Appendix G. Geological Resources

Transcription

1 Appendix G Geological Resources

2 TECHNICAL MEMORANDUM Geological Resources Alta Infill II Wind Energy Project PREPARED FOR: PREPARED BY: COPIES: Alta Windpower Development, LLC Tom Lae, CH2M HILL Aarty Joshi, CH2M HILL Patti Murphy, CH2M HILL DATE: Revised July 7, Introduction This technical memorandum describes the geologic and soil characteristics of the Alta Infill II Wind Energy Project site and the potential for impacts associated with the project. The project area consists of approximately 11,315 acres split into three segments, shown on Figure 1, within the northern portion of Antelope Valley. In addition to the wind turbine generators (WTGs), major components of the project include additional temporary and permanent service roads, overhead and underground transmission and collection lines, electrical switchyards, up to six collector substations, meteorological towers, communication cables, up to two concrete batch plants, and two warehouse facilities. A description of the environmental setting (affected environment) for geology and soils is presented in Section 2.0, including discussion of the geologic setting (soils and geologic formations, faults, and seismic history), and geologic and seismic hazards (slope stability, soil hazards, faults and seismicity, strong ground shaking, fault rupture, liquefaction). The regulatory setting applicable to geology and soils is presented in Section 3.0. Section 4.0 includes a discussion on the affected environment, and Section 5.0 presents and the environmental impact analysis, including discussion of project impacts and associated mitigation measures. 2.0 Environmental Setting The project site is located in the Antelope Valley in southern Kern County, near the town of Mojave, California. This area lies within the Mojave Desert geomorphic province. The project site terrain is mountainous in the northwest and generally flat in the southeast. The project site is located within an area of southern California known to be seismically active. 2.1 Regional Geology Area terrain is mountainous in the northwest along the Tehachapi Mountains and generally flat in the east with a southeasterly slope. The Mojave Desert region is geologically young and seismically active. The geology of the region around the site is very complex, reflecting geologically rapid processes driven by active tectonics and rapid erosion primarily the result of movement along the San Andreas and Garlock fault systems. Many active faults are present in the general site area (California Geological Survey [CGS], 2010). IS SAC/421269/

3 2.2 Local Geology The local geology of the project area is dominated by the elevated terrain of the southwestnortheast-trending Tehachapi Mountains and various drainage basins. The largest of these, and northwest of the project site area, is the Tehachapi Valley, which developed during the late Cenozoic by the continual erosion of Tertiary formations and by downwarp resulting from local synclinal folding. The current configuration of the Tehachapi Mountains was formed by faulting and local tilting in a period of Quaternary uplift, which created a series of northwest-trending ridges and valleys (Dibblee and Warne, 1970). The geology of the project area is predominantly underlain by pre-tertiary crystalline rocks mainly composed of granitic-type rocks of the Sierra Nevada batholith of Mesozoic age and roof pendants of older metasedimentary rocks. These crystalline rocks are overlain by Tertiary volcanic and sedimentary rocks, and/or by Quaternary alluvium and colluvium as slope wash and talus mantling the slopes. The valleys in the area are also underlain by Quaternary to Holocene age alluvial and lacustrial deposits (Leighton, 2008). Soil types mapped in the project vicinity include those typical of the eastern side of the Tehachapi Mountains and the western end of the Mojave Desert. The soils are typically coarse-grained to moderately fine-grained, moderately to excessively drained, and generally have low shrink-swell potential (USDA, 1981). Surficial geologic units within one mile of the project area are shown on Figure Seismic Setting Numerous historical earthquakes have affected the Tehachapi region where the project site is located. Several principal active faults are within approximately 35 miles of the project site. These include the Garlock Fault (which extends through the northern portion of the project site), the White Wolf Fault (approximately 24 miles to the west), the San Andreas Fault (approximately 23 miles to the southwest), the Pleito Thrust Fault (approximately 31 miles to west), and the San Gabriel Fault (approximately 36 miles to the southwest) (Jennings, 1994; CGS, 2010). These principal faults are shown on Figure 2. These faults have exhibited Holocene activity (within the last 11,000 years) and produced notable earthquakes within 35 miles of the project site. The earthquakes that have produced the highest recorded site accelerations include the 1852 un-named magnitude (Mw) 7.0 earthquake along the San Andreas Fault and the 1952 Arvin/Tehachapi Mw 7.7 earthquake on the White Wolf Fault (Blake 2004, U.S. Geological Survey [USGS], 2011 and CGS, 2010) The five major faults in the vicinity of the project site are described briefly below. Garlock Fault Western Segment The Garlock Fault is a 162-mile-long, left-lateral and east-to-northeast-striking, strike-slip fault that separates the Sierra Nevada and the Basin and Range geomorphic provinces on the north from the Mojave Desert geomorphic province on the south. The Garlock Fault is a major Holocene active fault that changes character between its western and eastern ends. West of Koehn Lake, the fault shows a relatively complex fault trace. A large step in fault trace also occurs at Koehn Lake. This feature has been used to divide the Garlock Fault into three segments. The western Garlock Fault segment extends from the complex intersection with the San Andreas Fault near Frazier Park east-northeast to a 1.8-mile-wide left-releasing IS SAC/421269/

