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HomeMy WebLinkAboutRS_CSWPPP_20250330_v2 Page 1 Sierra Heights Elementary School Construction SWPPP Narrative March 25, 2025 SIERRA HEIGHTS ELEMENTARY SCHOOL SCHOOL PARKING LOT UPGRADES CONSTRUCTION SWPPP NARRATIVE MARCH 25,2025 The following Construction Storm Water Pollution Prevention Plan (CSWPPP) Narrative is for the Sierra Heights Elementary School paving improvements project at 2501 Union Avenue NE in Renton, Washington. The narrative supplements the Temporary Erosion and Sediment Control (TESC) plan. This narrative has been prepared per Section 1.2.5 of the 2022 Renton Surface Water Design Manual (SWDM). Refer to the TESC plan (Sheet C-100 and C-101) and TESC details and notes (Sheet 300) for more information regarding any erosion or sediment control measures involved in this project. 1. CONSTRUCTION STORMWATER POLLUTION PREVENTION ELEMENTS 1) Clearing Limits: The limits of the disturbance are delineated by the “limit of work” line shown on Sheets C-100 and C-101. Areas impacted and not anticipated to be covered with final stabilization measures shall be stabilized using approved permanent TESC methods. 2) Cover Measures: It is possible that some of the earthwork and grading may occur in wet weather conditions. The site must be stabilized and no soils will be allowed to remain unstabilized for more than two days between October 1st and April 30th. From May 1 through September 30, install cover measures to protect disturbed areas that will remain unworked for seven days or more. By October 8, seed all areas that will remain unworked from October 1 through April 30. Mulch all seeded areas. Exposed slopes will be protected by Department of Ecology (DOE) approved coverage methods. BMPs including, but not limited to: C101, Preserving Natural Vegetation; C121, Mulching; C123, Plastic Covering; C130, Surface Roughening; C140, Dust Control; and T5.13 Post Construction Soil Amendment will be used to stabilize on-site soils during construction. 3) Perimeter Protection: DOE approved BMPs for sediment controls are shown on the TESC plan. Sediment will be controlled using storm drain inlet protection (BMP C220). 4) Traffic Area Stabilization: The existing pavement will be utilized as construction access and reinforced with quarry spalls (BMP C105) as necessary. The Contractor shall provide a wheel wash if necessary. 5) Sediment Retention: The majority of the earthwork on the project will be constructed during the dry season, therefore it is not anticipated that stormwater will convey sediment-laden water to the stormwater system. Sediment will be controlled using storm drain inlet protection (BMP C220). 6) Surface Water Collection: Drainage structures in areas where no work occurs will remain and will be protected; discharge points to the public storm drain main line will also be protected. To prevent discharge of turbid water downstream, all existing catch basins located within the disturbance area and outside of the disturbance area within approximately 300 feet downstream of the site will be protected with storm drain inlet DEVELOPMENT ENGINEERING njanders 06/05/2025 Page 2 Sierra Heights Elementary School Construction SWPPP Narrative March 25, 2025 protection (BMP C220). The Contractor shall remove inlet protection at the end of the project without releasing captured sediment into the storm system. 7) Dewatering Control: The majority of the earthwork on the project will be constructed during the dry season, therefore it is not anticipated that groundwater will be encountered in the excavations for this project. In the event that perched groundwater is encountered during any wet season construction, the Contractor shall route it to the sediment settling facility by pumping it out of the excavation. 8) Dust Control: Dust control will be provided to prevent dust created by disturbed soil surface from entering the stormwater system, roadways, or surface waters. Dust control shall be implemented per BMP C140 of Volume II of the DOE Manual. 9) Control Flow Rates: Stormwater flow control during construction is anticipated to be mitigated by routing runoff to a temporary sediment storage tank. Refer to the Sediment Tank Sizing calculations and the MGS Flood output included within Appendix B of the project’s Technical Information Report. The project does not involve permanent flow control facilities. 10) Control Pollutants: Temporary protection of the disturbed soils provides the first level of protection for pollution control, and perimeter measures downstream will mitigate the remaining pollutants. Construction debris will be removed from the site. The Contractor will be responsible for managing their construction equipment per DOE-approved BMPs. If a truck wheel wash is required, truck wheel wash water and concrete truck washout water shall be collected and discharged to the public sanitary sewer (SS) system. To apply for and obtain a SS release, contact the local sewer purveyors (City of Renton and King County Metro) for authorization. 11) Protecting Existing and Proposed Flow Control BMPs: Due to the locations of the replaced surfaces within other existing improvements, on-site BMPs are infeasible. 