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IMPACTS AND MITIGATION MEASURES OF THE PROJECT ALTERNATIVES Standards of Significance s The following standards are used in this analysis to assess the significance of project- related noise impacts: 65 dB Ldn at the property line of lands zoned for residential uses or within 100 feet of residences constructed on lands designated for agricultural uses. 75 dB Ldn at the property lines of lands which are not particularly noise sensitive (such as C-M, R-M, M-1 and M-2-zones). The significance of project-related ambient noise level increases is assessed as follows: 0-3 dB Leq increase - not significant 4-5 dB Leq increase - potentially significant 6 dB Leq or greater increase - significant Impact Analysis Impact 4.6-1 Unacceptable Noise Levels from Proposed Plants Noise measurements and modeling techniques were used to predict noise levels 9Y enerated b the proposed aggregate processing operations. Operational information for aggregates excavation and processing in the area was obtained from the proponent. Major noise sources associated with the processing areas include the aggregate crushing, screening and conveying equipment, the asphalt concrete plant, and load-out of materials involving heavy trucks and front-loaders. Noise measurement data collected at aggregate processing facilities of similar capacities was used to project the noise generated by various processing equipment. Given a single eight-hour operating shift, the relationship of Leg to Ldn would depend on the number of nighttime hours during which processing area activities are to occur. If all eight operating hours are during daytime hours (7 am to 10 pm), the computed Ldn would be 5 dB lower than the L.eq since Ldn is a 24-hour average and there would be no 10 dB penalties for operations occurring during nighttime hours. For a conservative estimate of typical s hours of operation, it was assumed that processing area activities could commence during the 5 Ann hour. Given two nighttime and six daytime hours of operation, the Ldn computed for steady-state sources is approximately equal to the Leq of those sources. Draft Environmental Impact Report 4-88 ER-96-3