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ElkRi Elk River cmvelMi�nnmrim <br /> ver <br /> Stormwater Analysis <br /> Trunk Highway 169 generally forms the drainage divide for the Elk River Gravel Mining Area. Proposed <br /> development on the west side of TH169 travels overland to the west to the existing system of county <br /> ditches. Flow in the ditches travels south through Woodland Trails Park to Upper Orono Lake. Upper <br /> Orono Lake is listed as impaired by the Minnesota Pollution Control Agency (MPCA)for <br /> nutrient/eutrophi cation biological indicators. Upper Orono Lake connects to Lower Orono Lake, which <br /> is also impaired for nutrients. The lakes discharge into Elk River(impaired for E coli)which finally <br /> discharges into the Mississippi River(impaired for PCB in fish tissues). The east side of the Gravel Mining <br /> Area travels east to a system of county ditches that outlet into Trott Brook. Trott Brook is not currently <br /> listed by the MPCA as impaired. <br /> Based on the Sherburne County Natural Resource Conservation Service (NRCS) Soil Survey the soils in <br /> the study area are generally characterized as hydrologic soil group (HSG)A. The existing land use is <br /> primarily gravel/sand mining, with woods and agricultural land use along the edges of the study area. <br /> When development occurs, the MPCA National Pollution Discharge Elimination System (NPDES) <br /> Construction General Permit requirements must be met. The City of Elk River and Sherburne County <br /> currently do not have any additional stormwater requirements. <br /> The ponding footprints shown on Figure 26 provide best locations for considering regional stormwater <br /> pond opportunities and would generally meet the NPDES Permit requirements for development within <br /> Phases 1 and 2. <br /> Due to the high infiltration potential of the existing soils, it is recommended that infiltration be utilized <br /> for meeting the stormwater requirements. Existing depressions where gravel mining is occurring are a <br /> good potential location for regional stormwater ponding, as shown on Figure 26.These sites were <br /> selected based on the proposed grading plan (existing low-lying areas) and the direction of existing <br /> drainage. <br /> 49 <br />