2.1.B) b25 = 0.65, b100 = 0.63 (Table 3.2.1.B) P25 = 3.40”, P100 = 3.90” (Figure 3.2.1.C & D) i25 = (2.66)(6.3)(-0.65) = 0.80 i100 = (2.61)(6.3)(-0.63) = 0.82 I25 = (3.40)(0.80) = 2.72 I100 = (3.90)(0.82) = 3.20 Q25 = (0.9)(2.72)(0.29) = 0.71 cfs Q100 = (0.9)(3.20)(0.29) = 0.84 cfs Pipe Capacity To estimate full flow capacity of the 8” pipe, Manning’s equation was used based on:  Qfull = (1.49/n)AR2/3S0.5  Manning’s n = 0.013 (Table 4.2.1.D)  Pipe flowing full, R = D/4  A, cross section of flow 6” pipe capacity @ 1.0% (min): Q = (1.49/0.013)(0.35sf)(.67 /4)2/3 (0.01)0.5 = 1.21 cfs  OK Page 26 Cedar River Station, Fueling Station The proposed private system consists of a 8” PVC conveyance pipe to the existing catch basin. Based on a minimum pipe slope of 1.0%, a 8” pipe has a conveyance capacity of 1.21 cfs. With the analysis max 100-year flow of 0.84, the system has sufficient capacity. VI. SPECIAL REPORTS AND STUDIES Geotechnical Report Geotechnical Engineering Study, Cedar River Station October 1, 2007; Prepared by earth Consulting incorporated. Infiltration Letter, Cedar River Chevron February 10, 2016; Prepared by Migizi Group. See Appendix C. Cedar River Station TIR Cedar River Station Technical Information report February 28, 2013, Revised: June 27, 2013; Prepared by ESM Consulting Engineers. Report is located in Appendix B of this report. VII. OTHER PERMITS There are currently no other permits that effect the drainage submittal or the Technical Information Report. VIII. CSWPPP ANALYSIS AND DESIGN Please refer to Appendix A for the prepared CSWPPP IX. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT A Bond Quantities Worksheet can be made available to the city upon request X. OPERATION AND MAINTENANCE MANUAL The Operations and Maintenance Manual can be made available to the City upon request. 6 ( 196.5 2 ' 1 ( 20 7 . 3 6 ' 150.1 4 ' 1 ( 20 2 . 1 1 ' SHEET OF JOB NUMBER NO . D E S C R I P T I O N I N I T . D A T E DR A W N B Y : CH E C K E D B Y : SC A L E : HO R Z : VE R T : DA T E : Pl a n . D e s i g n . Ma n a g e 1 1 EXISTING CB UPSTREAM PIPE BASIN (PH1 & PH2) IMPERVIOUS = 12,550 SF UPSTREAM PIPE Cedar River Station, Fueling Station XI. Appendices APPENDIX A – CSWPPP CEDAR RIVER STATION FUELING STATION Construction Stormwater Pollution Prevention Plan Prepared for: Summit Petroleum Group 20207 105th Ave SE Kent, WA 98031 September 16, 2015 Prepared by: Brandon Loucks, P.E. Reviewed by: Landon C. Beyler, P.E. Beyler Consulting 7602 Bridgeport Way W., Ste-3D Lakewood, WA 98499 253.301.4157 Project Number: 13-207 Cedar River Station Fueling Station RPT-Cedar River Fueling CSWPPP 2015.09.16.docx Cedar River Station Fueling Station BC#13-207 TABLE OF CONTENTS I. Construction Pollution Prevention Plan .................................... 3 Section 1 – Project Overview ......................................................... 3 Section 2 – Erosion Control Specialist ............................................. 3 Section 3 – Existing Site Conditions ................................................ 3 Section 4 – Adjacent Areas ............................................................ 3 Section 5 – Critical Areas .............................................................. 3 Section 6 – Soils .......................................................................... 4 Section 7 – Potential Erosion Problems............................................ 4 Section 8 – Construction Stormwater Pollution Prevention Elements ... 4 Section 9 – Construction Phasing ................................................... 6 Section 10 – Construction Schedule ................................................ 7 Section 11 – Financial/Ownership Responsibilities ............................ 7 Section 12 – Engineering Calculations ............................................. 7 Section 13 – Conclusion ................................................................ 7 **EROSION CONTROL RESPONSIBILITY** The Construction Stormwater Pollution Prevention Plan should be kept onsite with a copy of the plans at all time. The objective is to control erosion and prevent sediment and other pollutants from leaving the site during the construction of the project. The owner or assigned contractor shall be responsible for maintaining erosion control Best Management Practices during construction. All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. The owner or contractor shall identify a Certified Erosion and Sediment Control Lead. This person shall be on-site or on-call at all times. The Erosion Control Lead information shall be inserted into this report. The CSWPP shall be