VI. AIR QUALITY
It is typically not possible to accurately estimate the particulate concentrations that would occur at or adjacent to the construction site because such concentrations are very sensitive to local meteorology and topography and to variations in soil, silt, and moisture content. Construction is expected to begin in autumn, which is generally the time of year when soil has its lowest moisture content; however, the local clay-like adobe soil seldom dries out except for the very top layer. At the site, the local soil surface layer is made up of some gravel and fill, and the clay-like adobe mixed with this material tends to act as a binder of these materials, too. Additionally, the first rains of the season are typically received by mid- to late October, after which time the potential for any substantial particulate generation drops off. Regardless of the soil or season, dust generation can occur at any time during earthmoving related construction activities, including during the rainy season. However, the characteristics of local soils should assist in minimizing particulate generation, and thus construction activities are not expected to be a significant generator of particulate material.
The Bay Area Air Quality Management District (BAAQMD) considers construction emissions to be significant only if project-appropriate mitigation measures are not implemented. Dust is comprised of large particles (i.e., larger than 10 microns in diameter) which settle out rapidly on nearby horizontal surfaces and are easily filtered by human breathing passages. Much of the dust generated by construction is, therefore, of concern more as a soiling nuisance rather than for its unhealthful impacts. The remaining fraction of small particulates (under 10 micron diameter, referred to as PM-10), tend to remain suspended in the air and could have the potential to violate the state 24-hour average PM-10 standard in the vicinity of construction. Unless mitigation measures are implemented, elevated levels of PM-10 could occur throughout periods of project construction. Surrounding the site to the south and west is the Youngstown Mobile Home Park, to the north is the park’s storage area for recreational vehicles, and to the east is a light industrial parcel with residential, commercial, and industrial uses. Because the residences located within the mobile home park are located immediately adjacent to the project site, mitigation measures for construction impacts would be necessary.
The substation site is part of the Petaluma Service Center and includes a customer payment center, vehicle maintenance facility, employee offices, warehouse for gas and electric equipment, and a vehicle and construction equipment yard. The Service Center also serves as a staging and storage area for equipment and supplies during normal and emergency operating conditions. The proposed substation at full build-out is planned to be a remote-controlled facility requiring maintenance inspections only once a month. Operation of the proposed substation and maintenance of the connector line would not result in a significant increase in vehicle trips to the facility over and above those for the existing facility. Thus, no net air quality impact would result from the normal operation of the proposed substation.
The proposed project would allow for the delivery of electricity that would otherwise not be transmitted. Approximately 40 percent of California's electricity is generated by fossil fuels, the combustion of which results in air pollutant emissions at power plants. Consequently, fossil-fueled power plants within California would increase production to deliver the electricity demand facilitated by the proposed substation. However, these emissions could be generated from any or all of the air districts within California, or even from out-of-state generation sources. The environmental impact of air emissions from the individual power plants would be assessed at the time of power plant construction or permit issuance by the local air district. It is assumed that all power plants, whether new or existing, would operate within air emission caps created by the local air districts. The project itself would not induce demand for generation of additional electricity.
The following mitigation measure would reduce the potential impact of dust generation to a less-than-significant level:
Mitigation Measure V.a-1: PG&E shall require its construction contractors or crews to implement a dust abatement program during construction activities. The dust abatement program should include the following (as adapted from BAAQMD):
· Water exposed soils at all active construction sites at least twice daily on days without measurable rainfall at the site;
· Cover all trucks hauling soil, sand, and other loose materials or require all trucks to maintain at least two feet of freeboard;
· Pave, apply water three times daily, or apply (non-toxic) soil stabilizers on all unpaved access roads, parking areas, and staging areas at construction sites; and
· Sweep daily (with water sweepers) Corona Road, the paved access road to the substation site, and paved parking and staging areas at the substation site. Sweep each paved street area used to drill foundation holes and pour foundations for power line towers.
PG&E shall certify compliance with this measure in scheduled progress reports to the CPUC.
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