859 LOCUST ST 2022-07-20 - Laserfiche WebLink

i Stormwater Pollution Prevention Plan 2.0 Site Description 2.1 Existing Conditions The property currently encompasses a multi-family housing complex known as the Grandview Apartments. The project area was previously used as a playground and storage area. This area was comprised of approximately 6,600 square feet of asphalt and storage building roof area. This asphalt play area and storage building have since been demolished. The site is slightly sloped toward the west ranging from 2-8 percent slopes. The project area is currently comprised of lawn and gravel areas where demolition had taken place. Drainage from the site sheet flows west to existing catch basins and conveyed via existing combined sewer system. The USDA Soil Survey classifies the site as having Alderwood-Urban complex soils with 2 to 8 percent slopes. This soil type is classified as Hydrologic Soil Group B and is considered to have moderate infiltration rates when soils are thoroughly wet. 2.2 Proposed Construction Activities A clubhouse and clubhouse parking area for the Grandview Apartment complex is proposed to be built where the playground and storage building once were. A total of 10,900 square feet of non-pollution generating impervious surface will be added upon completion of the improvements. Stormwater runoff from the parking lot will sheet flow west and into a drainage swale located along the proposed sidewalk west of the parking area. Stormwater within the swale will flow north towards the clubhouse building and shall be captured within a 12-inch area drain with an atrium grate. The wall drain for the proposed lock-block wall on the east side of the parking lot will also drain to this point via 4"PVC pipe. Stormwater collected within the area drain shall be conveyed west to rain garden which shall be placed along the east side of the clubhouse building. Stormwater runoff from the clubhouse roof shall also be conveyed to the rain garden from the roof downspouts. The proposed rain garden shall provide 6 inches of ponding depth with a 6"underdrain installed at a minimum of 2.5' beneath the rain garden media. In the event that the 6"ponding depth is exceeded, stormwater will flow into a Type 1-L catch basin with a beehive grate which will be placed in the rain garden. Upon over-saturation of the rain garden soil media, excess stormwater will flow into the 6"perforated pipe and to the Type 1-1 catch basin intended for rain garden overflow. Stormwater collected within the catch basin will flow north via 6"PVC pipe and into the combined sewer conveyance system located on site. As this system is being routed to a combined sewer system,the Type 1-L catch basin located within the rain garden shall be Grandview Apartments Clubhouse SWPPP 3 March,2017