HomeMy WebLinkAboutAPPROVED_Hazen HS_Early CG CSWPPPConstruction Stormwater General Permit (CSWGP)
Stormwater Pollution Prevention Plan
(SWPPP)
for
Hazen High School Improvements
Prepared for:
Renton School District and Forma Construction
Permittee / Owner Developer Operator / Contractor
Renton School District Renton School District Forma Construction
1101 Hoquiam Avenue NE, Renton, WA, 98059
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) 293-9134
SWPPP Preparation Date
02 / 14 / 2025
Project Construction Dates
Activity / Phase Start Date End Date
Sitework and Building
Construction
April 2025 January 2029
DEVELOPMENT ENGINEERING
Michael Sippo 03/30/2025
Page | 1 Table of Contents 1.0 Project Information .......................................................................................................................... 4 1.1 Existing Conditions ......................................................................................................................... 4 1.2 Proposed Construction Activities .................................................................................................... 5 2.0 Construction Stormwater Best Management Practices (BMPs) ..................................................... 7 2.1 The 13 Elements ............................................................................................................................. 7 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits ........................................................... 7 2.1.2 Element 2: Establish Construction Access ............................................................................... 8 2.1.3 Element 3: Control Flow Rates ................................................................................................. 9 2.1.4 Element 4: Install Sediment Controls ...................................................................................... 10 2.1.5 Element 5: Stabilize Soils ........................................................................................................11 2.1.6 Element 6: Protect Slopes........................................................................................................12 2.1.7 Element 7: Protect Drain Inlets ................................................................................................13 2.1.8 Element 8: Stabilize Channels and Outlets .............................................................................14 2.1.9 Element 9: Control Pollutants ..................................................................................................15 2.1.10 Element 10: Control Dewatering .............................................................................................19 2.1.11 Element 11: Maintain BMPs ....................................................................................................20 2.1.12 Element 12: Manage the Project .............................................................................................21 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs ....................................................25 3.0 Pollution Prevention Team .............................................................................................................26 4.0 Monitoring and Sampling Requirements ........................................................................................27 4.1 Site Inspection ...............................................................................................................................27 4.2 Stormwater Quality Sampling ........................................................................................................27 4.2.1 Turbidity Sampling ..................................................................................................................27 4.2.2 pH Sampling ...........................................................................................................................29 5.0 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies ....................................30 5.1 303(d) Listed Waterbodies .............................................................................................................30 5.2 TMDL Waterbodies .......................................................................................................................30 6.0 Reporting and Record Keeping ......................................................................................................31 6.1 Record Keeping .............................................................................................................................31 6.1.1 Site Logbook ...........................................................................................................................31 6.1.2 Records Retention ..................................................................................................................31 6.1.3 Updating the SWPPP ..............................................................................................................31 6.2 Reporting .......................................................................................................................................32 6.2.1 Discharge Monitoring Reports .................................................................................................32 6.2.2 Notification of Noncompliance .................................................................................................32
Page | 2 List of Tables Table 1 – Summary of Site Pollutant Constituents ....................................................................... 5 Table 2 – Pollutants .....................................................................................................................15 Table 3 – pH-Modifying Sources .................................................................................................17 Table 4 – Dewatering BMPs ........................................................................................................19 Table 5 – Management ................................................................................................................21 Table 6 – BMP Implementation Schedule ....................................................................................23 Table 7 – Team Information .........................................................................................................26 Table 8 – Turbidity Sampling Method ..........................................................................................27 Table 9 – pH Sampling Method ...................................................................................................29 List of Appendices A. Site Map B. BMP Detail 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 | 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 1.0 Project Information Project/Site Name: Hazen High School Street/Location: 1101 Hoquiam Ave NE City: Renton State: WA Zip code: 98059 Subdivision: N/A Receiving waterbody: Lower Cedar River 1.1 Existing Conditions Hazen High School is a developed campus that is polygon-shaped and consists of 29.28 acres. The area within the district’s property boundary includes eight parcels: parcel 1 (1023059057) 0.78 acres, parcel 2 (1023059072) 3.66 acres, parcel 3 (1023059201) 14.93 acres, parcel 4 (1023059278) 4.10 acres, parcel 5 (1023059292) 0.45 acres, parcel 6 (1023059084) 0.45 acres, parcel 7 (1023059277) 2.54 acres, parcel 8 (1023059094) 2.37 acres. The school consists of a single primary school building on the east side of the campus, parking and drive areas on all sides of the building, a baseball field to the west, a track and field to the southwest, a softball field and tennis courts directly south, and landscaping around the property perimeter and in the parking lots. The main building is surrounded by low landscaping and concrete sidewalks. Total acreage: 29.28-acres Disturbed acreage: 5.09-acres Landscape topography: In general, the site topography of Hazen High School around the proposed project work scope is relatively flat at roughly 1%-2% for the existing baseball and softball fields located on the west and south sides of the school’s campus. Drainage patterns: The school site consists of (3) three Threshold Discharge Areas. Proposed drainage from each TDA will continue to discharge to the same point of connection to match existing drainage patterns. TDA #1 consists of the existing baseball field, which we assume to be underdrained and routed to an existing pond located near the southwest corner of the field, where water is then routed to a dispersion trench that flows to the west toward Duvall Ave NE through native vegetation. Duvall Ave NE was recently improved to include new curb, gutter and sidewalk with stormwater improvements to include water quality treatment and a new 12” storm main. The proposed improvements will continue to discharge toward Duvall Ave NE. The stormwater runoff from the disturbed areas within TDA #1 will be collected through interceptor swales around the baseball field perimeter, which is considered 100% impervious during the installation of the geothermal wells.
