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HomeMy WebLinkAbout!Ch 05.08 Geo 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-1 City of Chula Vista November 2013 5.8 Geology and Soils This section describes the geologic setting of Village 8 West and evaluates the potential for geological and soil impacts due to implementation of the SPA Plan and TM. As stated in Section 2.3, Purpose and Legal Authority, this EIR tiers from the 2013 GPA/GDPA SEIR (09- 01). The SEIR did not address geology and soils, but relies on analysis in the 1993 Program EIR for the GDP (EIR 90-01). Section 3.8, Geology and Soils, of the Otay Ranch GDP Program EIR (EIR 90-01) analyzed geology and soils impacts for the entire Otay Ranch. The Otay Ranch GDP Program EIR concluded that potentially significant impacts regarding seismic-related hazards, erosion, unstable soils, and expansive soils would occur with implementation of the Otay Ranch GDP. However, the potential geology and soils impacts were able to be mitigated to a less than significant level with incorporation of the mitigation measures recommended in site-specific geotechnical investigations into the design and construction of future development projects. The analysis and discussion of geology and soils contained in the 1993 Otay Ranch GDP Program EIR are incorporated by reference. The analysis is also based on the geotechnical investigation for Village 8 West prepared by Advanced Geotechnical Solutions, Inc., dated October 22, 2010. This report is included in Appendix G of this EIR. The geotechnical investigation updates the applicable information in the previously certified GDP EIR. 5.8.1 Existing Conditions A. Regulatory Framework 1. State a. California Geologic Survey The California Geologic Survey (CGS) provides guidance with regard to seismic hazards. The CGS’s Special Publications 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California (1997) provides guidance for evaluation and mitigation of earthquake-related hazards for projects within designated zones of required investigation. b. Alquist-Priolo Earthquake Fault Zoning Act 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. The Act helps define areas where fault rupture is most likely to occur. The 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. c. Uniform Building Code and California Building Code The Uniform Building Code (UBC) published by the International Conference of Building Officials forms the basis for about half the state building codes in the United States, including California’s. The UBC has been adopted by the state legislature together with additions, amendments, and repeals to address the specific building conditions and structural requirements in California. CCR Title 24, Part 2, the California 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-2 City of Chula Vista November 2013 Building Code (CBC), provides minimum standards for building design. Local codes are permitted to be more restrictive than Title 24, but are required to be no less restrictive. Chapter 16 of the CBC deals with general design requirements, including but not limited to regulations governing seismically resistant construction (Chapter 16, Division IV) and construction to protect people and property from hazards associated with excavation cave-ins and falling debris or construction materials. Chapters 18 and A33 deal with site demolition, excavations, foundations, retaining walls, and grading, including but not limited to requirements for seismically resistant design, foundation investigations, stable cut and fill slopes, and drainage erosion control. 2. Local a. Chula Vista General Plan Individual project development proposed on property under the City of Chula Vista’s juris diction is required through similar UBC and CBC requirements to comply with Objective E 14 and its three associated policies (E 14.1, E 14.2, and E 14.3) contained in the adopted General Plan. Implementation of this objective and policies are intended to reduce potential impacts associated with geological hazards and public safety. B. Geologic Setting Village 8 West is located within the Peninsular Ranges geomorphic province of California. This province, which stretches from the Los Angeles basin to the tip of Baja California, is characterized as a series of northwest trending mountain ranges separated by subparallel fault zones, and a coastal plain of subdued landforms. The mountain ranges are underlain primarily by Mezozoic metamorphic rocks that were intruded by plutonic rocks of the southern California batholith, while the coastal plain is underlain by subsequently deposited marine and non-marine sedimentary formations. The project site is located on the Otay Mesa, which is part of a broad, relatively undeformed, uplifted highland encompassing much of western and southern San Diego County. Otay Mesa is part of the Santa Ana sub-block of the Peninsular Ranges. Consistent with the geology of the Peninsular Ranges, Otay Mesa consists of Mesozoic metamorphic, volcanic and igneous rocks on which marine and non-marine sediments have been deposited. These deposits have been only mildly deformed and are easily recognized as widespread, near-horizontal, sedimentary beds forming the broad tablelands and rolling hills of Otay Mesa. The north and east portions of the site are underlain by the Otay Formation and consist of gently rolling terrain that is punctuated by south flowing V-shaped