4.4 GEOLOGY AND SOILS

Transcription

1 4.4 GEOLOGY AND SOILS This section analyzes potential geotechnical hazards that may adversely affect the project site or that may be exacerbated by implementation of the proposed project. Information presented in this section is summarized from the Geotechnical Feasibility Assessment, Proposed High-Rise, Mixed-Use Development, Northeast Corner of Beach Boulevard and Orangethorpe Avenue, City of Buena Park, California, prepared by Petra Geotechnical, Inc. in January 2008, and included in Appendix E of this Draft EIR. A complete description of the field investigation methodology and laboratory test procedures is in Appendix F METHODOLOGY The Geotechnical Feasibility Assessment includes (1) a review of published geologic maps for the general area and available geotechnical studies for other sites located within one-half mile radius of the Beach Boulevard and Orangethorpe Avenue intersection (i.e., sites close enough for geotechnical conditions to bear potential relevance to the project site); (2) a subsurface investigation; and (3) a laboratory testing program. The subsurface investigation includes exploratory soil borings and cone penetrometer tests (CPT). 1 Two exploratory hollow-stem auger soil borings were drilled to a depth of 81.5 feet below ground surface (bgs) and five CPT soundings were drilled to a maximum depth of 90 feet bgs. Soil samples were collected at selected depth intervals from the two exploratory borings for laboratory testing. There are a variety of natural soil characteristics that have the ability to adversely affect development of a site, and for which specific engineering measures must be implemented to counteract the presence of such limitations. For the project site, soil engineering characteristics that were investigated in laboratory tests included, but were not limited to, (1) determination of moisture content and dry density; (2) expansion potential; (3) soluble sulfate and chloride content; (4) soil potential of hydrogen (ph) and minimum resistivity; (5) consolidation potential; and (6) shear strength. Additionally, where deemed appropriate based on the CPT data, Standard Penetration tests (SPT) 2 were performed at selected depth intervals. SPT tests involve driving a sample tube a depth of 18 inches into the soil and recording the number of blows from the drill rig hammer needed to penetrate the soil six inches. Soil samples collected from the samplers were also tested in a laboratory. Because the project site is located within an Indentified Liquefaction Zone, a site-specific liquefaction analysis was also performed using the results of the CPT. The Geotechnical Feasibility Assessment is based on the Conceptual Development Plan for the project (site-specific grading and building plans have not yet been prepared) and assesses potential geotechnical constraints based on the construction of multiple high-rise buildings, subterranean parking (up to three levels below ground surface), paved access driveways, and extensive concrete hardscape and landscape areas. Site-specific geotechnical analyses would be required as the project design is refined. The determination of the proposed project s consistency with local and regional plans and policies relevant to geology and soils is discussed in Section 4.7, Land Use and Planning. 1 Cone penetrator testing, defined by ASTM D , is an in-situ test method used to determine the geotechnical engineering properties of soil and determine soil stratigraphy (layers). Soil samples are not collected. The test consists of pushing an instrumented cone tip first into the ground at a controlled rate and recording data from the instruments on the cone to be subsequently interpreted. 2 Standard penetration testing (SPT), defined by ASTM D1586, in an in-situ test method used primarily to determine the relative density of granular deposits, such as silts and sands, that are difficult to obtain in a disturbed sample. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

2 4.4.2 REGULATORY SETTING State California Building Code The California Building Code (CBC) is promulgated under the California Code of Regulations (CCR), Title 24, Parts 1 through 12 (also known as the California Building Standards Code), and is administered by the California Building Standards Commission (CBSC). The CBSC is responsible for administering California s building codes, including adopting, approving, publishing, and implementing codes and standards. The CBC is a compilation of three types of building standards from three different origins: Standards adopted by State agencies without change from the national model codes. Standards adopted and adapted from the national model code standards to meet California conditions. Standards authorized by the California legislature that constitute extensive additions not covered by the national model codes and adopted to address concerns particular to California. The national model code standards adopted into Title 24 apply to all occupancies in California except for modifications adopted by State agencies and local governing bodies. The current version of the CBC is the 2007 triennial edition (2007 CBC). Seismic Hazards Mapping Act of 1990 The Seismic Hazards Mapping Act of 1990 (Public Resources Code, Chapter 7.8, Section ) directs the State of California Department of Conservation to identify and map areas subject to earthquake hazards such as liquefaction, earthquake-induced landslides, and amplified ground shaking. Passed by the State legislature after the 1989 Loma Prieta earthquake, the Seismic Hazards Mapping Act was aimed at reducing the threat to public safety and minimizing potential loss of life and property in the event of a damaging earthquake event. A product of the resultant Seismic Hazards Mapping Program, Seismic Zone Hazard Maps identify Zones of Required Investigation; most developments designed for human occupancy within these zones must conduct site-specific geotechnical investigations to identify the hazard and to develop appropriate mitigation measures prior to permitting by local jurisdictions. As discussed below, the project site is within an identified Liquefaction Hazard Zone EXISTING CONDITIONS Regional and Local Geology The project site is located along the northeasterly margin of the Downey Plain (plain), a broad lowland area that comprises a large portion of the Central Block of the Los Angeles Basin. This plain is bound by the Santa Monica Mountains to the north; the Puente Hills and Santa Ana Mountains to the northeast and east and a northwest-trending alignment of hills; and mesas to the west and southwest that represent the surface expression of uplift along the Newport-Inglewood fault. In the project area, the soils that form this extensive plain are composed primarily of alluvial 3 materials, which were likely deposited as a result of 3 Deposited by running water during the natural processes of stream erosion and re-deposition of sediment. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

