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`r- <br />`- 125 Hz. There is a direct line of sight from this measure- <br />. ment position to the baghouse fan area at the top of the <br />~. <br />silos. Sound level decreases are attributed to installation <br />of silencers on those fans. <br />f) Pump House <br />lT A comparison of previous and present A-weighted sound levels <br />shows that a 3 - 5 dB drop has occurred which may be due in part <br />to the snow cover present at the time of the recent measurements. <br />A consistent decrease was observed in all octave bands and sound <br />levels were steady. <br />4.1.1 Summary of Effects of Significant Operations Changes <br />C <br />Installation of the silencers at the silo baghouse fans was effective <br />• in attenuating baghouse noise as was observed at site S-3. Effects on <br />noise levels at other sites could not be easily quantified due to increased <br />noise emanating from both the truck dump fan and the R-1 takeup. 125 Hz <br />beats noted during prior monitoring had orginally been caused by the inter- <br />) action of the three silo baghouse fans. Installation of the silencers has <br />Y; inhibited that interaction so that the beats have been eliminated. <br />J <br />4.1.2 Summary of Wear Induced Noise Fluctuations <br />~ Noise fluctuations at the R-1 takeup may be due solely to variations <br />~: i <br />'" in coal load on the conveyor. Sound level increases in the truck dump <br />area, however, can be attributed to wear on the truck dump baghouse fan and <br />stack. Excessive rattling and vibration were the primary contributors to <br />_• increased sound levels as is evidenced by the significant increases in the <br />mid and high frequencies. <br />