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HomeMy WebLinkAboutRS_Drainage_report_AHBL_241018_v1 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM TECHNICAL INFORMATION REPORT RSD Transportation Center Expansion 410 Park Ave N Renton, WA 98057 October 18, 2024 PREPARED FOR: Renton School District 7812 South 124th Street Seattle, WA 98178 PREPARED BY: Jacobson Consulting Engineers Sascha Eastman 206.426.2600 sascha@jacobsonengineers.com i Technical Information Report for Renton School District Transportation Expansion JCE Project No. C220041-0132 October 18, 2024 TABLE OF CONTENTS 1. PROJECT OVERVIEW ........................................................................................................................... 3 GENERAL DESCRIPTION .............................................................................................................................. 3 EXISTING CONDITIONS ................................................................................................................................. 3 PROPOSED DRAINAGE SYSTEM ................................................................................................................. 3 2. CONDITIONS AND REQUIREMENTS SUMMARY ..................................................................................... 5 CORE REQUIREMENT #1: DISCHARGE AT THE NATURAL LOCATION .................................................. 5 CORE REQUIREMENT #2: OFFSITE ANALYSIS ......................................................................................... 5 CORE REQUIREMENT #3: FLOW CONTROL FACILITIES.......................................................................... 5 CORE REQUIREMENT #4: CONVEYANCE SYSTEM .................................................................................. 6 CORE REQUIREMENT #5: CONSTRUCTION STORMWATER POLLUTION PREVENTION ................... 6 CORE REQUIREMENT #6: MAINTENANCE AND OPERATIONS ............................................................... 6 CORE REQUIREMENT #7: FINANCIAL GUARANTEES AND LIABILITY.................................................... 6 CORE REQUIREMENT #8: WATER QUALITY FACILITIES ......................................................................... 7 CORE REQUIREMENT #9: ON-SITE BMPS .................................................................................................. 7 SPECIAL REQUIREMENT #1: OTHER ADOPTED AREA-SPECIFIC REQUIREMENTS ........................... 8 SPECIAL REQUIREMENT #2: FLOOD HAZARD AREA DELINEATION ..................................................... 8 SPECIAL REQUIREMENT #3: FLOOD PROTECTION FACILITIES ............................................................ 8 SPECIAL REQUIREMENT #4: SOURCE CONTROLS .................................................................................. 8 SPECIAL REQUIREMENT #5: OIL CONTROL .............................................................................................. 8 SPECIAL REQUIREMENT #6: AQUIFER PROTECTION AREA .................................................................. 9 3. OFFSITE ANALYSIS .......................................................................................................................... 10 FIELD INSPECTION ......................................................................................................................................10 DRAINAGE SYSTEM PROBLEM DESCRIPTIONS .....................................................................................10 UPSTREAM ANALYSIS .................................................................................................................................10 DOWNSTREAM ANALYSIS ..........................................................................................................................10 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS .........................................................................10 4. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID), AND WATER QUALITY FACILITY ANALYSIS AND DESIGN .................................................................................................................................................. 11 FLOW CONTROL SYSTEM (PART D) .........................................................................................................11 WATER QUALITY SYSTEM (PART E) .........................................................................................................11 5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN .................................................................................. 12 6. SPECIAL REPORTS AND SUMMARY ................................................................................................... 14 7. CSWPP ANALYSIS AND DESIGN ......................................................................................................... 15 STANDARD REQUIREMENTS .....................................................................................................................15 8. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ..................................... 16 RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION ii BOND QUANTITIES WORKSHEET..............................................................................................................16 FLOW CONTROL AND WATER QUALITY FACILITY SUMMARY SHEET AND SKETCH .......................16 DECLARATION OF COVENANT FOR PRIVEATELY MAINTAINED FLOW CONTROL AND WATER QUALITY FACILITIES ....................................................................................................................................16 9. OPERATIONS AND MAINTENANCE MANUAL ....................................................................................... 17 10. FIGURES ......................................................................................................................................... 18 11. APPENDICES ................................................................................................................................... 19 RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 3 1. PROJECT OVERVIEW GENERAL DESCRIPTION The following Drainage Report provides the design narrative and discussion for the Renton School District Transportation Expansion project. The stormwater design for the project was based on the requirements outlined in the 2022 City of Renton Water Design Manual (RSWDM). The Renton School District Transportation facility is within the City of Renton jurisdictional limits at 410 Park Ave N, Renton, WA 98057 (parcel numbers 7224000676, 7224000675, 7564600105). The site is bounded by N 5th St to the north, Garden Ave N to the east, N 4th St to the south, and Park Ave N to the west. See Figure 2 – Vicinity Map. The proposed improvements are primarily located on parcels 7224000676 and 7224000675, and consist of a new paved parking lot with sidewalks, landscaping, and public amenity space at the northwest corner of the site. Additionally, some right-of-way improvements are proposed to remove existing driveways to the parcels and replace them with new sidewalk. EXISTING CONDITIONS The Renton School District Transportation facility is a fully developed site that contains an existing administration building, vehicle maintenance facility, and multiple parking lots for buses, fleet vehicles, staff, and visitors. The existing administration building and vehicle maintenance facility are located in the southwest portion of the site, while the rest of the site is primarily paved parking lots, drive aisles, and pockets of landscaping. The portion of the site to be redeveloped with this project consists of two asphalt parking lots and landscaping. The topography of the existing site is generally flat, sloping gently from south to north at approximately 1 – 2% slope. Stormwater in the existing conditions is collected in a series of catch basins and routed north to the storm system in N 5th Street, following the topography of the site. Geotechnical investigation on site has found site soils to consist of a surface layer of topsoil underlain by existing fill soils, and Holocene Alluvium deposits from the Cedar River. No groundwater was encountered in the most recent geotechnical testing, but was encountered approximately 10 feet below the surface in explorations for the construction of the transportation center in 2007. The project geotechnical engineer anticipates that perched groundwater may be encountered, but proposed improvements and utilities are not deep enough to be impacted by regional groundwater. See project geotechnical report and Figure 9 – Soils Map. Table 1 below summarizes the land cover characteristics of the existing current Disturbed Site Area, see Figure 3 – Existing Conditions TABLE 1 – PROJECT DISTURBED AREA EXISTING SITE CONDITIONS Land Cover Area (AC) Impervious Area 0.297 Landscape Area 0.211 Total Project Area 0.508 % Impervious of Project Area 58.5% PROPOSED DRAINAGE SYSTEM The proposed improvements consist of a new paved parking lot with sidewalks, landscaping, and public amenity space at the northwest corner of the site. New catch basins will be installed to collect surface runoff and route through water quality treatment prior to discharging to the existing storm main in N 5th Street. This project is required to comply with the Peak Rate Flow Control standard, however this project does not increase flows by more RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 4 than 0.15 CFS using a 15-minute timestep therefore flow control is not required for this project. Table 2 below summarizes the land cover characteristics of the proposed project disturbed areas. See Figure 4 – Proposed Conditions and Figure 5 - New + Replaced Impervious Areas. TABLE 2 – DEVELOPED PROJECT SITE CONDITIONS AREA BREAKDOWN Land Cover Area (AC) Impervious Area 0.378 Landscape Area 0.130 Total Project (Disturbed) Area 0.508 % Impervious of Project Area 74.4% RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 5 2. CONDITIONS AND REQUIREMENTS SUMMARY The proposed Renton School District Transportation facility project will result in more than 7,000 square feet of land disturbing activity with the various pavement improvements and will require Full Drainage Review by the City of Renton as directed in Section 1.1.1 of the 2022 Renton Surface Water Design Manual (RSWDM). See Figure 6 – Project Minimum Requirements Flow Chart for how the level of drainage review was determined for this project. This section of the report will address the (9) nine required minimum requirements and (6) six special requirements for Full Drainage Review as set forth by Section 1.1.2.4 of the 2022 RSWDM. CORE REQUIREMENT #1: DISCHARGE AT THE NATURAL LOCATION All storm water runoff and surface water from a project must be discharged at the natural location so as not to be diverted onto or away from downstream properties. The manner in which stormwater runoff and surface water are discharged from the project site must not create a significant adverse impact to downhill properties or drainage facilities (see "Discharge Requirements" below). Drainage facilities as described above means a constructed or engineered feature that collects, conveys, stores, treats, or otherwise manages surface water or stormwater runoff. “Drainage facility” includes, but is not limited to, a constructed or engineered stream, lake, wetland, or closed depression, or a pipe, channel, ditch, gutter, flow control facility, flow control BMP, water quality facility, erosion and sediment control facility, and any other structure and appurtenance that provides for drainage. Note: Projects that do not discharge all project site runoff at the natural location will require an approved adjustment of this requirement (see Section 1.4). CED may waive this adjustment, however, for projects in which only a small portion of the project site does not discharge runoff at the natural location and the runoff from that portion is unconcentrated and poses no significant adverse impact to downstream properties. Runoff from the site currently sheet flows and is collected in catch basins according to the survey and record drawings for the site. The proposed development will not alter existing drainage patterns, and runoff from the site will continue to drain to the existing 24” storm main in N 5th Street as it currently does today. CORE REQUIREMENT #2: OFFSITE ANALYSIS All proposed projects must submit an offsite analysis report that assesses potential offsite drainage and water quality impacts associated with development of the project site, and that proposes appropriate mitigation of those impacts. The initial permit submittal shall include, at minimum, a Level 1 downstream analysis as described in Section 1.2.2.1 of the RSWDM. If impacts are identified, the proposed projects shall meet any applicable problem-specific requirements specified in Section 1.2.2.2 for mitigation of impacts to drainage problems and Section 1.2.2.3 for mitigation of impacts to water quality problems. The project is NOT exempt from performing an Offsite Level 1 Downstream Analysis as the project adds more than 2,000 square feet of new impervious surface, even though the project will create less than 3/4 acres of new pervious surface, AND does not construct or modify a drainage pipe/ditch that is 12 inches or more in size/depth or that receives runoff from a drainage pipe/ditch that is 12 inches or more in size/depth, AND does not contain or lie adjacent to a landslide, steep slope, or erosion hazard area as defined in RMC 4-3-050. Additionally, there are no known Drainage Complaints downstream or adjacent to project property that are related to the Renton School District Transportation facility according to the City of Renton GIS and King County iMap. A Level 1 Downstream Analysis has been performed for this project. See Downstream Analysis in Section 3 Off-Site Analysis of this report and Figure 7 – Offsite Analysis. CORE REQUIREMENT #3: FLOW CONTROL FACILITIES All proposed projects, including redevelopment projects, must provide onsite flow control facilities to mitigate the impacts of storm and surface water runoff generated by new impervious surface, new pervious surface, and replaced impervious surface targeted for flow mitigation as specified in the following sections. Flow control facilities must be provided and designed to perform as specified by the RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 6 area-specific flow control facility requirement in Section 1.2.3.1 of the RSWDM and in accordance with the applicable flow control facility implementation requirements in Section 1.2.3.2. This project is required to comply with the Peak Rate Flow Control standard, however this project does not increase flows by more than 0.15 CFS using a 15-minute timestep therefore flow control is not required for this project. See Appendix B for MGS Flood calculations. CORE REQUIREMENT #4: CONVEYANCE SYSTEM All engineered conveyance system elements for proposed projects must be analyzed, designed, and constructed to provide a minimum level of protection against overtopping, flooding, erosion, and structural failure as specified in the following groups of requirements: • "Conveyance Requirements for New Systems," Section 1.2.4.1 • "Conveyance Requirements for Existing Systems," Section 1.2.4.2 • "Conveyance System Implementation Requirements," Section 1.2.4.3 This project is NOT exempt from considering Conveyance Requirements for New Systems as there are new pipe system additions from the proposed improvements. All new conveyance systems will be designed to meet requirements. CORE REQUIREMENT #5: CONSTRUCTION STORMWATER POLLUTION PREVENTION All proposed projects that will clear, grade, or otherwise disturb the site must provide erosion and sediment controls to prevent, to the maximum extent practicable, the transport of sediment from the project site to downstream drainage facilities, water resources, and adjacent properties. All proposed projects that will conduct construction activities onsite or offsite must provide stormwater pollution prevention and spill controls to prevent, reduce, or eliminate the discharge of pollutants to onsite or adjacent stormwater systems or watercourses. To prevent sediment transport and pollutant discharges as well as other impacts related to land-disturbing and construction activities, Erosion and Sediment Control (ESC) measures and Stormwater Pollution Prevention and Spill Control (SWPPS) measures that are appropriate to the project site must be applied through a comprehensive Construction Stormwater Pollution Prevention (CSWPP) plan as described in Sections 1.2.5.1 and 1.2.5.3 and shall perform as described in Section 1.2.5.2. In addition, these measures, both temporary and permanent, shall be implemented consistent with the requirements in Section 1.2.5.3 that apply to the proposed project. A SWPPP has been prepared for this project and is included in Appendix C of this report. A concept ESC plan with requirements for the Contractor to provide and implement a design for a system to treat construction runoff to no more than 25 NTU’s over baseline is included with the submittal. A baseline will be established at the start of construction and the contractor will be required to maintain levels no greater than 25 NTU’s above this level. See Appendix C for the project SWPPP. CORE REQUIREMENT #6: MAINTENANCE AND OPERATIONS Maintenance and operation of all drainage facilities is the responsibility of the applicant or property owner, except those facilities for which the City assumes maintenance and operation as described below and in RMC 4-6-030.M. Drainage facilities must be maintained and operated in accordance with the maintenance standards in Appendix A of this manual, or other maintenance standards as approved by the City. An operation and maintenance manual is included in Section 10 of this drainage report and will be provided to the School District for all stormwater BMPs proposed for this project that are maintained by the School District. CORE REQUIREMENT #7: FINANCIAL GUARANTEES AND LIABILITY In accordance with RMC 4-6-030, CED shall require all persons constructing any surface water facilities (including flow control/water quality facilities, conveyance systems, erosion control, and road drainage), to post with the City of Renton a bond, assignment of funds or certified check. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 7 The applicant must also maintain liability insurance as described in this Core Requirement #7. The owner of the proposed project, Renton School District (RSD), is a public agency and is not subject to bonding requirements. CORE REQUIREMENT #8: WATER QUALITY FACILITIES All proposed projects, including redevelopment projects, must provide water quality (WQ) facilities to treat the runoff from those new and replaced pollution-generating impervious surfaces and new pollution-generating pervious surfaces targeted for treatment as specified in the following sections. These facilities shall be selected from a menu of water quality facility options specified by the area-specific facility requirements in Section 1.2.8.1 and implemented according to the applicable WQ implementation requirements in Section 1.2.8.2. This project proposes more than 5,000 SF of pollution generating surfaces, therefore enhanced basic water quality treatment is required for this project. Water quality treatment will be provided by a Modular Wetland water quality treatment facility. CORE REQUIREMENT #9: ON-SITE BMPS All proposed projects, including redevelopment projects, must provide on-site flow control BMPs to mitigate the impacts of storm and surface water runoff generated by new impervious surface, new pervious surface, existing impervious surfaces, and replaced impervious surface targeted for mitigation as specified in the following sections. On-site BMPs must be selected and applied according to the basic requirements, procedures, and provisions detailed in this section and the design specifications for each BMP in Appendix C, Section C.2. In accordance with the RSWDM, Flow Control BMPs must be evaluated and implemented to the maximum extent feasible. Per section 1.2.9.2, this project site is over 22,000 SF and is subject to evaluating the Large Lot BMP Requirements as detailed in section 1.2.9.2.2 and described below: 1. Full Dispersion – The project site does not contain enough native vegetated surface to fully disperse all impervious surfaces proposed with this project, therefore it is not feasible to implement Full Dispersion for this project. 2. Full Roof Infiltration – No new roof surfaces are proposed with this project, therefore Full Roof Infiltration is not feasible for this project. 3. Full Infiltration – A geotechnical engineer has determined that soils on site are not suitable for infiltration, and this project is within Zone 1 of the City’s Aquifer Protection Area which prohibits infiltration BMPs, therefore Full Infiltration is not feasible for this project. 4. Limited Infiltration – A geotechnical engineer has determined that soils on site are not suitable for infiltration and this project is within Zone 1 of the City’s Aquifer Protection Area which prohibits infiltration BMPs, therefore Limited Infiltration is not feasible for this project. 5. Bioretention – A geotechnical engineer has determined that soils on site are not suitable for infiltration, and this project is within Zone 1 of the City’s Aquifer Protection Area which prohibits infiltration BMPs, therefore Bioretention is not feasible for this project. 6. Permeable Pavement – A geotechnical engineer has determined that soils on site are not suitable for infiltration, and all paved surfaces are replacing existing impervious surfaces or under roof overhangs, and this project is within Zone 1 of the City’s Aquifer Protection Area which prohibits infiltration BMPs, therefore Permeable Pavement is not feasible for this project. 7. Basic Dispersion – The minimum required flow path and maximum slope requirements cannot be met on this project therefore Basic Dispersion is not feasible. 8. Reduced Impervious Surface Credit – The proposed site improvements propose more than 4,000 SF of impervious surface and therefore the Restricted Footprint credit is not feasible for this site. No driveways are proposed with this project therefore the Wheel Strip Driveway credit is not feasible for this site. There are no proposed buildings with this project, therefore the Minimum Disturbance Foundation credit is RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 8 infeasible for this project. No open grid decks are proposed with this project therefore the Open Grid Decking credit is not feasible for this project. 9. Native Growth Retention Credit – This site does not contain any native vegetation, therefore the Native Growth Retention Credit is not feasible for this site. 10. Perforated Pipe Connection – No new buildings or downspouts are proposed with this project, therefore Perforated Pipe Connections are infeasible for this project. SPECIAL REQUIREMENT #1: OTHER ADOPTED AREA-SPECIFIC REQUIREMENTS The RSWDM is one of several adopted regulations in in the City of Renton that apply requirements for controlling drainage on an area-specific basis. Other adopted area-specific regulations with requirements that have a direct bearing on the drainage design of a proposed project are found in Section 1.3.1 of the RSWDM. To the best of our knowledge, there are no adopted area-specific requirements in the area of the proposed project site development that would impact the current Renton Surface Water Design Manual (RSWDM) requirements for this project. Therefore, the project will adhere to the requirements set forth in the 2022 RSWDM. SPECIAL REQUIREMENT #2: FLOOD HAZARD AREA DELINEATION Flood hazard areas are composed of the 100-year floodplain, zero-rise flood fringe, zero-rise floodway, FEMA floodway. If a proposed project contains or is adjacent to a flood hazard area as determined by CED, this special requirement requires the project to determine those components that are applicable and delineate them on the project’s site improvement plans and recorded maps. To the best of our knowledge in reviewing both only FEMA Flood Insurance Rate Maps and the King County iMap, the proposed project site area is not located within a 100-year floodplain. SPECIAL REQUIREMENT #3: FLOOD PROTECTION FACILITIES Flood protection facilities, such as levees and revetments, require a high level of confidence in their structural integrity and performance. Proper analysis, design, and construction is necessary to protect against the potentially catastrophic consequences if such facilities should fail. To the best of our knowledge in reviewing both FEMA Flood Insurance Rate Maps and the King County iMap, the proposed project site area is not located within a 100-year floodplain and not located adjacent to any rivers, streams, creeks, or other water bodies, and does not have any existing flood protection facilities installed on the existing property, nor are any new flood protection facilities proposed to be installed or warranted for this project. SPECIAL REQUIREMENT #4: SOURCE CONTROLS If a proposed project requires a commercial building or commercial site development permit then water quality source controls applicable to the proposed project shall be applied as described below in accordance with the King County Stormwater Pollution Prevention Manual and King County Code 9.12. No structural improvements are proposed that will require source controls. SPECIAL REQUIREMENT #5: OIL CONTROL Projects proposing to develop or redevelop a high-use site must provide oil controls in addition to any other water quality controls required by this manual. Such sites typically generate high concentrations of oil due to high traffic turnover, on-site vehicle or heavy or stationary equipment use, some business operations, e.g., automotive recycling, or the frequent transfer of liquid petroleum or coal derivative products. The project is not considered a high-use site and therefore will not require oil controls to be installed. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 9 SPECIAL REQUIREMENT #6: AQUIFER PROTECTION AREA Aquifer Protection Area(s) (APA) are identified in the RMC 4-3-050. If a proposed project is located within the APA, this special requirement requires the project to determine those components that are applicable and delineate them on the project’s site improvements plans. APA zones are depicted in the Wellhead Protection Area Zones layer of COR Maps (<https://maps.rentonwa.gov/Html5viewer/Index.html?viewer=cormaps>). The subject project is located in an Aquifer Protection Area Zone 1 according to the online City of Renton COR Maps, therefore open facilities, open conveyance systems, and on-site BMPs that rely on infiltration are prohibited. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 10 3. OFFSITE ANALYSIS FIELD INSPECTION A Site visit has been made on February 16, 2022 to gather information about the existing characteristics, including, but not limited to, review of the parking lots and drainage facilities. Please refer to Downstream Analysis below for more information. DRAINAGE SYSTEM PROBLEM DESCRIPTIONS There are no known drainage concerns or any existing drainage problems per review of the site with the Renton School District, the King County iMap, and City of Renton COR Maps ‘Drainage Complaints’ Layer. As such, no drainage problems are anticipated to be present in the redevelopment or exacerbate any existing problems. UPSTREAM ANALYSIS The existing Renton School District Transportation facility is bound by North 5th Street to the north, Garden Ave N to the east, North 4th Street to the south, and Park Avenue N to the west. To the best of our knowledge, the surrounding streets are fully developed with curb, gutter, and catch basins that collect stormwater. Therefore, no offsite flows are anticipated for this project. DOWNSTREAM ANALYSIS According to the project survey and the City of Renton COR GIS database, stormwater runoff from the existing transportation facility currently is collected on the north side of the site along North 5th Street in a 18-inch corrugated metal pipe that connects to a 24-inch corrugated metal pipe and runs west along North 5th Street. Then the pipe goes north along Burnett Avenue North until it reaches North 6th Street and heads west discharging into Cedar River that ultimately drains to Lake Washington. See Figure 7 – Offsite Analysis. MITIGATION OF EXISTING OR POTENTIAL PROBLEMS The site is not within or near any FEMA flood zones, no existing problems are known, and no potential problems are expected as a result of the proposed development. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 11 4. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID), AND WATER QUALITY FACILITY ANALYSIS AND DESIGN EXISTING SITE HYDROLOGY (PART A) Geotechnical investigation on site has found site soils to consist of a surface layer of topsoil underlain by existing fill soils, and Holocene Alluvium deposits from the Cedar River. See project geotechnical report and Figure 9 – Soils Map. The topography of the existing site is generally flat, sloping gently from south to north at approximately 1-2% slope. See Table 1 in Section 1 of this report and Figure 3 – Existing Conditions for a summary of the existing land cover characteristics for the project site. DEVELOPED SITE HYDROLOGY (PART B) The proposed improvements consist of a new paved parking lot with sidewalks, landscaping, and public amenity space at the northwest corner of the site. New catch basins will be installed to collect surface runoff and route through water quality treatment prior to discharging to the existing 24” storm main in N 5th Street. Table 2 in Section 1 of this report summarizes the land cover characteristics of the proposed project site redevelopment disturbed area (See Figure 4 – Proposed Conditions and Figure 5 – New + Replaced Impervious Areas). PERFORMANCE STANDARDS (PART C) Flow control conforming to Core Requirement #3 meeting the Peak Rate Flow Control standard is required for this project. Specifically, flow durations for the developed site must match flow durations for the existing site conditions between ½ the two-year and the 50-year storm events. In accordance with the RSWDM, MGS Flood Version 4, an approved continuous-modeling software, is used to model the existing and proposed site drainage basins. The target surfaces for this project do not increase flows by more than 0.15 CFS using a 15-minute timestep, therefore flow control is not required for this project. Table 3 below summarizes the land cover characteristics of the existing and proposed target surfaces. See Figure 4 – Proposed Conditions and Figure 5 - New + Replaced Impervious Areas and Appendix B of this report for MGS Flood modeling results. TABLE 3 – TARGET SURFACES BASINS AREA (AC) 100-YR FLOW (CFS) EXISTING BASIN Flat Parking 0.297 0.422 Flat Lawn 0.211 PROPOSED BASIN Flat Parking 0.378 0.481 Flat Lawn 0.13 0.508 AC 0.059 CFS Increase FLOW CONTROL SYSTEM (PART D) This project is exempt from providing flow control, therefore no flow control systems will be installed with this project. WATER QUALITY SYSTEM (PART E) This project proposes more than 5,000 SF of pollution generating surfaces, therefore enhanced basic water quality treatment is required for this project. Water quality treatment will be provided by a Modular Wetland water quality treatment facility. An area swap will be utilized in order to provide water quality treatment to all new PGIS surfaces. Additional details and sizing calculations will be provided in the forthcoming permit submittal. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 12 5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN PIPE SYSTEMS: 1. New pipe systems shall be designed with sufficient capacity to convey and contain (at minimum) the 25- year peak flow, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. - New pipe systems are designed to convey and contain the 25-year peak flow rate. 2. Pipe system structures may overtop for runoff events that exceed the 25-year design capacity, provided the overflow from a 100-year runoff event does not create or aggravate a severe flooding problem or severe erosion problem as described in Core Requirement #2, Section 1.2.2 (p. 1-27). Any overflow occurring onsite for runoff events up to and including the 100-year event must discharge at the natural location for the project site. In residential subdivisions, this overflow must be contained within an onsite drainage easement, tract, covenant, or public right-of-way. - Pipe systems are designed so that the 100-year runoff event does not create or aggravate a severe flooding or erosion problem. 3. The upstream end of a pipe system that receives runoff from an open drainage feature (pond, ditch, etc.) shall be analyzed and sized as a culvert as described below. - The upstream end of the proposed pipe system does not receive runoff from an open drainage feature. CULVERTS: 1. New culverts shall be designed with sufficient capacity to meet the headwater requirements in Section 4.3.1 and convey (at minimum) the 25-year peak flow, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. - No culverts are proposed with this project. 2. New culverts must also convey as much of the 100-year peak flow as is necessary to preclude creating or aggravating a severe flooding problem or severe erosion problem as described in Core Requirement #2, Section 1.2.2 (p. 1-27). Any overflow occurring onsite for runoff events up to and including the 100-year event must discharge at the natural location for the project site. In residential subdivisions, this overflow must be contained within an onsite drainage easement, tract, covenant or public right-of-way. - No culverts are proposed with this project. 3. New culverts proposed in streams with salmonids shall be designed to provide for fish passage as detailed in Section 4.3.2. Note: The County’s critical areas regulations (KCC 21A.24) or the state Department of Fish and Wildlife may require a bridge to facilitate fish passage. - No culverts are proposed with this project. DITCHES/CHANNELS: 1. New ditches/channels shall be designed with sufficient capacity to convey and contain, at minimum, the 25-year peak flow, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. - No new ditches or channels are proposed with this project. 2. New ditches/channels must also convey as much of the 100-year peak flow as is necessary to preclude creating or aggravating a severe flooding problem or severe erosion problem as described in Core Requirement #2, Section 1.2.2 (p. 1-27). Any overflow occurring onsite for runoff events up to and including the 100-year event must discharge at the natural location for the project site. In residential subdivisions, this overflow must be contained within an onsite drainage easement, tract, covenant, or public right-of-way. - No new ditches or channels are proposed with this project. TIGHTLINE SYSTEMS TRAVERSING STEEP SLOPES: 1. New tightline conveyance systems traversing slopes that are steeper than 15% and greater than 20 feet in height, or are within a steep slope hazard area as defined in KCC 21A.06, shall be designed with sufficient capacity to convey and contain (at minimum) the 100-year peak flow, assuming full build-out RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 13 conditions for all tributary areas, both onsite and offsite. Tightline systems shall be designed as detailed in Section 4.2.2. - No tightline conveyance systems that traverse a steep slope are proposed with this project. BRIDGES: 1. New bridges shall be designed to accommodate the 100-year peak flow as specified in Section 4.3.3 and in accordance with the floodplain development standards in KCC 21A.24. - No bridges are proposed with this project. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 14 6. SPECIAL REPORTS AND SUMMARY Please refer to the Geotechnical Engineering Report – by Associated Earth Sciences, dated October 4, 2024 Kirkland | Tacoma | Mount Vernon 425-827-7701 | www.aesgeo.com October 4, 2024 Project No. 20240196E001 Renton School District No. 403 7812 South 124th Street Seattle, Washington 98178 Attention: Andrew Hollenback Subject: Limited Geotechnical Engineering Study Renton School District Transportation Facility New Parking Lot 420 Park Avenue North Renton, Washington References: Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report, New Transportation Center, 1220 North 4th Street, Renton, Washington, AESI Project No. 20070040, March 20, 2007 Geologic Map of the Renton Quadrangle, King County, Washington, Mullineaux, D.R., 1965 Dear Andrew Hollenback: As requested, Associated Earth Sciences, Inc. (AESI) has completed a site reconnaissance, subsurface exploration, and limited geotechnical engineering study for the proposed new parking lot at the Renton School District Transportation Facility. We are familiar with the site having completed the site exploration and geotechnical design report (AESI, March 20, 2007) as well as providing observation and testing services during construction of the existing transportation facility in 2007. This study was completed in general accordance with our scope of work and cost proposal dated August 13, 2024. We were authorized to proceed by means of District Purchase Order #2012300302. This limited study was completed in accordance with local standards of practice in the field of geotechnical engineering at the time it was completed. No other warranty, express or implied, is made. Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 2 SITE AND PROJECT DESCRIPTION The proposed project will include converting the currently undeveloped northwest corner of the overall transportation facility property located at 420 Park Avenue North in Renton, Washington, as shown on the “Vicinity Map” (Figure 1), to a new parking lot measuring some 105 feet east-west by 200 feet north-south. This portion of the property previously had two buildings constructed which were demolished by 2020. The topography across the property is flat with total grade change north to south of just a few feet. Based on our review of conceptual site plans dated April 5, 2024, provided by Jacobson Consulting, we understand that the new parking lot will be close to existing grades, paved in asphalt with planters and landscaping providing separation from parking rows and the city right-of-way. The parking lot will also be provided with on-site lighting. SUBSURFACE EXPLORATIONS AND CONDITIONS Our field study included excavating two exploration pits on September 13, 2024. The various types of sediments, as well as depths where characteristics of the sediments changed, are indicated on the exploration logs presented in Appendix A. Our exploration locations were approximately determined on the property by measuring from known site features. The site and approximate locations of the subsurface explorations referenced in this study are presented on the “Site and Exploration Plan” (Figure 2). The conclusions and recommendations presented in this letter-report are based, in part, on the exploration pits completed for this study. The number, locations, and depths of the explorations were completed within site and budgetary constraints. Because of the nature of the exploratory work below ground, extrapolation of subsurface conditions between explorations is necessary. It should be noted that differing subsurface conditions may sometimes be present due to the random nature of deposition and the alteration of topography by past grading and/or filling. The nature and extent of variations between the field explorations may not become fully evident until construction. If variations are observed at that time, it may be necessary to re-evaluate specific recommendations in this letter-report and make appropriate changes. Previous Explorations AESI completed a geotechnical study in 2007 during the design phase of the existing transportation center. The 2007 study included six exploration borings which generally agree with the geologic findings of the current study. Copies of the 2007 exploration logs are included in Appendix A, along with logs of exploration pits recently completed for the current project Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 3 proposed. Generally, the 2007 study found fill within the surface 3 feet, underlain by soft/loose, recent, Quaternary Holocene alluvium deposits. We reviewed field reports from the construction phase of the current transportation center which indicated that parking area improvements consisted of a 12-inch-deep overexcavation, placement of Mirafi 500X, and replacement with 2-inch clean crushed rock. Visual on-site reconnaissance indicates that the near-surface remedial improvements were effective in providing structural support of the paved parking areas. We observed no concerning settlement or cracking, and the paved surface appeared to be performing well. New Exploration Pits For the current study, two new exploration pits were completed by Northwest Excavating, an independent firm working under subcontract to AESI, at the locations shown on Figure 2. The pits were completed using a 2.5-foot-wide, toothed bucket on a E50, tracked Bobcat Excavator. The pits permitted direct, visual observation of subsurface conditions. During excavation, samples were generally collected upon observation of a lithology change with depth. The excavation process was continuously observed and logged by a geologist from our firm. After logging the exposed soils, pits were backfilled with the excavated soil and lightly tamped with the excavator bucket. The various types of materials and sediments encountered in the explorations, as well as the depths where characteristics of these materials changed, are indicated on the exploration logs included in Appendix A. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types in the field. Disturbed soil samples were selected from the pits, placed in moisture-tight containers, and transported to AESI’s laboratory for further visual classification and testing, as necessary. The exploration logs in Appendix A are based on the field observations and inspection of the samples. SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from our field explorations accomplished for this study, visual reconnaissance of the site, and review of selected applicable geologic literature. Published Geologic and Soils Map Review of the regional geologic map, titled “Geologic Map of the Renton Quadrangle, King County, Washington,” U.S. Geological Survey, Geologic Quadrangle Map GQ-405, scale 1:24,000, prepared by D.R. Mullineaux (1965) indicates that the subject property is underlain by Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 4 widespread artificial fill with Quaternary alluvium deposited by the ancestral Cedar River mapped nearby. Review of the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Web Soil Survey indicates that the soils in the vicinity of the site consist predominately of Urban Land. The regional mapping is consistent with our subsurface observations. Stratigraphy As shown on the field logs, our explorations in the area of the planned parking lot generally encountered native, Holocene alluvium at shallow depths, overlain by about 1 to 3 feet of fill and topsoil. The following section presents more detailed subsurface information organized from the youngest (shallowest) to the oldest (deepest) sediment types. Copies of our exploration logs are included in Appendix A. Sod and Topsoil Both exploration pits in the current project area encountered up to 10 inches of sod and topsoil; the sod and topsoil are not suitable for structural support and should be stripped from structural areas. Fill Existing fill was encountered in both explorations; EP-1 was mixed with topsoil to a dept of about 10 inches and in EP-2 there was up to about 2 feet of variable fill under the topsoil, where the new parking lot will be constructed. Existing fill generally consisted of moist, gray, fine to coarse sandy, fine to coarse gravel with some plastic and brick debris. Excavation through fill was difficult for the contractor’s equipment and appeared firm. Fill in EP-2 extended to approximately a depth of about 3 feet below the ground surface. Existing fill is also expected to be found around buried utilities and structures, in areas of past grading, and beneath landscape improvements. Where existing fill is found to be firm and unyielding during a proof-roll with a fully loaded, tandem-axle dump truck, it may be suitable for structural support of the paved parking area. We recommend remedial preparation of surfaces where fill is not encountered to be consistent with preparation in areas where fill is encountered. Excavated existing fill may be suitable for reuse in structural fill applications provided it is free of excessive organic material and other deleterious material, at proper moisture content, and is allowed by project plans and specifications. Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 5 Holocene Alluvium Sediments encountered below the fill and topsoil generally consisted of interbedded clean sand, silty sand, and silt with some woody debris present. We interpret these sediments to be representative of alluvium deposited in former channels of the Cedar River. The alluvium extends past the depth of our deepest exploration pit of 11 feet below current ground surface. This concurs with the 2007 study which indicates a maximum boring depth of 95 feet below surface elevation. In general, the alluvium is very loose/soft to medium dense at depths shallower than 75 feet, as indicated by the 2007 study. Remedial action is recommended in planned paved areas to mitigate compressive settlement within the loose/soft soil. In general, the Holocene alluvium where moisture content is within the compactable range is considered suitable for reuse as structural fill. It should be noted that where soils are above their optimum moisture content for compaction, their reuse as structural fill during all but the driest times of the year will be difficult. However, it should be noted that the existing alluvial soil was observed to have a high silt content and is considered moisture-sensitive. Hydrology No groundwater was encountered during our current phase of exploration to depths of approximately 11 feet below the ground surface, or approximately elevation 25 feet (surface elevation 36). Groundwater is expected to be present at depth within the Holocene alluvium as an unconfined local aquifer. Shallow perched water may be present within the alternating silt and sand interbeds. During our previous study (2007, referenced above), groundwater was encountered at approximately 10 feet below the surface, or approximately elevation 25 (surface elevation 35). To our knowledge, the project specified no deep cuts that might encounter the regional groundwater aquifer. It should be noted that fluctuations in the level of the groundwater may occur due to the time of the year, variations in rainfall, and adjacent river levels. No utilities are anticipated to be installed at depths where the anticipated groundwater table might be encountered. Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 6 CONCLUSIONS AND RECOMMENDATIONS Our explorations completed in the location of the proposed new parking lot encountered loose/soft Holocene alluvium underlying 1 to 3 feet of existing fill which contains up to 10 inches of topsoil. These same conditions were reported in AESI’s “Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report” dated in 2007. Recommendations in this letter-report included near-surface remedial improvements for preparation of paved parking areas. Given that the adjacent parking areas with similarly described subsurface conditions performed well with the completion of near-surface remedial improvements, it is our opinion that the site is suitable for the proposed parking lot development, provided that recommendations contained herein are properly followed. Recommendations Site preparation of the planned paved parking area should include removal of all grass, topsoil, and any other deleterious surface materials and the remaining roots grubbed to a depth that will allow at least 12 inches of imported base material under the pavement section. Any loose existing fill soils below this elevation should be recompacted to a firm and unyielding condition prior to the placement of subsequent base stabilization. The finished parking lot subgrade should receive similar near-surface stabilization improvements as performed in the adjacent transportation center parking lot. Generally, this consists of a minimum of 12 inches of aggregate (crushed rock) over geotextile reinforcement fabric (Mirafi 500X equivalent or structurally better) on the stripped surface. Overexcavation to accommodate the specified thickness of aggregate may be necessary, depending on design elevations. Surface aggregate shall be comprised of a granular crushed rock or crushed recycled concrete material, compacted to a firm and unyielding condition prior to asphalt paving. Once the subgrade elevation is achieved, we recommend performing a proof-roll with a fully loaded, tandem-axle dump truck on the exposed excavated surface prior to placing geotextile fabric. This will allow the opportunity for visual performance verification of the exposed subgrade, and if needed, less invasive access to remedy any concerns that may arise. We recommend allowing budgetary flexibility should we identify any necessity for additional near-surface improvements. After recompaction of the exposed ground, if needed, additional structural fill may be placed to attain desired grades. Structural fill placed below parking areas should consist of a granular imported material such as crushed base course or clean chip rock which are free of organics and Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 7 other deleterious materials, placed in maximum 8-inch loose lifts. Each lift should be compacted to 95 percent of the modified Proctor maximum density using ASTM D-1557 as the standard. In the case of utility trench filling, the backfill should be placed and compacted in accordance with applicable codes and standards. The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material 72 hours in advance to perform a Proctor test and determine its field compaction standard. Pavement Recommendations AESI recommends that an engineering stabilization geotextile reinforcement such as Mirafi 500x (or approved equivalent) be placed over the stripped subgrade. The geotextile should be overlain with a minimum of 12 inches of 2-inch clean crushed rock or crushed recycled concrete. The fabric acts as a separation barrier between relatively fine-grained surficial materials on the site and the load-distributor aggregate. As a separator, it reduces the loss of costly aggregate material into the subgrade and prevents the upward pumping of contaminating silt into the aggregate. The high tensile strength and low modulus of elongation of the fabric also act to reduce localized stress by redistributing the traffic loads over a wider area of subgrade. In addition, the recommended method of installation (proof-rolling) identifies weak areas, which can be improved prior to paving. The majority of the new parking lot will accommodate light vehicle loads from passenger vehicles. In these light traffic load areas, we recommend a pavement section consisting of 3 inches of hot-mix asphalt (HMA) underlain by 4 inches of crushed surfacing. The eastern edge of the parking lot is proposed for a heavy-duty section. In these areas we recommend a minimum of 4 inches of HMA over 4 inches of crushed rock surfacing. The crushed rock will provide improved and consistent drainage. The crushed rock courses must be compacted to 95 percent of the maximum density, as determined by ASTM D-1557. All paving materials should meet gradation criteria contained in the current Washington State Department of Transportation (WSDOT) Standard Specifications. CLOSURE We are available to provide geotechnical engineering and monitoring services during construction if required. The integrity of the paved parking areas depend on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Renton School District Transportation Facility Limited Geotechnical New Parking Lot Engineering Study October 4, 2024 ASSOCIATED EARTH SCIENCES, INC. FGR/ld – 20240196E001-002 Page 8 We have enjoyed working with you on this study and are confident these recommendations will aid in the successful completion of your project. If you should have any questions or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington ______________________________ Forest Gheen-Regouski Matthew A. Miller, P.E. Natural Resource Scientist Principal Engineer Attachments: Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Appendix A: Exploration Logs G:\ G I S _ P r o j e c t s \ 2 0 2 4 \ 2 4 0 1 9 6 R e n t o n S D T r a n s p o r a t i o n S i t e \ _ a p r x \ 2 0 2 4 0 1 9 6 E 0 0 1 F 1 V M _ R e n t o n S D T r a n s p o r a t i o n . a p r x | 2 0 2 4 0 1 9 6 E 0 0 1 F 1 V M _ R e n t o n S D T r a n s p o r t a t i o n | 2 0 2 4 - 1 0 - 0 1 | m t r o p COUNTY LOCALE LOCATION PROJECT NO.DATE FIGURE 19/2420240196E001 RENTON SD TRANSPORATION SITE PARKING EXPANSION RENTON, WASHINGTON VICINITY MAP ESRI, USGS, NATIONAL GEOGRAPHIC,DELORME, NATURALVUE, I-CUBED, GEBCO:ARCGIS ONLINE BASEMAP. WADOT STATEROUTES 24K (12/20). KING CO: PARCELS,ROADS (8/24). NOTE: LOCATION AND DISTANCES SHOWNARE APPROXIMATE. BLACK AND WHITEREPRODUCTION OF THIS COLOR ORIGINALMAY REDUCE ITS EFFECTIVENESS AND LEADTO INCORRECT INTERPRETATION. KinJ CoXnt\ WE L L S A L Y N PE L L Y A V E N PE L L Y A L Y N GA R D E N A V E N N 5TH ST PA R K A V E N 405 16 900 169 /DNH WDVKLQJWRQ KING C O U N T Y KING COUNTY RENTON SEATTLE 0 2,000 FEET m SITE LOCATION AND DISTANCESSHOWN ARE APPROXIMATE. BLACK AND WHITE REPRODUCTION OFTHIS COLOR ORIGINAL MAY REDUCEITS EFFECTIVENESS AND LEAD TOINCORRECT INTERPRETATION.G:\ G I S _ P r o j e c t s \ 2 0 2 4 \ 2 4 0 1 9 6 R e n t o n S D T r a n s p o r a t i o n S i t e \ _ a p r x \ 2 0 2 4 0 1 9 6 E 0 0 1 F 2 E S _ R e n t o n S D T r a n s p o r a t i o n . a p r x | 2 0 2 4 0 1 9 6 E 0 0 1 F 2 E S _ R e n t o n S D T r a n s p o r t a t i o n | 2 0 2 4 - 1 0 - 0 3 | m t r o p PROJECT NO.DATE FIGURE ± 210/2420240196E001 RENTON SD TRANSPORATION SITE PARKING EXPANSION RENTON, WASHINGTON EXISTING SITE AND EXPLORATION PLAN DATA SOURCES/REFERENCES:KING COUNTY: PARCELS, ROADS (8/24). EAGLEVIEW TECHNOLOGIES,INC.: AERIAL IMAGERY (2023). WA DNR LIDAR:KING_COUNTY_WEST_2021, ACQUIRED 4/21, 1.5' CELL SIZE.CONTOURS DERIVED FROM LIDAR. 0 100 FEET GA R D E N A V E N PA R K AVE N N 4TH ST N 5TH ST EP124 EP224 EB10EB20 EB30 EB40 EB50EB0 4 42 38 34 3 32 44 40 3 3 2 4 4 4 3 3 32 3 3 3 3 3 34 LEGEND SITE EXPLORAION TYPE-YEAR EXPLORATION BORING EXPLORATION PIT CONTOUR 10 FT CONTOUR 2 FT PARCEL APPENDIX A Exploration Logs Classifications of soils in this report are based on visual field and/or laboratory observations, which include density/consistency, moisture condition, grain size, and plasticity estimates and should not be construed to imply field or laboratory testing unless presented herein. Visual-manual and/or laboratory classification methods of ASTM D-2487 and D-2488 were used as an identification guide for the Unified Soil Classification System. OH PT CH OL MH CL ML SM SC GW SP GC SW GM GP Well-graded gravel and gravel with sand, little to no fines Poorly-graded gravel and gravel with sand, little to no fines Clayey gravel and clayey gravel with sand Silty gravel and silty gravel with sand Well-graded sand and sand with gravel, little to no fines Poorly-graded sand and sand with gravel, little to no fines Clayey sand and clayey sand with gravel Organic clay or silt of low plasticity Organic clay or silt of medium to high plasticity Peat, muck and other highly organic soils Silty sand and silty sand with gravel Silt, sandy silt, gravelly silt, silt with sand or gravel Clay of low to medium plasticity; silty, sandy, or gravelly clay, lean clay Elastic silt, clayey silt, silt with micaceous or diatomaceous fine sand or silt Clay of high plasticity, sandy or gravelly clay, fat clay with sand or gravel (1 ) Hi g h l y Or g a n i c So i l s Fin e - G r a i n e d S o i l s - 5 0 % o r M o r e P a s s e s N o . 2 0 0 S i e v e (1 ) Co a r s e - G r a i n e d S o i l s - M o r e t h a n 5 0 % R e t a i n e d o n N o . 2 0 0 S i e v e Gr a v e l s - M o r e t h a n 5 0 % o f C o a r s e F r a c t i o n Re t a i n e d o n N o . 4 S i e v e 12 % F i n e s 5% F i n e s Sa n d s - 5 0 % o r M o r e o f C o a r s e F r a c t i o n Pa s s e s N o . 4 S i e v e Si l t s a n d C l a y s Li q u i d L i m i t L e s s t h a n 5 0 Sil t s a n d C l a y s Li q u i d L i m i t 5 0 o r M o r e (1 ) (1 ) 12 % F i n e s 5% F i n e s (2 ) (2 ) (2 ) (2 ) Terms Describing Relative Density and Consistency Estimated Percentage Moisture Content Percentage by Weight <5 5 to <12 12 to <30 30 to <50 Component Definitions Component Trace Some Modifier (silty, sandy, gravelly) Very modifier (silty, sandy, gravelly) Size Range and Sieve Number Larger than 12" Descriptive Term Smaller than No. 200 (0.075 mm) 3" to 12" Coarse- Grained Soils Fine- Grained Soils Density Very Loose Loose Medium Dense Dense Very Dense SPT blows/foot 0 to 4 4 to 10 10 to 30 30 to 50 >50 (3) 0 to 2 2 to 4 4 to 8 8 to 15 15 to 30 >30 Consistency Very Soft Soft Medium Stiff Stiff Very Stiff Hard SPT blows/foot(3) Test Symbols No. 4 (4.75 mm) to No. 200 (0.075 mm) Boulders Silt and Clay Gravel Coarse Gravel Fine Gravel Cobbles Sand Coarse Sand Medium Sand Fine Sand Dry - Absence of moisture, dusty, dry to the touch Slightly Moist - Perceptible moisture Moist - Damp but no visible water Very Moist - Water visible but not free draining Wet - Visible free water, usually from below water table G = Grain Size M = Moisture Content A = Atterberg Limits C = Chemical DD = Dry Density K = Permeability No. 4 (4.75 mm) to No. 10 (2.00 mm) No. 10 (2.00 mm) to No. 40 (0.425 mm) No. 40 (0.425 mm) to No. 200 (0.075 mm) 3" to No. 4 (4.75 mm) 3" to 3/4" 3/4" to No. 4 (4.75 mm) Symbols Sampler Type and Description Blows/6" or portion of 6"15 10 20 California Sampler Ring Sampler Continuous Sampling Grab Sample Portion not recovered Split-Spoon Sampler (SPT) Cement grout surface seal Bentonite seal Filter pack with blank casing section Screened casing or Hydrotip with filter pack End cap ATD At time of drilling Static water level (date) (1) Percentage by dry weight(2) Combined USCS symbols used for fines between 5% and 12%(3) (SPT) Standard Penetration Test (ASTM D-1586)(4) In General Accordance with Standard Practice for Description and Identification of Soils (ASTM D-2488) Groundwater depth i n c o r p o r a t e d e a r t h s c i e n c e s a s s o c i a t e d EXPLORATION LOG KEY FIGURE:A1Blo c k s \ d w g \ l o g _ k e y 2 0 2 2 . d w g L A Y O U T : L a y o u t 5 - 2 0 2 2 L o g d r a f t 0 2.5 5 7.5 10 12.5 15 17.5 20 Topsoil / Fill - 10 inches Moist, dark brown, silty, gravelly, fine to medium SAND; angular gravel (SM). Holocene Alluvium Moist, light brown, silty, fine SAND (SM). Very moist, gray with orange mottling, fine sandy, SILT; micaceous (ML). Becomes less orange mottling. Very moist, dark gray, fine to coarse SAND; some organic wood (2 to 4 inches thick); interbeds of gray, silt (SP). Occasional orange, fine sand. No seepage. No caving. Associated Earth Sciences, Inc. Exploration Pit EP-1 Renton SD Transportation Site Parking Expansion Renton, WA Date:9/13/2024 Logged By:FGR 20240196E001 Total Depth (ft):11 Approved By:JHS De p t h ( f t ) Description US C S 20 2 4 0 1 9 6 E 0 0 1 10 / 4 / 2 0 2 4 Elev.: »36 ft NAVD88 Sheet: 1 of 1 0 2.5 5 7.5 10 12.5 15 17.5 20 Topsoil - 6 inches Fill Slightly moist, gray, silty, fine to coarse sandy, fine to coarse GRAVEL; some plastic; brick debris (SM). Holocene Alluvium Very moist, orangish brown and gray, SILT; some interbed (2 to 3 inches thick) of orange, fine sand (ML). Moist, brown, fine SAND, some silt; discontinuous; interdeposits of gray, silt; bed (1 to 3 inches thick) (SP). Becomes gray. Very moist, gray, SILT; beds (0.5 to 2 inches thick) of gray, fine sand, and orange, fine to medium sand (ML). No seepage. No caving. Associated Earth Sciences, Inc. Exploration Pit EP-2 Renton SD Transportation Site Parking Expansion Renton, WA Date:9/13/2024 Logged By:FGR 20240196E001 Total Depth (ft):11 Approved By:JHS De p t h ( f t ) Description US C S 20 2 4 0 1 9 6 E 0 0 1 10 / 4 / 2 0 2 4 Elev.: »36 ft NAVD88 Sheet: 1 of 1 RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 15 7. CSWPP ANALYSIS AND DESIGN This section lists the requirements that were met when designing the TESC Plan for this site. STANDARD REQUIREMENTS Erosion/Sedimentation Plan shall include the following: 1. Clearing Limits – Construction limits are delineated or noted on the project erosion control plans and shall be physically laid out on the project site. 2. Cover Measures – Contractor will use plastic sheeting, hydroseeding, and mulching to protect soils from erosion. Gravel borrow or “hog fuel” may be used in areas of excessively moist soils that will support building or traffic loads, if necessary. 3. Perimeter Protection – Temporary construction fencing will be used to delineate and protect the project clearing limits and provide a secure site. Straw wattles will be used to prevent sediment-laden water from discharging from the site. 4. Traffic Area Stabilization – The existing drive aisles and parking lots will be utilized for construction access, staging, and laydown as needed. The contractor shall coordinate with the Renton School District prior to starting construction. Additional gravel borrow or “hog fuel” may be used in areas of excessively moist soils that will support traffic loads, if necessary. 5. Sediment Retention – Filter fabric protection will also be installed in all new area drain structures and remain until the site is stabilized. 6. Surface Water Collection – Interceptor swales will be used in the appropriate areas of the site to collect stormwater runoff, if necessary. 7. Dewatering Control – Dewatering is not necessary for this site; therefore, no dewatering control measures are implemented. 8. Dust Control – Dry soils will be appropriately sprinkled with water to limit airborne dust during dry weather. 9. Flow Control – Discharge will be restricted and will therefore serve as a flow control measure. 10. Control Pollutants – BMPs shall be implemented to prevent or treat contamination of stormwater runoff by pH modifying sources. Carbon dioxide sparging, using dry ice or a gas diffuser as a source of CO2 will be used as needed to adjust the pH level and prevent discharge of water with elevated pH levels to the City’s Storm System. In addition, dust control will be implemented as needed to prevent fugitive dust during the treatment process. In addition, all waste materials from the site will be removed in a manner that does not cause contamination of stormwater. 11. Protect Existing and Proposed Flow Control BMPs – The native vegetation will be protected with silt fencing and perimeter construction fencing. 12. Maintain BMPs – BMPs for the project will be monitored for effectiveness on a regular basis to ensure they are repaired and replaced as necessary. 13. Manage the Project – The project will be phased to take weather and seasonal work limits into account. The BMPs will be inspected, maintained, and repaired as needed to ensure their intended performance. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 16 8. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT BOND QUANTITIES WORKSHEET A bond quantities worksheet will be included in Appendix A in a forthcoming submittal. FLOW CONTROL AND WATER QUALITY FACILITY SUMMARY SHEET AND SKETCH A Facility Summary Sheet has been completed and is included in Appendix D. DECLARATION OF COVENANT FOR PRIVEATELY MAINTAINED FLOW CONTROL AND WATER QUALITY FACILITIES A draft Declaration of Covenant will be included in Appendix D for City review in a forthcoming submittal and will be recorded prior to permit issuance. RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 17 9. OPERATIONS AND MAINTENANCE MANUAL As stated in the Renton Surface Water Design Manual (RSWDM), the owner will maintain all privately owned facilities. Sections of the RSWDM outlining the operations and maintenance of these facilities have been included in this section along with maintenance manuals from proposed proprietary products. A COPY OF THE OPERATION AND MAINTENANCE MANUAL SHALL BE RETAINED ON SITE OR WITHIN REASONABLE ACCESS TO THE SITE AND SHALL BE TRANSFERRED WITH THE PROPERTY TO ANY NEW OWNER OPERATIONS AND MAINTENANCE MANUAL for RSD Transportation Expansion PARTY RESPONSIBLE FOR MAINTENANCE AND OPERATIONS: Renton School District CITY OF RENTON SURFACE WATER DESIGN MANUAL 2022 City of Renton Surface Water Design Manual 6/22/2022 A-1 APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS This appendix contains the maintenance requirements for the following typical stormwater flow control and water quality facilities and on-site BMPs (ctrl/click the title to follow the link): No. 1 – Detention Ponds No. 2 – Infiltration Facilities No. 3 – Detention Tanks and Vaults No. 4 – Control Structure/Flow Restrictor No. 5 – Catch Basins and Manholes No. 6 – Conveyance Pipes and Ditches No. 7 – Debris Barriers (e.g., trash racks) No. 8 – Energy Dissipaters No. 9 – Fencing No. 10 – Gates/Bollards/Access Barriers No. 11 – Grounds (landscaping) No. 12 – Access Roads No. 13 – Basic Bioswale (grass) No. 14 – Wet Bioswale No. 15 – Filter Strip No. 16 – Wetpond No. 17 – Wetvault No. 18 – Stormwater Wetland No. 19 – Sand Filter Pond No. 20 – Sand Filter Vault No. 21 – Proprietary Facility Cartridge Filter Systems No. 22 – Baffle Oil/Water Separator No. 23 – Coalescing Plate Oil/Water Separator APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-2 No. 24 – Catch Basin Insert (not allowed in the city for oil control) No. 25 – Drywell BMP No. 26 – Gravel Filled Infiltration Trench BMP No. 27 – Gravel Filled Dispersion Trench BMP No. 28 – Native Vegetated Surface/Native Vegetated Landscape BMP No. 29 – Perforated Pipe Connections BMP No. 30 – Permeable Pavement BMP No. 31 – Bioretention BMP No. 32 – RainWater Harvesting BMP No. 33 – Rock Pad BMP No. 34 – Sheet Flow BMP No. 35 – Splash Block BMP No. 36 – Vegetated Roof BMP No. 37 – Rain Garden BMP No. 38 – Soil Amendment BMP No. 39 – Retained Trees No. 40 – Filterra System No. 41 – Compost Amended Vegetated Filter Strip (CAVFS) No. 42 – Media Filter Drain (MFD) No. 43 – Compost-Amended Biofiltration Swale 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-15 NO. 9 – FENCING MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Erosion or holes under fence Erosion or holes more than 4 inches high and 12-18 inches wide permitting access through an opening under a fence. No access under the fence. Wood Posts, Boards and Cross Members Missing or damaged parts Missing or broken boards, post out of plumb by more than 6 inches or cross members broken No gaps on fence due to missing or broken boards, post plumb to within 1½ inches, cross members sound. Weakened by rotting or insects Any part showing structural deterioration due to rotting or insect damage All parts of fence are structurally sound. Damaged or failed post foundation Concrete or metal attachments deteriorated or unable to support posts. Post foundation capable of supporting posts even in strong wind. Metal Posts, Rails and Fabric Damaged parts Post out of plumb more than 6 inches. Post plumb to within 1½ inches. Top rails bent more than 6 inches. Top rail free of bends greater than 1 inch. Any part of fence (including post, top rails, and fabric) more than 1 foot out of design alignment. Fence is aligned and meets design standards. Missing or loose tension wire. Tension wire in place and holding fabric. Deteriorated paint or protective coating Part or parts that have a rusting or scaling condition that has affected structural adequacy. Structurally adequate posts or parts with a uniform protective coating. Openings in fabric Openings in fabric are such that an 8-inch diameter ball could fit through. Fabric mesh openings within 50% of grid size. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 6/22/2022 2022 City of Renton Surface Water Design Manual A-16 NO. 10 – GATES/BOLLARDS/ACCESS BARRIERS MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Chain Link Fencing Gate Damaged or missing members Missing gate. Gates in place. Broken or missing hinges such that gate cannot be easily opened and closed by a maintenance person. Hinges intact and lubed. Gate is working freely. Gate is out of plumb more than 6 inches and more than 1 foot out of design alignment. Gate is aligned and vertical. Missing stretcher bar, stretcher bands, and ties. Stretcher bar, bands, and ties in place. Locking mechanism does not lock gate Locking device missing, non-functioning or does not link to all parts. Locking mechanism prevents opening of gate. Openings in fabric Openings in fabric are such that an 8-inch diameter ball could fit through. Fabric mesh openings within 50% of grid size. Bar Gate Damaged or missing cross bar Cross bar does not swing open or closed, is missing or is bent to where it does not prevent vehicle access. Cross bar swings fully open and closed and prevents vehicle access. Locking mechanism does not lock gate Locking device missing, non-functioning or does not link to all parts. Locking mechanism prevents opening of gate. Support post damaged Support post does not hold cross bar up. Cross bar held up preventing vehicle access into facility. Bollards Damaged or missing bollards Bollard broken, missing, does not fit into support hole or hinge broken or missing. No access for motorized vehicles to get into facility. Bollards do not lock Locking assembly or lock missing or cannot be attached to lock bollard in place. No access for motorized vehicles to get into facility. Boulders Dislodged boulders Boulders not located to prevent motorized vehicle access. No access for motorized vehicles to get into facility. Evidence of vehicles circumventing boulders Motorized vehicles going around or between boulders. No access for motorized vehicles to get into facility. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-17 NO. 11 – GROUNDS (LANDSCAPING) MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to 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 growth of grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Trees and Shrubs Hazard tree identified Any tree or limb of a tree identified as having a potential to fall and cause property damage or threaten human life. A hazard tree identified by a qualified arborist must be removed as soon as possible. No hazard trees in facility. Damaged tree or shrub identified Limbs or parts of trees or shrubs that are split or broken which affect more than 25% of the total foliage of the tree or shrub. Trees and shrubs with less than 5% of total foliage with split or broken limbs. Trees or shrubs that have been blown down or knocked over. No blown down vegetation or knocked over vegetation. Trees or shrubs free of injury. Trees or shrubs which are not adequately supported or are leaning over, causing exposure of the roots. Tree or shrub in place and adequately supported; dead or diseased trees removed. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2022 City of Renton Surface Water Design Manual 6/22/2022 A-47 NO. 38 – SOIL AMENDMENT BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Soil Media Unhealthy vegetation Vegetation not fully covering ground surface or vegetation health is poor. Yellowing: possible Nitrogen (N) deficiency. Poor growth: possible Phosphorous (P) deficiency. Poor flowering, spotting or curled leaves, or weak roots or stems: possible Potassium (K) deficiency. Plants are healthy and appropriate for site conditions Inadequate soil nutrients and structure In the fall, return leaf fall and shredded woody materials from the landscape to the site when possible Soil providing plant nutrients and structure Excessive vegetation growth Grass becomes excessively tall (greater than 10 inches); nuisance weeds and other vegetation start to take over. Healthy turf- “grasscycle” (mulch-mow or leave the clippings) to build turf health Weeds Preventive maintenance Avoid use of pesticides (bug and weed killers), like “weed & feed,” which damage the soil Fertilizer needed Where fertilization is needed (mainly turf and annual flower beds), a moderate fertilization program should be used which relies on compost, natural fertilizers or slow-release synthetic balanced fertilizers Integrated Pest Management (IPM) protocols for fertilization followed Bare spots Bare spots on soil No bare spots, area covered with vegetation or mulch mixed into the underlying soil. Compaction Poor infiltration due to soil compaction  To remediate compaction, aerate soil, till to at least 8-inch depth, or further amend soil with compost and re-till  If areas are turf, aerate compacted areas and top dress them with 1/4 to 1/2 inch of compost to renovate them  If drainage is still slow, consider investigating alternative causes (e.g., high wet season groundwater levels, low permeability soils)  Also consider site use and protection from compacting activities No soil compaction Poor infiltration Soils become waterlogged, do not appear to be infiltrating. Facility infiltrating properly Erosion/Scouring Erosion Areas of potential erosion are visible Causes of erosion (e.g., concentrate flow entering area, channelization of runoff) identified and damaged area stabilized (regrade, rock, vegetation, erosion control matting).For deep channels or cuts (over 3 inches in ponding depth), temporary erosion control measures in place until permanent repairs can be made Grass/Vegetation Unhealthy vegetation Less than 75% of planted vegetation is healthy with a generally good appearance. Healthy vegetation. Unhealthy plants removed/replaced. Appropriate vegetation planted in terms of exposure, soil and soil moisture. Noxious Weeds Noxious weeds Listed noxious vegetation is present (refer to current County noxious weed list). No noxious weeds present. ENGINEERED SOLUTIONS Modular Wetlands® Linear Operatons & Maintenance Manual 2 MMOODDUULLAARR WWEETTLLAANNDDSS LLIINNEEAARR OOPPEERRAATTIIOONN && MMAAIINNTTEENNAANNCCEE MMAANNUUAALL TTAABBLLEE OOFF CCOONNTTEENNTTSS OOvveerrvviieeww ........................................................................................................................................................................ 3 SSaaffeettyy NNoottiiccee && PPeerrssoonnaall SSaaffeettyy EEqquuiippmmeenntt ................................................................................................................. 4 MMoodduullaarr WWeettllaannddss LLiinneeaarr CCoommppoonneennttss LLiisstt ................................................................................................................. 5 IInnssppeeccttiioonn SSuummmmaarryy && EEqquuiippmmeenntt LLiisstt ......................................................................................................................... 