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1 <br /> Table 7: Calculated Transmission Line Audible Noise Levels (3.28 feet above ground) 1 <br /> Audible Noise Levels at Edge of Right-of-Way <br /> Structure Type (dBA) <br /> L; Lso <br /> Single Pole Vertical Configuration with Post 1 <br /> Insulators, 115 kV Single-Circuit 14.5 11.0 <br /> Single Pole Davit Arm 115 kV/115 kV 1 <br /> Double-Circuit 233 19.8 <br /> Single Pole Davit Arm 115 kV/115kV Double <br /> 233 19.8 <br /> Circuit with Distribution Under Build <br /> Single Pole,Cross Arm,Y-Frame Structure 115 <br /> kV Single-Circuit 15.8 12.3 <br /> Source: Xcel Energy,June 7,2011;Xcel Energy,personal communication, November 7,2011. Calculations were <br /> performed using the EPRI Enviro software and the BPA standard method of calculation. <br /> Substation Noise <br /> Noise associated with substations includes the operation of transformers and switchgear.The <br /> transformers produce a constant low-frequency humming noise while the switchgear produces an <br /> impulsive or short duration noise during infrequent activation of the circuit breakers. <br /> The distance between the Xcel Orono Substation property boundary to nearby homes are <br /> approximately 180 feet to the south,across County Road 6,and approximately 270 feet to the west <br /> (Xcel Energy,personal communication,October 13). <br /> Xcel Energy proposes to install a 28MVA distribution transformer that is currently in storage. <br /> Future plans anticipate upgrading the 28MVA transformer to 50MVA and eventually adding a <br /> second 50 MVA transformer;the date of the upgrade and addition is dependent upon customer load <br /> growth demands (Xcel Energy,personal communication,November 21,2011). <br /> Xcel Energy is currently conducting a noise assessment of the Orono Substation site. Because no <br /> noise level data is available from Xcel Energy records or from the manufacturer of this transformer <br /> Xcel Energy is using an assumed 75 to 78 dBA noise level range at the transformer location. <br /> Mitigation Measures <br /> HVTL route permits require compliance with state noise standards established by the MPCA. <br /> The Project will be designed and constructed to comply with state noise standards established by <br /> MPCA during operation of the transmission line and substation. <br /> Construction activities would also need to comply with MPCA noise standards. Construction work <br /> would generally be limited to daytime hours,between 7 a.m. and 10 p.m on weekdays. Occasionally <br /> there may be construction outside of these hours or on a weekend if it becomes necessary to work <br /> around customer schedules or line outages. Heavy equipment would be equipped with sound <br /> attenuation devices such as mufflers to minimize noise levels (Xcel Energy,personal <br /> communication,November 14,2011). <br /> Environmental Assessment <br /> PUC Docket E002/TL-11-223 Page 28 <br />