Page | 5 Construction stormwater will be routed to temporary settlement tanks and discharged to the existing site storm system. TDA #2 consists of areas at the center of the site, including the grass play field to the north of the baseball field, parking lots to the west and south of the school building, the rubberized track and grass field, and grass softball field on the south side of the site, which flow to the south in a 12” storm pipe toward the existing storm system in NE 10th St. Stormwater runoff from the disturbed areas within TDA #2 will be collected by interceptor swales around the geothermal well system, which is considered 100% impervious during installation. Construction stormwater will be routed to temporary settlement tanks and discharged to the existing site storm system flowing to the south that eventually discharges stormwater to the existing storm system within NE 10th Street. TDA #3 consists of parking areas north, east and south of the school building, the existing grass multipurpose field, and tennis courts. TDA #3 connects to the existing storm system in Hoquiam Ave NE at multiple locations along the eastern school property line. There are no proposed areas of work within TDA #3 for the Clear and Grade permit, therefore drainage patterns will not be impacted. Existing Vegetation: The site is fully developed with a small pocket of native vegetation west of the existing baseball field. Critical Areas: No critical areas exist on the project parcel. List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: The project eventually discharges to the Duwamish River which is 303d listed impaired for water, sediment, and fish tissue. 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
Page | 6 1.2 Proposed Construction Activities Description of site development: Campus Improvements are proposed and will consist of early earthwork to install the geothermal system. This will consist of drilling for wells north of the baseball field, making connections to the building for the geothermal conduit, and installing an electrical vault to support the geothermal system. With the early construction of the geothermal system, TESC measures will be utilized. Description of construction activities (example: site preparation, demolition, excavation): The project will consist of site preparation, demolition, and geothermal well installation. Description of site drainage including flow from and onto adjacent properties. Must be consistent with the Site Map in Appendix A: Stormwater will be discharged to three locations on site: The first along the west property line to Duvall Ave NE, the second at the south property line within NE 10th St, and the last along the east property line to Hoquiam Ave SE. No permanent flow control systems are proposed for installation with this early clear and grade permit. The existing school is surrounded by single-family residences and established public right-of-way with drainage systems. Generally, the residences surrounding the site flow away from the school property, Therefore, there are no substantial areas of offsite flow entering the existing parcel. Description of final stabilization (example: extent of revegetation, paving, landscaping): At final stabilization, the project area located north of the baseball field will include new geothermal wells, utility connections, and associated replaced paving and landscape to be completed under the civil construction permit. 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 | 7 2.0 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. handwritten 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, if any, 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: BMP’s will be installed at the beginning of construction and be inspected and maintained throughout construction.
Page | 8 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: • Stabilized Construction Access (BMP C105) Installation Schedules: BMP’s will be installed at the beginning of construction and be inspected and maintained throughout construction.
Page | 9 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? Yes No Will you use permanent infiltration ponds or other low impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? Yes No In order to protect the properties and waterways downstream of the project site, stormwater discharge from the site will be controlled. The specific BMPs for flow control that shall be used on this project include: • 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 Check Dams (BMP C207) o Storm Drain Inlet Protection (BMP C220) o Silt Fence (BMP C233) o Straw Wattles (BMP C235) o Temporary Water Storage Tanks for Sedimentation Installation Schedules: BMP’s 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 | 10 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 prior to 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) • Temporary Water Storage Tanks for Sedimentation See Appendix B – Construction BMPs for BMP details. In addition, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on vehicle tires away from the site and to minimize wash-off of sediments from adjacent streets in runoff. Whenever possible, sediment laden water shall be discharged into on-site, level, vegetated areas. The following BMPs will be implemented as end-of-pipe sediment controls as required to meet permitted turbidity limits in the site discharge(s). Prior to the implementation of these technologies, sediment sources and erosion control, and soil stabilization BMP efforts will be maximized to reduce the need for end-of-pipe sedimentation controls. • Construction Stormwater Chemical Treatment (BMP C 250) (implemented only with prior written approval from Ecology) • Construction Stormwater Filtration (BMP C251) The above BMPs will ensure that the construction activities will not interfere with the movement of juvenile Salmonids attempting to enter off-channel areas or drainages. The above BMPs shall be installed at the beginning of construction and must be functional before other land disturbing activities – especially grading and filling – take place. Inspection and Maintenance Plan to be prepared by contractor in accordance with the BMP details from Volume II of the State of Washington Department of Ecology’s 2019 Stormwater Management Manual for Western Washington, found in Appendix B. The Responsible Staff for inspection and maintenance will be the operator/contractor.
Page | 11 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) • Dust Control (BMP C140) 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. Anticipated project dates: Start date: April 2025 End date: January 2029 Will you construct during the wet season? Yes No 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 include: • Plastic Covering (BMP C123) See Appendix B – Construction BMPs for BMP details. The project site is located west of the Cascade Mountain Crest. As such, no soil shall remain exposed and unworked for more than 7 days during the dry season (May 1 to September 30) and 2 days during the wet season (October 1 to April 30). Regardless of the time of year, all soil shall be stabilized at the end of the shift before a holiday or weekend if needed based on weather forecasts. All stockpiled soil shall be stabilized from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways, and drainage channels. Construction activities shall be scheduled in a way that limits the amount of time soil is exposed throughout the duration of the project.
Page | 12 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? Yes No All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes erosion. The following specific BMPs will be used to protect slopes for this project: • N/A; construction will not be occurring within sloped portions of the property.
Page | 13 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) • Check Dams (BMP C207) • Inlet Protection (BMP C220) • Silt Fence (BMP C233) • Straw Wattles (BMP C235) • Temporary Water Storage Tanks for Sedimentation Installation Schedules: BMP’s 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. Inspection and Maintenance Plan to be prepared by contractor in accordance with the BMP details from Volume II of the State of Washington Department of Ecology’s 2019 Stormwater Management Manual for Western Washington, found in Appendix B. The Responsible Staff for inspection and maintenance will be the operator/contractor.
Page | 14 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. There are no existing downstream channels or streams that the site will directly discharge stormwater runoff to, therefore no BMPs are proposed for Element 8. 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: • Inlet Protection (BMP C220) • Silt Fence (BMP C233) • Straw Wattles (BMP C235) Installation Schedules: BMP’s will be installed at the beginning of construction and be inspected and maintained throughout construction until site is fully stabilized, and permanent flow control facilities are functioning.
Page | 15 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 Excavation: Excess Soil Demolition: Dust, Soil, Debris Concrete and grout Sanitary wastewater Solid Waste 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 additionally, if it is 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 | 16 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). Sanitary wastewater: • Portable sanitation facilities will be firmly secured, regularly maintained, and emptied when necessary. Solid Waste: • Solid waste will be stored in secure, clearly marked containers. Other: • Other BMPs will be administered as necessary to address any additional pollutant sources on site. List and describe BMPs: • 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) Installation Schedules: BMP’s will be implemented at the beginning of construction and be inspected and maintained throughout construction until site is fully stabilized. Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site? Yes No Will wheel wash or tire bath system BMPs be used during construction? Yes No List and describe BMPs: N/A Installation Schedules: BMP’s will be installed at the beginning of construction and be inspected and maintained throughout construction until site is fully stabilized, and wheel wash is no longer needed.
