10312 EVERGREEN WAY GLINT CAR WASH 2023-07-31

GLINT CAR WASH - EVERETT STORMWATER REPORT • SECTION 2 - EXISTING CONDITIONS SUMMARY The site is located at 10312 Evergreen Way in Everett, Washington and includes three parcels of land totaling about 1.91 acres in size.The site is bound to the north by Olivia Park Road,to the east by Evergreen Way, to the south a car dealership, and to the west by residential properties. The site is currently an asphalt paved and gravel parking lot with two large concrete slabs. Existing vegetation area is limited to an 802 sf shrub and grass area at the southeast corner of the property. The site is relatively flat with an elevation change of less than 2 feet across the property. The total proposed redevelopment area equals 2.0 acres. Flow control for the redevelopment project was analyzed based on two(2)drainage basins totaling 1.95 acres;this area will have the same modeling Point of Connection #1. The remaining 0.05 acres involves existing gravel and landscape area along the south property line that will become new landscape planter;this area was excluded from our flow control modeling. Basin A(1.86 ac) Onsite parking and building slabs. Runoff drains to a series of onsite catchbasins which drain to a catch basin at the southwest corner of the site. This catch basin serves as a junction for a large 24- inch diameter CMP storm main which receives approximately 81 acres of upstream drainage. This main continues southward into the neighboring property to the south and then eastward to the storm system in Evergreen Way. Basin B (0.09 ac) Onsite parking and public sidewalk. Sheet drains to roadway storm system and continues southward along Evergreen Way. There are no onsite stormwater treatment, oil control or detention facilities. There are no onsite wetlands or sensitive areas. There is a wetland within the property to the west for which we have proposed a 60-foot setback with buffer plantings and a split rail fence. The property is not within a 100-yr floodplain. The site is underlain by 5 to 7.5 feet of very loose to medium dense fill comprised of silty sand with varying amounts of gravel over native deposits of loose to medium dense silty sand with varying amounts of gravel and sand with some silt,and localized very soft to very stiff organic silt and sandy silt. Dense to very dense deposits of silty SAND with varying amounts of gravel were encountered at depths of 7.5 to 15 feet. Groundwater seepage was encountered at each boring location at depths of 2.5 to 10 feet during our subsurface exploration. The observed seepage appears to be indicative of perched groundwater collecting above the underlying dense soil deposits. Terraforma Design Group, Inc. Page 6