12) Maintain BMPs: BMP maintenance will be required in accordance with Renton’s standard Grading and Erosion Control Notes, as shown on Sheet C-300. 13) Manage the Project: All phases of construction will be managed by the Contractor. The site must be stabilized and no soils will be allowed to remain exposed and unworked for more than two days between October 1st and April 30th and for more than seven days between May 1st and September 30th. The Contractor will provide maintenance and monitoring of TESC BMPs. Work of all contractors will be coordinated to minimize the duration of disturbance on the site. The best management practices shown on the TESC plan are minimum requirements. Failure to maintain SWPPP measures in accordance with adopted standards may result in the work being performed at the City’s direction and the costs assessed as a lien against the property where such facilities are located. Page 3 Sierra Heights Elementary School Construction SWPPP Narrative March 25, 2025 2. PROJECT DESCRIPTION The project will involve the replacement and installation of new pavement and concrete walkway onsite. Within the right-of-way on Union Avenue NE, new and replaced pavement and concrete walkway will be installed. According to Section 1.2.3.1 B in the SWDM, there are no target surfaces requiring flow control mitigation. Additionally, per section 1.2.8 of the SWDM, the project meets exemption 3 for the Core Requirement #8, therefore water quality facilities are not required. See the project’s Technical Information Report for more information on Core Requirements. Estimated earthwork quantities are to be determined. 3. EXISTING SITE CONDITIONS Sierra Heights Elementary School is located on two parcels (#0423059069 and #0423059176), totaling approximately 14.49 acres. The site is located in Section 4, Township 23 North, Range 5 East, Willamette Meridian. It is zoned School (Public). The site is located within the May Creek subbasin of the Cedar River/Lake Washington drainage basin. Stormwater runoff from the existing parking lots is collected by catch basins and conveyed to the public storm system in Union Avenue NE. Topographically, the property slopes down from south to north. The south parking lot elevation ranges from about 451 to 446 while the north parking lot goes from 445 to 440. The USDA Natural Resources Conservation Service lists the underlying soil for the site as Alderwood gravelly sandy loam, 8 to 15 percent slopes. 4. ADJACENT AREAS The school campus is bounded by a wooded area and single-family residential property to the north, Union Avenue NE to the east, single-family residential properties to the south, and a power line corridor to the west. 5. CRITICAL AREAS According to King County and City of Renton GIS mapping, there is a wetland on the far west side of the site. The proposed project is limited to the parking lots on the east side of the site and will not impact the wetland. There are no other critical areas shown within or adjacent to the site. 6. SOILS According to the USDA Web Soil Survey, the underlying soil for the site is Alderwood gravelly sandy loam, 8 to 15 percent slopes. 7. POTENTIAL EROSION PROBLEM AREAS The site is not within an erosion hazard area. Per the proposed contract documents, the contractor is to provide protection for soils to limit the exposure to erosion. The limitation of disturbance, adequate cover practices, seasonal work limitation, and runoff control are the most effective Page 4 Sierra Heights Elementary School Construction SWPPP Narrative March 25, 2025 methods for reduction of turbidity in stormwater runoff. Any runoff that occurs will be directed to the temporary sump and then pumped to the sediment settling tank. Areas that have not been permanently stabilized will be addressed using DOE-approved BMPs, per the construction documents. 8. CONSTRUCTION PHASING At this time, it is not expected that the project will be formally phased. The contractor is responsible for coordinating work of all subcontractors to keep the duration of site disturbance limited to the maximum extent possible. 9. CONSTRUCTION SCHEDULE Construction is expected to begin in June 2025 and be completed by September 2025. Earthwork activities are not expected to take place in the wet season, October 1st to April 30th. Should any wet weather conditions occur during construction, the contractor shall implement the de-watering procedures outlined in this SWPPP and applicable BMPs including, but not limited to C123, Plastic Covering; C121, Mulching; C122, Nets and Blankets; C126, Polyacrylamide for Soil Erosion Protection; C130, Surface Roughening. Page 5 Sierra Heights Elementary School Construction SWPPP Narrative March 25, 2025 10. FINANCIAL/OWNERSHIP RESPONSIBILITIES This property is owned and operated by the Renton School District. The accepted low bidder on the project will be responsible for posting a performance and payment bond with the Renton School District, and thus will be the responsible party for any liability associated with erosion and sedimentation impact. 11. ENGINEERING CALCULATIONS A copy of any calculations performed during design of the project and relevant storm drainage modeling discussions is included in the project’s Technical Information Report.