1010 N BROADWAY EVCC 2018-01-01 MF Import

Stormwater runoff from the remaining 30 percent of the Building site (Areas 4 and 5) sheet flows toward the Fitness Center and the Transit Center, where it disperses or is collected within existing drainage structures. Both the Fitness Center and the Transit Center discharge to the Tower Street storm system, described above. At the 10th Street Parking site, stormwater runoff from the building roof area and the parking lot sheet flows to the northeast corner, where it is captured in a catch basin and routed to the storm system within North Broadway. See Exhibit A-3 in Appendix A for existing conditions. As mentioned above, the North Broadway storm system combines with the 48-inch diameter city sewer main downstream. 2.2 Mitigation of Existing or Potential Problems As described by the City of Everett Public Works Department staff, the existing combined sewer system experiences capacity issues downstream of the project site. The City is pursuing separation of the storm and sewer lines to reduce flooding during significant storm events. For this reason, the storm pipe within Tower and Waverly Streets were upsized by Everett Community College in 2001 to separate stormwater runoff from sanitary sewer pipe and to provide capacity for future projects. This project is summarized in the Reid Middleton report provided in Appendix B, Exhibit B-8. Additionally, the AHBL analysis demonstrating sufficient capacity for the Building site is included in Appendix B, Exhibit B-9. The proposed Building and 10th Street Parking sites will result in a reduction of impervious surface when compared to the existing land cover, thus reducing the peak stormwater runoff. Additionally, a flow control facility and bio-retention areas, utilizing compost amended soils, will further reduce peak runoff, thus, mitigating existing or potential problems to the downstream conveyance system. 2.3 Upstream Analysis • At the Building site, stormwater runoff from upstream properties is collected and controlled before entering the project site and, therefore, is expected to be minimal. At the 10th Street Parking site,a small area of asphalt parking lot sheet flows onto the property and is collected in the northeast catch basin. See the Developed Conditions Maps in Appendix A for more information. 3.0 ANALYSIS AND DESIGN OF REQUIRED EROSION AND SEDIMENT CONTROL BMPS All new development that includes land alteration activities of 1 acre or more requires specific erosion and sediment control. As the site is not located near a sediment/erosion sensitive feature,there are no special seasonal limitations for this project. 3.1 Construction Stormwater Pollution Prevention Plan (SWPPP) Elements 1 through 12 1. Mark Clearing Limits—All areas to remain undisturbed during the construction of the project will be delineated prior to any site clearing or grading. 2. Construction Access—Construction access will be from North Broadway and 10th Street by a stabilized construction entrance per BMP C105. Stormwater Site iReport Everett Community College Q©Q O � Index Hall Replacement&Surface Parking Lot"M" 3 209459.10/209459.11