Laserfiche WebLink
0� OCTA I Santa Ana/Garden Grove Fixed Guideway Project <br />Noise and Vibration Technical Analysis Re-evaluation in Support of Minor Design Modifications <br />The 2012 Noise and Vibration Technical Report (URS) determined the following distances for <br />potential for vibration impacts due to the use of a piece of equipment such as a vibratory roller <br />during construction: <br />• Building damage to residential structure — 26 Feet <br />• Building damage to institutional structure — 15 Feet <br />• Human annoyance to residential land use — 145 Feet <br />• Human annoyance to institutional land use — 115 Feet <br />Any structures within the distances identified above would be considered impacted due to use of <br />construction equipment such as a vibratory roller. The proposed modified alignment would <br />reduce the minimum distance to a residential structure to 37 feet. While this distance is within <br />the annoyance area it is outside of the potential damage area. <br />Traction Power Substation Noise Analysis <br />The noise sources on traction power substation (TPSS) units are the transformer hum and noise <br />from cooling systems. The wall mounted HVAC units are the primary noise source on the <br />proposed TPSS units. The noise level at a distance of 40 ft from the cooling fan of a Gold Line <br />TPSS unit in South Pasadena was measured to be 51 dBA, which is equivalent to 49 dBA at a <br />distance of 50 ft. This measured noise level is consistent with the maximum sound level limit of <br />50 dBA at a distance of 50 feet from any surface included in the purchase agreement of TPSS <br />units used in several recently completed light rail projects. The audible noise from the TPSS unit <br />in South Pasadena was caused by a ventilation fan. The hourly TPSS noise levels are <br />converted to daily Ldn noise levels using the following formula: <br />Leq Leq+10 <br />Ldn =10*Log (15*1010 +910 10 )-13.8 <br />Using an hourly noise level of 50 dBA, the Ldn noise level for the TPSS units is 56 dBA at a <br />distance of 50 feet. <br />Table N shows the predicted noise level at the TPSS sites assuming the units are specified to <br />have a maximum sound level of 50 dBA at a distance of 50 feet from any surface. As shown, by <br />orienting the TPSS units so that the noise from the HVAC units is directed away from the <br />sensitive uses, the noise levels at all receptors closest to the TPSS units would result in no <br />impacts. The locations of the TPSS units relative to the closest sensitive uses are shown in <br />figures included in Attachment E. <br />Table N: Summary of Traction Power Substation Noise Impacts <br />14 <br />TPSS Noise <br />FTA Impact <br />Distance to <br />Level <br />Criteria <br />closest land <br />Land Use <br />Existing Noise Level <br />Ldn or Lday <br />Ldn or Lday <br />TPSS use (feet) <br />Cat. <br />Ldn or Lday (dBA) <br />(dBA) <br />(dBA) <br />Impact <br />1 75 <br />2 <br />50 <br />43 <br />54 <br />No Impact <br />2 180 <br />2 <br />50 <br />45 <br />54 <br />No Impact <br />14 <br />