6 IInnssppeeccttiioonn && MMaaiinntteennaannccee NNootteess .................................................................................................................................. 7 IInnssppeeccttiioonn PPrroocceessss ......................................................................................................................................................... 7 MMaaiinntteennaannccee IInnddiiccaattoorrss ................................................................................................................................................. 9 MMaaiinntteennaannccee SSuummmmaarryy && EEqquuiippmmeenntt LLiisstt..................................................................................................................... 9 MMaaiinntteennaannccee IInnssttrruuccttiioonnss .............................................................................................................................................11 RReeppllaacciinngg BBiiooffiillttrraattiioonn MMeeddiiaa iiff RReeqquuiirreedd ....................................................................................................................14 RReeppllaacciinngg DDrraaiinn DDoowwnn FFiilltteerr MMeeddiiaa ((OOnnllyy oonn OOllddeerr CCaalliiffoorrnniiaa MMooddeellss)) .....................................................................16 NNootteess .............................................................................................................................................................................17 IInnssppeeccttiioonn RReeppoorrtt .........................................................................................................................................................18 CClleeaanniinngg && MMaaiinntteennaannccee RReeppoorrtt ..................................................................................................................................19 3 OOVVEERRVVIIEEWW This operation and maintenance (O&M) manual is for the Modular Wetlands Linear Biofilter (MWL). Please read the instructions and equipment lists closely prior to starting. It is important to follow all necessary safety procedures associated with state and local regulations. Please contact Contech for more information on pre-authorized third-party service providers who can provide inspection and maintenance services in your area. For a list of service providers in your area, please visit www.conteches.com/maintenance. PPLLAACCEEHHOOLLDDEERR FFOORR MMAARRKKEETTIINNGG PPHHOOTTOO WWAARRNNIINNGG Confined space entry may be required. Contractor to obtain all equipment and training to meet applicable local and OSHA regulations regarding confined space entry. It is the Contractor’s or entry personnel’s responsibility to always proceed safely. 4 SSAAFFEETTYY NNOOTTIICCEE && PPEERRSSOONNAALL SSAAFFEETTYY EEQQUUIIPPMMEENNTT Job site safety is a topic and a practice addressed comprehensively by others. The inclusions here are merely reminders to whole areas of Safety Practice that are the responsibility of the Owner(s), Manager(s), and Service Provider(s). OSHA and Canadian OSH, Federal, State/Provincial, and Local Jurisdiction Safety Standards apply on any given site or project. The knowledge and applicability of those responsibilities is the Service Provider’s responsibility and outside the scope of Contech Engineered Solutions. Safety Boots Gloves Hard Hat Eye Protection Maintenance and Protection of Traffic Plan 5 MMOODDUULLAARR WWEETTLLAANNDDSS LLIINNEEAARR CCOOMMPPOONNEENNTTSS LLIISSTT The MWL system comes in multiple sizes and configurations, including side by side or end to end layouts, both as open planters or underground systems. See shop drawings (plans) for project specific details. The standard MWL system is comprised of the following components: 6 IINNSSPPEECCTTIIOONN SSUUMMMMAARRYY && EEQQUUIIPPMMEENNTT LLIISSTT Stormwater regulations require BMPs be inspected and maintained to ensure they are operating as designed to allow for effective pollutant removal and provide protection to receiving water bodies. It is recommended that inspections be performed multiple times during the first year to assess the site-specific loading conditions. The first year of inspections can be used to set inspection and maintenance intervals for subsequent years to ensure appropriate maintenance is provided. Inspect pre-treatment, biofiltration, and discharge chambers an average of once every six to twelve months. Varies based on site specific and local conditions. Average inspection time is approximately 15 minutes. Always ensure appropriate safety protocol and procedures are followed. The following is a list of equipment required to allow for simple and effective inspection of the MWL: Modular Wetlands Linear Inspection Form Flashlight Tape Measure Access Cover Hook Ratchet & 7/16” Socket (if required for older pre-filter cartridges that have two bolts holding the lids on) 7 IINNSSPPEECCTTIIOONN && MMAAIINNTTEENNAANNCCEE NNOOTTEESS 1.Following maintenance and/or inspection, it is recommended that the maintenance operator prepare a maintenance/inspection record. The record should include any maintenance activities performed, amount and description of debris collected, and condition of the system and its various filter mechanisms. 2.The owner should keep maintenance/inspection record(s) for a minimum of five years from the date of maintenance. These records should be made available to the governing municipality for inspection upon request at any time. 3.Transport all debris, trash, organics, and sediments to approved facility for disposal in accordance with local and state requirements. 4.Entry into chambers may require confined space training based on state and local regulations. 5.No fertilizer shall be used in the biofiltration chamber. 6.Irrigation should be provided as recommended by manufacturer and/or landscape architect. Amount of irrigation required is dependent on plant species. Some plants may not require irrigation after initial establishment. IINNSSPPEECCTTIIOONN PPRROOCCEESSSS 1.Prepare the inspection form by writing in the necessary information including project name, location, date & time, unit number and other information (see inspection form). 2.Observe the inside of the system through the access covers. If minimal light is available and vision into the unit is impaired, utilize a flashlight to see inside the system and all chambers. 3.Look for any out of the ordinary obstructions in the inflow pipe, pre-treatment chamber, biofiltration chamber, discharge chamber or outflow pipe. Write down any observations on the inspection form. 4.Through observation and/or digital photographs, estimate the amount of trash, debris accumulated in the pre- treatment chamber. Utilizing a tape measure or measuring stick, estimate the amount of sediment in this chamber. Record this depth on the inspection form. 5.Through visual observation, inspect the condition of the pre-filter cartridges. Look for excessive build-up of sediment on the cartridges, any build-up on the tops of the cartridges, or clogging of the holes. Record this information on the inspection form. The pre-filter cartridges can be further inspected by removing the cartridge tops and assessing the color of the BioMediaGREEN filter cubes (requires entry into pre-treatment chamber - see notes previous notes regarding confined space entry). Record the color of the material. New material is a light green color. As the media becomes clogged, it will turn darker in color, eventually becoming dark brown or black. The closer to black the media is the higher percentage that the media is exhausted and in need of replacement. 8 6.The biofiltration chamber is generally maintenance-free due to the system’s advanced pre-treatment chamber. For units which have open planters with vegetation, it is recommended that the vegetation be inspected. Look for any plants that are dead or showing signs of disease or other negative stressors. Record the general health of the plants on the inspection form and indicate through visual observation or digital photographs if trimming of the vegetation is required. 7.The discharge chamber houses the control riser (if applicable), drain down filter (only in California - older models), and is connected to the outflow pipe. It is important to check to ensure the orifice is in proper operating condition and free of any obstructions. It is also important to assess the condition of the drain down filter media which utilizes a block form of the BioMediaGREEN. Assess in the same manner as the cubes in the pre-filter cartridge as mentioned above. 8.Finalize the inspection report for analysis by the maintenance manager to determine if maintenance is required. 9 MMAAIINNTTEENNAANNCCEE IINNDDIICCAATTOORRSS Based upon the observations made during inspection, maintenance of the system may be required based on the following indicators: Missing or damaged internal components or cartridges. Obstructions in the system or its inlet and/or outlet pipes. Excessive accumulation of floatables in the pre-treatment chamber in which the length and width of the chamber is fully impacted more than 18”. Excessive accumulation of sediment in the pre-treatment chamber of more than 6” in depth. Excessive accumulation of sediment on the BioMediaGREEN media housed within the pretreatment cartridges. When media is more than 85% clogged, replacement is required. The darker the BioMediaGREEN, the more clogged it is and in need of replacement. Excessive accumulation of sediment on the BioMediaGREEN media housed within the drain down filter (California only - older models). Overgrown vegetation. MMAAIINNTTEENNAANNCCEE SSUUMMMMAARRYY && EEQQUUIIPPMMEENNTT LLIISSTT The time has come to maintain your MWL. All necessary pre-maintenance steps must be carried out before maintenance occurs. Once traffic control has been set up per local and state regulations and access covers have been safely opened, the maintenance process can begin. It should be noted that some maintenance activities require confined space entry. All confined space requirements must be strictly followed before entry into the system. In addition, the following is recommended: Prepare the maintenance form by writing in the necessary information including project name, location, date & time, unit number and other info (see maintenance form). Set up all appropriate safety and maintenance equipment. Ensure traffic control is set up and properly positioned. Prepared pre-checks (OSHA, safety, confined space entry) are performed. o A gas meter should be used to detect the presence of any hazardous gases prior to entering the system. If hazardous gases are present, do not enter the vault. Following appropriate confined space procedures, take steps such as utilizing a venting system to address the hazard. Once it is determined to be safe, enter the system utilizing appropriate entry equipment such as a ladder and tripod with harness. 10 The following is a list of equipment required for maintenance of the MWL: Modular Wetlands Linear Maintenance Form Flashlight Access Cover Hook Ratchet & 7/16” Socket (if required for older pre-filter cartridges that have two bolts holding the lids on) Vacuum Assisted Truck with Pressure Washer Replacement BioMediaGREEN (If Required) (order BioMediaGREEN from Contech’s Maintenance Team members at https://www.conteches.com/maintenance) 11 MMAAIINNTTEENNAANNCCEE IINNSSTTRRUUCCTTIIOONNSS 11..AACCCCEESSSS CCOOVVEERR RREEMMOOVVAALL Upon determining that the vault is safe for entry, remove all access cover(s) and position the vacuum truck accordingly. 22..PPRREESSSSUURREE WWAASSHH SSYYSSTTEEMM CCHHAAMMBBEERRSS With the pressure washer, spray down pollutants accumulated on the walls and floors of the pre- treatment and discharge chambers. Then wash any accumulated sediment from the pre-filter cartridge(s). 33..VVAACCUUUUMM SSYYSSTTEEMM CCHHAAMMBBEERRSS Vacuum out pre-treatment and discharge chambers and remove all accumulated pollutants including trash, debris, and sediments. Be sure to vacuum the pre- treatment floor until the pervious pavers are visible and clean.((MMWWLL ssyysstteemmss oouuttssiiddee ooff CCaalliiffoorrnniiaa mmaayy oorr mmaayy nnoott hhaavvee ppeerrvviioouuss ppaavveerrss oonn tthhee fflloooorr iinn tthhee pprree-- ttrreeaattmmeenntt cchhaammbbeerr)) If pre-filter cartridges require media replacement, proceed to SStteepp 44. If not, replace the access cover(s) and proceed to SStteepp 77. 12 44..PPRREE--FFIILLTTEERR CCAARRTTRRIIDDGGEE LLIIDD RREEMMOOVVAALL After successfully cleaning out the pre-treatment chamber, enter the chamber and remove the lid(s) from the pre-filter cartridge(s) by removing the two thumb screws. (Older pre-filter cartridges have two bolts holding the lids on that require a 7/16” socket to remove) 55..VVAACCUUUUMM EEXXIISSTTIINNGG PPRREE--FFIILLTTEERR MMEEDDIIAA Utilize the vacuum truck hose or hose extension to remove the filter media from each of the individual media cages. Once filter media has been sucked out, use a pressure washer to spray down the inside of the cartridge and its media cages. Remove cleaned media cages and place to the side. Once removed, the vacuum hose can be inserted into the cartridge to vacuum out any remaining material near the bottom of the cartridge. 66..PPRREE--FFIILLTTEERR MMEEDDIIAA RREEPPLLAACCEEMMEENNTT Reinstall media cages and fill with new media from the manufacturer or outside supplier. Manufacturer will provide specification of media and sources to purchase. The easiest way to fill the media cages is to utilize a refilling tray that can also be sourced from the manufacturer. Place the refilling tray on top of the cartridge and fill with new bulk media shaking it down into the cages. Using your hands, lightly compact the media into each filter cage. Once the cages are full (each cartridge will hold five heaping 5gal buckets of bulk media),remove the refilling tray and replace the cartridge top, ensuring fasteners are properly tightened. 13 77..MMAAIINNTTAAIINNIINNGG VVEEGGEETTAATTIIOONN In general, the biofiltration chamber is maintenance-free with the exception of maintaining the vegetation. The MWL utilizes vegetation similar to surrounding landscape areas, therefore, trim vegetation to match surrounding vegetation. If any plants have died, replace them with new ones. 88..IINNSSPPEECCTT UUNNDDEERRDDRRAAIINN SSYYSSTTEEMM Each vertical under drain on the biofiltration chamber has a removable threaded cap that can be taken off to check for any blockages or root growth. Once removed, a jetting attachment to the pressure washer can be used to clean out the under drain and orifice riser if needed. 99..RREEPPLLAACCEE AACCCCEESSSS CCOOVVEERRSS Once maintenance is complete, replace all access cover(s) 14 RREEPPLLAACCIINNGG BBIIOOFFIILLTTRRAATTIIOONN MMEEDDIIAA IIFF RREEQQUUIIRREEDD As with all biofilter systems, at some point the biofiltration media will need to be replaced, either due to physical clogging or sorptive exhaustion (for dissolved pollutants) of the media ion exchange capacity (to remove dissolved metals and phosphorous). The general life of this media is 10 to 20 years based on site specific conditions and pollutant loading, so replacing the biofiltration media should not be a common occurrence. In the event that the biofiltration media requires replacement, contact one of Contech’s Maintenance Team members at https://www.conteches.com/maintenance to order new biofiltration media. The quantity of media needed can be determined by providing the model number and unit depth. Media will be provided in super sacks for easy installation. Each sack will weigh between 1,000 and 2,000 lbs. Biofiltration media replacement can be done following the steps below: 11..VVAACCUUUUMM EEXXIISSTTIINNGG BBIIOOFFIILLTTRRAATTIIOONN MMEEDDIIAA Remove the mulch and vegetation to access the biofiltration media, and then position the vacuum truck accordingly. Utilize the vacuum truck to vacuum out all the media. Once all media is removed, use the pressure washer to spray down all the netting and underdrain systems on the inside of the media containment cage. Vacuum out any remaining debris after spraying down netting. Inspect the netting for any damage or holes. If the netting is damaged, it can be repaired or replaced with guidance by the manufacturer. 22..IINNSSTTAALLLLIINNGG NNEEWW BBIIOOFFIILLTTRRAATTIIOONN MMEEDDIIAA Ensure that the chamber is fully cleaned prior to installation of new media into the media containment cage(s). Media will be provided in super sacks for easy installation. A lifting apparatus (forklift, backhoe, boom truck, or other) is recommended to position the super sack over the biofiltration chamber. Add media in lifts to ensure that the riser pipes remain vertical. Be sure to only fill the media cage(s) up to the same level as the old media. 15 33..RREEPPLLAANNTT VVEEGGEETTAATTIIOONN Once the media has been replaced, replant the vegetation and cover biofiltration chamber with approved mulch (if applicable). If the existing vegetation is not being reused, and new vegetation is being planted, you will need to acquire new plant establishment media that will be installed just below the mulch layer at each plant location. (see plan drawings for details). Contact one of Contech’s Maintenance Team members at https://www.conteches.com/maintenance to order new plant establishment media. 16 RREEPPLLAACCIINNGG DDRRAAIINN DDOOWWNN FFIILLTTEERR MMEEDDIIAA ((OONNLLYY OONN OOLLDDEERR CCAALLIIFFOORRNNIIAA MMOODDEELLSS)) NOTE: The drain down filter is only found on units installed in California prior to 2023 If during inspection it was determined that the drain down filter media requires replacement, contact one of Contech’s Maintenance Team members at https://www.conteches.com/maintenance to order new media. 11..RREEMMOOVVEE EEXXIISSTTIINNGG DDRRAAIINN DDOOWWNN MMEEDDIIAA Pull knob back to unlock the locking mechanism and lift the drain down filter housing to remove the used BioMediaGREEN filter block. 22..IINNSSTTAALLLL NNEEWW DDRRAAIINN DDOOWWNN MMEEDDIIAA Ensure that the chamber and housing are fully cleaned prior to installation of new media, and then insert the new BioMediaGREEN filter block. The media filter block should fit snugly between the chamber walls and be centered under the filter housing. Lower the housing over the filter block and secure the locking mechanism. 17 NOTES _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ 18 For Office Use Only (city)(Zip Code)(Reviewed By) Owner / Management Company (Date) Contact Phone ( )_ Inspector Name Date //Time AM / PM Weather Condition Additional Notes Yes Depth: Yes No Modular Wetland System Type (Curb, Grate or UG Vault):Size (22', 14' or etc.): Other Inspection Items: Storm Event in Last 72-hours? No YesType of Inspection Routine Follow Up Complaint Storm Office personnel to complete section to the left. Inspection Report Modular Wetlands Linear Is the filter insert (if applicable) at capacity and/or is there an accumulation of debris/trash on the shelf system? Does the cartridge filter media need replacement in pre-treatment chamber and/or discharge chamber? Any signs of improper functioning in the discharge chamber? Note issues in comments section. Chamber: Is the inlet/outlet pipe or drain down pipe damaged or otherwise not functioning properly? Structural Integrity: Working Condition: Is there evidence of illicit discharge or excessive oil, grease, or other automobile fluids entering and clogging the unit? Is there standing water in inappropriate areas after a dry period? Damage to pre-treatment access cover (manhole cover/grate) or cannot be opened using normal lifting pressure? Damage to discharge chamber access cover (manhole cover/grate) or cannot be opened using normal lifting pressure? Does the MWS unit show signs of structural deterioration (cracks in the wall, damage to frame)? Project Name Project Address Inspection Checklist CommentsNo Does the depth of sediment/trash/debris suggest a blockage of the inflow pipe, bypass or cartridge filter? If yes, specify which one in the comments section. Note depth of accumulation in in pre-treatment chamber. Is there a septic or foul odor coming from inside the system? Is there an accumulation of sediment/trash/debris in the wetland media (if applicable)? Is it evident that the plants are alive and healthy (if applicable)? Please note Plant Information below. Sediment / Silt / Clay Trash / Bags / Bottles Green Waste / Leaves / Foliage Waste:Plant Information No Cleaning Needed Recommended Maintenance Additional Notes: Damage to Plants Plant Replacement Plant Trimming Schedule Maintenance as Planned Needs Immediate Maintenance ENGINEERED SOLUTIONS 19 For Office Use Only (city)(Zip Code)(Reviewed By) Owner / Management Company (Date) Contact Phone ( )_ Inspector Name Date //Time AM / PM Weather Condition Additional Notes Site Map # Comments: Inlet and Outlet Pipe Condition Drain Down Pipe Condition Discharge Chamber Condition Drain Down Media Condition Plant Condition Media Filter Condition Long: MWS Sedimentation Basin Total Debris Accumulation Condition of Media 25/50/75/100 (will be changed@ 75%) Operational Per Manufactures' Specifications (If not, why?) Lat:MWS Catch Basins GPS Coordinates of Insert Manufacturer / Description / Sizing Trash Accumulation Foliage Accumulation Sediment Accumulation Type of Inspection Routine Follow Up Complaint Storm Storm Event in Last 72-hours? No Yes Office personnel to complete section to the left. Project Address Project Name Cleaning and Maintenance Report Modular Wetlands LinearENGINEERED SOLUTIONS SUPPORT DRAWINGS AND SPECIFICATIONS ARE AVAILABLE AT WWW.CONTECHES.COM © 2024 CONTECH ENGINEERED SOLUTIONS LLC, A QUIKRETE COMPANY 800-338-1122 WWW.CONTECHES.COM ALL RIGHTS RESERVED. PRINTED IN THE USA. CONTECH ENGINEERED SOLUTIONS LLC PROVIDES SITE SOLUTIONS FOR THE CIVIL ENGINEERING INDUSTRY. CONTECH’S PORTFOLIO INCLUDES BRIDGES, DRAINAGE, SANITARY SEWER, STORMWATER AND EARTH STABILIZATION PRODUCTS. FOR INFORMATION ON OTHER CONTECH DIVISION OFFERINGS, VISIT CONTECHES.COM OR CALL 800-338-1122. ModWetLinear OM Manual 03/24 NOTHING IN THIS CATALOG SHOULD BE CONSTRUED AS A WARRANTY. APPLICATIONS SUGGESTED HEREIN ARE DESCRIBED ONLY TO HELP READERS MAKE THEIR OWN EVALUATIONS AND DECISIONS, AND ARE NEITHER GUARANTEES NOR WARRANTIES OF SUITABILITY FOR ANY APPLICATION. CONTECH MAKES NO WARRANTY WHATSOEVER, EXPRESS OR IMPLIED, RELATED TO THE APPLICATIONS, MATERIALS, COATINGS, OR PRODUCTS DISCUSSED HEREIN. ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND ALL IMPLIED WARRANTIES OF FITNESS FOR ANY PARTICULAR PURPOSE ARE DISCLAIMED BY CONTECH. SEE CONTECH’S CONDITIONS OF SALE (AVAILABLE AT WWW.CONTECHES.COM/COS) FOR MORE INFORMATION. ENGINEERED SOLUTIONS RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 18 10. FIGURES FIGURE 1 – TIR WORKSHEET FIGURE 2 – VICINITY MAP FIGURE 3 – EXISTING CONDITIONS FIGURE 4 – PROPOSED CONDITIONS FIGURE 5 – NEW AND REPLACED IMPERVIOUS AREAS FIGURE 6 – PROJECT MINIMUM REQUIREMENTS FLOW CHART FIGURE 7 – OFFSITE DRAINAGE FIGURE 8 – 100 YEAR FLOODPLAIN FIGURE 9 – SOILS MAP CITY OF RENTON SURFACE WATER DESIGN MANUAL 2022 City of Renton Surface Water Design Manual 6/22/2022 8-A-1 REFERENCE 8-A TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner _____________________________ Phone ___________________________________ Address __________________________________ _________________________________________ Project Engineer ___________________________ Company _________________________________ Phone ___________________________________ Project Name __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS  Land Use (e.g., Subdivision / Short Subd.)  Building (e.g., M/F / Commercial / SFR)  Grading  Right-of-Way Use  Other _______________________  DFW HPA  COE 404  DOE Dam Safety  FEMA Floodplain  COE Wetlands  Other ________  Shoreline Management  Structural Rockery/Vault/_____  ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (check one): Date (include revision dates): Date of Final:  Full  Targeted  Simplified  Large Project  Directed __________________ __________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final:  Full  Modified  Simplified __________________ __________________ __________________ FIGURE 1: TIR WORKSHEET Renton School District (206) 482-5253 7812 South 124th Street Seattle, WA 98178 Sascha Eastman Jacobson Consulting Engineers (206) 426-2600 Renton School District Transportation Expansion 410 Park Ave N Renton, WA 98057 23N 5E 08 N/A 10/18/2024 TBD 10/18/2024 TBD REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: _____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS  River/Stream ________________________  Lake ______________________________  Wetlands ____________________________  Closed Depression ____________________  Floodplain ___________________________  Other _______________________________ _______________________________  Steep Slope __________________________  Erosion Hazard _______________________  Landslide Hazard ______________________  Coal Mine Hazard ______________________  Seismic Hazard _______________________  Habitat Protection ______________________  _____________________________________ FIGURE 1: TIR WORKSHEET N/A N/A N/A Cedar River N/A N/A N/A N/A REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 9 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Holocene Alluvium 0% - 5%Moderate N/A Cedar River Drainage Basin FIGURE 1: TIR WORKSHEET 1 N/A TBD TBD TBD #1: < 0.15 cfs flow increase 2/16/2022 Peak Rate Standard REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ On-site BMPs Describe: Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): _______________ Datum: Flood Protection Facilities Describe: Source Control (commercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-Use Site: Yes / No Treatment BMP: _________________________________ Maintenance Agreement: Yes / No with whom? _____________________________________ Other Drainage Structures Describe: FIGURE 1: TIR WORKSHEET N/A N/A N/A REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2022 City of Renton Surface Water Design Manual 6/22/2022 Ref 8-A-5 Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION  Clearing Limits  Cover Measures  Perimeter Protection  Traffic Area Stabilization  Sediment Retention  Surface Water Collection  Dewatering Control  Dust Control  Flow Control  Control Pollutants  Protect Existing and Proposed BMPs/Facilities  Maintain Protective BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent BMPs/Facilities, restore operation of BMPs/Facilities as necessary  Flag limits of sensitive areas and open space preservation areas  Other _______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Description Water Quality Description On-site BMPs Description  Detention  Infiltration  Regional Facility  Shared Facility  Other _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  Other _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________  Full Dispersion  Full Infiltration  Limited Infiltration  Rain Gardens  Bioretention  Permeable Pavement  Basic Dispersion  Soil Amendment  Perforated Pipe Connection  Other _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ FIGURE 1: TIR WORKSHEET N/A N/A Modular Wetland N/A N/A REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 6/22/2022 2022 City of Renton Surface Water Design Manual 8-A-6 Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS  Drainage Easement  Covenant  Native Growth Protection Covenant  Tract  Other ____________________________  Cast in Place Vault  Retaining Wall  Rockery > 4′ High  Structural on Steep Slope  Other _______________________________ Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. ____________________________________________________________________________________ Signed/Date FIGURE 1: TIR WORKSHEET N/A N/A 10/18/2024 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.399.6233 | JACOBSONENGINEERS.COM206.426.2600 FIGURE 2: VICINITY MAPSCALE: NTS Project Site Project Site FIGURE 3: EXISTING CONDITIONS SCALE 1" = 40' 0 20 40 80 Existing Conditions Description Quantity Unit Impervious Surface 0.297 ac Landscape 0.211 ac X X X XX X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X XXXXX X X X X X X X X X X SCALE 1" = 40' 0 20 40 80 FIGURE 4: PROPOSED CONDITIONS Proposed Conditions Description Quantity Unit Impervious Surface 0.378 ac Landscape 0.130 ac New and Replaced Impervious Areas Description Quantity Unit New Impervious 0.147 ac Replaced Impervious 0.231 ac X X X XX X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X XXXXX X X X X X X X X X X FIGURE 5: NEW AND REPLACED IMPERVIOUS AREAS SCALE 1" = 40' 0 20 40 80 FIGURE 6: PROJECT MINIMUM REQUIREMENTS FLOWCHART FIGURE 7: OFFSITE ANALYSIS PROJECT SITE 1/4 MILE DOWNSTREAM DISCHARGES TO CEDAR RIVER FIGURE 8: 100 YR FLOODPLAIN PROJECT SITE FEMA FLOOD MAP 53033C0977G FIGURE 9: SOILS MAP 9 Custom Soil Resource Report Soil Map 52 5 9 8 6 0 52 5 9 8 7 0 52 5 9 8 8 0 52 5 9 8 9 0 52 5 9 9 0 0 52 5 9 9 1 0 52 5 9 9 2 0 525 9 9 3 0 52 5 9 9 4 0 525 9 9 5 0 52 5 9 9 6 0 525 9 8 6 0 52 5 9 8 7 0 525 9 8 8 0 52 5 9 8 9 0 525 9 9 0 0 52 5 9 9 1 0 525 9 9 2 0 52 5 9 9 3 0 525 9 9 4 0 52 5 9 9 5 0 525 9 9 6 0 560080 560090 560100 560110 560120 560130 560140 560150 560160 560080 560090 560100 560110 560120 560130 560140 560150 560160 47° 29' 25'' N 12 2 ° 1 2 ' 8 ' ' W 47° 29' 25'' N 12 2 ° 1 2 ' 4 ' ' W 47° 29' 21'' N 12 2 ° 1 2 ' 8 ' ' W 47° 29' 21'' N 12 2 ° 1 2 ' 4 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS840 25 50 100 150 Feet0 5 10 20 30 MetersMap Scale: 1:532 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation ServiceWeb Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 19, Aug 29, 2023 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 31, 2022—Aug 8, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI Ur Urban land 0.9 100.0% Totals for Area of Interest 0.9 100.0% RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 19 11. APPENDICES APPENDIX A – BOND QUANTITY WORKSHEET APPENDIX B – STORMWATER CALCULATIONS APPENDIX C – STORMWATER POLLUTION PREVENTION PLAN (SWPPP) APPENDIX D – FACILITY SUMMARY SHEET, DECLARATION OF COVENANT RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 20 APPENDIX A BOND QUANTITY WORKSHEET (TO BE PROVIDED IN A FORTHCOMING SUBMITTAL) RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 21 APPENDIX B STORMWATER CALCULATIONS ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.64 Program License Number: 201910001 Project Simulation Performed on: 10/18/2024 10:43 AM Report Generation Date: 10/18/2024 10:44 AM ————————————————————————————————— Input File Name: RSDTE_100YR.fld Project Name: RSD Transportation Expansion Analysis Title: 100-yr storm comparison Ex vs Dev Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 14 Precipitation Station : 96003605 Puget East 36 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961036 Puget East 36 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.508 0.508 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.508 0.508 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Predeveloped ---------- -------Area (Acres) -------- C, Lawn, Flat 0.211 PARKING/FLAT 0.297 FLOW CONTROL EXCEPTION CALCULATIONS ---------------------------------------------- Subbasin Total 0.508 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Post Developed ---------- -------Area (Acres) -------- C, Lawn, Flat 0.130 PARKING/FLAT 0.378 ---------------------------------------------- Subbasin Total 0.508 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Outflow Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Predeveloped 24.309 _____________________________________ Total: 24.309 FLOW CONTROL EXCEPTION CALCULATIONS Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Post Developed 14.977 Link: Outflow 0.000 _____________________________________ Total: 14.977 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.154 ac-ft/year, Post Developed: 0.095 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Outflow ********** 2-Year Discharge Rate : 0.152 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.05 cfs Off-line Design Discharge Rate (91% Exceedance): 0.03 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 169.24 Inflow Volume Including PPT-Evap (ac-ft): 169.24 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 169.24 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Predeveloped Scenario Postdeveloped Compliance Link: Outflow *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- FLOW CONTROL EXCEPTION CALCULATIONS 2-Year 0.126 2-Year 0.152 5-Year 0.169 5-Year 0.199 10-Year 0.197 10-Year 0.239 25-Year 0.262 25-Year 0.303 50-Year 0.352 50-Year 0.393 100-Year 0.422 100-Year 0.481 200-Year 0.447 200-Year 0.517 500-Year 0.479 500-Year 0.564 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals FLOW INCREASE IS LESS THAN 0.15 CFS FLOW CONTROL EXCEPTION CALCULATIONS ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.59 Program License Number: 201910001 Project Simulation Performed on: 08/29/2024 2:56 PM Report Generation Date: 08/29/2024 2:56 PM ————————————————————————————————— Input File Name: 2024-08-29 RSD Transportation Expansion TESC Sizing.fld Project Name: RSD Transportation Expansion Analysis Title: TESC Sizing Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 16 Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.470 0.470 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.470 0.470 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- C, Forest, Flat 0.470 ---------------------------------------------- TESC - SEDIMENTATION TANK SIZING CALCULATIONS Subbasin Total 0.470 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- SIDEWALKS/FLAT 0.470 ---------------------------------------------- Subbasin Total 0.470 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 0 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 89.444 _____________________________________ Total: 89.444 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 0.000 _____________________________________ Total: 0.000 Total Predevelopment Recharge is Greater than Post Developed TESC - SEDIMENTATION TANK SIZING CALCULATIONS Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.566 ac-ft/year, Post Developed: 0.000 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Subbasin: Subbasin 1 *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 1.183E-02 2-Year 0.193 5-Year 1.865E-02 5-Year 0.249 10-Year 2.319E-02 10-Year 0.293 25-Year 3.195E-02 25-Year 0.367 50-Year 3.509E-02 50-Year 0.440 100-Year 3.803E-02 100-Year 0.547 200-Year 5.630E-02 200-Year 0.583 500-Year 8.085E-02 500-Year 0.629 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals TESC - SEDIMENTATION TANK SIZING CALCULATIONS Proposed Runoff Conditions for TESC - Entire Site Total Site:Area (ac) Pervious Area 0.000 Impervious Area 0.470 Total Area 0.470 Stormshed Data Type Reduced Time Step 15-min MGS - Flood 2-Yr developed flow 0.193 cfs MGS - Flood 10-Yr developed flow 0.293 cfs MGS - Flood 25-Yr developed flow 0.367 cfs MGS - Flood 100-Yr developed flow 0.547 cfs Vr=S.A. x 3.5'Vr = Minimum Required Storage Volume S.A. = Minimum allowable top surface area of pond S.A. = (2Q2)/Vsed Q = design peak flow rate Vsed = 0.00096 Settling Velocity (0.00096 ft/sec) Q=0.193 cfs INPUT (note that this is the 10-yr design peak flow rate in cfs) S.A. = 402 sf Vr=1407 cf Volume Required 10,527 gal 1 sediment storage tanks are required. * the volume is based a minimum pond depth of 3.5' - this depth does not include the minimum sediment storage volume or freeboard Assume 18,900 gallons per sediment storage tank, then Temporary Sediment Trap Sizing: Storage Volume per Section D.2.1.5, ESC Measures: Selection of the Design Storm of the 2021 King County Surface Water Design Manual - Appendix D: 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 22 APPENDIX C STORMWATER POLLUTION PREVENTION PLAN (SWPPP) Construction Stormwater General Permit (CSWGP) Stormwater Pollution Prevention Plan (SWPPP) for RSD Transportation Expansion Prepared for: Renton School District Capital Planning & Construction Permittee / Owner Developer Operator / Contractor Renton School District Renton School District TBD 420 Park Ave N, Renton, WA 98057 Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number TBD TBD TBD SWPPP Prepared By Name Organization Contact Phone Number Sascha Eastman Jacobson Consulting Engineers Office: (206) 426-2600 SWPPP Preparation Date 10/18/2024 Project Construction Dates Activity / Phase Start Date End Date Sitework and Building Construction June 1, 2025 September 30, 2025 Page | 1 Table of Contents 1. Project Information .......................................................................................................................... 4 1.1 Existing Conditions ......................................................................................................................... 4 1.2 Proposed Construction Activities .................................................................................................... 5 2. Construction Stormwater Best Management Practices (BMPs) .................................................... 6 2.1 The 13 Elements ............................................................................................................................. 6 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits ........................................................... 6 2.1.2 Element 2: Establish Construction Access ............................................................................... 7 2.1.3 Element 3: Control Flow Rates ................................................................................................. 