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Orono Substation Replacement Project Noise Assessment 3.0 NOISE MONITORING RESULTS Monitored ambient levels from the spot readings(see Figure 1.2)with minimal influence from adjacent traffic or railroad noise are presented in Table 3.1. Measurements at the existing Orono Substation fence(i.e. spot readings at monitoring sites 1 to 4 on Figure 1.2)were used to establish a source level for the existing transformer. The other locations(shown on Figure 1.2 represent general ambient levels in the neighborhood with the existing substation. Table 3.1 Ambient Sound Levels with the Existing Orono Substation Monitoring Site dBA Location 1 58 Fence East 2 51 Fence North 3 57 Fence West 4 49 Fence South 5 41 24-hour Meter 6 46 South Side-6th Ave.N 7 44 6th Ave.N at Orchard Park Road 8 42 West Side-Hunter Farm Road 9 39 6th Ave.N at Hunter Farm Road The 24-hour statistical sound levels that provide an overall picture of sound level variation in the neighborhood near the existing Orono Substation are shown in Figure 3.1. The LO1 represents sound levels lasting longer than 6 seconds;L10 represents sound levels lasting longer than 1 minute;L50 longer than 5 minutes;and L90 longer than 9 minutes of each 10-minute interval. A 10-minute interval was used to ensure that a full 24 hours of data could be accommodated by the monitor memory. The 24-hour meter was located away from any homes or roadways and the existing substation to provide the minimum expected noise level in the area. It can be seen,however,that traffic on 6th Avenue North still dominates the sound environment except between about midnight and 4 a.m. The sound level during this quietest period is close to 34 dBA which is typical of rural areas in the winter. Summer levels could be higher due to sound from insects and other increased activity such as air conditioner operation. The high peaks in Figure 3.1 probably reflect passing trains to the northeast since these levels are similar to an observed and monitored train passage during the spot reading at Site 7. The number of peaks also correlates closely with the number of trains per day(9)on the MnDOT railroad map of the metro area(see Appendix A). David Braslau Associates,Inc. Page 5