Page | 17 Will pH-modifying sources be present on-site? Yes No 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 X Concrete pumping and mixer washout waters Recycled concrete Other (i.e. calcium lignosulfate) [please describe] Where pH-modifying sources may be encountered, steps must be taken to prevent pollutants from contaminating stormwater and raising the pH level above 8.5. The acceptable pH range for stormwater is between 6.5 and 8.5, beyond that, pH neutralization must occur. The specific BMPs for pH modification that shall be used in this project include: • High pH Neutralization Using CO2 (BMP C252). This BMP must be utilized as soon as a stormwater pH reaches higher than 8.5, which typically occurs when the aforementioned pH-modifying sources come into contact with stormwater. Inspection and Maintenance Plan to be prepared by contractor in accordance with the BMP details from Volume II of the State of Washington Department of Ecology’s 2019 Stormwater Management Manual for Western Washington, found in Appendix B. The Responsible Staff for inspection and maintenance will be the operator/contractor. 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. Will uncontaminated water from water-only based shaft drilling for construction of building, road, and bridge foundations be infiltrated provided the wastewater is managed in a way that prohibits discharge to surface waters? Yes No
Page | 18 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. • 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.
Page | 19 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 | 20 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 | 21 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 performance of their intended function. o Site inspections and monitoring will be conducted in accordance with Special Condition S4 of the CSWGP. Sampling locations are indicated on the Site Map. Sampling station(s) are located in accordance with applicable requirements of the CSWGP. • Maintain an updated SWPPP. o The SWPPP will be updated, maintained, and implemented in accordance with Special Conditions S3, S4, and S9 of the CSWGP. 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 site and maintain all ESC measures X Schedule major earthwork during the dry season Other (please describe) As this project site is located west of the Cascade Mountain Crest, the project will be managed according to the following key project components: Phasing of Construction • The construction project is being phased to the extent practicable in order to prevent soil erosion, and, to the maximum extent possible, the transport of sediment from the site during construction. • Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the clearing activities during each phase of construction, per the Scheduling BMP (C162).
Page | 22 Seasonal Work Limitations • From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if shown to the satisfaction of the local permitting authority that silt-laden runoff will be prevented from leaving the site through a combination of the following: o Site conditions including existing vegetative coverage, slope, soil type, and proximity to receiving waters; and o Limitations on activities and the extent of disturbed areas; and o Proposed erosion and sediment control measures. • Based on the information provided and/or local weather conditions, the local permitting authority may expand or restrict the seasonal limitation on site disturbance. • The following activities are exempt from the seasonal clearing and grading limitations: o Routine maintenance and necessary repair of erosion and sediment control BMPs; o Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil; and Inspection and Monitoring • All BMPs shall be inspected, maintained, and repaired as needed to ensure continued performance of their intended function. Site inspections shall be conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. This person has the necessary skills to: o Assess the site conditions and construction activities that could impact the quality of stormwater, and o Assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. • A Certified Erosion and Sediment Control Lead shall be on-site or on-call at all times. • Whenever inspection and/or monitoring reveals that the BMPs identified in this SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible. See Appendix B – Construction BMPs for BMP details. Inspection and Maintenance Plan to be prepared by contractor in accordance with the BMP details from Volume II of the State of Washington Department of Ecology’s 2019 Stormwater Management Manual for Western Washington, found in Appendix B. The Responsible Staff for inspection and maintenance will be the operator/contractor.
Page | 23 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 | 24 Phase of Construction Project Stormwater BMPs Date Wet/Dry Season [Insert construction activity] [Insert BMP] [MM/DD/YYYY] [Insert Season]
Page | 25 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 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 and C233). Topsoil 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 | 26 3.0 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 | 27 4.0 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 logbook. A site logbook 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 File a blank form under Appendix D. The site logbook must be maintained on-site within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See CSWGP Special Condition S8 and Section 5 of this template. 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 (see Appendix A) and in accordance with the applicable requirements of the CSWGP. 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 CSWGP. Sampling will be conducted at all discharge points at least once per calendar week. 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.
Page | 28 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 logbook. 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 logbook. 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 | 29 4.2.2 pH Sampling pH monitoring is required for “Significant concrete work” (i.e., greater than 1000 cubic yards 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 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 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 | 30 5.0 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? Yes No List the impairment(s): N/A List and describe BMPs: N/A 5.2 TMDL Waterbodies In order to protect the properties and waterways downstream of the project site and remain TMDL compliant, stormwater discharges from the site will be controlled. The specific BMPs for flow control that shall be used on this project include: • Storm Drain Inlet Protection (BMP C220) • Straw Wattles (BMP C235) In general, discharge rates of stormwater from the site will be controlled where increases in impervious area or soil compaction during construction could lead to downstream erosion, or where necessary to meet local agency stormwater discharge requirements. The Straw Wattles and Catch Basin Filter Socks shall be installed at the beginning of construction activities prior to significant excavation and grading work to ensure the protection of properties downstream to the maximum extent possible. These BMPs shall be inspected to ensure they are functioning properly before constructing site improvements. Inspection and Maintenance Plan to be prepared by contractor in accordance with Volume II of the State of Washington Department of Ecology’s 2019 Stormwater Management Manual for Western Washington, found in Appendix B. The Responsible Staff for inspection and maintenance will be the operator/contractor. Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point of discharge. NOTE: A Construction Stormwater General Permit is required for this project as it will disturb more than 1.0 acres of land.
Page | 31 6.0 Reporting and Record Keeping 6.1 Record Keeping 6.1.1 Site Logbook A site logbook 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 • Permit Coverage Letter • SWPPP • Site Logbook 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 | 32 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. 6.2.2 Notification of Noncompliance If any of the terms and conditions of the permit are 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. • Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit, Snohomish, or Whatcom County 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 | 33 Appendix/Glossary A. Site Map B. BMP Detail 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 | 34 Appendix A – Site Map Vicinity Map Temporary Erosion and Sediment Control (TESC) Plan TESC Details
APPENDIX A - SITE MAP
SCALE: NTS
PROJECT SITE
PROJECT SITE
□
IP
IP
INSTALL CB
PROTECTION (TYP)
SEE DETAIL
C110
7
FF
IS
FF
IS
FF
INTERCEPTOR SWALE
WITH ROCK CHECK DAMS
AT 50' O.C. SPACING
SEE DETAILS
C110
6
C111
5
INSTALL SILT FENCE
AROUND PERIMETER
OF FIELD (TYP)
SEE DETAIL
C111
9
SUMP AND 55 GALLON
DRUM WITH SUMP
PUMP INSTALLED AT
LOW POINT ON SITE
SEE DETAIL
C111
6
FF
CONTRACTOR TO UTILIZE
EXISTING SITE FENCING
FOR CONSTRUCTION
PERIMETER FENCING AND
SUPPLEMENT AS NEEDED
SEE CONSTRUCTION
FENCING NOTE WITHIN
THIS SHEET
PROTECT EX CATCH BASIN
AND STORM PIPING
DURING GEOTHERMAL
WELL INSTALLATION
PROTECT EX CATCH BASIN
AND STORM PIPING
DURING GEOTHERMAL
WELL INSTALLATION
EXISTING 10" WATER MAIN TO BE PROTECTED AT ALL TIMES.
