1. To minimize injury and the loss of life from hazardous natural events.

Transcription

1 Silverlakes Equestrian Sports Park Geology and Soils Geology and Soils Introduction This section describes the existing geology and soils setting and potential effects from project implementation on the proposed Silverlakes Equestrian and Sports Park ( Proposed Project ) site and its surrounding area that are evaluated in this Draft EIR. Descriptions and analysis in this Section are based on information contained in the Geotechnical Feasibility Investigation prepared on June 20, 2008 by Zeiser Kling Consultants as Appendix E. The California Geological Survey and the former Division of Mines and Geology (within the Department of Conservation) were also used to prepare this section of the Draft EIR Regulatory Framework State Alquist-Priolo Earthquake Fault Zoning Act In response to the severe fault rupture damage of structures by the 1971 San Fernando earthquake, the State of California enacted the Alquist-Priolo Earthquake Fault Zoning Act in This act required the State Geologist to delineate Earthquake Fault Zones (EFZs) along known active faults that have a relatively high potential for ground rupture. Faults that are zoned under the Alquist-Priolo Act must meet the strict definition of being sufficiently active and well-defined for inclusion as an EFZ. The EFZs are revised periodically, and they extend 200 to 500 feet on either side of identified fault traces. No structures for human occupancy may be built across an identified active fault trace. An area of 50 feet on either side of an active fault trace is assumed to be underlain by the fault, unless proven otherwise. Proposed construction in an EFZ is permitted only following the completion of a fault location report prepared by a California Professional Geologist City of Norco The following Goals and policies are from the City of Norco s Seismic Safety and Public Safety Element. The City s recommended goals for hazards reduction in the City of Norco are as follows: 1. To minimize injury and the loss of life from hazardous natural events. 2. To minimize damage to public and private property resulting from hazardous natural events. 3. To minimize social and economic dislocations resulting from injury, loss of life, and property damage caused by hazardous natural events. The following recommended policies complement the planning goals and define specific directions for the City to take in reducing natural hazards. 1.0 Adopt new ordinances and amend existing ordinances, which require the incorporation of seismic safety and safety considerations in developments under the City's jurisdiction. 2.0 Provide for the identification and evaluation of existing structural hazards. Michael Brandman Associates 4.6-1

2 Geology and Soils Silverlakes Equestrian Sports Park 3.0 Risks associated with hazardous structures should be reduced to acceptable levels through orderly hazard reduction programs. 4.0 Provide for more detailed scientific analyses of natural hazards in the study area. 5.0 Regulate land use in areas of significant natural hazard. 6.0 Provide for the education of the community regarding the nature and extent of natural hazards in the study area. 7.0 Provide for the maintenance and upgrading of disaster response plans. 8.0 Provide for review and upgrading of the Seismic Safety and Safety Elements Existing Conditions The Proposed Project site has been extensively disturbed in the past and supported a variety of fabricated recreational improvements, including a racehorse track, fishing lakes, a campground, driving range, etc. The current existing site improvements consist of remnant paved (asphalt concrete) and unpaved roads, dirt trails, an abandoned equestrian race track, an abandoned building, a small ranch consisting of a stable and at least three additional buildings, landscaping and related irrigation, and associated underground utilities. Regional Geology The Proposed Project site is located within the Peninsular Ranges Geomorphic Province, and consists of a series of northwest trending valleys and ranges. The site is located within the broad alluvial plain adjacent to the southeastern edge of Chino Hills, and directly north of the northwestern Santa Ana Mountains. Furthermore, the Project site is located on the structure block, known as the Perris Block, which located on the northern portion of the Peninsular Range. Site Geology The Proposed Project is located northwest of the Santa Ana River. The site consists of generally level and flat terrain with elevation declining gradually to the south and southeast (except for Hamner Avenue, which is slightly elevated along the west side of the site). Elevations onsite generally range from 605 feet above mean sea level (msl) at the northeast corner down to 580 feet above msl at the southwest corner, representing a slope of approximately 0.6 percent across the site. The Santa Ana River has flooded the area many times in the past, and several times the Proposed Project site has been inundated to various degrees during high flow events along the river, which has deposited extensive amounts of silt and sediment on the site. The Proposed Project site consists of young wash and young alluvial channel deposits that underlie the site. Tertiary sedimentary rocks and Cretaceous plutonic rocks likely underlie the alluvium at depth. In addition, artificial fill used in previously existing improvements are present on site and generally consist of a mixture of asphalt concrete and large gravel. Throughout the Proposed Project site the topsoil is moderately developed. These deposits are composed of silty to clayey sand with Michael Brandman Associates