4 step-over in the vicinity of Koehn Lake. The central Garlock segment extends from the leftreleasing step-over near Koehn Lake eastward to the Quail Mountains where the Owl Lake fault intersects the Garlock Fault zone. The eastern Garlock Fault segment extends from the Owl Lake Fault eastward to the complex intersection with the southern extent of the Southern Death Valley Fault zone. Aseismic fault creep has been reported along the westernmost 37 miles of the Garlock Fault. However, the USGS has not detected evidence of fault creep (Bryant, 2000a). The western segment of the Garlock Fault is approximately 68 miles long. The northern portion of the project site is located within the California Earthquake Fault Zone (EFZ) delineated along the active Garlock Fault. A Holocene slip rate for the western Garlock Fault segment of 1.6 to 3.3 millimeters/year (mm/year) has been reported at Oak Creek Canyon. The slip rate of the Garlock Fault east of its intersection with the Owl Lake Fault is not known with any certainty (Bryant, 2000a). Recurrence intervals reported for the Garlock Fault are 800 to 2,700, 190 to 3,405, and 200 to 3,000 years for the western, central, and eastern sections, respectively. Recurrence intervals are reported to be irregular at the El Paso Peaks, where preferred average recurrence intervals of 1,230 years are noted (Bryant, 2000a). White Wolf Fault The White Wolf Fault is an active 37-mile-long, left-lateral reverse fault. On July 21, 1952, the White Wolf Fault ruptured, producing the Mw 7.7 Arvin/Tehachapi earthquake and the subsequent extensive sequence of aftershocks. It is reported that although surface rupture formed along only 17 miles of the surface trace of the fault, rupture probably occurred along most of its entire 37 mile length (Jenkins and Oakeshott, 1955). The White Wolf Fault is located approximately 24 miles northwest of the project site. At its northeastern end, the fault is first evident in lower Tehachapi Canyon. It trends S50 W along steep, northwest-facing slopes from Bear Mountain to Comanche Point. From there, it extends across the southern end of the San Joaquin Valley to Wheeler Ridge. Indirect evidence suggests that the fault may extend farther toward the San Andreas Fault. Its southeast-dipping plane has been reported to dip between 60 and 70 degrees. However, surface exposures of the fault show highly variable dips (Jenkins and Oakeshott, 1955). The White Wolf Fault is thought to have initiated in Miocene time; it has been active for most if not all of the Pliocene, Pleistocene, and Holocene. Total uplift of the southeastern block is on the order of 10,000 feet; left lateral offset is no more than 2,000 feet. The detailed displacement history of the fault is unknown except for its 1952 movement (Jenkins and Oakeshott, 1955). Maximum reliably observed displacements in 1952 were 3 to 4 feet vertically and about 2 feet horizontally (left-lateral). In 1952, the main shock hypocenter (epicenter) was close to Wheeler Ridge. Surface rupture occurred along the northern and southern portions of the fault. Presumably, displacements were absorbed in sediments along the central portion of the fault where it crosses the San Joaquin Valley (Jenkins and Oakeshott, 1955). The Southern California Earthquake Center (SCEC, 2011) reports an approximate slip rate for this fault of 3.0 and 8.5 mm/year or possibly less. The interval between major ruptures is unknown. IS SAC/421269/

5 San Andreas Fault The approximately 684-mile-long Holocene and historically active San Andreas Fault system consists of a network of faults that collectively accommodates the majority of relative north-south motion between the North American and Pacific plates. The fault extends from the Gulf of California, Mexico, to Point Delgada on the Mendocino Coast in northern California. This fault is the largest active fault in California and is responsible for two major historic earthquakes, the 1857 Fort Tejon Mw 7.9 earthquake and the 1906 Mw 7.9 San Francisco earthquake. Movement on this fault is right-lateral strike-slip, with a total offset of approximately 348 miles. Over most of its length, the San Andreas Fault is a relatively simple, linear fault trace (SCEC, 1995). Geomorphic evidence for Holocene faulting includes scarps in Holocene deposits, right-laterally offset streams, shutter ridges, and closer linear depressions. Based on differences in geomorphic expression, fault geometry, paleoseismic chronology, slip rate, seismicity, and historic fault ruptures, the San Andreas Fault is divided into ten or more segments. Each of these segments is capable of rupturing either independently or in conjunction with adjacent segments. The project site is located closest to the boundary between the Mojave and the Cholame-Carrizo segments of the San Andreas Fault (Petersen et al., 1996; Bryant and Lundberg, 2002a and 2002b). Cholame-Carrizo Segment The Cholame-Carrizo segment is approximately 124 miles long, trends approximately N66 W, and is located approximately 35 miles southwest of the central portion of the project site. The Cholame-Carrizo segment was the source of the January 9, 1857, Mw 7.9 Fort Tejon earthquake. The Fort Tejon earthquake was one of the greatest earthquakes ever recorded in the United States, and left an approximately 224-mile-long surface rupture scar along the San Andreas Fault. Offsets of 26 to 32 feet along this segment near Wallace Creek were reported for the 1857 earthquake event (SCEC, 1995). The fastest, generally accepted Holocene slip rate for the San Andreas Fault is along the Cholame-Carrizo segment where a preferred late Holocene dextral slip rate of 33.9±2.9 mm/year was reported by Bryant and Lundberg (2002a). Several average values of recurrence have been reported for the San Andreas Fault. In general, they range from a little more than 100 to as many as 450 years. Bryant and Lundberg (2002a) assign a recurrence interval of 160 to 450 years for the Cholame-Carrizo segment. Mojave Segment The Mojave segment is approximately 66 miles long, trends approximately N67 W, and it is located approximately 23 miles southwest of the central portion of the project site. The Mojave segment is delineated by well-defined geomorphic features characteristic of Holocene dextral offset such as dextrally deflected and offset drainages, dextrally offset ridges, linear drainages and ridges, aligned saddles and benches, closed depressions, linear scarps on alluvium, linear troughs, sidehill benches, shutter ridges, and linear vegetation contrasts. Up to 12 earthquakes between the time period of 261 and 1857 have been identified along this segment, including the Mojave segment identified as the source of the December 8, 1812, Mw Wrightwood earthquake. Bryant and Lundberg (2002b) assign a recurrence interval for the Mojave segment of approximately 135 years for the time interval 734 to 1857, and 105 years for the past 500 years. IS SAC/421269/