3 sedimentation along the Santa Ana and San Gabriel Rivers, with additional materials contributed from smaller canyons that drain the adjoining upland areas to the northeast. The subsurface investigation performed as part of the Geotechnical Feasibility Assessment (included in Appendix F) determined that the project site is underlain predominantly by Quaternary-age alluvial deposits that extend to a depth of approximately 55 feet bgs. The Quaternary deposits consist of interlayered sands, silts, and clays of varying saturation and density. Semi-consolidated sedimentary bedrock of the late Pleistocene-age Lakewood Formation underlies the alluvial sediments to the maximum depth explored, which was 90 feet bgs. Additionally, at the two boring locations (B-1 and B-2), the native alluvial materials were capped by a five- to six-foot-thick layer of artificial fill, presumed to have been placed during historic grading operations on the site. Exhibit 4.4-1, Soil Boring and CPT Location Map, illustrates the soils on site and the location of exploratory soil borings and CPT soundings. Groundwater Information pertaining to the occurrence of groundwater in inland Orange County has primarily been obtained from borehole logs prepared during installation of water wells throughout the area. In general, groundwater occurs in at least three distinct bodies. In downward progression, they are: (1) semi-perched water within the upper portion of Holocene-age alluvial deposits; (2) fresh water within the lowermost portion of the recent alluvium and nearly all deposits of Pleistocene age and some Pliocene rocks; and (3) one or more bodies of saline water underlying the fresh-water aquifers. In the City of Buena Park, there is a shallow body of semi-perched groundwater that occurs within the upper 40 to 50 feet of alluvial sediments. This water typically occurs within thin layers of silty sand and sand at depths of between 5 and 50 feet bgs. In almost all cases, these shallow water-bearing sediments are separated from the underlying fresh-water zones by relatively impermeable layers of silt and clay. Based on the Seismic Hazard Zone report for the Anaheim quadrangle published by the California Geological Survey (CGS; formerly Division of Mines and Geology) and reviewed as part of the Geotechnical Study, the project site is within a Liquefaction Hazard Zone (i.e., within an area where shallow groundwater e.g., less than 40 feet bgs would be expected). Data in the Seismic Hazard Zone report indicate that the historical high groundwater depth for the site is approximately seven feet bgs. During the September 2007 subsurface investigation, static groundwater was encountered at approximate depths ranging between 15 to 20 feet bgs. These depths would be expected to fluctuate in response to seasonal precipitation and changes in the rates of local groundwater withdrawal. The closest wells for which California Department of Water Resources data is available indicate that the groundwater level within the deeper aquifer (i.e., the producing aquifer located within the Lakewood Formation) typically fluctuates from 49 to 100 feet bgs. 4 Additional information regarding groundwater conditions is provided in Section 4.6, Hydrology and Water Quality. Faults and Seismicity As with all of Southern California, the project site lies within a seismically active region. The Geotechnical Feasibility Assessment determined that there are no known active or potentially active faults traversing the project site and the project site is not included within an Alquist-Priolo 4 California Department of Water Resources Well Nos. 3S11W35J3S and 4S/11W1B1. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

