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2021.0330.PR0010 SW Site Plan_print Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan Prepared for June 2021 Prepared by June 2021 │ 216-1781-042 Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan Prepared for City of Yelm 106 Second St. SE Yelm, WA 98597 Prepared by Parametrix 1019 39th Avenue SE, Suite 100 Puyallup, WA 98374 T. 253.604.6600 F. 1.855.542.6353 www.parametrix.com CITATION Parametrix. 2021. Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan. Prepared by Parametrix, Puyallup, Washington. June 2021. Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 CERTIFICATION The technical material and data contained in this document were prepared under the supervision and direction of the undersigned, whose seal, as a professional engineer licensed to practice as such, is affixed below. Prepared by Jeffrey L. Coop, PE Checked by Randy Raymond, PE Approved by Brian Bunker, PE This Page Intentionally Left Blank Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 i TABLE OF CONTENTS 1. OVERVIEW ................................................................................................................................ 1-1 1.1 Step 1 – Analyze Existing Site Conditions to Determine LID Feasibility ....................................... 1-1 1.1.1 Schedule A, Liquid Stream Improvements ............................................................... 1-1 1.1.2 Schedule B, Solids Improvements ............................................................................ 1-2 1.2 Step 2 – Prepare the Preliminary Development Layout .............................................................. 1-3 1.2.1 Schedule A, Liquid Stream Improvements ............................................................... 1-3 1.2.2 Schedule B, Solids Improvements ............................................................................ 1-3 1.3 Step 3 – Perform an Off-Site Analysis.......................................................................................... 1-3 1.3.1 Schedule A, Liquid Stream Improvements ............................................................... 1-3 1.3.2 Schedule B, Solids Improvements ............................................................................ 1-3 1.4 Step 4 – Determine and Read the Applicable Minimum Requirements ...................................... 1-3 1.5 Step 5 – Prepare a Permanent Stormwater Control Plan ............................................................ 1-8 1.5.1 Schedule A, Liquid Stream Improvements ............................................................... 1-8 1.5.2 Schedule B, Solids Improvements ............................................................................ 1-8 1.6 Step 6 – Prepare a Construction Stormwater Pollution Prevention Plan .................................. 1-11 1.6.1 Schedule A, Liquid Stream Improvements ............................................................. 1-11 1.6.2 Schedule B, Solids Improvements .......................................................................... 1-11 1.7 Step 7 – Complete the Stormwater Site Plan ............................................................................ 1-12 1.7.1 Schedule A, Liquid Stream Improvements ............................................................. 1-12 1.7.2 Schedule B, Solids Improvements .......................................................................... 1-12 1.8 Step 8 – Check Compliance with All Applicable Minimum Requirements ................................. 1-12 LIST OF FIGURES Figure 1-1. Permanent Stormwater Control Plan .............................................................................. 1-9 LIST OF TABLES Table 1-1. Summary of Minimum Requirements ............................................................................... 1-4 Table 1-2. Summary of Existing Land Cover Area Calculations .......................................................... 1-7 Table 1-3. Summary of Post-Project Land Cover Area Calculations ................................................... 1-7 Table 1-4. Summary of Area Changes ................................................................................................ 1-8 APPENDICES A Stormwater Plans B Area Calculations C Construction SWPPP Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 iii ACRONYMS AND ABBREVIATIONS Ecology Manual Stormwater Management Manual for Western Washington Ecology Washington State Department of Ecology mgd million gallons per day Project WRF Phase 2 Upgrades sf square feet SWPPP Stormwater Pollution Prevention Plan TDA Threshold Discharge Area WRF Water Reclamation Facility Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 1-1 1. OVERVIEW The City of Yelm’s existing Water Reclamation Facility (WRF) was designed in 1995 to treat maximum monthly flows of up to 1.06 million gallons per day (mgd) to Class A reclaimed water standards using several treatment steps. If the quality of the treated water meets permit limits for reclaimed water and there is a demand for reuse later, the reclaimed water is pumped to the beneficial use sites. The WRF Phase 2 Upgrades Project (the Project) includes design of treatment processes to improve treatment levels to better meet the Class A reclaimed water standard. This portion of the Project is referred to as Schedule A, Liquid Stream Improvements. In addition to treatment improvements, the Project proposes solids handling improvements which includes the construction of a new receiving station and installation of equipment to produce a Class A biosolid. This portion of the Project is referred to as Schedule B, Solids Improvements. This Construction Stormwater Pollution Prevention Plan (SWPPP) has been prepared to reflect the two different schedules due to variations in the design schedule. The final SWPPP will reflect both Schedule A and Schedule B. Schedule A site modifications are located in Threshold Discharge Areas (TDA) 2, 3 and 4. Schedule A site modifications applicable to this SWPPP are summarized as follows: • A slab for a new generator; • A new electrical and mechanical building; • A new membrane bioreactor tank; • A new pump station building; and • New pavement for site circulation where proposed improvements are constructed within the footprint of the existing pavement. Schedule B site modifications are located in TDA 1. Those modifications applicable to this SWPPP are summarized as follows: • Construction of a new slab for loading biosolids. The slab will have a roof to prevent rainfall from falling on the biosolids during the loading process. 1.1 Step 1 – Analyze Existing Site Conditions to Determine LID Feasibility 1.1.1 Schedule A, Liquid Stream Improvements The site is not considered a redevelopment project based on the limited amount of stormwater-runoff generating impervious area. Consequently, the Project is considered a new Project. Based on the area calculations, all nine Minimum Requirements are triggered at the Project level. Minimum Requirement #5, On-Site Stormwater Management, is triggered because the Project is not exempt from flow control at the Project level even though stormwater on the site infiltrates due to the permeability of the soils. Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm 1-2 June 2021 │ 216-1781-042 Schedule A includes surfaces in TDA 2, 3, and 4. Surfaces include lawn/landscaping, roofs, and pavement. BMPs for Minimum Requirement #5 were selected from List 2 of Table I-3.2, The List Approach for MR5 Compliance, in Volume I, Chapter 3 of the Washington State Department of Ecology’s (Ecology’s) Stormwater Management Manual for Western Washington (Ecology Manual). Applicable BMPs are identified in Table 1-1 below. Other BMPs from List 2 of Table I-3.2 of Volume I, Chapter 3 of the Ecology Manual were not selected based on the following: • Roofs:  BMP T5.30: Full Dispersion – this could impact potential future expansion due to land encumbrance of the dispersion area.  BMP T5.10A: Downspout Full Infiltration – TDAs 2, 3, and 4 are exempt from flow control. Full infiltration is not required.  BMP T7.30: Bioretention – TDA 2 does not create additional pollution-generating impervious surface. TDAs 3 and 4 are below the thresholds triggering water quality treatment. Bioretention is not applicable.  BMP T5.10C: Perforated Stub-out Connections – There is limited existing conveyance systems to connect to. Although there are some proposed conveyance systems, they are not necessarily located near where downspouts would be located. This BMP is not applicable. • Other Hard Surfaces:  BMP T5.30: Full Dispersion – This could impact potential future expansion due to land encumbrance of the dispersion area.  BMP T5.15: Permeable Pavements – This BMP was not selected due to spill potential.  BMP T7.30: Bioretention – TDA 1 does not create additional pollution-generating impervious surface. TDAs 3 and 4 do not trigger water quality treatment. Bioretention is not applicable.  BMP T5.11: Concentrated Flow Dispersion – The site design for other hard surfaces does not result in concentrated flow discharges. This BMP is not applicable. 1.1.2 Schedule B, Solids Improvements Schedule B includes surfaces in TDA 1. Surfaces include roofs for the solids improvement area. Applicable BMPs are identified in Table 1-1 below. Other BMPs from List 2 of Table I-3.2 of Volume I, Chapter 3 of the Ecology Manual were not selected based on the following: • Roofs:  BMP T5.30: Full Dispersion – This could impact potential future expansion due to land encumbrance of the dispersion area.  BMP T5.10A: Downspout Full Infiltration – TDA 1 is exempt from flow control. Full infiltration is not required. Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 1-3  BMP T7.30: Bioretention – TDA 1 does not create additional pollution-generating impervious surface. Water quality treatment is not triggered. Bioretention is not applicable.  BMP T5.10C: Perforated Stub-out Connections – There are no existing conveyance systems to connect to; this BMP is not applicable. 1.2 Step 2 – Prepare the Preliminary Development Layout 1.2.1 Schedule A, Liquid Stream Improvements See the plans in Appendix A for the site layout. 1.2.2 Schedule B, Solids Improvements See the plans in Appendix A for the site layout. 1.3 Step 3 – Perform an Off-Site Analysis 1.3.1 Schedule A, Liquid Stream Improvements An off-site analysis is not applicable. Site soils are permeable. Stormwater will be dispersed and infiltrate or route directly to an existing infiltration swale. 1.3.2 Schedule B, Solids Improvements An off-site analysis is not applicable. Site soils are permeable. Stormwater will be dispersed and infiltrate or route directly to an existing infiltration swale. 1.4 Step 4 – Determine and Read the Applicable Minimum Requirements Minimum Requirements for both Schedule A, Liquid Stream Improvements, and Schedule B, Solids Improvements, are summarized in Table 1-1 below. Table 1-1 was prepared based on the results of the area calculations, which are summarized in Table 1-2, Table 1-3, and Table 1-4. Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm 1-4 June 2021 │ 216-1781-042 Table 1-1. Summary of Minimum Requirements Minimum Requirement Site, Liquid Stream Improvements + Solids Improvements Threshold Discharge Area (TDA) 1 Threshold Discharge Area (TDA) 2 Threshold Discharge Area (TDA) 3 Threshold Discharge Area (TDA) 4 1 Preparation of Stormwater Site Plans Applicable; Project results in 5,000 square feet (sf) or more of new plus replaced hard surface area Applicable at Site level 2 Construction Stormwater Pollution Prevention Plan (SWPPP) Applicable; Project results in 5,000 sf or more of new plus replaced hard surface area Applicable at Site level 3 Source Control of Pollution Applicable; Project results in 5,000 sf or more of new plus replaced hard surface area Applicable at Site level 4 Preservation of Natural Drainage Systems and Outfalls Applicable; Project results in 5,000 sf or more of new plus replaced hard surface area Applicable at Site level 5 On-Site Stormwater Management Applicable; Project results in 5,000 sf or more of new plus replaced hard surface area • Roof: BMP T5.10B: Downspout Dispersion Systems • Hard Surfaces: BMP T5.12: Sheet Flow Dispersion • Roof: BMP T5.10B: Downspout Dispersion Systems • Hard Surfaces: BMP T5.12: Sheet Flow Dispersion • Lawn/Landscaping: BMP T5.13: Post-Construction Soil Quality and Depth • Roof: BMP T5.10B: Downspout Dispersion Systems • Hard Surfaces: BMP T5.12: Sheet Flow Dispersion • Lawn/Landscaping: BMP T5.13: Post- Construction Soil Quality and Depth (table continues) Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 1-5 Minimum Requirement Site, Liquid Stream Improvements + Solids Improvements Threshold Discharge Area (TDA) 1 Threshold Discharge Area (TDA) 2 Threshold Discharge Area (TDA) 3 Threshold Discharge Area (TDA) 4 6 Runoff Treatment Applicable at Project level; review applicability at TDA level Not applicable; <5,000 sf of pollution- generating hard surface Not