3 Silverlakes Equestrian Sports Park Geology and Soils some silt and fine gravel. Topsoil is dry to damp and relative densities ranged from soft to firm. Generally, these deposits are at a depth of approximately 15 feet. Surficial deposits on the Project site consist of Quaternary alluvium. Quaternary alluvial deposits are generally several hundred feet thick and consist of inter-layered sand, silt and clay with minor gravels. Bedrock deposits that underlie the Quaternary alluvium generally consist of crystalline basement rock and are at an extreme depth. Undocumented artificial fills are found throughout the entire Project site because of previous improvements, which consists of well-graded gravels including asphalt concrete. These fills are considered unsuitable for the support of structures or pavements in their present condition. Fill materials vary from a couple of feet to several feet in depth. Younger alluvium deposits throughout most of the Project site are associated with the floodplain of the Santa Ana River and are composed of silty, clayey, and poorly graded sands with some clay and fine to large gravel. The younger alluvium is moist to wet and the relative densities range from loose to medium for coarse-grained soils and medium stiff for fine-grained soils. Generally, these deposits are at a thickness of approximately 45 feet. Older alluvium deposits are located in the northernmost portion of the Project site. These deposits are composed of clayey and well graded to poorly graded sands with silty clay and fine to medium gravel. In comparison to the younger alluvium, older alluvium was also moist to wet and relative densities ranged from very loose to very dense for coarse-grained soils, which are soft for finegrained soils. The older alluviums are at approximately 51 feet in depth. Slope and Surficial Stability Onsite slopes are relatively gentle (0.6 percent) from northeast to southwest and gradually decrease toward the Santa Ana River, except for Hamner Road Avenue which is slightly raised along the west boundary of the site. The Project site has been repeatedly disturbed by human activity and has supported a number of improvements in past. At present, there are no significant slopes onsite and local soils are considered relatively stable (ZKC 2008). Soils Conditions The underlie of the Project site generally consist of artificial fill associated with previously existing improvements, surficial deposits of topsoil, young wash and young alluvial channel deposits. The fill materials generally consist of a mixture of asphalt concrete and large gravel. Tertiary sedimentary rocks and Cretaceous plutonic rocks likely underlie the alluvium at depth. Surficial deposits consist of Quaternary alluvium deposits and are on the order of several hundred feet thick and consist of interlayered sand, silt and clay with minor gravels. Tertiary bedrock deposits underlie the Quaternary alluvium which is underlain by crystalline basement rock at extreme depth. Michael Brandman Associates 4.6-3

4 Geology and Soils Silverlakes Equestrian Sports Park In 1971, the U.S. Soil Conservation Service (SCS, now the Natural Resources Conservation Service) mapped soil units throughout western San Bernardino County. The mapping indicates that onsite soils consist mainly consist of Grangeville loamy fine sand (GoB, acres), Grangeville fine sandy loam (GuB, 18.9 acres), Dello loamy fine sand, (DmA, 2.8 acres), and Terrace escarpments (TeG, 2.2 acres). Soils on the Project site soils have poor drainage and have a slope from 0 to 5 percent. Table shows a summary of this soils information (Exhibit shows the soils onsite). Table 4.6-1: Onsite Soil Characteristics Soil Series Name (SCS) Ag Class Acres* Grangeville loamy fine sand (GoB, acres) IIs Grangeville fine sandy loam (GuB, 18.9 acres) IVw Dello loamy fine sand, (DmA, 2.8 acres) VIIw Terrace escarpments (TeG, 2.2 acres) VIIIe Percent of Site TOTAL Source: SCS 1971 *Approximate Groundwater and Flooding Groundwater Groundwater is present in depths ranged from nine (9) to twenty-six (26) feet below the existing ground surface. Depths to groundwater generally increases with distance away from the Santa Ana River (i.e., groundwater gradient is in a northwesterly direction away from the river). It should be noted that the Santa Ana River contains significant amounts of water during rainy season storms, which can temporarily raise groundwater levels in the local vicinity. Flooding According to the Federal Emergency Management Agency (FEMA), the Proposed Project site lays within Flood Zone A (see Exhibit 4.8-1, Hydrology and Water Quality). Areas in Flood Zone A are located in a 100-year flood zone. Due to the proximity of the Project site to the Santa Ana River and the relatively flat topography of the site, localized flooding may occur during rainy seasons, under current site conditions. Furthermore, due to inter-layered clayey layers of the subsurface alluvial materials, perched groundwater conditions may develop at relatively shallow depths within the subsurface areas from irrigation and periods of rainfall Michael Brandman Associates

