5.5. PCSR 02-13-2007 - Laserfiche WebLink

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Tiller Corporation Elk River and Livonia Quarries Noise Assessment . 4.0 PREDICTION 2007 AND FUTURE NOISE LEVELS 4.1. Modeling methodology and assumptions The computer prediction model used takes into account the decay of sound level with distance, atmospheric absorption of sound, shielding by barriers and topography and ground impedance. No additional attenuation from vegetation was assumed in the model since vegetation between mining operations and the closest residential receptor sites is limited and is assumed to have little effect in reducing sound level. The source levels in Table 3.2 which are based upon measurements at know distances from the equipment are assumed in the modeling of existing and future sound levels. The sound source elevation for the primary crushing equipment is assumed to be 12 feet above ground level. The source level for the cone crusher and screens is assumed to be 10 feet above ground level. The source level for the shale jig is also assumed to be 10 feet above ground level, while the loader is assumed to be 8 feet above ground level. In all cases, standard atmospheric conditions and a temperature of 590 F and 70% humidity are assumed. Since distances from equipment to nearby sources are less than 2000 ft, atmospheric absorption does not playa major role. The ground effect portion of the model assumes a slight downwind condition, although this adjustment to sound level is also relatively small. . 4.2. Livonia Mining Operation Assumed process equipment locations for 2007 and the future location closest to the Spencer resident are shown on Figure 4.1. The break in topography presented by the perimeter haul road along the easterly and northerly boundaries of the mining area is considered as a topographic barrier for noise from equipment in the pit. As noted in Section 2.1.2 a pit floor elevation of 965 feet is assumed. Predicted L50 levels from each source and the overall L50 level at the Spencer residence in 2007 and in the future when the process equipment is closest to the residence are shown in Table 4.1. Table 4.1 Livonia Mining Operation Sound Levels (L50 in dBA) 2007 Future S encer residence 46.4 49.9 Prim crusher 42.2 48.2 Cone and screens 41.9 42.4 Loader 40.4 41.2 . From Table 4.1, it can be seen the L50 50 dBA level associated mining activity is not expected to be approached at the Spencer residence until the process equipment is moved to the far north boundary of the mining area. Traffic noise from TH 169 is likely 50 dBA or higher during much of the day and will mask noise from the mine. If necessary, a small berm approximately 5 feet in height could be located along the west edge of the perimeter haul road to meet the nighttime L50 standard at the Spencer residence when traffic on TH 169 is minimal. However, the operation should be in compliance with the daytime L50 60 dBA level since the predicted levels are 10 dBA below that limit. David Braslau Associates, Inc. Page 13