4 Earthquake Fault Zone. There are a number of active and potentially active regional faults within 60 kilometers (km; approximately 37 miles) that are considered capable of generating strong ground motion at the site. The name and location of these faults relative to the project site is summarized in Table and are illustrated in Exhibit The closest known active fault considered capable of producing strong seismic shaking at the project site is the Whittier segment of the Elsinore-Whittier Fault zone, which is located approximately 7.6 miles northeast of the site. Further details of the nearest significant faults to the project site are described in the Geotechnical Feasibility Assessment (Appendix F). TABLE SIGNIFICANT FAULTS IN THE PROJECT VICINITY Approximate Distance & Maximum Fault Name Direction from Site Magnitude a Elsinore-Whittier 12.2 km (7.6 mi) northeast 6.8 Puente Hills Blind Thrust 12.4 km (7.7 mi) northwest 7.1 Newport-Inglewood (LA Basin) 14.7 km (9.1 mi) southwest 6.9 San Joaquin Hills Blind Thrust 14.9 km (9.2 mi) southeast 6.6 San Jose 22.7 km (14.1 mi) northeast 6.5 Chino-Central Avenue 25.4 km (15.8 mi) northeast 6.7 Palos Verdes 26.9 km (16.7 mi) southwest 7.1 Newport-Inglewood (Offshore) 30.9 km (19.2 mi) southwest 6.9 Raymond 32.0 km (19.9 mi) north 6.5 Sierra Madre 32.7 km (20.3 mi) north 7.0 Elsinore-Glen Ivy 33.2 km (20.6 mi) southwest 6.8 Verdugo 33.5 km (20.8 mi) northwest 6.7 Clamshell-Sawpit 35.3 km (22.0 mi) north 6.5 Hollywood 36.0 km (22.3 mi) northwest 6.5 Cucamonga 38.5 km (24.0 mi) northeast 7.0 Santa Monica 45.3 km (28.1 mi) northwest 6.6 Malibu Coast 53.0 km (33.0 mi) northwest 6.7 Sierra Madre (San Fernando) 54.0 km (33.5 mi) northwest 6.7 San Gabriel 57.3 km (35.6 mi) north 7.0 a Moment Magnitude (Mw ) Source: Petra 2008 (Appendix F). R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

5 PAS D:/Projects/BuensPa/J002/Graphics/Ex_boring_ ai Geotechnical Boring and CPT Location Map Exhibit Beach and Orangethorpe Mixed-Use Specific Plan Source: Petra Geotechnical, Inc PAS R:/Projects/BuenaPa/J002/Graphics/EIR/Ex4.4-1_boring_ pdf

6 This page is intentionally left blank. Beach and Orangethorpe Mixed-Use Specific Plan R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

7 Secondary Seismic Hazards Secondary seismic hazards include several types of ground failure that can occur as a result of severe ground shaking. These hazards include landsliding, ground subsidence, ground lurching, shallow ground rupture, liquefaction, and soil strength loss. The probability for each type of ground failure depends on the severity of the earthquake, the site s distance from the fault, the topography, and subsoil and groundwater conditions, among other factors. The Geotechnical Feasibility Assessment concludes that liquefaction and liquefaction-related phenomena (lateral spreading and lurching) are the primary concerns at the project site. The project site is identified as susceptible to earthquake-induced liquefaction on the Anaheim Quadrangle Seismic Hazard Zone Map prepared by the CGS THRESHOLDS OF SIGNIFICANCE The following significance criteria are derived from Appendix G of the State CEQA Guidelines. The project would result in a significant impact related to geology and soils if it would: Threshold 4.1: Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: Strong seismic ground shaking. Seismic-related ground failure, including liquefaction. Threshold 4.2: 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. 5 Threshold 4.3: Be located on expansive soil, as defined in Section of the 2007 California Building Code, creating substantial risks to life or property. As previously discussed in Section 2.2.2, Effects Found Not to be Significant, during preparation of the Initial Study, the City of Buena Park determined that the proposed project would not have a significant impact for the following thresholds and no further analysis of these issues is presented in this section. Would the project expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: o 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? o Landslides? 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? 5 As discussed in Section 2.0, Introduction, the Initial Study concluded that landslides would not impact the proposed project because the project site is flat. Therefore, landslides are not further discussed in the following impact analysis. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

8 4.4.5 ENVIRONMENTAL IMPACTS Standard Conditions SC 4-1 SC 4-2 The City of Buena Park adopted the 2007 California Building Code (CBC) in its entirety, as set forth in Chapter (Building Code) of the Buena Park City Code. The Property Owner/Developer shall comply with the requirements of the 2007 CBC as well as any applicable ordinances set forth by the City of Buena Park, or the most recent building and seismic codes in effect at the time the grading plans are approved. Prior to issuance of an encroachment permit by the California Department of Transportation (Caltrans), a preliminary geotechnical report shall be submitted and approved by Caltrans for grading and/or earthwork within Caltrans right-of-way. Corrective work within Caltrans right-of-way shall be done in accordance with Caltrans standard specifications. Impact Analysis Threshold 4.1: Would the project expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving strong seismic ground shaking and/or seismic-related ground failure, including liquefaction? Phase 1 and Phase 2 Seismic Shaking As with most areas of Southern California, the project site may experience moderate to occasionally high intensity ground shaking from a major earthquake on the above-described faults (Table 4.4-1) or other active regional faults in the Southern California area. The Geotechnical Feasibility Assessment included a site-specific probabilistic seismic hazard analysis (PSHA). 6 The PSHA determined that the estimated magnitude-weighted peak ground acceleration, defined as having a 10 percent chance of exceedance in 50 years, is g (39.5 percent of gravity [g]) at the project site. This means that the project site has a 10 percent chance in exceedance of 50 years of experiencing a seismic event resulting in ground motion that is 39.5 the force of gravity. Based on this quantified seismic risk, the Geotechnical Feasibility Assessment determined that implementation of the proposed project would result in less than significant impacts related to seismic ground shaking if the following occurs: (1) conformance with the 2007 CBC (refer to SC 4-1); (2) incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and (3) completion of subsequent design-level studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 and MM 4-2). Secondary Seismic Hazards Potential secondary seismic effects of strong seismic ground shaking at the site include liquefaction and associated settlement, localized lateral spreading, ground cracking and ground lurching, as discussed below. 6 The goal of probabilistic seismic hazard analysis (PSHA) is to quantify the rate (or probability) of exceeding various ground-motion levels at a site given all possible earthquakes. Peak ground acceleration is used to quantify ground motion in a PSHA. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

