1. Several hazardous substances would be used in the operation of the proposed substation. A 230/12 kV, 45 MVA transformer could contain up to 12,280 gallons of mineral oil, used as an insulating medium and coolant. The mineral oil would not contain Polychlorinated Biphenyls (PCBs). To prevent the release of mineral oil in the event of damage to the transformer, PG&E proposes that the transformer would be mounted on a sealed pad with drainage directed to a Spill Prevention Containment and Countermeasure (SPCC) pond that could hold the entire volume of oil from the transformer, together with rainwater from a two-year storm. A manually operated gate valve would retain any oil in the SPCC pond for collection and disposal at an approved site. EPA regulations require that the equipment and spill containment area be inspected monthly. PG&E would conduct the inspections.

    Batteries would be used for emergency back-up power at the substation. Similar to automobile batteries, these batteries would contain sulfuric acid in the electrolyte. The substation battery would have 60 cells and provide an output of 125 volts (in comparison, an automobile battery has 6 cells and provides an output of 12 volts). Release of material from the batteries in the event of a spill would be prevented by housing them in a building with a concrete floor and without drains.

    Nitrogen (N2) gas and Sulfur Hexafluoride (SF6) gas, both inert and non-toxic gases, would be used at the substation. Nitrogen gas would be used to slightly pressurize oil-filled equipment, while SF6 would be used as an insulator and arc suppresser in circuit breakers. SF6 would not be released under normal conditions; PG&E usually recycles the SF6 gas in the breakers during maintenance. The only hazard involved in either is a physical hazard of injury to a nearby person from the explosion of a cylinder containing high pressure gas. The likelihood of a cylinder explosion is low because the cylinders are designed to contain the gas under high pressure and are inspected by PG&E as part of regular maintenance. Because the site would not be staffed, risks to people would be small in the unlikely event of a cylinder explosion.

    In the long term operation of the substation, there is a finite risk of electrical arcing and short-circuits due to failure of the equipment. The design of the substation, including the placement of the wires, equipment and the fencing around the substation, is intended to prevent public access to high-voltage equipment and to minimize the risk to the public of shock or injury in the event of equipment failure.

    Fires at substations are rare events, and in general, the fire risk posed by the Vasona substation would be no different than that of other similar substations. The substation itself would be designed to provide adequate clearance around the transformers to prevent a fire from spreading were one to occur. The transformer pad and the surrounding area will be surfaced with cement, gunite, asphalt or gravel to prevent fires from off-site areas spreading to the transformers or to prevent a transformer-caused fire from spreading off the site. The recent fire in Los Gatos appears to have been related to vegetation that had encroached on a transmission right of way. No vegetation would be located near the transformers or the transmission lines on the site; therefore, this type of hazard would not be present at the Vasona substation site.

    PG&E's proposed mitigation measures are consistent with those employed at other substations and would be adequate to ensure a minimal risk of accidental explosion or release of hazardous substances. Assuming implementation of the mitigation measures proposed as part of the plan, additional mitigation is not required and the hazard is less than significant.
  1. No interference with an emergency response plan or emergency evacuation plan is evident from the construction or operation of this substation and the related facilities.
  1. The project will take high-voltage electricity from the PG&E Metcalf-Monta Vista 230 kV transmission line,
  2. step-down the voltage to 12 kV and distribute the electricity to local customers. By its nature, the project provides certain benefits and poses certain risks to the public. In addition to the issues discussed elsewhere in this section of the Initial Study, because the project will alter the electric and magnetic fields (EMF) in the vicinity of the site, concerns about potential health-related consequences of the EMF are addressed.

    The project is located within the right-of-way of the PG&E Metcalf-Monta Vista 230 kV transmission line, an operating high-voltage electric power transmission facility. The Metcalf-Monta Vista transmission line, under peak electrical load conditions, is estimated to generate a magnetic field strength of not more than 150 milliGauss (mG) at the edge of the right-of-way (PG&E, 1997a, p. 82) This value represents, in effect, a maximum baseline condition for the substation site, along the boundaries of the transmission line right-of-way; directly under the transmission line, the value would be higher.

    PG&E calculated the magnetic field strength that would be created by the operation of the substation at the proposed substation property boundaries. Based on ultimate build out of the substation with two 45 MVA transformer banks, eight 12 kV distribution feeders (four from each bank), maximum loading at nameplate capacity, balanced loading and normal operating conditions, it was determined that the strength of the magnetic field at the property boundary would range from 0.7 mG to 4.0 mG (Figure 6.3.1, follows p. 82, in the PEA shows the estimated magnetic field strengths on all sides of the site). The calculations do not include magnetic field strength contributions from the Metcalf-Monta Vista transmission line or the 12 kV transmission line along Winchester Boulevard. Although connections to both transmission lines are necessary, neither transmission line is a part of the proposed project.

