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Home My WebLink AboutDEIR Ch 05_05_GEO 5. Environmental Analysis 5.5 GEOLOGY AND SOILS The analysis in this section is based in part on the following technical report(s): . City of San Bernardino General Plan Update Technical Background Report, Chapter 5, Hazards, Envicom Corporation, February 1988. . Feasibility Study, Report of Preliminary Geotechnical Evaluation Proposed Mixed-Use Development, Arrowhead Springs, Soils Southwest, Inc., February 14, 2005 (see Volume III, Appendix D). 5.5.1 Environmental Setting 5.5.1.1 San Bernardino General Plan Update Geologic Setting General Discussion The City of San Bernardino lies within the Bunker Hill-San Timoteo Basin, which is bound by the active San Andreas Fault zone on the northeast and the active San Jacinto Fault zone on the southwest. The San Andreas Fault zone impedes movement of groundwater, producing springs and a groundwater level change that marks the fault trace along the northern boundary of the subbasin. The San Jacinto fault forms a strong barrier to groundwater that raises the water table nearly to the surface below the course of the Santa Ana River1. The Bunker HiII- San Timoteo Basin includes the cities of Rialto, Colton, Loma Linda, Redlands, and San Bernardino. ~ The City of San Bernardino lies on a broad, gently sloping lowland that flanks the southwest margin of the San Bernardino Mountains. The lowland is underlain by alluvial sediments eroded from bedrock in the adjacent mountains and washed by rivers and creeks into the valley region where they have accumulated in layers of gravel, sand, silt, and clay. Sediment accumulation has continued for a few million years, during which time increasing thicknesses of sediments have gradually buried the original hill and valley topography of the Bunker Hill-San Timoteo Basin. Shandin Hills and other smaller hills areas in the basin are remnants of the original topography. The San Bernardino Mountains, Shandin Hills, and other hilly areas are comprised predominantly of Mesozoic and older crystalline basement terrain. Younger sedimentary deposits consist of late Pleistocene alluvium outcroppings on the older alluvial fans northeast of the City, and underlying the younger Holocene alluvium of the San Bernardino Valley. These younger sediments accumulated in two different depositional environments. Alluvial fans that extend downslope from the mouths of the San Bernardino Mountain canyons consist of coarser-grained and more poorly-sorted boulders, cobbles, gravels, sands, silts and clays that decrease in size and abundance to the southwest. Floodplain deposits from the Santa Ana River and Cajon and Lytle Creeks in the vicinity of metropolitan San Bernardino are comprised predominantly of sand, sandy silt, and silt. The alluvial fan and floodplain deposits are interlain and form a highly variable and often times laterally discontinuous layering of various sizes of alluvial materials. 1 Department of Water Resources. Upper Santa Ana Valley Groundwater Basin, Bunker Hill Subbasin. California Groundwater Bulletin 118. Updated February 7. 2004. General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-1 5. Environmental Analysis This page left intentionally blank. Page 5.5-2 . The Planning Center July 2005 5. Environmental Analysis Geothermal Resources Arrowhead Hot Springs fIl Hallem Springs ....~ South San Bernardino Geothermal Resource Area Source: E1Rc'SOut'l."t: hlVl'stigariol1 of .tow amd ,Morknu:~ Temperature Geuthermal Af"t'.a5 in San Bf:rmuJinuj CaJ.{i,mia,jt August 11)(;1, California Division of Mine$. artd Geology Open file Repo" 82" II SAC. I 8. City of San Bernardino Municipal Water Department Geothermal Well N Distribution Line ....../ Proposed Distribution Line . .. City Boundary . .: Sphere of Influence Boundary NOT TO SCALE ~ Source: Envicom Corporation San Bernardino General Plan Update and Associated Spedfit: Plans EiR The Planning Centel'. Figure 5.5-1 5. Environmental Analysis This page left intentionally blank. Page 5.5-4 . The Planning Center July 2005 5. Environmental Analysis Geothermal Activity Geothermal activity is known to occur in the southern portion of the City of San Bernardino and the Arrowhead Springs area and is shown in Figure 5.5-1, Geothermal Resources. Geothermal springs in the City of San Bernardino come from a depth of 15,000 feet due to fractures of the San Andreas Fault Zone. These deep subterranean faults and cracks allow rainwater and snowmelt to seep underground where the water is heated by the inner earth and circulates back up to the surface, to appear as hot springs or thermal vents. Geothermal activity is a unique geologic resource inextricably connected to the hydrology and tec- tonic activity within the basin. Geothermal resources beneath the City are connected to the Bunker Hill-San Timoteo Basin (aquifer). While hot water created from geothermal activity from the San Andreas Fault Zone is contained in separate perched aquifers above the fresh water aquifer, these two hydrologic resources can affect one another2. According to the San Bernardino Municipal Water Department, there are approximately 90-1 00 geothermal wells and springs currently in operation, which are concentrated in the Commerce Center, Central City, Tri- City areas, and former Norton Air Force Base. Currently, the San Bernardino Municipal Water Department maintains two wells in the southern portion of the city for geothermal energy sources. For a geothermal resource, the most important features are the maximum temperature, aerial extent, depth, volume, and water quality for it to be used as a potential energy resource. The geothermal springs in the City of San Bernardino are among the hottest in the United States, with hottest historic temperatures in the City ranging from 700C (1580F) in the southern portions of the City to 1400C (2840F) in the Arrowhead Springs area in the San Bernardino Mountains. One of the hottest wells in the planning area was located in the southwestern portion of the City in the old "Urbita Springs"; however, the majority of the wells in the San Bernardino planning area exhibit well temperatures between 1200F and 140oF. 3 ~ The following describes the known areas containing historic springs within the City of San Bernardino (the Arrowhead Hot Springs are described in Section 5.5.1.2, Arrowhead Springs Specific Plan, below): South San Bernardino The Urbita Springs were originally developed as a mineral bath and amusement park in the late 1860, and water was piped at 1,000 feet. In 1966, the first contracts for the Inland Shopping Center were let in and the Urbita Hot Springs were destroyed. The site is currently under parking lots and department stores of the Inland Center Mall. Prior to construction, the site was excavated and removed to a depth of 12 feet and backfilled. Today, there is a large subterranean drain that passes under part of the shopping center and surfaces just east of the Interstate 215 freeway. A trickle of water in this drain is the last vestige of the Urbita Hot Springs. The De Sienna Hot Springs were located 0.6 mile southwest of the Urbita Hot Springs on the southeast flank of a small knoll, sometimes referred to as Bunker Hill. Historical data indicate that a 547-foot-deep well was drilled in 1926 and had a temperature of 370C (990F). Harlem and Rabel Hot Springs The Harlem Hot Springs are located just north of the intersection of Baseline Road and Victoria Avenue. Natural hot springs originally flowed into Warm Creek. Historical data indicate that in 1989 the first well was drilled to 300 feet and produced water of 460C (1150F). These hot springs were then developed as a recrea- 2 California Department of Mines and Geology. Resource Investigation of Low- and Moderate- Temperature Geothermal Areas in San Bernardino California. DMG Open File Report 82-11. 1981. 3 City of San Bernardino Municipal Water Department. Geothermal Energy. Heat from the Earth Power for the Future. Obtained in February 2005 from http://www.sbcitywater.org/ General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-5 5. Environmental Analysis tion park and picnic area and provided mineral water and mud baths. Use of this hot spring eventually deteriorated and now lowering geothermal water table and water temperatures at the Harlem Hot Springs threaten loss of this resource. The Rabel Hot Springs were located approximately 0.25 mile west of the Harlem Hot Springs. Development of the Rabel Hot Springs probably very closely paralleled that of Harlem Hot Springs. Rabel Hot Springs was operated as a spa in the late 1800s and offered mineral mud baths, but was closed as a spa in 1912. Soon afterwards this site was operated as a hog ranch until the Baseline Laundry was opened in 1916. The operating well on the property is used heavily by the laundry and temperature at the well was measured as 280C (82.40F) on April 22, 1981. Historical newspapers from 1966 detail that water levels at the Harlem Hot Springs and the Rabel Hot Springs have dropped 160 to 170 feet and water once hot, is now lukewarm. Both Rabel Hot Springs and Harlem Hot Springs were originally naturally flowing springs which comprised the principle source of the flow in Warm Creek. The apparent historical decrease in this geothermal area may suggest that the available geothermal resource there has a finite volume. Geologic Hazards Slope Failure (Landslides) General slope stability is determined by a number of factors including slope, vegetative cover, wildfire, bedrock, soil, precipitation, and human alteration. Slopes may be in temporary equilibrium until one of the above factors is modified by natural or human activity resulting in an unstable condition and potential failure. Figure 5.5-2, Soil-Slip Susceptibility, depicts areas in the City of San Bernardino which are potentially susceptible to slope failure. According to the Preliminary Soil-Slip Susceptibility Map for the southern half of San Bernardino, portions ofthe City of San Bernardino are located within areas designated as either having low, moderate, or high soil-slip susceptibility.4 Potential slope failures in the following potentially hazardous zones could affect buildings, reservoirs, roads and utilities. . Areas of low relief with low to moderate susceptibility which may contain small scale surficial soil slips, debris flow and mudflows on steep localized slopes. . Areas of moderate and high relief with low to moderate susceptibility which may contain small to large rotational slides, debris slides and combinations of surficial slides and flows. These areas contain individual landslides that have been included on the regional slope stability and landslides map Compressible Soils Poorly consolidated or highly compressible soils are expected to have low bearing capacities and therefore liable to differential settlement. With highly compressible soils, water drains faster than cohesive soils and the load is transferred immediately, this process is called compression, or settlement. The amount of settlement is dependent on the applied load, the moisture content and structure of the soil. Compression of the soils brought about by an increase in stress from construction, foundation or other results in a deformation and relocation of soil particles, and expulsion of water or air from void spaces. Examples of highly compressible materials are areas of fill such as dumping grounds and peat deposits at surface or at depth. In addition, younger soils, which include textured silty and sandy soils, contain less well compacted sediments and are therefore more susceptible to settlement (e.g., younger Holocene deposits include alluvial materials 500 to 1,000 years old). 