6 A dextral slip of 33 feet has been documented between the period of 735 and 1857 along this segment at Pallet Creek (Bryant and Lundberg, 2002b). The same authors have assigned an average slip rate greater of 5.0 mm/year to this section of the fault. Pleito Fault Eastern Section The Pleito Fault is a significant Holocene active south-dipping thrust fault located along the border of the Transverse Ranges and Great Valley geomorphic provinces. The Pleito Fault extends from Santiago Creek about 2.8 miles east of the San Andreas Fault eastward to about 2.5 miles east of Grapevine Canyon, for an approximate length of 24 miles. The Pleito Fault is divided into two sections, the Western and Eastern Pleito sections. The eastern section is approximately 9 miles long and trends N69 E versus N85 E for the whole fault. This fault segment is located approximately 37 miles west of the central portion of the project site. Traces of the eastern section of the Pleito Fault are delineated by a nearly continuous north-facing scarp that coincides in most places with the northern front of the San Emigdio Mountains. In Grapevine Canyon, the vertical separation across the latest Pleistocene to early Holocene alluvial fan surface is about 18 feet. East of Grapevine Canyon, the Eastern Pleito section is concealed by a massive landslide complex or the fault coincides with the toe of the landslide (Bryant, 2000b). Holocene thrust fault displacements have been documented along the Eastern Pleito section with a Holocene slip rate of 1.3 to 1.4 mm/year for the past 15,000 years. The net slip rate for the past 100,000 years is 0.3 to 2.0 mm/year. Based on observed average dip-slip displacement of 0.77 meter and a Holocene slip rate of 1.3 to 1.4 mm/year, geoscientists have inferred a recurrence interval of 500 to 600 years. One and possibly two events have occurred between 500 and 1,600 years ago (Bryant, 2000b). The Pleito Fault is a component of the Pleito-Wheeler Ridge thrust-fault system that forms the boundary between the San Emigdio Mountains (part of the Transverse Ranges geomorphic province) and the southern San Joaquin Valley. The Pleito-Wheeler Ridge thrust fault system consists of the south-dipping Pleito Fault and the south-dipping, predominantly blind Wheeler Ridge thrust fault located a few miles to the north. Cumulative dip-slip displacement on the Pleito-Wheeler Ridge fault system is about 4.3 miles during the past 5.0 million years. It has been reported that the assigned Holocene slip rate of 1.3 to 1.4 mm/yr is not sufficient to account for the geomorphic relief of the San Emigdio Mountains that has been produced during the past 2.5 to 3 million years. Geoscientists have concluded that the active trace of the Pleito Fault zone has migrated northward (basin-ward) and that a significant portion of slip occurs on the Wheeler Ridge fault (Bryant, 2000b). San Gabriel Fault The San Gabriel Fault extends southeastward from the Ridge Basin to the western San Gabriel Mountains, where most geoscientists recognize a north and a south branch. Regional geologic studies of the San Gabriel Fault have led to the conclusion that it is the ancestral segment of the San Andreas Fault within the Transverse Ranges. As a result, most geoscientists have proposed that the San Gabriel Fault at depth continues northwestward beneath the thrust sheets to join the San Andreas Fault. Although abandoned as the primary dislocation between plate boundaries in Pliocene time, offset geologic units indicate rightlateral slip on the order of 0.6 mile along the San Gabriel Fault within Holocene time (between Saugus and Castaic, California). However, a total right-lateral displacement of IS SAC/421269/

7 26 miles (half on each of the branches) for the entire fault is reported in the geologic literature. Evidence of dip slip is also documented, but is likely only localized. The fault trace extends for approximately 83 miles (SCEC, 2011) and is located approximately 33.6 miles south of the project site. It has been suggested that the San Gabriel Fault is a possible source of the May 19, 1893, Mw 5.75 Pico Canyon earthquake (USGS, 2011). According to the SCEC (2011), the slip rate for this fault ranges between 1 to 5 mm/year and the interval between major ruptures is unknown. Numerous historic earthquakes have affected the Mojave Desert region where the project site is located. Table 1 below provides a summary of major known seismic events. TABLE 1 Significant Historic Earthquakes in the Immediate Vicinity of the Alta Infill II Wind Energy Project Earthquake a, b Date c Maximum Moment Magnitude (Mw) c Site Acceleration (g) c Estimated Modified Mercalli Intensity c Approximate Site-to-Source Distance (miles) c, d Unnamed November 27, VII 23.2 Bakersfield July 22, VI 10.7 Kern County a, b July 23, VI 26.7 Arvin/Tehachapi July 21, VII 34.8 Kern County a, b July 25, VI 21.9 Kern County a, b August 26, VII 3.9 Unnamed May 1, VI 8.7 Unnamed June 22, V 8.9 Unnamed June 10, V 19.8 Unnamed July 11, V 23.5 Unnamed December 31, VI 8.2 a USGS, CGS, Blake, d Distance measured from the central portion of the project site. 3.0 Regulatory Setting Geologic resources and geotechnical hazards are governed primarily by local jurisdictions. The conservation elements and seismic safety elements of city and county general plans contain policies for the protection of geologic features and avoidance of hazards. In addition, the project proponent must comply with other applicable State of California and local applicable statutes, regulations and policies. Relevant and potentially relevant statutes, regulations and policies are discussed below. IS SAC/421269/

