6201 ASSOCIATED BLVD BASE FILE 2018-03-29

x c en 2.3 DESIGN ASSUMPTIONS The water quality wetpond treating all new pollution generating impervious surfacing will provide up to 85% of the required storage area in a deep (3-6') treatment cell. The remaining required dead storage will be contained within a 15% water quality treatment cell with an average cell depth of 2 feet. The rooftop area within Phase 2 not tributary to CEMEX's future stormwater management system will bypass the wetpond and connect into the bypass conveyance system in Associated Blvd. The 2:1 sloped areas outside of the paved level development will be compost amended and re- planted with native landscaping to re-establish pre-mining conditions to the greatest extent possible. These areas and are not included in any stormwater calculations. All areas within the new CEMEX site will match existing conditions according to the zero discharge stormwater management plan. 3.0 BASIN ANALYSIS 3.1 Soil and Curve Number Information Soil information at the project site was obtained from the Web Soil Survey website (http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx) published by the United States Department of Agriculture Natural Resources Conservation Service (NRCS). The soil series underlying the tributary area is comprised of Alderwood soil series. The soil is classified as a Hydrologic Group C. Appendix B of this report contains copies of the soils map. It is to be noted that this is a reclaimed mineral extraction site. Reclamation involved backfilling with predominately till derived soil. 3.2 Predevelopment Condition The project development is within the north portion of the CEMEX reclaimed mining area. The site is bound by Associated Boulevard to the west Merrill Creek Parkway to the north and Glenwood Avenue to the east. The site is elevated from Merrill Creek Parkway and Glenwood Avenue and generally slopes northward at 5 percent. The southern portion of the site is relatively flat and near the proposed finished grade of 425. The Glenwood regional facility discharges on the north side of Merrill Creek Parkway forming the headwaters of Glenwood Creek. There are also two beehive grates on the south side of Merrill Creek Parkway with a limited tributary area that also discharge on the north side of Merrill Creek Parkway. DAVID EVANS AND ASSOCIATES,INC. UNDERWOOD GARTLAND EVERETT FEBRUARY 3,2015 STORMWATER SITE PLAN PAGE 3