4.5 GEOLOGY AND SOILS

Transcription

1 4.5 GEOLOGY AND SOILS This section addresses the project site geology and soils and analyzes potential changes that would result from development of the Wye Specific Plan project Environmental Setting Topography The Wye Specific Plan area is located in the low rolling hills on the southern slope of the Burton Mesa. The Santa Ynez River lies approximately 4,500 feet south of the site. The majority of the property has a 3 to 7 percent slope to the south-southwest. A moderately steep, west-northwest facing slope including a deeply incised drainage is present in the northwest portion of the site, adjacent to State Highway 1. The topography has been modified in places for grading of unpaved ranch roads. Stratigraphy A soils engineering investigation completed by Earth Systems Consultants (1998a) (see Appendix F-1) for the 32-acre Plan Unit 1 indicates that near surface soils beneath the site consist of Orcutt Sand, which is generally sandy and highly erodible. However, such loose sandy soils are intermixed with localized areas of indurated (i.e., hard) Orcutt Formation sandstone. Geologic mapping completed by Dibblee (1988) indicates that Orcutt Sand similarly underlies the remainder of the project site. Faulting The project is located in a seismically active area typical of southern/central California. The California Uniform Building Code includes the project site within Seismic Zone 4, on a scale of 1 to 4, with 4 being most severe. The majority of coastal California is similarly classified within this zone. The California Geological Survey (formerly the California Division of Mines and Geology [CDMG]) defines active faults as those along which movement has occurred within Holocene time (about the last 11,000 years). Potentially active faults display evidence of movement during Quaternary time (past 1.6 million years). Inactive faults demonstrate no evidence of movement within Quaternary time (CDMG 1992). The potentially active Santa Ynez River and Lion s Head faults are located approximately 3 miles south and north of the site, respectively. The active San Andreas fault, considered one of the most active faults in California, is located about 54 miles northeast of the site. Other active faults in the vicinity of the site include the Los Alamos-West Baseline fault (11 miles to the northeast), Hosgri fault (19 miles to the northwest), and the main branch of the Santa Ynez fault (14 miles to the southeast) (Jennings 1994) (Figure 4.5-1). Although the potential for surface fault rupture during an earthquake is considered low, these faults could cause strong ground shaking during a seismic event, causing considerable damage to structures and underground utilities on-site. CDMG (1996) completed a probabilistic ground Wye Specific Plan EIR 4.5-1

2 Figure Regional Fault Map b&w Wye Specific Plan EIR

3 acceleration study for California. Ground movement caused by seismic waves is measured as ground acceleration (g). The CDMG model shows that there is a 10% chance of peak ground accelerations to exceed g in the vicinity of the site, over a 50-year time span. Liquefaction Liquefaction is a type of ground failure that occurs as a result of loss of shear strength or shearing resistance in loose and sometimes medium dense, saturated, cohesionless soils, due to seismically induced ground shaking. These conditions are most common in alluvial soils; however, some of the near-surface Orcutt Sand deposits on the project site also meet these criteria. The City of Lompoc Seismic and Geologic Conditions Study (The Morro Group 1987) depicts the project site as having a low potential for liquefaction, due to a lack of shallow groundwater. Similarly, the County Seismic Safety and Safety Element (1991) depicts the project site in an area of low liquefaction potential. However, geotechnical trenches excavated on Plan Unit 1 by Earth Systems Consultants (1998a, 1998b) (see Appendix F-1 and F-2, respectively) indicate that perched groundwater is present in loose silty sands, which locally overlie dense Orcutt Formation sandstone. This situation creates a moderate liquefaction potential in near-surface soils. Due to the dense nature of the underlying Orcutt Formation sandstone, the potential for deeper liquefaction at this site is very low. Subsidence Subsidence, as referred to in the County of Santa Barbara Seismic Safety Element (1991), involves deep-seated settlement due to the withdrawal of fluid (oil, natural gas, or water). The Seismic Safety Element states that there are no areas within the County where subsidence has been a problem. In addressing characteristics of the project site vicinity, the City of Lompoc Seismic and Geologic Conditions Study (The Morro Group 1987) concurs with these findings. Compressible/Collapsible Soils Compressible soils are fine-grained cohesive soil of low strength, which consolidate and cause settlement when subjected to fill or structural loads. Collapsible soils are low density, finegrained granular soils. When these soils are saturated with water, the grains are realigned into a configuration of less volume, resulting in a rapid settlement under relatively low loads. The County Seismic Safety Element (1991) depicts the project site as having a low potential for compressible- collapsible soils. Expansive Soils Clay-rich soils are sometimes prone to expansion and contraction during periods of successive wetting and drying. Such volume changes with moisture content can cause cracking of overlying structures. The County Seismic Safety Element (1991) depicts soils on the southern portion of the site (i.e., excluding Plan Unit 2) as having moderate to high expansion potential. However, soil sampling and analyses by Earth Systems Consultants (1998a, 1998b) on Plan Unit 1 of the subject property indicate that on-site soils are nonexpansive. The County Seismic Safety Element depicts soils on the Plan Unit 2 as having low expansion potential. Wye Specific Plan EIR 4.5-3

