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32-35. Civil ARB TIR
Technical Information Report for ARB Flagship Store Owner/Developer: ARB USA Auburn, WA Prepared by: 14900 Interurban Ave. S, Suite 291 Seattle, WA 98168 01/20/2023 Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 1 Draft Technical Information Report Table of Contents SECTION 1 - PROJECT OVERVIEW ..................................................................................................................... 7 1.1 Project Location and Overview ............................................................................................................... 7 SECTION 2 - CONDITIONS AND REQUIREMENTS SUMMARY .......................................................................... 10 2.1 Analysis of the 9 Core Requirements ........................................................................................................ 11 Core Requirement #1: Discharge at Natural Location ................................................................................ 11 Core Requirement #2: Offsite Analysis ....................................................................................................... 11 Core Requirement #3: Flow Control Facilities ............................................................................................ 11 Core Requirement #4: Conveyance System ............................................................................................... 11 Core Requirement #5: Construction Stormwater Pollution Prevention .................................................... 11 Core Requirement #6: Maintenance and Operations ................................................................................ 11 Core Requirement #7: Financial Guarantees and Liability ......................................................................... 11 Core Requirement #8: Water Quality Facilities .......................................................................................... 11 Core Requirement #9: On-site BMP’s ......................................................................................................... 12 2.1 Analysis of the 6 Special Requirements .................................................................................................... 12 Special Requirement #1: Other Adopted Area-Specific Requirements ...................................................... 12 Special Requirement #2: Flood Hazard Area Delineation .......................................................................... 12 Special Requirement #3: Flood Protection Facilities .................................................................................. 12 Special Requirement #4: Source Control .................................................................................................... 12 Special Requirement #5: Oil Control .......................................................................................................... 12 Special Requirement #6: Aquifer Protection .............................................................................................. 12 SECTION 3 - OFFSITE ANALYSIS ....................................................................................................................... 13 SECTION 4 - FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID), AND WATER QUALITY FACILITY ANALYSIS AND DESIGN .................................................................................................................................................... 13 SECTION 5 - CONVEYANCE SYSTEM ANALYSIS AND DESIGN .......................................................................... 14 SECTION 6 - SPECIAL REPORTS AND STUDIES ................................................................................................. 14 SECTION 7 - OTHER PERMITS .......................................................................................................................... 14 SECTION 8 - CSWPP PLAN ANALYSIS AND DESIGN ......................................................................................... 14 8.1 ESC Plan Analysis and Design (Part A) .................................................................................................. 14 8.2 SWPPS Plan Design (Part B) .................................................................................................................. 15 SECTION 9 - BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ....................... 15 SECTION 10 - OPERATIONS AND MAINTENANCE MANUAL ............................................................................ 16 Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 2 Draft Technical Information Report List of Figures: Figure 1 – TIR Worksheet Figure 2 – Project Location Figure 3 – Site Characteristics Figure 4 – Soils Figure 5 – Drainage Review Type Flowchart Figure 5 – Aquifer Protection Area Appendices Appendix A • Site Plan • Drainage Control Plan Appendix B – BMP Details Appendix C – Geotechnical Report Appendix D – Operation and Maintenance Manual Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 1 Draft Technical Information Report FIGURE 1 – TIR Worksheet (1/6) Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 2 Draft Technical Information Report FIGURE 1 – TIR Worksheet (2/6) Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 3 Draft Technical Information Report FIGURE 1 – TIR Worksheet (3/6) Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 4 Draft Technical Information Report FIGURE 1 – TIR Worksheet (4/6) Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 5 Draft Technical Information Report FIGURE 1 – TIR Worksheet (5/6) Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 6 Draft Technical Information Report FIGURE 1 – TIR Worksheet (6/6) Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 7 Draft Technical Information Report SECTION 1 - PROJECT OVERVIEW 1.1 Project Location and Overview The proposed project is located east of Rainier Ave S at 720 Rainier Ave S. The parcel number is 1923059053. The 37,702 square-foot site is located within the Commercial Arterial (CA) zoning classification, Auto Mall Area B, Urban Design District D, and Commercial Mixed Use comprehensive plan designation. The project proposes to occupy the existing 9540 square-foot auto sales building with a new ARB flagship store which would also include on-site retail sales of vehicle accessories and on-site vehicle accessory installation. In addition, the project would use the existing garage that is attached to the building for vehicle accessory installation. Proposed improvements would include remodeling of the interior, signage, and exterior parking lot restriping. The existing covered car port and storage shed east of the existing building would be demolished and replaced with a single story, 6,435 square foot addition. Site improvements would also include improvements in the Right of Way (ROW) to match the north and south sidewalk and planter strip, as well as frontage and interior parking lot landscaping. Existing site conditions consist of a 9,540 square-foot auto sales building. The rest of the surface is occupied by impervious area parking lot and raised car display area on the southwest corner, as well as existing water, sewer, and storm sewer utilities including an existing oil-water separator on the south edge of the project. No changes in drainage patterns are proposed. FIGURE 2 – PROJECT LOCATION Project Location Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 8 Draft Technical Information Report FIGURE 3 – SITE CHARACTERISTICS Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 9 Draft Technical Information Report FIGURE 4 – SOILS Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 10 Draft Technical Information Report SECTION 2 - CONDITIONS AND REQUIREMENTS SUMMARY This project is required to comply with Core Requirements 1-9 and Special Requirements 1-6. The flow chart below was used to identify the project type of drainage review. This project meets the characteristics of a Full Drainage Review. FIGURE 5 – DRAINAGE REVIEW TYPE FLOWCHART Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 11 Draft Technical Information Report 2.1 Analysis of the 9 Core Requirements Core Requirement #1: Discharge at Natural Location Currently, runoff from the site is collected via on-site catch basins which connect to the public storm system on Rainier Avenue South. There are no proposed changes to the existing site drainage discharge point. Core Requirement #2: Offsite Analysis The 2022 City of Renton Surface Water Design Manual (RSWDM) Section 1.2.2 lists 3 exemptions from Core Requirement #2. The third exemption states that if “the project does not change the rate, volume, duration, or location of discharges to and from the project site (e.g., where existing impervious surface is replaced with other impervious surface having similar runoff-generating characteristics, or where pipe/ditch modifications do not change existing discharge characteristics.)” This project falls under this exemption. Core Requirement #3: Flow Control Facilities The project site falls under Peak Rate Flow Control Standard which requires the developed peak discharge rates to match the existing site peak discharge rates for 2-year, 10-year, and 100-year periods. Flow control is discussed in more detail in Section 4.0. The project decreases the total impervious surface area, thus decreasing peak discharge rates. Core Requirement #4: Conveyance System Section 1.2.4.2 of the 2022 RSWDM states that “existing onsite conveyance systems that will not experience a change in flow characteristics (e.g. peak flows or volume of flows) as a result of the proposed project need not be analyzed for conveyance capacity.” This project falls under this category and does not require a conveyance system analysis. Core Requirement #5: Construction Stormwater Pollution Prevention A simplified Construction Stormwater Pollution Prevention Plan (CSWPPP) is included in Section 8 of this report. Core Requirement #6: Maintenance and Operations See Section 9 of this report. Core Requirement #7: Financial Guarantees and Liability See Section 10 of this report. Core Requirement #8: Water Quality Facilities The project site is exempt from this core requirement under the Surface Area Exemption. According to Section 1.2.8 of the 2022 RSWDM, the Surface Area Exemptions applies if “less than 5,000 square feet of new plus replaced pollution-generating impervious surfaces (PGIS) will be created and less than ¾ acre Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 12 Draft Technical Information Report of new pollution-generating pervious surfaces (PGPS) will be added.” This project has 3,954 square feet of new plus replaced PGIS and no new PGPS. Core Requirement #9: On-site BMP’s This project is classified as Large Lot Per Section 1.2.9.2 of the 2022 RSWDM. 1. Full dispersion is not feasible on this site as the site does not contain a native vegetated surface. 2. Full Infiltration and Limited Infiltration are not feasible on this site. See Appendix C for the Geotechnical Engineering Study. 3. Basic Dispersion is used. The project has 16,450 sf of target impervious surfaces. BMPs must be implemented for 20% of that area which is equal to 3,290 square feet. A 24-foot long infiltration trench will be used for the driveway/parking lot area. This corresponds with dispersing 1,680 square feet. The concrete patio area will be dispersed via sheet flow and drain to the landscape area west of the building. This corresponds with dispersing 1,740 square feet. The total area covered by Basic Dispersion BMPs is 3,420 square feet which meets the minimum requirement. 4. Perforated Pipe Connection: Any proposed roof downspout connections to the existing storm drain system on site will use perforated pipes. 