Chapter Geology and Soils

Transcription

1 Chapter Geology and Soils Introduction This section provides technical information to the proposed Project site s geology and soil characteristics and addresses the potential impacts from seismic hazards, seismicrelated ground failure, soil erosion, and expansive and unstable soils associated with construction and operation of the proposed Project. The geology and soils section describes the existing conditions of the Project site, the regulatory setting, and discusses the possible impacts from Project implementation as well as Project mitigation measures to reduce these impacts. The discussion in this chapter is based on information prepared by various consultants including EMCON Associates (1989 and 1991) and T.J. Cross Engineers (2004). In 2003, Geosyntec Consultants conducted an investigation of faulting potential at the Ridgecrest RSLF. In 2009, AMEC Geomatrix, Inc. prepared a water quality (AMEC, 2009a) and a water supply (AMEC, 2009b) assessment for the Ridgecrest RSLF (Appendix K and Appendix L, respectively). In 2010, Golder Associates (Golder) performed a study to document seismic stability and leachate generation issues related to the proposed vertical expansion at the Ridgecrest Recycling and Sanitary Landfill (Ridgecrest RSLF) (Appendix J). Based upon the review of the field investigations and analysis of the information presented in this section, no significant impacts are expected to occur as a result of the proposed Project. Concerns with regard to geology and soil impacts in response to the Notice of Preparation have been addressed in this section. The environmental analysis contained herein indicates adverse impacts upon the environment would be less than significant in regards to geologic conditions at the site Environmental Setting Geologic Setting The Ridgecrest RSLF is located in the southern portion of Indian Wells Valley. Indian Wells Valley is located in the southwestern corner of the Basin and Range geomorphic province, which is bordered by the Sierra Nevada province to the west and the Mojave Desert province to the south. The Basin and Range province is characterized by extensional tectonics, which have resulted in the formation of numerous horsts (structural range) and grabens (structural depression) throughout the region. Indian Wells Valley is a graben bordered by the Sierra Nevada to the west, the Argus Range to the east, the Coso Range to the north, and the El Paso Mountains to the south and southwest. The valley is a closed topographical depression and drainage from the surrounding hills and mountains is directed inward toward China Lake, an extensive desert playa formed at the east end of the valley (AMEC, 2009b). Draft Environmental Impact Report 4.6-1

2 Previous authors have grouped the geologic units of the Indian Wells Valley into two main categories (consolidated rocks and unconsolidated sediments) based on their capacity to contain and yield water (Dutcher and Moyle, 1973). Consolidated Rocks: The consolidated rocks include pre-tertiary basement complex, indurated Tertiary continental deposits, and Tertiary to Quaternary volcanic rocks. The basement complex consists of pre-tertiary metamorphic and igneous rocks underlying the valley and composing the surrounding hills and mountains (Berenbrock and Martin, 1991). The bedrock complex is unconformably overlain by poorly sorted and indurated continental deposits (Kunkel and Chase, 1969). These continental deposits are considered non-water bearing based on seismic refraction studies and electric logs of wells penetrating these rocks (Berenbrock and Martin, 1991). These rocks are believed to be correlative with the Ricardo and Goler Formations mapped by Dibblee in the northeastern El Paso Hills (Kunkel and Chase, 1969). In some locations, the continental deposits are unconformably overlain by Tertiary to Quaternary volcanic rocks derived from the Coso Range and Black Mountain Basalt (Kunkel and Chase, 1969; Berenbrock and Martin, 1991). Unconsolidated Sediments: Unconsolidated sediments consist of older alluvium, older lacustrine deposits, alluvial fan deposits, younger alluvium, younger lacustrine deposits, playa deposits, and aeolian deposits (Kunkel and Chase, 1969). These sediments are about 2,000 feet thick in the west-central portion of the valley (Berenbrock and Martin, 1991). Older and younger alluvium and fan deposits are typically located around the northern, western, and southern margins and the west-central portion of the valley. The older and younger lacustrine deposits are typically encountered in the eastern and east central portions of the valley (Kunkel and Chase, 1969; Berenbrock and Schroeder, 1994). The lithofacies of the alluvium and lacustrine deposits form laterally gradational contacts where the two units meet. Older alluvium unconformably overlies either the continental deposits or the basement complex and is considered early to middle Pleistocene in age (Kunkel and Chase, 1969). These sediments consist of more than 800 feet of lenticular beds of coarse sand and pebble-boulder conglomerates interbedded with cross-bedded silt and fine to coarse sand and gravel (Kunkel and Chase, 1969). The older alluvium is laterally interbedded with the older lacustrine deposits. Older lacustrine deposits consist of silt and silty white clay interbedded with thin beds of impure limestone, calcareous sandstone, conglomerate, and non-indurated sand (Kunkel and Chase, 1969). Older lacustrine sediments are sub-aerially exposed in some portions of Indian Wells Valley at elevations between 2,230 and 2,750 feet (Kunkel and Chase, 1969). These sediments generally occur beneath the east side of the valley, grading laterally into the older alluvium, and in some areas conformably overlying the older alluvium (Kunkel and Chase, 1969). Alluvial fan deposits have formed around the basin margins adjacent to the mountain fronts. They consist of heterogeneous mixtures of silt, angular sand, gravel, cobbles, and boulders of middle to late Pleistocene to Holocene age and grading laterally into younger and older alluvium (Kunkel and Chase, 1969). Draft Environmental Impact Report 4.6-2