modified, if during inspection or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the CSWPPP is ineffective in elimination or significantly minimizing pollutants in stormwater discharges from the site. The CSWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) calendar days following the inspection. Construction site operators are required to be covered by a Construction Stormwater General Permit through the Department of Ecology if they are engaged in clearing, grading, and excavating activities that disturb one or more acres and discharge stormwater to surface waters of the state. Smaller sites may also require coverage if they are part of a larger common plan of development that will ultimately disturb one acre or more. Page 3 Cedar River Station Fueling Station I. Construction Pollution Prevention Plan Section 1 – Project Overview The Cedar River Station project is a commercial development consisting of 3 buildings, Lot A (previously permitted) and a fueling station on a separate parcel , Lot B. This drainage report accompanies the site construction drawings for the proposed fueling station. The project is located within the city of Renton, parcel 2323059211. The fueling station proposal is to construction a new retail store, fueling area, associated parking & utilities, and a future car wash tunnel, which will be a part of Phase 2. Phase 2 calculations have been included in this report. The site is accessed by an entrance off of SR 169 constructed as a part of the Cedar River Station project. The existing parcel is has been rough graded under a separate permit and nearly flat with the exception of the north, south, and east perimeter where the grade slopes down to the adjacent parcels and the conveyance system within SR 169. The proposed project is located in the Lower Cedar River King County Drainage Basin (WRIA #8) within the Cedar River-Lake Washington watershed. The developed basin is made up of the entire Cedar River Station project which includes the three commercial bu ildings and the fueling station on the project parcel. All parts of this development are managed by a shared stormwater detention and treatment system. The Cedar River Station (CRS) project has previously permitted and constructed a combined water quality and detention vault with associated pipes to convey water to this flow control facility. The proposed fueling station will install additional conveyance measures to collect and convey stormwater to this facility. Stormwater discharge from the flow control facility is directed to a catch basin within the SR-169 ROW where stormwater is then released to a pipe/ditch system until runoff reach the Cedar River. Section 2 – Erosion Control Specialist An erosion control specialist is not required for the size and scope of this residential single family project. It will be responsible of the owner and/or the contractor to regularly inspect and maintain the proposed erosion control BMPs, and will take ad ditional measures, as necessary, to respond to changing site conditions. Should it become necessary the engineer will be made available to provide recommendations for additional erosion control measures to the site. Section 3 – Existing Site Conditions Existing conditions on the project site consists of a previously rough graded 0.80 acre property. As a part of the CRS project, the fueling station parcel was assumed to forested in nature, Till Forest, to determine a Predeveloped flow rate. Section 4 – Adjacent Areas The site is surrounded by SE Maple Valley Road to the North and 152 Ave SE to the west, with apartments ot the south, a mobile home part to the east, and a church to the west. Section 5 – Critical Areas There are not critical areas on or adjacent to the project site. Page 4 Cedar River Station Fueling Station Section 6 – Soils The soils are mapped as Alluvium. Alluvium is described as moderately sorted deposits of cobble gravel, pebbly sand, and sandy silt along major rivers and stream channels. Section 7 – Potential Erosion Problems Due to existing slopes and ground cover and that site is currently stabilized, a silt fence during construction anticipated to provide adequate erosion control protection of adjacent properties. Section 8 – Construction Stormwater Pollution Prevention Elements Element 1: Mark Clearing Limits The clearing limits shall be marked per the approved plans. Prior to beginning land disturbing activities, including clearing and grading, all clearing limits shall be clearly marked. Silt fence will be placed on downstream property boundaries as indicated on the project plans. Element 2: Establish Construction