5 Silverlakes Equestrian Sports Park Geology and Soils Regional and Local Faults There are no known faults within the Proposed Project site (Exhibit 4.6-2). The site is not within a California designated Alquist-Priolo Earthquake Fault zone. As shown in Table 4.6-2, the closest known active fault depicted by an Alquist-Priolo Earthquake Fault Zone is the Chino Fault located approximately 6 miles southwest of the Project site. Furthermore, there is no evidence of surface fault rupture on the Proposed Project site. Table 4.6-2: Local Faults Fault Name Approximate Distance from Site miles Chino - Central Ave. (Elsinore) 5.7 Whittier 8.3 Elsinore (Glen Ivy) 8.3 San Jose 13.5 Cucamonga 15.0 San Jacinto - San Bernardino 15.7 Sierra Madre 15.8 Elysian Park Thrust 16.0 San Jacinto - San Jacinto Valley 18.7 San Andreas - Southern 22.1 San Andreas - San Bernardino 22.1 Elsinore - Temecula 24.5 San Andreas Rupture 24.7 San Andreas - Mojave 24.7 Source: Zeiser Kling Consultants June 20, Michael Brandman Associates 4.6-5

6

7 Ha mner A v enue S c hleis man R oad th S treet Project Boundary Soil Types 1 DmA - Dello loamy sand, poorly drained, 0 to 2 percent slopes [2.8 acres] 2 GuB - Grangeville fine sandy loam, poorly drained, saline-alk ali, 0 to 5 percent slope [18.9 acres] 3 GoB - Grangeville loamy fine sand, drained, 0 to 5 percent slopes [ acres] 4 TeG - Terrace escarpments [2.2 acres] NORT H Source: NAIP for Riverside County (2005). 800 Michael Brandman Associates / _Soils.mxd Feet Exhibit Soils Map CITY OF NORCO SILVERLAKES EQUESTRIAN SPORTS PARK ENVIRONMENTAL IMPACT REPORT

8

9 Silverwood Lake S an G a br ie l F au lt Z on e rd lt Sa ci nt dd a au nf Ja o S to yo C an n San Bernardino NF Sa Angeles NF San Gabriel Reservoir Fa nb er n ul tz F au lt " $! # " $! # 15 Glendora ong 210 to Fa tz " $! # 60 S an B ernardino C ounty Chino " $! # " $! # Project Site 15 Ch! in o 60 Norco t Or lt ul r Fa u an ge Co Yorba Linda un Prado Flood Control Basin ty 91 El 241 si no re Fa ul Santiago Reservoir 215 Lake Mathews Orange " $! # Woodcrest Corona 91 E l Mo d P e ra lta e n o a n d H il ls F a u lts Riverside Fa i tti e R ivers ide C ounty Los Angeles County e Colton on 10 Ontario ul Pomona Walnut Wh c in F a u lt Not to Scale San Bernardino Ja Text Text Rialto Fontana! os e S an J 215 ll F Hi d Rancho Cucamonga Re Project Site ult n San Dimas a Fa Sa C m uc a lt au lt F au in o e C uc am on ga ard on Morris Reservoir tz on e " $! # El si no Cleveland NF Fa ul 241 tz on e Irvine El Toro " $! # 5 Michael Brandman Associates / _Faults.mxd El s in Lake Elsinore or ef au lt Z on e Source: Census 2000 Data, The CaSIL, MBA GIS NORT H Railroad Canyon Reservoir re 74 5 Miles Exhibit Regional Fault Map CITY OF NORCO SILVERLAKES EQUESTRIAN SPORTS PARK ENVIRONMENTAL IMPACT REPORT

