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Page 2 Planning Commission May 13, 1992 With new computer software, it is possible to predict the percentage of total suspended solid removal for a given ponding system. The Metropolitan Council has recommended that total suspended solid removal should be between 85% and 95%. Many local experts believe that this standard will eventually become law. Currently, however, only the city regulates stormwater quality. Our current ordinance does not have any standards for the design of stormwater treatment ponds or for pollutant removal efficiencies. Although not required ~ ordinance, it seems reasonable that as part of the PUD approval that the applicant be required to provide stormwater treatment within the range suggested~ the Metropolitan Council. Preliminary analysis indicates that this may be possible ~ raising the outlet of the pond as well as making the pond slightly larger. Currently, we estimate that the total suspended solid removal efficiency of the pond as designed is approximately 75%. The applicant's engineer has based the design of this pond on a standard suggested ~ the Rice Creek Watershed District (RCWD). (Note: This property is not in the RCWD.) The RCWD standard was developed from data collected ~ the Metropolitan Council on the McCarrons Lake treatment ponds installed ~ Roseville in 1986. The RCWD standard is not as stringent as those based on NURP. With regard to setbacks, the ci~'s shore land ordinance stipulates that all structures must be set back from the water bodies a minimum of 75 feet and all parking areas a minimum of 50 feet. On the Heritage proposal, the parking is set back approximately 65 feet and the closest building is set back approximately 110 feet from Sweeney Pond. Setbacks are measured from the ordinary high waterline of a given water body. The ordinary high waterline is defined as that point where the vegetation changes from predominantly aquatic to predominantly terrestrial. The Heritage Development proposal meets all required city shore land setbacks. Based on data collected from typical urban developments, this medium density residential proposal is expected to produce approximately 1.7 times the amount of suspended solids that would be produced from a single-family development on the same site. In most cases, however, no pre-treatment pond would be required of a single-family plat. With the pond as proposed, Heritage's proposed development would actually pollute Sweeney Pond with less suspended solids than a single-family development.