Access It is anticipated that one construction entrance will be established on this project site. With the use of this construction entrance vehicle access to and from the site is expected to track only minor amounts of dirt and other sediment onto the street. All sediment that is tracked onto the roadway due to construction activities will be cleaned at the end of each working day. Should sediment tracked onto the street become excessive, operations will cease until the tracked material has been removed by street sweeping and the pads have been refurbished. Element 3: Control Flow Rates Due to the size of the site and relatively minor slopes in and around the area of disturbance, existing and/or proposed check dams and interceptor ditches will not be necessary to control flow rates. The permanent stormwater system will be installed and connected to building downspouts early on in the project to control flow of runoff. Element 4: Install Sediment Controls The SWPPP plan for this project specifies the use of various erosion/sediment control measures: construction entrance and siltation fence as necessary. Th ese facilities shall be inspected weekly at the end of the work week and subsequent to each storm event. Sediment accumulation in excess of design limits shall be removed from the facilities upon identification of the condition and prior to a forecasted storm event. The construction superintendent, or owner, shall be responsible for these actions and shall be responsible for maintenance of the erosion and sediment control facilities. Site demolition and/or grading shall not occur on the site until after the silt fences have been installed. Element 5: Stabilize Soils The following constraints apply. From October 1 through April 30, no soils shall remain exposed and unworked for more than 2 days. From May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days. This condition will apply to all soils on site, whether at final grade or not. The areas outside of the roadway will be stabilized with mulch, grass planting or other approved erosion control treatment during the construction phase. Page 5 Cedar River Station Fueling Station Element 6: Protect Slopes There will be no construction or clearing in the location of the steep slopes on the site. Clearing limits are to be established and silt fence provided to protect the existing wetland and stream on site during construction. Other areas of slopes during construction will likely exist due to excavation of pipe trenches and other soil stockpiling. These slopes shall be minimized as much as possible by backfilling trenches at the end of each working da y and covering slopes that remain exposed and unworked as mentioned under Element 5. Element 7: Protect Drain Inlets The inlets to the proposed storm drainage dispersion trenches will be protected by keeping all pipe inlets closed/caped until permanent connection to prevent sediments from entering the conveyance system. The construction entrance to the site will minimize the tracking of dirt to the local streets. Element 8: Stabilize Channels and Outlets There are no channels either existing or proposed nor are there any existing or proposed outlets to channels. Element 9: Control Pollutants Control of pollutants are the responsibility of the construction superintendent. Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities that may result in discharge or spillage of pollutants to the ground or into stormwater runoff must be conducted using spill prevention measures, such as drip pans. Contaminated surfaces will be cleaned immediately following any discharge or spill incident. The superintendent will be expected to use his best judgment in addressing any and all conditions that are potentially damaging to the environment. Emergency repairs may be performed on-site using temporary plastic placed beneath and, if raining, over the vehicle. All pollutants, including waste materials and demolition debris that occur on-site during construction shall be handled and disposed of in a manner that does not cause contamination of stormwater. Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and non -inert wastes present on the site. The contractor shall provide a centralized area for the storage, maintenance, and refueling of construction equipment and for washing of concrete truck drums. All runoff from the area shall be intercepted by a trench around the downslope side of the area and detai ned until it can be removed by a ‘Vactor’ truck and properly disposed of in an approved facility. Element 10: Control De-Watering No requirement for de-watering is anticipated. However, if encountered, de-watering shall be discharged into a closed conveyance system for discharge from the site. Highly turbid or otherwise contaminated dewatering water, such as from construction equipment operation will be handled separately from stormwater. Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. All Page 6 Cedar River Station Fueling Station maintenance and repair will be conducted in accordance with standard procedures for the BMPs. Sediment control BMPs will be inspected weekly or after a runoff-producing storm event during the dry season and daily during the wet season. All temporary erosion and sediment control BMPs will be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil areas resulting from removal of BMPs or vegetation will be permanently stabilized with mulch, grass planting or other approved erosion control treatment. Element 12: Manage the Project Site construction will be performed after the erosion and sediment control measures have been constructed. From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if the transport of sediment from the construction site to receiving waters will be prevented through a combination of favorable site and weather conditions, limitations on extent of activity, and proposed erosion and sediment control measures. The Contractor and/or owner should stop the permitted activity if sediment leaves the construction site causing a violation of the surface water quality standard or if erosion and sediment control measures are not adequately maintained. Trenches will be opened only immediately prior to construction and the trenches will be backfilled immediately after any required testing or inspections of the installed improvements. Trenching spoils will be treated as other disturbed earthwork and measures will be taken to cover or otherwise stabilize the material, as required. All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Section 9 – Construction Phasing The recommended construction sequence will include these steps in this order, but some portions of the steps may be performed out of sequence as conditions require. The Construction Sequence is as follows: 1. Pre-construction meeting. 2. Post sign with name and phone number of esc supervisor (may be consolidated with the required notice of construction sign). 3. Flag or fence clearing limits. 4. Install catch basin protection if 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. Page 7 Cedar River Station Fueling Station 10. Maintain erosion control measures in accordance with appendix D of the surface water design manual and manufacturer's recommendations. 11. Relocate erosion control measures or install new measures so that as site conditions change the erosion and sediment control is always in accordance with the city’s erosion and sediment control 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, plastic sheeting 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. Contractor to make connections to existing facilities only after proposed storm and sewer systems have been inspected and accepted of by the City of Renton. All storm drainage facilities shall be protected in place from construction activity via brightly flagged stakes or, if necessary, temporary construction fencing. Section 10 – Construction Schedule The project is intended to begin construction within the year. Special consideration is required for source control during the wet season period, which may include phased construction, materials available for immediate stabilization of denuded areas and diligent review of site for noted erosion concerns. Section 11 – Financial/Ownership Responsibilities The property owner will be responsible for bonds and other required securities for this project. Section 12 – Engineering Calculations No calculations were required during the construction of this SWPPP plan. Section 13 – Conclusion Erosion control procedures as described in this report and illustrated on the design plans, if properly implemented, should mitigate anticipated erosion effects from the development of this project. The success of erosion control measures is usually related to the Contractor’s attention to maintenance of such measures. However, in some instances, even with proper attention being paid to erosion control, measures such as those shown on the plans are unable to prevent the discharge of turbid water to the city storm system. In this event, secondary measures may be required. These additional BMPs are provided in Volume II of the Surface Water Management Manual. Cedar River Station, Fueling Station APPENDIX B – CEDAR RIVER