PROTECTION SHALL INCLUDE, BUT NOT LIMITED TO,
PROHIBITION OF HEAVY MACHINERY AND DRILLING
EQUIPMENT ON TOP OF MAIN OR WITHIN EASEMENT.
VIBRATIONAL TESTING MAY BE REQUIRED FOR ANY DRILLING
OR PILING OCCURING NEAR THE MAIN. ADDITIONALLY, ANY
MACHINERY CROSSING THE WATER MAIN IN UNPAVED AREAS
WILL BE REQUIRED SHEETING OR SIMILAR MECHANISM TO
ENSURE THAT THE MAIN IS NOT SUBJECT TO DAMAGE LOADS.
PUMP CONSTRUCTION STORMWATER
TO SEDIMENT SETTLEMENT TANKS.
PUMP LINE TO BE TAKEN OFF LINE
AND REMOVED ONCE DETENTION
VAULT IS INSTALLED AND READY TO
USE AS TEMPORARY TESC MEASURE
STABILIZED
CONSTRUCTION ACCESS
SEE DETAIL
C110
5
CE
INSTALL ASPHALT
WEDGE
SALVAGE AND REMOVE EX
CHAINLINK FENCE TO INSTALL
CONSTRUCTION ENTRANCE
PROTECT EX CURB
100'20'SALVAGE AND REMOVE
EX SIGN AND POST
CITY OF
RENTON
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
43667 NSTATE OF WASHIN
GTONREGISTER E DPROF
ESSIONAL EN G INEEROSBO
CAJA.DLAREJTED-40-4326C24005771SCALE 1"=20'
0 10 20 40
HAZEN HIGH SCHOOL MODERNIZATION
DEMOLITION AND TESC PLAN
R-432605
LEGEND
SAWCUT LINE
REMOVE CURBING
REMOVE ASPHALT PAVEMENT
REMOVE CONCRETE PAVEMENT
TREE PROTECTION
INLET PROTECTION
PROPERTY LINE
TEMP CONSTRUCTION FENCINGCF
IP
VEG
SEE SHEET C001 FOR CITY OF RENTON
ESC STANDARD PLAN NOTES
MATCHLINE - SEE SHEET C103
CONSTRUCTION FENCING NOTE:
INSTALL CONSTRUCTION FENCING AROUND LIMITS OF WORK TO
PROTECT STAFF AND STUDENTS AND SECURE JOBSITE. CONTRACTOR
SHALL ERECT FENCE AROUND JOBSITE AND ADJUST AS
CONSTRUCTION CONDITIONS CHANGE OR AS PHASING ALLOWS.
CONTRACTOR CAN UTILIZE EXISTING PERIMETER FENCING AS
SECURITY FENCING AND THEN SUPPLEMENT ON THE WEST SIDE OF
THE SITE AS NEEDED. ANY EXISTING CHAINLINK FENCING THE
CONTRACTOR ELECTS TO UTILIZE DURING CONSTRUCTION SHALL
APPLY (IE ZIPTIES OR OTHER MEANS) HIGH VISIBILITY MATERIAL OR
SIMILAR METHOD TO BE APPLIED TO FENCING TO DELINEAT AS
CONSTRUCTION ZONE (TYP). ANY SECTIONS OF EXISTING FENCING
THAT IS NOT 6-FT HIGH SHALL HAVE TEMPORARY 6-FT HIGH
CHAINLINK FENCING INSTALLED NEXT TO IT. SEE DETAIL 10/C110.
SEE SHEET C001 FOR TESC
CONSTRUCTION SEQUENCE NOTES
SILT FENCE
INTERCEPTOR SWALEIS
FF
CONSTRUCTION ENTRANCE
APPENDIX A - TESC PLANS
NOTE:
SHEET HAS BEEN
PRINTED TO BE 11X17
AND NOT TO SCALE
VAULT EXCAVATION SCOPE
TO BE UNDER SEPARATE
CIVIL CONSTRUCTION
PERMIT #C24005771
DUVALL AVE. N.E.(A DEDICATED PUBLIC RIGHT OF WAY)IMPROVED BASEBALL FIELD.
SEE LANDSCAPE PLANS AND
CIVIL SHEET C203
EXISTING CITY OF
RENTON WATER
EASEMENT TO BE
PROTECTED AT
ALL TIMES
15'
IP
INSTALL CB
PROTECTION (TYP)
SEE DETAIL
C110
7
IP
IP
IP
PUMP "CLEAN" STORMWATER FROM TEMP
SEDIMENT SETTLEMENT TANKS TO EXISTING
CATCH BASIN. CONTRACTOR TO ENSURE ALL
DISCHARGE MEETS TURBIDITY REQUIREMENTS.
PUMP LINE TO BE TAKEN OFF LINE AND REMOVED
ONCE DETENTION VAULT IS INSTALLED AND
READY TO USE AS TEMPORARY TESC MEASURE
FF
IS
FF
FF
IS
PUMP CONSTRUCTION STORMWATER TO
SEDIMENT SETTLEMENT TANKS. PUMP LINE
TO BE TAKEN OFF LINE AND REMOVED ONCE
DETENTION VAULT IS INSTALLED AND READY
TO USE AS TEMPORARY TESC MEASURE
FFINTERCEPTOR SWALE
WITH ROCK CHECK DAMS
AT 50' O.C. SPACING
SEE DETAILS
C110
6
C111
5
SUMP AND 55 GALLON
DRUM WITH SUMP PUMP
INSTALLED AT LOW
POINT ON SITE
SEE DETAIL
C111
6
PUMP CONSTRUCTION STORMWATER
TO SEDIMENT SETTLEMENT TANKS.
