10901 27TH AVE SE 2025-07-29 - Laserfiche WebLink

• ' TEMPORARY EROSION CONTROL This project will use a two-phased construction schedule that will retain the four of the six ' existing school buildings and adjacent pavement while the new two-story school building is being constructed. A water quality treatment train will be used during the construction phase to treat construction stormwater runoff to comply with the State Water Quality Standards for ' construction stormwater discharge. Refer to the erosion control plans that are part of the construction plan set for details and notes associated with temporary erosion control measures. To maintain site control and safety,a security fence will be installed between the remaining four ' buildings and the new construction. A gravel work pad will be installed around the perimeter of the new building construction. To minimize soil disturbance in the early construction phase,the existing asphalt surfaces will be retained to mitigate exposing bare soils to heavy construction ' vehicles. Once the wet season has occurred,the existing asphalt surfaces will be removed and the surface will be prepared for gravel surfacing. This temporary gravel surfacing will provide the general contractor a surface for material laydown and circulation during the second and final Istages of construction. As construction progresses and the storm sewer systems are installed,the new inlets will receive inlet protection along with regular maintenance of the erosion sedimentation system. SOURCE CONTROL REQUIREMENTS The subject property is located in the North Creek watershed and is subject to the nutrient source control requirement. Because the land use activities include uncovered vehicle parking, only one source control BMP for nutrient control will be implemented as shown below. Refer to Appendix E for BMP description. BMP S2.00 Maintenance of Storm Drainage Facilities WATER QUALITY DESIGN ' Filterra Bioretention Structures placed throughout the parking areas will provide water quality treatment for the paved areas that receive vehicle traffic. Stormwater running along the curb will be directed to a throat opening to the Filterra structure. The Filterra structure is designed to treat the 6-month storm but bypass larger flows to a downstream catch basin that discharges to the underground detention facility. The Filterra Unit has a General Use Designation according to the Washington State Department of Ecology, and sizing is based on their design protocol. The ' 6-month storm flow rate and Filterra sizing were calculated using the WWHM software program. See Appendix C for WWHM Filterra sizing calculations. The Filterra Bioretention Structures will be maintained according to the manufacturer's most up- to-date recommendations. Current maintenance guidelines are included in Appendix E. The table below summarizes the Filterra Unit sizes in relation to the tributary area. The Filterra Units are sized for basic treatment using the sand filter module of the WWHM program. The James Monroe Elementary School 6 Reid iddleton Drainage Report