4 Morton. D.M. Alvarez. R.M & Campbell. R.H. Soil-Slip Susceptibility Map for the South Half of the San Bernardino 30' x 60' Quadrangle, Southern California. Preliminary Soil-Slip Susceptibility Maps. Southwestern California 2003 Page 5.5-6 . The Planning Center July 2005 .Q ..... ~ ~ ~ b ~ J ~ "EJ ~ ~ 0 g ~ " ~ ;S .~ " g Iri ~ ~ fr ~ ~ l!! ~ 8 " ;S ~ i:! '" ::s v " ~ .~ fr ~ N b " ~ fr '-' " ;- vi " ] '" ...... v B v " " "0 oS ~ '" :l ..::> " <:: J5 " -;;t '" '- '" ....!. "" V) " ~ " ..::> '" ;- " i,; ri "0 2:: ~ 1:: e .~ " .26l ~ '" :::E " b " g v ~ ..... ::r: .." ..::> " ~ 0 "" .~ .2 V) - '" " il- I ~ V ~ I ~ , Cl; r;; . ... , "" N .~ ~ ~ ~ - ~ ~ ~ ~ ~ ~ '... ;;:, :;:: ~ v\ 5. Environmental Analysis This page left intentionally blank. Page 5.5-8 . The Planning Center July 2005 5. Environmental Analysis Ground Subsidence In California, subsidence related to man's activities has been attributed to withdrawal of subsurface fluids such as oil and groundwater, oxidation of organic materials such as peat and coal, and by hydrocon- solidation (from excessive irrigation) of loose, dry soils in a semi-arid climate. Subsidence can affect structures sensitive to slight changes in elevation or slope such as highways, canals, pipelines, sewers and railroads. Subsidence commonly occurs in such slight magnitude and over large areas that it is not per- ceptible to an observer without detailed regional surveying studies. Smaller buildings within a uniform subsidence area may not sustain damage unless differential subsidence should occur. Differential subsidence may adversely affect the integrity of structures built within these areas. Historically, up to one foot of subsidence may have occurred within the City of San Bernardino. The historic area of subsidence was within the thick poorly consolidated alluvial and marsh deposits of the old artesian area north of Loma Linda. Potential subsidence in this area could potentially be as great as five to eight feet if ground water is depleted from the Bunker HiII- San Timoteo Basin. In the San Bernardino area, the potential for subsidence has been significantly reduced since 1972, when the San Bernardino Municipal Water District began to maintain groundwater levels from recharge to percolation basins, which in turn filter back into the alluvial deposits. Figure 5.5-3, Potential Subsidence Areas, depicts areas in the City of San Bernardino which may be susceptible to subsidence. Erosion Soil erosion is a naturally occurring process on all land. The agents of soil erosion are water and wind. Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing serious loss of topsoil. The rate and magnitude of soil erosion by water is controlled by the following factors: rainfall intensity and runoff; soil erodibility; slope gradient and length; and vegetation cover. ~ Soil erodibility is an estimate of the ability of soils to resist erosion, based on the physical characteristics of each soil. Some soil types are more susceptible to wind and rain erosion than others. Twenty-two soil series were identified in the City of San Bernardino and are listed in Table 5.5-1. The Delhi fine sand and Tujunga loamy sand are both susceptible to wind erosion if left exposed without adequate vegetative cover. Delhi fine sand and Tujunga loamy sand are found on old alluvial fan or floodplain areas on slopes from 0 to 15 percent. The fine sandy texture is especially prone to erosion during periods of high winds that frequent the region. The Cienaba sandy loam, Friant rock outcrop, Greenfield sandy loam, and Saugus sandy loam are all susceptible to water erosion. The Cienaba sandy loam, Friant rock outcrop, Greenfield sandy loam, and Saugus sandy loam are found on variable slopes from 2 to 50 percent depending on particular soil type. These soils commonly occur on alluvial fans, hills, and at the base of the San Bernardino Mountain front. Rapid precipitation runoff, sandy soil texture and denudation of vegetative cover can lead to potential water erosion of these soils. Hillside grading without proper erosion control plans, and off-road vehicle use in areas of erosion-prone soils can increase the hazard. General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-9 5. Environmental Analysis This page left intentionally blank. Page 5.5-10 . The Planning Center july 2005 5. Environmental Analysis Potential Subsidence Areas Nore: Degree of subsidence dependent on groundwater levels. Historic subsidence may have oocurred in above area. (Afrer Fife and others, 1976) Areas of Potential Ground Subsidence City Boundary .. Sphere of Influence Boundary NOT TO SCALE ~ San Bernardino General Plan Update and Associated Spedfii' Plans EiR The Planning Center · Figure 5.5-3 fIl 5. Environmental Analysis This page left intentionally blank. Page 5.5-12 . The Planning Center july 2005 5. Environmental Analysis Table 5.5-1 Soil Characteristics within the City of San Bernardino Soil (Symbol) Texture Potential Limitations Cieneba (CnD) Sandy Loam High erosion Cieneba (Cr) Rock Outcrop Slope Delhi (Db) Fine Sand High blowing soil Friant (Fr) Rock Outcrop High erosion Grangerville (Gr) Fine Sandy Loam None Grangerville (Gs) Fine Sandy Loam None Greenfield (GtC) Sandy Loam None Greenfield (GrD) Sandy Loam High erosion Hanford (HaC) Coarse Sandy Loam None Hanford (HaD) Coarse Sandy Loam High erosion Hanford (HbA) Sandy Loam None PsammentsjFluvents (Ps) - Flooding Ramona (RmC) Sandy Loam None Ramona (RmD) Sandy Loam High erosion Ramona (RmE2) Sandy Loam High erosion Saugus (ShF) Sandy Loam High erosion Soboba (SoC) Gravelly Loamy Sand None Soboba (SpC) Stony Loamy Sand None Tujunga (TuB) Gravelly Loamy Sand None Tujunga (TvC) Gravelly Loamy Sand High blowing soil Vista (Vr) Rock Outcrop Slope Wasteland (w) Variable Slope ~ Source: City of San Bernardino General Plan Update Technical Background Report, Chapter 5, Hazards, Envicorn Corporation, February 1988. Seismic Hazards Earthquake Faults Including Information on Historic Earthquakes The UBC Seismic Zone Map divides the United States into zones of potential earthquake damage. The four UBC Seismic Zones are Zone 0 (no damage), Zone 1 (minor damage), Zone 2 (moderate damage), and Zone 3 (major damage), and Zone 4 (major damage caused by near-by fault movements) was added. The City of San Bernardino is located is Seismic Zone 4. The following is a discussion of significant faults potentially affecting the City of San Bernardino. Table 5.5-2 lists the maximum credible earthquake magnitude of each fault. A description of the principle active faults that affect the City of San Bernardino is listed below. General Plan Update and Associated Specific Plans EIR City of San Bernardino - Page 5.5-13 5. Environmental Analysis Maximum Credible Earthquake Fault Magnitude (magnitude/peak g's) San Andreas 8.5 San Jacinto (includes Glen Helen and Lorna Linda) 7.5 Cucamonga-Sierra Madre 6.5+ Whittier-Elsinore 7.5-7.0 San Fernando 7.0 Hollywood-Raymond Hills 7.0 Newport-Inglewood 7.0 Santa Monica 7.0 Rialto-Colton 6.5 Helendale 7.0 Cleghorn 6.7 North Frontal 7.0 Crafton 6.4 Banning 6.9 Red Hill 6.5 Table 5.5-2 Principal Active Faults Source: City of San Bernardino General Plan Update Technical Background Report, Chapter 5, Hazards, Envicorn Corporation, February 1988. The San Andreas Fault system, including the north and south branches, forms the dominant fault feature in the City of San Bernardino area. Three of California's largest historic earthquakes have occurred along this fault in 1857 near Fort Tejon, 1906 near San Francisco, and 1989 near Santa Cruz.5 The fault segment that affects the City of San Bernardino begins at the Salton Sea, runs along the southern base of the San Bernardino Mountains, crosses through the Cajon Pass and continues to run northwest along the northern base of the San Gabriel Mountains. The fault segment southeast of Cajon Pass and within the San Bernardino planning area has not experienced a major earthquake for at least 265 years and possibly for as long as 600 years. Future predictions of magnitude and displacement currently cannot precisely be determined along the San Andreas Fault; however, regional studies indicate that a magnitude 8.0 or larger earthquake could be expected to occur in the future and should be considered for planning and design purposes. The San Jacinto fault system includes the Glen Helen, San Jacinto, and Loma Linda Faults in the City of San Bernardino. These faults display Late Quaternary to Holocene activity with small earthquakes evident near their fault traces. In terms of number of damaging earthquakes, the San Jacinto Fault zone has been the most prolific in historical time. At least 10 events have taken place from 1895 to 1980 over a fault length of 120 miles, with about half of these events causing damage in the San Bernardino-Riverside area. Regional studies suggest that a magnitude 7.0 to 7.5 earthquake is possible on the San Jacinto Fault system that would affect the City of San Bernardino. The Cucamonga-Sierra Madre fault system is part of a reverse and thrust fault zone that bounds the southern margin of the eastern San Gabriel Mountains, approximately 10 miles northwest of the central City area. The Cucamonga Fault is not known to have generated a significant earthquake in historic time, but a series of fault scarps in the Holocene alluvial fan deposits at the southeastern base of the San Gabriel 5 Information from the Envicom's 1988 Technical appendix was supplemented with information obtained from http://en.wikipedia.orq/wikilSan Andreas Fault on February 4,2005 for documentation of the 1989 Loma Prieta earthquake Page 5.5-14 . The Planning Center july 2005 5. Environmental Analysis Mountains attests to a succession of ground-rupturing earthquakes in the past. Earthquake scenarios that could affect the San Bernardino planning area range from magnitude 6.5 to 6.75. The Whittier-Elsinore fault system is located approximately 25 miles west of the city of San Bernardino. The Elsinore Fault system extends nearly 120 miles from the Mexican border areas, northwest, beyond the Santa Ana Mountains. The Whittier Fault extends further northwest from the Elsinore fault zone. A magnitude 6.5 design earthquake is considered to be reasonable for these faults. The San Fernando Fault is located approximately 64 miles west of the City of San Bernardino. The San Fernando Fault is a reverse fault near the back of the San Gabriel Mountains that is approximately 9 miles long and was the source of the 1971 Magnitude 6.6 San Fernando earthquake. The eastern terminus of the Hollywood-Raymond Hills fault system is located