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<br />To: Roseville Planning Commission <br /> <br />From: Karl P. Keel, Assistant Public Works Directo~ <br /> <br />RE: STORMWATER QUALITY, HERITAGE DEVELOPMENT PROPOSAL <br />Planning File 2244 <br /> <br />Date: May 12, 1992 <br /> <br />In recent years, increased attention has been given to water <br />quality issues and the affects of urban runoff on our local <br />environment. A large number of public agencies have responded to <br />this concern and have spent a great deal of money and effort on <br />research. <br /> <br />In the early 1980's, the U. S. Environmental Protection Agency <br />completed the Nationwide Urban Runoff Program (NURP). This <br />project collected a large amount of data and developed standards <br />that could be used to control urban stormwater runoff. <br /> <br />The Minnesota Pollution Control Agency (MPCA) used the <br />information provided ~ NURP to produce a publication titled <br />"Protecting Wat~r Quality in Urban Areas--Best Management <br />Practices for Minnesota." This document applied the NURP data to <br />Minnesota conditions and offers design criteria for pre-treatment <br />detention ponds. <br /> <br />Additional study has been done ~ Dr. William W. Walker. Like <br />the MPCA, Dr. Walker utilized data collected ~ NURP. His <br />studies present detailed design criteria to maximize stormwater <br />treatment including pond sizing, pond topography, and inlet and <br />outlet design. <br /> <br />All three of these studies (NURP, MPCA, and the Walker) are very <br />similar in that they require a minimum amount of dead storage to <br />allow suspended solids to settle. Dead storage is the volume of <br />water in a pond that is below the pond outlet. Suspended solids <br />are particles of material carried ~ stormwater that are not <br />water soluble. Many pollutants tend to cling to suspended <br />solids--especially the very small particles. Thus, ~ removing <br />suspended solids from stormwater, one is able to remove many <br />pollutants as well. <br /> <br />Dr. wal~'s method requires slightly more dead storage than the <br />MPCA method. The extra storage area provides room to accommodate <br />an estimated 25 years of sediment without affecting pond <br />performance. The standards presented in the above models (NURP, <br />MPCA, and Walker) are intended to provide the maximum amount of <br />suspended solid removal that can be achieved in a detention pond, <br />i.e. each attempts to provide for the best possible suspended <br />solid removal efficiency. <br />