PUMP LINE TO BE TAKEN OFF LINE
AND REMOVED ONCE DETENTION
VAULT IS INSTALLED AND READY TO
USE AS TEMPORARY TESC MEASURE
INSTALL SILT FENCE
AROUND PERIMETER OF
FIELD (TYP)
SEE DETAIL
C111
9
INTERCEPTOR SWALE
WITH ROCK CHECK DAMS
AT 50' O.C. SPACING
SEE DETAILS
C110
6
C111
5
FF
BOE = 442.50
FF
APPROXIMATE LIMITS OF
PROPOSED DETENTION SYSTEM
EXCAVATION FOR BASEBALL FIELD.
SEE SHEET C203
SALVAGE AND REMOVE EX PULL
UP BARS TO BE REINSTALLED
AFTER COMPLETION OF
GEOTHERMAL WELL FIELD
(4) 18,900 GALLON CAPACITY TEMPORARY
SEDIMENT SETTLEMENT TANKS ("BAKER TANK" OR
EQUAL). CONTRACTOR SHALL PROVIDE ALL PUMPS
REQUIRED TO MANAGE CONSTRUCTION
STORMWATER AND DISCHARGE AT THE SITE.
SETTLEMENT TANKS TO BE TAKEN OFF LINE AND
REMOVED ONCE DETENTION VAULT IS INSTALLED
AND READY TO USE AS TEMPORARY TESC MEASURE
PROTECT EX FIELD
PERIMETER FENCING
TO REMAIN
PROTECT EXISTING
SYNTHETIC TURF
DUGOUT TO REMAIN
PROTECT EXISTING
CONCRETE TO REMAIN
PROTECT EXISTING
SYNTHETIC TURF DUGOUT
AND SURROUNDING
FENCE TO REMAIN
PROTECT EXISTING 8"
STORM DURING PROPOSED
STORM INSTALLATION
SEE SHEET C203 (TYP)
PROTECT EX
CONCRETE RETAINING
WALL AND FENCE
IP
SUPPLEMENT SITE FENCING
DURING CONSTRUCTION AS
NEEDED TO SECURE
CONSTRUCTION WORK AREAS
SEE CONSTRUCTION FENCING
NOTE WITHIN SHEET
PROTECT EX CATCH BASIN
AND STORM PIPING
DURING GEOTHERMAL
WELL INSTALLATION
CONTRACTOR TO HAVE THE OPTION TO
UTILIZE PROPOSED DETENTION SYSTEM FOR
CONSTRUCTION STORMWATER SETTLEMENT
VAULT MUST BE CLEANED OF ALL SEDIMENT
PRIOR TO THE END OF CONSTRUCTION
IP
IP
PUMP CONSTRUCTION STORMWATER TO
SEDIMENT SETTLEMENT TANKS UNTIL
DETENTION VAULT IS INSTALLED AND READY
TO USE AS TEMPORARY TESC MEASURE
PROTECT EX TREES TO
REMAIN UNLESS
OTHERWISE NOTED
VEG
REMOVE AND REPLACE PORTION OF
EXISTING SIDEWALK AND ASPHALT AS
NEEDED FOR UTILITY INSTALLATION
REMOVE AND REPLACE
PORTION OF EXISTING
FENCE AS NEEDED FOR
UTILITY INSTALLATION
APPROXIMATE LIMITS OF
PROPOSED STORM PIPING
EXCAVATION FROM DETENTION
SYSTEM FOR BASEBALL FIELD.
SEE SHEET C203 FOR DEPTH OF
STORM SYSTEM.
REMOVE EX (2) 6" &
(1) 8" DECIDUOUS
TREE CLUSTER
REMOVE EX 10"
DECIDUOUS TREE
NOTE: ARBORIST SHALL BE ON-SITE
DURING TREE REMOVAL AND
STORM PIPING INSTALLATION
REMOVE EX 8"
DECIDUOUS TREE
REMOVE EX 26"
DECIDUOUS TREE
REMOVE EX 10"
DECIDUOUS TREE
REMOVE EX 14"
DECIDUOUS TREE
IP
IP
CONTRACTOR TO UTILIZE 4'
MAX VERTICAL CUT AT
BOTTOM OF EXCAVATION
448 449
450
451
452
453
454 4551:1 MAX CUT SLOPE
C111
3
EXISTING 10" WATER MAIN TO BE PROTECTED AT ALL TIMES.
PROTECTION SHALL INCLUDE, BUT NOT LIMITED TO,
PROHIBITION OF HEAVY MACHINERY AND DRILLING
EQUIPMENT ON TOP OF MAIN OR WITHIN EASEMENT.
VIBRATIONAL TESTING MAY BE REQUIRED FOR ANY DRILLING
OR PILING OCCURRING NEAR THE MAIN. ADDITIONALLY, ANY
MACHINERY CROSSING THE WATER MAIN IN UNPAVED AREAS
WILL BE REQUIRED SHEETING OR SIMILAR MECHANISM TO
ENSURE THAT THE MAIN IS NOT SUBJECT TO DAMAGE LOADS.
CF
4
5
0
4
5
5
REMOVE EX
22" CONIFER
REMOVE AND REPLACE EX
FENCE AS NEEDED FOR
DETENTION EXCAVATION AND
STORM INSTALLATION
IP
EXISTING 10" PRIVATE CLAY SEWER MAIN TO BE PROTECTED AT
ALL TIMES. PROTECTION SHALL INCLUDE, BUT NOT LIMITED TO,
PROHIBITION OF HEAVY MACHINERY AND DRILLING EQUIPMENT
ON TOP OF MAIN, VIBRATIONAL TESTING MAY BE REQUIRED FOR
ANY DRILLING OR PILING OCCURRING NEAR THE MAIN.
ADDITIONALLY, ANY MACHINERY CROSSING THE WATER MAIN IN
UNPAVED AREAS WILL BE REQUIRED TO UTILIZE SHEETING OR
SIMILAR MECHANISM TO ENSURE THAT DAMAGE DOES NOT
OCCUR TO THE MAIN.