4 Slope Stability and Landslides The City of Lompoc Seismic and Geologic Conditions Study (The Morro Group 1987) indicates that potentially unstable slopes in the vicinity of the site are limited to locally steep conditions along the flanks of canyons and gullies. The relatively flat-lying Orcutt Formation, consisting of sand and sandstone, underlies the site. The potential for slope instability is related primarily to the internal strength of the soil and rock, rather than to potential bedding plane failures. Slopes across the site generally range from 3 to 7 percent, except along the northwest property boundary, where a steep west-facing slope and deeply incised drainage is present above State Highway 1 in Land Use Area 7 (see Figure 2-3) Impacts and Mitigation Methodology Geology and soils impacts have been evaluated in two ways: 1) impacts of the proposed project on the local geologic environment; and 2) impacts of geohazards on components of the project that may result in substantial damage to structures or infrastructure or expose people to substantial risk of injury. Significance Criteria The following significance criteria are listed in the CEQA Guidelines Appendix G and are consistent with the City of Lompoc General Plan policies. Significant geology and soils impacts would occur if the project: GEO-1: Exposed people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: a. Strong seismic ground shaking and associated seismic related ground failure, including liquefaction; or b. Landslides. GEO-2: Is located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on or off-site landsliding, lateral spreading, subsidence, liquefaction, or collapse. Potential soil erosion impacts are addressed in Section 4.7, Hydrology and Water Quality. The Initial Study (Appendix A) determined that project development would not result in the exceedance of the following threshold criteria, and therefore are not discussed further: 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. The project site is located in an area that was given an overall low to moderate problem rating for geologic hazards in the Santa Barbara County Seismic Safety and Safety Element of the Wye Specific Plan EIR

5 Comprehensive Plan. There are no known earthquake faults that transverse the project site. Potential impacts associated with these geologic conditions would be less than significant. 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 Santa Barbara County Seismic Safety and Safety Element of the Comprehensive Plan indicates that the project site has a low to moderate problem rating for slope stability, landslides, and expansive soils. Potential impacts associated with these geologic conditions would be less than significant. Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for the disposal of wastewater. The project would be served by Mission Hills Community Services District wastewater treatment facility; no septic systems are proposed. Impact GEO-1a: The proposed project would expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving strong seismic ground shaking and associated seismic related ground failure, including liquefaction. The project site is located in a seismically active area where severe ground shaking can be expected during the life of the project. Although no earthquake faults are recorded within the project site or in the vicinity, near surface soils are moderately prone to liquefaction due to the presence of localized areas of perched groundwater in loose silty Orcutt Sand. In order to reduce the potential for differential structure settlement, residential development in Orcutt Sand deposits in northern Santa Barbara County typically requires overexcavation and recompaction of the upper several feet of soils (i.e., the upper 2 to 9 feet). During a substantial seismic event associated with a distant earthquake fault, such ground failure could cause considerable damage to structures and underground utilities on-site, resulting in potentially significant impacts. Mitigation Measures The following measures reduce potential impacts related to seismically induced ground shaking and liquefaction within the project vicinity. GEO-1a.1 Clearing, grubbing, grading, and construction activities on Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1) shall be completed in accordance with recommendations by Earth Systems Consultants (1998a, 1998b), or as amended by future geotechnical report conclusions prepared by a professional civil or geotechnical engineer and approved by the City of Lompoc, and development standards of the Wye Specific Plan. A complete list of recommendations is provided in Appendix F, however, the following recommendations are directly associated with liquefaction and include: a. Intercept drains shall be installed north of the most northerly residential units in Land Use Area 4 and 5 to prevent upslope surface water from seeping into near-surface soils that could enhance the potential for Wye Specific Plan EIR 4.5-5

