Agenda - Council - 02/09/1999 - Laserfiche WebLink

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5 The proposed design concept for the project includes construction of facilities to convey, detain and lreat this runoff and the accompanying pollutants from pavement stuff'aces, as required by NPDES permitting and Lower Rum R/vet Watershed Management Organization (WMO) requirements. The current design incorporates as "urban" roadway section (i.e. curb and gutter) to convey water from approximately 60 perccnt of the project conidor to three detention/treatment ponds designed to meet WMO and Nationwide Urban Runoff Program (NURP) standards. The remaining portions of the project corridor -- that cannot be conveyed to treatment ponds due to topographic constraints -- will be constructed to "rural" roadway sections, where water is conveyed and treated via ditches with ditch blocks. It should be noted that the sandy soils in the project a~'ea make it likely that much of the surface water being conveyed in the ditches/ditch blocks or held in ponds will infiltrate into thc soil, reducing the overall volume of water being discharged from the prqiect area, The details of the conveyance/trcatments facilities and the exact size of the proposed detention ponds are unknown at this time as design plm~s m'e still being finalized. ttowevcr, final design plans submitted for project permitting will incorporate Best Management Practices (BMPs) and design featttres as required to conform to the NPDES permit and Lower Rum River WMO requirements, 6 The need t'or a NPDES Storm Water Permit is noted in Section V.C, page 38 of the EA. 7 The assessment of wetland functions in the EA is brief and was meant to provide a general summary of functions provided by the wetlands in the project area. While storm water detention and downstream water quality protection is an important function of thc wetlands in the project m'ea, this function will not be exploited to detain or treat unt'matcd storm water from thc roadway. Storm warm' treatment facilities designed as part of the project will detain and treat storm water prior to discharge into the wetlands, as required by the NPDES Storm Water Permit for Construction Activity. In addition, thc Lower Rum River Watershed Management Organization's requires that proposed development in the area provide storm water treatment facilities for additional runoff generated by creation of additional impervious surfaces. 8 The planned wetland mitigation site is shown in Figure 3c in the EA. It includes created wetland and upland troffer at'cas as well as construction of a stormwater detention I~ond to improve thc quality of water being discharged into the wetlm~d mitigation site and the adjacent existing wctl~md (Basin A). Additional opportunities for creating wetland mitigation areas exist along the north side of Sunwood Drive, adjacent to wetland Basin A. Because the fi~al area of wetland impacts anticipated have not been determined, the wetland mitigation plans have not been finalized. Mom specific information os~ proposed wetland mitigation will be provided to federal, state and local regulatory agencies (including the MPCA for Section 401 Certification) during the permitting process, when project impacts and proposed mitigation plans are finalized.