The Preserve Master Plan EIR

5.5 GEOLOGY AND SOILS

5.5.1 INTRODUCTION

This section describes the characteristics of the rock units, the surficial (alluvial) deposits, and the geologic fault systems within and adjacent to the project area (the ‘plan area’), as those characteristics affect the future development potential. Existing geologic and soils conditions have been analyzed at the ‘plan’ level of environmental review. Areas where geologic/seismic and related hazards are likely to occur are identified in order to provide guidance for more detailed geologic assessments to occur with subsequent projects within the plan area.

This section summarizes a report of geologic, soils engineering and seismic conditions compiled for this plan area by Wilson Geosciences Inc. (2000). The impacts associated with various geologic hazards (fault rupture, ground shaking, liquefaction, foundation suitability, and slope stability) are addressed in this section.

5.5.2 EXISTING CONDITIONS

The plan area is entirely underlain by Pleistocene and Holocene (Recent) alluvium. There is a small bedrock exposure just west of the western boundary. Surficial units, faulting, seismicity, soils and slope, groundwater and subsidence conditions are described in this section.

Surficial Geologic Units

The surface geology of the plan area consists of four distinct alluvial units: two are Holocene (< 12,000 years old) and two are late Pleistocene (>12,000 years old).

Medium-Grained Holocene Alluvium (Qhm)

The youngest surficial unit is a medium-grained Holocene alluvium present in the stream valleys that trend northeast-southwest to northwest-southeast (mainly in the southern half of the property) and as fan deposit in the far northeast corner of the property (Figure 5.5-1). These are unconsolidated deposits of fine-to-coarse-grained sand with interbeds of gravel and silt. As such these sand deposits are moderately to highly permeable and subject to erosion.

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The Preserve Master Plan EIR

Qhm covers roughly 30 percent of the plan area. The edges of the Qhm deposits merge with and overlie the older fine-grained Holocene alluvium (Qhf) described below, in the northeast corner of the property. Qhm in the alluvial valleys overlies the much older fine- and medium-grained Pleistocene alluvium (Qpf and Qpm), which together make up nearly one-half of the plan area.

Engineering characteristics of the Qhm unit are expected to be variable, but generally will require precautions. It is expected that the materials will be relatively porous, compressible, and subject to consolidation under structural loads. Erosion potential is moderate to high.

Fine-Grained Holocene Alluvium (Qhf)

Qhf is the third most abundant geologic unit within the plan area (~25%). It underlies roughly the northern half, and is present along the east and southeast edges, of the property (Fig. 5.5-1). Deposition of this fine-grained unit was in a low-energy, possibly restricted basin. Qhf overlaps older Pleistocene (Qpf and Qpm) alluvium deposited from the north, and rests against the bedrock along the western boundary.

This alluvium is considered moderately permeable to impermeable, and moderately to slightly erodible. Engineering characteristics of the Qhf will require precautions with regard to porosity, compressibility, and long-term consolidation under structural loads.

Medium-Grained Late Pleistocene Alluvium (Qpm)

This Pleistocene alluvium (Qpm) is the least abundant of the four surficial units, covering about 15 percent of the plan area, and is distributed primarily in the southeast corner. Deposition was in a river and alluvial fan environment with sediment sources probably to the north and northeast.

Qpm consists of fine- to coarse-grained sand that is weakly to moderately consolidated. Engineering properties will be variable but generally superior to those of the younger units. Qpm will be porous, moderately permeable, slightly compressible, and subject to some consolidation under structural loads. Erosion potential should be moderate in fresh exposures. Foundation and backfill suitability should be high with proper preparation and compaction.