8 3.1 State of California The Alquist-Priolo Earthquake Fault Zoning Act of 1972 The Alquist-Priolo Earthquake Fault Zoning Act of 1972, (formerly the Special Studies Zoning Act) regulates development and construction of buildings intended for human occupancy to avoid the hazard of surface fault rupture. In accordance with this law, the CGS maps active faults and designates EFZs along mapped faults. This Act groups faults into categories of active, potentially active, and inactive. Historic and Holocene age faults are considered active, Late Quaternary and Quaternary age faults are considered potentially active, and pre-quaternary age faults are considered inactive. These classifications are qualified by the conditions that a fault must be shown to be sufficiently active and well defined by detailed site-specific geologic explorations in order to determine whether building setbacks should be established. Any project that involves the construction of buildings or structures for human occupancy, such as an operation and maintenance building, is subject to review under the Alquist-Priolo Earthquake Fault Zoning Act, and any structures for human occupancy must be located at least 50 feet from any active fault. The Seismic Hazards Mapping Act of 1990 In accordance with Public Resources Code, Chapter 7.8, Division 2, the California Department of Conservation, Division of Mines and Geology (now the California Geological Survey) is directed to delineate Seismic Hazard Zones. The purpose of the Act is to reduce the threat to public health and safety and to minimize the loss of life and property by identifying and mitigating seismic hazards, such as those associated with strong ground shaking, liquefaction, landslides, other ground failures, or other hazards caused by earthquakes. Cities, counties, and state agencies are directed to use seismic hazard zone maps developed by CGS in their land-use planning and permitting processes. In accordance with the Seismic Hazards Mapping Act, site-specific geotechnical investigations must be performed prior to permitting most urban development projects within seismic hazard zones. The California Building Code (California Building Standards Commission [CBCS], 2010) The State of California provides minimum standards for building design through the California Building Code (CBC). The latest version of the CBC is the 2010 version and is based on the Uniform Building Code (UBC), which is used widely throughout the United States (generally adopted on a state-by-state or district-by-district basis), and has been modified for conditions within California. In accordance with the CBC, a grading permit is required if more than 50 cubic yards of soil is moved during implementation of a proposed project. Chapter 16 of the CBC contains definitions of seismic sources and the procedure used to calculate seismic forces on structures. 3.2 Kern County Construction and operation of the proposed project is subject to policies and regulations contained within General and Specific Plans including the Kern County General Plan (County of Kern, 2007), Mojave Specific Plan (County of Kern, 2003), Soledad Mountain Elephant Butte Specific Plan (County of Kern, 1973), the Kern County Zoning Ordinance, and the Kern County Code of Building Regulations, which include policies for the avoidance of geologic hazards and/or the protection of unique geologic features, as well as for the preservation of paleontological resources. The policies, goals, and implementation IS SAC/421269/

9 measures in the Kern County General Plan for geology and soils applicable to the project are provided below. The Kern County General Plan contains additional policies, goals, and implementation measures that are more general in nature and are not specific to development such as the proposed project. Kern County General Plan (County of Kern, 2007) Section 1.3 Physical and Environmental Constraints Policy 1. Kern County will ensure that new developments will not be sited on land that is physically or environmentally constrained (Map Code 2.1 [Seismic Hazard], Map Code 2.2 [Landslide], Map Code 2.3 [Shallow Groundwater], Map Code 2.5 [Flood Hazard], Map Codes from , Map Code 2.10 [Nearby Waste Facility], and Map Code 2.11 [Burn Dump Hazard]) to support such development unless appropriate studies establish that such development will not result in unmitigated significant impact. Policy 6. Regardless of percentage of slope, development on hillsides will be sited in the least obtrusive fashion, thereby minimizing the extent of topographic alteration required and reducing soil erosion while maintaining soil stability. Policy 7. Ensure that effective slope stability, wastewater drainage, and sewage treatments in areas with steep slopes are adequate for development. Section 1.9 Resource (Land Use, Open Space, and Conservation Element) Policy 17. Lands classified as Mineral Resource Zone 2 (MRZ-2), as designated by the State of California, should be protected from encroachment of incompatible land uses. Section 4.3 Seismically Induced Surface Rupture, Ground Shaking, and Ground Failure (Safety Element) Policy 1. The County shall require development for human occupancy to be placed in a location away from an active earthquake fault in order to minimize safety concerns. Section 4.5 Landslides, Subsidence, Seiche, and Liquefaction (Safety Element) Policy 1. Determine the liquefaction potential at sites in areas of shallow groundwater (Map Code 2.3) prior to discretionary development and determine specific mitigation to be incorporated into the foundation design, as necessary, to prevent or reduce damage from liquefaction in an earthquake. Policy 2. Route major lifeline installations around potential areas of liquefaction or otherwise protect them against significant damage from liquefaction in an earthquake. Policy 3. Reduce potential for exposure of residential, commercial, and industrial development to hazards of landslide, land subsidence, liquefaction, and erosion. Section 5 Energy Element Policy 2. All wind energy development shall be subject to the development standards of Kern County Zoning Ordinance. IS SAC/421269/