6 liquefaction. The drains shall extend into the dense Orcutt Formation sandstone. Additional drains shall be needed in other areas where major cuts are planned (e.g., in excess of 8 feet to 10 feet in height). The necessity for additional drains shall be evaluated during and subsequent to grading by a licensed geologist or soils engineer. b. Upper soils containing loose and/or saturated soils shall be removed and recompacted in accordance with an on-site licensed geologist or soils engineer. The depth of removal shall be determined during grading. c. All clearing, grubbing, grading, and construction activities shall be completed in accordance with the most recently adopted California Building Code and local ordinances, which regulates clearing, grubbing, grading, and construction in seismically active areas. Plan Requirements: The applicant shall include the engineering specifications identified above or as amended by future geotechnical studies on the preliminary and final grading plans and construction plans for development within Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1). A preliminary and final soils report and as-built geologic report, documenting overexcavation depths, cut and fill slope configurations, and slope drains, shall be prepared by a licensed geologist or soils engineer. Timing: The preliminary soils report, preliminary as-built geological report, and preliminary grading plans shall be submitted with tentative maps. The preliminary soils report, preliminary as-built geological report, preliminary grading plans, and tentative maps shall be reviewed by the Community Development Department, Public Works Department, and Development Review Board prior to tentative map approval by the Planning Commission. The final soils report, final as-built geological report, and final grading plans shall be submitted concurrently with the Parcel Map or Final Map and Public Improvement Plans. Parcel Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to approval of the Parcel Map by the Planning Commission. Final Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to Final Map approval by the City Council. Final grading and construction plans shall be submitted for review and approval prior to issuance of grading permits for development in Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1). The final soils report shall be reviewed and approved upon completion of grading; the final as-built geologic report shall be reviewed and approved prior to issuance of building permits. No clearing, grubbing, or grading shall occur on-site prior to City approval. MONITORING: The City of Lompoc Community Development Department and Public Works Department, Engineering Division shall review the preliminary and final soils report, preliminary and final as-built geologic report, preliminary and final grading and construction plans, tentative maps, Parcel Map, Final Map, and Public Improvement Plans to ensure the engineering specifications are noted on approved plans prior to issuance of grading permits Wye Specific Plan EIR

7 in Plan Unit 1. The Public Works Department, Engineering Division and Community Development Department shall spot check during grading and construction to ensure compliance with approved plans. GEO-1a.2 A site-specific geotechnical investigation shall be completed for Land Use Areas 2 through 5 (Plan Units 2 through 8) to precisely evaluate potential seismic hazards and determine appropriate standard engineering practices for residential buildout. Clearing, grubbing, grading, and construction activities shall be completed in accordance with the recommendations of this geotechnical report. Plan Requirements: A preliminary and final site-specific geotechnical investigation shall be prepared by a state licensed geologist or soils engineer. Recommendations contained in the site-specific geotechnical investigation shall be noted on the preliminary and final grading plans and construction plans. Timing: The preliminary site-specific geotechnical investigation and preliminary grading plans shall be submitted with tentative maps. The preliminary sitespecific geotechnical investigation, preliminary grading plans, and tentative maps shall be reviewed by the Community Development Department, Public Works Department, and Development Review Board prior to tentative map approval by the Planning Commission. The final site-specific geotechnical investigation and final grading plans shall be submitted concurrently with the Parcel Map or Final Map and Public Improvement Plans. Parcel Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to approval of the Parcel Map by the Planning Commission. Final Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to Final Map approval by the City Council. Final grading and construction plans shall be reviewed and approved by the City of Lompoc prior to issuance of grading permits for development in Land Use Areas 2 through 5 (Plan Units 2 through 8). The final site-specific geotechnical investigation shall be approved by the Public Works Department prior to issuance of building permits. No clearing, grubbing, or grading shall occur on-site prior to City approval. MONITORING: The City of Lompoc Community Development Department and Public Works Department, Engineering Division shall review the preliminary and final site-specific geotechnical investigation, preliminary and final grading and construction plans, tentative maps, Parcel Map, Final Map, and Public Improvement Plans to ensure consistency with the recommended standard engineering practices for residential buildout. The Public Works Department, Engineering Division shall field inspect during clearing, grubbing, grading, and construction activities to ensure compliance with the approved plans. Wye Specific Plan EIR 4.5-7