Fine-Grained Late Pleistocene Alluvium (Qpf)

Qpf is the oldest surficial unit exposed, and along with Qhm, is the most widespread, occupying about 30% the plan area within the south-central portion and along the far western edge. Qpf consists of clay and silty clay. Engineering properties of the Qpf should be similar or somewhat superior to Qhf due to their similar lithology and depositional history. Therefore, Qpf will require precautions,

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Bedrock Formation

The Sycamore Canyon Member of the Puente Formation (upper Miocene) crops out just beyond the southwestern perimeter of The Preserve, on the lower slopes of the . It could be encountered in relatively shallow subsurface excavations within adjacent portions of the plan area. This unit consists of sandstone, conglomerate, siltstone, and shale deposited in a deep offshore marine basin. Provided that standard engineering geologic and soils engineering investigation recommendations are implemented, this bedrock should be suitable for engineering purposes (i.e., foundations and backfill)

Faulting

Large and/or shallow can result in surficial ground rupture along the fault trace. Both -induced shaking and fault rupture hazards are apparent within the plan area. Active (Holocene offset) and potentially active (Pleistocene) faults are potential sources for fault rupture in the plan area. In general, the more recent a fault's last movement, the higher its potential for future movement. Numerous faults in the vicinity of Chino have seismic potentials that can result in severe shaking. No Alquist-Priolo Earthquake Fault Zones are mapped on the site.

Central Avenue Fault

The plan area is just southeast of the potentially active Central Avenue fault. This buried fault is parallel to Central Avenue along its eastside, from just south of Kimball Avenue to the I-10 in Pomona The Central Avenue fault also parallels the Chino fault, which lies to the west along the base of the Chino Hills. Both faults are part of the Elsinore-Chino- system. Although only the North Elsinore and Whittier segments show clear evidence of Holocene offset, several factors suggest that the Central Avenue fault offsets near surface Holocene deposits.

Other Possible Late Quaternary or Younger Faults

An unnamed fault southeast of the plan area extends to the County line and can be projected northwesterly through the site on a trend that parallels the Central Avenue and Chino faults (Exhibit 5.5-2). This fault offsets late Pleistocene medium-grained alluvium (Qpm) on the on the terrace along south side of the Santa Ana River.

Aerial photographs reveal numerous lineaments in this area that appear to be of tectonic origin, but their history of movement is unknown. There is plausible evidence associated with lineaments and

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Seismicity

Table 5.5-1 lists data on the 20 active faults within 50-miles of the plan area that are capable of producing severe earthquakes. Of these, the Chino, Whittier-North Elsinore, and Sierra Madre-San Fernando faults have the potential to generate the strongest earthquakes in the plan area. The maximum probable earthquake is the 100-year event normally considered in design of non-critical structures, whereas the maximum credible event (MCE) must be considered in the design of critical or important facilities such as hospitals, dams, and class III landfills.

MCEs on the Chino, Whittier-North Elsinore, and Sierra Madre-San Fernando, and Elsinore faults would yield accelerations in the plan area ranging from 0.29 to 0.59 g. Although the two segments are capable of larger earthquakes with a higher probability of occurrence, their MCEs would yield peak horizontal ground accelerations here of only 0.25 to 0.26 g due to the distance from the epicenter and thick section of alluvium on top of the bedrock.

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3

1 2

1 2

0.55 g Severe Ground Shaking Potential 1 Potential Liquefaction Area - Very High SO/Euclid Ave. Boundary

Fault Study Zone 2 Potential Liquefaction Area - High City of Chino Boundary

3 Potential Liquefaction Area - Moderate

4 Potential Liquefaction Area - Low H

T Exhibit R 3250 1625 0 3250 5.5-2 O

N SCALE IN FEET Michael Brandman Associates Geologic Hazards

05760012 • 6/2001 CHINO SUBAREA 2 The Preserve Master Plan EIR

Soils and Slope

Four soil associations correspond to the areal distribution of geologic units underlying the plan area:

1. Foster-Grangeville (Fp-Gw; on Recent alluvial fans) 2. Tujunga-Delhi (TD-Dg/AR; on Recent alluvial fans) 3. Merrill-Chino (MB-CE); on older alluvial fans and terraces), and 4. Placentia (Py/BC; on older alluvial fans)

The soils overlying the recent alluvial deposits account for approximately 45% of plan area soils. Foster-Grangeville soils are deep, permeable, devoid of a profile, and formed from unconsolidated materials. Slopes range 0-9%, particles are generally more granular, runoff is slow, and depths reach 60 inches. Tujunga-Delhi soils extend to depths of 60 inches or more, are very permeable, loose and unconsolidated, and subject to wind erosion if unprotected. These soils generally correspond with surficial geologic units Qhm and Qpm in the southeast along the Santa Ana River.

