04/24/2013 Env Bd Packet - Laserfiche WebLink

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AECOM describes soils in the stormwater detention pond area as the above soils. They recommend a clay liner in the bottom and sidewalls of the pond in the pervious area of the soil profile in order to hold water. Since there is a RMP -3 rule to attenuate water volumes, there should be investigation into at least some infiltration into this layer of soils. In addition to the impervious infiltration/filtration requirement, the rule also requires the first .5 inch of rainfall over impervious areas be reduced only by reestablishment of effectively drained wetlands and floodplain meadows, upland restoration/conservation, restoration of degraded wetlands, impervious disconnection, and soil amendments /tilling. This could reestablish hydrology to wetlands on the site. The longer term impacts if any should be looked at of infiltrating on top of a confining layer. Care must be taken to maintain existing soil structure and prevent compaction in the pond excavation areas if infiltration will be used as part of surface water management. No soils should be imported to the site without authorization from city engineering. Soil spading should be used to incorporate topsoil into planting areas. Land Cover The MLCCS indicates Agricultural Corn Field Rare and Unique Resources There are no Threatened and Endangered Concerns within 0.5 miles of the development site, including National Heritage concerns. There are no site specific indicators that would place rare plants on the site. Tree Preservation There is an area that a few non - significant trees will be removed. The trees are various height pine plantation trees all of less than 12 feet. There are no tree preservation requirements. Surface Water Management The AUAR Mitigation Plan requires conformance with the Rice Creek Watershed District Rules and was initiated to address volume control and poor drainage. The Watershed District RMP -3 Rule was adopted in 2009. The Rule specifies that water volume rates leaving a site cannot exceed the preexisting condition. The rule also established new parameters for volume controls and incentives for avoiding wetlands. The water quality standard for the RMP -3 Rule is to treat the volume of runoff resulting from a 2 year, 24 hour duration precipitation event. The peak rate must be controlled at the pre- development conditions. 2 to r • f