10 Soledad Mountain-Elephant Butte Specific Plan (County of Kern, 1973) 5. Item Hazard Areas Recommendation. No permanent residence or structure or temporary residence or structure shall be allowed on slopes of 40% or more within lands subject to inundation or ponding, unless structure methods are employed to eliminate such hazards. Mojave Specific Plan (County of Kern, 2003) Section I Land Use Element Goal. Kern County will not permit new developments to be sited on land which is environmentally unsound to support such development. Objective 3.5. Protect the public from natural hazards including flooding and earthquakes. Policy Proposed projects within the seismic hazard overlay shall meet all requirements of the Kern County Building Code. Policy Proposed residential and commercial projects within the seismic hazard, steep slope or landslide overlay should be encouraged to develop using the cluster option. Section V Conservation Goal 1. Conserve known areas of mineral resources by limiting encroachment of incompatible urban uses. Section IX Seismic Safety Element Goal 1. Protect structures from potential damage caused by earthquakes. Goal 2. Promote awareness of potential flood and geologic hazards. Kern County Zoning Ordinance (Title 19 of the Ordinance Code of Kern County) Chapter Wind Energy Combining District The Wind Energy Combining District contains the following sections applicable to geology and soils: Section (A): All necessary building and grading permits shall be obtained from the Kern County Planning Department. For construction and permit purposes, all wind turbine generator towers shall conform to the regulations of the applicable seismic zone of the Uniform Building Code (UBC) and the applicable ground shaking zone. Section (K): Prior to issuance of any grading permit, a plan for the mitigation of potential soil erosion and sedimentation shall be prepared by a California registered civil engineer or other professional and submitted for the approval by the Director of the Engineering and Survey Services Department. Section (L): A minimum of on-site roadways shall be constructed. Temporary access roads utilized for initial machine installation shall be revegetated to a natural IS SAC/421269/

11 condition after completion of machine installation. The project proponent shall submit a plan of all proposed roads, temporary and permanent, for approval by the Planning Director prior to the issuance of any building permits. Section (M): Construction of any slopes steeper than four to one (4:1) shall be prohibited unless specifically authorized by the Kern County Planning Department and mitigation is provided. Section (N): Soil erosion and sedimentation control plan, including revegetation plan, as provided in Section (grading permits only). Kern County Code of Building Regulations (Title 17 of the Ordinance Code of Kern County) All construction in Kern County is required to conform to the Kern County Building Code (Chapter 17.08, Building Code, of the Kern County Code of Regulations). Kern County has adopted the Uniform Building Code (UBC), 2007 Edition, with some modifications and amendments. The entire County is in Seismic Zone 4, a designation previously used in the UBC to denote the areas of highest risk to earthquake ground motion. California has an Unreinforced Masonry program that details seismic safety requirements for Zone 4. Seismic provisions associated with Seismic Zone 4 have been adopted. Chapter Kern County Grading Code. The purpose of the Kern County Grading Code is to safeguard life, limb, property and the public welfare by regulating grading on private property. All requirements of the Kern County Grading Code will be applied during implementation of the proposed project. All required grading permit(s) shall be obtained prior to commencement of construction activities. Sections of the Grading Code that are particularly relevant to geology and soils are provided below. Section Erosion control. A. Slopes. The faces of cut and fill slopes shall be prepared and maintained to control against erosion. This control may consist of effective planting. The protection for the slopes shall be installed as soon as practicable and prior to calling for final approval. Where cut slopes are not subject to erosion due to the erosion-resistant character of the materials, such protection may be omitted. B. Other Devices. Where necessary, check dams, cribbing, riprap or other devices or methods shall be employed to control erosion and provide safety. C. Temporary Devices. Temporary drainage and erosion control shall be provided as needed at the end of each work day during grading operations, such that existing drainage channels would not be blocked. Dust control shall be applied to all graded areas and materials and shall consist of applying water or another approved dust palliative for the alleviation or prevention of dust nuisance. Deposition of rocks, earth materials or debris onto adjacent property, public roads or drainage channels shall not be allowed. IS SAC/421269/

12 Section Grading inspection. A. General. All grading operations for which a permit is required shall be subject to inspection by the building official. Professional inspection of grading operations and testing shall be provided by the civil engineer, soils engineer and the engineering geologist retained to provide such services in accordance with Subsection (E) for engineered grading and as required by the building official for regular grading. B. Civil Engineer. The civil engineer shall provide professional inspection within such engineer s area of technical specialty, which shall consist of observation and review as to the establishment of line, grade and surface drainage of the development area. If revised plans are required during the course of the work they shall be prepared by the civil engineer. C. Soils Engineer. The soils engineer shall provide professional inspection within such engineer s area of technical specialty, which shall include observation during grading and testing for required compaction. The soils engineer shall provide sufficient observation during the preparation of the natural ground and placement and compaction of the fill to verify that such work is being performed in accordance with the conditions of the approved plan and the appropriate requirements of this chapter. Revised recommendations relating to conditions differing from the approved soils engineering and engineering geology reports shall be submitted to the permittee, the building official and the civil engineer. D. Engineering Geologist. The engineering geologist shall provide professional inspection within such engineer s area of technical specialty, which shall include professional inspection of the bedrock excavation to determine if conditions encountered are in conformance with the approved report. Revised recommendations relating to conditions differing from the approved engineering geology report shall be submitted to the soils engineer. E. Permittee. The permittee shall be responsible for the work to be performed in accordance with the approved plans and specifications and in conformance with the provisions of this Code, and the permittee shall engage consultants, if required, to provide professional inspections on a timely basis. The permittee shall act as a coordinator between the consultants, the contractor and the building official. In the event of changed conditions, the permittee shall be responsible for informing the building official of such change and shall provide revised plans for approval. F. Building Official. The building official may inspect the project at the various stages of the work requiring approval to determine that adequate control is being exercised by the professional consultants. G. Notification of Noncompliance. If, in the course of fulfilling their responsibility under this chapter, the civil engineer, the soils engineer, or the engineering geologist finds that the work is not being done in conformance with this chapter or the approved grading plans, the discrepancies shall be reported immediately in writing to the permittee and to the building official. Recommendations for corrective measures, if necessary, shall also be submitted. IS SAC/421269/