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
43667 NSTATE OF WASHIN
GTONREGISTERE DPROF
E
SSIONAL E N G IN EEROSBO
CAJA.DLAREJTED-40-4326C24005771HAZEN HIGH SCHOOL MODERNIZATION
DEMOLITION AND TESC PLAN
R-432606
LEGEND
SAWCUT LINE
REMOVE CURBING
REMOVE ASPHALT PAVEMENT
REMOVE CONCRETE PAVEMENT
TREE PROTECTION
INLET PROTECTION
PROPERTY LINE
TEMP CONSTRUCTION FENCINGCF
IP
VEG
SEE SHEET C001 FOR CITY OF RENTON
ESC STANDARD PLAN NOTES
SEE SHEET C102 FOR TESC
CONSTRUCTION SEQUENCE NOTES
MATCHLINE - SEE SHEET C102
MATCHLINE - SEE SHEET C104
BOTTOM OF EXCAVATION
LEGEND
SCALE 1"=20'
0 10 20 40
CONSTRUCTION FENCING NOTE:
INSTALL CONSTRUCTION FENCING AROUND
LIMITS OF WORK TO PROTECT STAFF AND
STUDENTS AND SECURE JOBSITE. CONTRACTOR
SHALL ERECT FENCE AROUND JOBSITE AND
ADJUST AS CONSTRUCTION CONDITIONS CHANGE
OR AS PHASING ALLOWS. CONTRACTOR CAN
UTILIZE EXISTING PERIMETER FENCING AS
SECURITY FENCING AND THEN SUPPLEMENT ON
THE WEST SIDE OF THE SITE AS NEEDED. ANY
EXISTING CHAINLINK FENCING THE CONTRACTOR
ELECTS TO UTILIZE DURING CONSTRUCTION SHALL
APPLY (IE ZIPTIES OR OTHER MEANS) HIGH
VISIBILITY MATERIAL OR SIMILAR METHOD TO BE
APPLIED TO FENCING TO DELINEAT AS
CONSTRUCTION ZONE (TYP). ANY SECTIONS OF
EXISTING FENCING THAT IS NOT 6-FT HIGH SHALL
HAVE TEMPORARY 6-FT HIGH CHAINLINK FENCING
INSTALLED NEXT TO IT. SEE DETAIL 10/C110.
SILT FENCEFF
INTERCEPTOR SWALEIS
APPENDIX A - TESC PLANS
NOTE:
SHEET HAS BEEN
PRINTED TO BE 11X17
AND NOT TO SCALE
15'EXISTING CITY OF
RENTON WATER
EASEMENT
15'
EXISTING CITY OF
RENTON WATER
EASEMENT
PRIVATE
STORM MAIN
CITY OF RENTON
WATER MAIN
REMOVE PORTION OF EX
GRASS FIELD AS REQ'D TO
INSTALL NEW GEOTHERMAL
SERVICE AND RETURN PIPING
AND VAULT AND ELECTRICAL
CONDUITS. SEE SHEET C204 (TYP)
IP
IP
INSTALL CB
PROTECTION (TYP)
SEE DETAIL
C110
7
IP
RELOCATE EX BASEBALL STORAGE
SHIPPING CONTAINER
COORDINATE LOCATION WITH OWNER.
CONTRACTOR SHALL ASSUME A 600 SQ FT
6" THICK CONCRETE PAD FOR STORAGE
CONTAINER AND 250 SF 6" CONCRETE PAD
FOR PORTABLE TOILETS FOR PRICING
SAWCUT AND REMOVE EX
ASPHALT PAVEMENT FOR
UTILITY INSTALLATION
SEE SHEET C204
FF
REMOVE GRAVEL
SAWCUT AND REMOVE
PORTION OF EX CONCRETE
PAVEMENT FOR NEW MECH'L
PAD INSTALLATION. SEE
SHEET C204
EX BASEBALL FIELD SUBDRAINAGE
TIE IN POC AT EX CATCH BASIN.
STORMWATER THEN DRAINS WEST.
SEE SHEET C103
SAWCUT AND REMOVE EX
ASPHALT PAVEMENT FOR
UTILITY INSTALLATION
SEE SHEET C204
PROTECT EXISTING
BASEBALL FIELD PERIMETER
FENCING TO REMAIN
SILT FENCE (TYP)
SEE DETAIL
C111
9
IMPROVED BASEBALL FIELD.
SEE LANDSCAPE PLANS AND
CIVIL SHEET C204
EXISTING 10" WATER MAIN TO BE PROTECTED AT ALL TIMES.
PROTECTION SHALL INCLUDE, BUT NOT LIMITED TO,
PROHIBITION OF HEAVY MACHINERY AND DRILLING
EQUIPMENT ON TOP OF MAIN OR WITHIN EASEMENT.
VIBRATIONAL TESTING MAY BE REQUIRED FOR ANY DRILLING
OR PILING OCCURRING NEAR THE MAIN. ADDITIONALLY, ANY
MACHINERY CROSSING THE WATER MAIN IN UNPAVED AREAS
WILL BE REQUIRED SHEETING OR SIMILAR MECHANISM TO
ENSURE THAT THE MAIN IS NOT SUBJECT TO DAMAGE LOADS.
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
43667 NSTAT E OF WASHI
N
GTONREGISTERE DPROF
ESSIONAL E N G IN EEROSBOCAJA.DLAREJTED-40-4326C24005771SCALE 1"=10'
5 10 200
HAZEN HIGH SCHOOL MODERNIZATION
DEMOLITION AND TESC PLAN
R-432607
SEE SHEET C001 FOR CITY OF RENTON
ESC STANDARD PLAN NOTES
SEE SHEET C102 FOR TESC
CONSTRUCTION SEQUENCE NOTES
LEGEND
SAWCUT LINE
REMOVE CURBING
REMOVE ASPHALT PAVEMENT
REMOVE CONCRETE PAVEMENT
TREE PROTECTION
INLET PROTECTION
PROPERTY LINE
TEMP CONSTRUCTION FENCINGCF
IP
VEG
MATCHLINE - SEE SHEET C103
CONSTRUCTION FENCING NOTE:
INSTALL CONSTRUCTION FENCING AROUND
LIMITS OF WORK TO PROTECT STAFF AND
STUDENTS AND SECURE JOBSITE. CONTRACTOR
SHALL ERECT FENCE AROUND JOBSITE AND
ADJUST AS CONSTRUCTION CONDITIONS CHANGE
OR AS PHASING ALLOWS. CONTRACTOR CAN
UTILIZE EXISTING PERIMETER FENCING AS
SECURITY FENCING AND THEN SUPPLEMENT ON
THE WEST SIDE OF THE SITE AS NEEDED. ANY
EXISTING CHAINLINK FENCING THE CONTRACTOR
ELECTS TO UTILIZE DURING CONSTRUCTION SHALL
APPLY (IE ZIPTIES OR OTHER MEANS) HIGH
VISIBILITY MATERIAL OR SIMILAR METHOD TO BE
APPLIED TO FENCING TO DELINEAT AS
CONSTRUCTION ZONE (TYP). ANY SECTIONS OF
EXISTING FENCING THAT IS NOT 6-FT HIGH SHALL
HAVE TEMPORARY 6-FT HIGH CHAINLINK FENCING
INSTALLED NEXT TO IT. SEE DETAIL 10/C110.
