5. Environmental Analysis

Transcription

1 5.4 This section of the Draft Environmental Impact Report (DEIR) evaluates the potential for implementation of the San Gorgonio Pass Campus Master Plan to impact geological and soil resources. The analysis in this section is based in part on the following technical report(s): Geological Hazard Study for Proposed Banning Campus, SE Corner of Sunset Ave. & W. Westward Ave., Banning, California, Soils Engineering, Inc., July 8, Preliminary Geotechnical Investigation and Toxicity Survey, Tentative Tract 23964, City of Banning, Riverside County, California, GeoSoils, Inc., October 4, Geotechnical Exploration, Proposed San Gorgonio Pass Campus (Phase I), Mt. San Jacinto Community College (MSJCC), Banning, California, Leighton Consulting, Inc., April 22, Pershing Creek Setback Area, map, Higginson+Cartozian Architects, Re: San Gorgonio Pass Campus Pershing Creek, letter, Encompass Associates, August 7, Complete copies of these studies are included in the Technical Appendices to this Draft EIR (Volume II, Appendix E). Other resources that were used in this analysis are listed below and in the bibliography. Geologic Map of the Beaumont Quadrangle, Riverside County, California, Thomas W. Dibblee, Jr. and John A. Minch, December Beaumont Quadrangle, California-Riverside County, 7.5-Minute Series (Topographic), United States Geological Survey, Geology of the Los Angeles Basin, California: An Introduction, R. F. Yerkes, T. H. McCulloch, J. E. Schoellhamer and J. G. Vedder, Significant Earthquakes and Faults, Chronological Earthquake Index, Southern California Earthquake Data Center, The Riverside County Land Information System, Riverside County Transportation and Land Management Agency, Environmental Setting Regional Setting Geologic Setting The site is in the San Gorgonio Pass in the extreme northern part of the Peninsular Ranges Geomorphic Province. The Peninsular Ranges Geomorphic Province extends approximately 900 miles southward from the Los Angeles Basin to Baja California, Mexico and is characterized by elongated northwest-trending mountain ranges separated by sedimentfloored valleys (Yerkes 1965). The most dominant structural features of the province are the northwest-trending fault zones, most of which die out, merge with, or are terminated by the steep reverse faults at the southern margin of the San Gabriel and San Bernardino Mountains, which are about 4,500 feet north-northeast of the site in the Transverse Ranges Geomorphic Province. The San Bernardino Mountains are north of the site, the San Jacinto Mountains are southeast of San Gorgonio Pass Campus Master Plan Draft EIR Mt. San Jacinto Community College District Page 5.4-1

2 the site, and the San Timoteo Badlands are west of the site. The surface is covered by late Pleistocene alluvial deposits (Dibblee and Minch 2003). Faulting and Seismicity Southern California is a geologically complex area that includes several types of faults, including strike-slip, oblique thrust, and blind thrust faults. Any specific area is subject to seismic hazards of a varying degree, depending on the proximity and potential of nearby active fault, and the local geologic conditions. Seismic hazards include primary hazards from surface rupturing along active fault traces, and secondary hazards resulting from strong ground shaking. Project Site Topography The site has an undulating topography that generally slopes toward the southeast. The site elevation ranges from approximately 2,380 feet above mean sea level in the southern portion of the site to approximately 2,420 feet above mean sea level in the northwest portion of the site (USGS 1996). Surficial Units Much of the site is underlain by Pleistocene alluvial fan deposits. Alluvium consists of sediments that have been deposited by stream flow. The alluvial deposits in this region can range in grain size from clay to boulders; however, the alluvium onsite is generally fine-grained and consists primarily of interlayered sandy silt, sandy clayey silt, sandy clay, and sandy silty clay (overbank deposits). In drainage channel areas of the site, like along Pershing Creek, the lithology consists of Holocene clayey and sandy silt and silty sand with lenses of gravelly sand (Soils Engineering 2003). Faulting and Seismicity Active faults within 20 miles of the site include the Banning Fault, approximately 3.5 miles to the north; the San Andreas Fault, approximately 7.0 miles to the north; the San Jacinto Fault, approximately 8.9 miles to the southwest; and the Pinto Mountain Fault, approximately 14.6 miles to the northeast. The Alquist-Priolo Earthquake Fault Zone Map for the area is shown in Figure 5.4-1, Alquist-Priolo Earthquake Fault Zone Map. Historic Earthquakes Historic earthquakes of magnitude 5.0 or greater that caused substantial ground shaking in the project region are listed below in Table Page The Planning Center DC&E January 2013