8 2.1.4 Element 4: Install Sediment Controls ........................................................................................9 2.1.5 Element 5: Stabilize Soils ........................................................................................................10 2.1.6 Element 6: Protect Slopes........................................................................................................11 2.1.7 Element 7: Protect Drain Inlets ................................................................................................12 2.1.8 Element 8: Stabilize Channels and Outlets .............................................................................13 2.1.9 Element 9: Control Pollutants ..................................................................................................14 2.1.10 Element 10: Control Dewatering .............................................................................................17 2.1.11 Element 11: Maintain BMPs ....................................................................................................18 2.1.12 Element 12: Manage the Project .............................................................................................19 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs ....................................................22 3. Pollution Prevention Team .............................................................................................................23 4. Monitoring and Sampling Requirements ........................................................................................24 4.1 Site Inspection ...............................................................................................................................24 4.2 Stormwater Quality Sampling ........................................................................................................24 4.2.1 Turbidity Sampling ..................................................................................................................24 4.2.2 pH Sampling ...........................................................................................................................27 5. Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies ....................................28 5.1 303(d) Listed Waterbodies .............................................................................................................28 5.2 TMDL Waterbodies .......................................................................................................................28 6. Reporting and Record Keeping ......................................................................................................29 6.1 Record Keeping .............................................................................................................................29 6.1.1 Site Log Book ..........................................................................................................................29 6.1.2 Records Retention ..................................................................................................................29 6.1.3 Updating the SWPPP ..............................................................................................................29 6.2 Reporting .......................................................................................................................................30 6.2.1 Discharge Monitoring Reports .................................................................................................30 6.2.2 Notification of Noncompliance .................................................................................................30 Page | 2 List of Tables Table 1 – Summary of Site Pollutant Constituents ....................................................................... 5 Table 2 – Pollutants .....................................................................................................................14 Table 3 – pH-Modifying Sources .................................................................................................15 Table 4 – Dewatering BMPs ........................................................................................................17 Table 5 – Management ................................................................................................................19 Table 6 – BMP Implementation Schedule ....................................................................................20 Table 7 – Team Information .........................................................................................................23 Table 8 – Turbidity Sampling Method ..........................................................................................24 Table 9 – pH Sampling Method ...................................................................................................27 List of Appendices A. Site Map B. BMP Details C. Correspondence (N/A) D. Site Inspection Form E. Construction Stormwater General Permit (CSWGP) (N/A) F. 303(d) List Waterbodies / TMDL Waterbodies Information (N/A) G. Contaminated Site Information (N/A) H. Engineering Calculations Page | 3 List of Acronyms and Abbreviations Acronym / Abbreviation Explanation 303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies BFO Bellingham Field Office of the Department of Ecology BMP(s) Best Management Practice(s) CESCL Certified Erosion and Sediment Control Lead CO2 Carbon Dioxide CRO Central Regional Office of the Department of Ecology CSWGP Construction Stormwater General Permit CWA Clean Water Act DMR Discharge Monitoring Report DO Dissolved Oxygen Ecology Washington State Department of Ecology EPA United States Environmental Protection Agency ERO Eastern Regional Office of the Department of Ecology ERTS Environmental Report Tracking System ESC Erosion and Sediment Control GULD General Use Level Designation NPDES National Pollutant Discharge Elimination System NTU Nephelometric Turbidity Units NWRO Northwest Regional Office of the Department of Ecology pH Power of Hydrogen RCW Revised Code of Washington SPCC Spill Prevention, Control, and Countermeasure su Standard Units SWMMEW Stormwater Management Manual for Eastern Washington SWMMWW Stormwater Management Manual for Western Washington SWPPP Stormwater Pollution Prevention Plan TESC Temporary Erosion and Sediment Control SWRO Southwest Regional Office of the Department of Ecology TMDL Total Maximum Daily Load VFO Vancouver Field Office of the Department of Ecology WAC Washington Administrative Code WSDOT Washington Department of Transportation WWHM Western Washington Hydrology Model Page | 4 1 Project Information Project/Site Name: Renton Schol District Transportation Street/Location: 420 Park Ave N City: Renton State: WA Zip code: 98057 Subdivision: N/A Receiving waterbody: Puget Sound 1.1 Existing Conditions The project for the Renton School District Transportation is located at 420 Park Ave N, Renton, WA, 98057 on the property of the Renton School District. The area within the district’s property boundary includes three parcels. Parcel 1 (7564600105) which is 4.76 acres, parcel 2 (7224000675) which is 0.28 acres, and parcel 3 (7224000676) which is 0.17 acres. The parcels are completely developed and combined and are roughly rectangular. The property consists of the Renton School District Transportation Administration building, paved employee parking, paved bus parking, and adjacent landscaping surrounding the parking areas. The property slopes mildly to the north with approximately 3 feet of elevation change across the entire site. Total acreage: 5.21-acre Disturbed acreage: 0.48-acre Landscape topography: In general, the site topography of the Renton School District Transportation property is mild, and slopes to the north with an elevation change of approximately 3 vertical feet. Drainage patterns: Stormwater from the project site flows northwest except for a small portion that drains at the southwest corner. From the site to the north, water is taken offsite and enters the municipal system on N 5th Street. From 5th Street, it connects to Burnett Avenue N and then onto 6th Street N. The stormwater then connects to an outfall into the Cedar River which eventually drains into Lake Washington. Existing Vegetation: The entire site is developed, and the only vegetation exists in small, landscaped areas along the paved parking areas. Critical Areas: There are no critical areas in the vicinity of the proposed project work. List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: The project discharges to the Cedar River with no known TMDL and is not 303(d) listed. Page | 5 Table 1 below includes a list of suspected and/or known contaminants associated with the construction activity. Table 1 – Summary of Site Pollutant Constituents Constituent (Pollutant) Location Depth Concentration Oil and Grease Parking Lot Surface Typical concentration from parking lots Total Suspended Solids Buildings and Parking Lots Surface N/A pH Newly installed concrete areas Surface N/A 1.2 Proposed Construction Activities Description of site development: The proposed project consists of removing existing driveways, redeveloping and expanding the northwest parking lot Description of construction activities (example: site preparation, demolition, excavation): The project will consist of site preparation, demolition, paving, stormwater and electrical utility installation, and various landscaping elements. Description of site drainage including flow from and onto adjacent properties. Must be consistent with Site Map in Appendix A: Stormwater from the project site flows northwest except for a small portion that drains at the southwest corner. From the site to the north, water is taken offsite and enters the municipal system on N 5th Street. From 5th Street, it connects to Burnett Avenue N and then onto 6th Street N. The stormwater then connects to an outfall into the Cedar River which eventually drains into Lake Washington. Description of final stabilization (example: extent of revegetation, paving, landscaping): At final stabilization, the project will include a redeveloped parking lot expansion with asphalt and concrete pavements and landscaping, consisting of groundcover/shrub, trees, and grass. Contaminated Site Information: Proposed activities regarding contaminated soils or groundwater (example: on-site treatment system, authorized sanitary sewer discharge) - There are no contaminated soil or groundwater conditions known at the project site and therefore no proposed activities for the cleanup of existing contamination. Page | 6 2 Construction Stormwater Best Management Practices (BMPs) The SWPPP is a living document reflecting current conditions and changes throughout the life of the project. These changes may be informal (i.e. hand-written notes and deletions). Update the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design. 2.1 The 13 Elements 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land-disturbing activities begin. Trees that are to be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in the field and on the plans. In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. The BMPs relevant to marking the clearing limits that will be applied for this project include: List and describe BMPs: · Preserving Natural Vegetation (BMP C101) · High-Visibility Fence (BMP C103) Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction. Page | 7 2.1.2 Element 2: Establish Construction Access Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads, and wheel washing, street sweeping, and street cleaning shall be employed to prevent sediment from entering state waters. All wash wastewater shall be controlled on-site. The specific BMPs related to establishing construction access that will be used on this project include: List and describe BMPs: · N/A; the contractor shall utilize existing paved asphalt and concrete areas adjacent to the proposed project site for construction access, laydown, and staging. Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction. Page | 8 2.1.3 Element 3: Control Flow Rates In order to protect the properties and waterways downstream of the project site, stormwater discharges from the site will be controlled. The specific BMPs for flow control that shall be used on this project include: Will you construct stormwater retention and/or detention facilities? No Will you use permanent infiltration ponds or other low-impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? No List and describe BMPs: · The project will install Straw Wattles and Catch Basin Filter Socks to slow down and control any construction stormwater from entering the existing downstream storm system: o Interceptor Dike and Swale (BMP C200) o Storm Drain Inlet Protection (BMP C220) o Silt Fence (BMP C233) o Straw Wattles (BMP C235) o Sediment Trap (BMP C240) o Temporary Water Storage Tanks for Sedimentation Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction until the site is fully stabilized and permanent flow control facilities are functioning. Page | 9 2.1.4 Element 4: Install Sediment Controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or before being discharged to an infiltration facility. Specific BMPs to be used for controlling sediment on this project include: List and describe BMPs: · Inlet Protection (BMP C220) · Silt Fence (BMP C233) · Straw Wattles (BMP C235) · Sediment Trap (BMP C240) · Temporary Water Storage Tanks for Sedimentation Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction. Page | 10 2.1.5 Element 5: Stabilize Soils Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent erosion throughout the life of the project. The specific BMPs for soil stabilization that shall be used on this project are listed below: List and describe BMPs: · Temporary and Permanent Seeding (BMP C120) · Mulching (BMP C121) · Plastic Covering (BMP C123) West of the Cascade Mountains Crest Season Dates Number of Days Soils Can be Left Exposed During the Dry Season May 1 – September 30 7 days During the Wet Season October 1 – April 30 2 days Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Will you construct during the wet season? NO; project is not anticipating performing construction past October. Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction until the site is fully stabilized. Page | 11 2.1.6 Element 6: Protect Slopes All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes erosion during construction. Will steep slopes be present at the site during construction? No List and describe BMPs: · N/A; No steep slopes will be present at the site during construction, therefore no slope protection BMPs are necessary. Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction until the site is fully stabilized. Page | 12 2.1.7 Element 7: Protect Drain Inlets All storm drain inlets and culverts made operable during construction shall be protected to prevent unfiltered or untreated water from entering the drainage conveyance system. However, the first priority is to keep all access roads clean of sediment and keep street wash water separate from entering storm drains until treatment can be provided. Storm Drain Inlet Protection (BMP C220) will be implemented for all drainage inlets and culverts that could potentially be impacted by sediment-laden runoff on and near the project site. All inlets will be inspected weekly at a minimum and daily during storm events. Inlet protection devices will be cleaned or replaced when sediment has reached 1/3 capacity or as specified by the product manufacturer. List and describe BMPs: · Interceptor Dike and Swale (BMP C200) · Inlet Protection (BMP C220) · Silt Fence (BMP C233) · Straw Wattles (BMP C235) · Sediment Trap (BMP C240) · Temporary Water Storage Tanks for Sedimentation Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction until the site is fully stabilized and permanent flow control facilities are functioning. Page | 13 2.1.8 Element 8: Stabilize Channels and Outlets Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural discharge point, efforts will be taken to prevent downstream erosion. Temporary settlement tanks will be provided on-site to attenuate flows and remove sediment before discharging to the existing storm system. Hydrologic analysis has been performed and found in Appendix H. Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all conveyance systems. List and describe BMPs: · Interceptor Dike and Swale (BMP C200) · Sediment Trap (BMP C240) · Temporary Water Storage Tanks for Sedimentation Installation Schedules: BMPs will be installed at the beginning of construction and be inspected and maintained throughout construction until the site is fully stabilized and permanent flow control facilities are functioning. Page | 14 2.1.9 Element 9: Control Pollutants The following pollutants are anticipated to be present on-site: Table 2 – Pollutants Pollutant (and source, if applicable) Vehicles and construction equipment Demolition Concrete and grout All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well-organized, and free of debris. Vehicles, construction equipment, and/or petroleum product storage/dispensing: · All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. · On-site fueling tanks and petroleum product storage containers shall include secondary containment. · Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. · In order to perform emergency repairs on-site, temporary plastic will be placed beneath and, if raining, over the vehicle. · Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Demolition: · Dust released from demolished sidewalks, buildings, or structures will be controlled using Dust Control measures (BMP C140). · Storm drain inlets vulnerable to stormwater discharge carrying dust, soil, or debris will be protected using Storm Drain Inlet Protection (BMP C220 as described above for Element 7). · Process water and slurry resulting from sawcutting and surfacing operations will be prevented from entering the waters of the State by implementing Sawcutting and Surfacing Pollution Prevention measures (BMP C152). Page | 15 Concrete and grout: · Process water and slurry resulting from concrete work will be prevented from entering the waters of the State by implementing Concrete Handling measures (BMP C151) List and describe BMPs: · Materials on Hand (BMP C150) · Concrete Handling (BMP C151) · Sawcutting and Surfacing Pollution Prevention (BMP C152) · Material Delivery, Storage, and Containment (BMP C153) · Concrete Washout Area (BMP C154) Installation Schedules: BMPs will be implemented at the beginning of construction and be inspected and maintained throughout construction until the site is fully stabilized. Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site? No Will wheel wash or tire bath system BMPs be used during construction? No; the contractor shall utilize existing paved asphalt and concrete areas adjacent to the proposed project site for construction access, laydown, and staging Will pH-modifying sources be present on-site? YES Table 3 – pH-Modifying Sources None X Bulk cement Cement kiln dust Fly ash X Other cementitious materials X New concrete washing or curing waters X Waste streams generated from concrete grinding and sawing Exposed aggregate processes Dewatering concrete vaults Concrete pumping and mixer washout waters Recycled concrete Other (i.e. calcium lignosulfate) [please describe] Page | 16 List and describe BMPs: · Materials on Hand (BMP C150) · Concrete Handling (BMP C151) · Sawcutting and Surfacing Pollution Prevention (BMP C152) · Material Delivery, Storage and Containment (BMP C153) · Concrete Washout Area (BMP C154) · Treating and Disposing of High pH Water (BMP C252) Installation Schedules: BMP’s will be implemented at the beginning of construction and be inspected and maintained throughout construction as required. Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches, streets, or streams. Excess concrete must not be dumped on-site, except in designated concrete washout areas with appropriate BMPs installed. Page | 17 2.1.10 Element 10: Control Dewatering This project does not propose dewatering and therefore will not be implementing any dewatering BMPs associated with Element 10. Table 4 – Dewatering BMPs Infiltration Transport off-site in a vehicle (vacuum truck for legal disposal) Ecology-approved on-site chemical treatment or other suitable treatment technologies Sanitary or combined sewer discharge with local sewer district approval (last resort) Use of sedimentation bag with discharge to ditch or swale (small volumes of localized dewatering) List and describe BMPs: N/A Page | 18 2.1.11 Element 11: Maintain BMPs All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained and repaired as needed to ensure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP specification (see Volume II of the SWMMWW or Chapter 7 of the SWMMEW). Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to once every calendar month. All temporary ESC BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal of either BMPs or vegetation shall be permanently stabilized. Additionally, protection must be provided for all BMPs installed for the permanent control of stormwater from sediment and compaction. BMPs that are to remain in place following completion of construction shall be examined and restored to full operating condition. If sediment enters these BMPs during construction, the sediment shall be removed and the facility shall be returned to conditions specified in the construction documents. Page | 19 2.1.12 Element 12: Manage the Project The project will be managed based on the following principles: · Projects will be phased to the maximum extent practicable and seasonal work limitations will be taken into account. · Inspection and monitoring: o Inspection, maintenance, and repair of all BMPs will occur as needed to ensure the performance of their intended function. o Site inspections and monitoring will be conducted in accordance with City of Renton Standards. Sampling locations are indicated on the Site Map, included in Appendix A. · Maintain an updated SWPPP. o The SWPPP will be updated, maintained, and implemented in accordance with h City of Renton Standards and project specifications. As site work progresses the SWPPP will be modified routinely to reflect changing site conditions. The SWPPP will be reviewed monthly to ensure the content is current. Table 5 – Management X Design the project to fit the existing topography, soils, and drainage patterns X Emphasize erosion control rather than sediment control X Minimize the extent and duration of the area exposed X Keep runoff velocities low X Retain sediment on-site X Thoroughly monitor the site and maintain all ESC measures X Schedule major earthwork during the dry season Other (please describe) Page | 20 Table 6 – BMP Implementation Schedule Phase of Construction Project Stormwater BMPs Date Wet/Dry Season [Insert construction activity] [Insert BMP] [MM/DD/YYYY] [Insert Season] Page | 21 Phase of Construction Project Stormwater BMPs Date Wet/Dry Season [Insert construction activity] [Insert BMP] [MM/DD/YYYY] [Insert Season] Page | 22 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs The project will be implementing BMP T5.13 for Post-Construction Soil Quality and Depth. To comply with the requirements of this BMP, the duff layer and native topsoil’s will be stockpiled and retained on site during grading activities to be reapplied for use in post-construction soils prior to planting. Existing vegetation or landscaped areas will be protected during construction (BMP C101, C103, and C233). Topsoil’s will be imported as needed to meet BMP T5.13 requirements. Soil quality and depth will be established at the end of construction to prevent compaction from heavy machinery. Page | 23 3 Pollution Prevention Team Table 7 – Team Information Title Name(s) Phone Number Certified Erosion and Sediment Control Lead (CESCL) TBD Resident Engineer TBD Emergency Ecology Contact TBD Emergency Permittee/ Owner Contact TBD Non-Emergency Owner Contact TBD Monitoring Personnel TBD Ecology Regional Office Northwest Regional Office 425-649-7098 Page | 24 4 Monitoring and Sampling Requirements Monitoring includes visual inspection, sampling for water quality parameters of concern, and documentation of the inspection and sampling findings in a site log book. A site log book will be maintained for all on-site construction activities and will include: · A record of the implementation of the SWPPP and other permit requirements · Site inspections · Stormwater sampling data Please find a blank form under to be completed in Appendix D. The site logbook must be maintained on-site within reasonable access to the site and be made available upon request to the City of Renton. Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. Complete the following paragraph for sites that discharge to impaired waterbodies for fine sediment, turbidity, phosphorus, or pH: 4.1 Site Inspection Site inspections will be conducted at least once every calendar week and within 24 hours following any discharge from the site. For sites that are temporarily stabilized and inactive, the required frequency is reduced to once per calendar month. The discharge point(s) are indicated on the Site Map included in Appendix A. 4.2 Stormwater Quality Sampling 4.2.1 Turbidity Sampling Requirements include a calibrated turbidity meter or transparency tube to sample site discharges for compliance with the City of Renton Standards. Sampling will be conducted at all discharge points at least once per calendar week. Page | 25 Method for sampling turbidity: Table 8 – Turbidity Sampling Method X Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size) Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size) The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency of less than 33 centimeters. If the discharge’s turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to or greater than 6 cm, the following steps will be conducted: 1. Review the SWPPP for compliance with Special Condition S9. Make appropriate revisions within 7 days of the date the discharge exceeded the benchmark. 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period. 3. Document BMP implementation and maintenance in the site log book. If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following steps will be conducted: 1. Telephone or submit an electronic report to the applicable Ecology Region’s Environmental Report Tracking System (ERTS) within 24 hours. https://www.ecology.wa.gov/About-us/Get-involved/Report-an-environmental-issue · Central Region (Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, Yakima): (509) 575-2490 · Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman): (509) 329-3400 · Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish, Whatcom): (425) 649-7000 · Southwest Region (Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, Wahkiakum,): (360) 407-6300 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period 3. Document BMP implementation and maintenance in the site log book. Page | 26 4. Continue to sample discharges daily until one of the following is true: · Turbidity is 25 NTU (or lower). · Transparency is 33 cm (or greater). · Compliance with the water quality limit for turbidity is achieved. o 1 - 5 NTU over background turbidity, if background is less than 50 NTU o 1% - 10% over background turbidity, if background is 50 NTU or greater · The discharge stops or is eliminated. Page | 27 4.2.2 pH Sampling pH monitoring is required for “Significant concrete work” (i.e. greater than 1000 cubic yards of poured concrete or recycled concrete over the life of the project). The use of engineered soils (soil amendments including but not limited to Portland cement-treated base [CTB], cement kiln dust [CKD] or fly ash) also requires pH monitoring. For significant concrete work, pH sampling will start the first day the concrete is poured and continue until it is cured, typically three (3) weeks after the last pour. For engineered soils and recycled concrete, pH sampling begins when engineered soils or recycled concrete are first exposed to precipitation and continues until the area is fully stabilized. If the measured pH is 8.5 or greater, the following measures will be taken: 1. Prevent high pH water from entering storm sewer systems or surface water. 2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate technology such as carbon dioxide (CO2) sparging (liquid or dry ice). 3. Written approval will be obtained from Ecology or City of Renton prior to the use of chemical treatment other than CO2 sparging or dry ice. Method for sampling pH: Table 9 – pH Sampling Method X pH meter pH test kit Wide range pH indicator paper Page | 28 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies 5.1 303(d) Listed Waterbodies Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH? NO List the impairment(s): N/A List and describe BMPs: N/A 5.2 TMDL Waterbodies Waste Load Allocation for CWSGP discharges: This project site discharges to the Goat Trail Ravine Basin. The proposed development is not proposing any pollution generating surfaces and is therefore not required provide water quality treatment and does not discharge to a TMDL Waterbody. Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point of discharge. N/A; project site disturbance is less than 1.0 acres, therefore a CSWGP is not required for this project. Page | 29 6 Reporting and Record Keeping 6.1 Record Keeping 6.1.1 Site Log Book A site log book will be maintained for all on-site construction activities and will include: · A record of the implementation of the SWPPP and other permit requirements · Site inspections · Sample logs 6.1.2 Records Retention Records will be retained during the life of the project and for a minimum of three (3) years following the termination of permit coverage in accordance with Special Condition S5.C of the CSWGP. Permit documentation to be retained on-site: · CSWGP; N/A project site disturbance is less than 1.0 acres. · Permit Coverage Letter; N/A project site disturbance is less than 1.0 acres. · SWPPP · Site Log Book Permit documentation will be provided within 14 days of receipt of a written request from Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP. 6.1.3 Updating the SWPPP The SWPPP will be modified if: · Found ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. · There is a change in design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the State. The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine additional or modified BMPs are necessary for compliance. An updated timeline for BMP implementation will be prepared. Page | 30 6.2 Reporting 6.2.1 Discharge Monitoring Reports Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given monitoring period the DMR will be submitted as required, reporting “No Discharge”. The DMR due date is fifteen (15) days following the end of each calendar month. DMRs will be reported online through Ecology’s WQWebDMR System. N/A project site disturbance is less than 1.0 acres. 6.2.2 Notification of Noncompliance If any of the terms and conditions of the permit is not met, and the resulting noncompliance may cause a threat to human health or the environment, the following actions will be taken: 1. Ecology will be notified within 24-hours of the failure to comply by calling the applicable Regional office ERTS phone number (Regional office numbers listed below). 2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or correct the noncompliance. If applicable, sampling and analysis of any noncompliance will be repeated immediately and the results submitted to Ecology within five (5) days of becoming aware of the violation. 3. A detailed written report describing the noncompliance will be submitted to Ecology within five (5) days, unless requested earlier by Ecology. Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6 cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as required by Special Condition S5.A of the CSWGP. · Central Region at (509) 575-2490 for Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, or Yakima County · Eastern Region at (509) 329-3400 for Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, or Whitman County · Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit, Snohomish, or Whatcom County · Southwest Region at (360) 407-6300 for Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, or Wahkiakum Page | 31 Include the following information: 1. Your name and / Phone number 2. Permit number 3. City / County of project 4. Sample results 5. Date / Time of call 6. Date / Time of sample 7. Project name In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH water. Page | 32 Appendix/Glossary A. Site Map B. BMP Plans and Details C. Correspondence - N/A D. Site Inspection Form E. Construction Stormwater General Permit (CSWGP) F. 303(d) List Waterbodies / TMDL Waterbodies Information – N/A G. Contaminated Site Information - N/A H. Engineering Calculations Page | 33 Appendix A – Site Map Vicinity Map Temporary Erosion and Sediment Control (TESC) Plans & Details 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.399.6233 | JACOBSONENGINEERS.COM206.426.2600 VICINITY MAPSCALE: NTS Project Site Project Site NOTE - PLANS HAVE BEEN SCALED TO 11X17 NOTE - PLANS HAVE BEEN SCALED TO 11X17 Page | 34 Appendix B – BMP Details Preserving Natural Vegetation (BMP C101) High Visibility Fence (BMP C103) Temporary and Permanent Seeding (BMP C120) Mulching (BMP C121) Plastic Covering (BMP C123) Dust Control (BMP C140) Materials on Hand (BMP C150) Concrete Handling (BMP C151) Sawcutting and Surfacing Pollution Prevention (BMP C152) Material Delivery, Storage and Containment (BMP C153) Concrete Washout Area (BMP C154) Certified Erosion and Sediment Control Lead (BMP C160) Scheduling (BMP C162) Interceptor Dike and Swale (BMP C200) Storm Drain Inlet Protection (BMP C220) Silt Fence (BMP C233) Wattles (BMP C235) Sediment Trap (BMP C240) Construction Stormwater Chemical Treatment (BMP C250) Construction Stormwater Filtration (BMP C251) Treating and Disposing of High pH Water (BMP C252) BMP C101: Preserving Natural Vegetation Purpose The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site  disturbance is the single most effective method for reducing erosion. For example, conifers can hold  up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never  reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the  tree can be released slowly to the ground after the storm. Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent water- courses or swales, and on building sites in wooded areas.  l As required by local governments.  l Phase construction to preserve natural vegetation on the project site for as long as possible  during the construction period. Design and Installation Specifications Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines. The preservation of individual plants is more difficult because heavy equipment is generally used to  remove unwanted vegetation. The points to remember when attempting to save individual plants  are:  l Is the plant worth saving? Consider the location, species, size, age, vigor, and the work  involved. Local governments may also have ordinances to save natural vegetation and trees.  l Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground  disturbance away from the trees at least as far out as the dripline. Plants need protection from three kinds of injuries:  l Construction Equipment - This injury can be above or below the ground level. Damage results  from scarring, cutting of roots, and compaction of the soil. Placing a fenced buffer zone around  plants to be saved prior to construction can prevent construction equipment injuries.  l Grade Changes - Changing the natural ground level will alter grades, which affects the plant's  ability to obtain the necessary air, water, and minerals. Minor fills usually do not cause prob- lems although sensitivity between species does vary and should be checked. Trees can typ- ically tolerate fill of 6 inches or less. For shrubs and other plants, the fill should be less. When there are major changes in grade, it may become necessary to supply air to the roots of  plants. This can be done by placing a layer of gravel and a tile system over the roots before the  fill is made. The tile system should be laid out on the original grade leading from a dry well  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 271 around the tree trunk. The system should then be covered with small stones to allow air to cir- culate over the root area. Lowering the natural ground level can seriously damage trees and shrubs. The highest per- centage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can  cause serious injury. To protect the roots it may be necessary to terrace the immediate area  around the plants to be saved. If roots are exposed, construction of retaining walls may be  needed to keep the soil in place. Plants can also be preserved by leaving them on an undis- turbed, gently sloping mound. To increase the chances for survival, it is best to limit grade  changes and other soil disturbances to areas outside the dripline of the plant.  l Excavations - Protect trees and other plants when excavating for drainfields, power, water,  and sewer lines. Where possible, the trenches should be routed around trees and large  shrubs. When this is not possible, it is best to tunnel under them. This can be done with hand  tools or with power augers. If it is not possible to route the trench around plants to be saved,  then the following should be observed:  o Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a  wood dressing like asphalt base paint if roots will be exposed for more than 24-hours.  