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4. The MPCA requested three items relative to noise: · Report results of noise analysis for nighttime (10:00 PM to 7:00 AM) conditions; · Compare predicted noise levels to the Lso standards; and · Explain how noise monitoring results might change from the winter monitoring period to the summer conditions. Response: As noted in the EA W, "the majority of the proposed land uses for the Twin Lakes Development will operate during normal office hours (8:00 AM to 5:00 PM) and will generate little or no traffic during nighttime (10:00 PM to 7:00 AM) hours," Nighttime noise levels can be estimated based on the relationship between traffic volumes during the PM peak hour and the peak nighttime traffic hour (typically 6:00 to 7:00 AM). 24-hour Automatic Traffic Recorder (A TR) counts from 1994 on Fairview Avenue and County Road C indicate that traffic volumes during the peak nighttime traffic hour are approximately 30 percent of the traffic volume during the PM peak hour. This difference in volume would result in nighttime noise levels approximately 5 dBA less than the peak daytime levels reported in the EA W. The nighttime noise standard is LIO 55 dBA, If nighttime noise levels are 5 dBA less than the peak daytime noise levels reported in the EA W, nighttime noise levels would exceed the state standard at two of the three receiver sites analyzed in the EA W. The EA W reported monitored existing and predicted LIO noise levels. The Lso state standards are Lso 60 dBA for the daytime period and Lso 50 dBA for the nighttime period. Monitored lso daytime noise levels were: Receiver Site 1 -- 58 dBA · Receiver Site 2 -- 55 dBA Receiver Site 3 -- 52 dBA The noise prediction methodology used for this project does not yield a predicted Lso noise level. Based on the monitored levels, it is expected that the Lso noise levels will be 4 to 6 dBA less than the predicted LIO noise levels. Traffic noise levels monitored in the vicinity of the project during the winter could be slightly different than those experienced during the summer months for the following reasons: The noise monitoring was conducted during the months of February and March when there was snow on the ground and the roads were dry. Hard packed snow, such as existed during the monitoring, would tend to reflect more noise than vegetated ground surfaces that would be present during summer months. This would indicate that weather conditions could tend to result in slightly higher noise levels during the winter monitoring than would be experienced during the summer. According to the A TR traffic data, traffic volumes during the months of February and March could be as much as thirty percent less than during June. Traffic volumes thirty percent higher than those occurring during the monitoring would result in noise levels approximately 1 dBA higher. 4