Soils overlying older alluviums (3 and 4 above) comprise the remaining 55% of soils. Merrill-Chino and Placentia soils are silty and sandy loam overlying clay loam, and have 0-9% slopes and depths greater than 60 inches. These soils are moderately erodible and well drained, have a low to moderate permeability, and are associated with surficial geologic units Qhf and Qpf.

The geotechnical engineering properties of the soils in the plan area have not been studied in detail. Concerns and precautions for subsequent potential development activity exist, but no highly unusual or hazardous conditions are apparent.

Average surface slope across the plan area ranges about 0.5 to 1.0 %. Slopes into the primary drainages average about 2 to 3 %. Some gullies have slopes of 10 % or more. The incised Chino Creek and the larger flood plain have slopes of 0.5 to 0.6 % along the flowline. Areas between drainages and the flat valley surface tend to be of low relief and devoid of landslides. With standard geotechnical practices and adherence to Uniform Building Code (UBC) requirements, there is generally a low potential for instability. Slopes greater than 10% on any of the soils present a moderate risk of failure.

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TABLE 5.5-1 DETERMINISTIC SITE PARAMETERS FOR EARTHQUAKES ASSOCIATED WITH ACTIVE FAULTS LOCATED WITHIN APPROXIMATELY 50 MILES OF THE SITE AREA

Maximum Credible Event Maximum Probable Event Approximate Abbreviated Fault Name Peak MMI Peak MMI Distance (Miles) Magnitude Magnitude Acceleration Intensity Acceleration Intensity Chino 3 7.00 0.59 X 5.40 0.29 IX Whittier—North Elsinore 6 7.10 0.39 X 6.00 0.23 IX San Jose 10 6.7 0.23 IX 5.00 0.06 VI Sierra Madre—San Fernando 13 7.30 0.31 IX 6.30 0.17 VIII Cucamonga 14 6.90 0.22 IX 6.10 0.13 VIII Elsinore 14 7.50 0.29 IX 6.60 0.16 VIII Glen Helen Lytle Creek Claremont 19 7.00 0.15 VIII 6.70 0.12 VII Clamshell-Sawpit 23 6.60 0.10 VII 4.90 0.03 V San Andreas (San Bernardino Mountains) 23 8.00 0.26 IX 6.70 0.10 VII San Gorgonio Banning 23 7.50 0.19 VIII 6.60 0.10 VII San Andreas (Mojave Segment) 24 8.0 0.25 IX 7.40 0.16 VIII North Frontal Fault Zone(San Bernardino Mountains) 25 7.70 0.19 VIII 6.00 0.05 VI Raymond 26 7.50 0.16 VIII 4.90 0.02 IV Elysian Park Seismic Zone 29 7.10 0.11 VII 5.80 0.04 V Compton-Los Alamitos 30 7.20 0.17 VIII 5.80 0.06 VI Newport-Inglewood Offshore Zone of Deformation 30 7.10 0.10 VII 5.90 0.04 V San Gabriel 31 7.40 0.12 VII 5.60 0.03 V Verdugo 32 6.70 0.07 VI 5.20 0.02 IV Newport-Inglewood North 33 6.70 0.06 VI 4.20 0.01 II Casa Loma Clark (San Jacinto) 35 7.00 0.08 VII 7.00 0.08 VII

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TABLE 5.5-1 (Cont.) DETERMINISTIC SITE PARAMETERS FOR EARTHQUAKES ASSOCIATED WITH ACTIVE FAULTS LOCATED WITHIN APPROXIMATELY 50 MILES OF THE SITE AREA

