Agenda - Council - 09/14/2021 - Laserfiche WebLink

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Trott Brook Crossing EAW August 2021 increase in the post -construction rate, volume, and duration of runoff over existing conditions for the one- and two-year storms. LRRWMO Stormwater Standards require stormwater basins designed to store the volume of the 100-year storm; stormwater treatment to NURP standards prior to discharge to a lake, stream, wetland, or offsite; and infiltration of a runoff volume equal to 1 inch from all impervious surfaces on -site. The proposed project design will meet these requirements, and will provide volume reduction consistent with City requirements. Stormwater ponds designed to NURP criteria are considered effective in removing sediment, pollutants, and nutrients, as discussed in Protecting Water Quality in Urban Areas: Best Management Practices for Dealing with Storm Water Runoff from Urban, Suburban and Developing Areas of Minnesota (MPCA 2000). The NURP research projects conducted by the U.S. EPA concluded that 90% removal of total suspended solids was an attainable goal, and that significant removal of other pollutants, such as phosphorus, was also achievable. Although nutrient removal efficiency varies with site conditions, well -designed wet ponds and constructed wetland treatment systems are effective in removing sediment and associated pollutants, such as trace metals, nutrients and hydrocarbons. Stormwater basins also remove or treat oxygen -demanding substances, bacteria and dissolved nutrients. Stormwater and Erosion Control BMPs Because project construction will disturb more than one acre of land, the project proponent will be required to apply to the MPCA for coverage under the National Pollutant Discharge Elimination System/State Disposal System (NPDES/SDS) General Permit prior to initiating earthwork on the site. BMPs will be employed during construction to reduce erosion and sediment loading of stormwater runoff. Inspection of BMPs will be required after each rainfall exceeding 0.5 inches in 24 hours, and on a routine basis every 7 days. The NPDES permit will also require perimeter sediment control maintenance and sediment removal. BMPs to be implemented during construction include: 1. Construction of temporary sediment basins in the locations proposed for stormwater ponding, and development of these basins for permanent use following construction. 2. Installation of silt fence and other perimeter erosion controls prior to initiation of earthwork and maintenance of these controls until viable turf or ground cover is established on exposed areas. 3. Periodic street cleaning and installation of a rock construction entrance to reduce tracking of dirt onto public streets. 4. Stabilization of exposed soils within the time limits specified in the General NPDES permit. 5. Energy dissipation, such as riprap, installed at storm sewer outfalls. 6. Use of cover crops, native seed mixes, sod, and landscaping to stabilize exposed surface soils after final grading. Erosion control plans will be reviewed and accepted by the City of Ramsey and the LRRWMO prior to project construction initiation. Potential adverse effects from construction -related sediment and erosion on water quality will be minimized by implementation of the above BMPs during and after construction. 17