01896 deir 4.4 geology and soils 1
TRANSCRIPT
Microsoft Word - 01896 DEIR 4.4 Geology and Soils 1.docGEOLOGY AND
SOILS 4.4
The geology and soils analysis is based on the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc. (see Appendix E) and discusses potential impacts due to rupture of a known earthquake fault, strong seismic ground shaking, liquefaction, landslides, and unstable geologic units or soil. As analyzed in the Initial Study, the proposed project will not result in substantial erosion or loss of topsoil, be located on expansive soils, or include the use of septic tanks or alternative waste water disposal systems. Therefore, this DEIR does not further analyze these topics. No comments regarding geology and soils were submitted during circulation of the Notice of Preparation (NOP).
Existing Conditions
TOPOGRAPHY The southern portion of the site is relatively flat with a slight gradient to the north. Elevations begin to rise just south of the MacNeil Mansion. Several small retaining walls within the lower garden area are used to gain elevation. The site continues to gain elevation north of the MacNeil Mansion with additional retaining walls. Slopes ascend in the northern portion of the site and continue onto the adjacent properties as graded fill slopes. Elevations range from 680 feet above sea level (asl) in the southeast corner of the project site to 760 feet asl along the northern property boundary.
REGIONAL GEOLOGY The project site is located along the northern edge of the San Gabriel Valley, which is an alluvial filled valley bounded by the Sierra Madre Fault Zone and San Gabriel Mountains to the north, the Puente Hills on the south, the Covina and Indian Hills on the east, and by the Raymond Basin on the west. The project area is located in the foreland slopes at the foot of the San Gabriel Mountains. This foreland area is characterized by shallow to moderately steep slope flanks that are underlain by fan deposits that have been shed from the proto-mountains, which in turn mantle sedimentary bedrock. Surficial deposits including alluvial soils in the canyon bottoms, slopewash/mass wasted materials on the ridge flanks, weathered soils and artificial fill also mantle portions of the foreland area on and adjacent to the project site.
SUBSURFACE CONDITIONS The Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc. included a comprehensive evaluation of the seismic setting and focused on interpreted fault lineaments in the southern portion of the project site. The study included a review of existing published and unpublished reports and studies conducted on the adjacent properties. On-site subsurface investigations included seven bucket auger borings ranging from 11 to 36 feet deep, two Cone Penetrometer soundings to depths of 25 and 36 feet deep and the excavation and logging of an approximately 130 foot long, 15 to 20 foot deep trench. The trench was excavated across an interpreted fault lineament. Subsurface investigations found that the project site is underlain by artificial fill (af/Caf), alluvium (Qal), and bedrock of the Topanga Formation (Tt). Artifical fill (af/Caf) is non-engineered fill material (af). Artificial fill was placed on the project site as part of original site development. These materials were derived from near site sources and consist of a varied admixture of sand, silt, and clay. The fill materials, where encountered, were found to be dry to moist and loose to medium dense and varied in depth from a few feet to 5+ feet. Compacted/engineered fill (Caf) has been placed in the southeast portion of the site and along the north, east and south property boundaries. These materials were placed as part of the grading construction of the Rosedale Development and consist primarily of silty sand and sand that is moist and dense. The placement of these fill sections was observed and tested by the geotechnical consultant for the Rosedale project. Review of grading reports indicates that these materials were compacted and moisture conditioned to generally accepted industry standards. Alluvium (Qal)/older Alluvium (Qol) are alluvial soils that were deposited in tributary canyons by streams and/or surface flow. These materials have been mapped in the southern, western and eastern portions of the project site. Based on the boring logs and grading exposures, alluvium consists of loose to medium dense, dry to saturated sand and silty sands with occasional gravel and cobble sized material. Alluvial thicknesses vary from a few feet to as much as 35+ feet in the
Geology and Soils 4.4
4.4-2 Dhammakaya International Meditation Center
southern portion of the property. Older alluvium was observed in the recently excavated trench. These materials are similar to the younger alluvial soils but are dense and well consolidated. The Topanga Formation (Tt) underlies the site and is mantled by alluvium and fill deposits. Based on the trench exposure, this bedrock unit consists of thick bedded sandstone layers with thin clay and siltstone interbeds. The sandstone is weathered in the upper 1 to 2 feet and moderately to well indurated.
GEOLOGIC HAZARDS Various types of ground failure can occur as a result of earthquakes shaking and can cause substantial damage to the built environment. Ground failure types include settlement, collapse, subsidence, liquefaction, and slope failure.
SETTLEMENT Differential seismic settlement occurs when seismic ground shaking causes one type of soil or rock to settle more than another type. Settlement is more likely to occur in areas of alluvium. Settling can damage structures and infrastructure by unevenly depressing soils underlying building foundations. COLLAPSE Collapsible soils consist of loose, dry, low-density materials that collapse and densify with the addition of water or excessive loading. Such soils are typical in areas of young alluvial fans, debris flow sediments, and aeolian (wind-blown) deposits. Collapse occurs when subsurface soils are excessively saturated at levels deeper than those reached by an average rainfall and the clay bonds holding the soil grains together are weakened. Collapse can result in cracked foundations, floors, and walls.
SUBSIDENCE Land subsidence is a gradual settling or sudden sinking of the Earth’s surface due to subsurface movement of earth materials. More than 80 percent of the identified subsidence in the United States is caused through overdrafting of groundwater. Drainage of organic soils, undergrounding mining, natural compaction, and thawing of permafrost can also cause subsidence. Similar to collapse and settlement, subsidence causes large areas of land to sink, thereby potentially damaging foundations, walls, and floors.
LATERAL SPREAD Lateral spreading is the downslope movement of surface sediment due to liquefaction in a subsurface layer. The downslope movement is due to gravity and earthquake shaking combined. Such movement can occur on slope gradients of as little as one degree. Lateral spreading typically damages pipelines, utilities, bridges, and structures.