Maximum Credible Event Maximum Probable Event Approximate Abbreviated Fault Name Peak MMI Peak MMI Distance (Miles) Magnitude Magnitude Acceleration Intensity Acceleration Intensity Santa Monica-Hollywood 37 7.00 0.07 VI 5.80 0.03 V Wilshire Arch 37 5.70 0.04 V 5.00 0.02 IV Palos Verdes-Coronado Banks—Agua Blanca 38 7.20 0.08 VII 6.20 0.03 V Santa Monica Mountains Thrust 38 7.20 0.12 VII 6.30 0.06 VI Hot Springs Buck Ridge (San Jacinto) 42 7.00 0.06 VI 6.10 0.03 V Coronado Bank-Agua Blanca 46 7.50 0.08 VII 6.70 0.04 V

Notes: The maximum credible event is the largest estimated earthquake magnitude (Richter scale thought to be possible associated with a given fault or fault zone The maximum probable event is the largest estimated earthquake magnitude likely to occur iin a l00-year period associated with a given fault or fault zone Peak acceleration is the estimated peak horizontal ground acceleration in percent gravity abbreviated g) using the attenuation relationshiip of Campbell and Bozorgnia (I994) with an uncertainty of mean + 1-sigma The intensity is the estimated Modified Mercalli Intensity (MMI) at the site which represents an empirical measure of physical daamage to structures and of disturbance to the earth''s surface as a result of various magnitude earthquakes at various site distances.

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Groundwater

The southern Chino Basin area has a relatively shallow water table due to the large drainage area feeding the Santa Ana River and the natural restriction at Corona and the Santa Ana Canyon. In addition, tectonic activity along the Chino-North , which formed the Chino Hills and Santa Ana Mountains, has created a natural damming of the Chino Basin. Water-bearing strata in the Chino Basin are the Holocene and Pleistocene alluviums described above. These units vary in thickness from less than 300 feet along the western edge, to slightly more than 800 feet along a north- south axis through the center of the plan area.

Regional groundwater elevations at the site range from about 550 to 560 feet (depth of approximately 100 feet) at the northeast corner to 500 feet (depth of 30 feet) or less in the southern half. Seasonal variations are generally within a range of about 5 to 10 feet. In the early 1900s, the northern two- thirds of the site included an important zone of artesian ground water. However, groundwater migrated through the poor confining layers into perched zones at shallower depths.

Limited historic data for the upper Santa Ana River Valley indicates that minimum depth to water (MDW) in the project vicinity has ranged from less than 30 feet to greater than 100 feet. Imbalances in recharge versus discharge of the groundwater system suggest that MDW values may vary within the plan area.

Liquefaction

Liquefaction occurs when saturated cohesionless sediments (usually sand or silty sand) transform from a solid to a near liquid state due to an increase in pore-water pressure, often resulting from moderate to severe seismicity. Liquefaction can cause surface structures (e.g., bridges, buildings, storage tanks) to settle non-uniformly and buried structures (e.g., fuel tanks, pipelines) to float. In either situation, severe structural damage is highly likely. Liquefaction can also result in lateral spreading landslides, especially on steep slopes or relatively gentle slopes adjacent to bodies of water.

The expected level of ground shaking in the southerly portions of the plan area is above 0.5 g (Exhibit 5.5-2), high enough to initiate liquefaction. Two of the three key conditions that are conducive to liquefaction, shallow groundwater and cohesionless sands, are thought to be present within the plan area, however insufficient data exist to map either condition with precision. There is limited potential for liquefaction where water is greater than about 50 feet deep (LP ‘4’ on Exhibit 5.5-2), but the potential is higher with depths less than 50 feet (LP ‘3’ on Exhibit 5.5-2). Liquefaction potential is substantially higher where water is less than 30 feet deep (LH ‘1’ and ‘2’ on Exhibit 5.5-2).

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The expected level of seismicity is sufficient for liquefaction where there is shallow groundwater and cohesionless sands. The areas of highest liquefaction potential are those coincident with Holocene deposits (Qhm and Qhf) in the lowest lying areas where there was surface water in the late 1880s, where the water table has been reported at depths of less than 30 feet, and in the major drainages.