13 H. Transfer of Responsibility. If the civil engineer, the soils engineer, or the engineering geologist of record is changed during the course of the work, the work shall be stopped until: 1. The civil engineer, soils engineer, or engineering geologist, has notified the building official in writing that they will no longer be responsible for the work and that a qualified replacement has been found who will assume responsibility. 2. The replacement civil engineer, soils engineer, or engineering geologist notifies the building official in writing that they have agreed to accept responsibility for the work. 4.0 Affected Environment 4.1 Ground Rupture Ground rupture on a fault is caused when an earthquake produces fault displacement at the surface. The nearest area designated as an Alquist-Priolo EFZ is along the Garlock Fault, which extends through the northern portion of the project site. Portions of the project site and proposed transmission lines cross this principal EFZ. Ground rupture and ground failure could occur within 500 feet of an active trace of the Garlock Fault. The potential for ground rupture to occur at the site is high in these areas. 4.2 Seismic Shaking Seismic waves passing through the earth generated by earthquakes cause the ground to shake. Severe ground shaking is the most widespread and destructive aspect of earthquakes and the degree of ground shaking is a function of the distance from earthquake epicenter, magnitude of the earthquake, site-specific soil types, among other factors. The project area has experienced seismic activity with strong ground motion during past earthquakes, and it is likely that strong earthquakes causing seismic shaking will occur in the future. The significant geologic hazard at the project site is strong ground shaking due to an earthquake. Ground shaking from a Mw 8.0 earthquake could occur within an approximately 50-mile radius of the site (SEI, 2008). As stated previously, the controlling fault affecting the project site and proposed transmission line is the Garlock Fault. The Garlock Fault is a near vertical shear zone with a slip rate of approximately 6 mm/year with a maximum credible earthquake event of 7.3. A geotechnical evaluation was performed at the existing Alta Infill Wind Energy Project site (currently under construction) located adjacent to the west of the southern portion of the project site. The evaluation determined that the Garlock Fault was capable of generating a peak bedrock acceleration (PBA) of 0.55g (SEI, 2008) based on the Maximum Credible Earthquake event of 7.3 (SEI, 2008; WGECP, 2007). It is expected that the PBA would be similar at the project site, but, given the proximity to the Garlock Fault EFZ, this should be further assessed from site-specific geotechnical evaluation for the project site. IS SAC/421269/

14 4.3 Liquefaction During strong ground shaking, loose, saturated, cohesion-less soils can experience a temporary loss of shear strength and act as a fluid. This phenomenon is known as liquefaction. Liquefaction is dependent on depth to water, grain size distribution, relative density of the soils, degree of saturation, and intensity and duration of the earthquake. The potential hazard associated with liquefaction would be seismically induced settlement and possible surface displacement from lateral spreading. The lithology at the project site and proposed transmission line route predominantly consists of dense decomposed granitic material and rock. In addition, depth to groundwater generally is about 50 feet or deeper below ground surface (County of Kern, 2003). The project area has not been identified by Kern County as an area that is subject to liquefaction hazards (County of Kern, 2007). The potential for liquefaction to be a hazard at the site and along the transmission line is considered to be negligible. 4.4 Slope Stability Slope stability or mass wasting depends on steepness of the slope, underlying geology, surface soil strength, and moisture in the soil. Significant excavating, grading, or fill work during construction might introduce slope stability or mass wasting hazards at the project site. The project site, which is located in the foothills of the Tehachapi Mountains, may experience seismically induced landslides if/when ground motion causes unstable or steeply sloping and loosely aggregated soils and/or rocks to mobilize under the force of gravity. As described above, the project area has not been mapped by the County of Kern as an area that is susceptible to landslide potential (County of Kern, 2007). As a result, the potential for seismically induced slope failure, including ridgetop spreading, to occur is considered low. 4.5 Subsidence/Settlement Subsidence or settlement can be a natural or man-made phenomenon resulting from tectonic movement, consolidation, fluid removal (oil, gas, or water), or rapid sedimentation or oxidation of organic-rich soil. Organic-rich soils are not typically present in the project site. Based on a review of the geologic setting in the project site area, the lithology present in the subsurface appears to have a low potential for settlement or subsidence. 4.6 Expansive Soils Expansive soils shrink and swell with wetting and drying. The shrink-swell capacity of expansive soils can result in differential movement beneath foundations. The soils present at the site and along the proposed transmission line route are primarily sands, gravels, and gravely clay loams that may exhibit some degree of shrink and swell characteristics. Soils mapped in the project area include the Cajon, Arizo, Pajuela, Whitewolf, and Garlock Neuralia units. These soil units have been characterized as exhibiting a low shrink-swell potential (USDA, 1981). As a result, the potential for expansive soils to be present at the site is low. IS SAC/421269/