10

11 Silverlakes Equestrian Sports Park Geology and Soils Ground Motion Historically, over the past 205 years, a large number of moderate earthquakes have occurred and been recorded in the region of the Project site. Earthquakes within 62 miles of the site with magnitudes greater than Magnitude 5.0 (M5) have occurred during the years 1800 to 2004 and are summarized in Table Table 4.6-3: Recorded Ground Motion Time Period (1800 through 2004) Approximate distance to nearest historical earthquake with a magnitude greater than M5: 205 years 4.0 miles on December M7.0 Maximum historic, estimated, site acceleration: 0.693g on December 16, 1858 (San Bernardino Region) Number of events exceeding a magnitude M5 within a 100 km radius: 48 As shown in Table 4.6-2, approximately 48 seismic events have exceeded M5 within the last 100 years. The Chino-Central Avenue Fault is expected to generate the largest peak site acceleration at the Project site. The project geotechnical report indicates the Chino- Central Fault may produce a worstcase horizontal peak ground acceleration of 0.49 gravity (g) within the alluvium deposits of the Project area. Accelerations may be expected to occur with a 10 percent probability of exceedance over a 50-year period. Seismic Effects The Project site, as well as the rest of southern California, has a moderate to high seismic risk due to numerous faults and extensive historical and ongoing seismic activity. The actual potential for seismic damage depends on a number of factors, such as the proximity to active or potentially active fault zones and the geologic composition of the area. Seismic damage is generally less intense in consolidated materials, such as bedrock, than in unconsolidated materials, such as alluvium. The primary effects of an earthquake include surface rupture, ground-shaking, liquefaction, subsidence, differential settling, and seiches. The occurrence of any one of these effects depends on many factors, including earthquake intensity, distance from epicenter, soils type, and the moisture content of the soil. The following are considered primary and secondary seismic effects: Ground Rupture Generally considered to occur along pre-existing active faults. Review of available maps and current observations of the site and adjacent areas indicate that there is no active or potentially active faulting on the Project site. Subsidence Subsidence is the result of downward settling of the earth's surface, and may be caused by natural or fabricated processes including compaction or settlement over time and groundwater withdrawal. The Proposed Project site lies within a susceptible subsidence zone according to the Michael Brandman Associates

12 Geology and Soils Silverlakes Equestrian Sports Park Riverside County Land Information System. Based on the geologic setting, composition of on-site soils, and the presence of groundwater beneath the subject site, the potential for subsidence to occur at the site is considered moderate. Liquefaction This is caused by strong vibratory motion due to earthquakes. Research and historical data indicate that loose granular soils or soils of low plasticity below a near surface groundwater table are most susceptible. In order for the potential effects of liquefaction to be manifested at the ground surface, the soils generally have to be granular, or of low plasticity, loose to medium dense, saturated relatively near the ground surface and must be subjected to sufficient magnitude and ground shaking duration. According to the Riverside County Land Information System, the subject site lies within a high-risk zone for liquefaction. Therefore, the Project site is susceptible to liquefaction from the current groundwater surface to a depth of 30 to 40 feet, although this level may vary locally depending on the amount of water in the nearby Santa Ana River. Earthquake-Induced Settlement Ground accelerations generated from a seismic event can produce settlements in earth materials both above and below the water table. The earth materials onsite may undergo seismically induced settlement during the seismic event. The Project site s seismically induced settlement is approximately 1 inch, which is typically at depths between 10 and 48 feet below the existing ground surface. The seismically induced settlement is inversely proportional to the depth of existing groundwater (i.e. the shallower the groundwater the greater amount of estimated settlement). Therefore, the Project site is susceptible to earthquake-induced settlement. Seiches Ground-shaking can cause standing waves or oscillations, called seiches, of water contained in ponds and reservoirs. With severe shaking, onsite or offsite reservoirs may experience seiching, which could cause tank rupture during severe events. In a major event, structures immediately downstream of a reservoir or water tank may experience localized flooding. However, there are no reservoirs or water tanks immediately upstream of the Project site Thresholds of Significance According to the CEQA Guidelines Appendix G Environmental Checklist, to determine whether impacts to geology and soils are significant environmental effects, the following questions are analyzed and evaluated: a.) Exposing people or structures to potentially substantial adverse effects, including the risk of loss, injury or death involving: i. Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault. Refer to Division of Mines and Geology Special Publication Michael Brandman Associates