Subsidence

Subsidence is often a consequence of discharging groundwater much faster than it can be recharged, especially from thick aquifers of poorly consolidated sediments. Although groundwater withdrawal from such aquifers has been going on in the Chino Basin for approximately 100 years, subsidence in the Chino Basin has been recognized where there are ground fissures northwest of the plan area. It is not known if Chino Basin subsidence features are associated with faults, or if the identified lineaments are the result of subsidence.

5.5.3 THRESHOLDS OF SIGNIFICANCE

Pursuant to Appendix G of the Environmental Quality Act Guidelines (CEQA), a project would typically have a potentially significant impact for geologic, seismic and soil conditions if it would expose people or structures to major geologic or seismic hazards. For purposes of this analysis, if urban land uses and development are proposed within areas directly associated with one or more major hazards, then the impact is judged to be potentially significant.

A project would also be considered to have a potentially significant impact if it would result in one or more of the following:

• Trigger or accelerate processes such as landslides or erosion;

• Disturb or adversely affect significant mineral resources, or unique geologic features of unusual scientific value for study or interpretation;

• Include project grading or construction that would cause displacements, compaction, or over-covering of soil such that project development poses a reasonable probability of damage, endangerment, or other hazard to on- or offsite buildings or structures by ground or soil failure;

• Development of habitable structures in an Alquist-Priolo Earthquake Fault Zone; or

• Expose people to unacceptable risks due to the presence of geologic (including soil and groundwater) or seismic hazards.

Much of the plan area, particularly south of Pine Avenue, has one or more hazards present. Thresholds identified above are for impact assessment at the ‘plan level’ of environmental review.

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Subsequent development proposals and specific project plans must be accompanied by additional site-specific geologic and soils data in order to provide an adequate basis for ‘project-level’ environmental review.

5.5.4 PROJECT IMPACTS

Impacts of the proposed plan are described for the geotechnical properties of surficial geologic units, unique geologic formations, faulting, seismicity and groundshaking, liquefaction, subsidence, and near-surface groundwater.

Geotechnical Properties of Surficial Geologic Units

Qhf on the valley floor is generally devoid of landslides, and therefore has a very low potential for slope instability. Qhm and Qpf in the low relief areas are also generally devoid of landslides. Natural slope instability generally will be limited to surficial failures in Qhf, Qhm and Qpf on slopes greater than 10% that occur almost entirely within the planned open space system.

Slope stability evaluations, required for development within the plan area, must consider the effects of construction on both natural and newly created cut slopes. Design and construction mitigation measures (e.g., retaining walls, reduce slope angles, earth buttress) that conform to City of Chino and UBC (1997) standards must be employed to prevent slope instability. The planned development area is predominantly on slopes of 2% or less. Exceptions may include roadway cuts and fills to achieve grade separation (e.g. depressed Pine Avenue road section). No significant slope stability impacts are anticipated.

The clayey nature of Qhf and Qpf soils (including organic content and hydroconsolidation) make these units susceptible to high expansion coefficients and long-term consolidation. Of special concern in the plan area is the definition of the distribution, character and thickness of surface organic residue (e.g. manure and other organic deposition) within the soils that remain from activities of the dairy industry.

A related concern for development and building foundations is the potential accumulation and/or release of methane in soils with manure and other organic content. However, building code and grading code requirements, and engineering investigation report requirements are in place as safeguards to prevent unsafe design and construction practices related to soil stability and potentially unsuitable foundation conditions. With adherence to these codes and requirements, including implementation of standard mitigation measures (e.g., reinforced foundations, proper surface drainage, removal and replacement of expansive soils) adverse affects on slope stability, foundations and overlying structures can be reduced to less than significant levels.

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Unique Geologic Formations

Geologic formations are considered unique if their outcrop pattern, stratigraphic significance, or fossil content is relatively unusual among the local geology. Such a case may qualify the unit for scientific study of its unique character.

The late Pleistocene (Qpf and Qpm) deposits consist of clay, silty clay, silt, and sand deposited in restricted basin and riverine environments. They are considered unique because they have a limited distribution in the region and their vertebrate paleofauna is unusual and rare. In the Chino Basin area, significant fossils have been recovered within five feet of the surface, which is within the depth range of normal construction. Planned development activities have the potential to disturb or destroy significant paleontological resources that may exist in the near surface soil horizons. Thus, standard mitigation measures for paleontological resources will be included in subsequent project development plans.