approximately 42 miles west of the City of San Bernardino. The Hollywood-Raymond Hills fault system extends in an east-west direction along the south side of the Santa Monica Mountains and may be continuous with the Raymond Fault in the vicinity of Glendale. The Raymond Fault exhibits fault scarps, sag ponds, and deformation and offset of Holocene strata. The Newport-Inglewood Fault is a northwest trending fault displaying a complex zone of deformation from Beverly Hills to south of Laguna Beach. The Newport-Inglewood Fault has been the source of damaging earthquakes of up to magnitude 6.3 in 1933 at Long Beach. The fault is approximately 57 miles west of the City. The Santa Monica Fault is part of a major east-west trending system of reverse faults that extend from northeast of Santa Monica into the Santa Barbara Channel. Late Quaternary offset is evident and probable earthquake magnitudes of 6.5 could be expected along this fault, located approximately 70 miles west of the City of San Bernardino. ~ The Rialto-Colton Fault consists of two echelon strands with a total length of about 16 miles that trend in a northwest direction. No Surface offset is evident for this fault but small earthquakes have occurred near its subsurface trace. This fault is located approximately 4 miles from the City of San Bernardino. The Helendale Fault consists of numerous echelon strands up to 2.5 miles long trending northwest. Total length of the strands is approximately 54 miles. Holocene surface faulting is evident along with closely associated small earthquakes. The fault is approximately 38 miles from the City of San Bernardino and is located along the north side of the San Bernardino Mountains and east of Victorville. The Cleghorn Fault is a single strand trending northwest with probable Holocene offset and numerous small earthquake associated with the eastern end of the 14-mile-long trace. This fault is located along the northwest end of the San Bernardino Mountains is approximately 13 miles northwest of the city of San Bernardino. The North Frontal Fault zone is comprised of numerous discontinuous acuate strands averaging 1.5 to 2.5 miles in length with a total overall length of about 30 miles. Late Quaternary offset occurs along the fault zone; however, overlying Holocene alluvial fans are not faulted. Numerous closely associated small earthquakes have been recorded near the eastern end of the zone. The zone is located along the north front of the San Bernardino Mountains approximately 17 miles north of the City of San Bernardino. The Crafton Fault consists of accurate echelon strands about 5 miles in length with evidence of Late Quaternary offset. This fault is located approximately 7 miles south of the City of San Bernardino. The Banning Fault zone consists of two to three strands in a zone about 2.5 miles wide trending from northwest to west with a total length of approximately 27 miles. Holocene strata are offset in the zone General Plan Update and Associated Specific Plans EIR City of San Bernardino - Page 5.5-15 5. Environmental Analysis and numerous small earthquakes are also closely associated with the zone. The fault zone is located approximately 16 miles south-southeast of the City of San Bernardino. The Red Hill Fault is a presumed single strand fault trending northwest to nearly east-west with a length of about 9 miles. This fault extends through the Pomona area about 10 miles west of the City of San Bernardino. Holocene strata have been offset at the eastern end and scattered small earthquakes have occurred near the fault trace. Surface (Fault) Rupture As defined by the California Division of Mines and Geology (DMG), an active fault is one that has had surface displacement within Holocene time (roughly the last 11,000 years) and/or has an instrumental record of seismic activity while potentially active faults are those that show evidence of surface displacement during Quaternary time (the last two million years), but for which evidence of Holocene movement has not been established. Active faults are considered to be those most likely for renewal movement during the lifetime of any structures in a particular project and may be a possible source for surface ground displacement. The City of San Bernardino contains numerous strands of active faults that transverse the planning area, including the San Andreas and the San Jacinto faults. The Alquist-Priolo Earthquake Fault Zones Act requires the State Geologist to establish Earthquake Fault Zones to encompass all potentially active fault traces of the San Andreas and San Jacinto Faults. The Earthquake Fault Zones boundaries extend approximately 500 feet away from major active faults and about 200 to 300 feet away from well-defined minor faults. Within the City of San Bernardino planning area, the San Andreas Fault system and the San Jacinto Fault system, including the Glen Helen and Loma Linda Faults, are included within these Special Studies Zones. The locations of known faults within the City of San Bernardino are depicted in Figure 5.5-4, Regional Fault Locations. Faults in the City that are part of the Alquist-Priolo Earthquake Fault Zones are shown in Figure 5.5-5, Alquist-Priolo Earthquake Fault Zones, to show the location of known active faults that are defined as having the potential for surface rupture. Strong Seismic Groundshaking As seismic waves pass through the earth's crust, the severity and duration of ground-shaking at a particular site area depends on several factors including (1) total energy released from a particular magnitude earthquake in the form of seismic waves; (2) distance from the source of the earthquake; and (3) nature of the surface and subsurface earth materials including age, composition, density, thickness and water content. The San Bernardino planning area has been regionally designated as a high severity zone where major probable damage of probable maximum intensity IX or X, as defined by the Mercalli Intensity Scale, may occur from a maximum expectable earthquake. The Mercalli Intensity Scale differs from the Richter Magnitude Scale in that the effects of anyone earthquake vary greatly from place to place, so there may be many Intensity values measured from one earthquake. Each earthquake, on the other hand, should have just one Magnitude, although the several methods of estimating it will yield slightly different values. General structural damage on the Modified Mercalli Intensity Scale for IX and X includes masonry seriously damaged if reinforced, and destroyed if unreinforced, and general damage to wood frame structures. Page 5.5-16 . The Planning Center july 2005 .~ ~ ~ ~ ....... ~ ~ ~ ~ ~ ~ .... ;;. :;:: ~ tr\ ~ "EJ ~ g ~ ~ Iri i::' g l!! .:t:: " '"t! '" ::s " ~ ~ ~ " 0 '" ~ I:Q S\ . " ?! '" ...... " c i,; ri ~ C' " e '" ] " V " g '"t! .~ .~ c: '- " 0 j '" ~ 0 ~ I:Q ~ ~ i::' " Cl; -" . 0 J5' '" ,E N " " 'I ~ ~ " " 1 u " 0 .9- ? .. - .~ I~ " E ~ g << ::; '" f II ~l 1- 1 I .... .\., I 5 ~t~ ,. 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('..1 1 '"I"u \.1 ,_ill ~ rw~~'~ ~'~::_.--!d f()Ar~ ;1/; %')I,-) ---:IIr=l I~ fiffi:1cJ f=jJ.,~ .~~') ~ # )..' ~1 '" ij ~ ~ Y:1.)\ \ I ' Id 1171[\ J -I = 1--' r- ~ /? ..' Ft/"'" ~"" '\1(//1"/1 I\\\'IW)) \..r 'I ~lilH II "I ~~; I :;,I"~ ...- -W.J ~ . ,. )"..1 -'f,. '\V 1/1 I .1-' lL ""T---lj.'i Jl .... 5. Environmental Analysis This page left intentionally blank. Page 5.5-18 . The Planning Center july 2005 5. Environmental Analysis Alquist-Priolo Earthquake Fault Zones SA I ."'/(IAI>. · 'Y'D~€4. ' ' ..~,<:-"Iu. , 'I.,.s "'s~ \ ..r-.....j il4' ., I '<ii:~\ '\~, \ '~"'--, .....\. r/;~:\~\':\ \.'1 ~",_.c "..', I /-~~----I'.., "v f\ ~ \~", I "-\- \,r~1' ~\ ./.q . ~ 01"")':0 L.' l' .il -<- ... .f -1~.i""'TiJIT==l- ~{J-J!I I ~r" f" I I' fIl ,.. Approximate Fault Location Approximate location of Alquist Priolo Special Study Zones I City Boundary ... . .; Sphere of Influence Boundary NOT TO SCALE ~ San Bernardino Geneml Plan Update and Associated Specific Plans EIR The Platming Cmtel' · Figure 5.5-5 5. Environmental Analysis This page left intentionally blank. Page 5.5-20 . The Planning Center july 2005 5. Environmental Analysis Regional studies have suggested that various intensities of damage could be generated by either a maximum credible earthquake of 8.5 magnitude on the San Andreas Fault system, a maximum credible earthquake of 7.5 magnitude on the San Jacinto fault system, a maximum credible earthquake of 6.5 on the Cucamonga-Sierra Madre fault system, or a maximum credible earthquake of 7.5 magnitude on the Whittier- Elsinore fault system. Seismically Induced Slope Failure Currently, the City of San Bernardino is located outside a mapped area for Seismic Hazard Zones, which establishes regulatory zones that encompass areas prone to liquefaction (failure of water-saturated soil) and earthquake-induced landslides. However, the geologic setting of southern California locally is conducive to slope failures and slope-failure deposits (landslides) that can be a hazard to human life and property. These hazards are created when geologic materials are displaced down a topographic slope under the influence of gravity. Factors that determine slope-failure occurrence include: slope angle; geologic materials (substrate); climatic conditions; and earthquake shaking.6 According to the Preliminary Soil-Slip Susceptibility Map for the southern half of San Bernardino, portions of the City of San Bernardino are located within areas designated as having either low, moderate, or high soil-slip susceptibility which could be induced seismically.7 Liquefaction and Related Ground Failure Liquefaction is a process whereby strong earthquake shaking causes sediment layers that are saturated with groundwater to lose strength and behave as a fluid. This subsurface process can lead to near-surface or surface ground failure that can result in property damage and structural failure. If surface ground failure does occur, it is usually expressed as lateral spreading, flow failures, ground oscillation, and/or general loss of bearing strength. San boils (injections of fluidized sediment) can commonly accompany these different types of failure. ~ In order to determine a region's susceptibility to liquefaction, three major factors must be analyzed these include: 1) The age and textural characteristic of the alluvial sediments. Generally, the younger, less well compacted sediments tend to have a higher susceptibility to liquefaction. Textural characteristics also playa dominant role in determining liquefaction susceptibility. Sand and silty sands deposited in river channels and floodplains tend to be more susceptible to liquefaction and floodplains tend to be more susceptible to liquefaction than coarser or finer grained alluvial materials. In the San Bernardino area, finer grained alluvial deposits that have accumulated in the floodplains and channels of the Santa Ana River, Cajon Creek, and Lytle Creek are more susceptible to liquefaction than coarser grained materials deposited in alluvial fan areas nearer to the San Bernardino Mountain front. 