13 Silverlakes Equestrian Sports Park Geology and Soils ii. Strong seismic ground shaking. iii. Seismic-related ground failure, including liquefaction. iv. Landslides. b.) Result in substantial soil erosion or the loss of topsoil? c.) Be located on a geologic unit or soil that is unstable, or that would become unstable because of the project and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction or collapse? d.) 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? e.) 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? Project Impacts and Mitigation Measures This section discusses potential impacts associated with the development of the Project and provides mitigation measures where appropriate. Earthquakes Impact GS-1 Expose people or structures to potential substantial adverse effects, including the risk of loss, injury or death involving: i) Rupture of a known earthquake fault, as delineated on the most recent Alquist- Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault? Refer to Division of Mines and Geology Special Publication 42. ii) Strong seismic ground shaking? iii) Seismic-related ground failure, including liquefaction? iv) Landslides? [CEQA Geology and Soils Threshold 6(a)(i to iv)] Impact Analysis Earthquake Faults Based on the Geotechnical report produced by Zeiser Kling Consultants, the Project site does not contain any active or inactive faults, and none is known to exist in the immediate area. Therefore, the potential impact from surface fault rupture is considered low to negligible. Seismic Ground-shaking According to the Geotechnical report, the Chino-Central Avenue Fault would generate the largest peak site acceleration at the Project site. The Project site is also subject to moderate to strong groundshaking from seismic activity on a number of regional faults this condition is typical of the general southern California area. Structures will need to be designed in accordance with parameters given within Section 1613 of the 2007 Commercial Building Code (CBC); however, impacts from seismic ground-shaking are considered potentially significant for inhabited structures. Michael Brandman Associates

14 Geology and Soils Silverlakes Equestrian Sports Park Seismic-Related Ground Failure Liquefaction most often occurs in areas of shallow groundwater underlying areas with loose, unconsolidated soils. Liquefaction and seismic settlement are considered to have a moderate to high potential within the younger alluvial areas of the Project site. However, lateral spreading is considered less than significant given the subtle gradient of the Project site (less than 1 percent). The geotechnical report indicated that improvements proposed adjacent to the Santa Ana River banks could increase the likelihood of lateral spread and that the actual amount of lateral spread would need to be evaluated for any permanent buildings/foundations, especially those constructed near the Santa Ana River. The project development plan indicates that the only new permanent buildings will be the multi-purpose building and the hay barn located in the northwestern portion of the site. The buildings are relatively distant from the Santa Ana River, but the footings and related improvements for these buildings will need to be carefully designed to make sure they are safe given the expected ground-shaking, alluvial soils, and shallow groundwater conditions on the Project site. Landslides The Project site is relatively flat with no rocky outcroppings. The Project would not create or be affected by any landslides or falling rocks and therefore, no significant impacts are expected. Level of Significance Before Mitigation Potentially significant impact (ground-shaking, liquefaction, lateral spreading). Mitigation Measures MM GS-1a MM GS-1b Design for Expected Ground-shaking. Prior to the start of grading, new permanent buildings constructed or new temporary buildings installed as part of the Proposed Project will be designed to withstand expected levels of seismic ground-shaking for the area ( worst case peak horizontal acceleration of 0.49 g). The City will also ensure that project improvements are designed in accordance with the 2007 California Building Code (CBC) and the 2006 International Building Code (IBC), which was adopted January 1, 2008, as applicable. General Grading Guidelines. Prior to the start of grading, the following general guidelines shall be adhered to during grading, unless otherwise clarified or changed based on subsequent geotechnical/foundation investigations (see MM GS-1c). These guidelines shall be implemented to the satisfaction of the City Engineer and the City Parks Manager. All areas receiving fill shall be scarified and/or over-excavated, moisture-conditioned to at least two points above optimum moisture content, and compacted to a minimum of 90 percent of the maximum density as determined by ASTM DI Michael Brandman Associates

