Agenda - Council - 06/25/2013 - Laserfiche WebLink

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Enterprise Park to Crooked Lake 115 kV Transmission Line March 2012 Environmental Assessment Minnesota's Noise Pollution Control Rules (Minn Rules Chapter 7030) states that noise levels must meet specific standards based on Noise Area Classifications (NAC) established in the rule. The standards are summarized in Table 5.2. Table 5.2: Noise Area Classifications & Standards NAC Day (07:00-22:00) L50 L10 Night (22:00-7:00) L50 L10 1 60 65 50 55 2 65 70 65 70 3 75 80 75 80 The NAC is based on land use activity at the location of the receiver. For example, household units are defined under NAC 1, bus passenger terminals are defined under NAC 2, and transportation right-of-way is defined under NAC 3. NAC 1 also includes other noise -sensitive areas such as medical and other health services, religious services, educational services and camping areas. Minnesota's Noise Pollution Control Rules use the A -weighting scale and apply statistical sound levels (L-Level Descriptors) to account for changes in sound levels over a period time as shown in Table 5.2. The L10 is defined as the noise level exceeded 10 percent of the time, or for six minutes in an hour. The L50 is the noise level exceeded 50 percent of the time, or for thirty minutes in an hour. The L5 is the noise level exceeded five percent of the time, or for three minutes in an hour. Audible noise from electrical conductors is due to point source corona (minor breakdown of air insulating a conductor) and is a function of conductor voltage gradient. Noise emission from a transmission line occurs during heavy rain and wet conductor conditions. In foggy, damp, or rainy weather conditions, power lines can create a crackling sound due to the small amount of electricity ionizing the moist air near the wires. During dry weather, audible noise from transmission lines is barely perceptible. During heavy rain, the background noise level produced from the rainfall and wind is usually greater than the noise from the transmission line. Also, few people are outdoors and often windows are closed, which help to mitigate the level of noise to which a person is subjected. As a result, people do not normally notice audible noise from a transmission line during heavy rain. Table 5.3 summarizes the expected noise level from a 115-kV transmission line when it is exposed to heavy rain conditions (one inch per hour). These estimates are based on results from the Bonneville Power Administration Corona and Field Effects Program version 3 (U.S. Department of Energy, Bonneville Power Administration (BPA), Undated). 26