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

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Trott Brook Crossing EAW August 2021 effects from stormwater discharges. Describe stormwater pollution prevention plans including temporary and permanent runoff controls and potential BMP site locations to manage or treat stormwater runoff. Identify specific erosion control, sedimentation control or stabilization measures to address soil limitations during and after project construction. Pre -Construction Site Runoff Soils in the project area are sandy with high infiltration rates, and most precipitation likely infiltrates into the ground, resulting in little surface runoff. Surface runoff from the project area under existing conditions likely contains some sediment, pesticides, fertilizers, and other nutrients. Existing runoff on the northwest portion of the site drains to the northwest into a wetland complex that extends offsite. Existing runoff on the south and central portion of the site drains to the south into wetland adjacent to Trott Brook. Post -Construction Site Runoff Compliance with LRRWMO, City of Ramsey, and NPDES requirements will minimize and mitigate potential adverse effects on receiving waters. Project development will change the land use from agricultural and woodland to residential with streets and parks. This land use change is expected to have mixed effects on runoff water volume and quality. Post -development runoff water quality will be typical of suburban developments, and will likely be slightly degraded by pollutants carried in runoff from streets, roofs, and driveways. The proposed project will add about 36.32 acres of impervious surface, consisting of streets, homes, and driveways. The increased impervious surface area is expected to increase runoff volume and urban pollutants locally during significant storm events. However, stormwater rate and volume controls that comply with City of Ramsey and LRRWMO requirements will limit increases in runoff volume and associated pollutant transport. Much of the increased runoff and pollution is expected to be associated with large, infrequent storm events. The creation of stormwater ponds and infiltration basins is expected to mitigate potential adverse effects from the increased impervious surface area. The project will include approximately 17.03 acres of stormwater and infiltration basins in compliance with City of Ramsey and LRRWMO requirements. Potential adverse effects of runoff volume and quality will be mitigated by the construction of stormwater basins designed to manage peak runoff rates, runoff volume, and water quality. Storm water volume control and BMP's will have at least the total net new impervious routed to them to provide full credit. Storm events will discharge runoff at flow rates that are less than existing rates into Trott Brook and the wetland on the northwest portion of the site. Proposed stormwater management and erosion and sediment control practices are expected to minimize cumulative effects of post -development runoff on downstream waters. Project construction will include other water quality BMPs such as temporary sediment basins to comply with the MPCA General Stormwater Permit for Construction Activity. Section 117-392 of the of Ramsey City Code requires permanent stormwater pollution controls, including: (1) infiltrating or retaining the first inch of precipitation over the impervious surface of the site; (2) retaining the post -construction runoff volume on -site for the 95th percentile storm; and (3) no 16