15 Silverlakes Equestrian Sports Park Geology and Soils All grading shall be performed in accordance with the General Earthwork and Grading Specifications presented in Appendix G of the Geotechnical Report (ZKC 2008), unless specified by the subsequent foundation study, and should conform to all applicable governing agency requirements. Engineered fill materials shall be free from objectionable debris, rocks, or oversized material (material greater than 6 inches). The fill shall be placed in lifts, no greater than 8 inches in loose thickness. Final testing of these fills will be required to verify that the specified compaction has been obtained. All earthwork and grading operations shall be performed under the observation and testing of a qualified geotechnical professional. Any import soil, both select and general, shall be provided to a qualified geotechnical professional for testing at least 48 hours prior to transport to the Project site. Shallow spread foundations may be considered in preliminary design for the project if supported by a subsequent foundation report based on the actual location of structures and supplemental subsurface explorations to confirm these guidelines. For structures supported by conventional shallow spread and continuous footings, an allowable bearing pressure of 1500 pounds per square foot (psf) may be considered. This value may be increased by 200 and 100 psf for each additional foot of depth and width, respectively, to a maximum of 2000 psf. If normal code requirements are used, the allowable bearing pressure value may be increased by one-third for shortduration loads such as wind or seismic forces. These values assume that the foundations are supported by a minimum of 2 feet of engineered fill and that any existing undocumented fills have been completely removed and replaced as engineered fill. A friction coefficient of 0.30 between soil and concrete may also be used for design. For calculating passive pressure, an equivalent fluid weight of 250 psf for each foot of depth may be used, to a maximum total value of 1500 psf. A friction coefficient of 0.30 may be assumed for calculating the resistance to sliding between concrete and soil. MM GS-1c Foundation Studies. Prior to construction of any new buildings or structures on the site, a detailed geotechnical report shall be prepared by a qualified geotechnical professional. Any new reports will outline specific soil conditions and foundation requirements for new buildings based on the actual location of buildings and the specific type of building proposed. These actions shall be consistent with applicable guidelines in the project geotechnical report prepared by Zeiser Kling Consultants on Michael Brandman Associates

16 Geology and Soils Silverlakes Equestrian Sports Park June 20, 2008 as applicable. This measure shall be implemented to the satisfaction of the City Engineer and the City Parks Manager. Additional subsurface exploration, including borings and/or trenches, and additional testing and analysis may be required when finalized development and/or grading plans become available. The geotechnical consultant should review the final approved grading and/or construction plans when they become available in order to develop the requirements for supplemental subsurface exploration and detailed recommendations for the proposed earthwork and site improvements. MM GS-1d Monitoring Grading. Prior to the start of grading, the City will conduct geotechnical observation and testing during the following stages of grading, to the satisfaction of the City Engineer: Upon completion of clearing and grubbing; During excavation and over excavation in alluvial, as well as during removal of the undocumented fill; During all phases of grading, including fill placement and re-compaction; During subdrain and filter material installation; and When any unusual conditions are encountered during grading. Level of Significance After Mitigation Less than significant impact. Soil Erosion or Topsoil Loss Impact GS-2 Result in substantial soil erosion or the loss of topsoil? [CEQA Geology and Soils Threshold 6(b)] Impact Analysis Short-Term Impacts. The project would temporarily increase the potential for erosion by disturbing local soils during grading activities for roads, soccer/equestrian pads, and slopes. Measures would need to be in place to minimize the loss of onsite soils through both wind or water erosion. Construction activities associated with the Proposed Project would involve vegetation removal, grading, and excavation activities that could expose barren soils to sources of wind or water, resulting in erosion and sedimentation on and off the Project site. National Pollutant Discharge Elimination System (NPDES) Phase II stormwater permitting programs regulate stormwater quality from construction sites, which includes erosion and sedimentation. Under the NPDES permitting program, the preparation and implementation of a Storm Water Pollution Prevention Plan (SWPPP) is required for a construction activity more than one acre in size. The SWPPP must identify potential sources of erosion or sedimentation that may be reasonably expected to affect the quality of stormwater discharges as well as identify and implement Best Management Practices (BMPs) that ensure the Michael Brandman Associates