9 Liquefaction Liquefaction is defined as the transformation of a granular material from a solid state into a liquid state with vibration (most commonly seismic shaking) in the presence of water. It is a phenomenon that tends to occur in areas with shallow groundwater and where the soils are composed of loosely compacted granular materials. During an earthquake, saturated, cohesionless soil particles tend to decrease in volume (condense) because the vibration causes smaller particles to shift and fill in the voids (pores) between larger soil particles normally filled with water. As the soil condenses, less space is left for water, causing an increase in pore water pressure. 7 If the pore water pressure increases sufficiently, the soil loses its strength and transforms into a liquid state. This condition can lead to damage of overlying structures caused by loss of bearing, settlement, or subsidence of the soil. As previously noted, the project site is within a Liquefaction Hazard Zone. Therefore, liquefaction and associated phenomena (lateral spreading and lurching) may have an impact on the development during and after a large seismic event. As discussed above, the Geotechnical Feasibility Assessment included a site-specific liquefaction analysis was performed using the results of the CPT (Appendix F). The liquefaction analysis identified potentially liquefiable soil layers below a depth of ten feet at the CPT locations. Liquefaction was limited to isolated soil layers with a maximum thickness of less than 4 feet between the depths of 10 to 50 feet bgs. The Geotechnical Feasibility Assessment concluded that the thickness of the surficial nonliquefiable layer above the liquefiable zone would be sufficient to prevent liquefaction from occurring on the surface. With conformance to the 2007 CBC (refer to SC 4-1); incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and completion of subsequent design-level studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 and MM 4-2), implementation of the proposed at-grade structures and other project features would be feasible and would result in less than significant impacts related to liquefaction and liquefaction-induced settlement. For cases where the proposed finished grade is lower than the existing grade (such as subterranean parking), the Geotechnical Feasibility Assessment directs that additional liquefaction analysis and seismically induced settlement estimates be performed as site-specific buildings are proposed and designed for the project. Foundations for subterranean structures would likely be placed directly on a layer of liquefiable soil. The Geotechnical Feasibility Assessment concluded that, with conformance to the 2007 CBC (refer to SC 4-1); incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and completion of subsequent design-level studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 and MM 4-2), implementation of proposed subterranean structures would be feasible and would result in less than significant impacts related to liquefaction and liquefaction-induced settlement. Lateral Spreading Lateral spreading of the ground surface during an earthquake usually takes place along weak shear zones 8 that have formed within a liquefiable soil later. This phenomenon takes place towards a free-face (unobstructed slope) and can also take place on ground surfaces with very gentle slopes. Based on the results of the liquefaction analysis, significant lateral spreading 7 Pore water is the water existing in the pores, or spaces, between grains in sedimentary materials. 8 A shear zone is a zone of rock or sediment that has been deformed due to contiguous parts of a geologic body sliding relative to each other. Liquefaction can cause such a deformation in surficial sediments that result in weakened planes on either side of the shear zone, hence a weak shear zone. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