8 Residual Impacts Mitigation measures GEO-1a.1 and GEO-1a.2 would reduce potential effects related to seismically-induced ground shaking such that residual seismic impacts would be adverse, but less than significant (Class II). Impact GEO-1b: The proposed project would potentially expose people or structures to substantial adverse effects, including the risk of loss, injury, or death involving slope failure. No existing landslides are located on or immediately adjacent to project site. With the exception of Land Use Area 7, topography across the project site is gently to moderately sloping. Land Use Area 7, which includes a steep hillside along State Highway 1, would remain in open space, therefore avoiding impacts resulting from residential development. The generally flat-lying sands and sandstone of the Orcutt Formation throughout the remainder of the site are not prone to slope failure under existing conditions. However, creation of oversteepened slopes during grading on other developed areas could result in slope failure, which would be considered a significant impact. Mitigation Measures The following measures would minimize potential impacts associated with unstable slope conditions. GEO-1b.1 Clearing, grubbing, grading, and construction activities on Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1) shall be completed in accordance with recommendations by Earth Systems Consultants (1998a, 1998b), or as amended by future geotechnical report conclusions prepared by a professional civil or geotechnical engineer and approved by the City of Lompoc, and development standards of the Wye Specific Plan. A complete list of recommendations is provided in Appendix F, however, the following recommendations are directly associated with unstable slopes and include: a. Clearing, grubbing, and grading activities shall be designed to avoid cuts above 4 feet in height from base grade to top-of-slope and fills. b. Cut and fill slopes shall be no greater than 2:1 (horizontal to vertical) and should generally vary from 2:1 to 4:1. In retention basins, slopes shall be contoured and vary from 4:1 to 6:1 or flatter. c. Retaining walls shall be designed to be 4 feet high or less in common areas. d. Cut and fill slopes in common areas shall be hydro-seeded and landscaped with trees and shrubs as soon as practical after completion of grading. On private lots, slopes over 6 feet high shall be hydro-seeded upon completion of construction of buildings on those lots. e. All slope grading shall be designed in accordance with the recommendations of a soils engineer Wye Specific Plan EIR

9 Plan Requirements: The applicant shall include the engineering specifications identified above on the preliminary and final grading plans and construction plans for development within Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1). A preliminary and final soils report and an asbuilt geologic report, documenting overexcavation depths, cut and fill slope configurations, and slope drains, shall be prepared by a licensed geologist or soils engineer. Timing: The preliminary soils report, preliminary as-built geological report, and preliminary grading plans shall be submitted with tentative maps. The preliminary soils report, preliminary as-built geological report, preliminary grading plans, and tentative maps shall be reviewed by the Community Development Department, Public Works Department, and Development Review Board prior to tentative map approval by the Planning Commission. The final soils report, final as-built geological report, and final grading plans shall be submitted concurrently with the Parcel Map or Final Map and Public Improvement Plans. Parcel Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to approval of the Parcel Map by the Planning Commission. Final Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to Final Map approval by the City Council. Final grading and construction plans shall be submitted for review and approval prior to issuance of grading permits for development in Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1). The final soils report shall be reviewed and approved upon completion of grading; the final as-built geologic report shall be reviewed and approved prior to issuance of building permits. No clearing, grubbing, or grading shall occur on-site prior to City approval. MONITORING: The City of Lompoc Community Development Department and Public Works Department, Engineering Division shall review the preliminary and final soils report, preliminary and final as-built geologic report, preliminary and final grading plans and construction plans, tentative maps, Parcel Map, Final Map, and Public Improvement Plans to ensure the engineering specifications are noted on approved plans prior to issuance of grading permits in Plan Unit 1. The Public Works Department, Engineering Division and Community Development Department shall spot check during grading and construction to ensure compliance with approved plans. GEO-1b.2 A site-specific geotechnical investigation shall be completed for Land Use Areas 2 through 5 (Plan Units 2 through 8) to precisely evaluate potential slope stability hazards and determine appropriate standard engineering practices for residential buildout. Clearing, grubbing, grading, and construction activities shall be completed in accordance with the recommendations of this site-specific geotechnical report. Plan Requirements: A preliminary and final site-specific geotechnical investigation shall be prepared by a state licensed geologist or soils engineer. Recommendations contained in the site-specific geotechnical investigation shall Wye Specific Plan EIR 4.5-9