applicable; <5,000 sf of pollution- generating hard surface Not applicable; <5,000 sf of pollution- generating hard surface Not applicable; <5,000 sf of pollution- generating hard surface 7 Flow Control Applicable at Project level; review applicability at TDA level Not applicable; <10,000 sf effective impervious area Not applicable; <10,000 sf effective impervious area Not applicable; <10,000 sf effective impervious area Not applicable; <10,000 sf effective impervious area 8 Wetlands Protection Applicable; Project results in 5,000 sf or more of new plus replaced hard surface area Applicable at Site level 9 Operation and Maintenance Applicable; Project results in 5,000 sf or more of new plus replaced hard surface area Applicable at Site level Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 1-7 Table 1-2. Summary of Existing Land Cover Area Calculations Threshold Discharge Area (TDA) Grass Roof, NPGISa PGISb Impervious Subtotal Total Area 1 square feet 2,998 0 0 0 2,998 acre 0.069 0.000 0.000 0.000 0.069 2 square feet 1,393 0 0 0 1,393 acre 0.032 0.000 0.000 0.000 0.032 3 square feet 11,367 693 6,404 7,097 18,464 acre 0.261 0.016 0.147 0.163 0.424 4 square feet 13,715 4,966 14,866 19,832 33,546 acre 0.315 0.114 0.341 0.455 0.770 PROJECT square feet 29,473 5,659 21,270 26,929 56,402 acres 0.677 0.130 0.488 0.618 1.295 a NPGIS = nonpollution-generating impervious surface b PGIS = pollution-generating impervious surface Table 1-3. Summary of Post-Project Land Cover Area Calculations Threshold Discharge Area (TDA) New and Remaining Landscaping New and Remaining Roof and other NPGISa New and Remaining PGISb Total 1 square feet 0 2,998 0 2,998 acre 0.000 0.069 0.000 0.069 2 square feet 0 1,393 0 1,393 acre 0.000 0.032 0.000 0.032 3 square feet 757 4,501 8,807 14,064 acre 0.017 0.103 0.202 0.323 4 square feet 9,687 5,466 18,398 33,551 acre 0.222 0.125 0.422 0.770 PROJECT square feet 10,444 14,358 27,204 52,006 acre 0.240 0.330 0.625 1.194 a NPGIS = nonpollution-generating impervious surface b PGIS = pollution-generating impervious surface Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm 1-8 June 2021 │ 216-1781-042 Table 1-4. Summary of Area Changes Threshold Discharge Area (TDA) Net Change in Impervious Net Change in PGISa Added NPGISb Added PGIS Total Added NPGIS + PGIS 1 square feet 2,998 0 2,998 0 2,998 Acre 2 square feet 1,393 0 1,393 0 1,393 Acre 3 square feet 6,210 2,403 2,552 4,866 7,417 acre 4 square feet 4,032 3,532 0 3,975 3,975 acre PROJECT square feet 41,562 5,934 6,943 8,841 15,784 acre a PGIS = pollution-generating impervious surface b NPGIS = nonpollution-generating impervious surface 1.5 Step 5 – Prepare a Permanent Stormwater Control Plan 1.5.1 Schedule A, Liquid Stream Improvements See Figure 1-1 for the Permanent Stormwater Control Plan for the BMPs identified in Table 1-1 for Schedule A. Schedule A includes a pipe discharge to the existing swale for energy dissipation. The outlet will be stabilized with a rock pad. See Appendix B for the rock pad sizing calculations. 1.5.2 Schedule B, Solids Improvements See Figure 1 for the Permanent Stormwater Control Plan for the BMPs identified in Table 1-1 for Schedule B. PB ROOFROOFROOFSLABDRIVEWAYDRIVEWAYTDA 1TDA 3TDA 2TDA 4DATE: June 15, 2021 FILE: PS1781042-F010SCALE IN FEET60Yelm Water Reclamation Facility Phase 2 UpgradesYelm, WashingtonFigure 1Permanent StormwaterControl PlanBMP T5.13: POST-CONSTRUCTIONSOIL QUALITY AND DEPTHBMP T5.10B: DOWNSPOUTDISPERSION SYSTEMSBMP T5.12: SHEET FLOWDISPERSIONENERGY DISSIPATION50'25'LEGEND Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm June 2021 │ 216-1781-042 1-11 1.6 Step 6 – Prepare a Construction Stormwater Pollution Prevention Plan 1.6.1 Schedule A, Liquid Stream Improvements The Construction SWPPP is included in Appendix C. TESC BMPs identified for Schedule A include the following: • BMP C103, High-Visibility Fence • BMP C105, Stabilized Construction Access • BMP C151, Concrete Handling • BMP C152, Sawcutting and Surface Pollution Prevention • BMP C153, Material Delivery, Storage and Containment • BMP C154, Concrete Washout Area • BMP C160, Certified Erosion and Sediment Control Lead • BMP C162, Scheduling • BMP C220, Inlet Protection • BMP C251, Construction Stormwater Filtration • BMP C252, Treating and Disposing of High pH Water 1.6.2 Schedule B, Solids Improvements The Construction SWPPP is included in Appendix C. TESC BMPs identified for Schedule B include the following: • BMP C103, High-Visibility Fence • BMP C105, Stabilized Construction Access • BMP C151, Concrete Handling • BMP C153, Material Delivery, Storage and Containment • BMP C154, Concrete Washout Area • BMP C160, Certified Erosion and Sediment Control Lead • BMP C162, Scheduling • BMP C251, Construction Stormwater Filtration • BMP C252, Treating and Disposing of High pH Water Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm 1-12 June 2021 │ 216-1781-042 1.7 Step 7 – Complete the Stormwater Site Plan 1.7.1 Schedule A, Liquid Stream Improvements Stormwater conveyance and stormwater management BMPs applicable to Schedule A are shown in the plans in Appendix A. 1.7.2 Schedule B, Solids Improvements Stormwater conveyance and stormwater management BMPs applicable to Schedule B are shown in the plans in Appendix A. 1.8 Step 8 – Check Compliance with All Applicable Minimum Requirements Applicable Minimum Requirements are summarized in above in Table 1-1 in Step 5. There are no additional requirements. Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm April 2021 │ 216-1781-042 1-13 Appendix A Stormwater Plans Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm 1-14 April 2021 │ 216-1781-042 Appendix B Area Calculations PB OFCITY OF YELMYELM WATER RECLAMATION FACILITY PHASE 2UPGRADESYELM, WASHINGTON252PRELIM INARY 90%ENGINEERING . PLANNING . ENVIRONMENTAL SCIENCES1019 39TH AVENUE SE, SUITE 100 | PUYALLUP, WA 98374P 253.604.6600WWW.PARAMETRIX.COMIF NOT, SCALE ACCORDINGLYONE INCH AT FULL SCALE.REVIEW SUBMITTAL75C003OVERALL SITE PLANPLANSCALE IN FEET03060SOLIDS HANDLING BLDGMAINTENANCE BLDGCONTROL BLDGROOFGEN SET, SEE SHEET S422FUTURE PSE TRANSFORMEROPENTANKOPEN TANKOPENTANKROOFPSE TRANSFORMEROPEN TANKROOFROOFOPEN TANK60 ftExisting GrassExisting Roof or NPGISExisting PGIS2,723 sf136 sf128 sfTDA 1TDA 3209 sf448 sfTDA 21,243 sf1,174 sf952 sf21 sf9,054 sf5,124 sf1,280 sf1,767 sf13,715 sf3,574 sf1,751 sf11,292 sf1,447 sf50 sf223 sf50 sf11 sfMECH / ELECBLDGWASPUMPSTABLOWERBLDG /AERATIONBLOWERSHEADWORKSCENTRIFUGEFEED PUMPSTASOLIDSHANDLING &EQUIP PADSFILTERS PB OFCITY OF YELMYELM WATER RECLAMATION FACILITY PHASE 2UPGRADESYELM, WASHINGTON252PRELIM INARY 90%ENGINEERING . PLANNING . ENVIRONMENTAL SCIENCES1019 39TH AVENUE SE, SUITE 100 | PUYALLUP, WA 98374P 253.604.6600WWW.PARAMETRIX.COMIF NOT, SCALE ACCORDINGLYONE INCH AT FULL SCALE.REVIEW SUBMITTAL75C003OVERALL SITE PLANPLANSCALE IN FEET03060SOLIDS HANDLING BLDGMAINTENANCE BLDGCONTROL BLDGROOFGEN SET, SEE SHEET S422FUTURE PSE TRANSFORMEROPENTANKOPEN TANKOPENTANKROOFPSE TRANSFORMEROPEN TANKROOFROOFOPEN TANK60 ftPost-project GrassPost-project Roof or NPGISPost-project PGISExisting Roof or NPGIS to remainRedeveloped PGISExisting Grass to remainTDA 1TDA 3136 sf128 sf1,243 sf209 sf3,415 sf704 sf369 sf448 sf50 sf50 sf1,767 sf1,548 sf4,869 sf4,818 sf3,975 sf877 sfTDA 22,604 sf3,380 sf1,174 sf2,240 sf277 sf1,751 sf8,158 sf1,252 sf4,514 sf1,447 sf2,208 sfTDA 42,723 sf11 sfMECH / ELECBLDGWASPUMPSTABLOWERBLDG /AERATIONBLOWERSHEADWORKSCENTRIFUGEFEED PUMPSTASOLIDSHANDLING &EQUIP PADSFILTERS PB OFCITY OF YELMYELM WATER RECLAMATION FACILITY PHASE 2UPGRADESYELM, WASHINGTON252PRELIM INARY 90%ENGINEERING . PLANNING . ENVIRONMENTAL SCIENCES1019 39TH AVENUE SE, SUITE 100 | PUYALLUP, WA 98374P 253.604.6600WWW.PARAMETRIX.COMIF NOT, SCALE ACCORDINGLYONE INCH AT FULL SCALE.REVIEW SUBMITTAL75C003OVERALL SITE PLANPLANSCALE IN FEET03060SOLIDS HANDLING BLDGMAINTENANCE BLDGCONTROL BLDGROOFGEN SET, SEE SHEET S422FUTURE PSE TRANSFORMEROPENTANKOPEN TANKOPENTANKROOFPSE TRANSFORMEROPEN TANKROOFROOFOPEN TANK60 ftBased on aerial photography and presence of multiple open basins, site has less than 35% impervious cover. This is not a redevelopment project.Total new (added) impervious = 15,784 sq ftAll Minimum Requirements (MR) triggered at project levelTDA 1:Total new (added) impervious = 2,998 sq ftExempt from MR 7 (flow control); < 10,000 sq ft)TDA 2:Total new (added) impervious = 1,393 sq ftExempt from MR 7 (flow control); < 10,000 sq ft)TDA 3:Total new (added) PGHS = 4,866 sq ftExempt from MR 6 (runoff treatment) < 5,000 sq ftTotal new (added) impervious = 7,417 sq ftExempt from MR 7 (flow control); < 10,000 sq ft)TDA 4:Total new (added) impervious = 3,975 sq ftExempt from MR 7 (flow control); < 10,000 sq ft)Applicable MRs for each TDA:MR 1 - Preparation of Stormwater Site PlanMR 2 - Construction SWPPPMR 3 - Source Control of PollutantsMR 4 - Preservation of Natural Drainage Systems and OutfallsMR 5 - On-Site Stormwater ManagementMR 8 - Wetlands ProtectionMR 9 - Operation and MaintenanceNEW Post-project Roof orNPGISNEW Post-projectPGISTDA 1TDA 3136 sf128 sf209 sfTDA 21,243 sf2,657 sf3,380 sf208 sf103 sf1,174 sf3,992 sf50 sf50 sf11 sf2,723 sfMECH / ELECBLDGWASPUMPSTABLOWERBLDG /AERATIONBLOWERSHEADWORKSCENTRIFUGEFEED PUMPSTASOLIDSHANDLING &EQUIP PADSFILTERS CITY OF YELM WRF Phase 2 Upgrades Summary of Area Calculations Updated 6/11/21 Existing Cover Post-Project Cover TDA Grass Roof, NPGIS PGIS Impervious Subtotal Total area New and Remaining Landscaping New and Remaining Roof and other NPGIS New and Remaining PGIS Total Net Change in Impervious Net Change in PGIS Added NPGIS Added PGIS Total Added NPGIS + PGIS 1 sq ft 2,998 0 0 0 2,998 0 2,998 0 2,998 2,998 0 2,998 0 2,998 ac 0.069 0.000 0.000 0.000 0.069 0.000 0.069 0.000 0.069 2 sq ft 1,393 0 0 0 1,393 0 1,393 0 1,393 1,393 0 1,393 0 1,393 ac 0.032 0.000 0.000 0.000 0.032 0.000 0.032 0.000 0.032 3 sq ft 11,367 693 6,404 7,097 18,464 757 4,501 8,807 14,064 6,210 2,403 2,552 4,866 7,417 ac 0.261 0.016 0.147 0.163 0.424 0.017 0.103 0.202 0.323 4 sq ft 13,715 4,966 14,866 19,832 33,546 9,687 5,466 18,398 33,551 4,032 3,532 0 3,975 3,975 ac 0.315 0.114 0.341 0.455 0.770 0.222 0.125 0.422 0.770 PROJECT sq ft 29,473 5,659 21,270 26,929 56,402 10,444 14,358 27,204 52,006 41,562 5,934 6,943 8,841 15,784 ac 0.677 0.130 0.488 0.618 1.295 0.240 0.330 0.625 1.194 216-1781-042 StormAreaCalcs.xlsx \ 20210611Summary Page 1 of 1 Prepared June 2021 CITY OF YELM WRF Phase 2 Upgrades Area Calculations Updated 6/11/21 Existing Cover Post-project Cover TDA Area Description Grass Roof, NPGIS PGIS Impervious Subtotal Total area 1 Solids Handling Roof 2,998 0 0 0 2,998 Sub-total, sq ft 2,998 0 0 0 2,998 Sub-total, ac 0.069 0.000 0.000 0.000 0.069 2 Generator Pad, PSE Transformer Pads 1,393 0 0 0 1,393 Sub-total, sq ft 1,393 0 0 0 1,393 Sub-total, ac 0.032 0.000 0.000 0.000 0.032 3 Effluent Filters 448 448 448 Open tank 0 0 Centrifuge feed pump sta 209 0 209 Mech/Elec Building Roof 0 0 Existing pavement east of SBR Tanks 6,404 6,404 6,404 Sidewalk at Sludge Storage Tanks 223 223 223 Reject Water PS Vault 22 22 22 Paving around Drain PS 0 0 Pavement 0 0 Grass 11,158 0 11,158 Sub-total, sq ft 11,367 693 6,404 7,097 18,464 Sub-total, ac 0.261 0.016 0.147 0.163 0.424 4 Pavement 14,866 14,866 14,866 Pond embankment 3,198 3,198 3,198 Headworks Roof 0 0 WAS/Feed Forward PS 0 0 Blower Bldg / Aeration Blowers Roof 1,767 1,767 1,767 Grass 13,715 0 13,715 Sub-total, sq ft 13,715 4,966 14,866 19,832 33,546 Sub-total, ac 0.315 0.114 0.341 0.455 0.770 TOTAL, SQ FT 29,473 5,659 21,270 26,929 56,402 TOTAL, AC 0.677 0.130 0.488 0.618 1.295 TDA 2 + 3 12,760 693 6,404 7,097 19,857 0.293 0.016 0.147 0.163 0.456 216-1781-042 StormAreaCalcs.xlsx \ 20210611 Page 1 of 1 Prepared June 2021 CITY OF YELM WRF Phase 2 Upgrades Area Calculations Updated 6/11/21 Post-project Cover TDA Area Description Grass Existing Grass to remain Subtotal Roof, NPGIS Existing Roof, NPGIS to remain Subtotal PGIS Existing PGIS to remain Subtotal Total 1 Solids Handling Roof 0 2,998 2,998 0 2,998 Sub-total, sq ft 0 2,998 0 0 2,998 Sub-total, ac 0.000 0.069 0.000 0.000 0.069 2 Generator Pad, PSE Transformer Pads 0 1,393 1,393 0 0 0 1,393 Sub-total, sq ft 0 1,393 0 0 1,393 Sub-total, ac 0.000 0.032 0.000 0.000 0.032 3 Effluent Filters 448 448 877 877 0 1,325 Open tank -2,208 -2,208 0 0 -2,208 Centrifuge feed pump sta 0 209 209 0 209 Mech/Elec Building Roof 0 3,415 3,415 0 3,415 Existing pavement east of SBR Tanks 0 0 2,604 2,604 2,604 Sidewalk at Sludge Storage Tanks 0 0 0 0 Reject Water PS Vault 0 0 0 0 Paving around Drain PS 0 0 369 369 369 Pavement 0 0 3,380 1,280 4,660 4,660 Grass 277 2,240 2,517 0 1,174 1,174 3,691 Sub-total, sq ft 757 4,501 4,923 8,807 14,064 Sub-total, ac 0.017 0.103 0.113 0.202 0.323 4 Pavement 0 0 3,975 12,671 16,647 16,647 Pond embankment 0 1,447 1,447 1,751 1,751 3,198 Headworks Roof 0 1,548 1,548 0 1,548 WAS/Feed Forward PS 0 704 704 0 704 Blower Bldg / Aeration Blowers Roof 0 1,767 1,767 0 1,767 Grass 9,687 9,687 0 0 9,687 Sub-total, sq ft 9,687 5,466 5,726 18,398 33,551 Sub-total, ac 0.222 0.125 0.131 0.422 0.770 TOTAL, SQ FT 10,444 14,358 10,649 27,204 52,006 TOTAL, AC 0.240 0.330 0.244 0.625 1.194 TDA 2 + 3 757 5,894 8,807 15,457 0.017 0.135 0.202 0.355 216-1781-042 StormAreaCalcs.xlsx \ 20210611 Page 1 of 1 Prepared June 2021 CITY OF YELM WRF Phase 2 Upgrades Area Calculations Updated 6/11/21 TDA Area Description Net Change in Impervious Net Change in PGIS Added NPGIS Added PGIS Total Added NPGIS + PGIS 1 Solids Handling Roof 2,998 Sub-total, sq ft 2,998 0 2,998 0 2,998 Sub-total, ac 2 Generator Pad, PSE Transformer Pads 1,393 Sub-total, sq ft 1,393 0 1,393 0 1,393 Sub-total, ac 3 Effluent Filters Open tank Centrifuge feed pump sta 209 Mech/Elec Building Roof 2342.7 Existing pavement east of SBR Tanks Sidewalk at Sludge Storage Tanks Reject Water PS Vault Paving around Drain PS 311.9 Pavement 3,380 Grass 1,174 Sub-total, sq ft 6,210 2,403 2,552 4,866 7,417 Sub-total, ac 4 Pavement 3,975 Pond embankment Headworks Roof WAS/Feed Forward PS Blower Bldg / Aeration Blowers Roof Grass Sub-total, sq ft 4,032 3,532 0 3,975 3,975 Sub-total, ac TOTAL, SQ FT 41,562 5,934 6,943 8,841 15,784 TOTAL, AC 216-1781-042 StormAreaCalcs.xlsx \ 20210611 Page 1 of 1 Prepared June 2021 Water Reclamation Facility – Phase 2 Upgrades Stormwater Site Plan City of Yelm April 2021 │ 216-1781-042 1-15 Appendix C Construction SWPPP Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) Prepared for June 2021 Prepared by June 2021 │ 216-1781-042 Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) Prepared for City of Yelm 106 Second St. SE Yelm, WA 98597 Prepared by Parametrix 1019 39th Avenue SE, Suite 100 Puyallup, WA 98374 T. 253.604.6600 F. 1.855.542.6353 www.parametrix.com CITATION Parametrix. 