IV. WATER

Discussion

The project area covers the lower portions of three river catchments: Coyote Creek, the Guadalupe River and San Tomas Aquino Creek. North of State Route 237, the creeks converge into the Baylands that form a system of natural and channelized courses along the southern margin of San Francisco Bay. The major waterways have been channelized and contained in levees, and were relocated for purposes of flood control. The proposed Nortech Substation site is located about on-half mile from the southern edge of San Francisco Bay. Most of the area below about elevation nine feet above NGVD, that is, most of the area north of State Route 237, including the proposed Nortech Substation site, is susceptible to flooding from San Francisco Bay during periods of extremely high tides. Flooding of the project area, including the Nortech Substation site, Trimble Substation and portions of the proposed power line alignments, has occurred in historic time on all three streams. The project area in general has a relatively high groundwater table, especially the area north of State Route 237. Portions of the project area (primarily the northerly end of the Kifer-Nortech power line alignment) are located on former landfills which may contain contaminated groundwater and that alignment also passes near a contamination zone of a leaking underground storage tank (Rotten Robbie Gas Station).

  1. The proposed project would require paving an added portion of the proposed Nortech Substation site, which would reduce infiltration and slightly increase the amount and rate of runoff. Because the existing site is partially paved and the soils are compacted, a slight increase in runoff at the site could result from the project. The project would not alter runoff at either the Trimble Substation or Kifer Receiving Station. Construction of poles would create a negligible impact on runoff in the project area. Stormwater collected in the Spill Prevention Control and Countermeasure (SPCC) system and pond located at each of the two existing substations and at the proposed Nortech Substation would contain some of the site runoff and regulate the peak discharge offsite, compared to the current conditions. The SPCC system and pond would have a capacity of 11, 220 gallons (PG&E, 1998a). The impact would be less than significant.

Storm water runoff from other portions of the yards that are not directed into the SPCC pond would drain separately and be discharged to the storm drainage pipe system. This storm drainage pipe system would discharge to the existing city storm pipes. The proposed design would be adequate to reduce operational impacts related to the expected small increase in storm water discharge to a less than significant level. Additional mitigation is not required.

b) The project area is within a zone of flood hazard as defined by the Federal Emergency Management Agency, Flood Insurance Program. The proposed Nortech Substation site is located within a 100-year flood hazard zone, with flood inundation expected to reach Elevation 9. As the site at present is at Elevation 2.4, PG&E proposes to place fill raise the foundation by two to three feet. While the fill would reduce the depth of inundation during a 100-year flood, the site would be flooded. PG&E does not anticipate that the expected level of flooding would impair operation of the substation, although this would make access to the substation difficult.

Portions of the power line alignments are located in inundation zones of the 100-year flood. Most of the Trimble-Nortech power line are located in areas with shallow (one to three feet depth) inundation hazard. The power line north of State Route 327 lies within a zone of deeper inundation, similar to that at the Nortech Substation site. Most of the Kifer-Nortech power line is located within a zone outside the 100-year flood inundation zone; only the portion immediately westerly of the Nortech Substation site is within the 100-year flood zone, with a hazard similar to the substation site. Inundation of the areas with the pole lines is not expected to pose a significant hazard to the poles themselves. The chief hazard would result from a failure of the levees containing one of the rivers. In that event, the erosive force of the water and entrained debris could tip one of the poles. The Santa Clara Valley Water District is undertaking levee improvement projects in the area. Thus, the likelihood is remote that the power lines or substations would be subject to that type of hazard.

A large earthquake potentially could result in dam failures at reservoirs upstream of the project area. According to dam failure inundation maps (ABAG, 1980) the project site could be impacted by flooding in a dam failure of the Lexington, Vasona, Calero, Almaden or Guadalupe Reservoirs. Considering the distance of the reservoirs from the project area, topography, and flood control structures currently in place on Coyote Creek and Guadalupe River, and the protection of the Nortech site created by the State Route 237 embankment, inundation in this area is likely to be shallow and the quantity of flood water and entrained debris from a dam failure flood would not impair operations at the substation. Therefore, this is considered to have a less than significant impact.

