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Orono Substation Replacement Project Noise Assessment 5.0 SUMMARY AND CONCLUSIONS Existing sound levels in the vicinity of the existing Orono Substation were monitored to provide a basis for determining a source level for the existing transformer,to provide existing ambient sound levels in the neighborhood,and serve as a basis for confirming the accuracy of noise model predictions at selected locations for the proposed Orono Substation Replacement Project. Sound levels near the proposed Orono Substation Replacement site have been predicted based upon the following four alternative transformer configurations: 1. TR#1 78 dBA 2. TR#1 75 dBA 3. TR#1 78 dBA+TR#2 68 dBA 4. TR#1 68 dBA+TR#2 68 dBA Sound levels at the nearest residences are predicted to be below the State of Minnesota Nighttime Noise Standard for residential land uses(L50 is 50 dBA),but above the existing ambient sound level. To provide a greater margin of confidence that the sound levels remain below the State Nighttime Noise Standard, sound walls close to TR#1 where a 78 dBA transformer would be installed was analyzed. The sound walls would be located south and west of the transformer where the closest residences are located. Sound level predictions with the walls in place show that sound levels will be 6 dBA or more below the Nighttime Noise Standard(L50 is 50 dBA),and within 5 dBA of the predicted existing ambient levels,except for the home immediately south of the transformer where the level may be 8 dBA above the predicted ambient level(Home 5). Increase in the wall height to 16 feet would reduce the sound level at Home 5 bringing it closer to the existing ambient. When a 68 dBA transformer is added at the TR#2 position,a 16 foot wall would be needed to maintain the level at Home 5 instead of the 14 foot wall for the 78 dBA transformer alone. y:\jobs\2011 jobs\211065\report\orono-substation-noise-assessment-011212.doc David Braslau Associates,Inc. Page 13