3 Table Historic Regionally Significant Earthquakes of M 5.0 or Greater Earthquake Location Fault Date Magnitude Notable Effects 1899 San Jacinto Near San Jacinto San Jacinto December 25, deaths; near total devastation to brick buildings in San Jacinto and Hemet 1918 San Jacinto San Jacinto San Jacinto April 21, death; damage to masonry buildings in San Jacinto and Hemet Lytle Creek Near Cajon Pass? North Palm Springs Six miles northwest of North Palm Springs Banning or Garnet Hill September 12, July 8, Whittier Narrows Near South El Monte Thrust fault October 1, Upland Near Upland San Jose February 28, Landers Big Bear Hector Mine In Mojave Desert 6 miles north of Yucca Valley In San Bernardino Mountains In Mojave Desert 47 miles east-southeast of Barstow Johnson Valley and several others June 28, Unknown June 28, Lavic Lake and Bullion October 16, Chino Hills Near Chino Hills Yorba Linda July 29, deaths; severe damage in older parts of some communities east of Los Angeles Considerable damage near epicenter 1 death; quake occurred in sparsely populated area. Substantial damage in Big Bear Lake area Negligible damage due to remoteness of area Source: SCEDC Other Hazards Based on the reports by Soils Engineering and GeoSoils, there appears to be a low potential for landslides or liquefaction at the site. Once final plans are generated for building locations, a preliminary geotechnical investigation should be performed to verify the conclusions of previous reports. Liquefaction Liquefaction refers to loose, saturated sand or silt deposits that behave as a liquid and lose their load-supporting capability when strongly shaken. Loose granular soils and silts that are saturated by relatively shallow groundwater are susceptible to liquefaction. The potential for liquefaction-induced settlement onsite is considered very low due to the lack of shallow groundwater and the relatively high density of the coarse-grained alluvial soils at depth. The project site is not mapped by Riverside County as being in a zone of liquefaction susceptibility. Lateral Spreading Lateral spreading is the downslope movement of surface sediment due to liquefaction in a subsurface layer. Such movement can occur on slope gradients of as little as one degree. Lateral spreading typically damages pipelines, utilities, bridges, and structures. Lateral spreading is considered unlikely at the site due to the low potential for liquefaction. San Gorgonio Pass Campus Master Plan Draft EIR Mt. San Jacinto Community College District Page 5.4-3

4 Regulatory Setting 2010 California Building Code Current law states that every local agency enforcing building regulations, such as cities and counties, must adopt the provisions of the California Building Code (CBC) within 180 days of its publication. The publication date of the CBC is established by the California Building Standards Commission and the code is also known as Title 24, Part 2 of the California Code of Regulations. The most recent building standard adopted by the legislature and used throughout the state is the 2010 version of the CBC, often with local, more restrictive amendments that are based on local geographic, topographic, or climatic conditions. These codes provide minimum standards to protect property and public safety by regulating the design and construction of excavations, foundations, building frames, retaining walls, and other building elements to mitigate the effects of seismic shaking and adverse soil conditions. The CBC contains provisions for earthquake safety based on factors including occupancy type, the types of soil and rock onsite, and the strength of ground shaking with specified probability of occurring at a site. Division of the State Architect Plan Approval The Division of the State Architect (DSA) provides design and construction oversight for K 12 schools, community colleges, and various other state-owned and leased facilities. The DSA also develops accessibility, structural safety, fire and life safety, and historical building codes and standards utilized in various public and private buildings throughout the State of California. The San Gorgonio Pass Campus Master Plan project is subject to review and plan approval by DSA, prior to and during construction Thresholds of Significance According to Appendix G of the CEQA Guidelines, a project would normally have a significant effect on the environment if the project would: G-1 Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: i) 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. (Refer to Division of Mines and Geology Special Publication 42.) ii) Strong seismic ground shaking. iii) Seismic-related ground failure, including liquefaction. iv) Landslides. G-2 Result in substantial soil erosion or the loss of topsoil. G-3 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. Page The Planning Center DC&E January 2013