2021. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP). Prepared by Parametrix, Puyallup, Washington. June 2021. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm June 2021 │ 216-1781-042 CERTIFICATION The technical material and data contained in this document were prepared under the supervision and direction of the undersigned, whose seal, as a professional engineer licensed to practice as such, is affixed below. Prepared by Jeffrey L. Coop, PE Checked by Randy Raymond, PE Approved by Brian Bunker, PE This Page Intentionally Left Blank Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm June 2021 │ 216-1781-042 i TABLE OF CONTENTS 1. OVERVIEW ................................................................................................................................ 1-1 1.1 Element 1: Preserve Vegetation/Mark Clearing Limits ............................................................... 1-2 1.1.1 Schedule A, Liquid Stream Improvements ............................................................... 1-2 1.1.2 Schedule B, Solids Improvements ............................................................................ 1-2 1.2 Element 2: Establish Construction Access ................................................................................... 1-2 1.2.1 Schedule A, Liquid Stream Improvements ............................................................... 1-2 1.2.2 Schedule B, Solids Improvements ............................................................................ 1-2 1.3 Element 3: Control Flow Rates .................................................................................................... 1-2 1.3.1 Schedule A, Liquid Stream Improvements ............................................................... 1-2 1.3.2 Schedule B, Solids Improvements ............................................................................ 1-2 1.4 Element 4: Install Sediment Controls .......................................................................................... 1-2 1.4.1 Schedule A, Liquid Stream Improvements ............................................................... 1-2 1.4.2 Schedule B, Solids Improvements ............................................................................ 1-3 1.5 Element 5: Stabilize Soils ............................................................................................................. 1-3 1.5.1 Schedule A, Liquid Stream Improvements ............................................................... 1-3 1.5.2 Schedule B, Solids Improvements ............................................................................ 1-3 1.6 Element 6: Protect Slopes ........................................................................................................... 1-3 1.6.1 Schedule A, Liquid Stream Improvements ............................................................... 1-3 1.6.2 Schedule B, Solids Improvements ............................................................................ 1-3 1.7 Element 7: Protect Drain Inlets ................................................................................................... 1-4 1.7.1 Schedule A, Liquid Stream Improvements ............................................................... 1-4 1.7.2 Schedule B, Solids Improvements ............................................................................ 1-4 1.8 Element 8: Stabilize Channels and Outlets .................................................................................. 1-4 1.8.1 Schedule A, Liquid Stream Improvements ............................................................... 1-4 1.8.2 Schedule B, Solids Improvements ............................................................................ 1-4 1.9 Element 9: Control Pollutants ..................................................................................................... 1-4 1.9.1 Schedule A, Liquid Stream Improvements ............................................................... 1-4 1.9.2 Schedule B, Solids Improvements ............................................................................ 1-4 1.10 Element 10: Control Dewatering ............................................................................. 1-5 1.10.1 Schedule A, Liquid Stream Improvements ............................................................... 1-5 1.10.2 Schedule B, Solids Improvements ............................................................................ 1-5 1.11 Element 11: Maintain BMPs .................................................................................... 1-5 1.11.1 Schedule A, Liquid Stream Improvements ............................................................... 1-5 1.11.2 Schedule B, Solids Improvements ............................................................................ 1-5 1.12 Element 12: Manage the Project ............................................................................. 1-5 1.12.1 Schedule A, Liquid Stream Improvements ............................................................... 1-5 1.12.2 Schedule B, Solids Improvements ............................................................................ 1-5 Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm TABLE OF CONTENTS (CONTINUED) ii June 2021 │ 216-1781-042 1.13 Element 13: Protect Low Impact Development BMPs ............................................. 1-6 1.13.1 Schedule A, Liquid Stream Improvements ............................................................... 1-6 1.13.2 Schedule B, Solids Improvements ............................................................................ 1-6 APPENDICES A Temporary Erosion and Sediment Control (TESC) Plans B Hydrologic Calculations C Excerpts from Ecology Manual Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm June 2021 │ 216-1781-042 iii ACRONYMS AND ABBREVIATIONS BMPs best management practices CSWGP Construction Stormwater General Permit Ecology Manual Stormwater Management Manual for Western Washington Ecology Washington State Department of Ecology LID low impact development mgd million gallons per day Project WRF Phase 2 Upgrades SSP Stormwater Site Plan SWPPP Stormwater Pollution Prevention Plan TDAs Threshold Discharge Areas TESC Temporary Erosion and Sediment Control WRF Water Reclamation Facility Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm June 2021 │ 216-1781-042 1-1 1. OVERVIEW The City of Yelm’s existing Water Reclamation Facility (WRF) was designed in 1995 to treat maximum monthly flows of up to 1.06 million gallons per day (mgd) to Class A reclaimed water standards using several treatment steps. If the quality of the treated water meets permit limits for reclaimed water and there is a demand for reuse later, the reclaimed water is pumped to the beneficial use sites. The WRF Phase 2 Upgrades Project (the Project) includes design of treatment processes to improve treatment levels to better meet the Class A reclaimed water standard. This portion of the Project is referred to as Schedule A, Liquid Stream Improvements. In addition to treatment improvements, the Project proposes solids handling improvements which includes the construction of a new receiving station and installation of equipment to produce a Class A biosolid. This portion of the Project is referred to as Schedule B, Solids Improvements. This Construction Stormwater Pollution Prevention Plan (SWPPP) has been prepared to reflect the two different schedules due to variations in the design schedule. The final SWPPP will reflect both Schedule A and Schedule B. The site is relatively flat, has no critical areas, and highly infiltrative soils. There are no permanent stormwater management best management practices (BMPs) for flow control or water quality treatment. However, there are permanent BMPs that are triggered for Minimum Requirement 5, On- Site Stormwater Management. Schedule A site modifications applicable to this SWPPP are summarized as follows: • Clearing and grading; • Building demolition; • Pavement removal; • A slab for a new generator; • A new electrical and mechanical building; • A new membrane bioreactor tank; • A new pump station building; and • New pavement for site circulation where proposed improvements are construction within the footprint of existing pavement. Schedule B site modifications applicable to this SWPPP are summarized as follows: • Clearing and grading; and • Construction of a new slab for loading biosolids. The slab will have a roof to prevent rainfall from falling on the biosolids during the loading process. The contractor will be required to submit the Notice of Intent for coverage under the Construction Stormwater General Permit (CSWGP) and for compliance with all CSWGP testing, monitoring and reporting requirements. The Temporary Erosion and Sediment Control (TESC) BMPs identified in this Construction SWPPP are anticipated to be the minimum required. The contractor shall identify all applicable TESC BMPs based on the contractor’s Schedule And construction sequencing in a contractor- prepared SWPPP. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm 1-2 June 2021 │ 216-1781-042 1.1 Element 1: Preserve Vegetation/Mark Clearing Limits 1.1.1 Schedule A, Liquid Stream Improvements Vegetation preservation BMPs are not applicable to Schedule A. The location of clearing limits using BMP C103, High Visibility Fence, are shown in the plans in Appendix A. 1.1.2 Schedule B, Solids Improvements Vegetation preservation BMPs are not applicable to Schedule B. The location of clearing limits using BMP C103, High Visibility Fence, are shown in the plans in Appendix A. 1.2 Element 2: Establish Construction Access 1.2.1 Schedule A, Liquid Stream Improvements The location of stabilized construction entrances and exit using BMP C105, Stabilized Construction Access, are shown in the plans in Appendix A. 1.2.2 Schedule B, Solids Improvements The location of stabilized construction entrances and exit using BMP C105, Stabilized Construction Access, are shown in the plans in Appendix A. 1.3 Element 3: Control Flow Rates 1.3.1 Schedule A, Liquid Stream Improvements Based on the Stormwater Site Plan, flow control is not applicable to any of the Project’s Threshold Discharge Areas (TDAs). Also, there are no adjacent critical areas, stormwater management BMPs, or development which would require controlling flow rates during construction in Schedule A. Temporary flow rate control BMPs are not applicable. 1.3.2 Schedule B, Solids Improvements Based on the Stormwater Site Plan, flow control is not applicable to any of the Project’s TDAs. Also, there are no adjacent critical areas, stormwater management BMPs, or development which would require controlling flow rates during construction in Schedule A. Temporary flow rate control BMPs are not applicable. 