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HomeMy WebLinkAboutPN_Project Narrative_Shoreline_Exemption_180309_v1 King County South Plant Biogas and Heating Systems Improvements 1 ESA / D150513.00 Shoreline Exemption February 2018 Shoreline Exemption – Temporary Construction Entrance Project Narrative Project name, size and location of site and brief description of proposed work As part of King County’s South Plant Biogas and Heating System Project, King County proposes to construct a temporary construction entrance which will provide construction machinery access to the proposed spoils placement area onsite. Work will be restricted to temporary grading for installation of the temporary construction entrance. Construction and use of the temporary construction entrance would occur within a portion of the shoreline jurisdiction of Springbrook Creek. The 4,375 square foot (175-foot x 25-foot) temporary stabilized construction entrance would extend from the existing South Treatment Plant (STP) road west of Springbrook Creek to provide access to the spoils placement location within an open lawn area of the STP site further to the west. The construction entrance would consist of 4-inch to 8-inch quarry spalls that are 12 inches thick and underlain by geotextile. Hog fuel may be substituted for or combined with quarry spalls. Fencing would be installed to restrict traffic to the construction entrance. If the entrance does not prevent sediment from being tracked onto pavement, alternative measures will be used to keep the streets free of sediment (e.g., street sweeping, increase in dimensions of the entrance, installation of a wheel wash). If washing is done, it would occur on an area covered with crushed rock and washed water would drain into a sediment trap or pond. Following grading activities on the spoils placement site, the temporary stabilized construction entrance would be removed, grades would be restored to their preconstruction condition, and the area would be permanently stabilized with mulch followed by seeding per Sections C.3.2 and C.3.10, respectively, of the 2017 City of Renton Surface Water Design Manual. The proposed temporary construction entrance is located at King County’s South T reatment Plant at 1200 Monster Road SW in Renton, Washington (King County Parcel Numbers 2423049097 and 24230490) in the NE Quarter-Section, Section 24, Township 23 North, Range 9 East. Background. The King County South Plant Biogas and Heating Systems Project, includes construction of the Heat and Energy Recovery Building (HERB), a new thermal oxidizer, heating system improvements within the existing Digester Equipment Building, and utility connections. King County proposes to replace South Plant’s Biogas Upgrading System (BUS) and heating system to improve the beneficial use of digester gas at South Plant while also reliably supplying heat to meet process and space heating demands. As part of the project, approximately 17,000 cubic yards of soil would be excavated and placed on a 1-acre area south of the digesters, located within an open lawn area in the center of the STP site. Spoils would be compacted and seeded to match existing grades and vegetation type. Transport of the spoils would require construction of a temporary access road off of the Plant perimeter drive. Shoreline Exemption - Temporary Construction Entrance Project Narrative King County South Plant Biogas and Heating Systems Improvements 2 ESA / D150513.00 Shoreline Exemption February 2018 Basis for the exemption request Total cost of the activity is $6,900.00, which is less than the current Washington Department of Ecology shoreline exemption threshold of $7,047.00. Anticipated dates of work Project construction is scheduled to begin in May 2019 and end in May 2021. Other permits required for the proposed project Permits related to this activity, as part of the larger King County South Plant Biogas and Heating Systems Project, include the following: City of Renton  Land Use Permits, including: o Conditional Use Permit o Site Plan Review o Critical Areas Review o Street Frontage Improvements Waiver  Building Permits, including: o Building Permit o Civil Construction Permit o Drainage Review and Approval Puget Sound Clear Air Agency  Notice of Application Washington Department of Ecology  National Pollutant Discharge Elimination System (NPDES) Construction Stormwater General Permit Shoreline Exemption – Temporary Construction Entrance Project Narrative King County South Plant Biogas and Heating Systems Improvements 3 ESA / D150513.00 Shoreline Exemption February 2018 Current and proposed use of site The spoils site is currently vacant land within King County’s STP. The proposed activity for this shoreline exemption request is a temporary use. The site will be restored following construction. Special site features (i.e. wetlands, water bodies, steep slopes) The site of the proposed temporary construction entrance is located in an area that was filled and graded as part of previous STP construction projects. There are no wetlands, water bodies or steep slopes present within the proposed temporary construction access. Statement addressing soil type and drainage conditions In general, the site overlies previous fill consisting of silty sand with gravel to a depth of approximately 25 feet. The fill layer is underlain by native sand, silt, and gravel to a depth of approximately 80 feet. The entire project site is within Drainage Basin 7, which drains to the stormwater sewer system on the site and ultimately discharges to the Black River (see the Technical Information Report (Full Drainage Review)). A temporary erosion and sediment control plan will be developed and implemented during construction and operation of the temporary construction entrance. Post construction, the temporary construction entrance would be regraded and revegetated. No permanent changes to drainage conditions would occur. Total estimated construction cost and estimated fair market value of the proposed project The total cost of the temporary construction access is estimated at $6,900.00. Estimated quantities and type of materials involved if any fill or excavation is proposed Approximately 290 cubic yards (CY) of soil would be excavated and approximately 120 CY of quarry spalls would be temporarily placed to construct the temporary construction entrance. Quarry spalls will be removed following construction and excavated soil will be reused onsite to restore the existing grades. Number, type and size of any trees to be removed No trees would be removed within the shoreline. Distance from closest area of work to the Ordinary High Water Mark of the shoreline The proposed temporary construction entrance would be located 128 feet from the ordinary high water mark at its closest point. Shoreline Exemption - Temporary Construction Entrance Project Narrative King County South Plant Biogas and Heating Systems Improvements 4 ESA / D150513.00 Shoreline Exemption February 2018 Nature of the existing shoreline (e.g., high bank, naturalize, rip rap, bulkhead, etc.) Springbrook Creek in the City was extensively modified and straightened for agricultural drainage in the 1920s by King County Drainage District No. 1. The channel area abutting the project was improved in the 1980s and 1990s for flood control by the City in cooperation with the Natural Resource Conservation Service. The stream is constrained and channelized throughout the shoreline. Levees that define the streambank limit the width of the riparian corridor. Wetlands Assessment A wetland assessment is not applicable for this shoreline exemption. The closest wetland is more than 100 feet from the shoreline activity. Flood Hazard Data Construction of the temporary construction entrance is not anticipated to result in impacts within the flood hazard area. See the grading plan for the nature, location, dimensions, and elevations of temporary fill. The flood hazard area for Springbrook Creek has been determined using the best available GIS data provided by the City of Renton, and in review of the effective FEMA Flood Insurance Rate Map (FIRM) for the City of Renton, and is shown on the Temporary Erosion and Sediment Control (TESC) Plans (see Civil Plan Sheet C2240103). Construction activities proposed within the flood hazard area will be restricted to temporary grading for installation of the temporary construction entrance, which will provide construction machinery access to the spoils placement area. The site will be restored after construction. Habitat Data Report The proposed shoreline activity is not located in, nor does it directly abut, a critical habitat. Therefore, a habitat data report is not included.