Fault Rupture

It is uncertain if the trace of the Central Avenue fault transects the plan area. However, the trace of this feature extends only within the planned open space system south of Pine Avenue, Habitable structures and critical or important public facilities are not allowed within the open space system below the 566 foot high water inundation elevation. Therefore, no significant impact to planned development is anticipated.

Geomorphologic features (‘lineaments’) aligned northwest are generally parallel to the Central Avenue and Chino faults. These features observed from aerial photographs are located predominantly south of Pine Avenue. Although these lineaments are of uncertain origin and significance, their general trend suggests that they are related to faulting. The lineaments may indicate locations with potential in the future to experience ground rupture from a possible severe local earthquake on the Chino-Elsinore fault zone, severe ground shaking from a moderate-to-severe earthquake under the basin, and differential movement and ground fissures from local subsidence and groundwater withdrawal.

Seismicity and Groundshaking

Current Uniform Building Code Standards (ICBO, 1997) set a threshold for horizontal ground acceleration at approximately 0.4 g. for design of non-critical residential structures, and some commercial and industrial facilities. A potentially significant impact exists where this value has a high likelihood of being exceeded during the design life of planned structures (e.g., the MPE acceleration assumed to occur in a 100-year period). This is especially true for this area due to the high water table and thick alluvium, which can amplify seismic waves. As peak horizontal ground

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Standard mitigation for seismic and groundshaking effects includes compliance with building codes and engineering investigation report requirements. However, a higher standard of caution is warranted for these higher levels of acceleration, particularly for critical, important, or high occupancy facilities (e.g. the Community Core, police/fire and civic facilities, schools, churches, medical facilities). Major facilities, and other critical facilities and structures, should receive a more intensive seismic design, review, and possible upgrades with consideration of site-specific geologic conditions and actual earthquake accelerograms.

Liquefaction

In general, liquefaction potential increases through the plan area from north to south, generally corresponding with reduced depth to groundwater (Exhibit 5.5-2). Accurate assessment of liquefaction potentials for specific locations will require data from geotechnical borings and groundwater level monitoring. The depth and intensity of study will vary according to location and type of use/facility for each site-specific project.

Mitigation measures established for development in liquefaction-prone areas include excavation and removal or recompaction of liquefiable soils, in situ ground densification, ground modification and improvement, deep foundations, reinforced shallow foundations, and reinforced structures to resist deformation during liquefaction.

Subsidence

There is currently no specific information on subsidence within the plan area, although subsidence may have induced ground fissures nearby at the California Institution for Men and further to the northwest at Ayala Park. Evidence suggests that the artesian zone encompassing the northern 60% of the plan area has undergone (and may still be undergoing) subsidence. As a result, it is assumed there is a significant potential for subsidence throughout the plan area.

A stepwise program of data evaluation should be conducted, beginning with all existing leveling survey data, to determine subsidence areas and to identify specific measures to reduce potentially significant impacts.

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Near-Surface Groundwater

Groundwater in the Chino Basin occurs at depths of about 100 feet at the northeast corner of the plan area and possibly less than 30 feet in the southern portions. The potential for perched water zones at very shallow levels also exists throughout the plan area. These occurrences can be dealt with in a comprehensive geotechnical engineering investigation that includes subsurface borings to the depth of influence for the proposed construction.

Two potential concerns exist for the presence of shallow groundwater. These relate to 1) water seepage that may collect within, around, or on a structure (e.g., foundations, slabs, cut/fill slopes, and utility trenches), and 2) water that may be intercepted in a deep excavation causing potential dewatering and safety problems. The first instance could cause damage and/or nuisance with regard to the long-term care and maintenance of facilities. The second instance could cause safety problems for workers, as well as the aforementioned problems.

Geologic, hydrologic, and soils engineering/geotechnical investigations should be performed to determine if shallow groundwater may be present at a given site. Such investigations will specify measures to be taken to mitigate the potential affects of any significant hydrologic and engineering concerns.