17 Silverlakes Equestrian Sports Park Geology and Soils reduction of these pollutants during stormwater discharges. Typical BMPs intended to control erosion include sand bags, detention basins, silt fencing, landscaping, hydro-seeding, storm drain inlet protection, street sweeping where applicable, and monitoring of water bodies. Prior to construction grading, the applicant must file a Notice of Intent (NOI) to comply with the General NPDES Permit issued to the RWQCB and prepare the SWPPP, which addresses the measures that would be included in the project to minimize and control construction and postconstruction runoff to the maximum extent practicable. In addition, the Proposed Project would be required to comply with the City s code requirements pertaining to grading and excavation. Implementation of the above requirements, including the preparation and implementation of a SWPPP and compliance with City code requirements, would reduce potential construction-related erosion impacts to less than significant levels. Over the long-term, the Proposed Project would result in the coverage of the Project site with impervious surfaces and landscaping, which would eliminate the potential for erosion to occur once the project has been completed. Long-Term Impacts. After the Proposed Project is constructed, potential erosion on the site would be reduced by covering over native soils with turf, graveled access roads and parking areas, and related recreational improvements. Except for building roofs and areas with limited concrete or asphalt cover, the site will have pervious surfaces (i.e., grass, dirt with gravel, sand, etc.) which will further help to reduce potential erosion on the site (and runoff from leaving the site). Given the soil characteristics, and proximity to the Santa Ana River, erosion hazards are considered potentially significant. Level of Significance Before Mitigation Potentially significant impact. Mitigation Measures MM GS-2a Prior to the start of grading, the developer shall prepare a Water Quality Management Plan (WQMP), a Storm Water Pollution Protection Plan (SWPPP), and a Grading Plan to identify all specific actions and Best Management Practices (BMPs) that it will implement to prevent stormwater pollution from construction of the Silverlakes Equestrian and Sports Park for approval by the City Engineer. The SWPPP shall identify BMP implementation, contingency measures, responsible parties, agency contacts, and conditions in construction contracts requiring the Plan to be implemented and shall have the ability to enforce the requirement through fines and other penalties. The plans shall incorporate control measures in the following categories: Soil stabilization practices; Dewatering practices (if necessary); Sediment and runoff control practices; Michael Brandman Associates

18 Geology and Soils Silverlakes Equestrian Sports Park Monitoring protocols; and Waste management and disposal control practices. Once approved by the City, all project contractors shall be responsible throughout the duration of the project for installing, constructing, inspecting, and maintaining the control measures included in the SWPPP and the Grading Plan. The SWPPP shall identify pollutant sources that could affect the quality of stormwater discharges from the project construction site. Control practices shall include those that effectively treat target pollutants in stormwater discharges anticipated from project construction sites. To protect receiving water quality, the SWPPP shall include, but is not limited to, the following elements: Temporary erosion control measures (such as fiber rolls, staked straw bales, detention basins, temporary inlet protection, check dams, geofabric, sandbag dikes, and temporary revegetation or other ground cover) shall be employed for disturbed areas. No disturbed surfaces will be left without erosion control measures in place during the winter and spring months (September 30 March 30). Sediment shall be retained onsite by a system of sediment basins, traps, or other appropriate measures. Of critical importance is the protection of any basins or facilities that might eventually drain to the Santa Ana River. The construction contractor shall prepare Standard Operating Procedures for the handling of hazardous materials on the construction site to eliminate or reduce discharge of materials to storm drains. Where applicable, BMPs performance and effectiveness shall be determined either by visual means (i.e., observation of above-normal sediment release), or by actual water sampling in cases where verification of contaminant reduction or elimination, (inadvertent petroleum release) is required to determine adequacy of the measure. Native grasses or other appropriate vegetative cover shall be established on the construction site as soon as possible after disturbance. MM GS-2b General Drainage and Erosion Control Measures. Prior to the start of grading, drainage over graded areas shall be a minimum one (1) percent gradient, or as required by applicable City of Norco or County of Riverside standards, to nonerosive drainage facilities. Any area drains shall be directed to appropriate storm drainage facilities and shall be routinely checked and repaired as necessary to maintain proper functioning Michael Brandman Associates