o Backfill the trench as soon as possible.  o Tunnel beneath root systems as close to the center of the main trunk to preserve most  of the important feeder roots. Some problems that can be encountered with a few specific trees are:  l Maple, Dogwood, Red alder, Western hemlock, Western red cedar, and Douglas fir do not  readily adjust to changes in environment and special care should be taken to protect these  trees.  l The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock  is moderate. The danger of windthrow increases where dense stands have been thinned.  Other species (unless they are on shallow, wet soils less than 20 inches deep) have a low  windthrow hazard.  l Cottonwoods, maples, and willows have water-seeking roots. These can cause trouble in  sewer lines and infiltration fields. On the other hand, they thrive in high moisture conditions  that other trees would not.  l Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir, Sitka  spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause ser- ious disease problems. Disease can become established through damaged limbs, trunks,  roots, and freshly cut stumps. Diseased and weakened trees are also susceptible to insect  attack. Maintenance Standards Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been  removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be  repaired or replaced immediately and visibility restored. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 272 If tree roots have been exposed or injured, “prune” cleanly with an appropriate pruning saw or lop- pers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees  (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. BMP C102: Buffer Zones Purpose Creation of an undisturbed area or strip of natural vegetation or an established suitable planting that  will provide a living filter to reduce soil erosion and stormwater runoff velocities. Conditions of Use Buffer zones are used along streams, wetlands and other bodies of water that need protection from  erosion and sedimentation. Contractors can use vegetative buffer zone BMPs to protect natural  swales and they can incorporate them into the natural landscaping of an area. Do not use critical-areas buffer zones as sediment treatment areas. These areas shall remain com- pletely undisturbed. The local permitting authority may expand the buffer widths temporarily to allow  the use of the expanded area for removal of sediment. The types of buffer zones can change the level of protection required as shown below: Designated Critical Area Buffers - buffers that protect Critical Areas, as defined by the Washington  State Growth Management Act, and are established and managed by the local permitting authority.  These should not be disturbed and must protected with sediment control BMPs to prevent impacts.  The local permitting authority may expand the buffer widths temporarily to allow the use of the expan- ded area for removal of sediment. Vegetative Buffer Zones - areas that may be identified in undisturbed vegetation areas or managed  vegetation areas that are outside any Designated Critical Area Buffer. They may be utilized to  provide an additional sediment control area and/or reduce runoff velocities. If being used for pre- servation of natural vegetation, they should be arranged in clumps or strips. They can be used to pro- tect natural swales and incorporated into the natural landscaping area. Design and Installation Specifications  l Preserving natural vegetation or plantings in clumps, blocks, or strips is generally the easiest  and most successful method.  l Leave all unstable steep slopes in natural vegetation.  l Mark clearing limits and keep all equipment and construction debris out of the natural areas  and buffer zones. Steel construction fencing is the most effective method to protect sensitive  areas and buffers. Alternatively, wire-backed silt fence on steel posts is marginally effective.  Flagging alone is typically not effective.  l Keep all excavations outside the dripline of trees and shrubs.  l Do not push debris or extra soil into the buffer zone area because it will cause damage by  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 273 N/A burying and smothering vegetation.  l Vegetative buffer zones for streams, lakes or other waterways shall be established by the  local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undis- turbed. Replace all damaged flagging immediately. Remove all materials located in the buffer area  that may impede the ability of the vegetation to act as a filter. BMP C103: High-Visibility Fence Purpose High-visibility fencing is intended to:  l Restrict clearing to approved limits.  l Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undis- turbed.  l Limit construction traffic to designated construction entrances, exits, or internal roads.  l Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used:  l At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared.  l As necessary to control vehicle access to and on the site. Design and Installation Specifications High-visibility plastic fence shall be composed of a high-density polyethylene material and shall be at  least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center  (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches  with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as  a top stringer to prevent sagging between posts. The fence color shall be high-visibility orange. The  fence tensile strength shall be 360 lbs/ft using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233:  Silt Fence to act as high-visibility  fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of  this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 274 Crushed rock, gravel base, etc., shall be added as required to maintain a stable driving surface and  to stabilize any areas that have eroded. Following construction, these areas shall be restored to pre-construction condition or better to pre- vent future erosion. Perform street cleaning at the end of each day or more often if necessary. BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established vegetative cover is one of  the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will  remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September  1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch or an erosion control blanket  until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of  September. Otherwise, vegetation will not establish itself enough to provide more than average pro- tection. Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and  transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding.  See BMP C121: Mulching for specifications. Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final sta- bilization means the completion of all soil disturbing activities at the site and the establishment of a  permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement,  riprap, gabions, or geotextiles) which will prevent erosion. See BMP T5.13: Post-Construction Soil  Quality and Depth. Design and Installation Specifications General  l Install channels intended for vegetation before starting major earthwork and hydroseed with a  Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control  blankets over the top of hydroseed. Before allowing water to flow in vegetated channels,  establish 75 percent vegetation cover. If vegetated channels cannot be established by seed  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 284 before water flow; install sod in the channel bottom — over top of hydromulch and erosion con- trol blankets.  l Confirm the installation of all required surface water control measures to prevent seed from  washing away.  l Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 per- cent tackifier. See BMP C121: Mulching for specifications.  l Areas that will have seeding only and not landscaping may need compost or meal-based  mulch included in the hydroseed in order to establish vegetation. Re-install native topsoil on  the disturbed soil surface before application. See BMP T5.13: Post-Construction Soil Quality  and Depth.  l When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up  in contact with the soil surface. This reduces the ability to establish a good stand of grass  quickly. To overcome this, consider increasing seed quantities by up to 50 percent.  l Enhance vegetation establishment by dividing the hydromulch operation into two phases:  o Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in  the first lift.  o Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by:  o Installing the mulch, seed, fertilizer, and tackifier in one lift.  o Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per  acre.  o Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance  vegetative establishment. The increased cost may be offset by the reduced need for:  o Irrigation.  o Reapplication of mulch.  o Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum) and Bon- ded Fiber Matrix/ Mechanically Bonded Fiber Matrix (BFM/MBFMs) (3,000 pounds per acre  minimum).  l Seed may be installed by hand if:  o Temporary and covered by straw, mulch, or topsoil.  o Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or  erosion blankets.  l The seed mixes listed in Table II-3.4: Temporary and Permanent Seed Mixes include  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 285 recommended mixes for both temporary and permanent seeding.  l Apply these mixes, with the exception of the wet area seed mix, at a rate of 120 pounds per  acre. This rate can be reduced if soil amendments or slow-release fertilizers are used. Apply  the wet area seed mix at a rate of 60 pounds per acre.  l Consult the local suppliers or the local conservation district for their recommendations. The  appropriate mix depends on a variety of factors, including location, exposure, soil type, slope,  and expected foot traffic. Alternative seed mixes approved by the local authority may be used,  depending on the soil type and hydrology of the area. Common Name Latin Name % Weight % Purity % Germination Temporary Erosion Control Seed Mix A standard mix for areas requiring a temporary vegetative cover. Chewings or   annual blue grass Festuca rubra var. commutata or Poa anna 40 98 90 Perennial rye  Lolium perenne 50 98 90 Redtop or colonial  bentgrass  Agrostis alba or  Agrostis tenuis 5 92 85 White dutch clover Trifolium repens 5 98 90 Landscaping Seed Mix A recommended mix for landscaping seed. Perennial rye blend Lolium perenne 70 98 90 Chewings and red  fescue blend Festuca rubra var. commutata or Fes- tuca rubra 30 98 90 Low-Growing Turf Seed Mix A turf seed mix for dry situations where there is no need for watering. This mix requires very little main- tenance. Dwarf tall fescue  (several  varieties) Festuca arundin- acea 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 Bioswale Seed Mix A seed mix for bioswales and other intermittently wet areas. Tall or meadow fes-Festuca arundin-75-80 98 90 Table II-3.4: Temporary and Permanent Seed Mixes 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 286 Common Name Latin Name % Weight % Purity % Germination cue acea or   Festuca elatior Seaside/Creeping  bentgrass Agrostis palustris 10-15 92 85 Redtop bentgrass Agrostis alba or  Agrostis gigantea 5-10 90 80 Wet Area Seed Mix A low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wet- lands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Tall or meadow fes- cue Festuca arundin- acea or Festuca elatior 60-70 98 90 Seaside/Creeping  bentgrass Agrostis palustris 10-15 98 85 Meadow foxtail Alepocurus praten- sis 10-15 90 80 Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 Meadow Seed Mix A recommended meadow seed mix for infrequently maintained areas or non-maintained areas where col- onization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seed- ing should take place in September or very early October in order to obtain adequate establishment prior to  the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending  the soil can reduce the need for clover. Redtop or Oregon  bentgrass Agrostis alba or  Agrostis ore- gonensis 20 92 85 Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Table II-3.4: Temporary and Permanent Seed Mixes (continued) Roughening and Rototilling  l The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk  slopes before seeding if engineering purposes require compaction. Backblading or smoothing  of slopes greater than 4H:1V is not allowed if they are to be seeded.  l Restoration-based landscape practices require deeper incorporation than that provided by a  simple single-pass rototilling treatment. Wherever practical, initially rip the subgrade to  improve long-term permeability, infiltration, and water inflow qualities. At a minimum,  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 287 permanent areas shall use soil amendments to achieve organic matter and permeability per- formance defined in engineered soil/landscape systems. For systems that are deeper than 8  inches complete the rototilling process in multiple lifts, or prepare the engineered soil system  per specifications and place to achieve the specified depth. Fertilizers  l Conducting soil tests to determine the exact type and quantity of fertilizer is recommended.  This will prevent the over-application of fertilizer.  l Organic matter is the most appropriate form of fertilizer because it provides nutrients (includ- ing nitrogen, phosphorus, and potassium) in the least water-soluble form.  l In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium) fertilizer at a rate of 90  pounds per acre. Always use slow-release fertilizers because they are more efficient and  have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agit- ate, more than 20 minutes before use. Too much agitation destroys the slow-release coating.  l There are numerous products available that take the place of chemical fertilizers. These  include several with seaweed extracts that are beneficial to soil microbes and organisms. If  100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be  necessary. Cottonseed meal provides a good source of long-term, slow-release, available  nitrogen. Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix  l On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix  (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre  with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during  application. Numerous products are available commercially. Most products require 24-36  hours to cure before rainfall and cannot be installed on wet or saturated soils. Generally,  products come in 40-50 pound bags and include all necessary ingredients except for seed and  fertilizer.  l Install products per manufacturer's instructions.  l BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation  establishment. Advantages over blankets include:  o BFM and MBFMs do not require surface preparation.  o Helicopters can assist in installing BFM and MBFMs in remote areas.  o On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses  for safety.  o Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 288 Maintenance Standards Reseed any seeded areas that fail to establish at least 75 percent cover (100 percent cover for areas  that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such  as sodding, mulching, nets, or blankets.  l Reseed and protect by mulch any areas that experience erosion after achieving adequate  cover. Reseed and protect by mulch any eroded area.  l Supply seeded areas with adequate moisture, but do not water to the extent that it causes run- off. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not  pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions  may choose not to accept these products, or may require additional testing prior to consideration for  local use. Products that Ecology has approved as functionally equivalent are available for review on  Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C121: Mulching Purpose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant  establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating  soil temperatures. There are a variety of mulches that can be used. This section discusses only the  most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used:  l For less than 30 days on disturbed areas that require cover.  l At all times for seeded areas, especially during the wet season and during the hot summer  months.  l During the wet season on slopes steeper than 3H:1V with more than 10 feet of vertical relief. Mulch may be applied at any time of the year and must be refreshed periodically. For seeded areas, mulch may be made up of 100 percent:   l cottonseed meal;   l fibers made of wood, recycled cellulose, hemp, or kenaf;  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 289  l compost;   l or blends of these. Tackifier shall be plant-based, such as guar or alpha plantago, or chemical-based such as poly- acrylamide or polymers.  Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that  products should be evaluated for PCBs prior to use. Refer to BMP C126:  Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM  shall not be directly applied to water or allowed to enter a water body. Any mulch or tackifier product used shall be installed per the manufacturer’s instructions. Design and Installation Specifications For mulch materials, application rates, and specifications, see Table II-3.6: Mulch Standards and  Guidelines. Consult with the local supplier or the local conservation district for their recom- mendations. Increase the application rate until the ground is 95% covered (i.e. not visible under the  mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or  other areas highly susceptible to erosion. Where the option of “Compost” is selected, it should be a coarse compost that meets the size grad- ations listed in Table II-3.5: Size Gradations of Compost as Mulch Material when tested in accord- ance with Test Method 02.02-B found in Test Methods for the Examination of Composting and Compost (Thompson, 2001). Sieve Size Percent Passing 3"100% 1"90% - 100% 3/4"70% - 100% 1/4"40% - 100% Table II-3.5: Size Gradations of Compost as Mulch Material Mulch used within the ordinary high-water mark of surface waters should be selected to minimize  potential flotation of organic matter. Composted organic materials have higher specific gravities  (densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (HPA) for  mulch mixes if applicable. Maintenance Standards The thickness of the mulch cover must be maintained. Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the  erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 290 Mulch Mater- ial Guideline Description Straw Quality Standards Air-dried; free from undesirable seed and coarse material. Application Rates 2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per acre Remarks Cost-effective protection when applied with adequate thickness. Hand- application generally requires greater thickness than blown straw. The  thickness of straw may be reduced by half when used in conjunction with  seeding. In windy areas straw must be held in place by crimping, using a  tackifier, or covering with netting. Blown straw always has to be held in  place with a tackifier as even light winds will blow it away. Straw, however,  has several deficiencies that should be considered when selecting mulch  materials. It often introduces and/or encourages the propagation of weed  species and it has no significant long-term benefits It should also not be  used within the ordinary high-water elevation of surface waters (due to flot- ation). Hydromulch Quality Standards No growth inhibiting factors. Application Rates Approx. 35-45 lbs per 1,000 sf or 1,500 - 2,000 lbs per acre Remarks Shall be applied with hydromulcher. Shall not be used without seed and  tackifier unless the application rate is at least doubled. Fibers longer than  about 3/4 - 1 inch clog hydromulch equipment. Fibers should be kept to less  than 3/4 inch. Compost Quality Standards No visible water or dust during handling. Must be produced per WAC 173- 350, Solid Waste Handling Standards, but may have up to 35% biosolids. Application Rates 2" thick min.; approx. 100 tons per acre (approx. 750 lbs per cubic yard) Remarks More effective control can be obtained by increasing thickness to 3". Excel- lent mulch for protecting final grades until landscaping because it can be dir- ectly seeded or tilled into soil as an amendment. Compost used for mulch  has a coarser size gradation than compost used for BMP C125: Topsoiling  / Composting or BMP T5.13: Post-Construction Soil Quality and Depth. It  is more stable and practical to use in wet areas and during rainy weather  conditions. Do not use near wetlands or near phosphorous impaired water  bodies. Chipped Site Veget- ation Quality Standards Gradations from fines to 6 inches in length for texture, variation, and inter- locking properties. Include a mix of various sizes so that the average size  is between 2- and 4- inches. Application Rates 2" thick min.; Table II-3.6: Mulch Standards and Guidelines 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 291 Mulch Mater- ial Guideline Description Remarks This is a cost-effective way to dispose of debris from clearing and grub- bing, and it eliminates the problems associated with burning. Generally, it  should not be used on slopes above approx. 10% because of its tendency  to be transported by runoff. It is not recommended within 200 feet of sur- face waters. If permanent seeding or planting is expected shortly after  mulch, the decomposition of the chipped vegetation may tie up nutrients  important to grass establishment.  Note: thick application of this material over existing grass, herbaceous spe- cies, and some groundcovers could smother and kill vegetation. Wood- Based Mulch Quality Standards No visible water or dust during handling. Must be purchased from a supplier  with a Solid Waste Handling Permit or one exempt from solid waste reg- ulations. Application Rates 2" thick min.; approx. 100 tons per acre (approx. 750 lbs. per cubic yard) Remarks This material is often called "wood straw" or "hog fuel". The use of mulch  ultimately improves the organic matter in the soil. Special caution is  advised regarding the source and composition of wood-based mulches. Its  preparation typically does not provide any weed seed control, so evidence  of residual vegetation in its composition or known inclusion of weed plants  or seeds should be monitored and prevented (or minimized). Wood Strand Mulch Quality Standards A blend of loose, long, thin wood pieces derived from native conifer or  deciduous trees with high length-to-width ratio. Application Rates 2" thick min. Remarks Cost-effective protection when applied with adequate thickness. A min- imum of 95-percent of the wood strand shall have lengths between 2 and  10-inches, with a width and thickness between 1/16 and 1/2-inches. The  mulch shall not contain resin, tannin, or other compounds in quantities that  would be detrimental to plant life. Sawdust or wood shavings shall not be  used as mulch. [Specification 9-14.4(4) from the Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT, 2016) Table II-3.6: Mulch Standards and Guidelines (continued) BMP C122: Nets and Blankets Purpose Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place  on steep slopes and in channels so that vegetation can become well established. In addition, some  nets and blankets can be used to permanently reinforce turf to protect drainage ways during high  flows.  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 292 BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30 days,  except as stated below.  l Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However, the rel- atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications  greater than six months.  l Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that  might be adversely impacted by concentrated runoff. Such areas include steep and/or  unstable slopes.  l Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on- site measures to counteract the increases. Creating a trough with wattles or other material  can convey clean water away from these areas.  l To prevent undercutting, trench and backfill rolled plastic covering products.  l Although the plastic material is inexpensive to purchase, the cost of installation, maintenance,  removal, and disposal add to the total costs of this BMP.  l Whenever plastic is used to protect slopes, install water collection measures at the base of the  slope. These measures include plastic-covered berms, channels, and pipes used to convey  clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a  plastic covered slope with dirty runoff from a project.  l Other uses for plastic include:  o Temporary ditch liner.  o Pond liner in temporary sediment pond.  o Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel  being stored.  o Emergency slope protection during heavy rains.  o Temporary drainpipe (“elephant trunk”) used to direct water. Design and Installation Specifications  l Plastic slope cover must be installed as follows:  1. Run plastic up and down the slope, not across the slope.  2. Plastic may be installed perpendicular to a slope if the slope length is less than 10 feet. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 298  3. Provide a minimum of 8-inch overlap at the seams.  4. On long or wide slopes, or slopes subject to wind, tape all seams.  5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope  and backfill with soil to keep water from flowing underneath.  6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them  together with twine to hold them in place.  7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This  prevents high velocity runoff from contacting bare soil, which causes extreme erosion.  8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be  staked in place.  l Plastic sheeting shall have a minimum thickness of 0.06 millimeters.  l If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall  be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance Standards  l Torn sheets must be replaced and open seams repaired.  l Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi- ation.  l Completely remove plastic when no longer needed.  l Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not  pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions  may choose not to accept these products, or may require additional testing prior to consideration for  local use. Products that Ecology has approved as functionally equivalent are available for review on  Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C124: Sodding Purpose The purpose of sodding is to establish turf for immediate erosion protection and to stabilize drainage  paths where concentrated overland flow will occur. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 299 BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, drainage  ways, and surface waters. Conditions of Use Use dust control in areas (including roadways) subject to surface and air movement of dust where  on-site or off-site impacts to roadways, drainage ways, or surface waters are likely. Design and Installation Specifications  l Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching,  or paving is impractical, apply gravel or landscaping rock.  l Limit dust generation by clearing only those areas where immediate activity will take place,  leaving the remaining area(s) in the original condition. Maintain the original ground cover as  long as practical.  l Construct natural or artificial windbreaks or windscreens. These may be designed as enclos- ures for small dust sources.  l Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout of  mud onto the street, refer to BMP C105:  Stabilized Construction Access and BMP C106:  Wheel Wash.  l Irrigation water can be used for dust control. Irrigation systems should be installed as a first  step on sites where dust control is a concern.  l Spray exposed soil areas with a dust palliative, following the manufacturer’s instructions and  cautions regarding handling and application. Used oil is prohibited from use as a dust sup- pressant. Local governments may approve other dust palliatives such as calcium chloride or  PAM.  l PAM (BMP C126:  Polyacrylamide (PAM) for Soil Erosion Protection) added to water at a rate  of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is more effect- ive than water alone. This is due to increased infiltration of water into the soil and reduced  evaporation. In addition, small soil particles are bonded together and are not as easily trans- ported by wind. Adding PAM may reduce the quantity of water needed for dust control. Note  that the application rate specified here applies to this BMP, and is not the same application  rate that is specified in BMP C126:  Polyacrylamide (PAM) for Soil Erosion Protection, but the  downstream protections still apply. Refer to BMP C126:  Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use.  PAM shall not be directly applied to water or allowed to enter a water body.  l Contact your local Air Pollution Control Authority for guidance and training on other dust con- trol measures. Compliance with the local Air Pollution Control Authority constitutes  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 313 compliance with this BMP.  l Use vacuum street sweepers.  l Remove mud and other dirt promptly so it does not dry and then turn into dust.  l Techniques that can be used for unpaved roads and lots include:  o Lower speed limits. High vehicle speed increases the amount of dust stirred up from  unpaved roads and lots.  o Upgrade the road surface strength by improving particle size, shape, and mineral types  that make up the surface and base materials.  o Add surface gravel to reduce the source of dust emission. Limit the amount of fine  particles (those smaller than .075 mm) to 10 to 20 percent.  o Use geotextile fabrics to increase the strength of new roads or roads undergoing recon- struction.  o Encourage the use of alternate, paved routes, if available.  o Apply chemical dust suppressants using the admix method, blending the product with  the top few inches of surface material. Suppressants may also be applied as surface  treatments.  o Limit dust-causing work on windy days.  o Pave unpaved permanent roads and other trafficked areas. Maintenance Standards Respray area as necessary to keep dust to a minimum. BMP C150: Materials on Hand Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times  to be used for regular maintenance and emergency situations such as unexpected heavy rains. Hav- ing these materials on-site reduces the time needed to replace existing or implement new BMPs  when inspections indicate that existing BMPs are not meeting the Construction SWPPP require- ments. In addition, contractors can save money by buying some materials in bulk and storing them at  their office or yard. Conditions of Use  l Construction projects of any size or type can benefit from having materials on hand. A small  commercial development project could have a roll of plastic and some gravel available for  immediate protection of bare soil and temporary berm construction. A large earthwork project,  such as highway construction, might have several tons of straw, several rolls of plastic, flexible  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 314 pipe, sandbags, geotextile fabric and steel “T” posts.  l Materials should be stockpiled and readily available before any site clearing, grubbing, or  earthwork begins. A large contractor or project proponent could keep a stockpile of materials  that are available for use on several projects.  l If storage space at the project site is at a premium, the contractor could maintain the materials  at their office or yard. The office or yard must be less than an hour from the project site. Design and Installation Specifications Depending on project type, size, complexity, and length, materials and quantities will vary. A good  minimum list of items that will cover numerous situations includes:  l Clear Plastic, 6 mil  l Drainpipe, 6 or 8 inch diameter  l Sandbags, filled  l Straw Bales for mulching  l Quarry Spalls  l Washed Gravel  l Geotextile Fabric  l Catch Basin Inserts  l Steel "T" Posts  l Silt fence material  l Straw Wattles Maintenance Standards  l All materials with the exception of the quarry spalls, steel “T” posts, and gravel should be kept  covered and out of both sun and rain.  l Re-stock materials as needed. BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of  which can violate water quality standards in the receiving water. Concrete spillage or concrete dis- charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, con- crete process water, and concrete slurry from entering waters of the State. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 315 Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction project com- ponents include, but are not limited to:  l Curbs  l Sidewalks  l Roads  l Bridges  l Foundations  l Floors  l Runways Disposal options for concrete, in order of preference are:  1. Off-site disposal  2. Concrete wash-out areas (see BMP C154: Concrete Washout Area)  3. De minimus washout to formed areas awaiting concrete Design and Installation Specifications  l Wash concrete truck drums at an approved off-site location or in designated concrete  washout areas only. Do not wash out  concrete trucks onto the ground (including formed areas  awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to BMP  C154: Concrete Washout Area for information on concrete washout areas.  o Return unused concrete remaining in the truck and pump to the originating batch plant  for recycling. Do not dump excess concrete on site, except in designated concrete  washout areas as allowed in BMP C154: Concrete Washout Area.  l Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats,  trowels, and wheelbarrows) into designated concrete washout areas or into formed areas  awaiting concrete pour.  l At no time shall concrete be washed off into the footprint of an area where an infiltration fea- ture will be installed.  l Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.  l Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly  (without detention or treatment) to natural or constructed stormwater conveyances.  l Contain washwater and leftover product in a lined container when no  designated concrete  washout areas (or formed areas, allowed as described above) are available. Dispose of con- tained concrete and concrete washwater (process water) properly. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 316  l Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface  waters.  l Refer to BMP C252:  Treating and Disposing of High pH Water for pH adjustment require- ments.  l Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring require- ments if the project involves one of the following activities:  o Significant concrete work (as defined in the CSWGP).  o The use of soils amended with (but not limited to) Portland cement-treated base,  cement kiln dust or fly ash.  o Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for  high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles  and high pH (concrete cutting), both of which can violate the water quality standards in the receiving  water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to  minimize and eliminate process water and slurry created through sawcutting or surfacing from enter- ing waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Saw- cutting and surfacing operations include, but are not limited to:  l Sawing  l Coring  l Grinding  l Roughening  l Hydro-demolition  l Bridge and road surfacing 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 317 Design and Installation Specifications  l Vacuum slurry and cuttings during cutting and surfacing operations.  l Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.  l Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ- ing stormwater systems. This may require temporarily blocking catch basins.  l Dispose of collected slurry and cuttings in a manner that does not violate ground water or sur- face water quality standards.  l Do not allow process water generated during hydro-demolition, surface roughening or similar  operations to drain to any natural or constructed drainage conveyance including stormwater  systems. Dispose of process water in a manner that does not violate ground water or surface  water quality standards.  l Handle and dispose of cleaning waste material and demolition debris in a manner that does  not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an  appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter  waters of the state. If inspections show that a violation of water quality standards could occur, stop  operations and immediately implement preventive measures such as berms, barriers, secondary  containment, and/or vacuum trucks. BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses  from material delivery and storage. Minimize the storage of hazardous materials on-site, store mater- ials in a designated area, and install secondary containment. Conditions of Use Use at construction sites with delivery and storage of the following materials:  l Petroleum products such as fuel, oil and grease  l Soil stabilizers and binders (e.g., Polyacrylamide)  l Fertilizers, pesticides and herbicides  l Detergents  l Asphalt and concrete compounds 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 318  l Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing compounds  l Any other material that may be detrimental if released to the environment Design and Installation Specifications  l The temporary storage area should be located away from vehicular traffic, near the con- struction entrance(s), and away from waterways or storm drains.  l Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be  kept in their original labeled containers.  l Hazardous material storage on-site should be minimized.  l Hazardous materials should be handled as infrequently as possible.  l During the wet weather season (Oct 1 – April 30), consider storing materials in a covered  area.  l Materials should be stored in secondary containments, such as an earthen dike, horse trough,  or even a children’s wading pool for non-reactive materials such as detergents, oil, grease,  and paints. Small amounts of material may be secondarily contained in “bus boy” trays or con- crete mixing trays.  l Do not store chemicals, drums, or bagged materials directly on the ground. Place these items  on a pallet and, when possible, within secondary containment.  l If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater  on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of  drums, preventing water from collecting.  l Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be  stored in approved containers and drums and shall not be overfilled. Containers and drums  shall be stored in temporary secondary containment facilities.  l Temporary secondary containment facilities shall provide for a spill containment volume able  to contain 10% of the total enclosed container volume of all containers, or 110% of the capa- city of the largest container within its boundary, whichever is greater.  l Secondary containment facilities shall be impervious to the materials stored therein for a min- imum contact time of 72 hours.  l Sufficient separation should be provided between stored containers to allow for spill cleanup  and emergency response access.  l During the wet weather season (Oct 1 – April 30), each secondary containment facility shall  be covered during non-working days, prior to and during rain events.  l Keep material storage areas clean, organized and equipped with an ample supply of appro- priate spill clean-up material (spill kit).  l The spill kit should include, at a minimum: 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 319  o 1-Water Resistant Nylon Bag  o 3-Oil Absorbent Socks 3”x 4’  o 2-Oil Absorbent Socks 3”x 10’  o 12-Oil Absorbent Pads 17”x19”  o 1-Pair Splash Resistant Goggles  o 3-Pair Nitrile Gloves  o 10-Disposable Bags with Ties  o Instructions Maintenance Standards  l Secondary containment facilities shall be maintained free of accumulated rainwater and spills.  In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed  into drums. These liquids shall be handled as hazardous waste unless testing determines  them to be non-hazardous.  l Re-stock spill kit materials as needed. BMP C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting  washout off-site, or performing on-site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where:  l Concrete is used as a construction material  l It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant,  etc.).  l Concrete truck drums are washed on-site. Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete  handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheel- barrows) may be washed into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will  be installed. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 320 Design and Installation Specifications Implementation  l Perform washout of concrete truck drums at an approved off-site location or in designated con- crete washout areas only.  l Do not wash out concrete onto non-formed areas, or into storm drains, open ditches, streets,  or streams.  l Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.  l Do not allow excess concrete to be dumped on-site, except in designated concrete washout  areas as allowed above.  l Concrete washout areas may be prefabricated concrete washout containers, or self-installed  structures (above-grade or below-grade).  l Prefabricated containers are most resistant to damage and protect against spills and leaks.  Companies may offer delivery service and provide regular maintenance and disposal of solid  and liquid waste.  l If self-installed concrete washout areas are used, below-grade structures are preferred over  above-grade structures because they are less prone to spills and leaks.  l Self-installed above-grade structures should only be used if excavation is not practical.  l Concrete washout areas shall be constructed and maintained in sufficient quantity and size to  contain all liquid and concrete waste generated by washout operations. Education  l Discuss the concrete management techniques described in this BMP with the ready-mix con- crete supplier before any deliveries are made.  l Educate employees and subcontractors on the concrete waste management techniques  described in this BMP.  l Arrange for the contractor’s superintendent or Certified Erosion and Sediment Control Lead  (CESCL) to oversee and enforce concrete waste management procedures.  l A sign should be installed adjacent to each concrete washout area to inform concrete equip- ment operators to utilize the proper facilities. Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor  agreements. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 321 Location and Placement  l Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains,  open ditches, water bodies, or wetlands.  l Allow convenient access to the concrete washout area for concrete trucks, preferably near the  area where the concrete is being poured.  l If trucks need to leave a paved area to access the concrete washout area, prevent track-out  with a pad of rock or quarry spalls (see BMP C105:  Stabilized Construction Access). These  areas should be far enough away from other construction traffic to reduce the likelihood of acci- dental damage and spills.  l The number of concrete washout areas you install should depend on the expected demand  for storage capacity.  l On large sites with extensive concrete work, concrete washout areas should be placed in mul- tiple locations for ease of use by concrete truck drivers. Concrete Truck Washout Procedures  l Washout of concrete truck drums shall be performed in designated concrete washout areas  only.  l Concrete washout from concrete pumper bins can be washed into concrete pumper trucks  and discharged into designated concrete washout areas or properly disposed of off-site. Concrete Washout Area Installation  l Concrete washout areas should be constructed as shown in the figures below, with a recom- mended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to  contain all liquid and concrete waste generated by washout operations.  l Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free  of holes, tears, or other defects that compromise the impermeability of the material.  l Lath and flagging should be commercial type.  l Liner seams shall be installed in accordance with manufacturers’ recommendations.  l Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the  plastic lining material. Maintenance Standards Inspection and Maintenance  l Inspect and verify that concrete washout areas are in place prior to the commencement of con- crete work.  l Once concrete wastes are washed into the designated washout area and allowed to harden,  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 322 the concrete should be broken up, removed, and disposed of per applicable solid waste reg- ulations. Dispose of hardened concrete on a regular basis.  l During periods of concrete work, inspect the concrete washout areas daily to verify continued  performance.  o Check overall condition and performance.  o Check remaining capacity (% full).  o If using self-installed concrete washout areas, verify plastic liners are intact and side- walls are not damaged.  o If using prefabricated containers, check for leaks.  l Maintain the concrete washout areas to provide adequate holding capacity with a minimum  freeboard of 12 inches.  l Concrete washout areas must be cleaned, or new concrete washout areas must be con- structed and ready for use once the concrete washout area is 75% full.  l If the concrete washout area is nearing capacity, vacuum and dispose of the waste material in  an approved manner.  l Do not discharge liquid or slurry to waterways, storm drains or directly onto ground.  l Do not discharge to the sanitary sewer without local approval.  l Place a secure, non-collapsing, non-water collecting cover over the concrete washout  area prior to predicted wet weather to prevent accumulation and overflow of pre- cipitation.  l Remove and dispose of hardened concrete and return the structure to a functional con- dition. Concrete may be reused on-site or hauled away for disposal or recycling.  l When you remove materials from a self-installed concrete washout area, build a new struc- ture; or, if the previous structure is still intact, inspect for signs of weakening or damage, and  make any necessary repairs. Re-line the structure with new plastic after each cleaning. Removal of Concrete Washout Areas  l When concrete washout areas are no longer required for the work, the hardened concrete,  slurries and liquids shall be removed and properly disposed of.  l Materials used to construct concrete washout areas shall be removed from the site of the work  and disposed of or recycled.  l Holes, depressions or other ground disturbance caused by the removal of the concrete  washout areas shall be backfilled, repaired, and stabilized to prevent erosion. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 323 Figure II-3.7: Concrete Washout Area with Wood Planks 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 324 3m Minimum -e- -e-Lath and flagging on 3 sides Sandbag0□ CD □ '>TI SandbagBermc> 10 mil plastic lining□Varies A iAf 'Xo-o-1 m •x Q —I Berm 10 CD CD Section A-A6 10 mil plastic liningPlan Notes: 1.Actual layout determined in the field. A concrete washout sign shall be installed within 10 m of the temporary concrete washout facility. Type "Below Grade ii 2. 3m Minimum JSL JHL T8T Wood frame securely fastened around entire perimeter with two stakes B BtI■s-a ■s-a Varies 10 mil plastic lining S 3 E VStake (typ.) M Section B-Bw 10 mil plastic lining Two-stacked 2x12 rough wood frame Plan Type "Above Grade" with Wood Planks NOT TO SCALE Concrete Washout Area with Wood Planks Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Figure II-3.8: Concrete Washout Area with Straw Bales 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 325 Straw bale 10 mil plastic lining Binding wire Staples (2 per bale)Native material (optional) Wood or metal stakes (2 per bale) Plywood 1200 mm x 610 mm painted white Wood post (89 mm x 89 mm x 2.4 m)Lag screws (12.5 mm)Section B-B Black letters 150 mm heightILCONCRETE WASHOUT' U915 mm f 915 mm T3m Minimum Concrete Washout Sign Detail (or equivalent)Stake (typ)A B Bt1 i 50 mm 3.05 mm dia. steel wire Varies 200 mm f Staple Detail 10 mil plastic lining Notes:Straw bale (typ)1. Actual layout determined in the field. The concrete washout sign shall be installed within 10 m of the temporary concrete washout facility. Plan 2. Type "Above Grade" with Straw Bales NOT TO SCALE Concrete Washout Area with Straw Bales Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Figure II-3.9: Prefabricated Concrete Washout Container w/Ramp 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 326 ■•-0 \riy l-j X - NOT TO SCALE Prefabricated Concrete Washout Container w/Ramp Revised June 2016DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyright.htmMor copyright notice including permissions, limitation of liability, and disclaimer.State of Washington BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge of  erosion and sediment control (ESC), and water quality protection. The designated person shall be  responsible for ensuring compliance with all local, state, and federal erosion and sediment control  and water quality requirements. Construction sites one acre or larger that discharge to waters of the  State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the responsible  representative. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur- face waters of the state. Sites less than one acre may have a person without CESCL certification  conduct inspections. The CESCL shall:  l Have a current certificate proving attendance in an erosion and sediment control training  course that meets the minimum ESC training and certification requirements established by  Ecology. Ecology has provided the minimum requirements for CESCL course training, as well as a list  of ESC training and certification providers at:  https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed- iment-control  OR  l Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional inform- ation go to:  http://www.envirocertintl.org/cpesc/ Specifications  l CESCL certification shall remain valid for three years.  l The CESCL shall have authority to act on behalf of the contractor or project proponent and  shall be available, or on-call, 24 hours per day throughout the period of construction.  l The Construction SWPPP shall include the name, telephone number, fax number, and  address of the designated CESCL. See II-2 Construction Stormwater Pollution Prevention  Plans (Construction SWPPPs).  l A CESCL may provide inspection and compliance services for multiple construction projects  in the same geographic region, but must be on site whenever earthwork activities are  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 327 occurring that could generate release of turbid water.  l Duties and responsibilities of the CESCL shall include, but are not limited to the following:  o Maintaining a permit file on site at all times which includes the Construction SWPPP  and any associated permits and plans.  o Directing BMP installation, inspection, maintenance, modification, and removal.  o Updating all project drawings and the Construction SWPPP with changes made.  o Completing any sampling requirements including reporting results using electronic Dis- charge Monitoring Reports (WebDMR).  o Facilitate, participate in, and take corrective actions resulting from inspections per- formed by outside agencies or the owner.  o Keeping daily logs, and inspection reports. Inspection reports should include:  n Inspection date/time.  n Weather information; general conditions during inspection and approximate  amount of precipitation since the last inspection.  n Visual monitoring results, including a description of discharged stormwater. The  presence of suspended sediment, turbid water, discoloration, and oil sheen shall  be noted, as applicable.  n Any water quality monitoring performed during inspection.  n General comments and notes, including a brief description of any BMP repairs,  maintenance or installations made as a result of the inspection.  n A summary or list of all BMPs implemented, including observations of all  erosion/sediment control structures or practices. The following shall be noted:  1. Locations of BMPs inspected.  2. Locations of BMPs that need maintenance.  3. Locations of BMPs that failed to operate as designed or intended.  4. Locations of where additional or different BMPs are required. BMP C162: Scheduling Purpose Sequencing a construction project reduces the amount and duration of soil exposed to erosion by  wind, rain, runoff, and vehicle tracking. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 328 Conditions of Use The construction sequence schedule is an orderly listing of all major land-disturbing activities  together with the necessary erosion and sedimentation control measures planned for the project.  This type of schedule guides the contractor on work to be done before other work is started so that  serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land-disturbing activities and the  installation of control measures is perhaps the most cost-effective way of controlling erosion during  construction. The removal of ground cover leaves a site vulnerable to erosion. Construction sequen- cing that limits land clearing, provides timely installation of erosion and sedimentation controls, and  restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations  l Minimize construction during rainy periods.  l Schedule projects to disturb only small portions of the site at any one time. Complete grading  as soon as possible. Immediately stabilize the disturbed portion before grading the next por- tion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses. II-3.3 Construction Runoff BMPs BMP C200: Interceptor Dike and Swale Purpose Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the peri- meter of a disturbed construction area to convey stormwater. Use the dike and/or swale to intercept  the runoff from unprotected areas and direct it to areas where erosion can be controlled. This can  prevent storm runoff from entering the work area or sediment-laden runoff from leaving the con- struction site. Conditions of Use Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be con- veyed to an erosion control BMP which can safely convey the stormwater.  l Locate upslope of a construction site to prevent runoff from entering the disturbed area.  l When placed horizontally across a disturbed slope, it reduces the amount and velocity of run- off flowing down the slope.  l Locate downslope to collect runoff from a disturbed area and direct it to a sediment  BMP (e.g.  BMP C240:  Sediment Trap or BMP C241:  Sediment Pond (Temporary)). 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 329 Conditions of Use The construction sequence schedule is an orderly listing of all major land-disturbing activities  together with the necessary erosion and sedimentation control measures planned for the project.  This type of schedule guides the contractor on work to be done before other work is started so that  serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land-disturbing activities and the  installation of control measures is perhaps the most cost-effective way of controlling erosion during  construction. The removal of ground cover leaves a site vulnerable to erosion. Construction sequen- cing that limits land clearing, provides timely installation of erosion and sedimentation controls, and  restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations  l Minimize construction during rainy periods.  l Schedule projects to disturb only small portions of the site at any one time. Complete grading  as soon as possible. Immediately stabilize the disturbed portion before grading the next por- tion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses. II-3.3 Construction Runoff BMPs BMP C200: Interceptor Dike and Swale Purpose Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the peri- meter of a disturbed construction area to convey stormwater. Use the dike and/or swale to intercept  the runoff from unprotected areas and direct it to areas where erosion can be controlled. This can  prevent storm runoff from entering the work area or sediment-laden runoff from leaving the con- struction site. Conditions of Use Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be con- veyed to an erosion control BMP which can safely convey the stormwater.  l Locate upslope of a construction site to prevent runoff from entering the disturbed area.  l When placed horizontally across a disturbed slope, it reduces the amount and velocity of run- off flowing down the slope.  l Locate downslope to collect runoff from a disturbed area and direct it to a sediment  BMP (e.g.  BMP C240:  Sediment Trap or BMP C241:  Sediment Pond (Temporary)). 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 329 Design and Installation Specifications  l Dike and/or swale and channel must be stabilized with temporary or permanent vegetation or  other channel protection during construction.  l Steep grades require channel protection and check dams.  l Review construction for areas where overtopping may occur.  l Can be used at the top of new fill before vegetation is established.  l May be used as a permanent diversion channel to carry the runoff.  l Contributing area for an individual dike or swale should be one acre or less.  l Design the dike and/or swale to contain flows calculated by one of the following methods:  o Single Event Hydrograph Method: The peak volumetric flow rate calculated using a 10- minute time step from a Type 1A, 10-year, 24-hour frequency storm for the worst-case  land cover condition. OR  o Continuous Simulation Method: The 10-year peak flow rate, as determined by an  approved continuous runoff model with a 15-minute time step for the worst-case land  cover condition. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analysis  (in most cases, this would be the land cover conditions just prior to final landscaping). Interceptor Dikes Interceptor dikes shall meet the following criteria:  l Top Width: 2 feet minimum.  l Height:  1.5 feet minimum on berm.  l Side Slope: 2H:1V or flatter.  l Grade: Depends on topography, however, dike system minimum is 0.5%, and maximum is  1%.  l Compaction: Minimum of 90 percent ASTM D698 standard proctor.  l Stabilization: Depends on velocity and reach. Inspect regularly to ensure stability.  l Ground Slopes <5%: Seed and mulch applied within 5 days of dike construction (see BMP  C121: Mulching).  l Ground Slopes 5 - 40%: Dependent on runoff velocities and dike materials. Stabilization  should be done immediately using either sod or riprap, or other measures to avoid erosion.  l The upslope side of the dike shall provide positive drainage to the dike outlet. No erosion shall  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 330 occur at the outlet. Provide energy dissipation measures as necessary. Sediment-laden runoff  must be released through a sediment trapping facility.  l Minimize construction traffic over temporary dikes. Use temporary cross culverts for channel  crossing.  l See Table II-3.8: Horizontal Spacing of Interceptor Dikes Along Ground Slope for recom- mended horizontal spacing between dikes. Average Slope Slope Percent Flowpath Length 20H:1V or less 3-5%300  feet (10 to 20)H:1V 5-10%200  feet (4 to 10)H:1V 10-25%100  feet (2 to 4)H:1V 25-50%50  feet Table II-3.8: Horizontal Spacing of Interceptor Dikes Along Ground Slope Interceptor Swales Interceptor swales shall meet the following criteria:  l Bottom Width: 2 feet minimum; the cross-section bottom shall be level.  l Depth: 1-foot minimum.  l Side Slope: 2H:1V or flatter.  l Grade: Maximum 5 percent, with positive drainage to a suitable outlet (such as BMP C241:   Sediment Pond (Temporary)).  l Stabilization: Seed as per BMP C120: Temporary and Permanent Seeding, or BMP C202:   Riprap Channel Lining, 12 inches thick riprap pressed into the bank and extending at least 8  inches vertical from the bottom. Maintenance Standards  l Inspect diversion dikes and interceptor swales once a week and after every rainfall. Imme- diately remove sediment from the flow area.  l Damage caused by construction traffic or other activity must be repaired before the end of  each working day.  l Check outlets and make timely repairs as needed to avoid gully formation. When the area  below the temporary diversion dike is permanently stabilized, remove the dike and fill and sta- bilize the channel to blend with the natural surface. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 331 thickness is 2 feet.  o For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), use an  engineered energy dissipator.  o Filter fabric or erosion control blankets should always be used under riprap to prevent  scour and channel erosion. See BMP C122:  Nets and Blankets.  l Bank stabilization, bioengineering, and habitat features may be required for disturbed areas.  This work may require a Hydraulic Project Approval (HPA) from the Washington State Depart- ment of Fish and Wildlife. See I-2.11 Hydraulic Project Approvals. Maintenance Standards  l Inspect and repair as needed.  l Add rock as needed to maintain the intended function.  l Clean energy dissipator if sediment builds up. BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- bilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed  areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and  within 500 feet of a disturbed or construction area, unless  those inlets are preceded by a sediment  trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction. These small and  numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof  drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap  these drains to prevent sediment from entering the system until completion of landscaping. Provide  18-inches of sod around each finished lawn and yard drain. Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods  for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain- age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with  additional end-of-pipe treatment where stormwater ponding would cause a hazard. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 356 Type of Inlet Pro- tection Emergency Overflow Applicable for Paved/ Earthen Sur- faces Conditions of Use Drop Inlet Protection Excavated  drop  inlet protection Yes, temporary  flooding may   occur Earthen Applicable for heavy flows. Easy   to maintain. Large area requirement:   30'x30'/acre Block  and gravel  drop inlet pro- tection Yes Paved or Earthen Applicable for heavy  concentrated flows.  Will not pond. Gravel and wire  drop inlet pro- tection No Paved or Earthen Applicable for  heavy concentrated flows.  Will pond. Can withstand traffic. Catch  basin filters Yes Paved or Earthen Frequent maintenance  required. Curb Inlet Protection Curb  inlet pro- tection with  wooden weir Small capacity  overflow Paved Used for sturdy, more compact  install- ation. Block and gravel  curb inlet pro- tection Yes Paved Sturdy, but  limited filtration. Culvert Inlet Protection Culvert  inlet sed- iment trap N/A N/A 18 month expected life. Table II-3.10: Storm Drain Inlet Protection Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet.  Sediment settles out of the stormwater prior to entering the storm drain. Design and installation spe- cifications for excavated drop inlet protection include:  l Provide a depth of 1-2 ft as measured from the crest of the inlet structure.  l Slope sides of excavation should be no steeper than 2H:1V.  l Minimum volume of excavation is 35 cubic yards.  l Shape the excavation to fit the site, with the longest dimension oriented toward the longest  inflow area.  l Install provisions for draining to prevent standing water.  l Clear the area of all debris. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 357  l Grade the approach to the inlet uniformly.  l Drill weep holes into the side of the inlet.  l Protect weep holes with screen wire and washed aggregate.  l Seal weep holes when removing structure and stabilizing area.  l Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass  flow. Block and Gravel Filter A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel.  See Figure II-3.17: Block and Gravel Filter. Design and installation specifications for block gravel fil- ters include:  l Provide a height of 1 to 2 feet above the inlet.  l Recess the first row of blocks 2-inches into the ground for stability.  l Support subsequent courses by placing a pressure treated wood 2x4 through the block open- ing.  l Do not use mortar.  l Lay some blocks in the bottom row on their side to allow for dewatering the pool.  l Place hardware cloth or comparable wire mesh with ½-inch openings over all block openings.  l Place gravel to just below the top of blocks on slopes of 2H:1V or flatter.  l An alternative design is a gravel berm surrounding the inlet, as follows:  o Provide a slope of 3H:1V on the upstream side of the berm.  o Provide a slope of 2H:1V on the downstream side of the berm.  o Provide a 1-foot wide level stone area between the gravel berm and the inlet.  o Use stones 3 inches in diameter or larger on the upstream slope of the berm.  o Use gravel ½- to ¾-inch at a minimum thickness of 1-foot on the downstream slope of  the berm. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 358 Figure II-3.17: Block and Gravel Filter   2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 359 A Drain grate r>Aft> QS, SSL ogjfe Q. ~ _ ?rygioSOso^cy.;Concrete block Sfei A* o• o>cr> °i?o ^•Pa- ■sPc^I? 4 STTO <&', Gravel backfill■osVf\ A-°i ° _?o “■'frvSPP^ •§?° to. gdp> §0-^<S> q® v«r.^4y A Plan View Concrete block Wire screen or filter fabric Overflow water Gravel backfill Ponding height |5»S Water'^n iplllpfls^Drop inlet Section A-A Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas, (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure. NOT TO SCALE Block and Gravel Filter Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does not  provide an overflow. Design and installation specifications for gravel and wire mesh filters include:  l Use a hardware cloth or comparable wire mesh with ½-inch openings.  o Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey- ond each side of the inlet structure.  o Overlap the strips if more than one strip of mesh is necessary.  l Place coarse aggregate over the wire mesh.  o Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at  least 18-inches on all sides. Catch Basin Filters Catch  basin filters are designed by manufacturers for construction sites. The limited sediment stor- age capacity increases the amount of inspection and maintenance required, which may be daily for  heavy sediment loads. To reduce maintenance requirements, combine a catch  basin filter with  another type of inlet protection. This type of inlet protection provides flow bypass without overflow  and therefore may be a better method for inlets located along active rights-of-way. Design and install- ation specifications for catch basin filters include:  l Provides 5 cubic feet of storage.  l Requires dewatering provisions.  l Provides a high-flow bypass that will not clog under normal use at a construction site.  l Insert the catch  basin filter in the catch  basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb  inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection  with wooden weirs include:  l Use wire mesh with ½-inch openings.  l Use extra strength filter cloth.  l Construct a frame.  l Attach the wire and filter fabric to the frame.  l Pile coarse washed aggregate against the wire and fabric.  l Place weight on the frame anchors. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 360 Block and Gravel Curb Inlet Protection Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and  gravel. See Figure II-3.18: Block and Gravel Curb Inlet Protection. Design and installation spe- cifications for block and gravel curb inlet protection include:  l Use wire mesh with ½-inch openings.  l Place two concrete blocks on their sides abutting the curb at either side of the inlet opening.  These are spacer blocks.  l Place a 2x4 stud through the outer holes of each spacer block to align the front blocks.  l Place blocks on their sides across the front of the inlet and abutting the spacer blocks.  l Place wire mesh over the outside vertical face.  l Pile coarse aggregate against the wire to the top of the barrier. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 361 Figure II-3.18: Block and Gravel Curb Inlet Protection   2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 362 A Catch basin Back of sidewalk 2x4 Wood stud Curb inletBack of curb Concrete block pt < 1'[ ]o a & Wire screen or filter fabric 3c§ i?$C5 3Ko..om,o jOjsQi 0»Wm JS SS A Concrete block% inch (20 mm) Drain gravel Plan View Ponding height % inch (20 mm) Drain gravel Overflow w I□Curb inlet Wire screen or filter fabric r2x4 Wood stud (100x50 Timber stud)/iCatch basin Concrete block Section A-A Notes: 1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street 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.NOT TO SCALE Block and Gravel Curb Inlet Protection Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Curb and Gutter Sediment Barrier Curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high and 3  feet wide in a horseshoe shape. See Figure II-3.19: Curb and Gutter Barrier. Design and installation  specifications for curb and gutter sediment barrier include:  l Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high  and 3 feet wide, at least 2 feet from the inlet.  l Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size the  trap to sediment trap standards for protecting a culvert inlet. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 363 Figure II-3.19: Curb and Gutter Barrier 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 364 Back of sidewalk Burlap sacks to overlap onto curb Back of curb Curb inletRunoff SpillwayRunoff Catch basin Plan View Gravel filled sandbags stacked tightly Notes: 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.NOT TO SCALE Curb and Gutter Barrier Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Maintenance Standards  l Inspect all forms of inlet protection frequently, especially after storm events. Clean and  replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the  inlet and clean or replace. An alternative approach would be to use the clogged rock as fill and  put fresh rock around the inlet.  l Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly  over the surrounding land area or stockpile and stabilize as appropriate. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not  pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions  may choose not to accept these products, or may require additional testing prior to consideration for  local use. Products that Ecology has approved as functionally equivalent are available for review on  Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C231: Brush Barrier Purpose The purpose of brush barriers is to reduce the transport of coarse sediment from a construction site  by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland  flow. Conditions of Use  l Brush barriers may be used downslope of disturbed areas that are less than one-quarter acre.  l Brush barriers are not intended to treat concentrated flows, nor are they intended to treat sub- stantial amounts of overland flow. Any concentrated flows must be directed to a sediment trap- ping BMP. The only circumstance in which overland flow can be treated solely by a brush  barrier, rather than by a sediment trapping BMP, is when the area draining to the barrier is  small.  l Brush barriers should only be installed on contours. Design and Installation Specifications  l Height: 2 feet (minimum) to 5 feet (maximum).  l Width: 5 feet at base (minimum) to 15 feet (maximum).  l Filter fabric (geotextile) may be anchored over the brush berm to enhance the filtration ability  of the barrier. Ten-ounce burlap is an adequate alternative to filter fabric. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 365 N/A BMP C233: Silt Fence Purpose Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary  physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas.  l Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the  top of the silt fence, but shall allow the water to pass through the fence.  l Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial  amounts of overland flow. Convey any concentrated flows through the drainage system to a  sediment trapping BMP.  l Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide  an adequate method of silt control for anything deeper than sheet or overland flow. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 370 Figure II-3.22: Silt Fence 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 371 Joints in geotextile fabric shall be spliced at posts. Use staples, wire rings or equivalent to attach fabric to posts 2"x2" by 14 Ga. wire or equivalent, if standard strength fabric used x x X VX' XX>0<A xoi Rx Xxx>-X>:X XXXX’1 I EEj-X X I I: ;■;<>'_ >' *X xvwy !>x x ■,x' _n------ i ii i 6' max IMinimum 4''x4'' trench I II Post spacing may be increased to 8' if wire backing is used 2"x2" wood posts, steel fence posts, or equivalent 2''x2" by 14 Ga. wire or equivalent, if standard strength fabric used Geotextile fabric 2' min 7 Backfill trench with native soil or %" - 1.5" washed gravel r 'ToplE -T.\\ Minimum 4''x4'' trench . V 2"x2" wood posts, steel fence posts, or equivalent NOT TO SCALE Silt Fence Revised July 2017 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Design and Installation Specifications  l Use in combination with other construction stormwater BMPs.  l Maximum slope steepness (perpendicular to the silt fence line) 1H:1V.  l Maximum sheet or overland flow path length to the silt fence of 100 feet.  l Do not allow flows greater than 0.5 cfs.  l Use geotextile fabric that meets the following standards. All geotextile properties listed below  are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or  exceed the values shown in Table II-3.11: Geotextile Fabric Standards for Silt Fence): Geotextile Property Minimum Average Roll Value Polymeric  Mesh AOS  (ASTM D4751) 0.60 mm maximum for slit film  woven (#30 sieve).  0.30 mm  maximum for all other geotextile types (#50 sieve).  0.15 mm minimum for all fabric types (#100 sieve). Water  Permittivity  (ASTM D4491) 0.02 sec-1 minimum Grab  Tensile Strength  (ASTM D4632) 180 lbs. Minimum for extra  strength fabric.  