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104. The project would result in short-term noise during construction. In order to <br /> comply with MPCA noise standards construction work would be limited to daytime <br /> hours, between 7 a.m. and 10 p.m.10° <br /> 105. Heavy equipment would be equipped with sound attenuation devices such as <br /> mufflers to minimize noise levels. 01 <br /> 106. Xcel Energy anticipates that, on occasion, construction outside of daytime hours <br /> or on weekends may be scheduled to work around customer schedules or line <br /> outages.102 <br /> 107. The city of Orono noise regulations limit construction activities to between 7 a.m. <br /> and 8 p.m. on weekdays and 8 a.m. to 8 p.m. on weekends.103 <br /> 108. Noise associated with substation operation includes the operation of transformers <br /> and switchgear. Transformers produce a constant low-frequency humming noise <br /> while switchgear produces an impulsive or short duration noise. <br /> 109. The distance between the Xcel Orono Substation property boundary to nearby <br /> homes are approximately 180 feet to the south, across County Road 6, and <br /> approximately 270 feet to the west. The Noise Assessment monitored existing <br /> noise at nine sites at the Orono Substation and surrounding residences. <br /> 110. Xcel Energy anticipates replacing the existing 69 kV/13.8 kV transformer with a <br /> 115 kV/13.8 kV transformer as part of the project. Although not part of the project, <br /> Xcel Energy has also modeled the possible addition of another 115 kV/13.8 kV <br /> transformer that may be added at some point in the future.104 <br /> 111. Using the measured existing noise levels, the Noise Assessment estimated noise <br /> from the new transformer(s) at the nine monitoring sites with and without sound <br /> walls around the transformers. Sound estimates after the addition of the project <br /> transformer at nearby homes are estimated to be in the range of 40.3 to 49.4 dBA <br /> without noise walls, and 35.1 to 44.3 dBA with noise walls.105 With two 115 kV <br /> transformers at the substation, sound estimates at nearby homes range from 40.7 to <br /> 49.8 dBA without noise walls and 35.1 to 44.3 dBA with noise walls.106 <br /> 112. Noise Standards developed by the Minnesota Pollution Control Agency (MPCA) <br /> establish a nighttime noise standard L50 of 50 dBA in residential areas.107 <br /> loo Ex. 12 at pp.27-28(EA) <br /> 1°' Ibid. <br /> 102 Ibid. <br /> 103 Ex.22(Hearing Comments,city of Orono) <br /> 104 Ex.24 at p.7(Noise Assessment) <br /> los Ibid. at p. 10 <br /> 1°6 Ibid.at p. 12 <br /> 107 Ex. 12 at p.28(EA) <br /> 22 <br />