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Orono Substation Replacement Project Noise Assessment II From Figure 4.2 it can be seen that the predicted level at exceeds 40 dBA only when TR#1 is assumed to be a 78 dBA or 75 dBA transformer. The highest level at Home 5,which is immediately south of the Orono Substation site across 6th Avenue North,is just below 50 dBA. Therefore,based upon the assumed transformer sound levels,all of the alternatives are expected to comply with the L50 50 dBA NNS. To provide a margin of confidence in the predictions and to bring the predicted levels closer to the existing ambient level in the area,a concrete sound wall has been evaluated for TR#1. Since the highest sound levels are expected to be south and west of the proposed substation replacement,an L-shaped wall south and west of TR#1 was analyzed. Both the south and west sections for the sound wall are assumed to be 14 feet high and placed 8 feet from the main transformer surface as shown on Figure 4.3. The south wall would be 36 feet long while the west wall would be 24 feet long. These lengths also ensure that the homes to the south and west will receive benefit from the sound wall. If needed,the sound wall could be provided with sound absorption on the side facing the transformer to ensure that the sound level is not increased due to the proximity of the wall. Benefits in sound reduction expected from the wall are presented in Table 4.2 for a 78 dBA transformer in the TR#1 position. The predicted sound reduction benefits do not include some limited additional mitigation from installing sound absorption material on the side facing the transformer. Table 4.2 Predicted Sound Reduction Benefits of Sound Walls(without Sound Absorption Material) With No Wall Wall Benefit Home (dBA) (dBA) (dBA) 1 41.9 36.7 5.2 2 40.4 35.4 5.1 3 46.2 41.1 5.1 4 44.8 40.7 4.0 5 49.4 44.3 5.1 6 40.3 35.1 5.1 7 42.1 36.9 5.2 From Table 4.2 it can be seen that,all but Home 4 should expect at least a 5 dBA reduction in sound level,while Home 4 should expect a 4 dBA reduction in sound level. Placing sound absorption material on the side of the wall facing the transformer can provide some limited additional sound reduction benefit. Except for Home 5 located south of the site,predicted sound levels will be close to or within about 5 dBA of the lowest observed existing level on a winter night(see Figure 4.2). A 16 foot high wall south of TR#1 could lower the sound level at Home 5. With the addition of a 68 dBA transformer at the TR#2 position,a 16 foot high wall would be needed to maintain the sound level at Home 5. Predicted levels and benefits with both the 78 dBA and 68 dBA transformers with a 16 foot high south wall and 14 foot high west wall are presented in Table 4.3. David Braslau Associates,Inc. Page 10