10 within the potentially liquefiable layers beneath the site is not expected. The Geotechnical Feasibility Assessment also considers the potential for lateral spreading associated with the concrete-lined storm drain channel (Fullerton Creek Channel) that runs in an east-west direction less than 200 feet from the northern property boundary. The channel bottom is approximately 17 feet below the existing grade of the project site. The Geotechnical Feasibility Assessment determined that lateral spreading of the site soils towards Fullerton Creek is unlikely. The channel bottom is at a higher elevation than the top of the shallowest soil layer on the project site that is subject to seismically induced liquefaction and lateral spreading. No significant impacts related to lateral spreading would result from the proposed project. Lurching Lurching is a phenomenon in which near-surface soils move in a wave-like manner in response to intense seismic ground shaking, forming ridges or cracks at the ground surface. Because the site is underlain by thick alluvium that consists of interbedded, cohesionless, and clay-rich soils with high moisture content, the potential for ground lurching is likely. In general, only site improvements with light loading (such as pavement, fences, pipelines, and walkways) are severely affected by lurching. More heavily loaded structures would resist such deformation. The Geotechnical Feasibility Assessment notes that the potential for ground lurching at the project site is not considered any greater than for any other site in coastal Orange County having similar subsurface soil and groundwater conditions. The Geotechnical Feasibility Assessment concluded that, with conformance to the 2007 CBC (refer to SC 4-1); incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and completion of subsequent design-level studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 and MM 4-2), implementation of proposed project would be feasible and would result in less than significant impacts related to ground lurching. Off-Site Project Features and Caltrans-Related Project Features Off-site utility and intersection improvements would be subject to the same potential seismic-related geotechnical hazards as described above for the proposed development. The off-site project features do not include habitable structures that would pose a substantial risk to people or structures during a seismic event and would be constructed in compliance with applicable code requirements, and would therefore have less than significant impacts. Because utility improvements would require excavation, there would be the potential for trench wall slope failures, groundwater seepage, and/or damage to pavement in the work area during construction. These utilities (natural gas, water, sewer, etc.) are typically encountered at depths of 2 feet to greater than 20 feet bgs. Recommended actions to preclude impacts may include trench wall support, continuous monitoring of the shoring elements and existing ground surfaces in the adjacent area for movement, as well as off-site pavement rehabilitation, as needed (Petra 2008). MM 4-3 requires that appropriate geotechnical measures, to be identified in the site-specific geotechnical investigation (MM 4-1), be reflected in the contractor specifications prior to issuance of a grading permit that involves work in on- or off-site trenches. As identified in SC 4-2, a preliminary geotechnical report shall be submitted and approved by the California Department of Transportation (Caltrans) for grading and/or earthwork within Caltrans right-of-way and corrective work within Caltrans right-of-way shall be done in accordance with Caltrans standard specifications. With implementation of SC 4-1, conformance to the 2007 CBC; incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and completion of subsequent designlevel studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 through MM 4-3), R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

11 there would be less than significant impacts related to implementation of off-site project features from seismic shaking or secondary seismic hazards. Impact 4.1: Significant impacts related to the potential for strong seismic ground shaking and secondary seismic effects, including liquefaction and liquefaction-induced settlement, can be mitigated to a less than significant level with implementation of all recommendations developed for the proposed project in the Geotechnical Feasibility Assessment as well as site-specific geotechnical investigaton(s) to be prepared in conformance with the requirements of the 2007 CBC, as per SC 4-1 and MM 4-1 through 4-3. Threshold 4.2: Is the project 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 4.3: Is the project located on expansive soil, as defined in Section of the 2007 California Building Code, creating substantial risks to life or property? Phase 1 and Phase 2 There are a variety of natural soil characteristics that have the ability to adversely affect development of a site and for which specific engineering measures must be implemented. The soil constraints identified in the Geotechnical Feasibility Assessment (Appendix F) for the project site are discussed below. Compressible Soils The site contains undocumented artificial fill and native alluvial soils that may be subject to compression under the anticipated building loads that may influence the foundations of structures, if not managed appropriately. Near surface unsuitable alluvial soils would need to be removed and/or recompacted during grading. Remedial grading would create a layer of engineered compacted fill that would extend to a depth of approximately eight feet beneath the foundations for the proposed on-site structures. Ground settlement as a result of consolidation of fill and near-surface alluvium is anticipated to remain within typical construction tolerances for well-designed foundations; this represents a less than significant impact for structures supported on shallow (i.e., less than three feet deep) foundations. For structures that would have deeper subterranean levels, a strengthened or deepened foundation system would be required, as stated in the geotechnical recommendations presented in MM 4-2. The Geotechnical Feasibility Assessment concluded that, with conformance to the 2007 CBC (refer to SC 4-1); incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and completion of subsequent design-level studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 and MM 4-2), implementation of the proposed project would be feasible and would result in less than significant impacts related to compressible soils. Dewatering and Subsidence The project proposes the construction of subterranean parking that would require excavation to depths of approximately 30 feet. Such excavation would encounter perched groundwater and, if R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