    According to PG&E's analysis, under the maximum electrical load conditions, the contribution of the project to the magnetic field strength at the property boundaries would range from 0.7 mG to 4 mG, as follows: along the boundary with the Boccardo Corporation property, 07. mG to 1.7 mG; along the Charter Oaks boundary, 0.7 mG to 1.3 mG; and along the boundary with the Santa Clara County Fire District property, 1.2 mG to 4.0 mG.
    Compared to present maximum contributions of up to 150 mG from the Metcalf-Monta Vista transmission line and an undetermined contribution from the 12 kV transmission line along Winchester Boulevard, the range from 0.7 mG to 4 mG would be approximately from 0.5% to 3% of the existing magnetic field strength present.

    Average annual electrical load conditions for the substation would be roughly 40% of the maximum load, and the contribution of the project to the magnetic field strength at the property boundaries would be about correspondingly lower. Further, typical magnetic field strengths at the edge of transmission line rights-of-way would be 10 mG to 90 mG (PG&E, 1997a, PEA p. 82).

    Two underground 12 kV distribution circuits would connect the Vasona Substation to the existing electric distribution system. They would contribute to electro-magnetic fields at the site. The undergrounded feed to the 12 kV distribution line along Winchester Boulevard would exit the substation site on the Winchester Boulevard frontage. At that point, as well as over the portions of the site within the right-of-way of the 230 kV Metcalf-Monta Vista transmission line, the contributions from the 230 kV transmission line and the 12 kV distribution line would substantially exceed the contribution from the substation equipment. The calculated magnetic field profile in the PEA is estimated to be 42 mG for the underground distribution lines along Winchester Boulevard (PG&E, 1997b). The calculated magnetic field range for the existing 21 kV overhead lines along Winchester Boulevard would not exceed 36 mG (PG&E, 1997b). These contributions would occur within the existing rights-of-way for the two power lines and not on surrounding residential or commercial properties. Members of the public that would be exposed to these fields include anyone walking within the rights-of-way or along the Vasona substation frontage.

    The PEA contains summary discussions about possible relationships between exposure to electric and magnetic fields and potential health-related effects, summarizing information from the U.S. National Academy of Sciences, American Medical Association, American Cancer Society, California Department of Health Services, National Institute of Environmental Health Sciences and U.S. Department of Energy, and the California Public Utilities Commission (PG&E, 1997a, PEA pp. 72-79). The U.S. National Academy of Sciences study (NAS, 1996) is the most recent comprehensive evaluation of the topic. The committee concluded that the current body of evidence does not show that exposure to power-frequency electric and magnetic fields presents a human hazard (p.1).

    In response to public concern about possible health effects of EMF from electric utility facilities, the California Public Utilities Commission opened an investigation of the hazards. On November 2, 1993, the CPUC issued Decision 93-11-013, which recognized the public concern, but which declined to "adopt any specific numerical standard in association with EMF until we have a firm scientific basis for adopting any particular value." However, in that decision, the CPUC did direct all publicly owned utilities to take "no cost and low-cost" EMF reduction steps on transmission, substation and distribution facilities to reduce exposure of the public to magnetic fields.

    In accordance with that requirement, the proposed design of the Vasona substation includes the following "no cost and low-cost" EMF reduction measures:
  1. raise the transmission line's tubular steel poles or conductors by 10 ft. to reduce EMF at ground level;
  1. use metal clad switchgear to reduce magnetic field contributions from the 12 kV bus; and,
  1. use compact equipment spacing, which reduces the site area used and allows equipment to be shifted away from the residential property (Charter Oaks) and provides more distance between the equipment and the property lines in order to reduce magnetic field strength at the property line.

In conclusion, there is no evidence that the existing EMF from the 230 kV Metcalf-Monta Vista transmission line (and the 12 kV distribution line along Winchester Boulevard) presents a health hazard to those individuals who live and/or work in the vicinity of the site. Further, there is no evidence that the additional EMF contributed by the proposed Vasona substation would create a health hazard or potential health hazard. The impact is less than significant and additional mitigation is not required.

Operation of the proposed Vasona substation would decrease the number of people working on or using the site, so the project would not increase the total exposure of people to any existing sources of potential health hazards.

  1. The site is currently cleared of vegetation, and would be substantially paved with the construction of the substation. The cleared area within the substation would be maintained and kept free of shrubs or trees that might colonize the site; this would prevent any hazard of arcing leading to a fire that would spread to the landscaping trees on the perimeter of the site. There would be no increase in fire hazard on the site or adjacent areas.
Forward to Next Section
Back to Previous Section
(Energy and Mineral Resources)
Back to Vasona Substation Main Page PG&E Substation Projects Main Page CPUC Home Page