1001 N BROADWAY EVCC 2025-10-03 - Laserfiche WebLink

f f Downstream Analysis Stormwater from the project site discharges to the existing combined sewer system at two j different locations (to the north and east) that eventually merge approximately 700 feet east of the project site. The combined sewer system continues south and east before discharging to the E municipal sewer treatment plant. A triangular-shaped area of parking, located west of the project site but within the school property, is tributary to the north subbasin via storm pipe. The project will intercept the conveyance piping and connect to the new stonn conveyance system within the north subbasin. Another paved parking area in the southwest corner of the property is tributary to the south subbasin. Stormwater will continue to drain as sheet flow into the south subbasin and be collected in the proposed bioretention cells. Site Soils Based on the 2019 geoteclmical report completed by GeoEngineers (see Appendix A), the underlying soils in the area consist of a layer of fill and reworked outwash deposit material and a layer of advance outwash deposits. The upper five to ten feet of the soil layers contain a high percentage of fines and are highly moisture sensitive. Infiltration rates are anticipated to be less than 0.4 inch per hour. Proposed Conditions This project will construct a new LRC Building (approximately 22,780 SF footprint), adjacent paved parking,pedestrian walkways and plazas, landscape islands, and a larger open space area north of the building. The existing access points to the site will remain, but the access approach to the 10"' Street intersection will be regraded to accommodate the new building elevation. ADA access routes and parking will be provided from areas adjacent to the building. Frontage improvements include removing the existing 5-foot sidewalk along N. Broadway Avenue and trees within the 12-foot landscape strip and replacing with a frontage layout that matches the WSU Extension development. The revised layout has an 8.5-foot landscape amenity zone and an 8-foot sidewalk. A driveway entrance with bollards will be constructed for emergency vehicle access for the WSU Extension building development. Proposed Storntwater Facilities The proposed stormwater system will maintain the general separation of the two existing subbasin areas to prevent exceeding the downstream pipe capacity of the combined sewer. Stormwater runoff from the paved parking area will be collected in new bioretention cells equipped with a perforated underdrain and overflow yard drains. These facilities will be located at low spots throughout the parking area to collect and provide water quality treatment for the pavement stormwater. A portion of these facilities will convey stormwater to the existing combined sewer system along the east property line. Stormwater from the building roof area is routed through the internal rain leader system of the building and discharges to a new conveyance system around the building. This roof conveyance Stormwater Site Plan 3 . Learning Resource Center-