12 not properly mitigated, water inflow into the excavation. Therefore, a dewatering program would be required to maintain sidewall and bottom stability within the excavations and to allow construction of permanent retaining structures to proceed. Section 4.6, Hydrology and Water Quality, fully addresses this topic. The lowering of the groundwater table as a result of dewatering activities on the project site could result in the settlement of the subsurface fine-grained soils within the zone of influence of the dewatering, resulting in surface subsidence. Depending on seasonal variations in groundwater depth, the actual excavation depth and proximity of adjoining existing structures, this could result in a significant impact to the proposed structures and existing off-site improvements adjacent to the project site. The site-specific geotechnical study to be prepared pursuant to MM 4-2 would further define the risk of subsidence as well as engineering design and field monitoring measures related to potential subsidence. The Geotechnical Feasibility Assessment concludes that appropriate engineering design and field monitoring of the dewatering system that would be implemented during proposed project construction and/or operation per the geotechnical recommendations to (MM 4-1 and MM 4-2), there would be a less than impacts related to potential subsidence. Expansive Soils At the completion of grading, the project site would be underlain by competent alluvium or engineered fill that exhibits expansion potentials that range from Low to Medium (as classified per Table 18-I-B of the 2001 California Building Code). Site development would require compliance with the applicable sections of the 2007 CBC that specify special foundation/slab design for construction on soils that have an expansion potential of Low or greater. All foundation and slab design recommendations would be subject to the approval of the City s building official prior to implementation of the proposed project. Therefore, with conformance to the 2007 CBC (refer to SC 4-1); incorporation of all engineering recommendations from the Geotechnical Feasibility Assessment (refer to MM 4-2); and completion of subsequent designlevel studies to be prepared when detailed grading and building plans are available and implementation of the recommendations from these reports (refer to MM 4-1 and MM 4-2), implementation of the proposed project would be feasible and would result in less than significant impacts related to expansive soils. Seismically Induced Ground Failure Seismic-related soil instabilities (liquefaction and lateral spreading) are addressed under the Threshold 4.1 analysis. Off-Site and Caltrans-Related Project Features Off-site utility and intersection improvements would be subject to the same potential geotechnical constraints as described for the proposed development. As with the proposed project, off-site improvements would be constructed in compliance with applicable code requirements. As discussed above under Threshold 4.1, because off-site utility improvements would require excavation, there would be the potential for common geotechnical constraints to occur, including trench wall slope failures, groundwater seepage, and/or damage to pavement in the work area during construction. Recommended mitigation would mitigate impacts to a less than significant level related to unstable geologic units or expansive soils. Impacts 4.2 through 4.3: Significant impacts related to location of compressible soils, potentially expansive soils, and/or settlement can be mitigated to a less than R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

13 4.4.6 CUMULATIVE IMPACTS Beach and Orangethorpe Mixed-Use Specific Plan significant level with implementation of all recommendations developed for the proposed project in the Geotechnical Feasibility Assessment and the site-specific geotechnical investigation(s) to be prepared in conformance with the requirements of the 2007 CBC, as per SC 4-1, SC 4-2, and MM 4-1 through MM 4-3. Geology and soils impacts are generally site specific and there is typically little, if any, cumulative relationship between the development of the proposed project and development within a larger cumulative area, such as the citywide development. For example, development at the project site would not alter geologic events or soil features/characteristics (such as groundshaking, seismic intensity, or soil expansion); therefore, the project would not affect the level of intensity at which a seismic event on an adjacent site is experienced. However, project development and future development in the area may expose more persons to seismic hazards. However, the proposed project, as well as the foreseeable projects, would be required to comply with the applicable State and local requirements, such as the CBC. As such, potential impacts would be reduced to a less than significant level and to the maximum extent practicable under current engineering practices. Seismic impacts are a regional issue and are also addressed through compliance with applicable codes and design standards. For these reasons, the project s contribution to cumulative geotechnical and soils impacts would be less than significant. There is the possibility of a zone of influence of dewatering activity extending beyond a project s boundaries (Appendix H-3). This zone cannot yet be exactly defined based on the conceptual project design. However, the preliminary dewatering evaluation estimated that the lateral extent of influence from dewatering would extend approximately 30 feet beyond the project boundary within a year of steady pumping at five gallons per minute. While the preliminary evaluation is dependent on assumed input parameters, that shall be defined as site-specific designs are developed, the results indicate that the zone of influence from dewatering activity is essentially in the immediate vicinity of the project site. Thus, because there are no related projects located within one block of the project site, there would be no potential for cumulative impacts related to dewatering MITIGATION PROGRAM Based on available project information, limited subsurface investigation was conducted for the Specific Plan. In addition to SCs 4-1 and 4-2, the following mitigation measures are required. MM 4-1 Prior to issuance of each grading permit and in compliance with Section et. seq. of the City of Buena Park Municipal Code, the Property Owner/Developer shall prepare a site-specific final geotechnical investigation. Comprehensive buildingspecific subsurface investigations and design-level geotechnical studies shall be prepared by a licensed soils/engineering geologist and/or geotechnical engineer (geotechnical consultant) once definitive grading plans and building foundation details are available for individual buildings. As part of the design-level study, supplemental liquefaction analyses and seismically induced settlement estimates shall be performed for both above ground and subterranean structures. For lightly loaded structures, additional recommendations for foundation design (based on the expansive potential and other engineering characteristics of the on-site soils) shall be provided by the geotechnical consultant. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