3 Younger alluvium consists of lenticular beds of clay, silt, sand, and gravel derived mostly from the Sierra Nevada and to a lesser extent the other surrounding mountains and hills (Kunkel and Chase, 1969). These sediments unconformably overlie the older alluvium and are considered middle to late Pleistocene to Holocene age. The unconformity between the older and younger alluvium occurs at elevations of 1,800 to 2,000 feet above mean sea level (MSL) in the area of the Ridgecrest RSLF (Berenbrock and Martin, 1991). This contact throughout the valley was well delineated in seismic surveys conducted by R.T. Zbur (Zbur, 1963) but is generally indistinguishable in well logs (Dutcher and Moyle, 1973). The younger alluvium grades laterally into younger lacustrine deposits of prehistoric China Lake (Kunkel and Chase, 1969). Younger lacustrine deposits are composed primarily of beds of clay and micaceous silt. These beds are occasionally interbedded with thin beds of sand and sandy silt. Calcareous cemented gravel and calcareous tufa have also been encountered in the younger lacustrine deposits (Kunkel and Chase, 1969). Holocene playa deposits associated with China Lake overlie the younger lacustrine deposits. Playa deposits consist of gray silt; yellow, green, and blue plastic clays; and occasional sand lenses (Kunkel and Chase, 1969). Alkali and salt crusts are common within the playa deposits. The demarcation of the contact between the younger lacustrine and playa deposits is unclear (Kunkel and Chase, 1969). Soils Four soil series that have been identified within one mile of the site are the Cajon, Neuralia, Helendale, and Cerro Coso (EMCON, 1989). These soils are deep, well drained, and derived primarily from granitic source rocks. These soils are found on alluvial fans, plains, and terraces. The Cerro Coso soils are sodic. Material at the surface consists of sand, gravelly sand, and sandy gravel derived principally from a granitic source. Outcrops occurring in the pit walls of the landfill indicate that bedding is horizontal to slightly north-dipping and that beds vary from tabular to U-shaped bodies ranging in thickness from two to seven feet. It is interpreted that these sediments were deposited in channels on alluvial fans by intermittent streams flowing from the surrounding areas (see Figure 4.6-1). Cover soil for landfill operations is currently excavated from the onsite borrow pit and is sufficient to provide interim soils during the vertical expansion. Once the soils from the current borrow area are exhausted, the eastern buffer area around the landfill will be used to provide soils for the remainder of the landfill operations, as well as for final closure cover. For a discussion of groundwater quality and potential impacts, please refer to Chapter 4.9, Hydrology and Water Quality. Draft Environmental Impact Report 4.6-3