19 Silverlakes Equestrian Sports Park Geology and Soils Drainage within 5 feet of any structure foundation shall be graded away from the foundation at a minimum gradient of 2 percent. Drainage shall be carried away from the structure by means of suitable area drainage devices and outlet to a storm drain system or appropriate detention facility. Drainage must not be permitted to flow in an uncontrolled manner over a constructed slope, or be allowed to pond in a graded pad area. Level of Significance After Mitigation Less than significant impact. Unstable Geologic Location Impact GS-3 Be located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction or collapse? [CEQA Geology and Soils Threshold 6(c)] Impact Analysis The Project site is relatively flat with no rocky outcroppings. Therefore, the project would not create or be affected by any landslides or falling rocks, and no significant impacts are expected in this regard. There are no known faults or any California designated Alquist-Priolo Earthquake Fault Zones within the Project site. However, the Project site, as well as the rest of southern California, has a moderate to high seismic risk due to numerous regional faults and extensive historical and ongoing seismic activity. Impacts related to seismic shaking are addressed in Section GS-1. The Project area is subject to moderate to high ground-shaking from numerous regional faults. The site also contains alluvial soils and groundwater levels are relatively shallow (i.e. less than 50 feet in depth). For these reasons, the Riverside County Land Information System (RCLIS) indicates that the Project site lies within a high-risk liquefaction zone and is therefore susceptible. The RCLIS database also indicates the Project site has a moderate potential for subsidence. Level of Significance Before Mitigation Potentially significant impact. Mitigation Measures Implementation of Mitigation Measures GS-1a through GS-1d will help reduce potential impacts related to liquefaction and subsidence to less than significant levels. Level of Significance After Mitigation Less than significant impact. Expansive Soils Impact GS-4 Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), creating substantial risks to life or property? Michael Brandman Associates

20 Geology and Soils Silverlakes Equestrian Sports Park [CEQA Geology and Soils Threshold 6(d)] Impact Analysis Information from the federal Natural Resource Conservation Service (NRCS, formerly the Soil Conservation Service) and the project geotechnical report (ZKC 2008) indicate that the Project site contains sandy loam and loamy sand soils, and do not have a high potential for expansion due to their low clay content. However, historical flooding may have deposited silt and clay materials in isolated locations onsite that were not revealed during the project geotechnical investigation. Since the Proposed Project site contains occupied structures, this risk is considered potentially significant until soil conditions beneath specific building foundation locations can be identified. Level of Significance Before Mitigation Potentially significant impact. Mitigation Measures Implementation of Mitigation Measures GS-1c and GS-1d will help reduce potential impacts related to expansive soils to less than significant levels. Level of Significance After Mitigation Less than significant impact. Wastewater Disposal Systems Impact GS-5 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? [CEQA Geology and Soils Threshold 6(e)] Impact Analysis The Proposed Project will construct various equestrian facilities and sports fields on the site. No new occupied structures are proposed, but there are several restroom facilities proposed as part of the park improvements. Permanent restroom facilities will be connected to City sewer system, while portable restrooms (i.e., porta-potties) will have sealed tanks that are pumped regularly to remove wastes. The recreational vehicle park will also be connected to the City sewer system. Since the Proposed Project will be connected to the sewer system, this impact is considered less than significant. Level of Significance Before Mitigation Less than significant impact. Mitigation Measures None required. Level of Significance After Mitigation Less than significant impact Michael Brandman Associates

21 Silverlakes Equestrian Sports Park Geology and Soils Authors: The table of contents below is for authors and editors to use. To refresh, place your cursor in the table of contents area and press F Geology and Soils Introduction Regulatory Framework Existing Conditions Thresholds of Significance Project Impacts and Mitigation Measures Table 4.6-1: Onsite Soil Characteristics Table 4.6-2: Local Faults Table 4.6-3: Recorded Ground Motion Exhibit 4.6-1: Soils Map Exhibit 4.6-2: Regional Fault Map Michael Brandman Associates

22 Geology and Soils Silverlakes Equestrian Sports Park Bibliography: Please record your references as you draft your section. Author's Name. Year. Report Title. Author's Name. Year. Report Title. Author's Name. Year. Report Title. Author's Name. Year. Report Title. General Instructions We use an author date system within the narrative of the text and a similar format for recording the entry in the references. Web resources In the narrative: (Delano Union School District 2006) In the bibliography: Website name. Year. The web address you visited. The date you accessed the site. For example: Delano Union School District Website Accessed April 23, Personal communications In the narrative: (Sayers, pers. comm.) In the bibliography: Contact s last name, first name. Title, firm or company. Personal communication: form of pers comm ( , telephone, fax, etc.). Date of communication. For example: Sayers, Dorothy. Managing Editor, Bloomsbury Industries. Personal communication: . April 23, Reports in the narrative: (A J Environmental, Inc. 2005) In the bibliography: Firm s name as author; if person, last name, initials only. Year published. Title of Report. Month day published (if known.) For example: A J Environmental, Inc City of Bakersfield Phase I Environmental Site Assessment, Bakersfield OHV Park, Kern County, California, August Michael Brandman Associates