1.4 Element 4: Install Sediment Controls 1.4.1 Schedule A, Liquid Stream Improvements The plans in Appendix A are based on using BMP C251, Construction Stormwater Filtration, to temporarily control sediments during construction in Schedule A. BMP C240, Sediment Trap, or BMP C241, Sediment Pond (Temporary) may be an alternative; however, those may encumber more site area Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm June 2021 │ 216-1781-042 1-3 during construction and may require more piping and pumping to discharge to existing conveyance systems. Infiltration at temporary sediment traps or temporary sediment ponds may be feasible if adequate treatment is provided to protect groundwater. Preliminary flow rate calculations are included in Appendix B. The contractor-prepared SWPPP will need to identify the contractor-selected sediment controls and document final sizing calculations and discharge points. The contractor-prepared SWPPP shall also include BMP C250, Construction Stormwater Chemical Treatment, if proposed. The contractor will be required to obtain Washington State Department of Ecology (Ecology) approval if BMP C250 is proposed. 1.4.2 Schedule B, Solids Improvements The plans in Appendix A are based on using BMP C251, Construction Stormwater Filtration, to temporarily control sediments during construction in Schedule A. BMP C240, Sediment Trap, or BMP C241, Sediment Pond (Temporary) may be an alternative; however, those may encumber more site area during construction and may require more piping and pumping to discharge to existing conveyance systems. Infiltration at temporary sediment traps or temporary sediment ponds may be feasible if adequate treatment is provided to protect groundwater. The contractor-prepared SWPPP will need to identify the contractor-selected sediment controls and document final sizing calculations and discharge points. Preliminary flow rate calculations are included in Appendix B. The contractor-prepared SWPPP shall also include BMP C250, Construction Stormwater Chemical Treatment, if proposed. The contractor will be required to obtain Ecology approval if BMP C250 is proposed. 1.5 Element 5: Stabilize Soils 1.5.1 Schedule A, Liquid Stream Improvements Disturbed areas in Schedule A that are to be vegetated are to be restored in accordance with the landscaping plans as indicated in the TESC plans in Appendix A. 1.5.2 Schedule B, Solids Improvements Disturbed areas in Schedule A that are to be vegetated are to be restored in accordance with the landscaping plans as indicated in the TESC plans in Appendix A. 1.6 Element 6: Protect Slopes 1.6.1 Schedule A, Liquid Stream Improvements Slope project is not applicable in Schedule A. 1.6.2 Schedule B, Solids Improvements Slope project is not applicable in Schedule B. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm 1-4 June 2021 │ 216-1781-042 1.7 Element 7: Protect Drain Inlets 1.7.1 Schedule A, Liquid Stream Improvements The locations of inlet protection for Schedule A using BMP C220, Inlet Protection, are shown in the plans in Appendix A. 1.7.2 Schedule B, Solids Improvements There are no existing or proposed inlets in Schedule B for which BMP C220, Inlet Protection, is applicable. 1.8 Element 8: Stabilize Channels and Outlets 1.8.1 Schedule A, Liquid Stream Improvements A permanent rock pad for energy dissipation is needed for Schedule A for the storm drain discharge into the existing swale along the westerly side of the site. The location of the rock pad is shown on the plans in Appendix A. See the Stormwater Site Plan (SSP) for details. 1.8.2 Schedule B, Solids Improvements There are no channels or outlets in Schedule B requiring temporary stabilization BMPs. 1.9 Element 9: Control Pollutants 1.9.1 Schedule A, Liquid Stream Improvements Potential pollutant sources in Schedule A include sawcutting and pavement demolition and placement of concrete. BMPs identified in the plans in Appendix A include: • BMP C151, Concrete Handling; • BMP C154, Concrete Washout Area; • BMP C152, Sawcutting and Surface Pollution Prevention; and • BMP C252, Treating and Disposing of High pH Water. 1.9.2 Schedule B, Solids Improvements Potential pollutant sources in Schedule B include placement of concrete. BMPs identified in the plans in Appendix A include: • BMP C151, Concrete Handling; • BMP C154, Concrete Washout Area; and • BMP C252, Treating and Disposing of High pH Water. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm June 2021 │ 216-1781-042 1-5 1.10 Element 10: Control Dewatering 1.10.1 Schedule A, Liquid Stream Improvements Dewatering in Schedule A is not anticipated due to the depth to groundwater. 1.10.2 Schedule B, Solids Improvements Dewatering in Schedule A is not anticipated due to the depth to groundwater. 1.11 Element 11: Maintain BMPs 1.11.1 Schedule A, Liquid Stream Improvements See the excerpts in Appendix C from the Stormwater Management Manual for Western Washington (Ecology Manual) for maintenance requirements of TESC BMPs in Schedule A. 1.11.2 Schedule B, Solids Improvements See the excerpts in Appendix C from the Ecology Manual for maintenance requirements of TESC BMPs in Schedule B. 1.12 Element 12: Manage the Project 1.12.1 Schedule A, Liquid Stream Improvements The contractor will need to manage the Project so that stormwater discharges during construction meet the requirements of the CSWGP. To support this, Appendix C includes the following BMPs for Schedule A: • BMP C153, Material Delivery, Storage and Containment; • BMP C160, Certified Erosion and Sediment Control Lead; and • BMP C162, Scheduling. 1.12.2 Schedule B, Solids Improvements The contractor will need to manage the Project so that stormwater discharges during construction meet the requirements of the CSWGP. To support this, Appendix C includes the following BMPs for Schedule A: • BMP C153, Material Delivery, Storage and Containment; • BMP C160, Certified Erosion and Sediment Control Lead; and • BMP C162, Scheduling. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm 1-6 June 2021 │ 216-1781-042 1.13 Element 13: Protect Low Impact Development BMPs 1.13.1 Schedule A, Liquid Stream Improvements There are no existing or proposed low impact development (LID) BMPs in Schedule A to be protected. However, the roof downspout dispersion systems as shown in the plans with the SSP include vegetated areas downstream of splashblocks or rock splash pads. Those areas will need to be protected if they are constructed prior to the roof downspouts being installed. 1.13.2 Schedule B, Solids Improvements There are no existing or proposed LID BMPs in Schedule A to be protected. However, the roof downspout dispersion systems as shown in the plans with the SSP include vegetated areas downstream of splashblocks or rock splash pads. Those areas will need to be protected if they are constructed prior to the roof downspouts being installed. Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm April 2021 │ 216-1781-042 1-1 Appendix A Temporary Erosion and Sediment Control (TESC) Plans Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm 1-2 April 2021 │ 216-1781-042 Appendix B Hydrologic Calculations CITY OF YELM WRF Phase 2 Upgrades TESC Calculations for filtration systems, BMP C251, Construction Stormwater Filtration Updated 6/11/21 for updated biodryer footprint Drawdown time, hours:8 Factor: Area Description SS2G name Grass Roof, NPGIS PGIS Total Impervious 10-yr 24-hr runoff volume, cu ft 1.5 Treatment rate, gpm Solids Handling Roof TDA 1 0 2,998 0 2,998 Acres 0.000 0.069 1,192.75 1,789 28 Generator Pad, Mech/Elec Bldg, & MBR Tank Vicinity TDA 2 3 757 5,894 8,807 14,701 Acres 0.017 0.337 5,942.65 8,914 139 Pump Sta and Headworks Vicinity TDA 4 9,687 5,466 18,398 23,864 Acres 0.222 0.548 10,975.93 16,464 257 Parameters for StormShed3G: Time of concentration, minutes:5 Hydrologic Soil Group, per geotechnical report A CN, impervious:98 CN, pervious, grass:68 39 per TR 55 per Ecology Manual. Lawn cover, good condition, HSG A but 68 in SS3G Precipitation depth:5 216-1781-042 StormAreaCalcs.xlsx \ 20210611TESC Page 1 of 1 Prepared June 2021 216-1781-042 Page 1 of 4 20210611_SS3G_Calcs.docx Prepared June 2021 CITY OF YELM WRF Phase 2 TESC calculations for BMP C251, Construction Stormwater Filtration TDA1 Event Summary Event Peak Q (cfs) Peak T (hrs) Hyd Vol (acft) Area (ac) Method 2 yr 24 hr 0.0387 8.00 0.0131 0.069 SBUH 10 year 0.0792 8.00 0.0274 0.069 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Record Id: TDA1 Design Method SBUH Rainfall type TYPE1a.rac Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 0.00 ac DCIA 0.069 ac Pervious CN 0.00 DC CN 98.00 Pervious TC 0.00 min DC TC 5.00 min DCI - CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc) 0.069 ac 98.00 DC Composited CN (AMC 2) 98.00 DCI - TC Calc Type Description Length Slope Coeff Misc TT Sheet 0.00 ft 0.0% 5.0 0.00 in 5.00 min 216-1781-042 Page 2 of 4 20210611_SS3G_Calcs.docx Prepared June 2021 Pervious TC 5.00 min TDA2_3 Event Summary Event Peak Q (cfs) Peak T (hrs) Hyd Vol (acft) Area (ac) Method 2 yr 24 hr 0.1891 8.00 0.0643 0.354 SBUH 10 year 0.3933 8.00 0.1364 0.354 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Record Id: TDA2_3 Design Method SBUH Rainfall type TYPE1a.rac Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 0.017 ac DCIA 0.337 ac Pervious CN 68.00 DC CN 98.00 Pervious TC 5.00 min DC TC 5.00 min Pervious CN Calc Description SubArea Sub cn Open spaces, lawns,parks (>75% grass) 0.017 ac 68.00 Pervious Composited CN (AMC 2) 68.00 Pervious TC Calc 216-1781-042 Page 3 of 4 20210611_SS3G_Calcs.docx Prepared June 2021 Type Description Length Slope Coeff Misc TT Sheet 0.00 ft 0.0% 5.0 0.00 in 5.00 min Pervious TC 5.00 min DCI - CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc) 0.337 ac 98.00 DC Composited CN (AMC 2) 98.00 DCI - TC Calc Type Description Length Slope Coeff Misc TT Sheet 0.00 ft 0.0% 5.0 0.00 in 5.00 min Pervious TC 5.00 min TDA4 Event Summary Event Peak Q (cfs) Peak T (hrs) Hyd Vol (acft) Area (ac) Method 2 yr 24 hr 0.3093 8.00 0.1108 0.768 SBUH 10 year 0.7103 8.00 0.252 0.768 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Record Id: TDA4 Design Method SBUH Rainfall type TYPE1a.rac 216-1781-042 Page 4 of 4 20210611_SS3G_Calcs.docx Prepared June 2021 Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 0.22 ac DCIA 0.548 ac Pervious CN 68.00 DC CN 98.00 Pervious TC 5.00 min DC TC 5.00 min Pervious CN Calc Description SubArea Sub cn Open spaces, lawns,parks (>75% grass) 0.22 ac 68.00 Pervious Composited CN (AMC 2) 68.00 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet 0.00 ft 0.0% 5.0 0.00 in 5.00 min Pervious TC 5.00 min DCI - CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc) 0.548 ac 98.00 DC Composited CN (AMC 2) 98.00 DCI - TC Calc Type Description Length Slope Coeff Misc TT Sheet 0.00 ft 0.0% 5.0 0.00 in 5.00 min Pervious TC 5.00 min Water Reclamation Facility – Phase 2 Upgrades Construction Stormwater Pollution Prevention Plan (SWPPP) City of Yelm April 2021 │ 216-1781-042 1-3 Appendix C Excerpts from Ecology Manual Volume II Construction Stormwater Pollution Prevention ___________________________________________ Stormwater Management Manual for Western Washington     Prepared by:   Washington State Department of Ecology Water Quality Program   July 2019 Publication Number 19-10-021 Excerpts for Yelm WRF Phase 2 Construction SWPPP Appendix C II-3 Construction Stormwater BMPs II-3.1 A Summary of Construction Stormwater BMPs This chapter contains standards and specifications for temporary BMPs, used as appropriate during  the construction phase of a project. Often using BMPs in combination is the best method to meet  Construction Stormwater Pollution Prevention Plan (Construction SWPPP) requirements. The standards  and specifications in this chapter are not intended to limit innovative efforts to effect- ively control erosion and sedimentation. Construction SWPPPs can contain experimental BMPs or  make minor modifications to standard BMPs. However, the permitting authority (state, local, or both)  must approve such practices before use. Experimental and modified BMPs must achieve the same  or better performance than the BMPs listed below. None of the BMPs listed below will work successfully throughout the construction project without  inspection and maintenance. Regular inspections to identify problems with the operation of each  BMP, and the timely repair of any problems are essential to the continued operation of the BMPs. As  site conditions change, BMPs must change to remain in compliance. Construction stormwater BMPs are divided into two categories: Construction Source Control BMPs  and Construction Runoff BMPs. Table II-3.1: Construction Stormwater BMPs by SWPPP Element shows the relationship of the Con- struction Stormwater BMPs to the Construction SWPPP Elements described in I-3.4.2 MR2: Con- struction Stormwater Pollution Prevention Plan (SWPPP). Construction Storm- water BMP Construction SWPPP Element # #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 Construction Source Control BMPs BMP C101: Preserving  Natural Vegetation ü              BMP C102: Buffer  Zones ü            ü BMP C103:  High-Vis- ibility Fence ü            ü BMP C105:  Stabilized  Construction Access  ü             BMP C106: Wheel  Wash  ü             Table II-3.1: Construction Stormwater BMPs by SWPPP Element 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 267 Construction Storm- water BMP Construction SWPPP Element # #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 BMP C107: Con- struction Road / Parking  Area Stabilization  ü             BMP C120: Temporary  and Permanent Seeding     ü ü         BMP C121: Mulching     ü ü         BMP C122:  Nets and  Blankets     ü ü  ü       BMP C123:  Plastic  Covering     ü ü         BMP C124:  Sodding     ü ü         BMP C125: Topsoiling /  Composting     ü          BMP C126:  Poly- acrylamide (PAM) for  Soil Erosion Protection     ü          BMP C130:  Surface  Roughening     ü ü         BMP C131:  Gradient  Terraces     ü ü         BMP C140:  Dust Con- trol     ü          BMP C150:  Mater- ials on Hand           ü ü   BMP C151: Concrete  Handling         ü      BMP C152:  Sawcutting  and Surfacing Pollution  Prevention         ü      BMP C153: Material  Delivery, Storage, and  Containment         ü      Table II-3.1: Construction Stormwater BMPs by SWPPP Element (continued) 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 268 Construction Storm- water BMP Construction SWPPP Element # #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 BMP C154: Concrete  Washout Area         ü      BMP C160:  Certified  Erosion and Sediment  Control Lead           ü ü   BMP C162:  Scheduling            ü   Construction Runoff BMPs BMP C200: Interceptor  Dike and Swale      ü       ü BMP C201: Grass- Lined Channels      ü       ü BMP C202:  Riprap  Channel Lining        ü       BMP C203: Water Bars   ü   ü    ü     BMP C204: Pipe Slope  Drains      ü         BMP C205:  Subsurface  Drains      ü         BMP C206:  Level  Spreader      ü    ü     BMP C207:  Check  Dams   ü   ü  ü     ü BMP C208:  Triangular  Silt Dike (TSD)      ü       ü BMP C209: Outlet Pro- tection   ü     ü       BMP C220:  Inlet Pro- tection       ü        BMP C231:  Brush Bar- rier    ü         ü BMP C232:  Gravel Fil- ter Berm    ü           Table II-3.1: Construction Stormwater BMPs by SWPPP Element (continued) 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 269 Construction Storm- water BMP Construction SWPPP Element # #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 BMP C233:  Silt Fence    ü         ü BMP C234:  Vegetated  Strip    ü         ü BMP C235:  Wattles   ü ü           BMP C236:  Vegetative  Filtration          ü     BMP C240:  Sediment  Trap   ü ü           BMP C241:  Sediment  Pond (Temporary)  ü ü           BMP C250:  Con- struction Stormwater  Chemical Treatment    ü     ü      BMP C251:  Con- struction Stormwater  Filtration    ü     ü      BMP C252:  Treating  and Disposing of High  pH Water         ü      Construction SWPPP Elements: Element 1: Preserve Vegetation  /  Mark Clearing Limits Element 2: Establish Construction Access Element 3: Control Flow Rates Element 4: Install Sediment Controls Element 5: Stabilize Soils Element 6: Protect Slopes Element 7: Protect Drain Inlets Element 8: Stabilize Channels and Outlets Element 9: Control Pollutants Element 10: Control Dewatering Element 11: Maintain BMPs Element 12: Manage the Project Element 13: Protect Low Impact Development BMPs Table II-3.1: Construction Stormwater BMPs by SWPPP Element (continued) II-3.2 Construction Source Control BMPs 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 270 burying and smothering vegetation.  l Vegetative buffer zones for streams, lakes or other waterways shall be established by the  local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undis- turbed. Replace all damaged flagging immediately. Remove all materials located in the buffer area  that may impede the ability of the vegetation to act as a filter. BMP C103: High-Visibility Fence Purpose High-visibility fencing is intended to:  l Restrict clearing to approved limits.  l Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undis- turbed.  l Limit construction traffic to designated construction entrances, exits, or internal roads.  l Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used:  l At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared.  l As necessary to control vehicle access to and on the site. Design and Installation Specifications High-visibility plastic fence shall be composed of a high-density polyethylene material and shall be at  least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center  (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches  with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as  a top stringer to prevent sagging between posts. The fence color shall be high-visibility orange. The  fence tensile strength shall be 360 lbs/ft using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233:  Silt Fence to act as high-visibility  fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of  this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 274 See detail on plans Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and  visibility restored. BMP C105: Stabilized Construction Access Purpose Stabilized construction accesses are established to reduce the amount of sediment transported onto  paved roads outside the project site by vehicles or equipment. This is done by constructing a sta- bilized pad of quarry spalls at entrances and exits for project sites. Conditions of Use Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction  site if paved roads or other paved areas are within 1,000 feet of the site. For residential subdivision construction sites, provide a stabilized construction access for each res- idence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient  length/width to provide vehicle access/parking, based on lot size and configuration. On large commercial, highway, and road projects, the designer should include enough extra mater- ials in the contract to allow for additional stabilized accesses not shown in the initial Construction  SWPPP. It is difficult to determine exactly where access to these projects will take place; additional  materials will enable the contractor to install them where needed. Design and Installation Specifications See Figure II-3.1: Stabilized Construction Access for details. Note: the 100’ minimum length of the  access shall be reduced to the maximum practicable size when the size or configuration of the site  does not allow  the full length (100’). Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls,  a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed con- crete, cement, or calcium chloride for construction access stabilization because these products raise  pH levels in stormwater and concrete discharge to waters of the State is prohibited. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up  into the rock pad. The geotextile shall meet the standards listed in Table II-3.2: Stabilized Con- struction Access Geotextile Standards. Geotextile Property Required Value Grab Tensile  Strength (ASTM D4751)200  psi min. Table II-3.2: Stabilized Construction Access Geotextile Standards 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 275 See detail on plans Geotextile Property Required Value Grab Tensile  Elongation (ASTM D4632)30%  max. Mullen Burst  Strength (ASTM D3786-80a)400  psi min. AOS (ASTM D4751)20-45  (U.S. standard sieve size) Table II-3.2: Stabilized Construction Access Geotextile Standards (continued)  l Consider early installation of the first lift of asphalt in areas that will be paved; this can be used  as a stabilized access. Also consider the installation of excess concrete as a stabilized access.  During large concrete pours, excess concrete is often available for this purpose.  l Fencing (see BMP C103:  High-Visibility Fence) shall be installed as necessary to restrict  traffic to the construction access.  l Whenever possible, the access shall be constructed on a firm, compacted subgrade. This can  substantially increase the effectiveness of the pad and reduce the need for maintenance.  l Construction accesses should avoid crossing existing sidewalks and back of walk drains if at  all possible. If a construction access must cross a sidewalk or back of walk drain, the full length  of the sidewalk and back of walk drain must be covered and protected from sediment leaving  the site. Alternative Material Specification WSDOT has raised safety concerns about the Quarry Spall rock specified above. WSDOT observes  that the 4-inch to 8-inch rock sizes can become trapped between Dually truck tires, and then  released off-site at highway speeds. WSDOT has chosen to use a modified specification for the rock  while continuously verifying that the Stabilized Construction Access remains effective. To remain  effective, the BMP must prevent sediment from migrating off site. To date, there has been no per- formance testing to verify operation of this new  specification. Jurisdictions may use the alternative  specification, but must perform increased off-site inspection if they use, or allow others to use, it. Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Stand- ard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1) (WSDOT, 2016)  for ballast except for the following special requirements. The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access  Alternative Material Requirements. Sieve Size Percent Passing 2½″99-100 Table II-3.3: Stabilized Construction Access Alternative Material Requirements 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 276 Sieve Size Percent Passing 2″65-100 ¾″40-80 No. 4 5 max. No. 100 0-2 % Fracture 75 min. Table II-3.3: Stabilized Construction Access Alternative Material Requirements (continued)  l All percentages are by weight.  l The sand equivalent value and dust ratio requirements do not apply.  l The fracture requirement shall be at least one fractured face and will apply the combined  aggregate retained on the No. 4 sieve in accordance with FOP for AASHTO T 335. Maintenance Standards Quarry spalls shall be added if the pad is no longer in accordance with the specifications.  l If the access is not preventing sediment from being tracked onto pavement, then alternative  measures to keep the streets free of sediment shall be used. This may include replace- ment/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of  the access, or the installation of BMP C106: Wheel Wash.  l Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep- ing. The sediment collected by sweeping shall be removed or stabilized on site. The pavement  shall not be cleaned by washing down the street, except when high efficiency sweeping is inef- fective and there is a threat to public safety. If it is necessary to wash the streets, the con- struction of a small sump to contain the wash water shall be considered. The sediment would  then be washed into the sump where it can be controlled.  l Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high effi- ciency mechanical sweeper because this creates dust and throws soils into storm systems or  conveyance ditches.  l Any quarry spalls that are loosened from the pad, which end up on the roadway shall be  removed immediately.  l If vehicles are entering or exiting the site at points other than the construction access(es),  BMP C103:  High-Visibility Fence shall be installed to control traffic. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 277  l Upon project completion and site stabilization, all construction accesses intended as per- manent access for maintenance shall be permanently stabilized. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 278 pipe, sandbags, geotextile fabric and steel “T” posts.  l Materials should be stockpiled and readily available before any site clearing, grubbing, or  earthwork begins. A large contractor or project proponent could keep a stockpile of materials  that are available for use on several projects.  l If storage space at the project site is at a premium, the contractor could maintain the materials  at their office or yard. The office or yard must be less than an hour from the project site. Design and Installation Specifications Depending on project type, size, complexity, and length, materials and quantities will vary. A good  minimum list of items that will cover numerous situations includes:  l Clear Plastic, 6 mil  l Drainpipe, 6 or 8 inch diameter  l Sandbags, filled  l Straw Bales for mulching  l Quarry Spalls  l Washed Gravel  l Geotextile Fabric  l Catch Basin Inserts  l Steel "T" Posts  l Silt fence material  l Straw Wattles Maintenance Standards  l All materials with the exception of the quarry spalls, steel “T” posts, and gravel should be kept  covered and out of both sun and rain.  l Re-stock materials as needed. BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of  which can violate water quality standards in the receiving water. Concrete spillage or concrete dis- charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, con- crete process water, and concrete slurry from entering waters of the State. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 315 Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction project com- ponents include, but are not limited to:  l Curbs  l Sidewalks  l Roads  l Bridges  l Foundations  l Floors  l Runways Disposal options for concrete, in order of preference are:  1. Off-site disposal  2. Concrete wash-out areas (see BMP C154: Concrete Washout Area)  3. De minimus washout to formed areas awaiting concrete Design and Installation Specifications  l Wash concrete truck drums at an approved off-site location or in designated concrete  washout areas only. Do not wash out  concrete trucks onto the ground (including formed areas  awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to BMP  C154: Concrete Washout Area for information on concrete washout areas.  o Return unused concrete remaining in the truck and pump to the originating batch plant  for recycling. Do not dump excess concrete on site, except in designated concrete  washout areas as allowed in BMP C154: Concrete Washout Area.  l Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats,  trowels, and wheelbarrows) into designated concrete washout areas or into formed areas  awaiting concrete pour.  l At no time shall concrete be washed off into the footprint of an area where an infiltration fea- ture will be installed.  l Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.  l Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly  (without detention or treatment) to natural or constructed stormwater conveyances.  l Contain washwater and leftover product in a lined container when no  designated concrete  washout areas (or formed areas, allowed as described above) are available. Dispose of con- tained concrete and concrete washwater (process water) properly. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 316  l Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface  waters.  l Refer to BMP C252:  Treating and Disposing of High pH Water for pH adjustment require- ments.  l Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring require- ments if the project involves one of the following activities:  o Significant concrete work (as defined in the CSWGP).  o The use of soils amended with (but not limited to) Portland cement-treated base,  cement kiln dust or fly ash.  o Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for  high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles  and high pH (concrete cutting), both of which can violate the water quality standards in the receiving  water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to  minimize and eliminate process water and slurry created through sawcutting or surfacing from enter- ing waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Saw- cutting and surfacing operations include, but are not limited to:  l Sawing  l Coring  l Grinding  l Roughening  l Hydro-demolition  l Bridge and road surfacing 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 317 Design and Installation Specifications  l Vacuum slurry and cuttings during cutting and surfacing operations.  l Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.  l Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ- ing stormwater systems. This may require temporarily blocking catch basins.  l Dispose of collected slurry and cuttings in a manner that does not violate ground water or sur- face water quality standards.  l Do not allow process water generated during hydro-demolition, surface roughening or similar  operations to drain to any natural or constructed drainage conveyance including stormwater  systems. Dispose of process water in a manner that does not violate ground water or surface  water quality standards.  l Handle and dispose of cleaning waste material and demolition debris in a manner that does  not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an  appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter  waters of the state. If inspections show  that a violation of water quality standards could occur, stop  operations and immediately implement preventive measures such as berms, barriers, secondary  containment, and/or vacuum trucks. BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses  from material delivery and storage. Minimize the storage of hazardous materials on-site, store mater- ials in a designated area, and install secondary containment. Conditions of Use Use at construction sites with delivery and storage of the following materials:  l Petroleum products such as fuel, oil and grease  l Soil stabilizers and binders (e.g., Polyacrylamide)  l Fertilizers, pesticides and herbicides  l Detergents  l Asphalt and concrete compounds 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 318  l Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing compounds  l Any other material that may be detrimental if released to the environment Design and Installation Specifications  l The temporary storage area should be located away from vehicular traffic, near the con- struction entrance(s), and away from waterways or storm drains.  l Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be  kept in their original labeled containers.  l Hazardous material storage on-site should be minimized.  l Hazardous materials should be handled as infrequently as possible.  l During the wet weather season (Oct 1 – April 30), consider storing materials in a covered  area.  l Materials should be stored in secondary containments, such as an earthen dike, horse trough,  or even a children’s wading pool for non-reactive materials such as detergents, oil, grease,  and paints. Small amounts of material may be secondarily contained in “bus boy” trays or con- crete mixing trays.  l Do not store chemicals, drums, or bagged materials directly on the ground. Place these items  on a pallet and, when possible, within secondary containment.  l If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater  on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of  drums, preventing water from collecting.  l Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be  stored in approved containers and drums and shall not be overfilled. Containers and drums  shall be stored in temporary secondary containment facilities.  l Temporary secondary containment facilities shall provide for a spill containment volume able  to contain 10% of the total enclosed container volume of all containers, or 110% of the capa- city of the largest container within its boundary, whichever is greater.  l Secondary containment facilities shall be impervious to the materials stored therein for a min- imum contact time of 72 hours.  l Sufficient separation should be provided between stored containers to allow for spill cleanup  and emergency response access.  l During the wet weather season (Oct 1 – April 30), each secondary containment facility shall  be covered during non-working days, prior to and during rain events.  l Keep material storage areas clean, organized and equipped with an ample supply of appro- priate spill clean-up material (spill kit).  l The spill kit should include, at a minimum: 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 319  o 1-Water Resistant Nylon Bag  o 3-Oil Absorbent Socks 3”x 4’  o 2-Oil Absorbent Socks 3”x 10’  o 12-Oil Absorbent Pads 17”x19”  o 1-Pair Splash Resistant Goggles  o 3-Pair Nitrile Gloves  o 10-Disposable Bags with Ties  o Instructions Maintenance Standards  l Secondary containment facilities shall be maintained free of accumulated rainwater and spills.  In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed  into drums. These liquids shall be handled as hazardous waste unless testing determines  them to be non-hazardous.  l Re-stock spill kit materials as needed. BMP C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting  washout off-site, or performing on-site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where:  l Concrete is used as a construction material  l It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant,  etc.).  l Concrete truck drums are washed on-site. Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete  handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheel- barrows) may be washed into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will  be installed. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 320 See details on plans. Design and Installation Specifications Implementation  l Perform washout of concrete truck drums at an approved off-site location or in designated con- crete washout areas only.  l Do not wash out concrete onto non-formed areas, or into storm drains, open ditches, streets,  or streams.  l Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.  l Do not allow excess concrete to be dumped on-site, except in designated concrete washout  areas as allowed above.  l Concrete washout areas may be prefabricated concrete washout containers, or self-installed  structures (above-grade or below-grade).  l Prefabricated containers are most resistant to damage and protect against spills and leaks.  Companies may offer delivery service and provide regular maintenance and disposal of solid  and liquid waste.  l If self-installed concrete washout areas are used, below-grade structures are preferred over  above-grade structures because they are less prone to spills and leaks.  l Self-installed above-grade structures should only be used if excavation is not practical.  l Concrete washout areas shall be constructed and maintained in sufficient quantity and size to  contain all liquid and concrete waste generated by washout operations. Education  l Discuss the concrete management techniques described in this BMP with the ready-mix con- crete supplier before any deliveries are made.  l Educate employees and subcontractors on the concrete waste management techniques  described in this BMP.  l Arrange for the contractor’s superintendent or Certified Erosion and Sediment Control Lead  (CESCL) to oversee and enforce concrete waste management procedures.  l A sign should be installed adjacent to each concrete washout area to inform concrete equip- ment operators to utilize the proper facilities. Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor  agreements. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 321 Location and Placement  l Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains,  open ditches, water bodies, or wetlands.  l Allow convenient access to the concrete washout area for concrete trucks, preferably near the  area where the concrete is being poured.  l If trucks need to leave a paved area to access the concrete washout area, prevent track-out  with a pad of rock or quarry spalls (see BMP C105:  Stabilized Construction Access). These  areas should be far enough away from other construction traffic to reduce the likelihood of acci- dental damage and spills.  l The number of concrete washout areas you install should depend on the expected demand  for storage capacity.  l On large sites with extensive concrete work, concrete washout areas should be placed in mul- tiple locations for ease of use by concrete truck drivers. Concrete Truck Washout Procedures  l Washout of concrete truck drums shall be performed in designated concrete washout areas  only.  l Concrete washout from concrete pumper bins can be washed into concrete pumper trucks  and discharged into designated concrete washout areas or properly disposed of off-site. Concrete Washout Area Installation  l Concrete washout areas should be constructed as shown in the figures below, with a recom- mended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to  contain all liquid and concrete waste generated by washout operations.  l Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free  of holes, tears, or other defects that compromise the impermeability of the material.  l Lath and flagging should be commercial type.  l Liner seams shall be installed in accordance with manufacturers’ recommendations.  l Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the  plastic lining material. Maintenance Standards Inspection and Maintenance  l Inspect and verify that concrete washout areas are in place prior to the commencement of con- crete work.  l Once concrete wastes are washed into the designated washout area and allowed to harden,  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 322 the concrete should be broken up, removed, and disposed of per applicable solid waste reg- ulations. Dispose of hardened concrete on a regular basis.  l During periods of concrete work, inspect the concrete washout areas daily to verify continued  performance.  o Check overall condition and performance.  o Check remaining capacity (% full).  o If using self-installed concrete washout areas, verify plastic liners are intact and side- walls are not damaged.  o If using prefabricated containers, check for leaks.  l Maintain the concrete washout areas to provide adequate holding capacity with a minimum  freeboard of 12 inches.  l Concrete washout areas must be cleaned, or new concrete washout areas must be con- structed and ready for use once the concrete washout area is 75% full.  l If the concrete washout area is nearing capacity, vacuum and dispose of the waste material in  an approved manner.  l Do not discharge liquid or slurry to waterways, storm drains or directly onto ground.  l Do not discharge to the sanitary sewer without local approval.  