2) The intensity and duration of ground-shaking: in the San Bernardino area. It is probable that the tectonic setting and seismic history of the region suggest that earthquakes strong enough to generate liquefaction in susceptible alluvial materials have occurred in the past and are likely to occur in the future from fault movement on the San Andreas Fault, the San Jacinto Fault, and the Cucamonga Fault. 6 United States Geological Survey. Southern California Geology. Slope failure hazards in Southern California. Obtained on February 11, 2005 from http://scamp.wr.usgs.gov/scamp/html/scg_slop.html 7 Morton, D.M, Alvarez, R.M & Campbell, R.H. Soil-Slip Susceptibility Map for the South Half of the San Bernardino 30' x 60' Quadrangle, Southern California. Preliminary Soil-Slip Susceptibility Maps, Southwestern California 2003 General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-21 5. Environmental Analysis 3) The depth to the groundwater: Groundwater saturation of sediments is required in order for earthquake induced liquefaction to occur. In general, groundwater depths shallower than ten feet to the surface can cause the highest liquefaction susceptibility. This factor is the most variable and may be the most important determinant because of the rapid changes in the historical groundwater levels in the Bunker Hill and San Timoteo Groundwater Basin that underlies the City of San Bernardino. Currently, the City of San Bernardino is located outside a mapped area for Seismic Hazard Zones, which establishes regulatory zones that encompass areas prone to liquefaction (failure of water-saturated soil) and earthquake-induced landslides. However, two general zones have been identified within the regional area, "high" and "moderately high to moderate" zones based on past technical studies. High zones are concentrated adjacent to the San Andreas Fault zone north and northeast of the City and in the old artesian area between the San Andreas and San Jacinto Faults in the central and southern parts of the City. These zones delineate regional susceptibility; however, they can vary greatly due to groundwater level changes. These zones are depicted in Figure 5.5-6, Liquefaction Susceptibility. Hazardous Buildings (Unreinforced Masonry) The principal threat in an earthquake is not limited to ground-shaking, fault rupture, or liquefaction, but the damage that the earthquake causes to buildings that house people or an essential function. Continuing advances in engineering design and building code standards over the past decade have greatly reduced the potential for collapse in an earthquake of most of our new buildings. However, many buildings were built in past decades, before some of the earthquake design standards were incorporated into the building code. Several specific building types are a particular concern in this regard. Unreinforced Masonry Buildings In the late 1800s and early 1900s, unreinforced masonry was the most common type of construction for larger downtown commercial structures and for multi-story apartment and hotel buildings. These were recognized as a collapse hazard following the San Francisco earthquake of 1906, Santa Barbara earthquake of 1925, and again the aftermath of the Long Beach earthquake of 1933. These buildings are still recognized as the most hazardous buildings in an earthquake. Because of the concentrated development of the San Bernardino planning area by the early 1930s, a substantial number of unreinforced masonry buildings may still exist within the City. Per Senate Bill 547, local jurisdictions are required to enact structural hazard reduction programs by (a) inventorying pre-1943 unreinforced masonry buildings, and (b) developing mitigation programs to correct the structural hazards. Currently, the City maintains a list of pre-1943 unreinforced masonry buildings within the City, which are predominantly located in the central city, north of Mills Street, South of 30th Street, east of Rancho Avenue and west of Waterman Avenue. Currently there are 136 unreinforced masonry buildings in the City8. Pre-cast Concrete Tilt-up Buildings This building type was introduced following World War II and gained popularity for use in light industrial development during the late 1950s and 1960s. Extensive damage to concrete tilt-up buildings in the 1971 San Fernando earthquake revealed the need for better anchoring of walls to the roof, floor and foundation elements of the building, and for stronger roof diaphragms. In the typical damage to these buildings, the concrete wall panels would fall outward and the adjacent roof would collapse creating a direct life hazard. 8 Personal communication with Lease Jo at the City of San Bernardino on February 17, 2005. Page 5.5-22 . The Planning Center july 2005 5. Environmental Analysis Liquefaction Susceptibility ....HI .-- ....HMHI .... .. Boundary Sphere of Influence Boundary NOTTO SCAU! ~ · Figure 5.5-6 5. Environmental Analysis This page left intentionally blank. Page 5.5-24 . The Planning Center july 2005 5. Environmental Analysis New design standards for tilt-up buildings, developed after the 1971 earthquake, were incorporated into the 1976 Uniform Building Code. However, a large majority of existing tilt-up buildings were designed under the former code standards and may be subject to collapse under strong ground-shaking. Light industrial or commercial areas of the City that were developed in the late 1950s and 1960s may contain these types of buildings. The older tilt-up construction was used primarily for single-story industrial and warehouse buildings with solid wall panels and few or no window openings. However, recent application of tilt-up construction techniques has expanded to two- and three-story commercial, retail and mass housing uses, with poor connection details and a high proportion of glass openings in the wall panels. Other adaptations combine concrete, masonry, and cast-in-place concrete in a complex manner that no longer retains the seismic integrity of the original code intent. Soft-Story Buildings "Soft-Story" buildings are those in which at least one story, commonly the ground floor, has significantly less rigidity and/or strength than the rest of the structure. This can form a weak link in the structure, unless special design features are incorporated to give the building adequate structural integrity. Typical examples of soft- story construction are buildings with glass curtain walls on the first floor only, or buildings placed on stilts or columns, leaving the first story open for landscaping, street-friendly building entry, parking, or other purposes. The failure of the modern Olive View Hospital in the 1971 San Fernando earthquake, as well as the Imperial County Service Buildings in the 1979 Imperial Valley event, led to the repeated recognition of the seismic vulnerability of soft-story construction. In the early 1950s to early 1970, soft story buildings were a popular construction style for low- and mid-rise concrete frame structures. The City of San Bernardino may still have a number of concrete frame buildings of this vintage. ~ Non-Ductile Concrete Frame Buildings The brittle behavior of non-ductile concrete frame buildings can create major damage and even collapse under strong ground-shaking. This type of construction, which generally lacks masonry shear walls, was common in the very early days on reinforced concrete buildings, and they continued to be built until the codes were changed to require ductility in the moment-resisting frame in 1973. Large numbers of these buildings were built for commercial and light industrial use in California's older, densely populated cities. Many of these are four to eight stories; however, many others are in the lower height range. This category also includes one-story parking garages with heavy concrete roof systems supported by nonductile concrete columns. The history of construction in the City of San Bernardino spans the dates and uses common for this potentially hazardous building type. 5.5.1.2 Arrowhead Springs The Arrowhead Springs Specific Plan area is located in the northeastern portion of the San Bernardino planning area. Generally, the Arrowhead Springs Specific Plan area has the same regional geological setting as the City of San Bernardino as they are adjacent to each other. However, while the City lies mainly at the base of the steeper slopes of the San Bernardino Mountains, the Arrowhead Springs planning area extends up the flank of the San Bernardino Mountains. The Arrowhead Springs Specific Plan area lies at an elevation of 1,480 feet to 2,400 feet above mean sea level (msl). Arrowhead Springs is located in the Waterman Canyon 0Nest Twin Creek) and East Twin Creek Watersheds and three primary water courses flow through the planning area: the East Twin Creek, Strawberry Creek, and West Twin Creek which flows through Waterman Canyon. The Arrowhead Springs planning area can generally be described as hilly marked with sharp terrain, valleys, and inaccessible steep slopes of the San Bernardino Mountains. General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-25 5. Environmental Analysis In general the Arrowhead Springs Specific Plan area consists of numerous small canyons trending north- south. Ridges are underlain by either Potato Formation or by granitic-metamorphic complex. These units are deeply weathered and are offset by faulting of uncertain age. Hot springs travertines and quartz deposits mark the ridge exposures of these faults as do active hot springs. Deep cut for roads and tanks all exhibit the deep weathering as do steep-walled ravines cut into these crystalline basement units. Within areas of the upper plateau and ridges, near the south, the subgrade soils are comprised of moderate- ly dense, deeply weathered gravely sand with some silts. Within the upper plateau and hillsides near the north, subgrades are expected to consist of grayish brown to gray highly fractured metamorphic rocks, weathered gravelly sand of decomposed granitic origin, and/or calcite as derived from old hot springs. Within the canyon bottoms, subgrade soils consist of alluviums of silty fine sand and fine to medium coarse gravelly sand of variable consistency along with numerous cobbles and isolated rocks. Subgrade soils underlying the upper described alluviums are expected to consist of well consolidated gravelly sand or weathered bedrock of siltstone/sandstone origin, generally compressible in nature. Figure 5.5-7 shows the major geologic units in the vicinity of the Arrowhead Springs area. Geothermal Activity The hot springs in the Arrowhead Springs Specific Plan area are actually located in two canyons in the foothills of the San Bernardino Mountains on a splay of the San Andreas Fault. The splay seems to be related to the bifurcation of the fault into the northern and southern segments which continue southeast toward the Salton Trough. The hot springs in the area are divided into two distinct groups and are located in two canyons about one-half mile apart on the property. The Arrowhead hot springs are located on the south flank ofthe San Bernardino Mountains (near the historic resort). The Arrowhead hot springs are comprised of the Pal Hot Springs, Penuygal Hot Springs, and Granite Hot