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Each area is based on actual proposed layout percentages for land cover. This breakdown <br /> is as follows(including whole site area): <br /> Land Use <br /> Pavement Area 24.1% <br /> Roof Area 19.6% <br /> Lawns/Landscaping 5.8% <br /> Buffer Enhancement 50.5% <br /> TOTAL 100.0% <br /> Developed Drainage Area Map is attached in Appendix D. <br /> Streambank Erosion Control BMPS: <br /> A detention vault with storage requirements per Everett Stormwater Management Manual <br /> (SMM)has been designed. <br /> Hydraflow software using Hydrograph Method with DOE hyetograph, SCS curve <br /> numbers,and TR-55 to calculate Time of Concentrations were used to design <br /> Streambank Erosion Control BMPS. <br /> Following requirements were used to control discharge rates: <br /> 1. The peak developed discharge rate for the 2-year, 24-hour storm not exceed 50% <br /> of the peak runoff for the same existing conditions. <br /> 2. The peak developed discharge rate for the 10-year and 100-year, 24-hour storm <br /> not exceed peak runoff for the same existing conditions. <br /> Volume Correction Factor of 0.45 was used to account for the effects of back-to-back <br /> storm events per Figure 1-3.1 of Everett SMM. <br /> Results are provided in Appendix G. <br /> Water Treatment System: <br /> Infiltration was not feasible option on this project because underlying layer of peat <br /> material and low season ground water elevation. Contech CDS system pre-treatment <br /> followed by StormFilters,both GULD treatments by Washington State DOE, have been <br /> designed. <br /> Water Quality calculations for CDS and StormFilters were done by Contech Stormwater <br /> Solutions. <br /> See Appendix H. <br /> 5 <br />