Environmental Assis for Orono Substation Expansion

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Potential groundwater impacts from overhead transmission lines are typically associated with the construction phase of the project and may result from structure placement or sedimentation release into shallow aquifers from equipment vibration. Transmission structures will require excavation of approximately 15 to 25 feet, depending on soil conditions. As such, the placement of the transmission structures would not have an impact on the groundwater supply or domestic wells in the area of the project. The Project would not install any wells. Surface Water The proposed project area is located in the Minnehaha Creek Watershed District, which is part of the Mississippi Watershed of the Upper Mississippi River Basin. The Upper Mississippi River Basin is approximately 20,100 square miles in size and stretches from the Headwaters of the Mississippi to the metro area. Drainage typically flows south towards the Mississippi River, the largest river in the watershed (MPCA, 2010). Lakes located in the general vicinity of the project include Katrina Lake, located approximately 540 feet north of the Baker Park Reserve Route Alternative and Lake Classen, located approximately 4,000 miles east of the Project. Katrina Lake is identified as an impaired lake with a TMDL for nutrients (MPCA, 2009). Painter Creek is crossed by the Proposed Route. Land that forms the transition from aquatic to terrestrial ecosystems along streams, lakes, and open water wetlands are known as riparian areas. The MnDNR shoreland standards define riparian areas as the land that is within 300 feet of a public waters watercourse and within 1,000 feet of the ordinary high water level of a public water, lake, pond or flowage. Orono's shoreland overlay district is discussed in Section 5.8. During construction, there is the potential for sediment to reach surface waters due to ground disturbances vegetation clearing, excavation, grading, and construction traffic. During the operation of the Project, there is potential for runoff from the substation site to impact surface waters. Minimum grading will be done around the pole sites. The graded area of the existing Orono Substation is approximately 0.1 acres, the graded area of the replacement substation will include approximately 1.4 acres, with an additional graded road area of approximately 0.2 acres. In addition to the graded area, a berm to the west of the substation may be constructed to provide a visual buffer between the substation and the homes to the west. Mitigation Measures Because no impacts to groundwater are anticipated from the Project, no Mitigation measures are proposed. HVTL permits issued by the Commission typically require that structures be located to span watercourses, wetlands and floodplains to the extent practicable. Upon completion of construction in a specific area route permit conditions require that contours be graded so that all surfaces drain naturally, blend with the natural terrain, and are left in a condition that will facilitate re -vegetation, provide for proper drainage, and prevent erosion. All areas disturbed during construction of the facilities must be returned to their pre -construction condition. Environmental Assessment PUC Docket E002/TL-11-223 Page 46