10/30/2013 Env Bd Packet - Laserfiche WebLink

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• • (a) Maximize water quality and flood control on individual project sites through Better Site Design practices and stormwater management. (b) Minimize land use impacts and improve operational and maintenance efficiency by using stormwater BMPs, when needed, regionally unless local resources would be adversely affected. (c) Treat stormwater runoff before discharge to surface water - bodies and wetlands, while considering the historic use of District water features. (d) Ensure that future peak rates of runoff are less than or equal to existing rates. (e) Reduce the existing conditions peak rate of discharge along Lower Rice Creek and the rate of discharge and volume of runoff reaching Long Lake, to preserve the remaining floodplain storage volume within Long Lake and mitigate the historic loss of floodplain storage. (f) Preserve remaining floodplain storage volume within the Rice Creek Watershed to minimize flood potential throughout the District. The development is required to meet both water quality and volume regulations consistent with RCWD and City requirements. A watershed district permit is required for development on this site. There is no confirmation at this time from our City Engineers at WSB or the watershed that the storm features on the site are correctly designed, or control water quality and quantity (no loss of flood plain) requirements are met. One part of the rule that the design does not appear to meet is the infiltration area "separation from the water table ". The elevation difference must be 3 feet. Furthermore; the sand, and highly permeable National Urban Runoff Pond (NURP) portion of the design is also pervious horizontally and can also infiltrate vertically during water table /ground water fluctuations. Contaminants from storm water falling on streets, driveways, rooftops and other impervious areas, flowing into this NURP can enter the Drinking Water Supply Management Area (DWSMA). This development site is in the Lino Lakes Central DWSMA area (See Central DWSMA Attachment). If determined that adequate separation is not available, a clay liner may be required to prevent contaminant seepage. The plan also includes the rerouting of an existing private drainage ditch. The ditch currently provides drainage from properties north of the site to County Ditch 25. Drainage capacity of the ditch will be retained. The ditch will be relocated along the north and east corners of the site and located within a conservation easement. The location will provide an additional buffer from adjacent residential uses and provide continuation of the corridor from the Preserve development. The new design will also allow for increased filtration and infiltration opportunities.