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5 Geologic Hazards Faults: Kern County is located in one of the more seismically active areas of California and may, at any time, be subject to moderate to severe ground shaking. This hazard exists because elastic strains that accumulate deep within the earth become so great that the rock can no longer be contained. When this happens, movement along a fracture zone occurs, releasing enormous amounts of energy (Kern County, 2004a). Kern County has experienced the effects of large, nearby earthquakes in recent historic times. In 1857, a quake with an estimated magnitude of 7.9 occurred on the San Andreas Fault approximately 80 miles southwest of the landfill. The Great Earthquake of 1872 occurred on the Owens Valley Fault, with a magnitude of 7.8, approximately 78 miles northwest of the landfill (T.J. Cross Engineers, 2004). In 1952, a quake with a magnitude of 7.7 occurred on the White Wolf Fault approximately 82 miles southwest of the landfill. The Ridgecrest general area, like most of Kern County, is considered to be seismically active. There are no identified active or potentially active faults underlying the site or adjacent areas. In 2003, GeoSyntec Consultants conducted an investigation of faulting potential at the Ridgecrest RSLF. A 1976 Kern County Seismic Hazard Atlas map (at a scale of 1:24,000) showed an unnamed north-striking fault transecting the east-central portion of the landfill (GeoSyntec Consultants, 2003). This fault was classified as offsetting Pleistocene (approximately 1.7 million years before present) or younger soils. The Pleistocene or younger age includes the Holocene (the past 11,000 years). If such a feature ruptures Holocene age sediments, it would be classified as an active fault according to State of California Statutes. The objective of Geosyntec s investigation was to evaluate the presence or absence of the fault identified in the Atlas and to evaluate the age of most recent faulting. The investigation consisted of 1) review of available geotechnical, geological, and seismological data; 2) field reconnaissance and geologic mapping/logging of exposed slopes; and 3) trench excavation and logging. Investigations of potential faulting at the landfill site indicate no evidence of faulting beneath the facility for at least the past 40,000 years and perhaps as long as 350,000 years. The current version of the Kern County Seismic Hazard Atlas Map (January, 2004) does not show any faults crossing the Project area. The landfill does not lie within an Alquist-Priolo Seismic Studies Zone. Figure shows locations of mapped Holocene (active and Quaternary potentially active) faults within regional proximity of the site. Among those considered to be presently active and near the landfill are the Little Lake Fault zone (2.7 miles to the east-northeast), the Garlock Fault (10.9 miles to the south-southeast), and the Sierra Nevada Fault zone (8.8 miles to the west-northwest) (Golder, 2010). The landfill site is subject to strong Draft Environmental Impact Report 4.6-5

6 ground shaking and possible surface readjustment in the event of a maximum magnitude earthquake from any of these faults. Potential for Structural Damage: While there are no identified geologic faults on the Kern County Seismic Hazard Atlas Maps crossing the Project area, the above mentioned faults are capable of producing earthquakes and subsequent ground shaking. This ground shaking could result in structural damage. The geotechnical investigation performed by Golder (Golder, 2010) included slope stability analyses of the waste mass under the proposed geometry after vertical expansion. Golder concluded that the proposed landfill slopes will be stable under static conditions and the design seismic event. A more detailed discussion can be found in section of this EIR. Permanent structures on the site consist of a 10 X 20 gatehouse and a 50 X 100 special waste facility. A landfill gas extraction system also exists on the Project site. These facilities were constructed in compliance with the Building Code s seismic standards. During the design and construction of the onsite structures the best available technology to account for seismic risk in this area was used for the time period. Also onsite is a 56,370-gallon water storage tank. This welded steel storage tank is approximately 20 feet in diameter and 24 feet tall. The tank is a flat bottom tank, unanchored, and resting on a gravel foundation with grade band. [This Space Intentionally Left Blank] Draft Environmental Impact Report 4.6-6