drainages. Most of the drainages are broad and relatively shallow; however, some steeper gradients exist. Low-relief river terraces occupy the southernmost portion of this terrain. The southwest portion of the project site reflects more rugged terrain underlain by Santiago Peak Volcanics. Surface outcrops and large in-place exposed boulders are common, reflecting the bedrock’s resistant character. The local stratigraphy reflects the regional, near-horizontal to gently southwest dipping Oligocene Otay Formation, and a Tertiary un-named fanglomerate. These mapped units overlie volcanic and metavolcanic rocks of the Mesozoic Santiago Peak Volcanics. In turn, various Pleistocene and Holocene non-marine sediments mantle those formations, particularly in the south part of the site. The components of the site stratigraphy are described in greater detail below. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-3 City of Chula Vista November 2013 C. Otay Formation (To) Figure 5.8-1, Geologic Formations, shows the predominant geologic formations within the site, as identified in the geotechnical investigation for the proposed project (Appendix G to this EIR). The Oligocene Otay Formation underlies most of the study area. The formation is typically brown to light gray sandstone/gritstone. Infrequent to common gray bentonite beds occur throughout the formation. Typically, these beds are one to several feet thick and have relatively sharp contact with the interbedded sandstones. The clay beds are expansive and exhibit low shear strengths when wet. Harder and more resistant gritstone sub-units are common within the Otay Formation and can range from a few feet to tens of feet thick. Breccia sub-units consisting of rounded to angular cobbles to boulder-sized clasts can also be found within the Otay Formation near the contact of the Santiago Peak Volcanics. These beds are likely equivalent to the Tertiary Fanglomerate. The Breccia subunits consist of gravel to cobble-sized clasts. The Otay Formation is less resistant than the Santiago Peak Volcanics and unnamed Fanglomerate and thus forms subdued, rolling topography exemplifying Otay Mesa. Its steepest slopes occur where young tributaries to the Otay River are actively eroding headward and downward. 1. Santiago Peak Volcanics (Jsp) The Santiago Peak Volcanics crop out in the southwest part of the property near Rock Mountain. The Santiago Peak Volcanics are overlain by much younger geologic units. Some of the younger geologic units have been eroded and have revealed portions of this ancient landscape, creating modern topographic highs such as Rock Mountain. The Santiago Peak Volcanics are generally dense and mildly metamorphosed volcanic rocks. Large in-place surface boulders occur on natural slope areas. Outside of boulder areas, this formation is only a few feet thick. Below this formation the rock is very dense. Blasting operations occur in the nearby quarry, where the formation has been mined for aggregate. 2. Unnamed Fanglomerate Deposits (Tfg) A fanglomerate outcropping is located in the lower elevation slopes of the site above the Otay River. Angular metamorphic boulders are typical within the unit. The unit is dense and moderately to well cemented. 3. Terrace Deposits Veneers of Pleistocene cobbley to bouldery, well oxidized, dense sands have been mapped on surfaces 90 to 170 feet above the modern Otay River channel. These deposits are depicted as terrace deposits in Planning Areas U and V in the southeast corner of Village 8 West and along the majority of the sewer access road alignment. These deposits vary from a few tens of feet thick to only a veneer of lag gravel composed of residual dense cobbles and boulders. 4. Alluvium (Qal), Topsoil, and Artificial Fills Alluvium is a soil that is deposited by water and occupies the on-site drainages. The alluvium observed is porous, expansive, and exhibits low in-situ density. Typically these sediments vary from a few feet to ten feet in thickness with local variations. A mantle of residual topsoil is present over much of the rolling hills underlain by Otay Formation . The soils are typically one to five feet thick, low density, organic-rich and porous. Generally, the areas underlain by Santiago Peak Volcanics have thinner soils and are locally absent as evidenced by the frequent occurrence of surface boulders. 0 0.25 0.5 Mile No Scale Source: William Hezmalhalch Architects, Inc. 2012 OTAY RANCH VILLAGE 8 WEST EIR GEOLOGIC FORMATIONS FIGURE 5.8-1 Oligocene-age Otay FormationToTo Quaternary-age alluvial and terrace depositsQoaQoa Jurassic-Cretaceous-age Santiago Peak VolcanicsKjmvKjmv Holocene active channel and wash depositsQwQw Holocene alluvial deposits QyaQya Pleistocene alluvial depositsQvoaQvoa Otay Formation-Miocene panglomerate faciesTofTof ± 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-5 City of Chula Vista November 2013 Significant deposits of artificial fill on the site are associated with the reservoir and also exist over the existing utilities crossing the site. Small prisms of fill that have not been mapped are primarily associated with unimproved trails. D. Groundwater No groundwater was observed during the geologic field mapping or subsurface investigation conducted as part of the geotechnical investigation. Seasonal, intermittent groundwater associated with precipitation may occur in on-site drainages. Water from precipitation may also become trapped along subsurface joints or beds, especially in the Santiago Peak Volcanics formation, and may be encountered during grading. E. Geologic Hazards The following discussion is an assessment of the existing setting pertaining to potential geologic hazards including faulting and seismicity, ground surface rupture, liquefaction, compressible and expansive soils, landslides, seismically induced tsunamis, seiches and flooding, and subsidence. 