2.1 Analysis of the 6 Special Requirements Special Requirement #1: Other Adopted Area-Specific Requirements The project site is not located within an area included in an adopted master drainage plan, basin plan, salmon conservation plan, stormwater compliance plan, hazard mitigation plan, lake management plan, or shared facility drainage plan. Special Requirement #2: Flood Hazard Area Delineation Consultation with FEMA map 53033C0977G shows that the project is not within a flood zone. Special Requirement #3: Flood Protection Facilities The project does not contain nor is it adjacent to any flood protection facilities. Special Requirement #4: Source Control No source control is proposed or expected to be necessary. Special Requirement #5: Oil Control The project has an existing oil and water separator. This project will not result in more than 5,000 square feet of pollution generating replaced impervious area (4,095 sf). Special Requirement #6: Aquifer Protection Per City of Renton Mapping, this project is located within an aquifer protection area zone 2. Facilities in this zone require a liner for proposed facilities that allow runoff to have direct contact with the soil or Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 13 Draft Technical Information Report open channel conveyance systems that are not concrete lined. There are no new storm drain facilities that proposed as part of this project. FIGURE 5– AQUIFER PROTECTION AREA SECTION 3 - OFFSITE ANALYSIS This project is exempt from this section. See Section 2.1, Core Requirement #2: Offsite Analysis. SECTION 4 - FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID), AND WATER QUALITY FACILITY ANALYSIS AND DESIGN The project site falls under Peak Rate Flow Control Standard which requires the developed peak discharge rates to match the existing site peak discharge rates for 2-year, 10-year, and 100-year periods. Project Area Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 14 Draft Technical Information Report The project decreases the total impervious surface area, thus decreasing peak discharge rates. See Table 1. Surface Pre-Development Area (sf) Post-Development Area (sf) Pollution-Generating Asphalt/Concrete 18,250 sf 4,095 sf Concrete Patio/Sidewalk 2,990 sf 3,925 sf Roof 0 sf 8,430 sf Landscape 0 sf 4,790 sf Table 1 – Pre- and Post-Development Areas The project site is exempt from water quality requirements under the Surface Area Exemption. According to Section 1.2.8 of the 2022 RSWDM, the Surface Area Exemptions applies if “less than 5,000 square feet of new plus replaced pollution-generating impervious surfaces (PGIS) will be created and less than ¾ acre of new pollution-generating pervious surfaces (PGPS) will be added.” This project has 4,095 sf of new plus replaced PGIS and no new PGPS. SECTION 5 - CONVEYANCE SYSTEM ANALYSIS AND DESIGN This project is exempt from this section. See Section 2.1, Core Requirement #4: Offsite Conveyance System. SECTION 6 - SPECIAL REPORTS AND STUDIES There are no special reports or studies included in this report. SECTION 7 - OTHER PERMITS Construction and Grading Permits will be obtained from the City of Renton. SECTION 8 - CSWPP PLAN ANALYSIS AND DESIGN A drainage control plan was prepared as part of the conditional use permit submittal (see Appendix A). 8.1 ESC Plan Analysis and Design (Part A) 1. Clearing Limits: Clearing limits are shown on the drainage control plan and are limited to the site frontage where existing pavement will be converted into a 10-foot landscape buffer. 2. Cover Measures: No cover measures are proposed; no areas are proposed to be worked on for more than 2 days. 3. Perimeter Protection: Compost filter socks or sandbag barriers will be installed adjacent to roadway curb for ROW work. 4. Traffic Area Stabilization: No traffic area stabilization is required. 5. Sediment Retention: No sediment traps or basins are required. No offsite discharge of surface water is anticipated. Inlet protection will be installed on all storm drain inlets within or near the project site. Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 15 Draft Technical Information Report 6. Surface Water Collection: No surface water collection is required. 7. Dewatering Control: No dewatering control is required. 8. Dust Control: No dust generation is required; no dust generation is anticipated during construction. 9. Flow Control: Not required; no increase to the existing site conditions runoff peak is proposed. 10. Control Pollutants: Best Management Practices (BMPs) used for control of pollutants from construction activities will be discussed in Section 8.2. 11. Protect Existing and Proposed Stormwater Facilities and On-site BMPs: Inlet protection will be used on existing storm drain inlets in and near the project area. 12. Maintain Protective BMPs: BMPs established at the site will be protected and maintained per CoR CSWPP Requirements. 13. Manage the Project: BMPs at the site will be inspected, maintained, or replaced per CoR CSWPP Requirements. 8.2 SWPPS Plan Design (Part B) See Appendix C for BMP details. 1. All Pollutants, including waste materials, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of storm water. 2. Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and non-insert wastes present on the site. 3. Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge of spillage of pollutants to the ground or into stormwater runoff must be conducted using spill prevention measures, such as drip pans. Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Emergency repairs may be performed onsite using temporary plastic placed beneath, and if raining, over the vehicle. 4. Application of agricultural chemicals, including fertilizers and pesticides, shall be conducted in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers’ recommendations for application rates and procedures shall be followed. 5. Stormwater discharges shall not cause or contribute to a violation of the water quality standard for pH in the receiving water. Measures shall be used to prevent or treat contamination of stormwater runoff by pH modifying sources such as: bulk cement, cement kiln dust, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, and exposed aggregate processes, and concrete pumping and mixer washout water. SECTION 9 - BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT All required bonds, facility summaries, and covenants will be provided prior to final approval. Prepared by CRW Engineering Group ARB Flagship Store August 2022 Page 16 Draft Technical Information Report SECTION 10 - OPERATIONS AND MAINTENANCE MANUAL The on-site storm drain facilities will be privately maintained by the property owner. An Operation and Maintenance Manual is included in Appendix D of this report. Appendix A Site Plan Drainage Control Plan NO.DATEDESCRIPTION01KEVIN J. BRODERICKSTATE OF WASHINGTON4532REGISTEREDARCHITECTTHIS DOCUMENT REPRESENTS A PROPRIETARY DESIGN OWNED BY THE ARCHITECT AND SHALL NOT BE USED ON OTHER PROJECTS OR ADDITIONS TO THIS PROJECT OR FOR COMPLETION OF THIS PROJECT BY OTHERS EXCEPT BY PRIOR ARRANGEMENT IN WIRTING COPYRIGHT © 1:26 PM ON Tuesday, January 17, 2023 BY BRODERICK ARCHITECTS, PLLC21.035 PLOT DATE: 1/17/23 El Teodoro 21.035 ARB Renton_221122_AC25720 RAINIER AVENUE S • RENTON, WA 98057ARB FLAGSHIP STORETENANT IMPROVEMENT & CHANGE OF USEDEDICATED APPROVAL STAMP SPACEA0.2 SITE PLAN 10/28/22 CUP SUBMITTAL 01/17/23 CUP SUBMITTAL CORRECTION 1UP 50.50'9.00'72.00' 9.00' 17.00' COMPACT STALLS36.00' 18.00' 42.50' 7 COMPACT STALLS (30% MAX)20.38'18' MIN.AISLE16.00' 18.00' 11.00' ADA9.00' 9.00'16.00' MI N.23.30'31.00'22.01'2.67'21.89'30.00'14.83'10.00'44.48' 51.5 1' 4 5.00' 47 .03' 8.96'20.05' 14.98'29.62'(5' MIN. CLR)10.67' 28.00' REQ. TURNING RADIUS 20'-0" MIN.20.00' MIN.REQ. FIRE LANE47.00' 103.00' 150.00' REQ. TOTAL FIRE LANE 128.00' 150.00' HOSE TOTAL 14.00'8.00' 150.00' HOSE TOTAL 20.00' MIN. 28.00'REQ. TURNING RADIUS 71.51' UNPROTECTED 67.47'1.07'0' REQ'DSIDE YARD SETBACK37.00'0' REQ'D SIDE YARD SETBACK4 .7 0 '0 ' R E Q 'D R E A R Y A R D S E T B A C K 24.82'15' MIN. REQ'DFRONT YARD SETBACK c = 60 . 7 1'C = 2 6' (E) CONC SIDEWALK (E) CONC DRIVEWAY RELOCATED (E) CONC SIDEWALK 40' OUTER RAD SHOWN, TYP 20' INNER RAD SHOWN, TYP (E) CANOPY TO REMAIN (E) CANOPY TO REMAIN REFUSE AREA MIN. 175 SF REQ'D PER TABLE A 23.54.040 SEE SHEET A2.3 FOR MORE INFO (N) LANDSCAPING (E) SIGNAGE TO BE REMOVED (N) LANDSCAPING (E) VAULT TO REMAIN (E) CURB MODIFIED COMPACT PARKING STALLS MAXIMUM NUMBER OF COMPACT SPACES OUTSIDE OF THE UC ZONES NOT TO EXCEED THIRTY PERCENT (30%) (Ord. 5030, 11-24-2003) PER RMC 4-4-080-F8c VAN ACCESSIBLE PARKING SPACE ONE VAN MINIMUM ACCESSIBLE SPACE PER RMC TABLE 4-4-080-F8g. VAN SPACE TO BE 132" MIN. WIDE WITH 60" MIN. ACCESS AISLE PER ANSI ICC A117, 1-2009, §502.2. (N) 60" MIN. HIGH ACCESSIBLE SIGN IDENTIFYING VAN SPACE MUST INCLUDE THE TERM "VAN ACCESSIBLE" PER ANSI §502.7. (E) PROPERTY LINE PROPOSED PLATER STRIP WITH STREET TRESS, BUSHES, & LIGHTING MATCH EXISTING CURB, PLANTING STRIP, & SIDEWALK 9' UTILITY EASEMENT MATCH EXISTING CURB, PLANTING STRIP, & SIDEWALK 10' WATER EASEMENT (N) LANDSCAPING 2" CAL. TILIA CORDATA 'CORZAM'/ CORINTHIAN LITTLELEAF LINDEN 2" CAL. TILIA CORDATA 'CORZAM'/ CORINTHIAN LITTLELEAF LINDEN EX. POLE LIGHT EX. POLE LIGHT EX. 7" TILIA AMERICANA/ AMERICAN BASSWOOD CITY OF RENTON STREET FRONTAGE LANDSCAPE REQUIREMENT: 10' ON-SITE LANDSCAPING 6'-0" FENCE, TYP. 6'-0" FENCE, TYP. (N) 4-0" FENCE & ENTRY GATE (N) BOLLARDS (N) ADDITION 1 STORY BLDG AREA: 6,332 SF 26242626 26 PL 222.24'PL 81.83'7.73'6.65'P L 3 12.33' P L 1 2 6 . 6 5' 8.16'RAINIER AVE SZONED CA / AUTO MALL AREA B 120° 120°TEMP CONSTEASEMENTCOMPACT COMPACT COMPACT COMPACT COMPACT COMPACT COMPACT 25 26 27 28 29 30 31 5.00'8.00'1.00'a = 102.18'A = 26'b = 205.82' B = 26' 633.5 sq ft PROPOSED RIGHT-OF-WAY DEDICATION LINE PROPOSED 10' PERMITER LANDSCAPING SCREEN WITH MINIMUM 2" LINEAL FEET OF STREET FRONTAGE 6'-0" FENCE, TYP. (E) COMMERCIAL BLDG 1 STORY + MEZZANINE BLDG AREA: 9,570 SF 720 RAINIER AVENUE S APN: 192305-9053 INTERIOR REMODEL & CHANGE OF USE (E) USE: VEHICLE SALES (WALKER'S RENTON MAZDA) (N) USE: RETAIL SALES (ARB) (N) ADDITION BREAK ROOM 650 SF (N) A D DITIO N M AIN E N T R Y 213 S F FF EL=26.0'ROOF EL=45.3' 26 B L D G 1 .1 'S WBLDG 1 .2 'S W LES SCHWAB TIRE CENTER PARCEL #: 1923059044 NEIGHBORING PROPERTY ZONED CA / AUTO MALL AREA B P ARCE L # : 1 9 2 3 0 5 9 0 6 3NE I GHB ORI NG P ROP E RT Y Z ON ED CAPL 75.05'P ARCEL #: 1 9 2 3 0 5 9 0 3 1NE I GHBORI NG P ROPER T Y Z ONE D CA / A UT O MA L L A REA BPA RC E L #: 192305 9 0 3 5 N E IGH B OR IN G PR O P ER TY Z O NE D CA (N) TRASH ENCLOSURE 175 SF 1 2 3 4 5 6 7 8 9 10 11 12 1 3 1 4 15 1 6 17 18 1 9 2 0 21 2 2 2 3 24 PROJECT NAME: ARB FLAGSHIP STORE TENANT IMPROVEMENT & CHANGE OF USE PROJECT ADDRESS: 720 RAINIER AVENUE S RENTON, WA 98057 PROJECT DESCRIPTION: USE OF THE PROPERTY AND SCOPE OF THE DEVELOPMENT PROPOSES TO REMODEL THE EXISTING BUILDING FOR ARB, WITH LIMITED FAÇADE IMPROVEMENTS (PRIMARILY SIGNAGE), NEW MAIN ENTRY ADDITION (213 SF), NEW TRAINING ROOM ADDITION (650 SF), AND NEW 1-STORY ADDITION (6,332 SF). THE EXISTING 498 SF MEZZANINE WILL BE USED FOR STORAGE. THE EXISTING 9,570 SF BUILDING WILL BE THE PROPOSED ARB FLAGSHIP STORE THAT WOULD INCLUDE ON-SITE RETAIL SALES OF VEHICLE ACCESSORIES. THE 1-STORY ADDITION TO BE USED FOR THE ONSITE VEHICLE ACCESSORIES INSTALLATION AND GARAGE STORAGE. ACCESS TO THE SITE IS PROPOSED TO REMAIN VIA RELOCATED DRIVEWAY CURB CUT OFF RAINIER AVE S. PARCEL NUMBER: 192305-9053 LEGAL DESCRIPTION: LOT 1 LESS HWY PER DEED REC #20110815000477 OF RENTON LLA LUA-02-025-LLA REC 20020515900009 LOCATED IN NW 1/4 OF NE 1/4 OWNER: ARB USA 4810 D STREET NW, SUITE 103 AUBURN, WA 98001 425.264.1391 x1374 CONTACT: JEFF BLAKE jblake@arbusa.com ARCHITECT: BRODERICK ARCHITECTS 55 S. ATLANTIC STREET, SUITE 301 SEATTLE, WA 98134 206.682.7525 206.682.7529 (F) CONTACT: KEVIN BRODERICK kevin@broderickarchitects.com JURISDICTION: CITY OF RENTON ZONING: CA – COMMERCIAL ARTERIAL LOT AREA: 37,702 SF (0.87 ACRES) HEIGHT: 22'-10' (PROPOSED) PARKING: 31 STALLS (TOTAL PROPOSED) 21 EXISTING + 3 NEW + 7 GARAGE PER RMC 10-10-13 & 4-4-080 LOT COV. CALCULATIONS: (E) LOT COVERAGE 9,570 = 25.4% MAX. LOT COVERAGE 24,506 = 65.0% MAX PROPOSED ADDITION: (N) 1-STORY INSTALL = 6,332 SF (N) ADDITION ROOM = 650 SF (N) MAIN ENTRY = 213 SF TOTAL PROPOSED ADD. = 7,195 SF PROPOSED LOT COV: 9,570 + 7,195 = 16,765 SF (44.5%) (BELOW 65% MAX LOT COVERAGE) SETBACK REQUIREMENTS: FRONT YARD 15' MIN. REAR YARD NONE SIDE YARD NONE (EXCEPT IF ADJACENT TO LOT ZONED RES PER RMC 4-2-120A) A A FEC 0" W1 ELEVATION MARKER SECTION MARKER DETAIL MARKER CONSTRUCTION ASSEMBLY TYPE FLOOR ELEVATION FIRE EXTINGUISHER NO WORK IN SHADED AREA NEW INTERIOR WALL EXISTING WALL TO REMAIN DOOR TAG WINDOW TAG 01 01 01 NEIGHBORHOOD DETAILED MAP 1" = 20'1 PROPOSED SITE PLAN 0 10'20'40' PARCEL INFORMATION PLANNING NOTES SITE PLAN LEGEND LEGEND 1" = 200' SITE Appendix B BMP Details D.2.1.2 COVER MEASURES 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-21 Maintenance Standards for Plastic Covering 1. Torn sheets must be replaced and open seams repaired. 