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9 4.6.3 Regulatory Setting Geologic resources and geotechnical hazards are governed 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. CEQA is the major environmental statute that guides the design and construction of projects on non-federal lands in California. This statute sets forth a specific process of environmental impact analysis and public review. In addition, the project proponent must comply with other applicable State and local statutes, regulations and policies. Relevant and potentially relevant statutes, regulations and policies are discussed below Federal International Building Code The International Building Code is published by the International Code Council as a model code to promote public safety and welfare by adoption of minimum development standards. It is recognized by the Federal Emergency Management Administration as the latest code for the protection of property against natural disaster. These development standards, as implemented in state building codes and local ordinances, require the Project to comply with appropriate seismic design criteria, adequate drainage facility design and preconstruction soils and grading studies. Seismic design standards have been established to reduce many of the structural problems that may occur due to major earthquakes. Resource Conservation and Recovery Act, Subtitle D (40 CFR Part 258) The Resource Conservation and Recovery Act, Subtitle D regulates the management of non-hazardous solid waste. It establishes minimum federal technical standards and guidelines for state solid waste plans in order to promote environmentally sound management of solid waste (USEPA, 2009). Section 4001 of Subtitle D outlines the primary goals of the Act, which are: Promote environmentally sound disposal methods; Maximize the reuse of recoverable resources; and Foster resource conservation. Subtitle D Regulates the following: Garbage also known as municipal solid waste; Refuse Sludges from waste treatment plants, water supply treatment plans, or pollution control facilities; Draft Environmental Impact Report 4.6-9

10 Non-hazardous industrial wastes; and Other discarded material, including solid, semi-solid, liquid, or contained gaseous materials resulting from industrial and commercial activities State Porter-Cologne Water Quality Control Act Water Code section requires any person discharging waste, or proposing to discharge waste, in any region that could affect the waters of the state to file a report of discharge (an application for waste discharge requirements [WDRs]). Under the Porter-Cologne definition, the term waters of the state is defined as any surface water or groundwater, including saline waters, within the boundaries of the state. Although all waters of the United States that are within the borders of California are also waters of the state, the converse is not true (i.e., in California, waters of the United States represent a subset of waters of the state). Thus, California retains authority to regulate discharges of waste into any waters of the state, regardless of whether the United States Army Corps of Engineers has concurrent jurisdiction under Section California Building Code 2007 California Building Code, Title 24 CCR, Part 2 has been adopted by the California Building Standards Commission, Department of Housing and Community Development, and other agencies within the State of California. This Code implements the requirements contained in the 2006 International Building Code and other pertinent standards. The California Building Code applies to all applications for residential building permits. The California Building Code consists of 12 parts that contain administrative regulations of the California Building Standards Commission and regulations of all state agencies that implement or enforce building standards. Local agencies must ensure that development in their jurisdictions complies with guidelines contained in the code. Cities and counties can, however, amend the California Building Code to adopt more stringent building standards beyond those provided because of unique climatic, geological, or topographical conditions. Alquist-Priolo Earthquake Fault Zoning Act The Alquist-Priolo Earthquake Fault Zoning Act of 1972 (formerly the Special Studies Zoning Act) regulates development near active faults, with the specific intention of mitigating the hazard of surface fault rupture on buildings intended for human occupancy. In accordance with this law, the California Geological Survey maps active faults and designates Earthquake Fault Zones along mapped faults. This Act groups faults into categories of active (historic or Holocene age faults), potentially active (Quaternary age faults), and inactive (pre-quaternary age faults). Draft Environmental Impact Report

11 Local government agencies are mandated by the Act to require site-specific geologic investigations for proposed Projects contained within a designated Alquist-Priolo Earthquake Fault Zone area. Such investigations typically include subsurface trenching to determine the presence of faulting. Under the act, the California State Geologist identifies areas in the state that are at risk from surface fault rupture. The main purpose of the act is to prevent construction of buildings used for human occupancy where traces of active faults are evident on the earth s surface. Fault rupture generally occurs within 50 feet of an active fault line and is limited to the immediate area of the fault zone where the fault breaks along the surface. Such a rupture could potentially displace and/or deform the ground surface. Accordingly, the California Geologic Survey provides the following guidance: If an active fault is found, a structure for human occupancy cannot be placed over the trace of the fault and must be set back from the fault (generally 50 feet) (California Department of Conservation, 2007). Seismic Hazards Mapping Act of 1990 In accordance with Public Resources Code, Chapter 7.8, Division 2, the California Department of Conservation, Division of Mine and Geology (now the California Geological Survey [CGS]), is directed to delineate Seismic Hazard Zones. The Seismic Hazards Mapping Act of 1990, addresses non-surface fault rupture earthquake hazards, including liquefaction and seismically induced landslides. 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 mitigation seismic hazards, such as those associated with strong ground shaking, liquefaction, landslides, other ground failures, or other hazards caused by earthquakes. State, County, and City agencies are directed to use and incorporate sitespecific geotechnical hazard investigations seismic hazard zone maps developed by CGS in their land use planning, as part of their permit approval process. It provides a mechanism to identify when provisions beyond standard building codes are necessary to ensure safe development and to reduce future losses. Although the Act is chiefly aimed at reducing earthquake-related losses, its provisions for slope stability can be applied broadly Local Kern County General Plan The Kern County General Plan includes policies related to the construction and operation of the proposed Project, which are in the Land Use, Open Space, and Conservation Element and the Safety Element chapters (Kern County, 2004a). The policies and implementation measures in the General Plan applicable to the proposed Project are outlined below. The 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. Draft Environmental Impact Report