1. Faulting and Seismicity Village 8 West is located in the tectonically active southern California, and will likely experience some effects from future earthquakes. The type or severity of seismic hazards affecting a site is dependent upon the distance to and direction from the faults, the intensity and duration of the seismic event, and the on-site soil characteristics. The Otay Mesa is part of the Santa Ana sub-block of the Peninsular Ranges. The Santa Ana sub-block is bounded by the Elsinore Fault Zone on the east and by the Rose Canyon Fault Zone on the west. Regional faults in southernmost California typically trend northwest and display major right lateral slip. Significant faults of this system displaying Holocene offset are the San Andreas, Elsinore, San Jacinto, Coronado Bank, Newport-Inglewood, and Rose Canyon faults. Of these, the Rose Canyon fault is closest, at approximately 12 miles west of the project site. This fault has the potential to generate a seismic event with a maximum moment magnitude of 6.9. Another mapped fault in the vicinity of Village 8 West is the La Nacion fault, located about two miles to the west. This fault is a "pre-Quaternary" fault in and paralleling the Otay River. It is not considered active. In 1972, California passed the Alquist-Priolo Earthquake Zoning Act to help identify areas subject to severe ground shaking. The purpose of this Act is to prohibit the placement of most structures for human occupancy across the traces of active faults; thereby mitigating the hazard of fault ruptures. Alquist-Priolo Zones serve as an official notification of the probability of ground rupture for future earthquakes. Due to its distance from known active faults, no Alquist-Priolo Fault Hazard Zones have been designated within Otay Ranch. However, although no known active faults exist within the project limits, the site would potentially experience ground motion and associated effects from earthquakes generated along regional active faults such as those in the Elsinore Fault Zone. 2. Ground Surface Rupture Ground rupture results from movement on an active fault reaching the surface. Village 8 West is not located within any established Alquist-Priolo Fault Zone and no active, potentially active, or inactive faults are known to underlie the project area. Accordingly, the potential for fault surface rupture within 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-6 City of Chula Vista November 2013 the project is limited. A listing of active faults within about 65 miles of the site is presented in Table 5.8-1 with the estimated maximum seismic event potential for each fault. Table 5.8-1 Distance to Known Active Faults Fault Name Distance from Project Site (feet) Maximum Moment Magnitude (Mmax) Rose Canyon 12 6.9 Coronado Bank 28 7.4 Elsinore-Julian 43 7.1 Elsinore-Coyote Mountain 45 6.8 Earthquake Valley 46 6.5 Newport-Inglewood (Offshore) 47 6.5 Elsinore-Temecula 54 6.9 San Jacinto-Coyote Creek 63 6.8 San Jacinto-Borrego 63 6.6 Laguna Salada 66 7.0 Source: Advanced Geotechnical Solutions 2010 3. Liquefaction Liquefiable soil typically consists of cohesionless sands and silts that are loose to medium dense, and saturated. To liquefy, these soils must be subjected to a ground shaking of sufficient magnitude and duration. The effects of liquefaction at a site may include ground oscillations, loss of bearing, lateral spread, dynamic settlement, or flow failure. Village 8 West has a very low risk for liquefaction due to the dense nature of the on-site geologic units. The on-site geologic units consist of materials that are not susceptible to liquefaction. 4. Compressible and Expansive Soils Loose, compressible soils are found on site, including slope wash, topsoil and the undocumented artificial fill, and the highly weathered portions of older alluvium, terrace, Tertiary Fanglomerate, Otay Formation and metavolcanic rock. These materials are subject to settlement under increased loads or due to an increase in moisture content from site irrigation or change in drainage patterns. Expansive soils are soils that undergo volumetric change with change in water content. The soils will swell with increase in moisture content and will shrink with decrease in water content. Soils with high shrink-swell potential generally contain high percentages of certain clay minerals and can cause extensive damage to structures and improvements. The predominately clayey sand and sandy clay materials within the Otay Formation, as well as the other materials on site, have a high to very high expansion potential. 5. Landslides and Lateral Spreads The geotechnical investigation did not identify any significant landslides on Village 8 West during site reconnaissance or subsurface investigation. The Otay Formation, which underlies most of Village 8 West (see Figure 5.8-1, Geologic Formations), is susceptible to erosion and slumping in some areas but no slumps or landslides were observed in this formation on site. Surficial slumps and bedrock landslides 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-7 City of Chula Vista November 2013 were observed within the Otay Formation west of Village 8 West. No indications of past landslides were observed or mapped within the Santiago Peak Volcanics during the geotechnical investigation. This formation is erosion resistant with relatively stable, steep natural slopes. 