Environmental Assis for Orono Substation Expansion

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All construction projects disturbing one acre or more are required to apply for a construction stormwater permit through the MPCA. The permit states that prior to submitting a permit application, the owner must develop a Stormwater Pollution Prevention Plan (SWPPP) for the construction site. Xcel Energy would also be required to adhere to the terms and conditions of the National Pollution Discharge Elimination System (NPDES) permit and SWPPP. Erosion control methods and Best Management Practices (BMPs) pursuant to MPCA requirements will be utilized to minimize runoff during construction. Common mitigation measures employed in transmission projects include: • Utilizing seed to establish temporary and permanent vegetative cover on exposed soil. The Minnesota Department of Transportation (Mn/DOT) and MnDNR has researched various seed mixes and has identified mixes for specific site characteristics and uses. • Mulch may be applied to form a temporary and protective cover on exposed soils. Mulch can help retain moisture in the soil to promote vegetative growth, reduce evaporation, insulate the soil, and reduce erosion. A common mulch material used is hay or straw. • Erecting or using sediment control fences that are intended to retard flow, filter runoff, and promote the settling of sediment out of runoff via ponding behind the sediment control. Examples include biorolls, sandbags, and silt fences. • Using Erosion control blankets and turf reinforcement mats that are typically single or multiple layer sheets made of natural (wood) and/or synthetic materials that provide structural stability to bare surfaces and slopes. Mitigation measures to minimize soil compaction include: • Scheduling construction in areas of wet soils during frozen ground conditions. • Using construction mats to minimize impacts to wet soils. 5.12 Water Resources Potential impacts to both groundwater and surface water resources from transmission projects are generally related to the construction phase. Groundwater The project area lies within the Metro Province that is generally described as containing sand aquifers in thick sandy and clayey glacial drifts that are generally over 100 feet in depth overlying Precambrian sandstone and Cretaceous bedrock. The sedimentary bedrock underlaying this province provides good aquifer properties (MnDNR, 2011). Groundwater information specific to the project area was obtained using information from the MnDNR Waters Division and the MDH Minnesota County Well Index. A review of well construction records in the vicinity of the Project shows wells are dug to a depth of between 100 and 200 feet (MDH, 2007). Environmental Assessment PUC Docket E002/TL-11-223 Page 45