2. If the plastic begins to deteriorate due to ultraviolet radiation, it must be completely removed and replaced. 3. When the plastic is no longer needed, it shall be completely removed. D.2.1.2.5 STRAW WATTLES Code: SW Symbol: Purpose Wattles are erosion and sediment control barriers consisting of straw wrapped in biodegradable tubular plastic or similar encasing material. Wattles may reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sediment. Straw wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. The wattles are placed in shallow trenches and staked along the contour of disturbed or newly constructed slopes. Conditions of Use 1. Install on disturbed areas that require immediate erosion protection. 2. Use on slopes requiring stabilization until permanent vegetation can be established. 3. Can be used along the perimeter of a project, as a check dam in unlined ditches and around temporary stockpiles 4. Wattles can be staked to the ground using willow cuttings for added revegetation. 5. Rilling can occur beneath and between wattles if not properly entrenched, allowing water to pass below and between wattles Design and Installation Specifications 1. It is critical that wattles are installed perpendicular to the flow direction and parallel to the slope contour. 2. Narrow trenches should be dug across the slope, on contour, to a depth of 3 to 5 inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and during high rainfall events, the trenches should be dug to a depth of 5 to 7 inches, or ½ to 2/3 of the thickness of the wattle. 3. Start construction of trenches and installing wattles from the base of the slope and work uphill. Excavated material should be spread evenly along the uphill slope and compacted using hand tamping or other method. Construct trenches at contour intervals of 3 to 30 feet apart depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches should be constructed. 4. Install the wattles snugly into the trenches and abut tightly end to end. Do not overlap the ends. 5. Install stakes at each end of the wattle, and at 4 foot centers along the entire length of the wattle. 6. If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. 7. At a minimum, wooden stakes should be approximately ¾ x ¾ x 24 inches. Willow cuttings or 3/8 inch rebar can also be used for stakes. SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-22 8. Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake protruding above the wattle. Maintenance Standards 1. Inspect wattles prior to forecasted rain, daily during extended rain events, after rain events, weekly during the wet season, and at two week intervals at all other times of the year. 2. Repair or replace split, torn, raveling, or slumping wattles 3. Remove sediment accumulations when exceeding ½ the height between the top of the wattle and the ground surface. D.2.1.2 COVER MEASURES 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-23 FIGURE D.2.1.2.E STRAW WATTLES 1.STRAW ROLL INSTALLATION REQUIRES THE PLACEMENT AND SECURE STAKING OF THE ROLL IN A TRENCH, 3" x 5" (75-125mm) DEEP, DUG ON CONTOUR. 2.RUNOFF MUST NOT BE ALLOWED TO RUN UNDER OR AROUND ROLL. ROLL SPACING DEPENDS ON SOIL TYPE AND SLOPE STEEPNESS STRAW ROLLS MUST BE PLACED ALONG SLOPE CONTOURS 3'-4' (1.2m) 10'-25' (3-8m) 3"-5" (75-125mm) ADJACENT ROLLS SHALL TIGHTLY ABUT SEDIMENT, ORGANIC MATTER, AND NATIVE SEEDS ARE CAPTURED BEHIND THE ROLLS LIVE STAKE 1" x 1" STAKE 8"-10" DIA. (200-250mm) NOTES: STRAW WATTLES NTS SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-24 D.2.1.2.6 TEMPORARY AND PERMANENT SEEDING Code: SE Symbol: Purpose Seeding is intended to reduce erosion by stabilizing exposed soils. A well-established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use 1. Seeding shall be used throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. 2. Vegetation-lined channels shall be seeded. Channels that will be vegetated should be installed before major earthwork and hydroseeded or covered with a Bonded Fiber Matrix (BFM). 3. Retention/detention ponds shall be seeded as required. 4. At the County's discretion, seeding without mulch during the dry season is allowed even though it will take more than seven days to develop an effective cover. Mulch is, however, recommended at all times because it protects seeds from heat, moisture loss, and transport due to runoff. 5. At the beginning of the wet season, all disturbed areas shall be reviewed to identify which ones can be seeded in preparation for the winter rains (see Section D.2.4.2). Disturbed areas shall be seeded within one week of the beginning of the wet season. A sketch map of those areas to be seeded and those areas to remain uncovered shall be submitted to the DLS-Permitting inspector. The DLS- Permitting inspector may require seeding of additional areas in order to protect surface waters, adjacent properties, or drainage facilities. 6. At final site stabilization, all disturbed areas not otherwise vegetated or stabilized shall be seeded and mulched (see Section D.2.4.5). Design and Installation Specifications 1. The best time to seed is April 1 through June 30, and September 1 through October 15. Areas may be seeded between July 1 and August 31, but irrigation may be required in order to grow adequate cover. Areas may also be seeded during the winter months, but it may take several months to develop a dense groundcover due to cold temperatures. The application and maintenance of mulch is critical for winter seeding. 2. To prevent seed from being washed away, confirm that all required surface water control measures have been installed. 3. The seedbed should be firm but not compacted because soils that are well compacted will not vegetate as quickly or thoroughly. Slopes steeper than 3H:1V shall be surface roughened. Roughening can be accomplished in a variety of ways, but the typical method is track walking, or driving a crawling tractor up and down the slope, leaving cleat imprints parallel to the slope contours. 4. In general, 10-20-20 N-P-K (nitrogen-phosphorus-potassium) fertilizer may be used at a rate of 90 pounds per acre. Slow-release fertilizers are preferred because they are more efficient and have fewer environmental impacts. It is recommended that areas being seeded for final landscaping conduct soil tests to determine the exact type and quantity of fertilizer needed. This will prevent the over- application of fertilizer. Disturbed areas within 200 feet of water bodies and wetlands must use slow- release low-phosphorus fertilizer (typical proportions 3-1-2 N-P-K). 5. The following requirements apply to mulching: a) Mulch is always required for seeding slopes greater than 3H:1V (see Section D.2.1.2.2). D.2.1.2 COVER MEASURES 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-25 b) If seeding during the wet season, mulch is required. c) The use of mulch may be required during the dry season at the County's discretion if grass growth is expected to be slow, the soils are highly erodible due to soil type or gradient, there is a water body close to the disturbed area, or significant precipitation (see Section D.2.4.2) is anticipated before the grass will provide effective cover. d) Mulch may be applied on top of the seed or simultaneously by hydroseeding. 6. Hydroseeding is allowed as long as tackifier is included. Hydroseeding with wood fiber mulch is adequate during the dry season. During the wet season, the application rate shall be doubled because the mulch and tackifier used in hydroseeding break down fairly rapidly. It may be necessary in some applications to include straw with the wood fiber, but this can be detrimental to germination. 7. Areas to be permanently landscaped shall use soil amendments. Good quality topsoil shall be tilled into the top six inches to reduce the need for fertilizer and improve the overall soil quality. Most native soils will require the addition of four inches of well-rotted compost to be tilled into the soil to provide a good quality topsoil. Compost used should meet specifications provided in Reference 11-C of the SWDM. 8. The seed mixes listed below include recommended mixes for both temporary and permanent seeding. These mixes, with the exception of the wetland mix, shall be applied at a rate of 120 pounds per acre. This rate may be reduced if soil amendments or slow-release fertilizers are used. Local suppliers should be consulted for their recommendations because the appropriate mix depends on a variety of factors, including exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the County may be used. Table D.2.1.2.B presents the standard mix for those areas where just a temporary vegetative cover is required. TABLE D.2.1.2.B TEMPORARY EROSION CONTROL SEED MIX % Weight % Purity % Germination Chewings or red fescue Festuca rubra var. commutata or Festuca rubra 40 98 90 Annual or perennial rye Lolium multiflorum or Lolium perenne 40 98 90 Redtop or colonial bentgrass Agrostis alba or Agrostis tenuis 10 92 85 White dutch clover Trifolium repens 10 98 90 SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-26 Table D.2.1.2.C provides just one recommended possibility for landscaping seed. TABLE D.2.1.2.C LANDSCAPING SEED MIX % Weight % Purity % Germination Perennial rye blend Lolium perenne 70 98 90 Chewings and red fescue blend Festuca rubra var. commutata or Festuca rubra 30 98 90 This turf seed mix in Table D.2.1.2.D is for dry situations where there is no need for much water. The advantage is that this mix requires very little maintenance. TABLE D.2.1.2.D LOW-GROWING TURF SEED MIX % Weight % Purity % Germination Dwarf tall fescue (several varieties) Festuca arundinacea var. 45 98 90 Dwarf perennial rye (Barclay) Lolium perenne var. barclay 30 98 90 Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Table D.2.1.2.E presents a mix recommended for bioswales and other intermittently wet areas. Sod shall generally not be used for bioswales because the seed mix is inappropriate for this application. Sod may be used for lining ditches to prevent erosion, but it will provide little water quality benefit during the wet season. TABLE D.2.1.2.E BIOSWALE SEED MIX* % Weight % Purity % Germination Tall or meadow fescue Festuca arundinacea or Festuca elatior 75-80 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 92 85 Redtop bentgrass Agrostis alba or Agrostis gigantea 5-10 90 80 * Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix D.2.1.2 COVER MEASURES 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-27 The seed mix shown in Table D.2.1.2.F is a recommended low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands (if planting in wetland areas, see Section 6.3.1 of the King County Surface Water Design Manual). Other mixes may be appropriate, depending on the soil type and hydrology of the area. Apply this mixture at a rate of 60 pounds per acre. TABLE D.2.1.2.F WET AREA SEED MIX* % Weight % Purity % Germination Tall or meadow fescue Festuca arundinacea or Festuca elatior 60-70 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 98 85 Meadow foxtail Alepocurus pratensis 10-15 90 80 Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 * Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix The meadow seed mix in Table D.2.1.2.G is recommended for areas that will be maintained infrequently or not at all and where colonization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter months. The appropriateness of clover in the mix may need to be considered as this can be a fairly invasive species. If the soil is amended, the addition of clover may not be necessary. TABLE D.2.1.2.G MEADOW SEED MIX % Weight % Purity % Germination Redtop or Oregon bentgrass Agrostis alba or Agrostis oregonensis 40 92 85 Red fescue Festuca rubra 40 98 90 White dutch clover Trifolium repens 20 98 90 Maintenance Standards for Temporary and Permanent Seeding 1. Any seeded areas that fail to establish at least 80 percent cover within one month shall be reseeded. If reseeding is ineffective, an alternate method, such as sodding or nets/blankets, shall be used. If winter weather prevents adequate grass growth, this time limit may be relaxed at the discretion of the County when critical areas would otherwise be protected. SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-28 2. After adequate cover is achieved, any areas that experience erosion shall be re-seeded and protected by mulch. If the erosion problem is drainage related, the problem shall be fixed and the eroded area re-seeded and protected by mulch. 