6. Subsidence Subsidence occurs when a large-scale fluid withdrawal is performed causing surface settlement. This is common within large farming communities where groundwater is pumped from great depths over long periods of time. The Santiago Formation, Otay Formation, and the Fanglomerate/Terrace deposits on site are not susceptible to subsidence. The surficial units on site (alluvium, undocumented fill, and topsoil) are susceptible to minor amounts of subsidence. 5.8.2 Thresholds of Significance According to the CEQA Guidelines, Appendix G, impacts regarding geology and soils would be significant if the project would: ■ Threshold 1: 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. (Refer to Division of Mines and Geology Special Publication 42); strong seismic ground shaking; seismic-related ground failure, including liquefaction; and/or landslides. ■ Threshold 2: Result in substantial soil erosion or the loss of topsoil. ■ Threshold 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. ■ Threshold 4: 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. ■ Threshold 5: Be inconsistent with General Plan geotechnical policies thereby resulting in a significant physical impact. ■ Threshold 6: Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for disposal of wastewater. 5.8.3 Impact Analysis A. Threshold 1: Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving rupture of a known earthquake fault; strong seismic ground shaking; seismic-related ground failure, including liquefaction; and/or landslides. Village 8 West is not located within an established Alquist-Priolo Fault Zone and no active faults are known to underlie the project area. Therefore, ground surface rupture is not considered to be a significant geologic hazard at the site. As shown in Table 5.8-1, the closest active fault is the Rose Canyon fault, approximately 12 miles west of the project site. A major earthquake along this fault or other regional active faults listed in Table 5.8-1 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-8 City of Chula Vista November 2013 could subject future on-site development to moderate-to-severe ground shaking. Design of future structures within Village 8 West would be in accordance with the Chula Vista Grading Ordinance, current seismic design specifications of the Structural Engineering Association of California, current CBC standards, and other regulatory requirements. Compliance with these regulatory requirements would ensure that potential seismic ground-shaking impacts to people or structures are less than significant. The potential for liquefaction in Village 8 West is very low and does not present a significant risk to future development. Although no evidence of ancient landslides or slope instabilities was cited in the Geotechnical Investigation, grading activities associated with cut slopes could result in slope instabilities within the project area because grading could expose bentonitic claystone beds on the finished slope faces. Thus, slope stability is considered to be a potentially significant impact. B. Threshold 2: Result in substantial soil erosion or the loss of topsoil. Village 8 West is generally comprised of rolling hills covered predominantly with grassland and scrub habitat crossed by dirt roads. Existing runoff from the project site flows in one of two routes. The southern and eastern portions of Village 8 West drain in a southerly direction to the Otay River. The northwestern portion of the site drains in a westerly direction to Wolf Canyon, a tributary to the Otay River. During construction, erosion (including loss of topsoil), can occur or be accelerated by site preparation activities. Vegetation removal throughout the site could reduce soil cohesion, as well as the buffer provided by vegetation from wind, water, and surface disturbance, which could render the exposed soils more susceptible to erosive forces. Additionally, newly exposed soils from excavation or grading activities may also be vulnerable to erosion. Earth-disturbing activities associated with construction would be temporary and erosion effects would depend largely on the areas disturbed, the quantity of disturbance, and the length of time soils are subject to conditions that would be affected by erosion processes. All construction activities would comply with Chapter 29 of the CBC, which regulates excavation activities and the construction of foundations and retaining walls, and Chapter 70 of the CBC, which regulates grading activities, including drainage and erosion control. Furthermore, as described in Section 5.11, Hydrology and Water Quality, a site-specific SWPPP would be prepared prior to project construction in accordance with the National Pollutant Discharge Elimination System General Construction Permit and the Chula Vista Development Storm Water Manual. For coverage by the General Construction Permit, the applicant is required to submit to the State Water Resources Control Board (SWRCB) a Notice of Intent (NOI) and develop a SWPPP describing BMPs to be used during and