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I I transmission line operation (Jackson et al., 1994). All of these potential effects are considered to be relatively minor,and all but the ozone effects are short-term. I State and federal governments currently regulate permissible concentrations of ozone and nitrogen oxides. Ozone forms in the atmosphere when nitrogen oxides and volatile organic compounds react in the presence of heat and sunlight. Air pollution from cars, trucks, power plants, and solvents I contribute to the concentration of ground-level ozone through these reactions. Currently,both state and federal governments regulate permissible concentrations of ozone and nitrogen oxides. The national standard is 0.075 parts per million ("ppm") during an 8-hour averaging period. The state standard is 0.08 ppm based upon the fourth-highest 8-hour daily maximum average in one year. The only potential air emissions from a transmission line result from corona,and such emissions are limited. Corona consists of the breakdown or ionization of air within a few centimeters immediately I surrounding conductors and can produce ozone and oxides of nitrogen in the air surrounding the conductor. This process is limited because the conductor electrical gradient of a 115 kV transmission line is usually less than that necessary for the air to break down. Typically, some Iimperfection such as a scratch on the conductor or a water droplet is necessary to cause corona. Ozone is not only produced by corona, but also forms naturally in the lower atmosphere from I lightning discharges and from reactions between solar ultraviolet radiation and air pollutants such as hydrocarbons from auto emissions. The natural production rate of ozone is directly proportional to temperature and sunlight and inversely proportional to humidity. Thus, humidity (or moisture), the same factor that increases corona discharges from transmission lines, inhibits the production of ozone. Ozone is a reactive form of oxygen and combines readily with other elements and compounds in the atmosphere. Because of its reactivity, it is relatively short-lived. There are currently no non- Iattainment areas designated in Minnesota (U.S. Environmental Protection Agency,2010). During construction of the proposed transmission line, minor emissions from vehicles and other I construction equipment and fugitive dust from right-of-way clearing will occur, but will be limited. Air-quality impacts during the construction phase will also be temporary. The magnitude of construction emissions is heavily influenced by weather conditions and the I specific construction activity. Exhaust emissions, primarily from diesel equipment, will vary according to the phase of construction,but will be minimal and temporary. Adverse impacts on the surrounding environment will be minimal because of the short and intermittent nature of the Iemission and dust-producing construction phases. Mitigative Measures IXcel Energy will employ BMPs to minimize the amount of fugitive dust created by the construction process. Tracking control at access roads and wetting surfaces are examples of BMPs that will be I used to minimize fugitive dust. Based upon this,Xcel Energy anticipates no significant effects to air quality from the Project;therefore,no additional mitigative measures are proposed. 6.5.2 Water Quality IThe water resources located within the Project are identified in Appendix B-6 (see also Table 4). Although areas of the Project, such as a portion of the Orono Substation site,have a greater elevation I Orono Project June 7,2011 MPUC Docket No. E002/TL-11-223 53