12 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 paleontologic resources (please see Chapter 4.4 [Cultural Resources] for discussion of paleontologic resources relevant to the proposed Project). Physical and Environmental Constraints (Section 1.3 of the Kern County General Plan) 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 Water], Map Code 2.5 [Flood Hazard], Map Codes , 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 effective slope stability, wastewater drainage, and sewage treatments in areas with steep slopes are adequate for development. Seismically Induced Surface Rupture, Ground Shaking, and Ground Failure (Section 4.3 of the Kern County General Plan) 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. Landslides, Subsidence, Seiche, and Liquefaction (Section 4.5 of the Kern County General Plan) 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. Draft Environmental Impact Report

13 Policy 3. Reduce potential for exposure of residential, commercial, and industrial development to hazards of landslide, land subsidence, liquefaction and erosion. Appendix E Siting for Solid Waste Disposal Facilities This appendix is intended to provide procedural guidance and criteria to ensure land use compatibility for the health and safety of the residents of Kern County. Decision Procedure for Siting Solid Waste Disposal Facilities 1. Solid waste disposal facilities shall be designated on applicable General Plan maps or Specific Plan maps as "Solid Waste Disposal Facility" (Map Code 3.4). A. When planning new organic and municipal solid waste disposal facilities the following siting criteria shall apply. All sites for organic and municipal solid waste disposal facilities shall exclude: 7) Class VIII soils (rock outcrops). 8) Nonqualified soils based on Natural Resource Conservation Service criteria (soils presently not rated and not included in Table 9, page 149, Soil Survey for Southeastern Part of Kern County, 1981 edition). Kern County Building Code All construction in Kern County is required to conform to Chapter 17.08, Building Code, of the Kern County Code of Regulations, which is known as the Kern County Building Code. This Ordinance adopts the 2007 California Code that imposes substantially the same requirements as are contained in the International Building Code, 2006 Editions (with appendices and standards adopted and copyrighted by the International Conference of Building Officials), with particular minor modifications and amendments for conditions specific to Kern County. The requirements for seismic protection are the same as those of the California Building Codes. Chapter 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 call 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. Draft Environmental Impact Report

14 Other Devices. Where necessary, check dams, cribbing, riprap or other devices or methods shall be employed to control erosion and provide safety Impacts and Mitigation Measures Methodology The potential impacts associated with the proposed Project are evaluated on a qualitative and quantitative basis through a comparison of the anticipated Project effects on geologic resources. The technical reports prepared by GeoSyntec Consultants, AMEC Geomatrix Consultants, and Golder Associates present findings, conclusions, and recommendations concerning the development of the project site based upon the engineering analysis of geotechnical properties of the site, as discussed above. The change in the land use is significant if the effects described below occur. The evaluation of Project impacts as based on the significance criteria adopted by the County in the Kern County CEQA Implementation Document, which the County has determined to be appropriate criteria for this Draft EIR Threshold of Significance The Kern County CEQA Implementation Document and Kern County Environmental Checklist state that a project would have a significant impact on geology and soils if it would: a) Expose people or structures to potential adverse effects including risk of loss, injury, or death involving rupture of a known earthquake fault, strong seismic ground shaking, seismic-related ground failure (liquefaction), or landslides; b) Result in substantial soil erosion or loss of topsoil; c) Be located on a geologic unit or soil that is unstable; d) Be located on an expansive soil; and/or e) Have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for the disposal of waste water Impacts of the Proposed Project Impact 4.6-1: The proposed Project may expose people or structures to potential adverse effects resulting from seismic shaking. Strong earthquakes generated along a fault system generally create ground shaking that attenuates with distance from the fault. In general, the area affected by ground shaking depends upon the characteristics of the earthquake and the location of the epicenter. Effects of a strong seismic event could damage the Draft Environmental Impact Report