after construction to prevent discharge of sediment and other pollutants in storm water runoff from Village 8 West. The BMPs may include, but are not limited to, silt fences, fiber rolls, gravel bags, temporary desilting basins, velocity check dams, temporary ditches or swales, storm water inlet protection, or soil stabilization measures such as erosion control mats. Prior to the issuance of grading permits, the SWPPP would be required to be prepared to the satisfaction of the City Engineer and the Director of Public Works. Additionally, all construction activities would comply with the Chula Vista Development Storm Water Manual. In addition to the requiring compliance with the project-specific SWPPP and General Construction Permit, the manual requires proper inspection, monitoring, and maintenance of construction BMPs during dry and wet weather conditions. Compliance with applicable regulatory requirements described above, which is prescribed as mitigation measure 5.8-1 for the project, would ensure that potentially significant water quality impacts during on-site construction would be reduced to a less than significant level. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-9 City of Chula Vista November 2013 Following construction of the project, development of Village 8 West would include drainage improvements to minimize soil erosion and loss of topsoil on Village 8 West and along sloped areas. As discussed in detail within Section 5.11, Hydrology and Water Quality, the proposed on-site hydromodification detention basin within the storm drain system would reduce post-construction flows discharging into Wolf Canyon below existing flow volumes. However, the post-project peak flow from the project site to the Otay River is anticipated to increase up to approximately 34 percent over existing flows. The Savage Dam at the Lower Otay Reservoir impounds runoff from over 60 percent of the Otay River’s tributary watershed and as such, the flow capacity downstream of the dam for the Otay River is more than 20,000 cubic feet per second for the 100-year storm event. Village 8 West is downstream of the dam; therefore, the increase in flows associated with the project is a minor portion of the total flow capacity of the Otay River at the point where flows would enter the river. The impact of the increased flow at the project’s discharge point is negligible at peak river flow and would actually be considered beneficial to counteract degradation trends by replacing water impounded by the reservoir (see Appendix I1). Characteristics of the Otay River, including low gradients, significant natural peak flow attenuation, and wide floodplain areas result in this system having a low potential for channel erosion. Consequently, the Otay River system is exempt from hydromodification requirements (see Appendix I1). As a result, the project is not required to reduce post-project flows to pre-project conditions. However, the proposed outlet point from Village 8 West to the Otay River would include an USBR Type IV Energy Dissipater and additional erosion control provided by a section of rip rap. The proposed energy dissipater would reduce flow velocity from Village 8 West and minimize the potential for erosion, although flows to the river would still increase compared to existing conditions. Section 5.11, Hydrology and Water Quality, provides a comprehensive analysis of the existing and proposed hydrology and drainage features of the project. As discussed in Section 5.11, with implementation of the proposed drainage facilities, impacts related to runoff and erosion to would be reduced to a less than significant level. C. Threshold 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. Loose, compressible soils are found over much of the project area, including slope wash, topsoil and the undocumented artificial fill, and the highly weathered portions of older alluvium, terrace, Tertiary Fanglomerate, Otay Formation and metavolcanic rock. These materials may settle under increased loads, or due to an increase in moisture content from changes in irrigation or site drainage. Thus, soils could become unstable over time. As a result, there is the potential for landsliding, lateral spreading, liquefaction and/or collapse as a result on compressible soils. These impacts are considered to be potentially significant. D. Threshold 4: 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. The predominately clayey sand and sandy clay materials, such as bentonite clays, within the Otay Formation, as well as the other materials on site, have a high to very high expansion potential in some areas. However, due to the wide range of expansion potential typically exhibited by soils in this area, areas may possess a very low expansion potential. Expansive soils within pavement, foundation or slab subgrade could heave when wetted, resulting in cracking or failure of these developments improvements. This is considered to be a potentially significant impact. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-10 City of Chula Vista November 2013 E. Threshold 5: Be inconsistent with General Plan geotechnical policies, thereby resulting in a significant physical impact. The project is compared to the applicable General Plan objectives and policies in Table 5.8-2, and applicable GDP policies in Table 5.8-3. As shown in these tables, policy consistency impacts would be less than significant. Table 5.8-2 Project Consistency with Applicable General Plan Geology and Soils Policies Applicable Policies Evaluation of Consistency Objective E 14: Minimize the risk of injury, loss of life, and property damage associated with geologic hazards. Policy E 14.1: To the maximum extent practicable, protect against injury, loss of life, and major property damage through engineering analyses of potential seismic hazards, appropriate engineering design, and the stringent enforcement of all applicable regulations and standards. Policy E 14.2: Prohibit the subdivision, grading, or development of lands subject to potential geologic hazards in the absence of adequate evidence demonstrating that such development would not be adversely affected by such hazards and would not adversely affect surrounding properties. Policy E 14.3: Require site-specific geotechnical investigations for proposals within areas subject to potential geologic hazards; and ensure implementation of all measures deemed necessary by the City Engineer and/or Building Official to avoid or adequately mitigate such hazards. Consistent. The SPA Plan is consistent with these relevant policies in that it will protect against injury, loss of life, and major property damage through engineering analyses of potential seismic hazards, appropriate engineering design, and compliance with applicable regulations and standards; prohibit the subdivision, grading, or development of lands subject to potential geologic hazards; and provide site-specific geotechnical investigations within areas subject to potential geologic hazards and ensure that all measures deemed necessary by the City Engineer and/or Building official to avoid or adequately mitigate such hazards will be implemented. Table 5.8-3 Project Consistency with Applicable GDP Geology and Soils Policies Applicable Policies Evaluation of Consistency Part II, Chapter 8 – Safety Goal: Promote public safety and provide public protection from fire, flooding, seismic disturbances, geologic phenomena and manmade hazards in order to preserve life, health and property; continue government functions and public order; maintain municipal services; and rapidly resolve emergencies and return the community normalcy and public tranquility. Consistent. As discussed under Threshold 1, design of future structures within Village 8 West would be in accordance with the Chula Vista Grading Ordinance, current seismic design specifications of the Structural Engineering Association of California, current CBC standards, and other regulatory requirements. Compliance with these regulatory requirements would ensure that potential seismic ground-shaking impacts to people or structures are less than significant. Objective: Provide public protection from earthquakes, rockslides, and liquefaction in order to minimize loss of life, injury, property damage and disruption or community social and economic activity. Policy: Arrange land uses in a manner consistent with recognized seismic safety practice to promote the continuous services of governmental and emergency facilities and services. Consistent. Site grading and construction would be in accordance with the CBC and the Structural Engineering Association of California to reduce the effect of seismic shaking to the extent possible. As discussed under Threshold 1, liquefaction is not a significant risk on the project site. Compliance with the geotechnical investigation recommendations would reduce potential risks from landslides and unstable soil to a less than significant level. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-11 City of Chula Vista November 2013 Table 5.8-3 Project Consistency with Applicable GDP Geology and Soils Policies (continued) Applicable Policies Evaluation of Consistency Objective: Prevent property damage and loss of life due to landslides, rock falls, and erosion. Consistent. Compliance with the geotechnical investigation recommendations would reduce potential risks from landslides and unstable soil to a less than significant level. As discussed under Threshold 2, compliance with applicable regulatory requirements would ensure that impacts regarding substantial erosion or topsoil loss during future on-site construction activities are less than significant. Part II, Chapter 10 – Resource Protection, Conservation and Management Goal: Minimize soil loss due to development. Objective: Identify development activities, which present a large potential to create excessive runoff or erosion. Policy: Reduce soil loss through slope stabilization, vegetation protection, revegetation and other techniques. Consistent. As discussed under Threshold 2, compliance with applicable regulatory requirements would ensure that impacts regarding substantial erosion or topsoil loss during future on- site construction activities are less than significant. Techniques would include slope stabilization, vegetation protection, and revegetation. Goal: Reduce impacts to environmentally sensitive and potential geologically hazardous areas associated with steep slopes. Objective: Research existing slope conditions prior to land development activities. Policy: Provide geotechnical investigations with each SPA plan. Consistent. Compliance with the geotechnical investigation recommendations would reduce potential risks from landslides and unstable soil to a less than significant level. The geotechnical investigation is provided as Appendix G to this EIR. F. Threshold 6: Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for disposal of wastewater. All development under the SPA Plan and TM would be served by sewer service by the City of Chula Vista. Chula Vista operates and maintains its own sanitary sewer collection system that connects to the San Diego Metropolitan Sewerage System. Proposed sewer facilities that will serve Village 8 are shown on Figure 3-11, Sewer System. Therefore, septic tanks and alternative wastewater disposal systems would not be required and no impact would occur. 