The project itself would not directly expose people to flood hazards of the types described above. The hazards would only be to workers present at the substations during a flood. Because the substations are remote controlled and personnel are onsite only during occasional inspection and maintenance visits, the hazard to people is minimal. The impact is less than significant.

c) Stormwater discharges during construction might contain high concentrations of pollutants from spills of hazardous substances and total suspended solids. Since this project includes proposed construction activity that would disturb less than five acres of land, the project is not subject to regulation by the state General Storm Water National Pollution Discharge Elimination System (NPDES) permit. The project would discharge into the city storm drains, that in turn empty into surface waters (Guadalupe River, Coyote Creek and San Tomas Aquino Creek) and eventually into San Francisco Bay. Construction of foundations for poles would require borings to a depth of 10-25 feet. If rain occurs during the construction period, some of the removed soil could be discharged in runoff into storm drains, clogging or reducing their capacity. Mitigation included in this Initial Study would result in a less than significant effect on surface waters.

Surface water runoff from the Nortech Substation site after construction is expected to contain minor concentrations of a variety of pollutants typical of electrical substations (e.g., automobile fluids, suspended solids, metals, and organics), but is not expected to be substantially different than the pollutants currently released from the project vicinity, which is now a parking and storage area. It is not expected that surface water runoff pollutants from long-term operations would occur in concentrations that would be acutely toxic to aquatic life.

Three proposed electrical transformer banks would each contain up to 9,500 gallons of inert mineral oil at the Nortech Substation. The transformers would be installed on sealed concrete foundations, and the substation would be surfaced to direct any leaks into an on-site, concrete-lined SPCC pond, to be designed in accordance with PG&E DCS Guideline D-G0052 (January, 1998). The SPCC pond would be designed to contain oil and rainfall equal to 110% of the largest oil container or oil and rainfall quantity equal to 10% of the total aggregate oil volume contained in the drainage area (DCS Guideline D-G0052). A built-in weir system with a skimmer to collect oil would be constructed to segregate oil from the water, providing stormwater spillover and oil retention. The DCS Guideline requires that the skimmer weir accommodate discharge for a 25-year design storm in combination with no oil. In heavy storm periods, the SPCC pond would be monitored for operational effectiveness of the containment system and proper release of storm discharge. Oil released from a transformer would be directed to the SPCC pond through berm-enclosed surface drainage or through underground piping. The SPCC pond would be equipped with a manually operated isolation valve. Pursuant to Environmental Protection Agency requirements, the equipment and spill containment area are inspected on a monthly basis. Operators would not release accumulated rainwater until the SPCC pond is inspected for oil or sheen. This should be adequate to prevent unplanned releases and overflows.

Mitigation

The following mitigation measure would reduce the potential impact of surface water discharge to a less-than-significant level.

Measure IV.c.1. If construction is scheduled during the rainy season, PG&E shall employ best construction management practices to prevent discharges of silt and other substances from construction into storm drains. PG&E shall develop and implement a plan to control excavated soils and runoff, specifying practices such as the use of detention basins, straw bales, silt fences or other deterrents, and site clean-up procedures and practices to minimize contact of construction materials with stormwater. PG&E shall file a copy of the plan with the CPUC for review and final approval and shall certify compliance with this measure in progress reports to the CPUC.

d) No water bodies are present at the Nortech or other substation sites (site visit July 17, 1998). The Kifer-Nortech power line crosses the course of the Guadalupe River on the north side of State Route 237. The Guadalupe River could be spanned by the power line without impact to the river channel. The project would result in no quantifiable change in impervious surface area and associated storm water runoff. This level of increase would not result in a significant change in the amount of water in any water body.

e) No watercourse is present on the proposed Nortech Substation site or at the Trimble Substation and Kifer receiving Station (site visit July 17, 1998). The proposed project would have no effect on the course or direction of surface waters. Installation of the new power line spanning the Guadalupe River is not expected to disturb the riverbed within the limits of the floodplain. No proposed facilities are located near the channels of Coyote Creek or San Tomas Aquino Creek.