Springs. Table 5.5-3 displays the 1910 and 1980-1981 recorded temperatures at these hot springs at the Arrowhead hot springs location and the Waterman hot springs (near Waterman Canyon). The area has been developed as a bathing spa and recreational area since the late 1800s, and most of the original hot spring locations have been altered from their original character by the construction of baths and collection pools. The California Division of Mines and Geology, 1975 noted that one spring at the Arrowhead hot springs actually boils having a temperature of 990C (21 OOF). Location 1910 Temperature 1980-1981 Temperature Palm Hot Springs 820C (1800F) 840C (183OF) Penuygal Hot Springs 940C (202OF) 870C (189OF) Granite Hot Springs 700C (159OF) 81 OC (178OF) Waterman Hot Springs 70-930C (158-2000F) 81 OC (178OF) Table 5.5-3 Recorded Temperatures at the Arrowhead Hot Springs Source: California Departrnent of Conservation, Division of Mines and Geology. Resource Investigation of Low- and Moderate-Ternperature Geotherrnal Areas in San Bernardino California. DMG Open -File Report 82-11, 1981 Page 5.5-26 . The Planning Center july 2005 5. Em)iron1l1C1ltctl AIl?IIYJiJ Arrowhead Springs Geologic Map Qal Recent Alluvium or Fan Deposits Qls Landslide Debris, Age not determined Qoal - Older Alluvium or Fan Deposits Qo{ - Older Fan Deposits Qmf - Mudnow Deposits Tp - Potato FUrn1<ltion Kmg - Biotite Monzogtanite (Cretaceous) Mzps - Pelona Schist Mzc - Quartz Monzogranite of Crcsdine Mzdc Gneiss of Devil Canyon U llspccifi<:d Liln<:stone formntiotl Source.' SOils Southwest, Inc. ,,',m Run,ndillo C;('/l('}."t PI,m Uf}r/,tfI' ,md ,-!fwd,Hed ,\jll..'I~(it Pll1lf fIR ~~ 'Fbe PI,fi/J/iJl,'!, Ctwtd . Figure 5~5-7 5. Environmental Analysis This page left intentionally blank. Page 5.5-28 . The Planning Center july 2005 5. Environmental Analysis Geothermal temperatures at Arrowhead hot springs have changed very little in the past 100 years. Today there is still near boiling water issuing from the surface. Two springs, the Palm Hot Springs and Granite Hot Springs, are currently hotter than 1910 measurements. At these locations, wells were drilled and hot water now flows from some unknown depth rather than naturally emitting at the surface. Penuygal Hot Springs is cooler than known 1910 temperatures and sediment and debris may be impeding the natural flow to the surface. This impedance may allow the waters to cool more near the surface than in the past when the spring was maintained. The Waterman hot springs are approximately one-half mile west of the Arrowhead hot springs. The hot waters issue from an alluvial terrace deposit that, along a short stretch, forms the east bank of the Waterman Canyon. Four caves were dug into the side of the alluvial fill covering fractured bedrock from which steam and hot water was flowing. Currently, the caves are bulldozed over to keep out trespassers and still show signs of warm ground and surface steam. Historically, the temperatures of the steam caves were described as being dependent on the location with respect to the fault which lies directly to the east. The temperature was observed to decrease regularly as the distance from the fault increased.9 The Arrowhead of Arrowhead Springs A unique geologic feature on the slopes of Arrowhead Peak above the Arrowhead Springs resort area is the outline of an Indian arrowhead from which the resort and mountain is named. The arrowhead is 1,115 feet long and 396 feet wide. The arrowhead is clearly visible on the mountain because it appears to be white against a dark background. The soil which forms this mark is composed mostly of disintegrated white quartz and light gray granite, on which grow weeds and a short, white grass, while the soil around it is of a different formation, sustaining vegetation and shrubs of a dark green color, which covers the rest of the face of the mountain.lO In 1957, the United States National Forest Service designated the natural Arrowhead a "Landmark Geological Area." The Arrowhead can be seen in the lower photo of Figure 5.1-4 in Section 5.1, Aesthetics. ~ Geologic Hazards (Site Specific to AHS) Slope Failure (Landslides) Numerous landslides are present in the Arrowhead Springs area, comprised of remnants of bedrock of broken sandstone with gravel deposits, related to localized slumping of weathered bedrock materials. Minor surficial slopewash and/or minor surficial slides may be associated with the north-south direction canyons near the northwest of the Arrowhead Springs Specific Plan area. Slope surface includes minor slippage along with upper loose silty gravelly sand (top-soils), overlying moderately dense gravelly sand and/or weathered and fractured bedrock. Compressible Soils Compression of the soils brought about by an increase in stress from construction, foundation or other which results in a deformation and relocation of soil particles, and expulsion of water or air from void spaces. In the Arrowhead Springs Specific Plan area, upper alluviums in canyon bottoms are generally considered compressible in nature and consist of well consolidated gravelly sand or weathered bedrock of siltstone/ sandstone origin. Consolidation tests conducted on representative undisturbed soils sampled at depth and on remolded bulk soil sample exhibited relatively "low" compressibility under anticipated structural loading. 9 Jones, Victor 1. & Burtell, S.G. (2002) Hydrocarbon Flux Variations in Natural and Anthropogenic Seeps. Exploration Technologies, Inc. Obtained from http://www.eti-geochemistry.com/flux/ 10 California Genealogy. Additional Towns of San Bernardino County, California, Arrowhead Hot Springs. Obtained March 2005 from http://www.californiagenealogy.org/sanbernardino/towns2.htm General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-29 5. Environmental Analysis Expansion tests conducted on representative near grade soils exhibited "very low" expansion potential with Expansion Index (EI) less than 20. Ground Subsidence Subsidence of the ground surface is generally caused by the withdrawal of groundwater and/or hydro- carbons. Withdrawal of groundwater in the Arrowhead Springs Specific Plan area has traditionally been associated with domestic use, irrigation and heating from the geothermal wells. However, groundwater levels in the southern boundary of Arrowhead Springs and along the National Forest boundary areas are expected at about 10 feet below grade. Shallow depth groundwater, however, should be expected within the southern low-lying areas. Erosion See above discussion pertaining to erosion for the San Bernardino area. Seismic Hazards (applicable site specific to AHS) Earthquake Faults Including Information on Historic Earthquakes See above discussion pertaining to earthquake faults for the San Bernardino area. Surface (Fault) Rupture The southern flank of the San Bernardino Mountains is bounded by the San Andreas Fault zone, which is a designated Alquist-Priolo zone. Portions of the Alquist-Priolo zones exist on the west side and southerly end of the project area (see Figure 5.5-5). However, these active faults have not been trenched to locate fault traces in a precise manner. Strong Seismic Groundshaking The entire planning area of Arrowhead Springs lies in the near source zone of the San Andreas Fault. The Arrowhead Springs Specific Plan area is located 7 kilometers from the near source zone of the Class B Frontal Fault system, 13 kilometers from this zone ofthe Class A Cucamonga Fault system and 9 kilometers from the near source zone of the San Jacinto Fault. Earthquakes on these faults could generate vibrations on site with maximum horizontal accelerations ranging from OAg to 0.7g and with durations of string shaking exceeding 20 seconds. Seismically Induced Slope Failure See above discussion pertaining to seismically induced slope failure for the San Bernardino area. Liquefaction and Related Ground Failure Liquefaction is caused by build-up of excess hydrostatic pressure in saturated cohensionless soils due to cyclic stress generated by ground-shaking during an earthquake. The significant factors on which lique- faction potential of a soil deposit depends, among others include, soil type, relative soil density, intensity of earthquake, duration of ground-shaking, and depth of groundwater. Liquefaction is possible near the southerly end of the project due to the high groundwater. Natural spring water is expected during grading and construction. Shallow depth groundwater, however, should be expected within the southern low-lying areas. As per USGS Bulletin 1898, groundwater within the southern boundary of Arrowhead Springs and along the National Forest boundary areas are expected at about 10 feet below grade. Page 5.5-30 . The Planning Center july 2005 5. Environmental Analysis Hazardous Buildings (Unreinforced Masonry) See above discussion pertaining to hazardous buildings for the San Bernardino area. 5.5.2 Thresholds of Significance According to Appendix G of the CEQA Guidelines, a project would normally have a significant effect on he environment if the project would: G-1 Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: . Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault? (Refer to Division of Mines and Geology Special Publication 42.) . Strong seismic ground-shaking. . Seismic-related ground failure, including liquefaction G-2 Result in substantial soil erosion or the loss of topsoil. G-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. ~ G-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. G-5 Have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for the disposal of waste water. The Initial Study, included as Volume II, Appendix A, substantiates that impacts associated with threshold G-5 would be less than significant. This threshold will not be discussed further in this EI R. 5.5.3 Environmental Impacts 5.5.3.1 San Bernardino General Plan Update The following impact analysis addresses thresholds of significance for which the Initial Study disclosed potentially significant impacts. The applicable thresholds are identified in parentheses after the impact statement. GP IMPACT 5.5-1: CITY OF SAN BERNARDINO RESIDENTS, VISITORS, AND WORKERS WOULD BE SUBJECTED TO POTENTIAL SEISMIC-RELA TED HAZARDS. [THRESHOLD G-1 J Impact Analysis: The City of San Bernardino and Sphere of Influence areas (SOl) are crisscrossed by numerous faults and trace faults, many of which are located within the Alquist-Priolo Earthquake Fault Zone. Faults located within the Alquist-Priolo Earthquake Fault Zone are considered to have been active during the Holocene time and therefore have the potential for surface rupture. In addition to active faults in the Alquist- Priolo Earthquake Fault Zone, other active faults also crisscross through the San Bernardino planning area, which also have the potential for surface rupture. In accordance with the Unreinforced Masonry Law the City General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-31 5. Environmental Analysis of San Bernardino has identified structures within the City, which may be hazardous in the event of surface rupture. Structures and persons residing in these structures within