l Place a secure, non-collapsing, non-water collecting cover over the concrete washout  area prior to predicted wet weather to prevent accumulation and overflow of pre- cipitation.  l Remove and dispose of hardened concrete and return the structure to a functional con- dition. Concrete may be reused on-site or hauled away for disposal or recycling.  l When you remove materials from a self-installed concrete washout area, build a new struc- ture; or, if the previous structure is still intact, inspect for signs of weakening or damage, and  make any necessary repairs. Re-line the structure with new  plastic after each cleaning. Removal of Concrete Washout Areas  l When concrete washout areas are no longer required for the work, the hardened concrete,  slurries and liquids shall be removed and properly disposed of.  l Materials used to construct concrete washout areas shall be removed from the site of the work  and disposed of or recycled.  l Holes, depressions or other ground disturbance caused by the removal of the concrete  washout areas shall be backfilled, repaired, and stabilized to prevent erosion. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 323 BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge of  erosion and sediment control (ESC), and water quality protection. The designated person shall be  responsible for ensuring compliance with all local, state, and federal erosion and sediment control  and water quality requirements. Construction sites one acre or larger that discharge to waters of the  State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the responsible  representative. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur- face waters of the state. Sites less than one acre may have a person without CESCL certification  conduct inspections. The CESCL shall:  l Have a current certificate proving attendance in an erosion and sediment control training  course that meets the minimum ESC training and certification requirements established by  Ecology. Ecology has provided the minimum requirements for CESCL course training, as well as a list  of ESC training and certification providers at:  https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed- iment-control  OR  l Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional inform- ation go to:  http://www.envirocertintl.org/cpesc/ Specifications  l CESCL certification shall remain valid for three years.  l The CESCL shall have authority to act on behalf of the contractor or project proponent and  shall be available, or on-call, 24 hours per day throughout the period of construction.  l The Construction SWPPP shall include the name, telephone number, fax number, and  address of the designated CESCL. See II-2 Construction Stormwater Pollution Prevention  Plans (Construction SWPPPs).  l A CESCL may provide inspection and compliance services for multiple construction projects  in the same geographic region, but must be on site whenever earthwork activities are  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 327 occurring that could generate release of turbid water.  l Duties and responsibilities of the CESCL shall include, but are not limited to the following:  o Maintaining a permit file on site at all times which includes the Construction SWPPP  and any associated permits and plans.  o Directing BMP installation, inspection, maintenance, modification, and removal.  o Updating all project drawings and the Construction SWPPP with changes made.  o Completing any sampling requirements including reporting results using electronic Dis- charge Monitoring Reports (WebDMR).  o Facilitate, participate in, and take corrective actions resulting from inspections per- formed by outside agencies or the owner.  o Keeping daily logs, and inspection reports. Inspection reports should include:  n Inspection date/time.  n Weather information; general conditions during inspection and approximate  amount of precipitation since the last inspection.  n Visual monitoring results, including a description of discharged stormwater. The  presence of suspended sediment, turbid water, discoloration, and oil sheen shall  be noted, as applicable.  n Any water quality monitoring performed during inspection.  n General comments and notes, including a brief description of any BMP repairs,  maintenance or installations made as a result of the inspection.  n A summary or list of all BMPs implemented, including observations of all  erosion/sediment control structures or practices. The following shall be noted:  1. Locations of BMPs inspected.  2. Locations of BMPs that need maintenance.  3. Locations of BMPs that failed to operate as designed or intended.  4. Locations of where additional or different BMPs are required. BMP C162: Scheduling Purpose Sequencing a construction project reduces the amount and duration of soil exposed to erosion by  wind, rain, runoff, and vehicle tracking. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 328 thickness is 2 feet.  o For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), use an  engineered energy dissipator.  o Filter fabric or erosion control blankets should always be used under riprap to prevent  scour and channel erosion. See BMP C122:  Nets and Blankets.  l Bank stabilization, bioengineering, and habitat features may be required for disturbed areas.  This work may require a Hydraulic Project Approval (HPA) from the Washington State Depart- ment of Fish and Wildlife. See I-2.11 Hydraulic Project Approvals. Maintenance Standards  l Inspect and repair as needed.  l Add rock as needed to maintain the intended function.  l Clean energy dissipator if sediment builds up. BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- bilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed  areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and  within 500 feet of a disturbed or construction area, unless  those inlets are preceded by a sediment  trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction. These small and  numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof  drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap  these drains to prevent sediment from entering the system until completion of landscaping. Provide  18-inches of sod around each finished lawn and yard drain. Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods  for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain- age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with  additional end-of-pipe treatment where stormwater ponding would cause a hazard. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 356 See detail on plans. Type of Inlet Pro- tection Emergency Overflow Applicable for Paved/ Earthen Sur- faces Conditions of Use Drop Inlet Protection Excavated  drop  inlet protection Yes, temporary  flooding may   occur Earthen Applicable for heavy flows. Easy   to maintain. Large area requirement:   30'x30'/acre Block  and gravel  drop inlet pro- tection Yes Paved or Earthen Applicable for heavy  concentrated flows.  Will not pond. Gravel and wire  drop inlet pro- tection No Paved or Earthen Applicable for  heavy concentrated flows.  Will pond. Can withstand traffic. Catch  basin filters Yes Paved or Earthen Frequent maintenance  required. Curb Inlet Protection Curb  inlet pro- tection with  wooden weir Small capacity  overflow Paved Used for sturdy, more compact  install- ation. Block and gravel  curb inlet pro- tection Yes Paved Sturdy, but  limited filtration. Culvert Inlet Protection Culvert  inlet sed- iment trap N/A N/A 18 month expected life. Table II-3.10: Storm Drain Inlet Protection Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet.  Sediment settles out of the stormwater prior to entering the storm drain. Design and installation spe- cifications for excavated drop inlet protection include:  l Provide a depth of 1-2 ft as measured from the crest of the inlet structure.  l Slope sides of excavation should be no steeper than 2H:1V.  l Minimum volume of excavation is 35 cubic yards.  l Shape the excavation to fit the site, with the longest dimension oriented toward the longest  inflow area.  l Install provisions for draining to prevent standing water.  l Clear the area of all debris. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 357 Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does not  provide an overflow. Design and installation specifications for gravel and wire mesh filters include:  l Use a hardware cloth or comparable wire mesh with ½-inch openings.  o Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey- ond each side of the inlet structure.  o Overlap the strips if more than one strip of mesh is necessary.  l Place coarse aggregate over the wire mesh.  o Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at  least 18-inches on all sides. Catch Basin Filters Catch  basin filters are designed by manufacturers for construction sites. The limited sediment stor- age capacity increases the amount of inspection and maintenance required, which may be daily for  heavy sediment loads. To reduce maintenance requirements, combine a catch  basin filter with  another type of inlet protection. This type of inlet protection provides flow  bypass without overflow  and therefore may be a better method for inlets located along active rights-of-way. Design and install- ation specifications for catch basin filters include:  l Provides 5 cubic feet of storage.  l Requires dewatering provisions.  l Provides a high-flow bypass that will not clog under normal use at a construction site.  l Insert the catch  basin filter in the catch  basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb  inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection  with wooden weirs include:  l Use wire mesh with ½-inch openings.  l Use extra strength filter cloth.  l Construct a frame.  l Attach the wire and filter fabric to the frame.  l Pile coarse washed aggregate against the wire and fabric.  l Place weight on the frame anchors. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 360 Maintenance Standards  l Inspect all forms of inlet protection frequently, especially after storm events. Clean and  replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the  inlet and clean or replace. An alternative approach would be to use the clogged rock as fill and  put fresh rock around the inlet.  l Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly  over the surrounding land area or stockpile and stabilize as appropriate. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not  pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions  may choose not to accept these products, or may require additional testing prior to consideration for  local use. Products that Ecology has approved as functionally equivalent are available for review on  Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C231: Brush Barrier Purpose The purpose of brush barriers is to reduce the transport of coarse sediment from a construction site  by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland  flow. Conditions of Use  l Brush barriers may be used downslope of disturbed areas that are less than one-quarter acre.  l Brush barriers are not intended to treat concentrated flows, nor are they intended to treat sub- stantial amounts of overland flow. Any concentrated flows must be directed to a sediment trap- ping BMP. The only circumstance in which overland flow can be treated solely by a brush  barrier, rather than by a sediment trapping BMP, is when the area draining to the barrier is  small.  l Brush barriers should only be installed on contours. Design and Installation Specifications  l Height: 2 feet (minimum) to 5 feet (maximum).  l Width: 5 feet at base (minimum) to 15 feet (maximum).  l Filter fabric (geotextile) may be anchored over the brush berm to enhance the filtration ability  of the barrier. Ten-ounce burlap is an adequate alternative to filter fabric. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 365 treatment pond prior to decanting. Compliance with the water quality standards is determined in the  receiving water. Operator Training Each project site using chemical treatment must have a trained operator who is certified for oper- ation of an Enhanced Chemical Treatment system. The operator must be trained and certified by an  organization approved by Ecology. Organizations approved for operator training are found at the fol- lowing website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee- guidance-resources/Contaminated-water-on-construction-sites  Sediment Removal and Disposal  l Sediment shall be removed from the untreated stormwater storage pond and treatment cells  as necessary. Typically, sediment removal is required at least once during a wet season and  at the decommissioning of the chemical treatment system. Sediment remaining in the cells  between batches may enhance the settling process and reduce the required chemical  dosage.  