15 integrity of the landfill system with associated threats to public health and the environment. In the absence of appropriate engineering measures, such strong ground shaking could compromise the integrity of the landfill. Similarly, without appropriate structural design features, strong ground shaking could damage the landfill gatehouse, the special waste facility, the landfill gas extraction system and other site improvements with associated threats to lives and health. According to the Division of Mines and Geology Special Publication 42, the Project site is not located in an area of a known earthquake fault as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map. In 2003, GeoSyntec Consultants conducted an investigation of faulting potential at the Ridgecrest RSLF. The Kern County Seismic Hazard Atlas II-B-3 Ridgecrest South, prepared by Kern County Council of Governments in 1976, showed an unnamed north-striking fault transecting the east-central portion of the Ridgecrest RSLF (GeoSyntec Consultants, 2003). This fault was classified as offsetting Pleistocene (approximately 1.7 million years before present) or younger soils. The Pleistocene or younger age includes the Holocene (the past 11,000 years). If such a feature ruptures Holocene age sediments, it would be classified as an active fault according to State of California Statutes. The objective of Geosyntec s investigation was to evaluate the presence or absence of the fault identified in the Atlas and to evaluate the age of most recent faulting. The investigation consisted of 1) review of available geotechnical, geological, and seismological data; 2) field reconnaissance and geologic mapping/logging of exposed slopes; and 3) trench excavation and logging. Investigations of potential faulting at the landfill site indicate no evidence of faulting beneath the facility for at least the past 40,000 years and perhaps as long as 350,000 years. The current version of the Kern County Seismic Hazard Atlas Map (January, 2004) does not show any faults crossing the Project area. However, in accordance with California Code of Regulations Title 27, section 20370, the existing landfill has been designed and built to withstand the Maximum Probable Earthquake (MPE) so that the landfill systems are not compromised during a major seismic event. Similarly, the existing gatehouse and other onsite structures, as well as future structures to be placed in the relocated recycling/diversion areas, have been designed to accommodate the anticipated seismic load of the maximum probable earthquake in accordance with the applicable California Building Codes. Also on site is a 56,370-gallon water storage tank. This welded steel storage tank is approximately 20 feet in diameter and 24 feet tall. The tank is a flat Draft Environmental Impact Report