Soils

Soils in the plan area are generally susceptible to expansion, settlement, and possibly hydroconsolidation. Higher clay content in the soils and repeated episodes of wetting and drying will cause distress to structures in contact with such soils. Consolidation and long-term settlement is most prominent in clay-rich and silt-rich soils due to the loading pressure of man-made structures, including buildings or artificial fill. The added weight can reduce porosity, resulting in settlement of, and possibly damage to, overlying structures. Consolidation and settlement effects are more pronounced under severe seismic shaking (dynamic settlement). Hydroconsolidation can also lead to settlement, but includes the addition of water into the soil structure causing more rapid and more substantial settlements.

Potential impacts associated with expansion, consolidation/settlement, and hydroconsolidation potential can be mitigated through standard, comprehensive geotechnical and soils engineering investigation and analysis. Recommendations made in conjunction with such investigations will specify all necessary steps to be taken to mitigate the potential effects of these soils concerns.

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5.5.5 CUMULATIVE IMPACTS

Development of the proposed project and other approved, pending and probable future projects may expose future populations to regional seismic hazards. However, compliance with seismic safety standards for new construction, recommendations of project geotechnical engineering reports, and ongoing provisions for emergency preparedness and response are anticipated to reduce such risks, on a project-by-project basis, to acceptable levels. Other geologic and soils influences are largely site specific, and there is little if any cumulative relationship between proposed project development and development of cumulative projects identified in Section 4.2.

Impact Summary

The potentially significant geologic hazards affecting land use and development in the plan area are fault rupture and severe groundshaking due to a local moderate to large earthquake, liquefaction (including lateral spread landslides) due to shallow groundwater and severe groundshaking from local and major regional faults, and subsidence-induced ground fissures due to groundwater withdrawal.

Development and buildout according to the proposed plan will have the potential to expose additional people, residences, commercial and industrial development, and public facilities to these geologic and seismic hazards. However, numerous federal, state and local laws, regulations, codes, and policies are in effect to mitigate geologic and seismic hazards experienced within the region and at the project site. Examples are the Earthquake Hazards Reduction Act, the Uniform Building Code, the Alquist- Priolo Earthquake Fault Studies Zone Act, the municipal and county grading codes, Public Resources Code sections dealing with Division of Oil, Gas, and Geothermal Resources, the Subdivision Map Act, and the City of Chino General Plan policies.

While geologic and seismic hazards are expected to be adverse and potentially significant for development within the plan area, conformance with standard measures, code requirements, and recommendations of detailed geotechnical and soils engineering studies required for subsequent development projects, should serve to reduce hazards to less than significant levels.

5.5.6 MITIGATION MEASURES

GS-1. All applications for individual development projects shall include a detailed Geotechnical and Soils Engineering Study which addresses potential hazards associated with fault rupture, seismicity and groundshaking, liquefaction, subsidence and near-surface groundwater. Such studies shall:

• Conform to code requirements, and standards and guidelines established by the City of Chino;

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• Fully and accurately reflect site conditions regarding the possible hazards identified herein; and

• Include all mitigation measures necessary for reducing risks posed by geologic hazards on the project site.

GS-2. All individual developments shall be constructed according to requirements established in geologic studies pertaining to the project site, and general engineering practices established by the City of Chino.

GS-3. Grading operations on all former dairy lands and other agricultural properties will be conducted in accordance with the soils report prepared by a registered soils engineer approved by the City of Chino. The soils engineer will make recommendations concerning removal of any organic material or the proper handling of such material during grading. All manure from dairy corrals and other surface areas shall be stripped and removed prior to grading operations, in accordance with applicable codes and regulations. The potential for methane in remaining soils shall be specifically addressed in soils reports on all former dairy lands and other agricultural properties. Where the potential for methane accumulation or release is identified, soils testing shall occur with results and remedial measures identified in the soils report.

5.5.7 LEVEL OF SIGNIFICANCE AFTER MITIGATION

Compliance with policies, codes and standard conditions designed to reduce geologic and soil hazards, as well the identified mitigation measures, will reduce adverse impacts to less than significant levels.

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