3. Seeded areas shall be supplied with adequate moisture, but not watered to the extent that it causes runoff. D.2.1.2.7 SODDING Code: SO Symbol: Purpose The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize drainage ways where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas: 1. Disturbed areas that require short-term or long-term cover 2. Disturbed areas that require immediate vegetative cover 3. All waterways that require vegetative lining (except biofiltration swales—the seed mix used in most sod is not appropriate for biofiltration swales). Waterways may also be seeded rather than sodded, and protected with a net or blanket (see Section D.2.1.2.3). Design and Installation Specifications Sod shall be free of weeds, of uniform thickness (approximately 1-inch thick), and shall have a dense root mat for mechanical strength. The following steps are recommended for sod installation: 1. Shape and smooth the surface to final grade in accordance with the approved grading plan. 2. Amend four inches (minimum) of well-rotted compost into the top eight inches of the soil if the organic content of the soil is less than ten percent. Compost used shall meet compost specifications per SWDM Reference 11-C. 3. Fertilize according to the supplier's recommendations. Disturbed areas within 200 feet of water bodies and wetlands must use non-phosphorus fertilizer. 4. Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface. 5. Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V. 6. Roll the sodded area and irrigate. 7. When sodding is carried out in alternating strips or other patterns, seed the areas between the sod immediately after sodding. Maintenance Standards If the grass is unhealthy, the cause shall be determined and appropriate action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability, or some other cause, the sod shall be removed, the area seeded with an appropriate mix, and protected with a net or blanket. SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-40 12. A compost blanket extending 10 – 15 feet above the berm is recommended where the surface above the berm is rutted or uneven, to reduce concentrated flow and promote sheet flow into the berm. Maintenance Standards 1. Compost berms shall be regularly inspected to make sure they retain their shape and allow adequate flow-through of stormwater. 2. When construction is completed on site, the berms shall be dispersed for incorporation into the soil or left on top of the site for final seeding to occur. 3. Any damage to berms must be repaired immediately. Damage includes flattening, compacting, rills, eroded areas due to overtopping. 4. If concentrated flows are evident uphill of the berm, the flows must be intercepted and conveyed to a sediment trap or pond. 5. The uphill side of the berm shall be inspected for signs of the berm clogging and acting as a barrier to flows and causing channelization of flows parallel to the berm. If this occurs, replace the berm or remove the trapped sediment. 6. Sediment that collects behind the berm must be removed when the sediment is more than 6 inches deep. D.2.1.3.6 COMPOST SOCKS Code: COSO Symbol: Purpose Compost socks reduce the transport of sediment from a construction site by providing a temporary physical barrier to sediment-laden water and reducing the runoff velocities of overland flow. Compost socks trap sediment by filtering water that passes through the sock and allows water to pond behind the sock, creating a settling area for solids. Organic materials in the compost also may reduce metal and petroleum hydrocarbon concentrations in construction runoff. Compost socks function similarly to compost berms; however, because the compost is contained in a mesh tube, they are appropriate for both concentrated flow and sheet flow. Compost socks may be used to channel concentrated flow on hard surfaces. Conditions of Use 1. Compost socks may be used in areas requiring sediment or erosion control where runoff is in the form of sheet flow or in areas that silt fence is normally considered acceptable. Compost socks may also be used in sensitive environmental areas where migration of aquatic life, including turtles, salamanders and other aquatic life may be impeded by the used of silt fence. 2. Compost socks are not intended to treat substantial amounts of overland flow. However, compost socks may be subjected to some ponding and concentrated flows. If intended primarily as a filtration device, the socks should be sized and placed so that flows do not overtop the socks. 3. For purposes of long term sediment control objectives, compost socks may be seeded at the time of installation to create an additional vegetated filtering component. Design and Installation Specifications 1. Compost socks shall be produced using a pneumatic blower hose or equivalent to fill a mesh tube with compost to create a uniform cross-section and berm density. D.2.1.4 TRAFFIC AREA STABILIZATION 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-41 2. Socks shall be filled so they are firmly – packed yet flexible. Upon initial filling, the socks shall be filled to have a round cross-section. Once placed on the ground, it is recommended to apply weight to the sock to improve contact with the underlying surface. This may cause the sock to assume an oval shape. 3. Compost socks shall be a minimum of 8 inches in diameter. Larger diameter socks are recommended for areas where ponding is expected behind the sock. 4. Compost socks shall not be used on slopes greater than 2H:1V. 5. Compost shall meet criteria in Reference 11-C of the SWDM, except for the particle size distribution (see Bullet 7). 6. Compost shall be obtained from a supplier meeting the requirements in Reference 11-C. 7. Compost particle size distribution shall be as follows: 99% passing a 1 inch sieve, 90% passing a ¾ inch sieve and a minimum of 70% greater than the 3/8 inch sieve. A total of 98% shall not exceed 3 inches in length. 8. In order to prevent water from flowing around the ends of compost socks, the ends must be pointed upslope so the ends of the socks are at a higher elevation than the remainder of the sock. Maintenance Standards 1. Compost socks shall be regularly inspected to make sure the mesh tube remains undamaged, the socks retain their shape, and allow adequate flow through of surface water. If the mesh tube is torn, it shall be repaired using twine, zip-ties, or wire. Large sections of damaged socks must be replaced. Any damage must be repaired immediately upon discovery of damage. 2. When the sock is no longer needed, the socks shall be cut open and the compost dispersed to be incorporated into the soil or left on top of the soil for final seeding to occur. The mesh material must be disposed of properly as solid waste. If spills of oil, antifreeze, hydraulic fluid, or other equipment fluids have occurred that have saturated the sock, the compost must be disposed of properly as a waste. 3. Sediment must be removed when sediment accumulations are within 3 inches of the top of the sock. D.2.1.4 TRAFFIC AREA STABILIZATION Unsurfaced entrances, roads, and parking areas used by construction traffic shall be stabilized to minimize erosion and tracking of sediment off site. Stabilized construction entrances shall be installed as the first step in clearing and grading. At the County's discretion, road and parking area stabilization is not required during the dry season (unless dust is a concern) or if the site is underlain by coarse-grained soils. Roads and parking areas shall be stabilized immediately after initial grading. Purpose: The purpose of traffic area stabilization is to reduce the amount of sediment transported off site by construction vehicles and to reduce the erosion of areas disturbed by vehicle traffic. Sediment transported off site onto paved streets is a significant problem because it is difficult to effectively remove, and any sediment not removed ends up in the drainage system. Additionally, sediment on public right-of- way can pose a serious traffic hazard. Construction road and parking area stabilization is important because the combination of wet soil and heavy equipment traffic typically forms a slurry of easily erodible mud. Finally, stabilization also is an excellent form of dust control in the summer months. When to Install: The construction entrance is to be installed as the first step in clearing and grading. Construction road stabilization shall occur immediately after initial grading of the construction roads and parking areas. Measures to Use: There are two types of traffic area stabilization: (1) a stabilized construction entrance and (2) construction road/parking area stabilization. Both measures must be used as specified under "Conditions of Use" for each measure. D.2.1.5 SEDIMENT RETENTION 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-53 FIGURE D.2.1.5.D SEDIMENT POND RISER DETAIL 3.5' MIN. 18" MIN. 2X RISER DIA. MIN. CORRUGATED METAL RISER CONCRETE BASE ALTERNATIVELY, METAL STAKES AND WIRE MAY BE USED TO PREVENT FLOTATION DEWATERING ORIFICE, SCHEDULE 40 STEEL STUB MIN. DIAMETER AS PER CALCULATIONS 6" MIN. PROVIDE ADEQUATE STRAPPING POLYETHYLENE CAP PERFORATED DEWATERING DEVICE, SEE NOTE WATERTIGHT COUPLING TACK WELD NOTE: PERFORATED CORRUGATED POLYETHYLENE (CPE) DRAINAGE TUBING, DIAMETER MIN. 2" LARGER THAN DEWATERING ORIFICE. TUBING SHALL COMPLY WITH ASTM F667 AND AASHTO M294. D.2.1.5.3 STORM DRAIN INLET PROTECTION Code: FFP or CBI or CBP Symbol: or or Purpose Storm drain inlets are protected to prevent coarse sediment from entering storm drainage systems. Temporary devices around storm drains assist in improving the quality of water discharged to inlets or catch basins by ponding sediment-laden water. These devices are effective only for relatively small drainage areas. Conditions of Use 1. Protection shall be provided for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless the runoff that enters the catch basin will be conveyed to a sediment pond or trap. 2. Inlet protection may be used anywhere at the applicant's discretion to protect the drainage system. This will, however, require more maintenance, and it is highly likely that the drainage system will still require some cleaning. 3. The contributing drainage area must not be larger than one acre. Design and Installation Specifications 1. There are many options for protecting storm drain inlets. Two commonly used options are filter fabric protection and catch basin inserts. Filter fabric protection (see Figure D.2.1.5.E) is filter fabric (geotextile) placed over the grate. This method is generally very ineffective and requires intense maintenance efforts. Catch basin inserts (see Figure D.2.1.5.F) are manufactured devices that nest inside a catch basin. This method also requires a high frequency of maintenance to be effective. Both SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-54 options provide adequate protection, but filter fabric is likely to result in ponding of water above the catch basin, while the insert will not. Thus, filter fabric is only allowed where ponding will not be a traffic concern and where slope erosion will not result if the curb is overtopped by ponded water. Trapping sediment in the catch basins is unlikely to improve the water quality of runoff if it is treated in a pond or trap because the coarse particles that are trapped at the catch basin settle out very quickly in the pond or trap. Catch basin protection normally only improves water quality where there is no treatment facility downstream. In these circumstances, catch basin protection is an important last line of defense. It is not, however, a substitute for preventing erosion. The placement of filter fabric under grates is generally prohibited and the use of filter fabric over grates is strictly limited and discouraged. 