16 bottom tank, unanchored, and resting on a gravel foundation with grade band. In 2009, Dee Jaspar & Associates, Inc. (Dee Jaspar) performed an analysis of the water system at the Ridgecrest RSLF in which they stated that the tank is not in accordance with AWWA D100 Standards. In February of 2010, following a tank inspection performed by DJA Inspection Services, Dee Jaspar submitted a memorandum to the Kern County Waste Management Department which detailed the tasks and costs involved to bring the tank into compliance with the standards. It was estimated that a replacement cost of two to three times the repair cost would be required to design a tank in accordance with AWWA Standards as it will require a larger foundation, increase the footprint of the tank site, and require installation. Furthermore, a tank of the same size and height would require a concrete foundation and anchorage in order to comply with seismic design requirements. Refer to Chapter 4.8, Hazards and Hazardous Materials, section for the Project Design Feature the Kern County Waste Management Department would implement in case the water storage take fails. In 2010, Golder Associates, Inc. performed slope stability analyses of the waste mass under the proposed geometry after vertical expansion, using Bray et al and Spencer slope stability analysis methods. The final geometry after the proposed vertical expansion was developed assuming landfill side slopes of 3:1 (horizontal:vertical) and a maximum elevation of 2,592 feet above mean sea level (MSL). The analyses included stability under static and seismic conditions. The results of the stability analyses performed indicate that the proposed waste slopes have a static factor-of-safety greater than 2.2 and a seismic factor-of safety equal to 1, with a seismic displacement of less than 6 inch. Within the Golder report, the factor of safety was determining in the ratio of the resisting force and resisting moment divided by the driving force and driving moment. Based on the static and seismic slope stability and the seismic displacement analyses conducted on the proposed configuration, the 20-foot vertical expansion will be stable (Golder, 2010). The report prepared by Golder Associates is included in this EIR as Appendix J. Liquefaction: During moderate to strong ground shaking associated with seismic events, saturated sediments can undergo a type of failure referred to as liquefaction. During liquefaction, elevated pore water pressures cause a complete and sudden loss of strength and the sediments are transformed from a solid to liquid state. In a liquid state, the sediments have no bearing capacity and can flow. The results of flow can include collapse or settlement of the ground surface. Significant damage or collapse of structures built in areas affected by liquefaction can occur. Liquefaction takes place during some earthquakes when clay free soil deposits behave as viscous fluids. Poorly consolidated, watersaturated fine sands and silts located within 50 feet of the surface are typically considered the most susceptible to liquefaction. Soils and sediments that are not water-saturated and that consist of coarser or finer materials are generally less susceptible to liquefaction (Department of Conservation, 1997). Draft Environmental Impact Report

17 Liquefaction of the site soils is not a concern due to the depth to groundwater being greater than 40 below ground surface. Therefore, lateral spreading, subsidence, collapsible soils, and liquefaction are not a concern (Golder, 2010). The landfill is located on flat ground. The final cover and slopes of the waste unit will be constructed to withstand the maximum probable earthquake per Title 27 CCR, section 20164(a). Seismic stability calculations contained in the Golder Geotechnical Investigation (Golder, 2010) show that landfill slopes of 3:1 are stable and safe. The impact rating resulting from the implementation of the proposed Project would be less than significant. Mitigation Measures: No mitigation will be required. Level of Significance after Mitigation: Impacts are less than significant. Impact 4.6-2: The proposed Project may result in substantial soil erosion. All the drainage features that are currently part of the existing landfill and those that will be part of the proposed Project are designed to prevent erosion and ponding, and will minimize infiltration in the areas most subject to erosion. The surface water system has been sized with adequate hydraulic capacity to accommodate peak flows from a 100-year, 24-hour storm event. For the Ridgecrest RSLF, the point precipitation value calculated for the 100-year, 24- hour storm event is approximately three inches. On-site drainage channels will collect the stormwater runoff from the landfill unit and direct it into the historical drainage channel, north of the landfill. The landfill is currently classified as a Class III waste management unit by the Regional Water Quality Control Board (RWQCB). The RWQCB has issued WDRs to the Kern County Waste Management Department; the latest versions for the landfill are Order Nos and A1, adopted March and November Landfill surfaces will be revegetated following closure to further reduce erosion potential. Based on the site s soil characteristics, the surface water management system, and the planned revegetation of disturbed areas, a significant impact as a result of the Project is not anticipated. The impact rating resulting from the implementation of the proposed Project would be less than significant. Mitigation Measures: No mitigation will be required. Level of Significance after Mitigation: Impacts are less than significant. Draft Environmental Impact Report

