a) The active (surface displacement within the last 11,000 years) Hayward Fault is located approximately 4.5 miles east of the project site and the active San Andreas Fault lies approximately 13 miles west. The active Calaveras Fault lies approximately eight miles easterly of the proposed substation site. The active San Gregorio Fault is located approximately 25 miles to the west. Potentially active (surface displacement within the last 1.6 million years) traces of the Silver Creek and San Jose faults are located 0.5 mile and four miles, respectively, from the proposed substation site.

The Alquist-Priolo Earthquake Fault Zoning Act requires the delineation of zones along sufficiently active and well-defined faults. The purpose of the Act is to restrict construction of structures intended for human occupancy along traces of active faults, thus reducing the hazards associated with fault rupture. There is no evidence of the presence of an active fault crossing the site. The substation site is not located within an Alquist-Priolo Earthquake Fault Zone established for the active faults in this region. The substation and the power lines would operate unattended. The presence of a concealed fault, e.g., a low angle thrust fault, buried at great depth under the thick sediments of the area is a potential hazard that cannot be determined with available information. (An undiscovered concealed fault of this type was the source of the 1994 Northridge Earthquake in the Los Angeles area that damaged substation and transmission facilities.) While the possibility for a concealed fault cannot be entirely discounted, given the seismic history of the Santa Clara Valley, the potential hazard posed by a concealed undetected fault is considered speculative and a less than significant hazard.

c) Earthquakes or aftershocks may cause secondary ground failures. Ground failures are caused by soil losing its structural integrity. Examples of seismically induced ground failures are liquefaction, lateral spreading, ground lurching, and subsidence. Liquefaction (the rapid transformation of soil to a fluid-like state) affects loose saturated sands. Earthquake ground shaking induces a rapid rise in excess pore pressure and the soil loses its bearing strength, and it may spread laterally, undergo settlement and form fissures and sand boils (upwellings of sand at the surface). Lateral spreading is the horizontal movement of loose, unconfined sediment and fill deposits during seismic activity. Ground lurching is the horizontal movement of soil, sediments, or fills located on relatively steep embankments or scarps as a result of seismic activity, forming irregular ground surface cracks. The potential for lateral spreading or lurching is highest in areas underlain by soft, saturated materials, especially where bordered by steep banks of a river or adjacent hard ground. Subsidence is vertical downward movement of the ground surface as the soil densifies.

The Nortech Substation site is located in an area considered to have a low to moderate liquefaction potential. Soils in the vicinity of Coyote Creek (Trimble-Nortech power line) may have a high potential for liquefaction (rated low to high, indicating that the hazard is site specific) (PG&E, 1998). A low to high liquefaction rating is also indicated for the Kifer-Nortech power line. Lateral spreading, lurching and ground settlement (subsidence) are rated low to high hazards and localized in their effect. Lateral spreading or lurching could occur along the banks of the Guadalupe River, threatening the integrity of the proposed transmission poles. A loss of foundation support for the poles could cause them to tip, bringing down the conductors. If the wires were energized at the moment of tipping or collapse, the "hot" wire would pose a potential hazard to people in the area and could ignite fires. The project includes high-speed relays that would de-energize the line within about one-tenth of a second after detecting a broken line. See Section IX, Hazards. While the potential for earthquake induced hazards are unavoidable, conformance with industry design standards and CPUC design requirements for the poles and their foundations would reduce the hazard to an acceptable level of risk. Therefore, the impact, with proposed mitigation, is considered less than significant.

d) Earthquakes can cause tsunami ("tidal waves"), seiches (oscillating waves in enclosed water bodies), and landslide splash waves in enclosed water bodies such as lakes and reservoirs. The project site is not located near a tsunami run-up area or near an enclosed body of water such as a reservoir or lake. Therefore, this is considered a less than significant impact.

f) Unstable soil conditions include settlement and failure from low strength. Substation site soils are not of the types characterized by low strength. Settlement can occur either uniformly or differentially. Uniform settlement of a structure can cause poor drainage. Differential settlement can damage foundations and cause mechanical and structural problems within a structure. The magnitude of settlement of a fill or native clay material will depend on their properties, the manner in which the fills are placed, the thickness of the material, the type of underlying subsurface soil, and the load placed on the material. Differential settlement at the Nortech Substation site is rated as low to moderate. Settlement beneath the proposed transformer bank foundations is expected to occur due to compressibility of native, near-surface clay. Total settlement is expected to be low to moderate, on the order of a few inches. This could be accommodated within the project design. Settlement is generally a gradual hazard. As standard engineering, design, and construction practices are proposed in conformance with PG&E construction guidelines and CPUC required standards, impacts resulting from settlement, would be minor and the hazard would be less than significant. Differential settlement hazard is rated as low to high for both power lines. The slow action of settlement and the expected small amount of settlement is not expected to impair the operation of the power lines. Poles that settle differentially could create a requirement for corrective action as part of long-term maintenance requirements; this would constitute a less than significant impact.

The project site would require minimal additional grading of the flat site to construct the proposed Nortech Substation and would not result in any substantial changes in topography. Two to three feet of engineered fill would be placed at the substation site. No fills or changes in topography would be needed at the Trimble Substation and Kifer Receiving Station or for construction of the power lines. Construction of the substation would disturb site soils: temporarily exposed site soils may be subject to erosion by rain splash and overland flow of storm water for the duration of the construction activities. Site preparation would entail minor regrading, fill placement, resurfacing, and paving of portions of the site, eliminating any long-term hazard. Because the site is flat and the soils have a high clay content, soil erosion from construction activities would not result in significant hazards of gully formation. Runoff from the site could entrain loose soil and discharge it into storm drains. While the hazard is deemed less than significant, the impacts from erosion and sediment discharges could be eliminated by implementation of standard best construction management practices, as contained in Mitigation Measure IV.c.1, below.

g) Historic land subsidence due to extraction of groundwater from the underlying Santa Clara Formation has been recorded in this portion of the Santa Clara Valley. However, subsidence was virtually halted by 1971 due groundwater recharge and importation of water. The project would not require the removal of groundwater or any change in groundwater use; therefore, there would be no impact related to ground subsidence.

h) Expansivity, or shrink-swell, is the cyclic change in volume that occurs in fine-grained sediments because of expansion and contraction of clay caused by wetting and drying. Soils that are expansive (have shrink-swell potential) can damage foundations and other structures. This problem can be overcome with proper foundation engineering (Helley, 1979). Soils on the project site were observed to be clay mixtures with varying degrees of expansive potential. The hazard is rated as moderate to high for the Nortech Substation site and low to high for the proposed power lines. Foundation designs would be based on assumptions of high groundwater depth. A rise in groundwater following construction at the facility could cause the lean clays to swell. Proposed placement of engineered fill would reduce the hazard to the foundation of the Nortech Substation. Soils with high shrink-swell hazard potentially could affect some of the proposed poles. The slow action of expansive clay soils on the poles could cause them to lean out of plumb but is not expected to impair the operation of the power lines. Poles affected by expansive soils could create a requirement for corrective action as part of long-term maintenance requirements; this would constitute a less than significant impact.

i) The project area is essentially flat and has no unusual or unique geological features; therefore, there would be no impacts related to unique geologic or physical features. There is no evidence of potentially significant paleontological resources present in the area of the project. There are no significant mineral resources present in the project area. Soils in project area at one time were involved in extensive use for agriculture. Some of the soils along the power line routes potentially would be considered prime agricultural soils. However, as the area in general has been largely converted to urban uses, and because the project itself would not affect agricultural uses in the area, the use of these soils for the project would be a less than significant impact.

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