SILT FENCEFF
APPENDIX A - TESC PLANS
NOTE:
SHEET HAS BEEN
PRINTED TO BE 11X17
AND NOT TO SCALE
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
43667 NSTA TE OF WASHIN
GTONREGISTER E DPROF
ESSIONAL EN G INEEROSBO
CAJA.DLAREJTED-40-4326C24005771HAZEN HIGH SCHOOL MODERNIZATION
TESC DETAILS
R-4326136' FENCELINE POST (TYP)
2.375 INCH 0.D.
TOP RAIL
1.666 INCH O.D.
STRETCHER
BAR
BRACE RAIL
AND CABLE
1.666 INCH O.D.
TRUSS ROD 3/8" DIA
W/ TENSION DEVICE
TENSION WIRE
CONCRETE BLOCK
STD WGT GALVANIZED
CORNER POST
5/8" WIRE ROPE PROVIDE SECURE
END ATTACHMENT AT CORNER AND
GATE POSTS AND PROVIDE RUNNING
ATTACHMENT AT LINE POSTS AND
NEAR CENTER OF EACH FENCE PANEL
Inlet Protection 7NTS
Straw Wattle 8NTS
Construction Fence 10NTS
Check Dams 6NTS
Construction Entrance 5NTS
Not Used 9NTS
APPENDIX A - TESC DETAILS
BASEBALL DETENTION EXCAVATION SECTION
SCALE: 1" = 20'
420
440
460
480
420
440
460
480
X
XEXISTING GRADE
1:1 MAX CUT SLOPE
4' VERTICAL
CUT
BOE 442.50
PROTECT EX
FENCE AND
SYNTHETIC TURF
2'
6" GRAVEL BASE PER
STORMTRAP SPECS SEE PAGES C314 AND
C315 FOR DETENTION
VAULT DETAILS
4' VERTICAL CUT
SOFTBALL DETENTION EXCAVATION SECTION
SCALE: 1" = 20'
440
460
480
500
440
460
480
500
EXISTING GRADE
1:1 MAX CUT SLOPE
4' VERTICAL CUT
BOE 469.501'
9" GRAVEL BASE
SEE PAGE C314 FOR
DETENTION VAULT
DETAILS
MULTIPURPOSE DETENTION EXCAVATION SECTION
SCALE: 1" = 20'
440
460
480
500
440
460
480
500
EXISTING GRADE
1:1 MAX CUT SLOPE
2' VERTICAL CUT
BOE 471.401'
9" GRAVEL BASE
SEE PAGE C315 FOR
DETENTION VAULT
DETAILS
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
43667 NSTAT E OF WASHIN
GTONREGISTERE DPROF
ESSIONAL E N G IN EEROSBO
CAJA.DLAREJTED-40-4326C24005771HAZEN HIGH SCHOOL MODERNIZATION
TESC DETAILS
R-432614
6"=12" PERFORATE
PIPE AS NECESSARY
1'
TOP OF PIPE SHALL BE
6" MIN ABOVE GRADE
PROVIDE SOLID COVER
DISCHARGE TO SEDIMENT
POND VIA TEMP FORCE MAIN
5%30" MINRUNOFF WITH
SEDIMENT
FILTERED RUNOFF
WATER LEVEL CONCRETE BLOCKS
SUMP PUMP AND MOTOR
WIRE TIES
24"-36" PVC OR HDPE PIPE
W/ 2" DIA WEEP HOLES OR
APPROVED EQUAL
WRAP WITH PERMEABLE
FILTER FABRIC
PROVIDE 12" MIN
WASHED ROCK AROUND
PERIMETER OF PIPE
Temporary Sump and Pump 6NTS
Silt Fence 9NTS
Interceptor Swale 5NTS
10'TENSAR GS-1 SAFETY
FENCE OR EQUAL
GALVANIZED WIRE OR
OTHER APPROVED
MATERIAL
STEEL FENCE POST
CLIP FENCE TO WIRE
WIRE FENCE
TO STEEL POST
Clearing Limits Fence 7NTS
Section A 31"=20'
Section B 41"=20'
Section C 81"=20'
Tree Protection Fence 10NTS
APPENDIX A - TESC DETAILS
Page | 35 Appendix B – BMP Details Preserving Natural Vegetation (BMP C101) High-Visibility Fence (BMP C103) Stabilized Construction Access (BMP C105) 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) Storm Drain Inlet Protection (BMP C220) Silt Fence (BMP C233) Straw Wattles (BMP C235) Construction Stormwater Chemical Treatment (BMP C250) Construction Stormwater Filtration (BMP C251) High pH Neutralization Using CO2 (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
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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.
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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
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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.
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Maintenance Standards
If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and
visibility restored.
BMP C105: Stabilized Construction Access
Purpose
Stabilized construction accesses are established to reduce the amount of sediment transported onto
paved roads outside the project site by vehicles or equipment. This is done by constructing a sta-
bilized pad of quarry spalls at entrances and exits for project sites.
Conditions of Use
Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction
site if paved roads or other paved areas are within 1,000 feet of the site.
For residential subdivision construction sites, provide a stabilized construction access for each res-
idence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient
length/width to provide vehicle access/parking, based on lot size and configuration.
On large commercial, highway, and road projects, the designer should include enough extra mater-
ials in the contract to allow for additional stabilized accesses not shown in the initial Construction
SWPPP. It is difficult to determine exactly where access to these projects will take place; additional
materials will enable the contractor to install them where needed.
Design and Installation Specifications
See Figure II-3.1: Stabilized Construction Access for details. Note: the 100’ minimum length of the
access shall be reduced to the maximum practicable size when the size or configuration of the site
does not allow the full length (100’).
Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls,
a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed con-
crete, cement, or calcium chloride for construction access stabilization because these products raise
pH levels in stormwater and concrete discharge to waters of the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up
into the rock pad. The geotextile shall meet the standards listed in Table II-3.2: Stabilized Con-
struction Access Geotextile Standards.
Geotextile Property Required Value
Grab Tensile Strength (ASTM D4751)200 psi min.
Table II-3.2: Stabilized Construction Access
Geotextile Standards
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Geotextile Property Required Value
Grab Tensile Elongation (ASTM D4632)30% max.