14 MM 4-2 Recommendations from the Geotechnical Feasibility Assessment (Petra 2008) and forthcoming design-level geotechnical studies shall be included in the project site preparation and building design specifications prior to issuance of each tract map or parcel map, whichever comes first. Compliance with this requirement shall be verified by the City of Buena Park Engineer. Based on the Geotechnical Feasibility Assessment, preliminary recommendations to be included in the project specifications include, but are not limited to, those summarized below. Preliminary Earthwork and Ground-Modification Recommendations Dewatering shall occur in deeper excavations by dropping the groundwater table to a depth that provides an adequate factor of safety against groundwater intrusion into the sides or the bottom of the excavation. In addition, the groundwater level outside the excavation area shall be monitored to avoid claims for damages from any lowering of the original groundwater level (Petra 2008, 22 23). During construction of the subterranean parking structure, temporary excavations during site grading shall occur that include sidewalls of approximately 30 feet high. These excavations shall be observed by a qualified Geotechnical Consultant for any evidence of potential instability. If necessary, slope configurations shall be revised. All applicable requirements of the California Construction and General Industry Safety Orders, the Occupational Safety and Health Act of 1970, and the Construction Safety Act shall also be followed (Petra 2008, 24). In order to vertically excavate the on-site soils along the property boundaries, either soldier piles and wood or steel laggings shall be used to shore the excavation sidewalls after the dewatering program is installed. The Structural Engineer shall design a cantilever shoring system and triangular earth pressure distribution system for the type of soil to be retained. The Geotechnical Consultant shall observe all soldier pile installations and shall review the shoring design to confirm that they have been designed in accordance with the report recommendations (Petra 2008, 24 28). Excavation activities shall be monitored continuously for any signs of potential lateral and vertical movement. If any movement is observed, the Geotechnical Engineer shall be notified and excavation shall be suspended until appropriate corrective measures are taken (Petra 2008, 28). Although deeper remedial grading may be required after site and building plans become available, on-site soils in building areas shall be overexcavated to a depth of between four and six feet below existing grades and shall be replaced with properly compacted, engineered fill (Petra 2008, 28 29). For exterior hardscape areas, existing ground surfaces shall be overexcavated to a minimum depth of two feet below the existing grades or two feet below the proposed subgrade elevations, whichever is deeper. These excavated materials shall be replaced as properly compacted fill, and the horizontal overexcavation limits shall extend to a minimum horizontal distance of three feet beyond the perimeter of the proposed improvements. The Geotechnical Consultant shall determine actual removal depths based on in-grading observations and tests performed in each hardscape area (Petra 2008, 29). R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

15 Conventional earth-moving equipment shall be used for all grading up to approximately 30 feet. Excavation, and soil compaction for depths below approximately 30 feet, shall be completed using lightly loaded, track-mounted equipment (Petra 2008, 30). The Contractor shall perform remedial removals in accordance with the Geotechnical Report and shall use equipment so as to avoid excessive vibration. Once the Geotechnical Consultant has observed and documented the removal bottom, a layer of woven geotextile material (such as Mirafi HP-370, HP-570, or approved equivalent) shall be placed over the entire removal bottom (i.e., to the full horizontal limits of the overexcavated area) in accordance with manufacturer s specifications. Once this geotextile material has been installed, the Contractor shall place an approximate 12-inch-thick lift of fill material across the top of the material. Once the bottom surface has been adequately stabilized, fill placement shall proceed (Petra 2008, 30 31). Preliminary Structural Design Considerations Structures on the site shall be designed and constructed to resist the effects of seismic ground motions in accordance with the City of Buena Park-adopted 2007 California Building Code (CBC), Section 1613 (Petra 2008, 31 32). The proposed structures on the site shall be designed to withstand the differential settlement estimates provided in the Geotechnical Report (see Petra 2008, 32, Seismically Induced Settlement ). Once definitive grading and foundation plans for construction have been developed, special mitigation measures shall be provided to reduce liquefaction potential to a less than significant level (Petra 2008, 32 33). Foundation Design Considerations Buildings that will have subterranean levels shall have either concrete mat foundations or deepened foundation systems (such as concrete caissons or driven piles). If cast-in-place caisson foundations are considered, special construction techniques shall be required due to shallow groundwater conditions and the presence of cohesionless soil layers (Petra 2008, 33). Appropriate foundation design recommendations for deep subterranean structures shall be performed once the grading concept for the site has been developed and more details concerning the types of structures proposed become available (Petra 2008, 33). Shallow Conventional Foundations Footings shall be designed and constructed in accordance with Sections of the 2007 CBC (Petra 2008, 33 34). All proposed building footing setbacks from the tops of adjacent descending slopes shall conform to both the minimum setback requirements of Subarticle 10 of the County of Orange Grading and Excavation Code and Grading Manual and the minimum requirements of Figure , Section , Section , and Section of the 2007 CBC (Petra 2008, 34). R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