10 Residual Impacts be noted on the preliminary and final grading plans and construction plans. Timing: The preliminary site-specific geotechnical investigation and preliminary grading plans shall be submitted with tentative maps. The preliminary sitespecific geotechnical investigation, preliminary grading plans, and tentative maps shall be reviewed by the Community Development Department, Public Works Department, and Development Review Board prior to tentative map approval by the Planning Commission. The final site-specific geotechnical investigation and final grading plans shall be submitted concurrently with the Parcel Map or Final Map and Public Improvement Plans. Parcel Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to approval of the Parcel Map by the Planning Commission. Final Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to Final Map approval by the City Council. Final grading and construction plans shall be reviewed and approved by the City of Lompoc prior to issuance of grading permits for development in Land Use Areas 2 through 5 (Plan Units 2 through 8). The final site-specific geotechnical investigation shall be approved by the Public Works Department prior to issuance of building permits. No clearing, grubbing, or grading shall occur on-site prior to City approval. MONITORING: The City of Lompoc Community Development Department and Public Works Department, Engineering Division shall review the preliminary and final site-specific geotechnical investigation, preliminary and final grading and construction plans, tentative maps, Parcel Map, Final Map, and Public Improvement Plans to ensure consistency with the recommended standard engineering practices for residential buildout. The Public Works Department, Engineering Division shall field inspect during clearing, grubbing, grading, and construction activities to ensure compliance with the approved plans. Mitigation measures GEO-1b.1 and GEO-1b.2 would apply standard engineering practices that would reduce potential effects related to slope failure such that residual impacts related to slope stability would be adverse, but less than significant (Class II). Impact GEO-2: The proposed project is located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on or off-site landsliding or differential settlement. As indicated in Impact GEO-1b, Land Use Area 7 consists of a steep, west-facing slope located adjacent to State Highway 1. Although this area would be maintained in open space, increased impervious surfaces would be created on adjacent topography in Land Use Areas 2 and 4. Increased surface runoff due to an increase in impermeable surfaces to the east and southeast that drain into Land Use Area 7 could lead to increased surface flow down the slope, slope saturation, and associated shallow slope failure, which could impact the adjacent highway. In addition, the juxtaposition of loose Orcutt Sands and relatively dense Orcutt Formation Wye Specific Plan EIR

11 sandstone at shallow depth creates conditions prone to differential settlement of overlying structures and infrastructure. Impacts associated with both potential slope failure and differential settlement are considered potentially significant. Mitigation Measures The following measures would reduce potentially significant impacts associated with slope failure and differential settlement. GEO-2.1 Clearing, grubbing, grading, and construction activities on Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1) shall be completed in accordance with recommendations by Penfield & Smith (2001) (see Appendix E- 2), Earth Systems Consultants (1998a, 1998b) (see Appendix F), or as amended by future geotechnical report conclusions prepared by a professional civil or geotechnical engineer and approved by the City of Lompoc, and development standards of the Wye Specific Plan. A complete list of recommendations is provided in Appendices E-1 and F, however, the following recommendations are directly associated with differential settlement and slope failure and include: a. Diversion of drainage away from the bluffs at Plan Unit 2, through the use of brow ditches and downdrains; and b. Overexcavation and recompaction of soils subject to differential settlement located beneath proposed structures. Plan Requirements: The applicant shall include the engineering specifications identified above on the preliminary and final grading plans and construction plans for development within Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1). A preliminary and final as-built geologic report, documenting overexcavation depths, cut and fill slope configurations, and slope drains, shall be prepared by a licensed geologist or soils engineer. Timing: The preliminary as-built geological report and preliminary grading plans shall be submitted with tentative maps. The preliminary as-built geological report, preliminary grading plans, and tentative maps shall be reviewed by the Community Development Department, Public Works Department, and Development Review Board prior to tentative map approval by the Planning Commission. The final as-built geological report and final grading plans shall be submitted concurrently with the Parcel Map or Final Map and Public Improvement Plans. Parcel Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to approval of the Parcel Map by the Planning Commission. Final Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to Final Map approval by the City Council. Final grading and construction plans shall be submitted for review and approval prior to issuance of grading permits for development in Plan Unit 1 (Land Use Area 1 and portions of Land Use Area 2 within Plan Unit 1). The final as-built geologic report shall be reviewed and Wye Specific Plan EIR