2. It is sometimes possible to construct a small sump around the catch basin before final surfacing of the road. This is allowed because it can be a very effective method of sediment control. 3. Block and gravel filters, gravel and wire mesh filter barriers, and bag barriers filled with various filtering media placed around catch basins can be effective when the drainage area is 1 acre or less and flows do not exceed 0.5 cfs. It is necessary to allow for overtopping to prevent flooding. Many manufacturers have various inlet protection filters that are very effective in keeping sediment-laden water from entering the storm drainage system. The following are examples of a few common methods. a) Block and gravel filters (Figure D.2.1.5.G) are a barrier formed around an inlet with standard concrete block and gravel, installed as follows: • Height is 1 to 2 feet above the inlet. • Recess the first row of blocks 2 inches into the ground for stability. • Support subsequent rows by placing a 2x4 through the concrete block opening. • Do not use mortar. • Lay some blocks in the bottom row on their side for dewatering the pooled water. • Place cloth or mesh with ½ inch openings over all block openings. • Place gravel below the top of blocks on slopes of 2:1 or flatter. • An alternate design is a gravel donut. b) Gravel and wire mesh filters consist of a gravel barrier placed over the top of an inlet. This structure generally does not provide overflow. Install as follows: • Cloth or comparable wire mesh with ½ inch openings is placed over inlet. • Coarse aggregate covers the cloth or mesh. • Height/depth of gravel should be 1 foot or more, 18 inches wider than inlet on all sides. c) Curb inlet protection with a wooden weir is a barrier formed around an inlet with a wooden frame and gravel, installed as follows: • Construct a frame and attach wire mesh (½ inch openings) and filter fabric to the frame. • Pile coarse washed aggregate against the wire/fabric. • Place weight on frame anchors. d) Curb and gutter sediment barriers (Figure D.2.1.5.H) consist of sandbags or rock berms (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape, installed as follows: • Bags of either burlap or woven geotextile fabric, filled with a variety of media such as gravel, wood chips, compost or sand stacked tightly allows water to pond and allows sediment to separate from runoff. D.2.1.5 SEDIMENT RETENTION 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-55 • Leave a "one bag gap" in the top row of the barrier to provide a spillway for overflow. • Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 x 3 and at least 2 feet from the inlet. • Construct a horseshoe shaped sedimentation trap on the outside of the berm to sediment trap standards for protecting a culvert inlet. 4. Excavated drop inlet sediment traps are appropriate where relatively heavy flows are expected and overflow capability is needed. If emergency overflow is provided, additional end-of-pipe treatment may be required. Excavated drop inlets consist of an excavated impoundment area around a storm drain. Sediment settles out of the stormwater prior to enter the drain. Install according to the following specifications: a) The impoundment area should have a depth of 1 - 2 feet measured from the crest of the inlet structure. b) Side slopes of the excavated area must be no steeper than 2:1. c) Minimum volume of the excavated area should be 35 cubic yards. d) Install provisions for draining the area to prevent standing water problems. e) Keep the area clear of debris. f) Weep holes may be drilled into the side of the inlet. g) Protect weep holes with wire mesh and washed aggregate. h) Weep holes must be sealed when removing and stabilizing excavated area. i) A temporary dike may be necessary on the down slope side of the structure to prevent bypass flow. Maintenance Standards 1. Any accumulated sediment on or around inlet protection shall be removed immediately. Sediment shall not be removed with water, and all sediment must be disposed of as fill on site or hauled off site. 2. Any sediment in the catch basin insert shall be removed when the sediment has filled one-third of the available storage. The filter media for the insert shall be cleaned or replaced at least monthly. 3. Regular maintenance is critical for all forms of catch basin/inlet protection. Unlike many forms of protection that fail gradually, catch basin protection will fail suddenly and completely if not maintained properly. SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-56 FIGURE D.2.1.5.E FILTER FABRIC PROTECTION FIGURE D.2.1.5.F CATCH BASIN INSERT CATCH BASIN NOTE: ONLY TO BE USED WHERE PONDING OF WATER ABOVE THE CATCH BASIN WILL NOT CAUSE TRAFFIC PROBLEMS AND WHERE OVERFLOW WILL NOT RESULT IN EROSION OF SLOPES. GRATESTANDARD STRENGTH FILTER FABRIC NOTE: THIS DETAIL IS ONLY SCHEMATIC. ANY INSERT IS ALLOWED THAT HAS:•A MIN. 0.5 C.F. OF STORAGE,•THE MEANS TO DEWATER THE STORED SEDIMENT,•AN OVERFLOW, AND•CAN BE EASILY MAINTAINED. OVERFLOW GRATECATCH BASIN POROUS BOTTOM SOLID WALLS FILTER MEDIA FOR DEWATERING D.2.1.5 SEDIMENT RETENTION 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-57 FIGURE D.2.1.5.G BLOCK AND GRAVEL CURB INLET PROTECTION 1.USE BLOCK AND GRAVEL TYPE SEDIMENT BARRIER WHEN CURB INLET IS LOCATED IN GENTLY SLOPING SEGMENT, WHERE WATER CAN POND AND ALLOW SEDIMENT TO SEPARATE FROM RUNOFF. 2.BARRIER SHALL ALLOW FOR OVERFLOW FROM SEVERE STORM EVENT. 3.INSPECT BARRIERS AND REMOVE SEDIMENT AFTER EACH STORM EVENT. SEDIMENT AND GRAVEL MUST BE REMOVED FROM THE TRAVELED WAY IMMEDIATELY. 2x4 WOOD STUD OVERFLOW WATER A A PLAN VIEW NTS SECTION A-A NTS BLOCK AND GRAVEL CURB INLET PROTECTION NTS CATCH BASIN COVER CURB INLET CONCRETE BLOCKS CATCH BASIN COVER CURB INLET CATCH BASIN BACK OF SIDEWALK CURB FACE 3/4" DRAIN GRAVEL (20 mm) WIRE SCREEN OR FILTER FABRIC POND HEIGHT WIRE SCREEN OR FILTER FABRIC 2x4 WOOD STUD (100x50 TIMBER STUD) 3/4" DRAIN GRAVEL (20 mm) NOTES: SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-58 FIGURE D.2.1.5.H CURB AND GUTTER BARRIER PROTECTION RUNOFF RUNOFF SPILLWAY 1.PLACE CURB-TYPE SEDIMENT BARRIERS ON GENTLY SLOPING STREET SEGMENTS, WHERE WATER CAN POND AND ALLOW SEDIMENT TO SEPARATE FROM RUNOFF. 2.SANDBAGS OF EITHER BURLAP OR WOVEN GEOTEXTILE FABRIC ARE FILLED WITH GRAVEL, LAYERED AND PACKED TIGHTLY. 3.LEAVE A ONE-SANDBAG GAP IN THE TOP ROW TO PROVIDE A SPILLWAY FOR OVERFLOW. 4.INSPECT BARRIERS AND REMOVE SEDIMENT AFTER EACH STORM EVENT. SEDIMENT AND GRAVEL MUST BE REMOVED FROM THE TRAVELED WAY IMMEDIATELY. GRAVEL FILLED SANDBAGS STACKED TIGHTLY DRAIN GRATE GUTTER CURB FACE CURB INLET SANDBAGS TO OVERLAP ONTO CURB BACK OF SIDEWALK PLAN VIEW NTS CURB AND GUTTER BARRIER NTS NOTES: D.2.1.9 FLOW CONTROL 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-73 guidance within this manual must be followed if there are any discrepancies between this manual and the LID Technical Guidance Manual for Puget Sound (2012). D.2.1.11 MAINTAIN PROTECTIVE BMPS Protection measures shall be maintained to assure continued performance of their intended function, to prevent adverse impacts to existing flow control BMPs and areas of proposed flow control BMPs, and protect other disturbed areas of the project. Purpose: The purpose of maintaining protective BMPs is to provide continuous erosion and sediment control protection throughout the life of the project, and avoid sedimentation, soil compaction and contamination by other pollutants that would adversely affect infiltration and surface runoff. When to Maintain: Protection measures shall be monitored per Section D.2.4.4 at a minimum, and promptly maintained to fully functioning condition as necessary to assure continued performance of their intended function. Measures to Use: 1. Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. 2. Remove all temporary erosion and sediment control BMPs prior to final construction approval, or within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. 3. Provide protection to all BMPs installed for the permanent control of stormwater from sediment and compaction. All BMPs that are to remain in place following completion of construction shall be examined and placed in full operating conditions. If sediment enters the BMPs during construction, it shall be removed and the BMP shall be returned to the conditions specified in the construction documents or as required for full BMP replacement. 4. Remove or stabilize trapped sediment on site. Permanently stabilize disturbed soil resulting from removal of BMPs or vegetation. D.2.1.12 MANAGE THE PROJECT Coordination and timing of site development activities relative to ESC concerns (Section D.2.4), and timely inspection, maintenance and update of protective measures (Section D.2.3) are necessary to effectively manage the project and assure the success of protective ESC and SWPPS design and implementation. Projects shall assign a qualified CSWPP Supervisor (Section D.2.3.1) to be the primary contact for ESC and SWPPP issues and reporting, coordination with subcontractors and implementation of the CSWPP plan as a whole. Measures to Use: 1. Phase development projects to the maximum degree practicable and take into account seasonal work limits. 2. Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit and King County requirements. 3. Maintaining an updated construction SWPPP – Maintain, update, and implement the SWPPP in accordance with the Construction Stormwater General Permit and King County requirements. 4. Projects that disturb one or more acres must have, site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL) (see Section D.2.3.1). Project sites less than one acre (not part SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-74 of a larger common plan of development or sale) may have a person without CESCL certification conduct inspections. By the initiation of construction, the SWPPP must identify the CESCL or inspector, who shall be present on-site or on-call at all times. The CESCL or inspector (project sites less than one acre) must have the skills to assess the: • Site conditions and construction activities that could impact the quality of stormwater. • Effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. • The CESCL or inspector must examine stormwater visually for the presence of suspended sediment, turbidity, discoloration, and oil sheen. They must evaluate the effectiveness of BMPs and determine if it is necessary to install, maintain, or repair BMPs to improve the quality of stormwater discharges. Based on the results of the inspection, construction site operators must correct the problems identified by: • Reviewing the SWPPP for compliance with all construction SWPPP elements and making appropriate revisions within 7 days of the inspection. • Immediately beginning the process of fully implementing and maintaining appropriate source control and/or treatment BMPs as soon as possible, addressing the problems not later than within 10 days of the inspection. If installation of necessary treatment BMPs is not feasible within 10 days, the construction site operator may request an extension within the initial 10-day response period. • Documenting BMP implementation and maintenance in the site log book (applies only to sites that have coverage under the Construction Stormwater General Permit). • The CESCL or inspector must inspect all areas disturbed by construction activities, all BMPs, and all stormwater discharge points at least once every calendar week and within 24 hours of any discharge from the site. (For purposes of this condition, individual discharge events that last more than one day do not require daily inspections. For example, if a stormwater pond discharges continuously over the course of a week, only one inspection is required that week.) The CESCL or inspector may reduce the inspection frequency for temporary stabilized, inactive sites to once every calendar month D.2.2.1 CONCRETE HANDLING 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-77 D.2.2.1 CONCRETE HANDLING Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete process water, and concrete slurry from entering waters of the state. Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction projects include, but are not limited to, curbs, sidewalks, roads, bridges, foundations, floors, stormwater vaults, retaining walls, driveways and runways. Design and Installation Specifications 1. Assure that washout of concrete trucks, chutes, pumps, and internals is performed at an approved off- site location or in designated concrete washout areas. Do not wash out concrete trucks, chutes, pumps, or internals onto the ground, or into storm drains, open ditches, streets, or streams. Refer to BMP D.2.2.2 (p. D-78) for information on concrete washout areas. 2. 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. 3. Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels into formed areas awaiting future concrete pours only. 4. Do not wash out to formed areas awaiting infiltration BMPs. 5. Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances. 6. Do not allow washdown from areas, such as concrete aggregate driveways, to drain directly to natural or constructed stormwater conveyances. 7. Contain washwater and leftover product in a lined container when no formed areas are available,. Dispose of contained concrete in a manner that does not violate ground water or surface water quality standards. 8. Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. 9. Refer to BMPs D.2.2.7 and D.2.2.8 for pH adjustment requirements. 10. Refer to the Construction Stormwater General Permit for pH monitoring requirements if the project involves one of the following activities: • Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project). • The use of engineered soils amended with (but not limited to) Portland cement-treated base, cement kiln dust or fly ash. • Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. SECTION D.2.2 SWPPS MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-78 D.2.2.2 CONCRETE WASHOUT AREA Purpose Prevent or reduce the discharge of pollutants to stormwater from concrete waste by conducting washout off-site, or performing on-site washout in a designated area to prevent pollutants from entering surface waters or ground water. Conditions of Use Concrete washout area best management practices are implemented on construction projects where: • Concrete is used as a construction material • It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant, etc.). • Concrete trucks, pumpers, or other concrete coated equipment are washed on-site. Note: If less than 10 concrete trucks or pumpers need to be washed out on-site, the washwater may be disposed of in a formed area awaiting concrete or an upland disposal site where it will not contaminate surface or ground water. The upland disposal site shall be at least 50 feet from sensitive areas such as storm drains, open ditches, or water bodies, including wetlands. Design and Installation Specifications Implementation The following steps will help reduce stormwater pollution from concrete wastes: 1. Perform washout of concrete trucks at an approved off-site location or in designated concrete washout areas only. 2. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. 3. Do not allow excess concrete to be dumped on-site, except in designated concrete washout areas. 4. Concrete washout areas may be prefabricated concrete washout containers, or self-installed structures (above-grade or below-grade). 5. 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. 6. 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. 7. Self-installed above-grade structures should only be used if excavation is not practical. Education 1. Discuss the concrete management techniques described in this BMP with the ready-mix concrete supplier before any deliveries are made. 2. Educate employees and subcontractors on the concrete waste management techniques described in this BMP. 3. Arrange for contractor’s superintendent or Certified Erosion and Sediment Control Lead (CESCL) to oversee and enforce concrete waste management procedures. 4. A sign should be installed adjacent to each temporary concrete washout facility to inform concrete equipment operators to utilize the proper facilities. D.2.2.2 CONCRETE WASHOUT AREA 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-79 Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor agreements. Location and Placement 1. Locate washout area at least 50 feet from sensitive areas such as storm drains, open ditches, or water bodies, including wetlands. 2. Allow convenient access for concrete trucks, preferably near the area where the concrete is being poured. 3. If trucks need to leave a paved area to access washout, prevent track-out with a pad of rock or quarry spalls (see BMP D.2.1.4.2 (p. D-44)). These areas should be far enough away from other construction traffic to reduce the likelihood of accidental damage and spills. 4. The number of facilities you install should depend on the expected demand for storage capacity. 5. On large sites with extensive concrete work, washouts should be placed in multiple locations for ease of use by concrete truck drivers. On-site Temporary Concrete Washout Facility, Transit Truck Washout Procedures: 1. Temporary concrete washout facilities shall be located a minimum of 50 ft from sensitive areas including storm drain inlets, open drainage facilities, and watercourses. (See Figures D.2.2.2.A, D.2.2.2.B and D.2.2.2.C). 2. Concrete washout facilities shall be constructed and maintained in sufficient quantity and size to contain all liquid and concrete waste generated by washout operations. 3. Washout of concrete trucks shall be performed in designated areas only. 4. Concrete washout from concrete pumper bins can be washed into concrete pumper trucks and discharged into designated washout area or properly disposed of off-site. 5. Once concrete wastes are washed into the designated area and allowed to harden, the concrete should be broken up, removed, and disposed of per applicable solid waste regulations. Dispose of hardened concrete on a regular basis. 6. Temporary Above-Grade Concrete Washout Facility a. Temporary concrete washout facility (type above grade) should be constructed as shown on the details below, with a recommended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to contain all liquid and concrete waste generated by washout operations. b. 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. 7. Temporary Below-Grade Concrete Washout Facility a. Temporary concrete washout facilities (type below grade) should be constructed as shown on the details below, with a recommended minimum length and minimum width of 10 ft. The quantity and volume should be sufficient to contain all liquid and concrete waste generated by washout operations. b. Lath and flagging should be commercial type. c. Plastic lining material shall be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other defects that compromise the impermeability of the material. d. Liner seams shall be installed in accordance with manufacturers’ recommendations. e. Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the plastic lining material. SECTION D.2.2 SWPPS MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-80 Maintenance Standards Inspection and Maintenance 1. Inspect and verify that concrete washout BMPs are in place prior to the commencement of concrete work. 2. During periods of concrete work, inspect daily to verify continued performance. a. Check overall condition and performance. b. Check remaining capacity (% full). c. If using self-installed washout facilities, verify plastic liners are intact and sidewalls are not damaged. d. If using prefabricated containers, check for leaks. 3. Washout facilities shall be maintained to provide adequate holding capacity with a minimum freeboard of 12 inches. 4. Washout facilities must be cleaned, or new facilities must be constructed and ready for use once the washout is 75% full. 5. If the washout is nearing capacity, vacuum and dispose of the waste material in an approved manner. a. Do not discharge liquid or slurry to waterways, storm drains or directly onto ground. b. Do not use sanitary sewer without local approval. c. Place a secure, non-collapsing, non-water collecting cover over the concrete washout facility prior to predicted wet weather to prevent accumulation and overflow of precipitation. d. Remove and dispose of hardened concrete and return the structure to a functional condition. Concrete may be reused on-site or hauled away for disposal or recycling. 6. When you remove materials from the self-installed concrete washout, build a new structure; or, if the previous structure is still intact, inspect for signs of weakening or damage, and make any necessary repairs. Re-line the structure with new plastic after each cleaning. Removal of Temporary Concrete Washout Facilities 1. When temporary concrete washout facilities are no longer required for the work, the hardened concrete, slurries and liquids shall be removed and properly disposed of. 2. Materials used to construct temporary concrete washout facilities shall be removed from the site of the work and disposed of or recycled. 3. Holes, depressions or other ground disturbance caused by the removal of the temporary concrete washout facilities shall be backfilled, repaired, and stabilized to prevent erosion. D.2.2.2 CONCRETE WASHOUT AREA 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-81 FIGURE D.2.2.2.A CONCRETE WASHOUT AREA (ABOVE GRADE) SECTION B-B NTS SECTION A-A NTS STAPLE DETAIL NTS PLAN NTS ABOVE GRADE TEMPORARY CONCRETE WASHOUT FACILITY NTS CONCRETE WASHOUT SIGN DETAIL NTS 10 mil PLASTIC LINING PLAN NTS TYPE "ABOVE GRADE" WITH WOOD PLANKS TYPE "ABOVE GRADE" WITH STRAW BALES 10 mil PLASTIC LINING 16 GAUGE STEEL WIRE 2" 8" LAG SCREWS ( 12" ) BLACK LETTERS 6" HEIGHT PLYWOOD 4' X 2' PAINTED WHITE WOOD POST 312" x 312" x 8'3' 3' STRAW BALES (TYP.) STAKE (TYP.) WEDGE LOOSE STRAW BETWEEN BALES SAND OR GRAVEL-FILLED BAGS IN CORNERS 10' MIN. RECOMMENDED VARIES WOOD OR METAL STAKES (2 PER BALE) STRAW BALES (2 BALES HIGH, MAX.) ORIGINAL GROUND 10 mil PLASTIC LINING STAPLES (2 PER BALE) SAND OR GRAVEL-FILLED BAGS IN CORNERS NATIVE MATERIAL (OPTIONAL) 10 mil PLASTIC LINING WOOD FRAME SECURELY FASTENED AROUND ENTIRE PERIMETER WITH TWO STAKES TWO-STACKED 2x12 ROUGH WOOD FRAME STAKE (TYP.) 10' MIN. RECOMMENDED VARIES NOTES: 1.ACTUAL LAYOUT DETERMINED IN THE FIELD 2.THE CONCRETE WASHOUT SIGN SHALL BE INSTALLED WITHIN 30' OF THE FACILITY 1' MIN. Adapted from CalTrans Fig4-14 SAC 8-14-02 SECTION D.2.2 SWPPS MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-82 FIGURE D.2.2.2.B CONCRETE WASHOUT AREA (BELOW GRADE) EARTHEN BERM TYPICAL SECTION NTS BELOW GRADE TEMPORARY CONCRETE WASHOUT FACILITY NTS CONCRETE WASHOUT SIGN DETAIL NTS SANDBAG PLAN NTS Adapted from CalTrans Fig4-14 SAC 8-14-02 10 mil PLASTIC LINING LAG SCREWS ( 12" ) BLACK LETTERS 6" HEIGHT PLYWOOD 4' X 2' PAINTED WHITE WOOD POST 312" x 312" x 8'3' 3' EARTHEN BERM 10 mil PLASTIC LINING SANDBAG 10' MIN. RECOMMENDED VARIES BERM 3' LATH AND FLAGGING ON 3 SIDES NOTES: 1.ACTUAL LAYOUT DETERMINED IN THE FIELD 2.THE CONCRETE WASHOUT SIGN SHALL BE INSTALLED WITHIN 30' OF THE FACILITY FIGURE D.2.2.2.C PREFABRICATED CONCRETE WASHOUT CONTAINER W/RAMP D.2.2.3 SAWCUTTING AND SURFACING POLLUTION PREVENTION 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-83 D.2.2.3 SAWCUTTING AND SURFACING POLLUTION PREVENTION Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Sawcutting and surfacing operations include, but are not limited to, sawing, coring, grinding, roughening, hydro- demolition, bridge and road surfacing Design and Installation Specifications 1. Vacuum slurry and cuttings during cutting and surfacing operations. 2. Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight. 3. Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including stormwater systems. This may require temporarily blocking catch basins. 4. Dispose of collected slurry and cuttings in a manner that does not violate ground water or surface water quality standards. 5. Do not allow process water generated during hydro-demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose process water in a manner that does not violate ground water or surface water quality standards. 