STATION TIR Cedar River Station, Fueling Station APPENDIX C – INFILTRATION LETTER Page 1 of 3 MIGIZI GROUP, INC. PO Box 44840 PHONE (253) 537-9400 Tacoma, Washington 98448 FAX (253) 537-9401 February 10, 2016 Jaspinder “JP” Athwal 20207 105th Avenue SE Kent, WA 98031 Subject: Infiltration Letter Cedar River Chevron 15355 Maple Valley Highway Renton, Washington MGI Project P552-T16 Dear Mr. Athwal: Migizi Group, Inc. (MGI) is pleased to submit this letter describing estimated infiltration rates based on previously placed test pits by E3RA, Inc. (E3RA), described in their letter dated November 22, 2013, and borings and test pits by Earth Consulting Incorporated (ECI), dated October 1, 2007 for your site and the neighboring site to the west in Renton, Washington. Our scope of services is limited to surface observations, geotechnical research, and a review of the above referenced reports. This letter has been prepared for the exclusive use of Jaspinder “JP” Athwal, and his consultants, for specific application to this project, in accordance with generally accepted geotechnical practice. After reviewing the two test pit logs placed on your site (TP-1 and TP-2) and descriptions provided in the letter prepared by E3RA, we can provide prescriptive infiltration rates and an estimated design infiltration rate. In the area of test pit TP-1, silty sand (SM) was encountered to a depth of 7½ feet below ground surface (bgs) in existence at that time. Underlying the silty sand, they encountered a brown fine to medium sand (SP) to the termination depth of the test pit at 9 feet bgs. In the vicinity of test pit TP-2, silty sand (SM) was encountered to a depth of 4 feet bgs. Underlying the silty sand to the termination depth of the test pit at 9 feet bgs, fine to medium sand (SP) was encountered. No groundwater was encountered at the time of E3RA’s explorations assumed to be approximately at the time of letter preparation, was on or around November 22, 2013. No mottling or oxidation was identified in the E3RA’s test pits logs. E3RA’s test pits logs are in general agreement with the borings and test pit logs found in the ECI report. Jaspinder “JP” Athwal – Cedar River Chevron, 15355 Maple Valley Hwy, Renton, WA February 10, 2016 Infiltration Letter P552-T16 Migizi Group, Inc. Page 2 of 3 From the ECI report we can infer that the site is underlain by gravel at greater depths. The ECI report also indicates at the time of their boring explorations in winter of 2002 that groundwater was encountered at depths of approximately 7 feet bgs at that time and noted on the test pit logs (TP-4 and TP-5) during the summer of 2000 that mottling or oxidation was present at 5½ feet bgs in test pit TP-4 and 4 feet bgs in test pit TP-5. Their exploration log notes indicate that they expected seasonal groundwater to reach the depths of 5½ feet and 4 feet bgs, respectively, in these locations. Test pit TP-4 is the closest to your site approximately 100 feet west. Based on the above described test pit logs, we can estimate that the silty sands (SM) found in the upper 4 feet of test pit TP-2 and 7½ feet of test pit TP-1 will have a design infiltration rate of 0.5 inches/hr based on Table 3.7 – Recommended Infiltration Rates based on USDA soil textural Classification found in the Department of Ecology Stormwater Design Manual 2005. Based on the King County Stormwater Design Manual 2009, a prescriptive rate of 75 LF of infiltration trench per 1,000 sf of impervious surface or a drywell of 230 cubic feet per 1,000 sf of impervious surface can be used in the silty sands. Based on the above described test pit logs, we can estimate that the sand layer (SP) found below 4 feet in test pit TP-2 and below 7½ feet of test pit TP-1 will have a design infiltration rate of 2 inches/hr based on Table 3.7 – Recommended Infiltration Rates based on USDA soil textural Classification found in the Department of Ecology Stormwater Design Manual 2005. Based on the King County Stormwater Design Manual 2009, a prescriptive rate of 30 LF of infiltration trench per 1,000 sf of impervious surface or a drywell of 60 cubic feet per 1,000 sf of impervious surface can be used in the sands. We recommend the infiltration trenches be designed and placed according to the City of Renton drainage requirements and that soils be verified at the time of construction in the proposed infiltration locations to verify the estimated infiltration rates recommende d in this letter. This letter is written relying expressly on the soil log descriptions provided in E3RA’s letter and sealed by Dean White, P.E. and the Geotechnical Report prepared by ECI.