the Earthquake Fault Zone and within close proximity to other active faults within the City of San Bernardino may be exposed to substantial adverse effects, such as potential structural collapse, in the event of surface rupture. Due to the proximity and location of these active faults in relation to the City of San Bernardino planning areas, all structures within the City of San Bernardino planning area may be subject to seismic related impacts from severe ground-shaking. The San Bernardino planning area has been regionally designated as a high severity zone where major probable damage of probable maximum intensity IX or X, as defined by the Mercalli Intensity Scale, may occur from a maximum expectable earthquake. Structures and persons residing in these structures during periods of severe ground-shaking located within the City of San Bernardino may be exposed to substantial adverse effects. In addition to impacts from surface rupture and severe ground-shaking, many locations within the City are located in areas with "high" and "moderately-high to moderate" liquefaction potential which can be induced by seismic activity and can result in structural failure. Structures and persons residing in these structures within areas designated "high" and "moderately-high to moderate" liquefaction potential located within the City of San Bernardino may be exposed to substantial adverse effects in the event of structural failure as a result of liquefaction. GP IMPACT 5.5-2: UNSTABLE GEOLOGIC UNIT OR SOILS CONDITIONS, INCLUDING SOIL EROSION, COULD RESULT FROM IMPLEMENTATION OF THE CITY OF SAN BERNARDINO GENERAL PLAN. [THRESHOLDS G-2 AND G-3] Impact Analysis: The City of San Bernardino lies within a geological unit that contains soil types that are susceptible to both wind and water erosion which may be indicative of unstable geological conditions for development. Fine sandy soils found in the City of San Bernardino, such as the Delhi fine sand and the Tujunga loamy sand, are both susceptible to wind erosion if left exposed without adequate vegetative cover. The Cienaba sandy loam, Friant rock outcrop, Greenfield sandy loam, and Saugus sandy loam, which commonly occur on alluvial fans, hills, and at the base of the San Bernardino Mountain front, are susceptible to water erosion. Hillside grading without proper erosion control plans, and off-road vehicle use in areas of erosion-prone soils can increase these hazards. Development within areas that are characterized by these soil types within the City of San Bernardino may result in substantial soil erosion or the loss of topsoil. Hillside areas within the City of San Bernardino planning area are located in areas designated as having low, moderate, or high soil-slip susceptibility, which can be induced seismically. Common names for landslide types include slump, rockslide, debris slide, lateral spreading, debris avalanche, earth flow, and soil creep. Areas of low relief with low to moderate susceptibility may contain small scale surficial soil slips, debris flow and mudflows on steep localized slopes. Areas of moderate and high relief with low to moderate susceptibility may contain small to large rotational slides, debris slides and combinations of surficial slides and flows. Development located on these hillside areas is therefore susceptible to potential landslides. Portions of the City of San Bernardino planning area have been identified to have the potential for liquefaction and subsidence susceptibility, which could result in structural collapse if development were to occur. Continued overdraft of the Bunker Hill-San Timoteo Basin could lead to an increase in susceptibility to impacts from subsidence as a decrease in groundwater levels could initiate sinking to fill the empty space previously occupied by water or soluble minerals. This can be aggravated by weight, including surface developments such as roads, reservoirs, and buildings, and man-made vibrations from such activities as blasting, heavy truck or train traffic which can accelerate the natural processes of subsidence. However, groundwater recharge in the Bunker Hill-San Timoteo Basin has significantly reduced this hazard by reducing overdraft in the Basin. Page 5.5-32 . The Planning Center july 2005 5. Environmental Analysis In the San Bernardino planning area, finer grain alluvial deposits that have accumulated in floodplains ofthe Santa Ana River are more susceptible to liquefaction than coarser grained materials deposited in alluvial fan areas nearer to the San Bernardino Mountain Front. However, groundwater level is the most important determinant to liquefaction potential because of the rapid changes in the historic groundwater levels in the San Bernardino planning area. Groundwater saturation of the sediments is required in order for earthquake induced liquefaction to occur. Groundwater depth shallower than 10 feet to the surface can cause the highest liquefaction potential. Groundwater 10 to 30 feet below the surface can create a moderately high to moderate liquefaction potential. Groundwater 30 to 50 feet deep can create a moderate to low susceptibility. Historically, 1973 to 1983, groundwater levels in the old artesian area were within 10 feet or less of the surface and therefore historically have had a high liquefaction potential. In addition, due to the constrictive nature of groundwater movement along fault lines, groundwater levels along the San Andreas, San Jacinto, and the Cucamonga Faults in San Bernardino planning area are also known to have moderate to moderately high liquefaction potential. GP IMPACT 5.5-3: SOIL CONDITIONS PRESENT WITHIN THE CITY OF SAN BERNARDINO COULD RESULT IN RISKS TO LIFE OR PROPERTY. [THRESHOLD G-4] Impact Analysis: Expansive soils are defined as soils that shrink when dry and swell when wet. These characteristics apply to soils with a high percentage of clay. Movement that occurs during expansion can exert enough pressure to crack sidewalks, driveways, basement floors, pipelines and even foundations. Table 5.5-1 lists the soil types found within the City of San Bernardino. Although commonly found soils within the City are not characterized as expansive, the potential to encounter expansive soils within the City may exist. Potential risks to life or property, due to structural collapse as a result of construction on expansive soils could therefore occur within the City. City of San Bernardino General Plan Policies and Programs ~ The following City of San Bernardino General Plan policies and programs related to geological hazards include: Safety Element Policy 10.7.1: Minimize the risk to life and property through the identification of potentially hazardous areas, establishment or proper construction design criteria, and provision of public information. Policy 10.7.2: Require geologic and geotechnical investigations for new development in areas adjacent to known fault locations and approximate fault locations as part of the environmental and/or development review process and enforce structural setbacks from faults identified through those investigations. Policy 10.7.3: Enforce the requirements of the California Seismic Hazards Mapping and Alquist-Priolo Earthquake Fault Zoning Act when siting, evaluating, and constructing new projects within the City. Policy 10.7.4: Determine the liquefaction potential at a site prior to development, and require that specific measures be taken as necessary, to prevent or reduce damage in an earthquake. Policy 10.7.5: Evaluate and reduce the potential impacts of liquefaction on new and existing lifelines. Policy 10.8.1: Enforce the requirements of the California Seismic Hazards Mapping and Alquist-Priolo Earthquake Fault Zoning Acts when siting, evaluating, and constructing new projects in the City. Policy 10.8.2: Require that lifelines crossing a fault be designed to resist the occurrence of fault rupture. Policy 10.8.3: Adopt a program for the orderly and effective upgrading of seismically hazardous buildings in the City for the protection of health and safety. Compliance with the Unreinforced Masonry Law shall include General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-33 5. Environmental Analysis the enactment of an effective program for seismic upgrading of unreinforced masonry buildings within the City. Policy 10.9.1: Minimize risk to life and property by properly identifying hazardous areas, establishing proper construction design criteria, and distribution of public information. Policy 10.9.2: Require geologic and geotechnical investigations in areas of potential geologic hazards as part of the environmental and/or development review process for all new structures. Policy 10.9.3: Require that new construction and significant alterations to structures located within potential landslide areas be evaluated for site stability, including potential impact to other properties during project design and review. 5.5.3.2 Arrowhead Springs The Arrowhead Springs Specific Plan details the overall development that would occur in the 1916 acre plan area. The Arrowhead Springs Specific Plan would result in balanced cut and fill of approximately 7,000,000 cubic feet of soil to accommodate the proposed pads sites. An additional 1,000,000 cubic yards of cut and fill maybe required for remedial grading to ensure stability of slopes where potential for landslides is evident. For a map of the conceptual grading plan refer to Figure 3.3-7 in Section 3.0, Project Description. Most of the planned development pad sites should be accessible using a dozer and a tractor-mounted backhoe and the general project area is considered acceptable for a drill-rig. Extensive site preparation and grading are anticipated due to the varied terrain that consists of valleys, some with steep canyon walls and ridges. Existing slope gradients are estimated to vary anywhere from approximately 1 : 1: to 2: 1 (horizontal to vertical) or flatter. Minor surficial slopewash and/or minor surficial slides are present in multiple locations. All perma- nent manufactured slope banks are not expected to be constructed at a gradient greater than 2: 1 (horizontal to vertical), while cut slopes will not exceed 1 :1. Exceptions may be made in the case of rock or natural outcroppings. Grading in certain areas of the Specific Plan is anticipated to require major cuts into upper plateaus and ridges of up to 50 feet and to about 20 feet on hillsides. No blasting or jack-hammering is anticipated. New fill soil placements are anticipated for the valleys and most pad sites. The following impact analysis addresses thresholds of significance for which the Initial Study disclosed potentially significant impacts. The applicable thresholds are identified in parentheses after the impact statement. AHS IMPACT 5.5-1: FUTURE RESIDENCES, VISITORS, AND WORKERS WOULD BE SUBJECTED TO POTENTIAL SEISMIC-RELATED HAZARDS WITHIN THE ARROWHEAD SPRINGS SPECIFIC PLAN AREA. [THRESHOLD G-1 J Impact Analysis: The Arrowhead Springs Specific Plan area is crisscrossed by numerous faults and trace faults, some of which are associated with the Alquist-Priolo Earthquake Fault Zone (refer to Figures 5.5-4 and 5.5-5 for approximate