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• Orono Substation Replacement Project Noise Assessment EXECUTIVE SUMMARY The objectives of this noise assessment are to establish the existing ambient sound levels in the vicinity of the existing Orono Substation in Orono,Minnesota,and to assess the potential impacts on the surrounding residential area of the proposed Orono Substation replacement which would have larger transformers. The address of the Orono Substation is 3960 Sixth Avenue North,Orono,Hennepin County,Minnesota. Potential impacts are assessed with respect to the lowest State of Minnesota(State)Nighttime Noise Standards(NNS)and the existing ambient sound level. This sound assessment analyzes the most sensitive receptor sites which are the closest residential structures to the site that would be exposed to sound by the one or two transformers in the proposed replacement Orono Substation. Ambient sound levels were measured between December 5 and December 6,2011,just west of the existing substation to establish the existing ambient level over a 24-hour period. Spot readings were taken on December 5,2011,close to the existing substation to establish a source sound level for the existing transformer and to provide a basis for confirming the noise prediction model for the existing and replacement substations. Sound levels near the proposed Orono Substation replacement have been predicted based upon the following four alternative transformer configurations with assumed sound levels: 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 The transformer configurations were provided by Xcel Energy for the proposed replacement Orono Substation,which initially involves replacement of the existing 69 kV transformer with one 115 kV transformer,and possible future buildout,which involves installation of a second 115 kV transformer. Sound levels of these transformer configurations at the nearest residences are predicted to be at or below the State NNS for residential land uses(L50 50 dBA)but above the existing ambient sound level. To provide a greater margin of confidence that the levels are below the State NNS, sound walls close to TR#1 where a 78 dBA transformer would be installed were analyzed. The sound walls would be located south and west of the planned transformer where the closest residences are located. With the addition of sound walls,predictions show that sound levels will be 6 dBA or more below the State NNS L50 50 dBA standard,and within 5 dBA of the predicted existing ambient levels except for the home immediately south of the transformer(Home 5). At Home 5 the predicted sound level with an assumed 78 dBA transformer may be 8 dBA above the predicted ambient level. Increasing the south sound wall height to 16 feet would reduce the sound level at Home 5 bringing it closer to the existing ambient sound level. When a 68 dBA transformer is added at the TR#2 position,a 16 foot wall would be needed to maintain the predicted sound level at Home 5 instead of the 14 foot wall for the 78 dBA transformer alone. David Braslau Associates,Inc.