2017.04.17 CC Packet - Laserfiche WebLink

Home

Adelaide Landing Residential Development EAW, Hugo January 31, 2017 50- or 100-year storm events will result in measurable increases in runoff volume and associated pollutant transport. The preservation and creation of open space in the form of buffers, parks, woodlands, wetlands and ponds will help to mitigate potential adverse effects from the increase in impervious surface. Runoff water quality will be typical of residential developments, and will likely be slightly degraded due to pollutants deposited on streets, roofs, private driveways and other impervious surfaces. Similar to current conditions, sediment, nutrient, and other pollutant removal will occur when much of the stormwater filters through upland buffers, vegetated drainage swales, stormwater ponds, and other best management practices. Preserved and newly seeded vegetation will provide filter strips to help remove sediment and nutrients before runoff discharges to area wetlands and surface waters, mitigating potential effects on water quality. Potential adverse effects of runoff volume and quality will be further mitigated by the construction of stormwater basins, which will be designed to reduce peak runoff rates and meet the requirements of the City of Hugo and the RCWD. The design of ponding areas and the quality of stormwater discharging from the development will meet the requirements of the MPCA General Stormwater Permit for Construction Activity (Minnesota Stormwater Manual), and applicable local regulations. In a storm event, stormwater will be retained in the ponds and discharged at or below existing peak runoff rates. Shallow groundwater that provides hydrology to on -site wetland complex will remain in the post development setting. The site also contains draintile to provide drainage for the agricultural existing uses. The stormwater management system will route treated surface water to the wetlands to provide additional hydrology to support the long-term health of the wetlands. The project proposer has hired a geotechnical engineer to perform regular piezometer measurements across the site. Data gathered indicates shallow groundwater that fluctuates from approximately 925 to 930, and is typically within a couple feet of the surface. This shallow groundwater condition prevents achieving 3 feet vertical separation between infiltration practice and the groundwater level. Therefore, infiltration is not a viable volume control best management practice (BMP) on this site. Other BMPs will be employed such as water reuse, biofiltration, filtration and others. The project proposer is exploring the use of deep water pond facilities for irrigation purposes (described further below). The anticipated water reuse volume will likely exceed the thresholds for a water appropriations permit. DNR permits will be obtained prior to installation of a water reuse system. BMPs will be employed during construction to reduce erosion and sediment loading of stormwater runoff. Inspection and maintenance of BMPs during construction will be consistent with NPDES/SDS General Permit requirements, including site inspection after rainfall events, perimeter sediment control maintenance, and sediment removal. The goal of the project will be to maintain peak discharge rates at or below the existing condition. Post -construction drainage will follow similar pathways, with minor differences in drainage routes and increases in the volume of road ditches and swale flows. Post -development stormwater runoff will either travel overland, into stormwater ponds, or through storm sewers prior to discharging to receiving waters. Other BMPs, such as natural swales and infiltration technologies, will be considered as project designs advance. 18