2219 PINEHURST AVE BASE FILE 2020-07-14

4 Existing Site Hydrology The site has a single drainage basin, with the majority of stormwater runoff infiltrating into a weathered till layer. Any additional runoff from the site flows overland to the south, and then west for approximately 2500 ft to an existing Stormwater catch basin. This catch basin has a 6 inch pipe that flows south. It should be noted that the Stormwater infrastructure in this area is virtually non-existent. This is due to the historic design of the combined sanitary sewer/Stormwater system. Developed Site Hydrology In an effort to mimic predeveloped drainage patterns, we will look at the feasibility of the Stormwater BMP's shown on list number 1 in volume 1 of the 2014 DOE manual. The roof run-off of the proposed house will be connected to downspouts to cleanouts and then tight lined to the proposed Sanitary Sewer Stub connection. The area of the proposed roof is 2632 SF. The proposed driveway(PGIS) is an additional 1043 sf, and will also be collected at a low point in and connected to the sewer stub. The combination of the soil types with the position of the proposed home on each lot site makes infiltration and dispersion infeasible. There is virtually no infiltration capacity in the Alderwood soils, with a depth to hardpan of less than 36". There is also very little flowpath length on these urban lots. Flowpath length of the front cleanouts for roof runoff is less than 20 ft to the r/w line. The minimum flowpath length for dispersion is 25 ft. Water Quality Measures There are no water quality measures proposed for this project as the total added PGIS for the project is less than 5,000 s.f. (1043 sf.). I should note that this is the only PGIS proposed for this permit. Construction stormwater management will be provided to control the release of sediment-laden runoff. A SWPPP prepared for the project, will emphasize erosion control rather than sediment control. In an effort to preserve natural vegetation and limit erosion and sediment disposition, construction activities will be confined to the smallest area possible. TESC BMPs facilities will be provided on-site during construction to assure flow rates are controlled. Performance Standards Flow Control and Stormwater Quality elements are subject to the requirements of the current The City of Everett Drainage Manual. The project is expected to infiltrate 100%of the tributary surface runoff, in order to meet flow control and water quality treatment requirements. Per the United States Department of Agriculture NRCS Web Soil Survey, site soils are Alderwood Urban Land Comples 2-8 percent slopes. Test pits excavated on the property for drain field design and the drainage design for the proposed residence are consistent with this soil type. Soil investigations indicate depth to restrictive feature: 20 to 39 inches to cemented horizon; 20 to 39 inches to densic material. The Natural drainage class is moderately well drained. The depth to the water table is about 18 to 36-inches. The interpretive Hydrologic Soil Group is C. Pinehurst Ave. Duplex Drainage Report