15 4.7 Geological Resources of Recreational, Commercial, or Scientific Value According to the maps of the State of California Division of Oil, Gas and Geothermal Resources (DOGGR, 2010), no oil or gas well fields or reserves occur in the project vicinity. According to the Mineral Land Classification Map for Southeast Kern County, part of the project site is within a mapped MRZ-3b (Au) area and is also adjacent to areas mapped as MRZ-2b along the southeast side of the project. Mineral resources located in this area include gold resources (CDMG, 1999). These classifications are defined as follows: MRZ-2b Areas underlain by mineral deposits where geologic data indicate that significant inferred resources are present. MRZ-3b Areas underlain by inferred mineral deposits, but contain an undetermined mineral resource significance. Several former or currently operating mines occur in the surrounding project vicinity. A detailed analysis for these mines was performed in March 2009 for the Golden Queen Mining Co. and is documented in the SRK Consulting report for the Soledad Mountain Project (SRK, 2006). At the project site, information obtained from the Kern County Engineering and Survey Services Department and the California Division of Mines and Geology indicated no active or abandoned mines on the project property (LAC, 2009). Mineral resource operations in proximity to the project site include: The California Portland Cement Company (CPC) Mojave Quarry and Creal Deposits (MRZ-2a) is approximately 3 miles west of the project site just south of Oak Creek Road. The CPC plant has been in production since The CPC produces limestone and accessory minerals for use in making Portland cement. Drill-indicated reserves at the plant are sufficient to maintain the current production level for more than 40 years. The CPC mines and plant are accessed via Oak Creek Road. Soledad Mountain Area (MRZ-2a/b, MRZ-3a) The Soledad Mountain Area is located approximately 1 mile east and south of the project site and contains 25 historical mines and prospects. The area also has two active mines, the Standard Hill Mine (California Mine ID no ) and the Golden Queen Mine (California ID no ), the latter of which is currently being converted from a gold mine to aggregate production. The Soledad Mountain gold resource area is accessed via State Route 14 and Silver Queen Road. Middle Butte Area (MRZ-2a/b, MRZ-3a/b) The Middle Butte Area is located approximately 2.5 miles south of the project site and contains 11 historic mines and prospects. The area also has one active mine (California Mine ID no ), which is undergoing reclamation. The Middle Butte gold resource area is accessed via Backus Road and Tehachapi Willow Springs Road. IS SAC/421269/

16 5.0 Environmental Impacts and Recommendations Potential effects from construction and operation of the project (including the proposed transmission line route) on geologic resources and risks to life and property from geologic hazards are presented in the following section. Adverse effects in terms of geological hazards and soil resources could occur when a proposed action: Exposes people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: Rupture of a known earthquake fault (Alquist-Priolo Fault Zone) Strong seismic ground shaking Seismic-related ground failure, including liquefaction. Is located on a geologic unit or soil that is unstable or that would become unstable as a result of the project, and potentially result in on- or offsite landslide, lateral spreading, subsidence, liquefaction, or collapse. Results in the loss of availability of a known mineral resource that would be of value to the region and the residents of the state. Results in the loss of availability of a locally important mineral resource recovery site delineated on a local plan, specific plan, or other land use plan. 5.1 Geologic Hazards There is potential for moderate to severe seismic ground shaking or surface fault rupture to affect the project site in the event of a large magnitude earthquake occurring on fault segments near the project, particularly as related to the Garlock Fault EFZ (extending through the northern portion of the project site). Given that portions of the project site cross the EFZ, damage to wind turbines and project facilities could occur from an earthquake event that causes ground rupture occurring on the Garlock EFZ or other fault segments near the project and in the region. Under the Alquist-Priolo Earthquake Fault Zoning Act, no commercial or industrial structures may be located within an EFZ delineated on an official map unless geologic investigations are conducted at the site. Adherence to the California Building Code (CBC) standards will reduce the potential for structural damage to project facilities to the extent possible. However, given the proximity of the project to the Garlock Fault EFZ, and the potential regional seismic activity, structural damage could occur (CGS, 2010). As a result, seismic hazards are considered potentially significant and mitigation will be required. Seismic and ground rupture hazards will be minimized by conformance with the recommended seismic design criteria of the 2010 CBC (CBSC, 2010). Soil types at the project site predominantly consist of sand, gravel, cobbles, and gravelly clay loams. The potential for erosion depends on such factors as soil texture and content, surface roughness, vegetative cover, soil moisture, wind, and slope grade and length. According to Kern County hazard mapping (County of Kern, 2003 and 2007), the probability of liquefaction, mass wasting, or subsidence at the project site and along the transmission line route is low to negligible. However, during construction of the proposed project, destabilization of natural or constructed slopes could occur as a result of excavation and/or IS SAC/421269/