100 lbs  minimum for standard strength fabric. Grab Tensile Strength  (ASTM D4632) 30% maximum Ultraviolet  Resistance  (ASTM D4355) 70%  minimum Table II-3.11: Geotextile Fabric Standards for Silt Fence  l Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire,  safety fence, or jute mesh to increase the strength of the geotextile. Silt fence materials are  available that have synthetic mesh backing attached.  l Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum  of six months of expected usable construction life at a temperature range of 0°F to 120°F.  l One-hundred percent biodegradable silt fence is available that is strong, long lasting, and can  be left in place after the project is completed, if permitted by the local jurisdiction.  l Refer to Figure II-3.22: Silt Fence for standard silt fence details. Include the following Stand- ard Notes for silt fence on construction plans and specifications:  1. The Contractor shall install and maintain temporary silt fences at the locations shown in  the Plans.  2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those  activities. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 372  3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the original  ground surface.  4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric  lengths as required. Locate all sewn seams at support posts. Alternatively, two sections  of silt fence can be overlapped, provided  that the overlap is long enough and that the  adjacent silt fence sections are close enough together to prevent silt laden water from  escaping through the fence at the overlap.  5. Attach the geotextile fabric on the up-slope side of the posts and secure with staples,  wire, or in accordance with the manufacturer's recommendations. Attach the geotextile  fabric to the posts in a manner that reduces the potential for tearing.  6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of  the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely  to the up-slope side of the posts with the geotextile fabric up-slope of the mesh.  7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2- inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh  shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh  must be as resistant to the same level of ultraviolet radiation as the geotextile fabric it  supports.  8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill  and tamp soil in place over the buried portion of the geotextile fabric, so that no flow can  pass beneath the silt fence and scouring cannot occur. When wire or polymeric back-up  support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches  min.  9. Drive or place the silt fence posts into the ground 18-inches min. A 12–inch min. depth  is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be  reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of  3H:1V or steeper and the slope is perpendicular to the fence. If required post depths  cannot be obtained, the posts shall be adequately secured by bracing or guying to pre- vent overturning of the fence due to sediment loading.  10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a max- imum of 6-feet. Posts shall consist of either:  l Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall be  free of defects such as knots, splits, or gouges.  l No. 6 steel rebar or larger.  l ASTM A 120 steel pipe with a minimum diameter of 1-inch.  l U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft.  l Other steel posts having equivalent strength and bending resistance to the post  sizes listed above.  11. Locate silt fences on contour as much as possible, except at the ends of the fence,  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 373 where the fence shall be turned uphill such that the silt fence captures the runoff water  and prevents water from flowing around the end of the fence.  12. If the fence must cross contours, with the exception of the ends of the fence, place  check dams perpendicular to the back of the fence to minimize concentrated flow and  erosion. The slope of the fence line where contours must be crossed shall not be  steeper than 3H:1V.  l Check dams shall be approximately 1-foot deep at the back of the fence. Check  dams shall be continued perpendicular to the fence at the same elevation until  the top of the check dam intercepts the ground surface behind the fence.  l Check dams shall consist of crushed surfacing base course, gravel backfill for  walls, or shoulder ballast. Check dams shall be located every 10 feet along the  fence where the fence must cross contours.  l Refer to Figure II-3.23: Silt Fence Installation by Slicing Method for slicing method details. The  following are specifications for silt fence installation using the slicing method:  1. The base of both end posts must be at least 2- to 4-inches above the top of the geo- textile fabric on the middle posts for ditch checks to drain properly. Use a hand level or  string level, if necessary, to mark base points before installation.  2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart in standard  applications.  3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as  possible to the geotextile fabric, enabling posts to support the geotextile fabric from  upstream water pressure.  4. Install posts with the nipples facing away from the geotextile fabric.  5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8- inches of the fabric. Attach each tie diagonally 45 degrees through the fabric, with each  puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post  nipple when tightening to prevent sagging.  6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure  with 3 ties.  7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level.  8. Compact the soil immediately next to the geotextile fabric with the front wheel of the  tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the  upstream side first and then each side twice for a total of four trips. Check and correct  the silt fence installation for any deviation before compaction. Use a flat-bladed shovel  to tuck the fabric deeper into the ground if necessary. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 374 Figure II-3.23: Silt Fence Installation by Slicing Method 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 375 Ponding height max. 24" \v 3: 3:POST SPACING: 7 max. on open runs 4' max. on pooling areasAttach fabric to upstream side of post Top of Fabric I'////A E'////// Belt * FLOW POST DEPTH: As much below ground as fabric above ground top 8" Drive over each side of silt fence 2 to 4 times with device exerting 60 p.s.i. or greater i Diagonal attachment doubles strength100% compaction100% compaction r33n TT~ J]=I iLE inWo Q.ILEt Attachment Details: • Gather fabric at posts, if needed. • Utilize three ties per post, all within top 8" of fabric. • Position each tie diagonally, puncturing holes vertically a minimum of 1" apart. • Hang each tie on a post nipple and tighten securely. Use cable ties (50 lbs) or soft wire. oQ. Q.31HM1I meii=iii=iii i=in No more than 24" of a 36" fabric is allowed above ground Roll of silt fenceOperation Post installed after compaction Fabric above groundPIo Silt Fence ifJC il==U 200 - jj=ji 300mmIrmssrSlicing blade (18 mm width) Horizontal chisel point (76 mm width) Completed Installation Vibratory plow is not acceptable because of horizontal compaction NOT TO SCALE Silt Fence Installation by Slicing Method Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Maintenance Standards  l Repair any damage immediately.  l Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap- ping BMP.  l Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to  flow and then causing channelization of flows parallel to the fence. If this occurs, replace the  fence and remove the trapped sediment.  l Remove sediment deposits when the deposit reaches approximately one-third the height of  the silt fence, or install a second silt fence.  l Replace geotextile fabric that has deteriorated due to ultraviolet breakdown. BMP C234: Vegetated Strip Purpose Vegetated strips reduce the transport of coarse sediment from a construction site by providing a  physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use  l Vegetated strips may be used downslope of all disturbed areas.  l Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat  substantial amounts of overland flow. Any concentrated flows must be conveyed through the  drainage system to BMP C241:  Sediment Pond (Temporary) or other sediment trapping  BMP. The only circumstance in which overland flow can be treated solely by a vegetated strip,  rather than by a sediment trapping BMP, is when the following criteria are met (see Table II- 3.12: Contributing Drainage Area for Vegetated Strips): Average Contributing Area Slope Average Contributing Area Per- cent Slope Max Contributing area Flowpath Length 1.5H : 1V or flatter 67% or flatter 100 feet 2H : 1V or  flatter 50% or flatter 115 feet 4H : 1V or  flatter 25% or flatter 150  feet 6H : 1V or  flatter 16.7% or flatter 200  feet 10H : 1V or  flatter 10% or flatter 250  feet Table II-3.12: Contributing Drainage Area for Vegetated Strips 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 376 Design and Installation Specifications  l The vegetated strip shall consist of a continuous strip of dense vegetation with topsoil for a min- imum of a 25-foot length along the flowpath. Grass-covered, landscaped areas are generally  not adequate because the volume of sediment overwhelms the grass. Ideally, vegetated strips  shall consist of undisturbed native growth with a well-developed soil that allows for infiltration  of runoff.  l The slope within the vegetated strip shall not exceed 4H:1V.  l The uphill boundary of the vegetated strip shall be delineated with clearing limits. Maintenance Standards  l Any areas damaged by erosion or construction activity shall be seeded immediately and pro- tected by mulch.  l If more than 5 feet of the original vegetated strip width has had vegetation removed or is being  eroded, sod must be installed.  l If there are indications that concentrated flows are traveling across the vegetated strip, storm- water runoff controls must be installed to reduce the flows entering the vegetated strip, or addi- tional perimeter protection must be installed. BMP C235: Wattles Purpose Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or other  material that is wrapped in netting made of natural plant fiber or similar encasing material. They  reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sed- iment. Conditions of Use  l Wattles shall consist of cylinders of plant material such as weed-free straw, coir, wood chips,  excelsior, or wood fiber or shavings encased within netting made of natural plant fibers  unaltered by synthetic materials.  l Use wattles:  o In disturbed areas that require immediate erosion protection.  o On exposed soils during the period of short construction delays, or over winter months.  o On slopes requiring stabilization until permanent vegetation can be established.  l The material used dictates the effectiveness period of the wattle. Generally, wattles are effect- ive for one to two seasons. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 377  l Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water from  passing between them. Design Criteria  l See Figure II-3.24: Wattles for typical construction details.  l Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length.   l Install wattles perpendicular to the flow direction and parallel to the slope contour.  l Place wattles in shallow trenches, staked along the contour of disturbed or newly constructed  slopes. Dig narrow trenches 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 areas with high rainfall,  the trenches should be dug to a depth of 5- to 7- inches, or 1/2 to 2/3 of the thickness of the  wattle.  l Start building trenches and installing wattles from the base of the slope and work up. Spread  excavated material evenly along the uphill slope and compact it using hand tamping or other  methods.  l Construct trenches at intervals of 10- to 25-feet depending on the steepness of the slope, soil  type, and rainfall. The steeper the slope the closer together the trenches.  l Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12 inches  behind one another.  l Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle.  l If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle  and into the soil.  l Wooden stakes should be approximately 0.75 x 0.75 x 24 inches min. Willow cuttings or 3/8- inch rebar can also be used for stakes.  l Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake pro- truding above the wattle. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 378 Figure II-3.24: Wattles 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 379 3' -4' (1,2 m) jjlSi\fc Viz Overlap adjacent rolls 12" behind one another / /■y \Straw rolls must be placed along slope contours /// \/ \ v-C »S \J/10' - 25' (3-8m)d ■■■ Spacing depends on soil type and slope steepness y. Sediment, organic matter, and native seeds are captured behind the rolls.*3 3"-5" (75-125mm) N\ 8"-10" Dia. (200-250mm)A///-<A.//A Live Stake // // // 1"x1" Stake £/ (25 x 25mm)/ \/ V NOTE:l 1. Straw roll installation requires the placement and secure staking of the roll in a trench, 3" - 5" (75-125mm) deep, dug on contour. Runoff must not be allowed to run under or around roll. A NOT TO SCALE Wattles Revised December 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Maintenance Standards  l Wattles may require maintenance to ensure they are in contact with soil and thoroughly  entrenched, especially after significant rainfall on steep sandy soils.  l Inspect the slope after significant storms and repair any areas where wattles are not tightly  abutted or water has scoured beneath the wattles. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not  pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions  may choose not to accept these products, or may require additional testing prior to consideration for  local use. Products that Ecology has approved as functionally equivalent are available for review on  Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C236: Vegetative Filtration Purpose Vegetative filtration as a BMP is used in conjunction with detention storage in the form of portable  tanks or BMP C241:  Sediment Pond (Temporary), BMP C206:  Level Spreader, and a pumping sys- tem with surface intake. Vegetative filtration improves turbidity levels of stormwater discharges by fil- tering runoff through existing vegetation where undisturbed forest floor duff layer or established lawn  with thatch layer are present.  Vegetative filtration can also be used to infiltrate dewatering waste  from foundations, vaults, and trenches as long as runoff does not occur. Conditions of Use  l For every five acres of disturbed soil use one acre of grass field, farm pasture, or wooded  area. Reduce or increase this area depending on project size, ground water table height, and  other site conditions.  l Wetlands shall not be used for vegetative filtration.  l Do not use this BMP in areas with a high ground water table, or in areas that will have a high  seasonal ground water table during the use of this BMP.  l This BMP may be less effective on soils that prevent the infiltration of the water, such as hard  till.  l Using other effective source control measures throughout a construction site will prevent the  generation of additional highly turbid water and may reduce the time period or area need for  this BMP.  l Stop distributing water into the vegetated filtration area if standing water or erosion results. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 380 Maintenance Standards  l Monitor the spray field on a daily basis to ensure that over saturation of any portion of the field  doesn’t occur at any time. The presence of standing puddles of water or creation of con- centrated flows visually signify that over saturation of the field has occurred.  l Monitor the vegetated spray field all the way down to the nearest surface water, or farthest  spray area, to ensure that the water has not caused overland or concentrated flows, and has  not created erosion around the spray nozzle(s).  l Do not exceed water quality standards for turbidity.  l Ecology recommends that a separate inspection log be developed, maintained and kept with  the existing site logbook to aid the operator conducting inspections. This separate “Field Filtra- tion Logbook” can also aid in demonstrating compliance with permit conditions.  l Inspect the spray nozzles daily, at a minimum, for leaks and plugging from sediment particles.  l If erosion, concentrated flows, or over saturation of the field occurs, rotate the use of branches  or spray heads or move the branches to a new field location.  l Check all branches and the manifold for unintended leaks. BMP C240: Sediment Trap Purpose A sediment trap is a small temporary ponding area with a gravel outlet used to collect and store sed- iment from sites during construction. Sediment traps, along with other perimeter controls, shall be  installed before any land disturbance takes place in the drainage area. Conditions of Use  l Sediment traps are intended for use on sites where the tributary drainage area is less than 3  acres, with no unusual drainage features, and a projected build-out time of six months or less.  The sediment trap is a temporary measure (with a design life of approximately 6 months) and  shall be maintained until the tributary area is permanently protected against erosion by veget- ation and/or structures.  l Sediment traps are only effective in removing sediment down to about the medium silt size  fraction. Runoff with sediment of finer grades (fine silt and clay) will pass through untreated,  emphasizing the need to control erosion to the maximum extent first.  l Projects that are constructing permanent Flow Control BMPs, or Runoff Treatment BMPs  that use ponding for treatment, may use the rough-graded or final-graded permanent BMP  footprint for the temporary sediment trap. When permanent BMP footprints are used as tem- porary sediment traps, the surface area requirement of the sediment trap must be met. If the  surface area requirement of the sediment trap is larger than the surface area of the per- manent BMP, then the sediment trap shall be enlarged beyond the permanent BMP footprint  to comply with the surface area requirement. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 383  l A floating pond skimmer may be used for the sediment trap outlet if approved by the Local Per- mitting Authority.  l Sediment traps may not be feasible on utility projects due to the limited work space or the  short-term nature of the work. Portable tanks may be used in place of sediment traps for utility  projects. Design and Installation Specifications  l See Figure II-3.26: Cross Section of Sediment Trap and Figure II-3.27: Sediment Trap Outlet  for details.  l To determine the sediment trap geometry, first calculate the design surface area (SA) of the  trap, measured at the invert of the weir. Use the following equation: SA = FS(Q2/Vs)   where Q2 =   o Option 1 - Single Event Hydrograph Method: Q2 = Peak volumetric flow rate calculated using a 10-minute time step from a Type 1A,  2-year, 24-hour frequency storm for the developed condition. The 10-year peak volu- metric flow rate shall be used if the project size, expected timing and duration of con- struction, or downstream conditions warrant a higher level of protection.   o Option 2 - For construction sites that are less than 1 acre, the Rational Method may be  used to determine Q2. Vs = The settling velocity of the soil particle of interest. The 0.02 mm (medium silt) particle with  an assumed density of 2.65 g/cm3 has been selected as the particle of interest and has a set- tling velocity (Vs) of 0.00096 ft/sec. FS = A safety factor of 2 to account for non-ideal settling. Therefore, the equation for computing sediment trap surface area becomes: SA  = 2 x Q2/0.00096  or 2080 square feet per cfs of inflow  l Sediment trap depth shall be 3.5 feet minimum from the bottom of the trap to the top of the  overflow weir.  l To aid in determining sediment depth, all sediment traps shall have a staff gauge with a prom- inent mark 1-foot above the bottom of the trap. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 384  l Design the discharge from the sediment trap by using the guidance for discharge from tem- porary sediment ponds in BMP C241:  Sediment Pond (Temporary). Maintenance Standards  l Sediment shall be removed from the trap when it reaches 1-foot in depth.  l Any damage to the trap embankments or slopes shall be repaired. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 385 Figure II-3.26: Cross Section of Sediment Trap 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 386 Surface area determined at top of weir 4' Min.i1' Min.Overflow1iV Min. T I T11' Min.u 3.5' - 5'&1.5' Min.i Flat Bottom I %" -1.5" Washed gravel Geotextile Discharge to stabilized conveyance, outlet, or level spreader Note: Trap may be formed by berm or by partial or complete excavation.2" - 4" Rock Rip Rap NOT TO SCALE Cross Section of Sediment Trap Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Figure II-3.27: Sediment Trap Outlet 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 387 6' Min. HiSiSiS V Min. depth overflow spillway I I T* -\in Min. T depth 2" - 4" rock Min. 1'depth %" -1-5" washed gravelNative soil or compacted backfill Geotextile NOT TO SCALE Sediment Trap Outlet Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyhght.html for copyright notice including permissions, limitation of liability, and disclaimer.State of Washington Maintenance Standards  l Remove sediment from the pond when it reaches 1 foot in depth.  l Repair any damage to the pond embankments or slopes. BMP C250: Construction Stormwater Chemical Treatment Purpose This BMP applies when using chemicals to treat turbidity in stormwater by either  batch or flow- through chemical treatment. Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a con- struction site. BMP C241:  Sediment Pond (Temporary) is effective at removing larger particulate  matter by gravity settling, but is ineffective at removing smaller particulates such as clay and fine silt.  Traditional Construction Stormwater BMPs may not be adequate to ensure compliance with the  water quality standards for turbidity in the receiving water. Chemical treatment can reliably provide exceptional reductions of turbidity and associated pol- lutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements,  especially when construction proceeds through the wet season. Conditions of Use Formal written approval from Ecology is required for the use of chemical treatment, regardless of  site size. See https://fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of  the Request for Chemical Treatment form. The Local Permitting Authority may also require review  and approval. When authorized, the chemical treatment systems must be included in the Con- struction Stormwater Pollution Prevention Plan (SWPPP). Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organ- isms. The Chemical Technology Assessment Protocol - Ecology (CTAPE) must be used to evaluate  chemicals proposed for stormwater treatment. Only chemicals approved by Ecology under the  CTAPE may be used for stormwater treatment. The approved chemicals, their allowable application  techniques (batch treatment or flow-through treatment), allowable application rates, and conditions  of use can be found at the Department of Ecology Emerging Technologies website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee- guidance-resources/Emerging-stormwater-treatment-technologies Background on Chemical Treatment Systems Coagulation and flocculation have been used for over a century to treat water. The use of coagu- lation and flocculation to treat stormwater is a very recent application. Experience with the treatment  of water and wastewater has resulted in a basic understanding of the process, in particular factors  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 396 that affect performance. This experience can provide insights as to how to most effectively design  and operate similar systems in the treatment of stormwater. Fine particles suspended in water give it a milky appearance, measured as turbidity. Their small size,  often much less than 1 µm in diameter, give them a very large surface area relative to their volume.  These fine particles typically carry a negative surface charge. Largely because of these two factors  (small size and negative charge), these particles tend to stay in suspension for extended periods of  time. Thus, removal is not practical by gravity settling. These are called stable suspensions. Chem- icals like polymers, as well as inorganic chemicals such as alum, speed the settling process. The  added chemical destabilizes the suspension and causes the smaller particles to flocculate. The pro- cess consists of three primary steps:  coagulation, flocculation, and settling or clarification.  Ecology  requires a fourth step, filtration, on all stormwater chemical treatment systems to reduce floc dis- charge and to provide monitoring prior to discharge. General Design and Installation Specifications  l Chemicals approved for use in Washington State are listed on Ecology's TAPE website,  http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.html, under the "Con- struction" tab.  l Care must be taken in the design of the withdrawal system to minimize outflow velocities and  to prevent floc discharge. Stormwater that has been chemically treated must be filtered  through BMP C251:  Construction Stormwater Filtration for filtration and monitoring prior to dis- charge.  l System discharge rates must take into account downstream conveyance integrity.  l The following equipment should be located on site in a lockable shed:  o The chemical injector.  o Secondary containment for acid, caustic, buffering compound, and treatment chemical.  o Emergency shower and eyewash.  o Monitoring equipment which consists of a pH meter and a turbidimeter.  l There are two types of systems for applying the chemical treatment process to stormwater:  the batch chemical treatment system and the flow-through chemical treatment system. See  below for further details for both types of systems. Batch Chemical Treatment Systems A batch chemical treatment system consists of four steps: coagulation, flocculation, clarification, and  polishing and monitoring via filtration. Step 1: Coagulation Coagulation is the process by which negative charges on the fine particles are disrupted. By dis- rupting the negative charges, the fine particles are able to flocculate. Chemical addition is one  method of destabilizing the suspension, and polymers are one class of chemicals that are generally  effective. Chemicals that are used for this purpose are called coagulants. Coagulation is complete  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 397 when the suspension is destabilized by the neutralization of the negative charges. Coagulants per- form best when they are thoroughly and evenly dispersed under relatively intense mixing. This rapid  mixing involves adding the coagulant in a manner that promotes rapid dispersion, followed by a short  time period for destabilization of the particle suspension. The particles are still very small and are not  readily separated by clarification until flocculation occurs. Step 2: Flocculation Flocculation is the process by which fine particles that have been destabilized bind together to form  larger particles that settle rapidly. Flocculation begins naturally following coagulation, but is  enhanced by gentle mixing of the destabilized suspension. Gentle mixing helps to bring particles in  contact with one another such that they bind and continually grow to form "flocs." As the size of the  flocs increase, they become heavier and settle. Step 3: Clarification The final step is the settling of the particles, or clarification. Particle density, size and shape are  important during settling. Dense, compact flocs settle more readily than less dense, fluffy flocs.  Because of this, flocculation to form dense, compact flocs is particularly important during chemical  treatment. Water temperature is important during settling. Both the density and viscosity of water are  affected by temperature; these in turn affect settling. Cold temperatures increase viscosity and dens- ity, thus slowing down the rate at which the particles settle. The conditions under which clarification is achieved can affect performance. Currents can affect set- tling. Currents can be produced by wind, by differences between the temperature of the incoming  water and the water in the clarifier, and by flow conditions near the inlets and outlets. Quiescent  water, such as that which occurs during batch clarification, provides a good environment for settling.  One source of currents  in batch chemical treatment systems is movement of the water leaving the  clarifier unit. Because flocs are relatively small and light, the velocity of the water must be as low as  possible. Settled flocs can be resuspended and removed by fairly modest currents. Step 4: Filtration After clarification, Ecology requires stormwater that has been chemically treated to be filtered and  monitored prior to discharge. The sand filtration system continually monitors the stormwater effluent  for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the  water is returned to the untreated stormwater pond where it will begin the treatment process again. Design and Installation of Batch Chemical Treatment Systems A batch chemical treatment system consists of a stormwater collection system (either a temporary  diversion or the permanent site drainage system), an untreated stormwater storage pond, pumps, a  chemical feed system, treatment cells, a filtering and monitoring system, and interconnecting piping. The batch treatment system uses a storage pond for untreated stormwater, followed by a minimum  of two lined treatment cells. Multiple treatment cells allow for clarification of chemically treated water  in one cell, while other cells are being filled or emptied. Treatment cells may be ponds or tanks.  Ponds with constructed earthen embankments greater than six feet high or which impound more  than 10 acre-feet are subject to the Washington Dam Safety Regulations (Chapter 173-175 WAC).  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 398 See BMP D.1: Detention Ponds for more information regarding dam safety considerations for  ponds. Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to  an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater  is stored until treatment occurs. It is important that the storage pond is large enough to provide  adequate storage. The first step in the treatment sequence is to check the pH of the stormwater in the untreated storm- water storage pond. The pH is adjusted by the application of carbon dioxide or a base until the storm- water in the untreated storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon  dioxide is added immediately downstream of the transfer pump. Typically sodium bicarbonate (bak- ing soda) is used as a base, although other bases may be used. When needed, base is added dir- ectly to the untreated stormwater storage pond. The stormwater is recirculated with the treatment  pump to provide mixing in the storage pond. Initial pH adjustments should be based on daily bench  tests. Further pH adjustments can be made at any point in the process. See BMP C252:  Treating  and Disposing of High pH Water for more information on pH adjustments as a part of chemical treat- ment. Once the stormwater is within the desired pH range (which is dependant on the coagulant being  used), the stormwater is pumped from the untreated stormwater storage pond to a lined treatment  cell as a coagulant is added. The coagulant is added upstream of the pump to facilitate rapid mixing. The water is kept in the lined treatment cell for clarification. In a batch mode process, clarification typ- ically takes from 30 minutes to several hours. Prior to discharge, samples are withdrawn for analysis  of pH, coagulant concentration, and turbidity. If these levels are acceptable, the treated water is with- drawn, filtered, and discharged. Several configurations have been developed to withdraw treated water from the treatment cell. The  original configuration is a device that withdraws the treated water from just beneath the water sur- face using a float with adjustable struts that prevent the float from settling on the cell bottom. This  reduces the possibility of picking up floc from the bottom of the cell. The struts are usually set at a min- imum clearance of about 12 inches; that is, the float will come within 12 inches of the bottom of the  cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up  and down with the water level. More recent designs have an H-shaped array of pipes, set on the hori- zontal.This scheme provides for withdrawal from four points rather than one. This configuration  reduces the likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vor- tex to form. Inlet diffusers, a long floating or fixed pipe with many small holes in it, are also an option. Safety is a primary concern. Design should consider the hazards associated with operations, such  as sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds  should have life rings, ladders, or steps extending from the bottom to the top. Sizing Batch Chemical Treatment Systems Chemical treatment systems must be designed to control the velocity and peak volumetric flow rate  that is discharged from the system and consequently the project site. See Element 3: Control Flow  Rates for further details on this requirement. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 399 The total volume of the untreated stormwater storage pond and treatment cells must be large  enough to treat stormwater that is produced during multiple day storm events. It is recommended  that at a minimum the untreated stormwater storage pond be sized to hold 1.5 times the volume of  runoff generated from the site during the 10-year, 24-hour storm event. Bypass should be provided  around the chemical treatment system to accommodate extreme storm events. Runoff volume shall  be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst-case  land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases,  this would be the land cover conditions just prior to final landscaping). Primary settling should be encouraged in the untreated stormwater storage pond. A forebay with  access for maintenance may be beneficial. There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a lar- ger volume of water each time a batch is processed. However, the larger the cell, the longer the time  required to empty the cell. A larger cell may also be less effective at flocculation and therefore  require a longer settling time. The simplest approach to sizing the treatment cell is to multiply the  allowable discharge flow rate (as determined by the guidance in Element 3: Control Flow Rates)  times the desired drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour  work period, given 1 hour of flocculation followed by two hours of settling. See BMP C251:  Construction Stormwater Filtration for details on sizing the filtration system at the  end of the batch chemical treatment system. If the chemical treatment system design does not allow you to discharge at the rates as required by  Element 3: Control Flow Rates, and if the site has a permanent Flow Control BMP that will serve the  planned development, the discharge from the chemical treatment system may be directed to the per- manent Flow Control BMP to comply with Element 3: Control Flow Rates. In this case, all discharge  (including water passing through the treatment system and stormwater bypassing the treatment sys- tem) will be directed into the permanent Flow Control BMP. If site constraints make locating the  untreated stormwater storage pond difficult, the permanent Flow Control BMP may be divided to  serve as the untreated stormwater storage pond and the post-treatment temporary flow control  pond. A berm or barrier must be used in this case so the untreated water does not mix with the  treated water. Both untreated stormwater storage requirements, and adequate post-treatment flow  control must be achieved. The designer must document in the Construction SWPPP how the per- manent Flow Control BMP is able to attenuate the discharge from the site to meet the requirements  of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified  for temporary construction flow control purposes, the construction of the permanent Flow Control  BMP must be finalized, as designed for its permanent function, at project completion. Flow-Through Chemical Treatment Systems Background on Flow-Through Chemical Treatment Systems A flow-through chemical treatment system adds a sand filtration component to the batch chemical  treatment system's treatment train following flocculation. The coagulant is added to the stormwater  upstream of the sand filter so that the coagulation and flocculation step occur immediately prior to the  filter. The advantage of a flow-through chemical treatment system is the time saved by immediately  filtering the water, as opposed to waiting for the clarification process necessary in a batch chemical  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 400 treatment system. See BMP C251:  Construction Stormwater Filtration for more information on fil- tration. Design and Installation of Flow-Through Chemical Treatment Systems At a minimum, a flow-through chemical treatment system consists of a stormwater collection system  (either a temporary diversion or the permanent site drainage system), an untreated stormwater stor- age pond, and a chemically enhanced sand filtration system. As with a batch treatment system, stormwater is collected at interception point(s) on the site and is  diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated storm- water holding area. The stormwater is stored until treatment occurs. It is important that the holding  pond be large enough to provide adequate storage. Stormwater is then pumped from the untreated stormwater storage pond to the chemically  enhanced sand filtration system where a coagulant is added. Adjustments to pH may be necessary  before coagulant addition. The sand filtration system continually monitors the stormwater effluent for  turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the  water is returned to the untreated stormwater pond where it will begin the treatment process again. Sizing Flow-Through Chemical Treatment Systems Refer to BMP C251:  Construction Stormwater Filtration for sizing requirements of flow-through  chemical treatment systems. Factors Affecting the Chemical Treatment Process Coagulants Cationic polymers can be used as coagulants to destabilize negatively charged turbidity particles  present in natural waters, wastewater and stormwater. Polymers are large organic molecules that  are made up of subunits linked together in a chain-like structure. Attached to these chain-like struc- tures are other groups that carry positive or negative charges, or have no charge. Polymers that  carry groups with positive charges are called cationic, those with negative charges are called  anionic, and those with no charge (neutral) are called nonionic. In practice, the only way to determ- ine whether a polymer is effective for a specific application is to perform preliminary or on-site test- ing. Aluminum sulfate (alum) can also be used as a coagulant, as this chemical becomes positively  charged when dispersed in water. Polymers are available as powders, concentrated liquids, and emulsions (which appear as milky  liquids). The latter are petroleum based, which are not allowed for construction stormwater treat- ment. Polymer effectiveness can degrade with time and also from other influences. Thus, man- ufacturers' recommendations for storage should be followed. Manufacturer’s recommendations  usually do not provide assurance of water quality protection or safety to aquatic organisms. Con- sideration of water quality protection is necessary in the selection and use of all polymers. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 401 Application Application of coagulants at the appropriate concentration or dosage rate for optimum turbidity  removal is important for management of chemical cost, for effective performance, and to avoid  aquatic toxicity. The optimum dose in a given application depends on several site-specific features.  Turbidity of untreated water can be important with turbidities greater than 5,000 NTU. The surface  charge of particles to be removed is also important. Environmental factors that can influence dosage  rate are water temperature, pH, and the presence of constituents that consume or otherwise affect  coagulant effectiveness. Laboratory experiments indicate that mixing previously settled sediment  (floc sludge) with the untreated stormwater significantly improves clarification, therefore reducing  the effective dosage rate. Preparation of working solutions and thorough dispersal of coagulants in  water to be treated is also important to establish the appropriate dosage rate. For a given water sample, there is generally an optimum dosage rate that yields the lowest residual  turbidity after settling. When dosage rates below this optimum value (underdosing) are applied,  there is an insufficient quantity of coagulant to react with, and therefore destabilize, all of the turbidity  present. The result is residual turbidity (after flocculation and settling) that is higher than with the  optimum dose. Overdosing, application of dosage rates greater than the optimum value, can also  negatively impact performance. Like underdosing, the result of overdosing is higher residual turbidity  than that with the optimum dose. Mixing The G-value, or just "G", is often used as a measure of the mixing intensity applied during coagu- lation and flocculation. The symbol G stands for “velocity gradient”, which is related in part to the  degree of turbulence generated during mixing. High G-values mean high turbulence, and vice versa.  High G-values provide the best conditions for coagulant addition. With high G's, turbulence is high  and coagulants are rapidly dispersed to their appropriate concentrations for effective destabilization  of particle suspensions. Low G-values provide the best conditions for flocculation. Here, the goal is to promote formation of  dense, compact flocs that will settle readily. Low G's provide low turbulence to promote particle col- lisions so that flocs can form. Low G's generate sufficient turbulence such that collisions are effective  in floc formation, but do not break up flocs that have already formed. pH Adjustment The pH must be in the proper range for the coagulants to be effective, which is typically 6.5 to 8.5. As  polymers tend to lower the pH, it is important that the stormwater have sufficient buffering capacity.  Buffering capacity is a function of alkalinity. Without sufficient alkalinity, the application of the polymer  may lower the pH to below 6.5. A pH below 6.5 not only reduces the effectiveness of the polymer as  a coagulant, but it may also create a toxic condition for aquatic organisms. Stormwater may not be  discharged without readjustment of the pH to above 6.5. The target pH should be within 0.2 stand- ard units of the receiving water's pH. Experience gained at several projects in the City of Redmond has shown that the alkalinity needs to  be at least 50 mg/L to prevent a drop in pH to below 6.5 when the polymer is added. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 402 Maintenance Standards Monitoring At a minimum, the following monitoring shall be conducted. Test results shall be recorded on a daily  log kept on site. Additional testing may be required by the NPDES permit based on site conditions.  l Operational Monitoring  o Total volume treated and discharged.  o Flow must be continuously monitored and recorded at not greater than 15-minute inter- vals.  o Type and amount of chemical used for pH adjustment.  o Type and amount of coagulant used for treatment.  o Settling time.  l Compliance Monitoring  o Influent and effluent pH, flocculent chemical concentration, and turbidity must be con- tinuously monitored and recorded at not greater than 15-minute intervals.   o pH and turbidity of the receiving water.  l Biomonitoring  o Treated stormwater must be non-toxic to aquatic organisms. Treated stormwater must  be tested for aquatic toxicity or residual chemicals. Frequency of biomonitoring will be  determined by Ecology.  o Residual chemical tests must be approved by Ecology prior to their use.  o If testing treated stormwater for aquatic toxicity, you must test for acute (lethal) toxicity.  Bioassays shall be conducted by a laboratory accredited by Ecology, unless otherwise  approved by Ecology. Acute toxicity tests shall be conducted per the CTAPE protocol  and Appendix G of Whole Effluent Toxicity Testing Guidance and Test Review Criteria  (Marshall, 2016). Discharge Compliance Prior to discharge, treated stormwater must be sampled and tested for compliance with pH, floc- culent chemical concentration, and turbidity limits. These limits may be established by the Con- struction Stormwater General Permit or a site-specific discharge permit. Sampling and testing for  other pollutants may also be necessary at some sites. pH must be within the range of 6.5 to 8.5 stand- ard units and not cause a change in the pH of the receiving water by more than 0.2 standard units.  Treated stormwater samples and measurements shall be taken from the discharge pipe or another  location representative of the nature of the treated stormwater discharge. Samples used for determ- ining compliance with the water quality standards in the receiving water shall not be taken from the  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 403 treatment pond prior to decanting. Compliance with the water quality standards is determined in the  receiving water. Operator Training Each project site using chemical treatment must have a trained operator who is certified for oper- ation of an Enhanced Chemical Treatment system. The operator must be trained and certified by an  organization approved by Ecology. Organizations approved for operator training are found at the fol- lowing website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee- guidance-resources/Contaminated-water-on-construction-sites  Sediment Removal and Disposal  l Sediment shall be removed from the untreated stormwater storage pond and treatment cells  as necessary. Typically, sediment removal is required at least once during a wet season and  at the decommissioning of the chemical treatment system. Sediment remaining in the cells  between batches may enhance the settling process and reduce the required chemical  dosage.  l Sediment that is known to be non-toxic may be incorporated into the site away from drain- ages. BMP C251: Construction Stormwater Filtration Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Conditions of Use Traditional Construction Stormwater BMPs used to control soil erosion and sediment loss from con- struction sites may not be adequate to ensure compliance with the water quality standard for tur- bidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove  sediment as small as fine silt (0.5 µm). The reduction in turbidity will be dependent on the particle  size distribution of the sediment in the stormwater. In some circumstances, sedimentation and fil- tration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treat- ment chemicals are not used. Filtration in conjunction with BMP C250:  Construction Stormwater  Chemical Treatment requires testing under the Chemical Technology Assessment Protocol – Eco- logy (CTAPE) before it can be initiated. Approval from Ecology must be obtained at each site where  chemical use is proposed prior to use. See https://- fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of the Request for  Chemical Treatment form. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 404 Design and Installation Specifications Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow.  Rapid filtration systems are the typical system used for water and wastewater treatment. They can  achieve relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have auto- matic backwash systems to remove accumulated solids.  Slow filtration systems have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do  not have backwash systems. Slow filtration systems have generally been used as post construction  BMPs to treat stormwater (see V-6 Filtration BMPs). Slow filtration is mechanically simple in com- parison to rapid filtration, but requires a much larger filter area. Filter Types and Efficiencies Sand media filters are available with automatic backwashing features that can filter to 50 µm particle  size. Screen or bag filters can filter down to 5 µm. Fiber wound filters can remove particles down to  0.5 µm. Filters should be sequenced from the largest to the smallest pore opening. Sediment  removal efficiency will be related to particle size distribution in the stormwater. Treatment Process and Description Stormwater is collected at interception point(s) on the site and diverted to an untreated stormwater  sediment pond or tank for removal of large sediment, and storage of the stormwater before it is  treated by the filtration system. In a rapid filtration system, the untreated stormwater is pumped from  the pond or tank through the filtration media. Slow filtration systems are designed using gravity to  convey water from the pond or tank to and through the filtration media. Sizing Filtration treatment systems must be designed to control the velocity and peak volumetric flow rate  that is discharged from the system and consequently the project site. See Element 3: Control Flow  Rates for further details on this requirement. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the volume of run- off generated from the site during the 10-year, 24-hour storm event, minus the filtration treatment  system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the filtration  treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft2. Other  hydraulic loading rates may be more appropriate for other systems. Bypass should be provided  around the filtration treatment system to accommodate extreme storm events. Runoff volume shall  be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst-case  land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases,  this would be the land cover conditions just prior to final landscaping). If the filtration treatment system design does not allow you to discharge at the rates as required by  Element 3: Control Flow Rates, and if the site has a permanent Flow Control BMP that will serve the  planned development, the discharge from the filtration treatment system may be directed to the per- manent Flow Control BMP to comply with Element 3: Control Flow Rates. In this case,  all discharge  (including water passing through the treatment system and stormwater bypassing the treatment  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 405 system) will be directed into the permanent Flow Control BMP. If site constraints make locating the  untreated stormwater storage pond difficult, the permanent Flow Control BMP may be divided to  serve as the untreated stormwater storage pond and the post-treatment temporary flow control  pond. A berm or barrier must be used in this case so the untreated water does not mix with the  treated water. Both untreated stormwater storage requirements, and adequate post-treatment flow  control must be achieved. The designer must document in the Construction SWPPP how the per- manent Flow Control BMP is able to attenuate the discharge from the site to meet the requirements  of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified  for temporary construction flow control purposes, the construction of the permanent Flow Control  BMP must be finalized, as designed for its permanent function, at project completion. Maintenance Standards  l Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set  pressure drop across the filter. If the backwash water volume is not large or substantially more  turbid than the untreated stormwater stored in the holding pond or tank, backwash return to  the untreated stormwater pond or tank may be appropriate. However, other means of treat- ment and disposal may be necessary.  l Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged.  l Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically,  sediment removal is required once or twice during a wet season and at the decommissioning  of the ponds.  l Disposal of filtration equipment must comply with applicable local, state, and federal reg- ulations. BMP C252: Treating and Disposing of High pH Water Purpose When pH levels in stormwater rise above 8.5, it is necessary to lower the pH levels to the acceptable  range of 6.5 to 8.5 prior to discharge to surface or ground water. A pH level range of 6.5 to 8.5 is typ- ical for most natural watercourses, and this neutral pH range is required for the survival of aquatic  organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may  become stressed and may die. Conditions of Use  l The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Storm- water with pH levels exceeding water quality standards may be either neutralized on site or  disposed of  to a sanitary sewer or concrete batch plant with pH neutralization capabilities.  l Neutralized stormwater may be discharged to surface waters under the Construction Storm- water General permit.  l Neutralized process water such as concrete truck wash-out, hydro-demolition, or saw-cutting  slurry must be managed to prevent discharge to surface waters. Any stormwater  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 406 contaminated during concrete work is considered process wastewater and must not be dis- charged to waters of the State or stormwater collection systems.  l The process used for neutralizing and/or disposing of high pH stormwater from the site must  be documented in the Construction Stormwater Pollution Prevention Plan. Causes of High pH High pH at construction sites is most commonly caused by the contact of stormwater with poured or  recycled concrete, cement, mortars, and other Portland cement or lime containing construction  materials. (See BMP C151: Concrete Handling for more information on concrete handling pro- cedures). The principal caustic agent in cement is calcium hydroxide (free lime). Calcium hardness can contribute to high pH values and cause toxicity that is associated with high pH  conditions. A high level of calcium hardness in waters of the state is not allowed. Ground water stand- ard for calcium and other dissolved solids in Washington State is less than 500 mg/l. Treating High pH Stormwater by Carbon Dioxide Sparging Advantages of Carbon Dioxide Sparging  l Rapidly neutralizes high pH water.  l Cost effective and safer to handle than acid compounds.  l CO2 is self-buffering. It is difficult to overdose and create harmfully low pH levels.  l Material is readily available. The Chemical Process of Carbon Dioxide Sparging When carbon dioxide (CO2) is added to water (H2O), carbonic acid (H2CO3) is formed which can  further dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reac- tion as well. The colder the water temperature is, the slower the reaction occurs. The warmer the  water temperature is, the quicker the reaction occurs. Most construction applications in Washington  State have water temperatures in the 50°F or higher range so the reaction is almost simultaneous. The Treatment Process of Carbon Dioxide Sparging High pH water may be treated using continuous treatment, continuous discharge systems. These  manufactured systems continuously monitor influent and effluent pH to ensure that pH values are  within an acceptable range before being discharged. All systems must have fail safe automatic shut  off switches in the event that pH is not within the acceptable discharge range. Only trained operators  may operate manufactured systems. System manufacturers often provide trained operators or train- ing on their devices. The following procedure may be used when not using a continuous discharge system: 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 407  1. Prior to treatment, the appropriate jurisdiction should be notified in accordance with the reg- ulations set by the jurisdiction.  2. Every effort should be made to isolate the potential high pH water in order to treat it separately  from other stormwater on-site.  3. Water should be stored in an acceptable storage facility, detention pond, or containment cell  prior to pH treatment.  4. Transfer water to be treated for pH to the pH treatment structure. Ensure that the pH treat- ment structure size is sufficient to hold the amount of water that is to be treated. Do not fill the  pH treatment structure completely, allow at least 2 feet of freeboard.  5. The operator samples the water within the pH treatment structure for pH and notes the clarity  of the water. As a rule of thumb, less CO2 is necessary for clearer water. The results of the  samples and water clarity observations should be recorded.  6. In the pH treatment structure, add CO2 until the pH falls into the range of 6.9-7.1. Adjusting  pH to within 0.2 pH units of receiving water (background pH) is recommended. It is unlikely  that pH can be adjusted to within 0.2 pH units using dry ice. Compressed carbon dioxide gas  should be introduced to the water using a carbon dioxide diffuser located near the bottom of  the pH treatment structure, this will allow carbon dioxide to bubble up through the water and  diffuse more evenly.  7. Slowly discharge the water, making sure water does not get stirred up in the process. Release  about 80% of the water from the pH treatment structure leaving any sludge behind. If turbidity  remains above the maximum allowable, consider adding filtration to the treatment train. See  BMP C251:  Construction Stormwater Filtration.  8. Discharge treated water through a pond or drainage system.  9. Excess sludge needs to be disposed of properly as concrete waste. If several batches of  water are undergoing pH treatment, sludge can be left in the treatment structure for the next  batch treatment. Dispose of sludge when it fills 50% of the treatment structure volume.  10. Disposal must comply with applicable local, state, and federal regulations. Treating High pH Stormwater by Food Grade Vinegar Food grade vinegar that meets FDA standards may be used to neutralize high pH water. Food  grade vinegar is only 4% to 18% acetic acid with the remainder being water.  Food grade vinegar  may be used if dosed just enough to lower pH sufficiently. Use a treatment process as described  above for CO2 sparging, but add food grade vinegar instead of CO2. This treatment option for high pH stormwater does not apply to anything but food grade vinegar.  Acetic acid does not equal vinegar. Any other product or waste containing acetic acid must go  through the evaluation process in Appendix G of Whole Effluent Toxicity Testing Guidance and Test Review Criteria (Marshall, 2016).  2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 408 Disposal of High pH Stormwater Sanitary Sewer Disposal Local sewer authority approval is required prior to disposal via the sanitary sewer. Concrete Batch Plant Disposal  l Only permitted facilities may accept high pH water.  l Contact the facility to ensure they can accept the high pH water. Maintenance Standards Safety and materials handling:  l All equipment should be handled in accordance with OSHA rules and regulations.  l Follow manufacturer guidelines for materials handling. Each operator should provide:  l A diagram of the monitoring and treatment equipment.  l A description of the pumping rates and capacity the treatment equipment is capable of treat- ing. Each operator should keep a written record of the following:  l Client name and phone number.  l Date of treatment.  l Weather conditions.  l Project name and location.  l Volume of water treated.  l pH of untreated water.  l Amount of CO2 or food grade vinegar needed to adjust water to a pH range of 6.9-7.1.  l pH of treated water.  l Discharge point location and description. A copy of this record should be given to the client/contractor who should retain the record for three  years. 2019 Stormwater Management Manual for Western Washington Volume II -Chapter 3 -Page 409 Page | 35 Appendix D – Site Inspection Form Construction Stormwater Site Inspection Form Page 1 Project Name Permit # Inspection Date Time Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre Print Name: Approximate rainfall amount since the last inspection (in inches): Approximate rainfall amount in the last 24 hours (in inches): Current Weather Clear Cloudy Mist Rain Wind Fog A. Type of inspection: Weekly Post Storm Event Other B. Phase of Active Construction (check all that apply): Pre Construction/installation of erosion/sediment controls Clearing/Demo/Grading Infrastructure/storm/roads Concrete pours Vertical Construction/buildings Utilities Offsite improvements Site temporary stabilized Final stabilization C. Questions: 1. Were all areas of construction and discharge points inspected? Yes No 2. Did you observe the presence of suspended sediment, turbidity, discoloration, or oil sheen Yes No 3. Was a water quality sample taken during inspection? (refer to permit conditions S4 & S5) Yes No 4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No 5. If yes to #4 was it reported to Ecology? Yes No 6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken, and when. *If answering yes to # 4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/ transparency is 33 cm or greater. Sampling Results: Date: Parameter Method (circle one) Result Other/Note NTU cm pH Turbidity tube, meter, laboratory pH Paper, kit, meter Construction Stormwater Site Inspection Form Page 2 D. Check the observed status of all items. Provide “Action Required “details and dates. Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 1 Clearing Limits Before beginning land disturbing activities are all clearing limits, natural resource areas (streams, wetlands, buffers, trees) protected with barriers or similar BMPs? (high visibility recommended) 2 Construction Access Construction access is stabilized with quarry spalls or equivalent BMP to prevent sediment from being tracked onto roads? Sediment tracked onto the road way was cleaned thoroughly at the end of the day or more frequent as necessary. 3 Control Flow Rates Are flow control measures installed to control stormwater volumes and velocity during construction and do they protect downstream properties and waterways from erosion? If permanent infiltration ponds are used for flow control during construction, are they protected from siltation? 4 Sediment Controls All perimeter sediment controls (e.g. silt fence, wattles, compost socks, berms, etc.) installed, and maintained in accordance with the Stormwater Pollution Prevention Plan (SWPPP). Sediment control BMPs (sediment ponds, traps, filters etc.) have been constructed and functional as the first step of grading. Stormwater runoff from disturbed areas is directed to sediment removal BMP. 5 Stabilize Soils Have exposed un-worked soils been stabilized with effective BMP to prevent erosion and sediment deposition? Construction Stormwater Site Inspection Form Page 3 Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 5 Stabilize Soils Cont. Are stockpiles stabilized from erosion, protected with sediment trapping measures and located away from drain inlet, waterways, and drainage channels? Have soils been stabilized at the end of the shift, before a holiday or weekend if needed based on the weather forecast? 6 Protect Slopes Has stormwater and ground water been diverted away from slopes and disturbed areas with interceptor dikes, pipes and or swales? Is off-site storm water managed separately from stormwater generated on the site? Is excavated material placed on uphill side of trenches consistent with safety and space considerations? Have check dams been placed at regular intervals within constructed channels that are cut down a slope? 7 Drain Inlets Storm drain inlets made operable during construction are protected. Are existing storm drains within the influence of the project protected? 8 Stabilize Channel and Outlets Have all on-site conveyance channels been designed, constructed and stabilized to prevent erosion from expected peak flows? Is stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes and downstream conveyance systems? 9 Control Pollutants Are waste materials and demolition debris handled and disposed of to prevent contamination of stormwater? Has cover been provided for all chemicals, liquid products, petroleum products, and other material? Has secondary containment been provided capable of containing 110% of the volume? Were contaminated surfaces cleaned immediately after a spill incident? Were BMPs used to prevent contamination of stormwater by a pH modifying sources? Construction Stormwater Site Inspection Form Page 4 Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 9 Cont. Wheel wash wastewater is handled and disposed of properly. 10 Control Dewatering Concrete washout in designated areas. No washout or excess concrete on the ground. Dewatering has been done to an approved source and in compliance with the SWPPP. Were there any clean non turbid dewatering discharges? 11 Maintain BMP Are all temporary and permanent erosion and sediment control BMPs maintained to perform as intended? 12 Manage the Project Has the project been phased to the maximum degree practicable? Has regular inspection, monitoring and maintenance been performed as required by the permit? Has the SWPPP been updated, implemented and records maintained? 13 Protect LID Is all Bioretention and Rain Garden Facilities protected from sedimentation with appropriate BMPs? Is the Bioretention and Rain Garden protected against over compaction of construction equipment and foot traffic to retain its infiltration capabilities? Permeable pavements are clean and free of sediment and sediment laden- water runoff. Muddy construction equipment has not been on the base material or pavement. Have soiled permeable pavements been cleaned of sediments and pass infiltration test as required by stormwater manual methodology? Heavy equipment has been kept off existing soils under LID facilities to retain infiltration rate. E. Check all areas that have been inspected. All in place BMPs All disturbed soils All concrete wash out area All material storage areas All discharge locations All equipment storage areas All construction entrances/exits Construction Stormwater Site Inspection Form Page 5 F. Elements checked “Action Required” (section D) describe corrective action to be taken. List the element number; be specific on location and work needed. Document, initial, and date when the corrective action has been completed and inspected. Element # Description and Location Action Required Completion Date Initials Attach additional page if needed Sign the following certification: “I certify that this report is true, accurate, and complete, to the best of my knowledge and belief” Inspected by: (print) (Signature) Date: Title/Qualification of Inspector: Page | 36 Appendix H – Engineering Calculations Proposed Runoff Conditions for TESC - Entire Site Total Site:Area (ac) Pervious Area 0.000 Impervious Area 0.470 Total Area 0.470 Stormshed Data Type Reduced Time Step 15-min MGS - Flood 2-Yr developed flow 0.193 cfs MGS - Flood 10-Yr developed flow 0.293 cfs MGS - Flood 25-Yr developed flow 0.367 cfs MGS - Flood 100-Yr developed flow 0.547 cfs Vr=S.A. x 3.5'Vr = Minimum Required Storage Volume S.A. = Minimum allowable top surface area of pond S.A. = (2Q2)/Vsed Q = design peak flow rate Vsed = 0.00096 Settling Velocity (0.00096 ft/sec) Q=0.193 cfs INPUT (note that this is the 10-yr design peak flow rate in cfs) S.A. = 402 sf Vr=1407 cf Volume Required 10,527 gal 1 sediment storage tanks are required. * the volume is based a minimum pond depth of 3.5' - this depth does not include the minimum sediment storage volume or freeboard Assume 18,900 gallons per sediment storage tank, then Temporary Sediment Trap Sizing: Storage Volume per Section D.2.1.5, ESC Measures: Selection of the Design Storm of the 2021 King County Surface Water Design Manual - Appendix D: 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.59 Program License Number: 201910001 Project Simulation Performed on: 08/29/2024 2:56 PM Report Generation Date: 08/29/2024 2:56 PM ————————————————————————————————— Input File Name: 2024-08-29 RSD Transportation Expansion TESC Sizing.fld Project Name: RSD Transportation Expansion Analysis Title: TESC Sizing Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Full Period of Record Available used for Routing Climatic Region Number: 16 Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.470 0.470 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.470 0.470 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- C, Forest, Flat 0.470 ---------------------------------------------- TESC - SEDIMENTATION TANK SIZING CALCULATIONS Subbasin Total 0.470 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- SIDEWALKS/FLAT 0.470 ---------------------------------------------- Subbasin Total 0.470 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 0 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 89.444 _____________________________________ Total: 89.444 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 0.000 _____________________________________ Total: 0.000 Total Predevelopment Recharge is Greater than Post Developed TESC - SEDIMENTATION TANK SIZING CALCULATIONS Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.566 ac-ft/year, Post Developed: 0.000 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Subbasin: Subbasin 1 *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 1.183E-02 2-Year 0.193 5-Year 1.865E-02 5-Year 0.249 10-Year 2.319E-02 10-Year 0.293 25-Year 3.195E-02 25-Year 0.367 50-Year 3.509E-02 50-Year 0.440 100-Year 3.803E-02 100-Year 0.547 200-Year 5.630E-02 200-Year 0.583 500-Year 8.085E-02 500-Year 0.629 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals TESC - SEDIMENTATION TANK SIZING CALCULATIONS RENTON SCHOOL DISTRICT TRANSPORTATION EXPANSION 23 APPENDIX D FACILITY SUMMARY SHEET DECLARATION OF COVENANT (TO BE PROVIDED IN A FORTHCOMING SUBMITTAL) STORMWATER FACILITY SUMMARY SHEET ( provide one Stormwater Facility Summary Sheet per Natural Discharge Location) Major Basin Name __ Immediate Basin Name GENERAL FACILITY INFORMATION: Detention Infiltration Water Quality Flow Control Type # of Type # of Type #of Performance Std Pond s Ponds Ponds □ Basic Vaults Tanks Vaults □ Conservation Tanks renches Tanks □ Flood Problem DPER Permit No. Date NPDES Permit No. Parcel No. Retired Parcel No. Project includes Landscape Management Plan? yes □ (include copy with TIR as Appendix) no □ Declarations of Covenant Recording No. Leachable Metals Impervious Surface Limit Flow Control BMPs Clearing Limit Drainage Facility Landscape Management Plan If no flow control facility, check one: □ Project qualifies for KCSWDM Exemption (KCSWDM 1.2.3): □ Basic Exemption □ Impervious Surface Exemption for Transportation Redevelopment projects □ Cost Exemption for Parcel Redevelopment projects □ Direct Discharge Exemption □ Other___________________ □ Project qualifies for 0.1 cfs Exception per KCSWDM 1.2.3 □ No flow control required per approved KCSWDM Adjustment No.________________ □ Flow control provided in regional/shared facility per approved approved KCSWDM Adjustment No.________________ Shared Facility Name/Locati nn____________________ □ No flow control required (other, provide justification): TREATMENT SUMMARY FOR TOTAL IMPERVIOUS SURFACES (Applies to Commercial parcels only)Area % of Total Total Acreage (ac) Total Impervious Acreage (ac) Total impervious surface served by flow control facility(ies) (sq ft) Impervious surface served by flow control facility(ies) designed 1990 or later (sq ft) Impervious surface served by pervious surface absorption (sq ft) Impervious surface served by approved water quality facility(ies) (sq ft) PROVIDE FACILITY DETAILS AND FACILITY SKETCH FOR EACH FACILITY ON REVERSE. USE ADDITIONAL SHEETS AS NEEDED FOR ADDITIONAL FACILITIES 2021 KING COUNTY SURFACE WATER DESIGN MANUAL, REFERENCE D 7/23/2021 Page 1 RSD Transportation Expansion 420 Park Ave N, Renton, WA 98057 East Lake Washington - Renton Cedar River / Lake Washington N/A N/A 1 7224000676, 7224000675, 7564600105 0 0 0.508 0.378 74.4 0 0 0 0 14,992 91.1 N/A STORMWATER FACILITY PRELIMINARY SUMMARY SHEET TBD STORMWATER FACILITY SUMMARY SHEET DPER Permit No. ( provide one Stormwater Facility Summary Sheet per Natural Discharge Location) Project Name Project Location Downstream Drainage Basins: Major Basin Nam__________ Immediate Basin Nam______ FLOW CONTROL FACILITY: Basin: Facility Name/Number___________________________________□ New Facility □ Existing FacilityFacility Location UIC? □ yes □ no UIC Site ID: Live Storage □ cu.ft. Volume □ ac.ft. Live Storage Depth (ft) Volume Factor of Safety ______ Project Impervious Acres Served % of Total Project Impervious Acres Served No. of Lots Served Control Structure location:_ Type of Control Structure: □ Riser in vault □ Riser in Type II CB □ Weir in Type II CB No. of Orifices/Restrictions Size of Orifice/Restriction (in.) (numbered starting with lowest orifice): (inches in decimal format) N o . 1 No.2 No.3 No.4 Dam Safety Regulations (WA State Dept of Ecology): Re servoir Volume above natural grade □ cu.ft. □ ac.ft. Depth of Reservoir above natural grade (ft) WATER QUALITY FACILITIES Indicate no. of water quality facilities/BMPs for each type: _____Flow dispersion _____Filter strip _____Biofiltration swale □ regular, □ wet or □ continuous inflow _____Wetvault □ combined w/detention _____Wetpond □ basic □ large □ combined w/detention _____Pre-settling pond Design Information Water Quality design flow (cfs) Water Quality treated volume (sandfilter) (cu.ft.) Water Quality storage volume (wetpool) (cu.ft.) □ Landscape management plan □ Farm management plan High flow bypass structure (e.g., flow-splitter catch basin) Oil/water separator □ baffle □ coalescing plate _torm filter Stormwater wetland Sand filter □ basic □ large Sand bed depth Catch basin inserts (Manufacturer: ) □ regular □ linear □ vault (inches)__urce controls • Is facility lined? □ yes □ no If so, what marker is used above liner?What type of liner is used? Facility Summary Sheet Sketch: All detention, infiltration and water quality facilities must include a detailed sketch (11"x17" reduced size plan sheets preferred). 2021 KING COUNTY SURFACE WATER DESIGN MANUAL, REFERENCE D 7/23/2021 Page 2 RSD Transportation Expansion 420 Park Ave N, Renton, WA 98057 East Lake Washington - Renton Cedar River / Lake Washington N/A 1 STORMWATER FACILITY PRELIMINARY SUMMARY SHEET Modular Wetland N/A WATER QUALITY FACILITY NOTE: THIS SHEET HAS BEEN RESIZED TO BE 11X17 AND IS NOT TO SCALE