12 approved prior to issuance of building permits. No clearing, grubbing, or grading shall occur on-site prior to City approval. MONITORING: The City of Lompoc Community Development Department and Public Works Department, Engineering Division shall review the preliminary and final as-built geologic report, preliminary and final grading and construction plans, tentative maps, Parcel Map, Final Map, and Public Improvement Plans to ensure the engineering specifications are noted on approved plans prior to issuance of grading permits in Plan Unit 1. The Public Works Department, Engineering Division and Community Development Department shall spot check during grading and construction to ensure compliance with approved plans. GEO-2.2 A preliminary and final site-specific geotechnical investigation shall be completed for Land Use Areas 2 through 5 (Plan Units 2 through 8) to evaluate potential slope stability and differential settlement hazards. Clearing, grubbing, grading, and construction activities shall be completed in accordance with recommendations of the site-specific geotechnical report. Plan Requirements: A preliminary and final site-specific geotechnical investigation shall be prepared by a state licensed geologist or soils engineer. Recommendations contained in the preliminary and final site-specific geotechnical investigation shall be noted on the preliminary and final grading plans and construction plans. Timing: The preliminary site-specific geotechnical investigation and preliminary grading plans shall be submitted with tentative maps. The preliminary site-specific geotechnical investigation, preliminary grading plans, and tentative maps shall be reviewed by the Community Development Department, Public Works Department, and Development Review Board prior to tentative map approval by the Planning Commission. The final site-specific geotechnical investigation and final grading plans shall be submitted concurrently with the Parcel Map or Final Map and Public Improvement Plans. Parcel Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to approval of the Parcel Map by the Planning Commission. Final Maps and Public Improvement Plans shall be reviewed by the Community Development Department and Public Works Department prior to Final Map approval by the City Council. Final grading and construction plans shall be reviewed and approved by the City of Lompoc prior to issuance of grading permits for development in Land Use Areas 2 through 5 (Plan Units 2 through 8). The final site-specific geotechnical investigation shall be approved by the Public Works Department prior to issuance of building permits. No clearing, grubbing, or grading shall occur on-site prior to City approval. MONITORING: The City of Lompoc Community Development Department and Public Works Department, Engineering Division shall review the preliminary and final site-specific geotechnical investigation, preliminary and final grading and construction plans, tentative maps, Parcel Map, Final Map, and Wye Specific Plan EIR

13 Residual Impact Public Improvement Plans to ensure consistency with the recommended standard engineering practices for residential buildout. The Public Works Department, Engineering Division shall field inspect during clearing, grubbing, grading, and construction activities to ensure compliance with the approved plans. Mitigation measures GEO-2.1 and GEO-2.2 would reduce potential effects related to slope failure and differential settlement such that residual impacts would be adverse, but less than significant (Class II) Cumulative Impacts Potentially significant impacts would occur in association with buildout of the Wye Specific Plan, due to potential seismically induced liquefaction, unstable slopes, and differential settlement. Probable future related projects that would be subject to similar geohazard impacts include those projects identified in Chapter 3.0 (Table 3-1). Cumulative impacts of these projects would be potentially significant but feasibly mitigated with implementation of standard geotechnical investigations and resultant grading and construction design. Similarly, the project s contribution to cumulative impacts would be significant but feasibly mitigated (Class II) with implementation of mitigation measures GEO-1a.1, GEO-1a.2, GEO-1b.1, GEO-1b.2, GEO-2.1, and GEO-2.2. In addition, nearby projects would also be subject to environmental review and appropriate mitigations established for each project prior to development Consistency with Plans and Policies Safety Element Policy 1.4 The City shall avoid placement of critical facilities in hazardous areas as identified on the Geologic and Soils Hazard Areas map, including slope and liquefaction hazard areas. Consistent. The project is not located in a City designated geologic hazard area. However, the site is not currently within the City nor the City s sphere of influence, so no such designated areas would be expected on the site. The project site would potentially be subject to seismically induced ground failure, including liquefaction. Although a school has been proposed for Land Use Area 5, the potential for liquefaction would be reduced to less than significant levels through incorporation of mitigation measures GEO-1a.1 and GEO-1a.2, resulting in project consistency with this policy. In addition, Land Use Area 7 is comprised of steep slopes. However, this area would remain as open space, resulting in no impacts to the proposed project. Therefore, the proposed project would be consistent with this policy. Policy 4.1 The City shall not permit placement of critical facilities as identified in the Emergency Preparedness Element in areas prone to slope instability or liquefaction during an earthquake. Wye Specific Plan EIR