18 Impact 4.6-3: The proposed Project may be located on soil that is unstable. With proper landfill operations, the soils on the landfill top deck and side slopes would not be subject to significant lateral spreading, subsidence, liquefaction, collapse, or soil blowing. The Ridgecrest RSLF is an existing facility. In 2010, Golder Associates, Inc. conducted slope stability analyses to evaluate the effects of raising the vertical height of the landfill beyond its permitted maximum. The stability study included model-generated deformation predictions that would be expected in the event of a maximum probable earthquake. Based on the static, pseudo-static and displacement analyses conducted on the proposed design configuration, it was concluded that the 20-foot vertical expansion will be stable. The impact rating resulting from the implementation of the proposed Project would be less than significant. Mitigation Measures: No mitigation will be required. Level of Significance after Mitigation: Impacts are less than significant. Impact 4.6-4: The proposed Project may be located on expansive soil. Soil types at the site consist of coarse sands, intermixed with fine to medium gravel, and the facility is not located on a floodplain or lake area. Coarse grained alluvial soils have a small potential to shrink and swell. This condition occurs when expansive soils undergo alternate cycles of wetting (swelling) and drying (shrinking). During these cycles, the volume of the soil changes significantly. Structural damage, warping and cracking of roads and sidewalks, and rupture of utility lines may occur if the potential for expansive soils is not considered during design and construction of improvements. In addition, the bearing capacity of the alluvial soils may not be sufficient to support the structures. If the soils cannot support the overlying structures, the resulting differential building settlement could damage the structures. Geotechnical borings, test pits, and boreholes drilled for monitoring wells at the site did not indicated the presence of expansive soils. The gatehouse on the site was constructed in compliance with the California Building Code s standards. The Building Code states that when expansive soils are present, the local building official may require that special provisions be made in the foundation design and construction to safeguard against damage due to the expansiveness. Standards for the design of slab-on-ground foundations to resist the effects of expansive soils are found under Chapter 18 of the current California Building Code. With implementation of the Building Code standards, the potential impacts associated with expansive soils on the site would be considered less than significant. Draft Environmental Impact Report

19 The impact rating resulting from the implementation of the proposed Project would be less than significant. Mitigation Measures: No mitigation will be required. Level of Significance after Mitigation: Impacts are less than significant Cumulative Impacts of the Proposed Project Impact 4.6-5: The proposed Project may have cumulative impacts to geology and soils. Cumulative impacts are two or more individual impacts that, when considered together, are considerable or that compound or increase other environmental impacts. The cumulative impact scenario for the Project includes 7 specific projects identified by Kern County, 33 specific projects identified by the City of Ridgecrest, and build out of the Kern County General Plan (see Tables 3-6 and 3-7). A cumulative impact analysis first identifies whether a cumulatively significant impact exists in the given resource area. If so, it determines whether the proposed Project will make a considerable contribution to that impact. Where a cumulative impact is severe, even a small contribution may be considerable (Section 15130(b) of the State CEQA Guidelines). As discussed above, the proposed Project area is within the seismically active Indian Wells Valley, which is bordered by major fault systems, including the Little Lake and Sierra Nevada Fault zones, and the Garlock Fault. The proposed Project is not located within any Alquist-Priolo Special Studies Zones; however, seismic activity is probable in and around the Project area. The seismic conditions that occur within the Project area exist to varying degrees throughout Kern County. As noted, Kern County is considered seismically active. The projects in Tables 3-6 and 3-7 in Chapter 3, Project Description, would all have varying degrees of vulnerability in a seismic event, with the degree of impact directly related to site-specific conditions such as location of faults, location of structures, areas of potential liquefaction, subsidence and unstable slopes. However, the effects of these projects are not of a nature to cause cumulatively significant effects from geologic impacts on the soils resource. Cumulative impacts could occur in a seismic event if a potential hazard, such as a power plant, were located near a populated area. However, no such facilities are planned within the development area where the proposed Project is located. All planned projects in the vicinity of the proposed Project would be subject to environmental review, and the possible preparation of separate environmental documents. Additionally, all projects would be in conformance with the Kern County General Plan, the Zoning Ordinance and relevant building codes which would minimize the potential impacts caused by seismic events. Draft Environmental Impact Report

20 As currently designed, the proposed Project, as well as past, present, or reasonably foreseeable projects, would not contribute to any cumulative impact for seismic hazards or related seismic events, including liquefaction, subsidence or unstable slopes. Mitigation Measures: No mitigation will be required. Level of Significance after Mitigation: Cumulative impacts are less than significant Feasible and Reasonable Mitigation Analysis It is not anticipated that this proposed Project would result in significant impacts to geology and soils based on the above analysis. No mitigation will be required as geology and soil impacts were determined to have a less than significant rating. [This Space Intentionally Left Blank] Draft Environmental Impact Report