l Sediment that is known to be non-toxic may be incorporated into the site away from drain- ages. BMP C251: Construction Stormwater Filtration Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Conditions of Use Traditional Construction Stormwater BMPs used to control soil erosion and sediment loss from con- struction sites may not be adequate to ensure compliance with the water quality standard for tur- bidity 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 fil- tration 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 treat- ment chemicals are not used. Filtration in conjunction with BMP C250:  Construction Stormwater  Chemical Treatment requires testing under the Chemical Technology Assessment Protocol – Eco- logy (CTAPE) before it can be initiated. Approval from Ecology must be obtained at each site where  chemical use is proposed prior to use. See https://- fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of the Request for  Chemical Treatment form. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 404 See calculation results on plans. Design and Installation Specifications Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow.  Rapid filtration systems are the typical system used for water and wastewater treatment. They can  achieve relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have auto- matic backwash systems to remove accumulated solids.  Slow filtration systems have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do  not have backwash systems. Slow filtration systems have generally been used as post construction  BMPs to treat stormwater (see V-6 Filtration BMPs). Slow  filtration is mechanically simple in com- parison to rapid filtration, but requires a much larger filter area. Filter Types and Efficiencies Sand media filters are available with automatic backwashing features that can filter to 50 µm particle  size. Screen or bag filters can filter down to 5 µm. Fiber wound filters can remove particles down to  0.5 µm. Filters should be sequenced from the largest to the smallest pore opening. Sediment  removal efficiency will be related to particle size distribution in the stormwater. Treatment Process and Description Stormwater is collected at interception point(s) on the site and diverted to an untreated stormwater  sediment pond or tank for removal of large sediment, and storage of the stormwater before it is  treated by the filtration system. In a rapid filtration system, the untreated stormwater is pumped from  the pond or tank through the filtration media. Slow filtration systems are designed using gravity to  convey water from the pond or tank to and through the filtration media. Sizing Filtration treatment systems must be designed to control the velocity and peak volumetric flow rate  that is discharged from the system and consequently the project site. See Element 3: Control Flow   Rates for further details on this requirement. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the volume of run- off generated from the site during the 10-year, 24-hour storm event, minus the filtration treatment  system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the filtration  treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft2. Other  hydraulic loading rates may be more appropriate for other systems. Bypass should be provided  around the filtration treatment system to accommodate extreme storm events. Runoff volume shall  be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst-case  land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases,  this would be the land cover conditions just prior to final landscaping). If the filtration treatment system design does not allow you to discharge at the rates as required by  Element 3: Control Flow Rates, and if the site has a permanent Flow  Control BMP that will serve the  planned development, the discharge from the filtration treatment system may be directed to the per- manent Flow  Control BMP to comply with Element 3: Control Flow Rates. In this case,  all discharge  (including water passing through the treatment system and stormwater bypassing the treatment  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 405 system) will be directed into the permanent Flow Control BMP. If site constraints make locating the  untreated stormwater storage pond difficult, the permanent Flow  Control BMP may be divided to  serve as the untreated stormwater storage pond and the post-treatment temporary flow control  pond. A berm or barrier must be used in this case so the untreated water does not mix with the  treated water. Both untreated stormwater storage requirements, and adequate post-treatment flow   control must be achieved. The designer must document in the Construction SWPPP how  the per- manent Flow  Control BMP is able to attenuate the discharge from the site to meet the requirements  of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified  for temporary construction flow  control purposes, the construction of the permanent Flow  Control  BMP must be finalized, as designed for its permanent function, at project completion. Maintenance Standards  l Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set  pressure drop across the filter. If the backwash water volume is not large or substantially more  turbid than the untreated stormwater stored in the holding pond or tank, backwash return to  the untreated stormwater pond or tank may be appropriate. However, other means of treat- ment and disposal may be necessary.  l Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged.  l Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically,  sediment removal is required once or twice during a wet season and at the decommissioning  of the ponds.  l Disposal of filtration equipment must comply with applicable local, state, and federal reg- ulations. BMP C252: Treating and Disposing of 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 prior to discharge to surface or ground water. A pH level range of 6.5 to 8.5 is typ- ical for most natural watercourses, and this neutral 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  l The water quality standard for pH  in Washington State is in the range of 6.5 to 8.5. Storm- water with pH levels exceeding water quality standards may be either neutralized on site or  disposed of  to a sanitary sewer or concrete batch plant with pH neutralization capabilities.  l Neutralized stormwater may be discharged to surface waters under the Construction Storm- water General permit.  l 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  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 406 See note on plans. contaminated during concrete work is considered process wastewater and must not be dis- charged to waters of the State or stormwater collection systems.  l The process used for neutralizing and/or disposing of high pH stormwater from the site must  be documented in the Construction Stormwater Pollution Prevention Plan. Causes of High pH High pH at construction sites is most commonly caused by the contact of stormwater with poured or  recycled concrete, cement, mortars, and other Portland cement or lime containing construction  materials. (See BMP C151: Concrete Handling for more information on concrete handling pro- cedures). The principal caustic agent in cement is calcium hydroxide (free lime). 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. Ground water stand- ard for calcium and other dissolved solids in Washington State is less than 500 mg/l. Treating High pH Stormwater by Carbon Dioxide Sparging Advantages of Carbon Dioxide Sparging  l Rapidly neutralizes high pH water.  l Cost effective and safer to handle than acid compounds.  l CO2 is self-buffering. It is difficult to overdose and create harmfully low pH levels.  l Material is readily available. The Chemical Process of Carbon Dioxide Sparging When carbon dioxide (CO2) is added to water (H 2O), carbonic acid (H2CO3) is formed which can  further dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below: CO2 + H 2O ↔ H2CO3 ↔ H+ + HCO3- The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reac- tion as well. The colder the water temperature is, the slower the reaction occurs. 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. The Treatment Process of Carbon Dioxide Sparging High pH water may be treated using continuous treatment, continuous discharge systems. These  manufactured systems continuously monitor influent and effluent pH to ensure that pH values are  within an acceptable range before being discharged. All systems must have fail safe automatic shut  off switches in the event that pH is not within the acceptable discharge range. Only trained operators  may operate manufactured systems. System manufacturers often provide trained operators or train- ing on their devices. The following procedure may be used when not using a continuous discharge system: 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 407  1. Prior to treatment, the appropriate jurisdiction should be notified in accordance with the reg- ulations set by the jurisdiction.  2. Every effort should be made to isolate the potential high pH water in order to treat it separately  from other stormwater on-site.  3. Water should be stored in an acceptable storage facility, detention pond, or containment cell  prior to pH  treatment.  4. Transfer water to be treated for pH  to the pH treatment structure. Ensure that the pH treat- ment structure size is sufficient to hold the amount of water that is to be treated. Do not fill the  pH treatment structure completely, allow at least 2 feet of freeboard.  5. The operator samples the water within the pH treatment structure for pH  and notes the clarity  of the water. As a rule of thumb, less CO2 is necessary for clearer water. The results of the  samples and water clarity observations should be recorded.  6. In the pH  treatment structure, add CO2 until the pH falls into the range of 6.9-7.1. Adjusting  pH to within 0.2 pH units of receiving water (background pH) is recommended. It is unlikely  that pH can be adjusted to within 0.2 pH units using dry ice. Compressed carbon dioxide gas  should be introduced to the water using a carbon dioxide diffuser located near the bottom of  the pH  treatment structure, this will allow carbon dioxide to bubble up through the water and  diffuse more evenly.  7. Slowly discharge the water, making sure water does not get stirred up in the process. Release  about 80% of the water from the pH treatment structure leaving any sludge behind. If turbidity  remains above the maximum allowable, consider adding filtration to the treatment train. See  BMP C251:  Construction Stormwater Filtration.  8. Discharge treated water through a pond or drainage system.  9. Excess sludge needs to be disposed of properly as concrete waste. If several batches of  water are undergoing pH treatment, sludge can be left in the treatment structure for the next  batch treatment. Dispose of sludge when it fills 50% of the treatment structure volume.  10. Disposal must comply with applicable local, state, and federal regulations. Treating High pH Stormwater by Food Grade Vinegar Food grade vinegar that meets FDA standards may be used to neutralize high pH  water. Food  grade vinegar is only 4% to 18% acetic acid with the remainder being water.  Food grade vinegar  may be used if dosed just enough to lower pH sufficiently. Use a treatment process as described  above for CO2 sparging, but add food grade vinegar instead of CO2. This treatment option for high pH stormwater does not apply to anything but food grade vinegar.  Acetic acid does not equal vinegar. Any other product or waste containing acetic acid must go  through the evaluation process in Appendix G of Whole Effluent Toxicity Testing Guidance and Test Review Criteria (Marshall, 2016).  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 408 Disposal of High pH Stormwater Sanitary Sewer Disposal Local sewer authority approval is required prior to disposal via the sanitary sewer. Concrete Batch Plant Disposal  l Only permitted facilities may accept high pH water.  l Contact the facility to ensure they can accept the high pH  water. Maintenance Standards Safety and materials handling:  l All equipment should be handled in accordance with OSHA rules and regulations.  l Follow  manufacturer guidelines for materials handling. Each operator should provide:  l A diagram of the monitoring and treatment equipment.  l A description of the pumping rates and capacity the treatment equipment is capable of treat- ing. Each operator should keep a written record of the following:  l Client name and phone number.  l Date of treatment.  l Weather conditions.  l Project name and location.  l Volume of water treated.  l pH of untreated water.  l Amount of CO2 or food grade vinegar needed to adjust water to a pH range of 6.9-7.1.  l pH of treated water.  l Discharge point location and description. A copy of this record should be given to the client/contractor who should retain the record for three  years. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 409