14 Measure 26 Policy 4.2 Policy 4.3 Policy 5.1 Measure 24 Consistent. A school has been proposed for Land Use Area 5. This area is not prone to slope instability. The potential for liquefaction would be reduced to less than significant levels through incorporation of mitigation measures GEO-1a.1 and GEO-1a.2, resulting in project consistency with this policy. The City shall require the liquefaction potential to be evaluated by a Registered Soils Engineer for all critical facilities and major structures (reinforced concrete or steel frame, two-stories or more in height) located on the floor of the Lompoc Valley. Consistent. The project is not located on the Lompoc Valley floor. Although a school has been proposed for Land Use Area 5, the potential for liquefaction would be reduced to less than significant levels through incorporation of mitigation measures GEO-1a.1 and GEO-1a.2, resulting in project consistency with this policy. The City shall continue to identify all existing seismically vulnerable buildings and require that they be reinforced to minimize risk of personal injury during an earthquake. Consistent. No existing structures would be retained as part of the project; therefore, the project would be consistent with this policy. The City shall ensure that all new development is constructed in accordance with current seismic safety design standards. Consistent. Mitigation measures GEO-1a.1 and GEO-1a.2 would ensure that grading and construction is completed in accordance with current seismic safety design standards; therefore, the project would be consistent with this policy. The City may permit development on hillsides only where it can be demonstrated that geologic conditions are sound for construction purposes. Consistent. The only steep slopes on the property (Land Use Area 7) would be retained as open space. The remaining gentle to moderately sloping topography would be graded in accordance with standard geotechnical engineering (mitigation measures GEO-1a.1, GEO-1b.1, and GEO-1b.2). Therefore, the project would be consistent with this policy. The City shall require the following in the slope hazard areas as delineated on the Geologic and Soils Hazards map: As a part of the environmental review process, a preliminary engineering geologic report shall be prepared under City direction which includes recommendations for remedial measures to ensure the stability of natural and manufactured slopes within the area affected by the development. The report shall be prepared by a Certified Engineering Geologist, licensed in the State of California; Prior to the approval of construction permits, the applicant shall submit a final engineering geologic report of the graded site addressing the stability of natural and manufactured slopes based on conditions as actually encountered during grading. The Wye Specific Plan EIR

15 report shall be prepared by a Certified Engineering Geologist, licensed in the State of California, and shall include an as-graded geologic map; and The City shall require the following for areas with 20% slopes or greater: Stability of slopes shall be addressed by a Registered Soils Engineer as a part of the routine soils investigations required by the City. Measure 28 Consistent. The project site is not located within a geologic hazard area, as designated on the Geologic and Soils Hazards Map. However, any potential slope stability issues would be addressed through implementation of mitigation measures GEO-1b.1 and GEO-1b.2, such that the project would be consistent with this policy. The City shall amend the Zoning Ordinance to require developers proposing structures on or adjacent to steep slopes to: 1) Develop and implement hillside drainage plans to reduce the risk of further movement by existing landslides; 2) Site new structures away from steep hillsides and the toes of existing landslide surfaces, reducing the potential for damage from landslide movement or burial; and 3) Perform site-specific slope stability investigations and analyses by a Registered Geotechnical Engineer. Consistent. The northwest portion of the project site is comprised of steep slopes that would be geotechnically unfit for residential development. The Wye Specific Plan has designated this area (Land Use Area 7) as open space. Mitigation measure GOE-1a.1 would require intercept drains to be installed adjacent to the most northerly structures in Land Use Area 4 and 5 in order to prevent upslope surface water from seeping into near-surface soils. In addition, mitigation measure GEO-2.1 would ensure that drainage is diverted away from this steep slope, to avoid potential slope instability, in accordance with a drainage plan and geotechnical investigation prepared for the project. Adherence to these mitigation measures would ensure that the project would be consistent with this policy. Land Use Element Policy 6.2 The City shall maintain an Open Space designation for all areas in which topographic, geologic, or soil conditions indicate a significant danger to future occupants. Consistent. The northwest portion of the project is comprised of steep slopes which would be geotechnically unfit for residential development. The Wye Specific Plan has designated this area (Land Use Area 7) as open space; therefore, the project would be consistent with this policy. Wye Specific Plan EIR

16 This page intentionally left blank Wye Specific Plan EIR