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Colorado Division of Water Resources. This permit is required to ensure that any discharge of dirty groundwater does not return directly to surface waters of the United States without first passing through some type of treatment system such as straw bales and silt fences. Based on a letter received from the Department of the Army Corp of Engineers dated November 26, 1999 and enclosed within Appendix 4, the proposed regional detention pond site,will not require a Department of the Army 404 permit in order to proceed with construction. E. Feasibility Construction Feasibility: As noted earlier in this study, on July 29, 1999, Kevin Gingery and Russell Dahlgren visited the Tri-Town Basin to observe the project components and locations of adjacent residential and commercial buildings with reference to the feasibility of constructing the proposed improvements. The proposed regional detention pond site is currently open and free of obstructions that could prevent construction of the proposed improvements. From the preliminary design drawing within Appendix 4, it appears that excess earthen soil is available from the proposed regional detention pond site to construct the regional detention pond embankment. Other construction materials such as riprap and concrete will need to be imported to the project site in order to complete the proposed improvements. Benefit/Cost Analysis: The benefit/cost analysis was conducted in order to provide the information needed to evaluate the economic feasibiliry and relative value of the propased improvements. The benefits of the proposed drainage improvements equal the value of the flooding damages that are prevented or avoided by construction of the improvements. This analysis was conducted using the general methodology and guidelines presented in the Methodology for Evalclation of Feasibility; Mc�lti- Jacrisdictional Urban Drainage and Flood Control Projects, Urban Drainage and Flood Control District, Febrafary, 1977 manual. The procedure used for the benefit/cost analysis is summarized below: l. Flood depths for the affected areas in the District were determined for the 100 year, 50 year, 10 year, and zero damage flood events. The zero damage event was assumed to be the 2 year flood. The flood depths were based on information in the FEMA Flood Insurance Study and FEMA Flood Insurance Rate Map for the communities of Frederick, Evanston, and 22