17 grading operations required for installation of project infrastructure or facilities. Unmapped landslides and areas of localized slope instability may also be present. Excavation operations associated with turbine foundation construction and grading operations for temporary and permanent access roads and construction activities in areas of hilly or sloping terrain could result in slope instability, landslides, soil creep, or debris flows. Soil types at the project site include those that have low shrink-swell potential. The presence of expansive soils should be evaluated further in the geotechnical evaluation for the project. If expansive soils are identified to be present, they can be mitigated by removal or blending with non-expansive soils. Geotechnical studies conducted during final siting of project facilities should identify sitespecific geologic conditions to be considered in facilities siting. Based on the study, project facilities (turbines, warehouse, substations, and transmission poles) should be placed upon bedrock hill tops or ridges that are not subject to slope failure or loss of strength. The areas may also be graded to minimize the potential for movement. In summary, compliance with the 2010 CBC requirements will reduce the exposure of people to the risks associated with large seismic events and ground rupture to less-thansignificant levels. In addition, major structures will be designed to withstand the strong ground motion of a Design Basis Earthquake, as defined by the 2010 CBC. By complying with CBC standards, and with implementation of the mitigation measures identified below, impacts associated with geologic hazards will be less than significant. 5.2 Geological Resources While the project site is within a mapped MRZ-3b (Au) area, the proposed project would not result in a loss of availability of a known mineral resource that would be of value to the region and the residents of the state. In addition, the project would not result in the loss of availability of a locally important mineral resource recovery site delineated on a local plan, specific plan, or other land use plan. No impacts on geologic resources are anticipated. 5.3 Mitigation Measure To address potential impacts related to geologic hazards, the mitigation measures identified for the approved Alta Oak Creek Mojave (AOCM) Project will be incorporated, where applicable, to the project. AOCM mitigation measures are incorporated by reference and are listed below. AOCM Mitigation Measures through require design measures to avoid fault traces during construction, as well as minimization of horizontal and vertical displacement. AOCM Mitigation Measures through reduce potential project impacts and cumulative impacts involving substantial soil erosion or the loss of topsoil to below the level of significance. 6.0 References Blake, T EQSEARCH V Thomas F. Blake Computer Services and Software, Thousand Oaks, CA. IS SAC/421269/

18 Bryant, W. A., compiler. 2000a. Fault number 69a, Garlock fault zone, Western Garlock section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, Accessed January Bryant, W. A., compiler. 2000b. Fault number 76b, Pleito fault zone, Eastern Pleito section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, Accessed on January 11, Bryant, W. A., and M. M. Lundberg, compilers. 2002a. Fault number 1g, San Andreas fault zone, Cholame-Carrizo section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, Accessed on January 11, Bryant, W. A., and M. M. Lundberg, compilers. 2002b. Fault number 1h, San Andreas fault zone, Mojave section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, Accessed January California Building Standards Commission (CBSC) California Building Code, California Code of Regulations. Based on 2010 International Building Code. California Division of Oil, Gas, and Geothermal Resources (DOGGR) Oil and Gas Field Maps. Available online: Website accessed May California Division of Mines and Geology (CDMG) Mineral Land Classification of Southeastern Kern County, CA. Open-File Report California Geological Survey (CGS) Fault Activity Map of California. Available online: Website accessed July County of Kern Specific Plan for Soledad Mountain Elephant Butte & Vicinity South of Mojave. March. Available online: County of Kern Mojave Specific Plan. October. Available online: County of Kern Kern County General Plan, Safety Element. March. Available online: Dibblee, Jr., T.W., and A. H. Warne Geologic Map of the Cummings Mountain Quadrangle, Kern County, California, United States Geological Survey, Miscellaneous Geologic Investigation Map I-611, Scale of 1:62,500. Jenkins, O. P. and Oakeshott, G. B., 1955, Earthquakes in Kern County California During 1952: California Division of Mines and Geology, Bulletin 171, 282 Pages. Jennings, Charles Fault Activity Map of California and Adjacent Area. Department of Mines and Geology. Compiled by Charles Jennings. IS SAC/421269/

19 LandAmerica Assessment Corporation (LAC) Environmental Site Assessment Report, BLM Sun Creek, Parcels ; ; Kern County, California. February. Leighton Consulting, Inc Geotechnical Draft Existing Conditions Report, Greater Tehachapi Area Specific Plan, Kern County, California. Prepared for RGP Planning and Development Services. July. Petersen, M. D., W. A. Bryant, C. H. Cramer, T. Cao, M. S. Reichle, A. D. Frankel, J. J. Lienkaemper, P. A. McCroy, and D. P. Schwartz Probabilistic Seismic Hazard Assessment for the State of California, California Division of Mines and Geology, Open File Report 96-08Soils Engineering Inc (SEI), Limited Feasibility Level Geological and Geotechnical Evaluation for the Proposed Alta-Oak Creek Mojave Project, Near Mojave, California. October. Soils Engineering Inc (SEI), Limited Feasibility Level Geological and Geotechnical Evaluation for the Proposed Alta-Oak Creek Mojave Project, Near Mojave, California. October. Southern California Earthquake Center (SCEC) Working Group on California Earthquake Probabilities, Seismic Hazards in Southern California: Probable Earthquakes, 1994 to 2024: Bulletin of the Seismological Society of America, Volume 85, Number 2, Pages Southern California Earthquake Center (SCEC) Alphabetical Fault Index, accessed on January SRK Consulting (SPK) NI Technical Report. Soledad Mountain Project. Mojave, CA. March. United States Department of Agriculture (USDA) Soil Survey of Kern County, California, Southeastern Part. Soil Conservation Service. United States Geological Survey (USGS) California Earthquake History 1769 Present, accessed on January Working Group on California Earthquake Probabilities (WGECP) Fault Magnitude and Rate Data Spreadsheet. Uniform California Earthquake Rupture Forecast, Version 2. Accessed online at April IS SAC/421269/

20

21 IS BAO