7016 EVERGREEN WAY 2016-01-01 MF Import

� Sunrisc Scrvices-Drain�igc Suidy � 3. DRAINAGE PROPOSAL The drainage proposal indudes providing detention and water quality treatment for an 8,600-ft'' parking lot within 0.27-acres of the 0.50-acre parccl. New impervious area added to thc site for development is approximately 0.20 acres or 74% of the Development C Area. ?n accordancc with City of �vem,t standards, the detention system will be designed to detain the 2-year, 10-year, anci i00-year (24-I-Iour) developed s�orm volumes and relense at �/z of the pre-existing 3-yenr, 1G-year, and 100-year frequency stonn event rates. As � mquired by the Washington State Department of Ecology, a safety factor has Ueen added to the detention volume to account for the ir;iperfections oC the Santa Barbara Hydrograph moilel based upon �verett Pig. 1-3.1 the Volume Correction Pactor for Streambank Erosion Con[roL The figure presented in the Appendices indicates that for a site with 74 % impervious surface, n correction facior of 0.415 must be opplied to the � detention volumr, calculated by the Santa Barbara UI-I Method. To achieve complinnce to this standard, [he detention volume has been increased by 42°l0, from the calculated detention volume. The detention system will have a rotal volume of approximately 1,400 CF of storage not � including water quality storage. A flow restrictor/oil pollution control device (PROP) �vill controlthe discharge Flo�vs out ofthe pipe. Less than 10,000 ft` of parking and driving surfaces arc proposed for the site. Ciry of Everett standards require a combination of underground dead storage for partide sctding and an open pond celi for vegetadve filtration of pollutants. The wet-txnk storaae �vould � be required to hold u� to 85S'o the volume oC the 6-month devcloped sto��n, which is calculated to be 625 ft , with 3 feet of dead storage. Sizing calculations are provided later in this report.. { R'ESTLILN C�GI�CC•RS, ING j/3 f I'KOJCCP�.01�'_07a