09/11/2001 P&Z Packet - Laserfiche WebLink

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11'03/2000 08:15 612- 479 -4270 • PAGE 03 The noise limits are in decibels, abbreviated dB, on the A scale, further abbreviated dBA. The L10 is the level exceeded for 10% of the time; the L,, is the level exceeded for 50% of the time and is considered the "average" sound level. The M[olin facility is an NAC 3. The receiving areas to the north (residential) are NAC 1. MEASUREMENT RESULTS The first round of measurements was made on October 24, 2000 during normal outdoor production operations. Two sets of readings were made; one from 0430 to 0530 and another from 0530 to 0630. The earlier measurement was expected to have lesser background contamination by traffic noise from nearby I -35W. The results are shown below: Parameter October 24; 0430 -0530 October 24; 0530 -0630 State Limit (Nighttime) L;( 50.2 dBA 51.1 dBA 55 dBA L;0 46.4 dBA 48.2 dBA 50 dBA Both sets of readings show compliance with the Minnesota Noise Rules for the nighttime period. The second set (0530 -0630) shows a slight increase as morning traffic builds. A second set of measurements was made on October 25, 2000 without outdoor production operations. Only one set of readings was made from 0430 to 0530, The results are shown below: Parameter October 25; 0430 -0530 State Limit (Nighttime) La) 47.4 dBA 55 dBA L50 44.5 dBA 50 dBA As expected. the results show compliance with the Minnesota Noise Rules for the nighttime period. A slight decrease was noted due to the absence production operations. Since the measurements indicate compliance with the Minnesota Noise Rules for the nighttime period. no recommendations are necessary at this time. SUPPLEMENTAL INFORMATION ?'vfecrsrrremenrt Instrumentation The sound level measurements were made using a Larson -Davis brand Model 812 (S/N 0265) sound level meter. The meter was used with a 1/2" diameter random incidence Larson -Davis Model 2560 (S/N 2156) microphone connected to a Larson -Davis Model PRM828 (S/N 1724) microphone preamplifier. The sound level meter was used in the data - logging mode to measure and store the sound level readings (in dBA. "fast" response) during the measurement period. The measurements were conducted with the foam windscreen covering the microphone. At the conclusion of the measurement period. the meter calculates and displays various statistical measures (including the LID & L;,,) regarding the sound level distribution.