9931 19TH AVE SE 2018-01-02 MF Import

1.0 GENERAL INFORMATION The proposed project consists of developing approximately 0.86 acres into an ARCO AM/PM Mini - Market facility. The site is located at the northeast corner of the intersection of SR-527 and 100th Street S.E. within the jurisdiction of the City of Everett. (See Figure 1, Vicinity Map.) The site is currently partially developed with a couple existing buildings and a driveway located near the central portion of the site. A rockery retaining wall also exists along the west and south property lines. The remainder of the property is grass or bare ground with a few trees. Half the site currently drains in a soutl�easterly direction toward 100th Street S.E.; the retraining portion of the site drains in a northwesterly direction toward SR-527. The ultimate discharge point for runoff from the site is Silver Creek, except for approximately 2,700 square feet (0.06 acres) which drains toward the Woods Creek drainage basin. This proposal requires the complete demolition and removal of all of the existing structures, including the rockery. The new development will be a mini -market facility and pump island surrounded by appropriate parking areas, drive aisle and landscaping. Since the project will increase the impervious surface area of the property, consequently increasing the stormwater runoff, detention of stormwater will be provided. The current requirements as dictated by the City of Everett are to follow the January 1997 Stormwater Management Manual published by the City of Everett. 2.0 STORMWATER QUANTITY CONTROL Current stormwater regulations developed by the City of Everett, dated January 1997, require on -site detention systems to be designed according to the requirements of the Department of Ecology's Stormwater Management Manual for the Puget Sound Basin. The proposed method of detention for this project is by an underground concrete vault with a control structure and restricted release by orifice and notch weir. The release rate shall be one-half the 2-year/24-hour pre -developed flow during a 2-year/24-hour design storm, and a 10-year/24-hour pre -developed flow rate during a 10- year/24-hour design storm, and likewise for the 100-year/24-hour pre- and post -developed storms. As shown in the calculations in Appendix "A" approximately 3,400 cubic feet of runoff is required to be detained. 2.1 DELINEATION OF DRAINAGE BASIN By using the boundary and topographic survey prepared by our office (see Figure 2), the tributary area has been identified. The site consists of two drainage basins, however, the vast majority of the site flows toward the Silver Lake drainage basin. The remainder of the site, approximately 0.06 acres, drains to the Woods Creek drainage basin. For the purposes of this report, since that area is less than 0.10 acres, runoff from that area will not be discharged to the Woods Creek drainage basin as it currently does, however, it will be detained and released to the Silver Lake drainage basin with the development of this project. No off -site rttnoff shall drain onto the property as dictated by topography. In addition, the storm drainage system shall be situated such that nearly all on -site runoff shall be collected. -1- 2918.011 [JJ/sml