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Orono Substation Replacement Project Noise Assessment 4.0 PREDICTED SOUND LEVELS Sound levels were predicted at each of the residences shown on Figure 2.1 from four different alternative transformer replacement options(see Table 4.1 below). The transformer alternatives were provided by Xcel Energy for the proposed replacement Orono Substation project for replacing the existing 69 kV transformer with a 115 kV transformer,and for the possible future buildout of the substation site which would involve adding a second 115 kV transformer. It should be noted that similarly sized transformers can operate at varying sound levels. This is due to variations in design,materials,construction,and operational conditions of the transformers and where they operate. Xcel Energy does not have specific sound information for the initial transformer. Therefore,the sound level for this transformer has been estimated. According to Xcel Energy,Alternatives 1 and 2 involve use of an existing Xcel Energy 115 kV transformer(TR#1)with an assumed low to high sound level ranging from 75 to 78 dBA. No sound data are available from the manufacturer of this transformer and the assumed 75 dBA to 78 dBA sound level range is based upon past use of the transformer,best engineering estimates and the age of the transformer. Alternatives 3 and 4 would occur if,in the future,a second transformer would be needed at the Orono Substation site. The sound levels for TR#2 are current low noise rated levels currently available from transformer manufacturers. If a second 115 kV transformer is needed in the future at the Orono Substation site,Xcel Energy would install a low noise model. The proposed grading plan for the replacement Orono Substation project is shown in Figure 4.1. Positions for two transformers are shown on the figure. Initially,one transformer is planned for the TR#1 (east)position. Two alternatives have been analyzed for this position,a 78 dBA and a 75 dBA transformer. In the future,another transformer could be added in the TR#2(west) position. The alternatives with two transformers include a 78 dBA and 68 dBA transformer,and two 68 dBA transformers. The four alternatives analyzed are summarized in Table 4.1. Table 4.1 Proposed Transformer Alternatives Alternative TR#1 (east location) TR#2(west location) 1 78 dBA None 2 75 dBA None 3 78 dBA 68 dBA 4 68 dBA 68 dBA Predicted sound levels for the existing Orono Substation and the four alternatives for the proposed substation replacement are presented in Figure 4.2. David Braslau Associates,Inc. Page 7