Mullen Burst Strength (ASTM D3786-80a)400 psi min.
AOS (ASTM D4751)20-45 (U.S. standard sieve size)
Table II-3.2: Stabilized Construction Access
Geotextile Standards (continued)
l Consider early installation of the first lift of asphalt in areas that will be paved; this can be used
as a stabilized access. Also consider the installation of excess concrete as a stabilized access.
During large concrete pours, excess concrete is often available for this purpose.
l Fencing (see BMP C103: High-Visibility Fence) shall be installed as necessary to restrict
traffic to the construction access.
l Whenever possible, the access shall be constructed on a firm, compacted subgrade. This can
substantially increase the effectiveness of the pad and reduce the need for maintenance.
l Construction accesses should avoid crossing existing sidewalks and back of walk drains if at
all possible. If a construction access must cross a sidewalk or back of walk drain, the full length
of the sidewalk and back of walk drain must be covered and protected from sediment leaving
the site.
Alternative Material Specification
WSDOT has raised safety concerns about the Quarry Spall rock specified above. WSDOT observes
that the 4-inch to 8-inch rock sizes can become trapped between Dually truck tires, and then
released off-site at highway speeds. WSDOT has chosen to use a modified specification for the rock
while continuously verifying that the Stabilized Construction Access remains effective. To remain
effective, the BMP must prevent sediment from migrating off site. To date, there has been no per-
formance testing to verify operation of this new specification. Jurisdictions may use the alternative
specification, but must perform increased off-site inspection if they use, or allow others to use, it.
Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Stand-
ard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1) (WSDOT, 2016)
for ballast except for the following special requirements.
The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access
Alternative Material Requirements.
Sieve Size Percent Passing
2½″99-100
Table II-3.3: Stabilized
Construction Access
Alternative Material
Requirements
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Sieve Size Percent Passing
2″65-100
¾″40-80
No. 4 5 max.
No. 100 0-2
% Fracture 75 min.
Table II-3.3: Stabilized
Construction Access
Alternative Material
Requirements
(continued)
l All percentages are by weight.
l The sand equivalent value and dust ratio requirements do not apply.
l The fracture requirement shall be at least one fractured face and will apply the combined
aggregate retained on the No. 4 sieve in accordance with FOP for AASHTO T 335.
Maintenance Standards
Quarry spalls shall be added if the pad is no longer in accordance with the specifications.
l If the access is not preventing sediment from being tracked onto pavement, then alternative
measures to keep the streets free of sediment shall be used. This may include replace-
ment/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of
the access, or the installation of BMP C106: Wheel Wash.
l Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep-
ing. The sediment collected by sweeping shall be removed or stabilized on site. The pavement
shall not be cleaned by washing down the street, except when high efficiency sweeping is inef-
fective and there is a threat to public safety. If it is necessary to wash the streets, the con-
struction of a small sump to contain the wash water shall be considered. The sediment would
then be washed into the sump where it can be controlled.
l Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high effi-
ciency mechanical sweeper because this creates dust and throws soils into storm systems or
conveyance ditches.
l Any quarry spalls that are loosened from the pad, which end up on the roadway shall be
removed immediately.
l If vehicles are entering or exiting the site at points other than the construction access(es),
BMP C103: High-Visibility Fence shall be installed to control traffic.
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l Upon project completion and site stabilization, all construction accesses intended as per-
manent access for maintenance shall be permanently stabilized.
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Figure II-3.1: Stabilized Construction Access
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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
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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
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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
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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,
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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.
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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;
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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.
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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
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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.
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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.
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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.
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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
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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
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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.
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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.
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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
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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
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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:
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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.
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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.
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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
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 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
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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
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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.
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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.
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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
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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.
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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
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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
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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:
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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).
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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.
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Page | 36 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 | 37 Appendix E – Construction Stormwater General Permit (CSWGP) A NPDES permit and coverage under the NPDES Construction Stormwater General Permit (CSWGP) will be required for this project as it will perform more than 1.0 acre of land disturbing activity. An NPDES Permit will be applied for by the Owner for the project prior to starting construction. The NPDES Permit will then be transferred to the General Contractor (TBD) who will maintain both the NPDES and SWPPP for the project until the end of construction.
Page | 38 Appendix H – Engineering Calculations
————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.64 Program License Number: 201910001 Project Simulation Performed on: 02/13/2025 1:45 PM Report Generation Date: 02/13/2025 1:45 PM ————————————————————————————————— Input File Name: 2024-08-19 Hazen HS Baseball TESC Sizing.fld Project Name: Hazen HS Analysis Title: TESC Sizing Comments: Baseball Basin ———————————————— 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) 3.750 3.750 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 3.750 3.750 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- C, Forest, Flat 3.750 ----------------------------------------------
Subbasin Total 3.750 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- C, Lawn, Flat 0.650 SIDEWALKS/FLAT 3.100 ---------------------------------------------- Subbasin Total 3.750 ************************* 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 1 713.650 _____________________________________ Total: 713.650 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 83.780 _____________________________________ Total: 83.780
Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 4.517 ac-ft/year, Post Developed: 0.530 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 9.442E-02 2-Year 1.340 5-Year 0.149 5-Year 1.753 10-Year 0.185 10-Year 2.098 25-Year 0.255 25-Year 2.550 50-Year 0.280 50-Year 3.161 100-Year 0.303 100-Year 3.932 200-Year 0.449 200-Year 4.153 500-Year 0.645 500-Year 4.433 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals
TESC Sediment Trap Sizing (BMP C240) - Baseball Field
Total Site:
Pervious Area
Impervious Area
Total Area
0.65 ac
3.10 ac
3.75 ac
SA = FS (Q2 / VS )
SA = Surface Area (ft2)
FS = Factor of Safety = 2
Q2 = 2-year, 24-hour storm flow rate (ft3/s)
VS = Settling Velocity = 0.00096 ft/s
Per MGS TESC Sizing Report:
2-year, 24-hour storm event Q2 = 1.34 ft3/s
Surface Area Calculation:
SA = 2 (1.34/ 0.00096)
SA = 2,791 ft2
VR = SA * 3.5 ft minimum storage depth
VR = 2,791 * 3.5
VR = 9,768 ft3 Storage Volume Required
VR = 9,768 ft3 * (7.48 gal/ 1 ft3)
VR = 73,067 Gallons Required
Volume Provided:
(4) 18,900 Gallon sediment storage tanks
V = 4 * 18,900
V = 75,600 Gallons Provided