location of active and inactive faults and faults within the Alquist-Priolo Earthquake Fault Zone). Although the majority of the residential and commercial development is located outside the Earthquake Fault Zone, portions of the Arrowhead Springs Specific Plan designated as residential in the southernmost portions of the planning area are located within the Earthquake Fault Zone. In addition, active fault traces are known to cross the area proposed for commercial uses. Structures and persons residing in these structures within the Earthquake Fault Zone and within close proximity to other active faults within the Arrowhead Springs Specific Plan area may be exposed to substantial adverse effects in the event of surface rupture. Page 5.5-34 . The Planning Center july 2005 5. Environmental Analysis Due to the proximity and location of active faults in relation to the Arrowhead Springs Specific Plan area, all structures within the planning area may be subject to seismic related impacts from severe ground-shaking. Earthquakes could generate vibrations on site with maximum horizontal accelerations ranging from OAg to O.7g and with durations of string shaking exceeding 20 seconds. Structures and persons residing in these structures during periods of severe ground-shaking located within the Arrowhead Springs Specific Plan area may be exposed to substantial adverse effects. In addition to impacts from surface rupture and severe ground-shaking, many locations within the Arrowhead Springs Specific Plan area are located in areas with potential for liquefaction do to groundwater levels within 10 feet of the surface. Structures and persons residing in these structures if liquefaction were to occur within the Arrowhead Springs Specific Plan area may be exposed to substantial adverse effects in the event of structural failure as a result of liquefaction. AHS IMPACT 5.5-2: UNSTABLE GEOLOGIC UNIT OR SOILS CONDITIONS, INCLUDING SOIL EROSION, COULD RESULT DUE TO BUILD-OUT OF THE ARROWHEAD SPRINGS SPECIFIC PLAN. [THRESHOLDS G-2 AND G-3] Impact Analysis: Much of the area located within the Arrowhead Springs Specific Plan is located in areas designated as having either low, moderate, or high soil-slip susceptibility, which can be induced seismically. According to results of shear tests, exposed slope surface areas and ridge tops under increased moisture conditions indicate moderate shear strengths for slope stability. The proposed development plan of the Arrowhead Springs Specific Plan would result in slope modification and cuts into the ridges and manufactured slopes. Approximately 7,000,000 cubic yards of balanced cut and fill would be required to support individual proposed building pads envisioned in the Arrowhead Springs Specific Plan. In order to support existing and man made slopes proposed in the Conceptual Grading Plan, remedial grading of an additional 1,000,000 cubic yards would be required to prevent erosion or potential for landslides within the planning area. Modification of the existing geography in the Arrowhead Springs Specific Plan could therefore have the potential to increase soil-slip susceptibility hazards. ~ In the Arrowhead Springs Specific Plan area, valley areas are considered susceptible to soil consolidation which can result in unequal settlements to footings and are considered unsuitable for structural support or new structural fill soils placement. These undesirable site soils are also expected to exist within 5 feet of the surface on the upper ridges and upper plateau, and within 12 to 18 feet or more of the surface in the canyon bottoms. In addition, site soils are considered highly susceptible to caving. Soil consolidation and caving can lead to possible structural collapse. Hot springs and geothermal activity within the Arrowhead Springs Specific Plan area are indicative of the potential to encounter high groundwater levels. In addition, portions ofthe Arrowhead Springs planning area are identified on Figure 5.5-6 as having high susceptibility to liquefaction. As a result, portions of the project area may have the potential for liquefaction, which could result in structural collapse if development were to occur. Due to high depth of groundwater, the Arrowhead Springs Area is not considered susceptible to subsidence. AHS IMPACT 5.5-3: SOIL CONDITIONS PRESENT WITHIN THE ARROWHEAD SPRINGS SPECIFIC PLAN AREA COULD RESULT IN RISKS TO LIFE OR PROPERTY. [THRESHOLD G-4] Impact Analysis: Expansive soils are defined as soils that shrink when dry and swell when wet. These characteristics apply to soils with a high percentage of clay. Movement that occurs during expansion can exert enough pressure to crack sidewalks, driveways, basement floors, pipelines and even foundations. The Arrowhead Springs area is located in the mountainous regions of the City of San Bernardino and the General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-35 5. Environmental Analysis potential to encounter soils with expansive properties is low according to the geotechnical study for the site conducted by Soils Southwest Inc. (see Appendix D. Vol. III). Arrowhead Springs Specific Plan Development Standards The following general development standards contained within the Arrowhead Springs Specific Plan related to hillside development techniques for the Arrowhead Spring area include: . All permanent manufactured slope banks shall be constructed at a gradient of not greater than 2: 1 (horizontal to vertical), unless the Project civil and/or geotechnical engineer can certify slope stability for any cut slope greater than 2: 1. Cut slopes shall not exceed 1: 1. Exceptions may be made in the case of rock or natural outcroppings. . Incorporating the recommendations of the Project civil and/or geotechnical engineer, the following standards and specifications for benching and terrace drains on manufactured cut and fill slopes should be used in grading design and implementation: o If any slope benches are required by the project civil engineer or geotechnical engineer, then slope benches of six feet in width shall be provided at not more than 40- foot vertical intervals and shall include a drainage swale on all cut or fill slopes to control surface drainage and debris, except that where only one terrace is required, it shall be mid-height. o For cut or fill slopes greater than 80 feet and up to 120 feet in vertical height, one terrace at- approximately mid-height shall be 12 feet in width. Terrace widths and spacing for cut and fill slopes greater than 120 feet in height shall be designed by the Project civil and/or geotechnical engineer and approved by the City Engineer. o Suitable access shall be provided to permit proper cleaning and maintenance. o Subject to the approval of the Project civil and/or geotechnical engineer, manufactured slopes less than 40 feet in vertical height do not require any benching. o Grading operations shall not result in substantial damage to, or alteration of, significant permanent natural resource areas, wildlife habitats or native vegetation areas, which are designated by the Master Tentative Subdivision Map to be preserved. o To the extent feasible, exposed manufactured slopes per the Grading Ordinance as determined by the City Engineer and the Development Services Director shall be naturalized by the use of natural contour grading to approximate natural slopes. To the extent feasible, exposed slopes in excess of 20 vertical feet shall be rounded at the top and toe. If feasible, exposed manufactured slopes in excess of 30 feet shall undulate with varying slope gradients. Both the top and toe of slopes shall be modulated to affect the slope undulation. o Special landscaping techniques using plant material of varying heights and massing shall be used in conjunction with contour grading to create a modulated slope appearance. o Existing landforms may be re-contoured, as necessary, to provide a smooth and gradual transition to graded slopes, while, preserving the basic character of the site. o Local internal streets as well as collector streets shall be meandered where possible to undulate and minimize slope banks. Split-level streets may be utilized where possible to minimize impacts to the natural terrain. Page 5.5-36 . The Planning Center july 2005 5. Environmental Analysis o It is anticipated that topsoil from graded areas could be stockpiled for reapplication to manufactured slope areas. o Phasing of grading within each planning area shall provide for the safety and maintenance of other planning areas already developed or under construction and visual mitigation (revegetation) of all manufactured slopes. o Where possible, phasing shall preclude hauling of earth over residential streets of developed areas. All import and/or export activities of earth material to or from the Arrowhead Springs site shall conform to Sections 15.04-210, 15.04-545, 15.38 of the San Bernardino Municipal Code. o Temporary runoff/erosion control devices shall be installed prior to any grading activities. Runoff/erosion control and maintenance shall be employed subject to the City of San Bernardino Division of Public Works Grading Policies and Procedures. o Prior to October 15 of each year, all graded but not permanently landscaped slopes shall be hydro-seeded for slope stabilization as necessary for erosion control, to the satisfaction of the City Engineer. The application for any grading permit must provide assurance to the City Engineer that manufactured slope banks will be properly landscaped and irrigated, and that the landscape will be, maintained by either the developer, the property owner(s) or by a Landscaping Maintenance District. o A revegetation plan shall be prepared for review and approval by the City Engineer and the Development Services Director for manufactured slopes occurring adjacent to undisturbed native plant communities. ~ o Hauling of earth or construction materials over residential streets in developed areas shall be avoided. A truck hauling route shall be submitted to the City Engineer for approval prior to commencement of any grading operation. The approved haul routes may require the construction of a greater structural section along haul routes, to the satisfaction of the City Engineer and/or the Director of Public Works. o Crib and/or retaining walls may be allowed in situations where significant grading can be saved and where approved by the soils engineer and accepted by the City Engineer. o Any off-site grading shall be reviewed and approved by the City Engineer as part of a grading review package. A letter of permission from the affected property owner(s) shall be required prior to issuance of any grading permit for off-site work. Absent such permission, grading plans shall conform to the required grading setbacks s provided in the City's Grading ordinance. o Prior to work in any streambed, permits shall be obtained from the California Department of Fish and Game, the U.S. Army Corps of Engineers and the California State Water Quality Control Board. General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-37 5. Environmental Analysis 5.5.4 Existing Regulations and Standard Conditions 5.5.4.1 San Bernardino