5.8.4 Level of Significance Prior to Mitigation A. Exposure to Seismic Related Hazards The exposure of people and structures to moderate-to-severe ground shaking generated from potential earthquakes along active faults in the region is considered to be a less than significant impact. However, grading activities could result in slope instabilities or landslides within the project area. This is considered a potentially significant impact. B. Soil Erosion or Topsoil Loss Impacts associated with soil erosion and topsoil loss during and following project construction would be potentially significant. Compliance with applicable regulatory requirements would ensure that impacts associated with erosion and loss of topsoil would be minimized during construction activities. Following construction, implementation of the proposed drainage plan would reduce the long -term potential for erosion. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-12 City of Chula Vista November 2013 C. Slope Stability The presence of loose compressible materials within Village 8 West could become unstable as a result of the project. As a result, there is the potential for landsliding, lateral spreading, liquefaction and/or collapse. These impacts are considered to be potentially significant. D. Expansive Soils Soils within Village 8 West have high to very high expansion potential. Development of structures on these soils could create substantial risks to life or property. This is considered a potentially significant impact. E. Consistency with Geotechnical Policies No significant impacts related to consistency with geotechnical policies have been identified for implementation of the SPA Plan and TM. F. Waste Water Disposal Systems No significant impacts related to alternative waste water disposal systems have been identified for implementation of the SPA Plan and TM. 5.8.5 Mitigation Measures A. Exposure to Seismic Related Hazards, Slope Stability, and Expansive Soils 5.8-1 Geotechnical Recommendations. Prior to the issuance of each grading permit for Village 8 West, the applicant shall verify that the applicable recommendations in the Geotechnical Investigation prepared by Advanced Geotechnical Solutions, Inc., dated October 22, 2010, have been incorporated into the final project design and construction documents to the satisfaction of the City Engineer. These recommendations address issues including but not limited to site grading, backdrain systems, undercuts, excavation and fill, monitoring, and soil testing. Geotechnical review of grading plans shall include a review of all proposed storm drain facilities to ensure the storm water runoff would not interfere with the proposed geotechnical recommendations. 5.8-2 Slope Factor of Safety. All graded slopes shall have a minimum factor of safety of 1.5. Strategies to increase stability may include, but are not limited to, a stability buttress or sheer pins. All slopes stability strategies shall be approved by the City Engineer. B. Soil Erosion or Topsoil Loss Implementation of mitigation measures 5.11-1 through 5.11-5 in Section 5.11, Hydrology and Water Quality, would reduce impacts related to soil erosion and topsoil loss to a less than significant level. C. Slope Stability Mitigation measures 5.8-1 and 5.8-2 would also reduce impacts related to slope stability. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-13 City of Chula Vista November 2013 D. Expansive Soils Mitigation measures 5.8-1 and 5.8-2 would also reduce impacts related to expansive soils. E. Consistency with Geotechnical Policies No mitigation measures are required. F. Waste Water Disposal Systems No mitigation measures are required. 5.8.6 Level of Significance After Mitigation A. Exposure to Seismic Related Hazards With implementation of mitigation measures 5.8-1 and 5.8-2 seismic hazard impacts related to the implementation of the SPA Plan and TM would be reduced to below a level of significance. B. Soil Erosion or Topsoil Loss With implementation of mitigation measures 5.11-1 through 5.11-5, geology and soil impacts related to soil erosion and topsoil loss would be reduced to below a level of significance. C. Slope Stability With implementation of mitigation measures 5.8-1 and 5.8-2 slope stability impacts related to the implementation of the SPA Plan and TM would be reduced to below a level of significance. D. Expansive Soils With implementation of mitigation measure 5.8-1, expansive soil impacts related to the implementation of the SPA Plan and TM would be reduced to below a level of significance. E. Consistency with Geotechnical Policies Impacts would be less than significant without mitigation. F. Waste Water Disposal Systems Impacts would be less than significant without mitigation. 5.8 Geology and Soils Otay Ranch Village 8 West EIR CV EIR 10-03; SCH No. 2010062093 Page 5.8-14 City of Chula Vista November 2013 This page intentionally left blank.