1. Construction activities would temporarily increase particulate concentrations in and around the project site. The site has been previously graded so that it is essentially flat, with a gentle slope. Equipment and vehicles would generate dust during clearing and excavation. Construction vehicle traffic on unpaved surfaces would generate dust, as would wind blowing over exposed earth.

    It is 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 proposed to begin in autumn, which is generally the time of year when the soil has its lowest moisture content. The first rains of the season typically are received by mid-to late October, after which time, the potential for substantial dust generation drops off. However, dust generation can occur at any time during construction, including during the rainy season.

    If appropriate Bay Area Air Quality Management District (BAAQMD) mitigation measures are implemented, no significant impacts would be associated with construction emissions. 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 might be sufficient to violate the state 24-hour average PM-10 standard in the vicinity of construction. Unless mitigation measures were implemented, elevated levels of PM-10 would occur throughout periods of project construction. Because residences are located immediately downwind of the project site, mitigation measures would be necessary.

    Because the project site is currently used as a staging area for PG&E tree trimming operations, the relocation of those activities and development of the site as an unstaffed substation would result in a net reduction of motor vehicle trips accessing the project site. This would be a beneficial impact on long term local concentrations of carbon monoxide. No relocation site for the tree trimming trucks has yet been established, but relocation would be unlikely to have a substantial effect on regional pollutant emissions, as most of the truck trips would continue to be regional in nature (i.e., trip lengths would not be substantially different).

    Not considering actions that could be taken by PG&E customers in the absence of the proposed project, it could allow the delivery of electricity that would otherwise not be generated and transmitted. Approximately 40 percent of California's electricity is generated by coal, oil, natural gas, or organic matter, the combustion of which results in air pollutant emissions. Fuel-combustion power plants serving California could increase production to deliver the electricity demand facilitated by the proposed substation. It is not possible to predict which power plants may specifically be the source of power to support this increase. Individual fossil fuel plant power generation, as measured by megawatt output or capacity factors, has varied substantially from year to year, largely as a function of weather and hydroelectric power availability, relative fuel costs and unscheduled plant outages. Although generation patterns may shift among PG&Es power plants, the generation from specific plants may decline if out-of-state power penetrates the California market to a greater extent than at present. Under the restructuring of public electric utilities in California, power generation from out-of-state plants may increase. On the other hand, if electric loads grow in the absence of new generation, in-state power plants could increase generation, with commensurate increases in air emissions. However, these emissions could be generated in any of the air districts within California, or even from out of state. Thus, the air quality effects related to power generation in general are speculative and the latter do not equate to effects on transmission. 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 construction contractors to implement a dust abatement program during construction activities. At a minimum, the dust abatement program should include (as adapted from Bay Area Air Quality Management District):

  1. As discussed in the response to item V.a, construction dust emissions could have a temporary impact on nearby residences. Residences occupied by very young children or the infirm could be considered sensitive receptors. However, the impact to these residences would likely be a nuisance impact of larger particle dust settling and not an impact related to a violation of PM-10 standards at the residences. Existing trees would intercept some of the dust before reaching the residences. With implementation of the above cited mitigation measure V.a-1, this impact would be less than significant.
  1. The proposed substation would not be a source of thermal emissions and would not represent the type of operation that could cause alteration of air movement, moisture, or temperature, or cause any change in climate. Therefore, there would be no impacts related to climate change.
  1. The proposed substation is not the type of operation identified by the BAAQMD as a typical odor source (BAAQMD, 1996). The project would not result in an odor-related impact.
Forward to Next Section
(Transportation and Circulation)
Back to Previous Section
Back to Vasona Substation Main Page PG&E Substation Projects Main Page CPUC Home Page