6. Handle and dispose cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and vacuum trucks. SECTION D.2.2 SWPPS MEASURES 7/23/2021 2021 Surface Water Design Manual – Appendix D D-84 D.2.2.4 MATERIAL DELIVERY, STORAGE AND CONTAINMENT Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a designated area, and install secondary containment. Conditions of Use These procedures are suitable for use at all construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g. Polyacrylamide) • Fertilizers, pesticides and herbicides • Detergents • Asphalt and concrete compounds • Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds • Any other material that may be detrimental if released to the environment Design and Installation Specifications The following steps should be taken to minimize risk: 1. Temporary storage area should be located away from vehicular traffic, near the construction entrance(s), and away from waterways or storm drains. 2. Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. 3. Hazardous material storage on-site should be minimized. 4. Hazardous materials should be handled as infrequently as possible. 5. During the wet weather season (Oct 1 – April 30), consider storing materials in a covered area. 6. Materials should be stored in secondary containments, such as earthen dike, horse trough, or even a children’s wading pool for non-reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in “bus boy” trays or concrete mixing trays. 7. Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, and within secondary containment. 8. 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. Material Storage Areas and Secondary Containment Practices: 1. 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. 2. Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater. D.2.2.4 MATERIAL DELIVERY, STORAGE AND CONTAINMENT 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-85 3. Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. 4. 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. 5. Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. 6. 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. 7. Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material (spill kit). 8. The spill kit should include, at a minimum: • 1-Water Resistant Nylon Bag • 3-Oil Absorbent Socks 3”x 4’ • 2-Oil Absorbent Socks 3”x 10’ • 12-Oil Absorbent Pads 17”x19” • 1-Pair Splash Resistant Goggles • 3-Pair Nitrile Gloves • 10-Disposable Bags with Ties • Instructions Appendix C Geotechnical Engineering Study April 19, 2022 JN 22150 GEOTECH CONSULTANTS, INC. ARB c/o Broderick Architects 55 South Atlantic Street, Suite, 301 Seattle, Washington 98134 Attention: Kevin Broderick via email: kevin@broderickarchitects.com Subject: Geotechnical Engineering Study Proposed Additions to Existing Building 720 Rainier Avenue South Renton, Washington Dear Mr. Broderick: We are pleased to present this geotechnical engineering report for the planned addition to the existing building in Renton. The scope of our services consisted of assessing the current site conditions and reviewing available geologic information for the site vicinity, and then developing this report to provide recommendations for general earthwork and design criteria for foundations. This work was authorized by your acceptance of our Contract for Professional Services. As a part of an interior remodel of the existing building, a small covered entry will be created at the southwest corner of the current structure. An employee break room is to be added to the south side of the eastern half of the existing building. We expect that this addition will be one-story in height. A more substantial addition for vehicle repair/service will be constructed between the east side of the current building and the eastern property line. We expect that the additions will have slab-on-grade floors near the existing site grades. The southern portion of the property will remain paved for parking and drive lanes. If the scope of the project changes from what we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE CONDITIONS SURFACE The subject property is located on the east side of Rainier Avenue South, three properties north of its intersection with South Grady Way. A building used as an automobile dealership occupies the northwestern portion of the property. The remainder of the irregularly-shaped lot is covered by pavement. The surrounding lots are, or have been, developed with commercial buildings used for automobile dealerships or automotive repair. There are no steep slopes on, or anywhere close to, the site. Consistent with the entire downtown Renton area, the subject property is essentially flat. ARB c/o Broderick Architects JN 22150 April 19, 2022 Page 2 GEOTECH CONSULTANTS, INC. The soils that underlie the site and the surrounding area have been deposited by various rivers that flowed through the deep valleys that remained after the last glaciers receded from the Puget Sound. These soils are known as alluvial deposits (alluvium). Published geologic maps confirm that the site vicinity is underlain by alluvium. Our firm has conducted borings for projects within one to two blocks of the subject site. These borings, which have extended to depths of at least 60 feet, found alluvial soils that typically consisted of finer-grained sediments (silt and silty, fine-grained sands) extending to depths of 20 to 25 feet. Below this depth, the alluvium becomes more coarse-grained, consisting of gravel and gravelly sand, having been deposited by faster flowing water. The groundwater table that underlies the entire area fluctuates seasonally, but often lies within 8 to 10 feet of the ground surface. CONCLUSIONS AND RECOMMENDATIONS GENERAL THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. Based on existing subsurface information, the site is underlain by alluvial soils and a relatively shallow groundwater table. Older structures supported on lightly-reinforced conventional shallow foundations on top of these soils typically have varying, sometimes noticeable, amounts of settlement due to consolidation over time. The loose sandy soils beneath the level of the groundwater table are susceptible to liquefaction during the design seismic event. Heavily-reinforced shallow foundation systems are being used on newer construction in the surrounding area, in order to limit excessive post-construction settlement, but also to protect against foundation collapse in the event of soil strength loss (seismic liquefaction) that could occur during a large earthquake. The smaller entry and break room additions should be constructed using reinforced mat foundations. A mat foundation is essentially a heavily-reinforced, slab-on-grade foundation that is intended to distribute the building loads, reduce the necessary bearing capacity, bridge over any excessively soft areas of soil or localized soil liquefaction (sand boils), and reduce the amount of differential settlement across the new construction. For the eastern addition, where there will not be any interior supports, the perimeter walls can be supported on heavily-reinforced continuous footings that are designed similar to grade beams. If the floor slab of the addition is to support heavy loads, such as from vehicle lifts, the slab should be reinforced. Any loose or soft soils encountered in the foundation or slab excavations should be removed and be replaced with imported granular soils. We recommend that the project geotechnical engineer assess the exposed footing and slab subgrades prior to placement of forms and/or rebar. The project budget should account for the potential that removal and replacement of unsuitable shallow soils, such as old fill and/or topsoil, could be necessary. The use of mat foundations and heavily-reinforced continuous footings will result in more uniform settlement of the new construction as the underlying soils continue to undergo long-term secondary compression. However, movement between the new and existing construction may be evident over time. This may cause some cosmetic issues, but should not be of structural concern. Settlement-tolerant construction such as wood and metal framing and siding should still be used for the new construction. Masonry, stucco, tile and other settlement- ARB c/o Broderick Architects JN 22150 April 19, 2022 Page 3 GEOTECH CONSULTANTS, INC. sensitive materials should be avoided, as they will more readily show the cosmetic effects of foundation settlement. Footing drains will not be needed for the new additions if their floors are at, or above, the surrounding grade. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. The site is generally flat, so the overall erosion potential should be low. The existing pavement areas should be maintained for truck loading and staging. Any soil spilled onto the pavements should be immediately cleaned up. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Following clearing or rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. On most construction projects, it is necessary to periodically maintain or modify temporary erosion control measures to address specific site and weather conditions. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. SEISMIC CONSIDERATIONS In accordance with the International Building Code (IBC) and ASCE 7-16, the site class within 100 feet of the ground surface is best represented by Site Class Type E (Soft Soil). As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (Ss) and 1.0 second period (S1) equals 1.44g and 0.49g, respectively, for ASCE 7-16. The IBC and ASCE 7 require that the potential for liquefaction (soil strength loss) be evaluated for the peak ground acceleration of the Maximum Considered Earthquake (MCE), which has a probability of occurring once in 2,475 years (2 percent probability of occurring in a 50-year period). The site is underlain by loose, saturated, alluvial sand soils. These soils have been demonstrated to have a moderate to high potential for liquefaction during a large earthquake. Using procedures developed by Seed, Idriss, et al. we have calculated the approximate total ground settlement that could result if liquefaction were to occur in the saturated, loose to medium-dense soils as the result of the design earthquake. Based on this analysis, it is probable that soil liquefaction could extend down to a depth of 25 to 30 feet following an earthquake as strong as the MCE. Our calculations for sites with similar subsurface conditions have indicated that total ground settlement of at least 4 to 6 inches could theoretically result during the MCE. Differential settlements across the structures would be mitigated by the heavily-reinforced foundations such that we would predict differential dynamic settlements of 2 to 3 inches across the structures. ARB c/o Broderick Architects JN 22150 April 19, 2022 Page 4 GEOTECH CONSULTANTS, INC. The foundation recommendations presented in this report are intended to prevent catastrophic foundation collapse of the new construction during the MCE. By preventing catastrophic settlement of the foundations, the safety of the occupants should be protected. The intent is not to prevent damage or ensure continued function of the structure after the design seismic event. REINFORCED FOUNDATIONS An allowable bearing pressure of 1,500 pounds per square foot (psf) should be used for the foundation design. A one-third increase in this design bearing pressure may be used when considering short-term wind or seismic loads. Heavily-reinforced continuous footings should be designed similar to grade beams, and should be sufficiently reinforced to be able to span a distance of at least 10 feet without soil support. This creates a rigid footing. The perimeter footings should extend to at least 18 inches below the surrounding grade. Mat foundations are typically designed using the approximate flexible method. Foundations designed using this method are also known as Winkler Foundations. For this analysis, we recommend using a coefficient of subgrade reaction of 90 pounds per cubic inch (lb/in3). Mat slabs should be thickened a minimum depth of 18 inches below the adjacent finish grade around the perimeter of the mat, and this thickened edge of the structural slabs should have a minimum width of 16 inches. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the subgrade soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, well-compacted fill. We recommend using the following ultimate values for the foundation's resistance to lateral loading: PARAMETER ULTIMATE VALUE Coefficient of Friction 0.45 Passive Earth Pressure 250 pcf Where: pcf is Pounds per Cubic Foot, and Passive Earth Pressure is computed using the Equivalent Fluid Density. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend maintaining a safety factor for the foundation's resistance to lateral loading, when using the above ultimate values. SLABS-ON-GRADE The mat foundations will serve as the either the floor slab, or the support for a topping slab for the lowest level of the buildings. Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil and concrete to the new constructed space above it. This can affect moisture- ARB c/o Broderick Architects JN 22150 April 19, 2022 Page 5 GEOTECH CONSULTANTS, INC. sensitive flooring, cause imperfections or damage to the slab, or simply allow excessive water vapor into the space above the slab. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on-grade slab that will be covered by tile, wood, carpet, impermeable floor coverings, or any moisture-sensitive equipment or products. ACI also notes that vapor retarders such as 6-mil plastic sheeting have been used in the past, but are now recommending a minimum 10-mil thickness for better durability and long term performance. A vapor retarder is defined as a material with a permeance of less than 0.3 perms, as determined by ASTM E 96. It is possible that concrete admixtures or topical applications to the surface of the slab may meet this specification, although the manufacturers of these products should be consulted. Where vapor retarders are used under slabs, their edges should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor barrier, as defined by ACI, is a product with a water transmission rate of 0.01 perms when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. We recommend that the contractor, the project materials engineer, and the owner discuss these issues and review recent ACI literature and ASTM E-1643 for installation guidelines and guidance on the use of the protection/blotter material. LIMITATIONS If the subsurface conditions encountered during construction are significantly different from those anticipated, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects This report has been prepared for the exclusive use of ARB, and their representatives for specific application to this project and site. Our conclusions and recommendations are professional opinions derived in accordance with our understanding of current local standards of practice, and within the scope of our services. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Our services also do not include assessing or minimizing the potential for biological hazards, such as mold, bacteria, mildew and fungi in either the existing or proposed site development. ADDITIONAL SERVICES Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confirm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the ARB c/o Broderick Architects JN 22150 April 19, 2022 Page 6 GEOTECH CONSULTANTS, INC. supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. During the construction phase, we will provide geotechnical observation and testing services when requested by you or your representatives. Please be aware that we can only document site work we actually observe. It is still the responsibility of your contractor or on-site construction team to verify that our recommendations are being followed, whether we are present at the site or not. Please contact us if you have any questions regarding this report, or if we can be of further assistance. Respectfully submitted, GEOTECH CONSULTANTS, INC. 4/19/2022 Marc R. McGinnis, P.E. Principal MRM:kg Appendix D Operation and Maintenance Manual APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-10 NO. 5 – CATCH BASINS AND MANHOLES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Structure Sediment accumulation Sediment exceeds 60% of the depth from the bottom of the catch basin to the invert of the lowest pipe into or out of the catch basin or is within 6 inches of the invert of the lowest pipe into or out of the catch basin. Sump of catch basin contains no sediment. Trash and debris Trash or debris of more than ½ cubic foot which is located immediately in front of the catch basin opening or is blocking capacity of the catch basin by more than 10%. No Trash or debris blocking or potentially blocking entrance to catch basin. Trash or debris in the catch basin that exceeds 1/3 the depth from the bottom of basin to invert the lowest pipe into or out of the basin. No trash or debris in the catch basin. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within catch basin. Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Damage to frame and/or top slab Corner of frame extends more than ¾ inch past curb face into the street (If applicable). Frame is even with curb. Top slab has holes larger than 2 square inches or cracks wider than ¼ inch. Top slab is free of holes and cracks. Frame not sitting flush on top slab, i.e., separation of more than ¾ inch of the frame from the top slab. Frame is sitting flush on top slab. Cracks in walls or bottom Cracks wider than ½ inch and longer than 3 feet, any evidence of soil particles entering catch basin through cracks, or maintenance person judges that catch basin is unsound. Catch basin is sealed and is structurally sound. Cracks wider than ½ inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Catch basin has settled more than 1 inch or has rotated more than 2 inches out of alignment. Basin replaced or repaired to design standards. Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the catch basin at the joint of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of inlet/outlet pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Inlet/Outlet Pipe Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-11 NO. 5 – CATCH BASINS AND MANHOLES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Inlet/Outlet Pipe (cont.) Damaged inlet/outlet pipe Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Metal Grates (Catch Basins) Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and debris Trash and debris that is blocking more than 20% of grate surface. Grate free of trash and debris. Damaged or missing grate Grate missing or broken member(s) of the grate. Any open structure requires urgent maintenance. Grate is in place and meets design standards. Manhole Cover/Lid Cover/lid not in place Cover/lid is missing or only partially in place. Any open structure requires urgent maintenance. Cover/lid protects opening to structure. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs. of lift. Cover/lid can be removed and reinstalled by one maintenance person. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-12 NO. 6 – CONVEYANCE PIPES AND DITCHES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Pipes Sediment & debris accumulation Accumulated sediment or debris that exceeds 20% of the diameter of the pipe. Water flows freely through pipes. Vegetation/root growth in pipe Vegetation/roots that reduce free movement of water through pipes. Water flows freely through pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to protective coating or corrosion Protective coating is damaged; rust or corrosion is weakening the structural integrity of any part of pipe. Pipe repaired or replaced. Damaged pipes Any dent that decreases the cross section area of pipe by more than 20% or is determined to have weakened structural integrity of the pipe. Pipe repaired or replaced. Ditches Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 square feet of ditch and slopes. Trash and debris cleared from ditches. Sediment accumulation Accumulated sediment that exceeds 20% of the design depth. Ditch cleaned/flushed of all sediment and debris so that it matches design. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to City personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where City personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Excessive vegetation growth Vegetation that reduces free movement of water through ditches. Water flows freely through ditches. Erosion damage to slopes Any erosion observed on a ditch slope. Slopes are not eroding. Rock lining out of place or missing (If applicable) One layer or less of rock exists above native soil area 5 square feet or more, any exposed native soil. Replace rocks to design standards. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-39 NO. 27 – GRAVEL FILLED DISPERSION TRENCH BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Preventive Blocking, obstructions Debris or trash limiting flow to dispersion trench or preventing spreader function. Dispersion trench able to receive full flow prior to and during wet season. Site Trash and debris Trash or debris that could end up in the dispersion trench is evident. No trash or debris that could get into the dispersion trench can be found. Pipes Plugged inlet The entrance to the pipe is restricted due to sediment, trash, or debris. The entrance to the pipe is not restricted. Vegetation/root growth in pipes Vegetation/roots that reduce free movement of water through pipes. Water flows freely through pipes. Plugged pipe Sediment or other material prevents free flow of water through the pipe. Water flows freely through pipes. Broken pipe or joint leaks. Damage to the pipe or pipe joints allowing water to seep out. Pipe does not allow water to exit other than at the outlet to the trench. Broken or missing cleanout caps Cleanout caps are broken, missing, or buried. Cleanout caps are accessible and intact. Structure Flow not reaching trench Flows are not getting into the trench as designed. Water enters and exits trench as designed. Perforated pipe plugged Flow not able to enter or properly exit from perforated pipe. Water freely enters and exits perforated pipe. Flow not spreading evenly at outlet of trench Outlet flows channelizing or not spreading evenly from trench. Sheet flow occurs at the outlet of the trench. Cleanout/inspection access does not allow cleaning or inspection of perforated pipe The cleanout/inspection access is not available. Cleanout/inspection access is available. Filter Media Plugged filter media Filter media plugged. Flow through filter media is normal. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-43 NO. 32 – RAINWATER HARVESTING BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Preventive Insufficient storage volume No rain water in storage unit at the beginning of the rain season. Maximum storage available at the beginning of the rain season (Oct. 1). Collection Area Trash and debris Trash of debris on collection area may plug filter system Collection area clear of trash and debris. Filter Restricted or plugged filter Filter is partially or fully plugged preventing water from getting in to the storage unit. Filter is allowing collection water into storage unit. NO. 33 – ROCK PAD BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Trash and debris accumulated on rock pad site. Rock pad site free of any trash or debris. Rock Pad Area Insufficient rock pad size Rock pad is not 2 feet by 3 feet by 6 inches thick or as designed. Rock pad is 2 feet by 3 feet by 6 inches thick or as designed. Vegetation growth Vegetation is seen growing in or through rock pad. No vegetation within rock pad area. Rock Exposed soil Soil can be seen through the rock pad. Full thickness of the rock pad is in place, no soil visible through rock pad. NO. 34 – SHEET FLOW BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Trash and debris accumulated on the sheet flow site. Sheet flow site free of any trash or debris. Sheet flow area Erosion Soil erosion occurring in sheet flow zone. Soil erosion is not occurring and rills and channels have been repaired. Concentrated flow Sheet flow is not occurring in the sheet flow zone. Sheet flow area is regraded to provide sheet flow. NO. 35 – SPLASH BLOCK BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Trash and debris accumulated on the splash block. Splash block site free of any trash or debris. Splash Block Dislodged splash block Splash block moved from outlet of downspout. Splash block correctly positioned to catch discharge from downspout. Channeling Water coming off the splash block causing erosion. No erosion occurs from the splash block. Downspout water misdirected Water coming from the downspout is not discharging to the dispersal area. Water is discharging normally to the dispersal area.