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5.0 Environmental Analysis 5.6 Noise <br />Avion Project SEIR <br />Page 5.6-6 <br />to 0.005 in/sec PPV at nearest residential property line 175 feet to the northeast, which would not <br />exceed 0.2 in/sec PPV from hydraulic hammering at local residences. <br />Table 5.6-1 <br />Predicted Hydraulic Hammering Vibration Levels <br />Distance to Construction <br />Non-rippable Rock <br />(feet) <br />Impact <br />Criteria <br />(in/sec PPV) <br />Predicted <br />Vibration Level <br />(in/sec PPV) <br />Potential <br />Significant <br />Impact <br />5 <br />0.2 <br />0.995 Yes <br />10 0.352 Yes <br />11 0.305 Yes <br />12 0.268 Yes <br />13 0.237 Yes <br />14 0.212 Yes <br />15 0.191 No <br />20 0.124 No <br />25 0.089 No <br />175 – nearest residence 0.005 No <br />in/sec = inches per second; PPV = peak particle velocity <br />Bold = Exceeds 0.2 in/sec PPV <br /> <br />Drilling <br />Noise <br />As an alternative to hammering, drilling may be used to prepare the boreholes for explosives. While <br />the numbers and diameters of the boreholes are dependent on the actual blasting process, the <br />noise levels generated by a rock drill would not vary. According to the FHWA, a rock drill typically <br />generates maximum noise levels of 85 dB(A) Leq at 50 feet. As discussed previously, this is reduced <br />by the actual time the equipment is generating the maximum noise in a given hour. Based on the <br />FHWA data, a rock drill generates the greatest noise levels for approximately 20 percent of an hour. <br />Thus, a single rock drill would generate an hourly noise level of 78 dB(A) Leq at 50 feet. Assuming the <br />use of a rock drill and a loader/backhoe are operating for a full hour, rock drilling operations would <br />generate hourly noise levels of 80 dB(A) Leq at 50 feet. Based on standard point source propagation <br />noise levels, noise levels would attenuate to 69 dB(A) Leq at the nearest residential property line <br />175 feet to the northeast, which is less than the City’s applicable construction noise level limit of <br />75 dB(A) Leq. <br />Vibration <br />According to the FTA, vibration levels associated with the use of rock drills are estimated to generate <br />0.089 in/sec PPV at 25 feet, which is the same level as the hydraulic impact hammer. Consequently, <br />vibration levels generated by rock drilling would be the same as those shown in Table 5.6-1, and <br />would attenuate to 0.005 in/sec PPV at nearest residential property line 175 feet to the northeast.