General Plan Update The following existing regulations and standard conditions apply to both the San Bernardino General Plan Update and the Arrowhead Springs Specific Plan. . If a project site is located in an Earthquake Fault Zone (formerly known as "Special Studies Zones"), the City of San Bernardino must withhold development permits for sites within the zones until geologic investigations demonstrate that the sites are not threatened by surface displacement from future faulting as required by the Alquist-Priolo Earthquake Fault Zoning Act. The purpose of this Act is "to regulate development near active faults so as to mitigate the hazard of surface fault rupture." Pursuant to this Act, structures for human occupancy are not allowed within 50 feet of the trace of an active fault. . The Seismic Hazard Mapping Act was adopted in 1990 for the purpose of protecting public safety from the effects of strong ground-shaking, liquefaction, landslides, or other ground failure caused by earthquakes. Currently, the City of San Bernardino is located outside a mapped area for Seismic Hazard Zones, which establishes regulatory zones that encompass areas prone to liquefaction (failure of water-saturated soil) and earthquake-induced landslides. Once the City of San Bernardino has been mapped pursuant to this Act, the City of San Bernardino must withhold development permits for a site within a designated Seismic Hazard Zone until the geologic conditions are investigated and appropriate mitigation measures, if any, are incorporated into the development plans. In addition, sellers (and their agents) of real property within a mapped Seismic Hazard Zone must disclose that the property lies within such a zone at the time of sale. . Development in the San Bernardino planning area is required to adhere to the building standards of the most recent California Building Code (CBC) and Uniform Building Code (UBC) , which regulates the design and construction of excavations, foundations, building frames, retaining walls, and other building elements to mitigate the effects of seismic shaking and adverse soil conditions. The procedures and limitations for the design of structures are based on site characteristics, occupancy type, configuration, structural system height, and seismic zoning for Seismic Zone 4. . All development proposals shall be evaluated in compliance with the California Environmental Quality Act (CEQA) and all General Plan environmental policies including, but not limited to, geologic hazards. Structures within 50 feet of an active or potentially active fault shall be prohibited. Development within these areas shall be subject to the submittal of appropriate report(s) prepared by qualified professionals which address the impacts of the proposed project; the identification of mitigation measures necessary to eliminate the significant adverse impacts; and, the provision of a program for monitoring, evaluating the effectiveness of, and insuring the adequacy of the specified mitigation measures. (Article III, Section 19.20.030, Section 6 of the City of San Bernardino Municipal Code) . All formal grading plans or site drainage plans must be reviewed and approved by the Engineering Section in the Department of Public works. This approval is required before building permits are issued. (Title 15 of the City of San Bernardino Municipal Code) . In addition to the requirements of Chapter A33 of the Uniform Building Code, the Municipal Code adds or makes provisions to mitigate against potential geological hazards in the City of San Bernardino: (1) Provisions for the applicability of the Alquist-Priolo Special Studies Zone. Within designated areas, reports on earthquake or liquefaction hazards are required. (13.04.130) Page 5.5-38 . The Planning Center july 2005 5. Environmental Analysis (2) Requires slopes to be on downhill lots unless specifically waived. (15.04.160) (3) Redefines setback from top to toe of slope. (15.04.190) (4) Requires slope planting of cut and fill slopes and review by the City Engineer. Slopes less than 5 feet may be waived under special circumstances. Provides for automatic irrigation on all slopes in excess of 15 feet. (15.04.200) (5) Provides for review of all grading projects by Environmental Review Committee where existing grade is 15% or greater, or more than 10,000 cubic yards, or material is to be moved. . The California Code of Regulations, Title 14, Chapter 4 Subchapter 4 Section 1942.1, Unstable Areas, defines unstable areas as areas that contain fumaroles, geysers, hot springs, mud pots, etc. where drilling any wells, including water wells, is prohibited unless the division determines, after a thorough geological investigation, that drilling in an unstable area is feasible. . The following are policies aimed at protection of geothermal resources and geothermal hazards contained in Section 13.20.360 of the City of San Bernardino Municipal Code. o Conserve and protect the geothermal fluids and ground water within and adjacent to the City, in order to enhance reservoir productivity and benefit; prevent wasteful extraction and disposal of geothermal fluids and thermal ground water; prevent geothermal fluid and thermal ground water temperature degradation; maintain stable static levels of geothermal fluids and thermal ground waters; prevent thermal pollution of surface environs and waters; and prevent harmful intermixing of geothermal fluids or thermal ground water with non- thermal ground waters; ~ o Increase and disseminate the scientific knowledge of geothermal and ground water resources; and o Protect the public health, safety, and welfare from improperly constructed, operated, maintained, or abandoned wells. 5.5.5 Level of Significance Before Mitigation 5.5.5.1 San Bernardino General Plan Update Upon consideration of policies and implementation of regulatory requirements and standard conditions of approval, the following impacts would be less than significant: GP Impact 5.5-1 Project residents (or occupants) within the San Bernardino planning area would be susceptible to potential impacts from surface rupture, severe ground-shaking and seismic induced liquefaction. However, new developments within the City would be required to ensure that structures could withstand the impacts from seismic related activity as required by the CBC for seismic related impacts within Seismic Zone 4. Furthermore, no structures are allowed within 50 feet of an active fault trace as required by the Alquist-Priolo Earthquake Fault Zoning Act and the Seismic Hazard Mapping Act. GP Impact 5.5-2 Portions of the City of San Bernardino and SOl areas are located on unstable geological units or have unstable soil conditions that may result in loss of topsoil or be susceptible to landslides, lateral spreading, liquefaction, subsidence, and General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-39 5. Environmental Analysis GP Impact 5.5-3 collapse. However, development in the San Bernardino planning area is required to adhere to the building standards of the most recent CBC and UBC, which regulates the design and construction of excavations, foundations, building frames, retaining walls, and other building elements to mitigate the effects of seismic shaking and adverse soil conditions. Portions of the City of San Bernardino and SOl areas may be located in areas with expansive soil conditions which can result in risks to life or property. However, in addition to adherence to the CBC and UBC, all formal grading plans must be reviewed and approved by the Engineering Section in the Department of Public works, which would ensure that site soil conditions are conducive to development and would not induce or be subject to impacts in this regard. 5.5.5.2 Arrowhead Springs Specific Plan Upon consideration of development standards and implementation of regulatory requirements and standard conditions of approval, the following impacts would be less than significant: AHS Impact 5.5-1 AHS Impact 5.5-3 Project residents (or occupants) within the Arrowhead Springs Specific Plan area would be susceptible to potential impacts from surface rupture, severe ground- shaking and seismic induced liquefaction. However, new developments within Arrowhead Springs would be required to ensure that structures could withstand the impacts from seismic related activity as required by the CBC for seismic related impacts within Seismic Zone 4. Furthermore, no structures are allowed within 50 feet of an active fault trace as required by the Alquist-Priolo Earthquake Fault Zoning Act and the Seismic Hazard Mapping Act. Soil conditions within the Arrowhead Springs Area exhibit very-low expansion potential and therefore do not pose a risk to life or property due to expansive soils conditions. AHS Impact 5.5-2 Without mitigation, the following impacts would be potentially significant: Portions of the Arrowhead Springs Specific Plan area are located on unstable geological units or have unstable soil conditions that may result in loss of topsoil or be susceptible to landslides, lateral spreading, liquefaction, subsidence, and collapse. 5.5.6 Mitigation Measures 5.5.6.1 San Bernardino General Plan Update 5.5.6.2 No significant impacts were identified and no mitigation measures are necessary. Arrowhead Springs AHS 5.5-2a AHS 5.5-2b All projects within the Arrowhead Springs Specific Plan area shall follow all geotechnical recommendations provided within the Report of Preliminary Geotechnical Evaluations produced by Soils Southwest Inc. Site specific geotechnical analysis shall be required for all new developments within the Arrowhead Springs Specific Plan area to determine existing soils conditions, soil recommendations for fill material prior to grading, and slope stability. Detailed Page 5.5-40 . The Planning Center july 2005 5. Environmental Analysis geologic and geotechnical evaluations shall be made for construction of structural footings and slab-on-grade for placement on compacted fill soils. AHS 5.5-2c No fill shall be placed, spread or rolled during unfavorable weather conditions. Where work is interrupted by heavy rains, fill operations shall not be resumed until moisture conditions are considered favorable by the soils engineer. AHS M 5.5-2d Proposed level structural pad areas shall be carefully evaluated by project geologist to determine whether these locations can be rendered safe and stable without potentially affecting offsite improvements. Excavated footings shall be inspected, verified and certified by soils engineer prior to steel and concrete placement to ensure their sufficient embedment and proper bearing. Structural backfill shall be placed under direct observation and testing. 5.5.7 Level of Significance After Mitigation The mitigation measures identified above would reduce potential impacts associated with geologic hazards to a level that is less than significant. Therefore, no significant unavoidable adverse impacts relating geology and soils have been identified. ~ General Plan Update and Associated Specific Plans EIR City of San Bernardino . Page 5.5-41 5. Environmental Analysis This page intentionally left blank. Page 5.5-42 . The Planning Center july 2005