  1. The proposed project is located in the Santa Clara County Groundwater Basin, which is managed by the Santa Clara Valley Water District. Historic groundwater pumping from the underlying Santa Clara Formation has caused land subsidence in portions of the Santa Clara Valley. However, subsidence was virtually halted by 1971 due groundwater recharge and importation of water (Helley and Lajoie, 1979). The lower portions of the project area and areas near the major watercourses have areas of high groundwater. Groundwater typically is within five to 20 feet of the surface. The Nortech Substation site is located in an area in which the groundwater table is located close to the surface (that is, the water table is expected to be near Bay level (2.4 feet below the surface) (PG&E, 1998 PEA). The near surface water is brackish and is not used for water supply.

The project area is underlain by groundwater-bearing aquifers (PG&E, 1998 PEA). The shallow, unconfined aquifer occurs within the shallow Bay Mud usually at depths ranging from 0 to 20 feet. The water is of poor quality and is not used for water supply. Between about 20 and 50 feet below grade is a upper confined aquifer. It has relatively poor yield. The upper aquifer is underlain by a clay layer (aquitard) that separates it from the lower aquifers (deeper than 150 feet) that are used for water supply. Those water supplies are of relatively good quality and until the early 1970ís were over-pumped, resulting in salt water intrusion. Groundwater management programs by the SCVWD have resulted in significant improvement of the aquifers and its quality.

The Nortech Substation construction would require shallow cuts that would intercept shallow groundwater or require significant construction de-watering. The effect would be temporary, as the site would be immediately filled by two to three feet of engineered cover fill. As the water is brackish, any dewatering would have no impact on a water supply. Subsidence related to dewatering would be minor and is not expected to affect any adjacent properties. In addition, PG&E may choose other construction methods which would not result in dewatering. The placement of some poles for the power line would require bores to a depth of up to 25 feet, potentially penetrating into the upper unconfined aquifer. Minor temporary (one or two days at each location) dewatering of the bore hole for placement of pole foundations may be required until the cement foundation is poured.. If piles are used, they may be one or two feet in diameter and from 50 to 100 feet deep. The small size of the holes for the piles is unlikely to have any identifiable effect on the aquifer and because of their number and spacing, the piles would not impede flows in the aquifer. These impacts would be less than significant.

The project would result in a negligible increase in impervious surface area and would not create other features that would reduce the potential for groundwater recharge. Therefore, there would be no impact related to any change in the quantity of groundwater.

g) The project would not require removal of substantial amounts of groundwater during construction and none during operation. The project would not include any substantial deep cuts or other features that would intercept or impede the flow of groundwater. The cement foundations to support the power lines poles would have a negligible effect as a barrier to groundwater movement: in most cases they would not intercept the water table at all. Therefore, the project would have no impact on the direction or rate of flow of groundwater.

h) Construction of the Kifer-Nortech power line could encounter contaminated soils near the site of the Rotten Robbie Gas Station on Lafayette Street. PG&E intends to avoid pole placement on sites with existing contamination. If contaminated sites cannot be avoided, PG&E will test the soil and groundwater using standard procedures. Construction could involve dewatering and disposal of the contaminated water in accordance with Regional Water Quality Control Board requirements. Construction also may involve use of protective casing outside of the piles or other method to seal off the shallow contaminated zone. Public access to the construction site may be restricted and workers would be required to follow OSHA protective procedures. If these procedures are followed the impact would be less than significant and additional mitigation would not be required.

The proposed compacted fills and impervious surface areas would prevent infiltration of contaminants into the soils. The proposed SPCC pond at the Nortech Substation would be concrete-lined to prevent infiltration of contaminants from the pond into the subsurface soils. Run off or percolation from the proposed project would not be expected to impact groundwater quality in the area (See also the discussion under checklist item IV.c). After constructing the bored holes for the power line poles, the holes would be immediately filled with cement. This would create a seal that would prevent infiltration of surface contaminants into the groundwater. Therefore, the project would have no impact on groundwater quality.

i) The project would not involve the need for use of groundwater resources, therefore it would not have an impact on water supplies from local groundwater. Water supplies for construction would come from the general groundwater and surface water supply sources provided by the SCVWD. The amount of water needed for construction would be minor. The impact on SCVWD water supplies would be less than significant. Long term operation of the project would have a negligible use of water and no impact on local groundwater supplies. Therefore, the project would have no impact on the availability of groundwater for public water supply.

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