5 5. Environmental Analysis Alquist-Priolo Earthquake Fault Zone Map Cherry Valley Beaumont Banning 10 W Ramsey St W Lincoln St W Westward Ave SITE S Sunset Ave Bob Cat Rd MAP EXPLANATION Active Faults Faults considered to have been active during Holocene time and to have potential for surface rupture: solid line where accurately located, long dash where approximately located, short dash where inferred, dotted where concealed; query (?) indicates additional uncertainty. Evidence of historic offset indicated by year of earthquake-associated event or C for displacement caused by fault creep. Earthquake Fault Zone Boundaries These are delineated as straight-line segments that connect encircled turning points so as to define Earthquake Fault Zone segments. Seaward projection of zone boundary Site Boundary 0 1 Scale (Miles) Source: State of California, Beaumont Quadrangle, San Gorgonio Pass Campus Master Plan Draft EIR Mt. San Jacinto Community College District Figure 5.4-1

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7 G-4 Be located on expansive soil, as defined in Table 18-1B of the Uniform Building Code (1994), creating substantial risks to life or property. G-5 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. The Initial Study, included as Appendix A, substantiates that impacts associated with the following thresholds would be less than significant: Threshold G-1 i, ii, and iii Threshold G-2 Threshold G-3 Threshold G-5 These impacts will not be addressed in the following analysis Environmental Impacts Phase II of the project involves the expansion of all permanent administration and classroom facilities to create an upgraded campus on approximately 16 acres of the project site (Figure 1-4, Phase II Site Plan). The expanded campus would retain the existing structures, which would be converted for student services use. Phase III of the project involves the full buildout of the campus on the 50.1-acre project site (Figure 1-5, Phase III Site Plan). The fully built-out campus would have 13 permanent buildings, a sustainable park, an amphitheater, a recreation area, and a student courtyard, plaza, and quad. The campus would include a total of 2,017 parking spaces. The following impact analysis addresses thresholds of significance for which the Initial Study disclosed potentially significant impacts. The applicable thresholds are identified in brackets after the impact statement. IMPACT 5.4-1: THE PROJECT COULD SUBJECT OCCUPANTS AND VISITORS TO POTENTIAL LANDSLIDE HAZARDS. [THRESHOLD G-1iv]) Impact Analysis: Most of the site exhibits no substantial elevation changes or unusual geographic features. However, the southern portion of the project site along Pershing Creek is very steep to vertical along most of this channel. Since the site displays gentle topography in the areas where construction is proposed and grading is expected to be necessary over most of the site, landslides are only a possibility along the ravine created by Pershing Creek. A minimum 60-foot setback from the banks of Pershing Creek is planned along the southern border of the site. The project boundaries have been set back as depicted in Exhibit A, Pershing Creek Setback Area to avoid any environmental impacts (Higginson+Cartozian 2012, Appendix E). The area between the project boundary and the creek would be maintained in its natural state, and no construction, landscaping, or any other activity would occur in this area. Erosion of the creek channel banks would continue, but it is not anticipated to result in significant incursion into the property at an accelerated rate (Encompass 2012). Review of aerial photographs dating back to 1996 indicate that the limits of the creek have not noticeably changed, and confirm the establishment of the creek at the current location. According to Soils Engineering (2003), the potential for landslides or rockfalls to impact the site in the event of a major earthquake is very low. IMPACT 5.4-2: EXPANSIVE SOIL CONDITIONS COULD RESULT IN RISKS TO LIFE OR PROPERTY. [THRESHOLD G-4] Impact Analysis: The existing fills, alluvium, and topsoil/colluvium are considered potentially expansive. Test results from a site soil sample indicated an expansion index of 42, indicating low expansion potential (GeoSoils 1988). A more recent test was conducted by Leighton (2010) and indicated an expansion index of 45, confirming the original low expansion potential results of GeoSoils. San Gorgonio Pass Campus Master Plan Draft EIR Mt. San Jacinto Community College District Page 5.4-7

8 5.4.4 Cumulative Impacts Impacts to geology and soils are specific to the geologic and soils conditions on a particular project site. Mitigation of geologic, seismic, and soil impacts of development projects would also be specific to each site. Compliance with modern building standards, such as the CBC, reduces seismic-related risks. Therefore, no adverse cumulative impacts related to soils and geology are anticipated Existing Regulations and Standard Conditions State 2010 California Building Code Division of the State Architect Plan Approval Level of Significance Before Mitigation Upon implementation of regulatory requirements and standard conditions of approval, the following impacts would be less than significant: and Mitigation Measures Upon implementation of regulatory requirements and standard conditions of approval, the impacts would be less than significant, and mitigation measures are not required. No significant unavoidable adverse impacts relating to geology and soils have been identified Level of Significance After Mitigation No significant unavoidable adverse impacts relating to geology and soils would occur. Page The Planning Center DC&E January 2013