16 Provided that remedial grading is performed within the site as recommended previously, an allowable bearing value of 1,500 pounds per square foot shall be used for the design of 24-inch-square pad footings and 12-inch-wide continuous footings founded at a minimum depth of 12 inches below the lowest adjacent final grade for low-height (2- to 3-story), lightly loaded structures. This value shall be increased by 20 percent for each additional 1 foot of width and/or depth, to a maximum value of 2,500 pounds per square foot. Additional recommendations for foundation design shall be provided once more comprehensive project design details are made available (Petra 2008, 34). Remedial grading shall be performed on site as recommended previously. Foundation design shall consider the anticipated seismically induced total and differential settlements of 1.25 inches and 0.8 inch over a horizontal span of 40 feet, respectively (Petra 2008, 34 35). A passive earth pressure of 250 pounds per square foot of depth to a maximum value of 2,500 pounds per square foot shall be used to determine lateral bearing for building footings provided that remedial grading and ground modification are performed within the site as previously recommended (Petra 2008, 35). The Structural Engineer shall design the proposed foundations in accordance with Section of the 2007 CBC, which are for foundations or footings placed on expansive soils. All slab-on-grade foundations shall be designed based on the design specifications of the Post-Tensioning Institute, as stated in Section of the 2007 CBC (Petra 2008, 35). Concrete Mat Foundations In order to provide for uniform bearing conditions, a minimum two-foot-thick blanket of well-compacted, engineered fill shall be constructed beneath the mat foundations. The mat foundations shall be designed taking into consideration presence of groundwater table and buoyancy forces associated with groundwater as appropriate (Petra 2008, 35). For preliminary planning purposes, an allowable bearing value of 2,000 pounds per square foot shall be used for design of the mat foundation. Bearing values for mats that are heavily loaded or non-uniformly loaded, and settlement estimates shall be provided when more information about dimensions of the mat foundations and bottom elevations of the mat foundations are established (Petra 2008, 36). For preliminary estimation purposes, a coefficient of subgrade reaction for a footing with dimensions of 1 foot by 1 foot shall be taken as 120 pounds per cubic inch (Petra 2008, 36). Preliminary Recommendations for Design of Deep Foundations Driven piles consisting of either 12-inch or 14-inch concrete piles shall be considered for design and shall be designed in accordance with Section 1808 of the 2007 CBC (Petra 2008, 36). For preliminary design of buildings that will have subterranean levels, the bottom of the pile cap elevation shall be at a depth of 30 feet below the ground surface R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils

17 (bgs) and a permanent dewatering program shall be incorporated into the site design in order to maintain the groundwater depth at or below 30 feet bgs. All piles shall be spaced at a minimum on-center spacing of three times the pile width (Petra 2008, 36 37). Soluble Sulfates and General Soil Corrosivity Based on preliminary testing, sulfate-resistant cement is not anticipated. However, the soluble sulfate content of near-surface soils on the site shall be further evaluated as part of the comprehensive design-phase geotechnical study and following the completion of grading operations. Revised recommendations shall be provided, if necessary, based on these evaluations (Petra 2008, 37 38). Results of preliminary chemical tests indicate that on-site soils are likely to be mildly corrosive to metallic building materials. A Qualified Corrosion Engineer shall complete additional on-site soil samples after grading is completed to evaluate the general corrosion potential of the on-site soils and any impact this will have on proposed construction. The Corrosion Engineer shall provide recommendations for mitigation of corrosive soil conditions as deemed appropriate. MM 4-3 Prior to issuance of each grading permit that includes any utility improvements or other work in trenches on or off the project site, the Property Owner/Developer shall demonstrate to the City of Buena Park that appropriate geotechnical measures, as defined in the site-specific geotechnical investigation, have been included in the contractor specifications. These recommendations may include, but not be limited to, trench wall support, continuous monitoring of the shoring elements and existing ground surfaces in the adjacent area for movement, as well as off-site pavement rehabilitation, as needed LEVEL OF SIGNIFICANCE AFTER MITIGATION There would be less than significant impacts related to geology and soils with implementation of SC 4-1, SC 4-2, and MM 4-1 through MM 4-3. R:\PAS\Projects\BuenaPa\J002\Draft EIR_Aug08\4.4_Geology doc Geology and Soils