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A. GEOLOGY and SOILS 1. Environmental Issue

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A. GEOLOGY and SOILS 1. Environmental Issue A. GEOLOGY AND SOILS 1. Environmental Issue This section of the EIR was prepared by Firma using the available geologic and soils investigation reports for properties within the Planning Area.1 These studies are preliminary in nature and would be expected to be updated with more detailed analyses at the time tentative tract maps or other specific development applications are submitted. The information presented below describes the basic topographic and geological conditions within the Planning Area properties. Topics of concern from the CEQA Guidelines include: • Seismic conditions, proximity to faults, risk of seismic related ground failure • Landslide risk • Risk of substantial soil erosion This section will evaluate the geologic hazards associated with future development within the Planning Area and identity the basic engineering measures which may be necessary to mitigate potential hazards related to seismic activity, slope failure and erosion. This section also describes features of the geology pertinent to other constraint topics such as air quality (asbestos bearing rock formations), and water quality (erosion potential). The topic of soil erosion is addressed in more detail in IV-D Drainage, Flooding and Water Quality. 2. Environmental & Regulatory Setting General Plan As described in more detail below in the Impact Analysis section, General Plan policies S-10 and S-11 establish Hazardous Overlay Zones on slopes over 10% to protect risks associated with seismic events and slope stability. Environmental Setting According to the City Safety Element of the General Plan, Pismo Beach is located in a seismically active area. However, no active faults are known to be present within or in the near vicinity of Pismo Beach and surface rupture resulting from fault movement is not considered a significant problem within the City. Additionally, the potential for landslides is considered to be negligible in rocks that underlie most of the city and its surrounding hills. Ground shaking could occur in Pismo Beach, primarily from the San Andreas Fault, which runs generally north-south from the Bay Area to southern California, the closest portion of which is 1 Preliminary Soils Engineering Review Spanish Springs Ranch, May 24,2005, GeoSolutions, Inc. Asbestos Discussion Report Northern Access Road Tract 2554, January 28,2008 GeoSolutions,Inc.. Geotechnical Feasibility Study for the Preserve, Earth Systems, May 10, 1999. Price Canyon (Planning Area R) General Plan Update and Spanish Springs Specific Plan EIR IV-A Geology and Soils. Page IV-A1 roughly 60 miles to the east of the City. The Nacimiento Fault is considered a secondary source of strong ground shaking but would have a negligible effect on Pismo Beach. An earthquake of Richter Magnitude 8.0 to 8.5 can be expected from a rupture along the San Andreas fault in the future, which would cause considerable groundshaking and potential structural damage in Pismo Beach. Secondary seismic hazards could result from the interaction of ground shaking with existing soil and bedrock conditions, and include liquefaction, settlement, landslides and tsunamis or “tidal waves”2. The Planning Area is largely within the area of the Pismo Formation geologic unit with the Edna and Miguelito members comprising much of the non-alluvial areas. The geology of these members is characterized by steep terrain and rock outcrops with bedded and inclined sandstone and shale layers. These formations are not highly prone to landslides or liquefaction. Areas within the creek alluvial plain are assumed to be subject to liquefaction and expansive soils. Regulatory Setting The California State Legislature has placed specific responsibilities on local government for identification and evaluation of seismic hazards and the formation of programs and regulations to reduce risk. Cities and counties must take seismic hazards into account in their planning programs. The basic objective is to reduce loss of life, injuries, damage to property, and economic and social dislocations resulting from future earthquakes 3. Impact Analysis Environmental Impact Significance Criteria General Plan policies S-10 and S-11 establish Hazardous Overlay Zones on slopes over 10% to protect risks associated with seismic events and slope stability. Development on slopes over 10% would be considered a potentially significant impact requiring mitigation. The General Plan indicates that the method for evaluating specific seismic and geologic hazards in the City is to perform site-specific geotechnical investigations, and to implement the recommendations included in those investigations, if development were to proceed. As indicated in policies S-10 and S-11 below, the Planning Area would be included within the Safety Element Hazardous Overlay and Protection Zone if annexed to the City, and site- specific geotechnical investigations would be required prior to approval of development permits. 2 Safety Element, page S-10, City of Pismo Beach Price Canyon (Planning Area R) General Plan Update and Spanish Springs Specific Plan EIR IV-A Geology and Soils. Page IV-A2 S-10 Hazardous Overlay Zone Land areas subject to hazards associated with steep slope, slope instability and drainage problems shall be included within the Hazardous Overlay and Protection Zone. Generally, all lands in excess of 10% slope shall be included. S-11 Development Review in Hazardous Overlay Zone Geologic reports may be required and shall be reviewed by the appropriate decision-making body, prior to approval of any development permits for projects located within the Hazardous Overlay Zone. In addition to these City policies, the CEQA Guidelines identify a potentially significant impact if implementation of a project would expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: • Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault, • Strong seismic ground shaking, • Seismic-related ground failure, including liquefaction, • Landslides, • Result in substantial soil erosion or the loss of topsoil, • Be 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 off-site landslide, lateral spreading, subsidence, liquefaction or collapse, • Be located on expansive soil, as defined in Table 18- 1-B of the Uniform Building Code (1994), creating substantial risks to life or property, Slope stability is typically a function soil type, geologic parent material, watershed characteristics as well as slope. In this context, it should be noted that there is not a geologic or engineering threshold that is triggered with respect to development on slopes over 30% that would necessarily result in greater safety risks, or other impacts. The existing General Plan policy prohibition on grading on slopes over 30% is aimed primarily at protecting visual resources. The concept of development on slopes exceeding 30% is therefore discussed in detail in section VI.A Visual Resources. Price Canyon (Planning Area R) General Plan Update and Spanish Springs Specific Plan EIR IV-A Geology and Soils. Page IV-A3 Analysis of Project Impacts GENERAL PLAN UPDATE The proposed General Plan Update to modify the boundaries of Planning Area R and the General Plan policies applicable to Planning Area R would not result in any significant or potentially significant impacts relating to geology or soils. While development within portions of Planning Area R is envisioned under the General Plan Update (development is also envisioned under current General Plan policies as well), the General Plan Update does not set forth any particular plan of development. Future development proposals for any of the properties within Planning Area R must be part of an approved Specific Plan, and Specific Plans require CEQA review prior to approval. The General Plan Update includes policy language that would allow limited grading in areas where slopes exceed 30% (current policy prohibits all such grading except for pre-existing lots along Price Canyon). The current General Plan prohibition per Policy CO-10 is concerned primarily with preserving open space and visual character. There is not a geologic or engineering threshold that is crossed on slopes over 30% that necessarily would result in greater safety risks, or other impacts, than on slopes less than 30% because slope stability is a factor of the soil, geologic parent material and watershed characteristics, as well as the slope of the land. There would be substantial grading and development in some areas that currently exceed 10% slope, but for this reason, policies S-10 and S-11 would require that these areas be placed in a Hazardous Overlay and Protection Zone requiring geotechnical investigations to ensure structures meet appropriate engineering standards to avoid safety impacts from seismic events or soil movement. Pursuant to General Plan Policy CO-31 all future development within the Planning Area will be subject to the Grading and Drainage regulations in that policy, the Municipal Code grading ordinance, and the California Building Code. Based on this, geologic impacts of future development would to a large extent be mitigated through existing General Plan policies. SPANISH SPRINGS SPECIFIC PLAN GRADING AND DEVELOPMENT ACTIVITIES Preliminary geotechnical investigations indicate
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