LIQUEFACTION Liquefaction is a phenomenon that occurs when soil undergoes transformation from a solid state to a liquefied condition due to the effects of increased pore-water pressure. This typically occurs where susceptible soils (particularly the medium sand to silt range) are located over a high (less than 50 feet from the surface) groundwater table. Affected soils lose all strength during liquefaction and foundation failure can occur.
Regulatory Setting
SEISMIC HAZARDS MAPPING ACT The California Geological Survey (CGS) provides guidance with regard to seismic hazards under the Seismic Hazards Mapping Act. Seismic hazard zones are identified and mapped by the CGS to assist local governments in land use planning. The intent of the Act is to protect the public from the effects of strong groundshaking, liquefaction, landslides, ground failure, or other hazards caused by earthquakes. In addition, CGS Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California, provides guidance for the evaluation and mitigation of earthquake-related hazards for projects within designated zones of required investigations.
Geology and Soils 4.4
Draft Environmental Impact Report 4.4-3
CALIFORNIA BUILDING CODE The California Building Standards Law states that every local agency enforcing building regulations must adopt the provisions of the California Building Code (CBC) within 180 days of its publication; however, each jurisdiction can require more stringent regulations issued as amendments to the CBC. The publication date of the CBC is established by the California Building Standards Commission and the code is known as Title 24 of the California Code of Regulations. In the past, the CBC was modeled on the Uniform Building Code (UBC); however, beginning with the 2007 version, the CBC is now modeled after the International Building Code (IBC). It should be emphasized that the building codes provide minimum requirements to prevent major structural failure and loss of life. The City of Azusa adopted the 2013 CBC through Chapter 14-1 (Codes Adopted) of the Municipal Code. The 2013 CBC bases its seismic design criteria on maximum considered ground motion through maps prepared by the USGS for the National Seismic Hazard Mapping Program (see Section 1613). Pursuant to the CBC, soils reports are required to be submitted prior to issuance of grading permits.
CITY OF AZUSA GENERAL PLAN The Azusa General Plan includes the following goals and policies related to geological hazards: Goal 1 Ensure the continued functioning of essential (critical, sensitive, and high occupancy) facilities following a
disaster; help prevent loss of life from the failure of critical and sensitive facilities in an earthquake; and help prevent major problems for post-disaster response, such as difficult or hazardous evacuations or rescues, numerous injuries, and major cleanup or decontamination of hazardous materials.
Goal 2 Minimize to the greatest extent feasible the loss of life, serious injuries, and major social and economic
disruption caused by the collapse of, or severe damage to, vulnerable structures (e.g., buildings, bridges, water storage facilities, key railroad components) resulting from an earthquake.
Goal 5 Encourage the preparation of a plan to facilitate the rapid and effective recovery of the city following an
earthquake. Identify alternative financing sources for the repair and reconstruction of disaster related damage.
Thresholds of Significance Significant impacts related to geology and soils would result from implementation of the proposed project if the project would:
A. 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;
ii. Strong seismic ground shaking; iii. Seismic-related ground failure, including liquefaction; iv. Landslides
B. 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
Geology and Soils 4.4
4.4-4 Dhammakaya International Meditation Center
Environmental Impacts Impact 4.4.A. – i – Impacts to life and property resulting from the rupture of a known earthquake fault as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map will be less than significant with mitigation incorporated. As stated within the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc., the project site is located within a zone requiring investigation as defined by the Alquist-Priolo Earthquake Fault Zoning Act based on the Earthquake Fault Zones map for the Azusa 7.5-minute quadrangle (released on November 6, 2014)1 (See Exhibit 4.4- 1,Earthquake Fault Zones & Seismic Hazard Zones). The Alquist-Priolo Earthquake Fault Zoning Act defines an active fault as one that “has had surface displacement within Holocene time (about the last 11,000 years).” The main objective of the Alquist Priolo Act is to prevent the construction of dwellings on top of active faults that could displace the ground surface resulting in loss of life and property. The Act sets forth standards of investigation and analysis that must be met in site studies. As a result, Petra Geotechnical, Inc. completed a comprehensive Fault Investigation and Evaluation (Appendix C of the Preliminary Geotechnical Review) for the project site including conclusions concerning the structural setting of the site, surrounding environs, and the possible existence of fault traces. The study included a review of earlier investigations, thus providing a regional context for the fault investigation and a review of published articles covering the regional geology. The subsurface evaluation consisted of seven bucket auger borings ranging from 11 to 36 feet deep, two Cone Penetrometer soundings to depths of 25 and 36 feet deep, and excavation and logging of a 130-foot long, 23-foot deep fault trench within the southern portion of the project site (See Exhibit 4.4-2, Fault Trench Profile). Alquist-Priolo-level fault investigations are not intended to assess the intensity and hence effects of ground motions on the proposed structures. The investigation is solely intended to avoid placement of habitable structures on active faults as defined by the State of California. Based on the results of the Fault Investigation and Evaluation, Petra Geotechnical, Inc. determined that the project site is within a tectonically active area characterized by the active and well located Sierra Madre fault and the less active and less well located Duarte fault (See Exhibit 4.4-1). As demonstrated by earlier investigations by consultants such as Earth Consultants International, Inc., Richard Mills and Associates, and Pacific Soils Engineering, faults located on the project site are not active per Alquist-Priolo requirements; that is, they have been documented not to displace Holocene sediments. According to the Fault Investigation and Evaluation, a review of stereo-paired aerial photographs identified two potential lineaments crossing the project site; one mapped in the northwestern portion of the project site in the vicinity of the Organizational Housing buildings and one mapped in the southern portion of the site, through the proposed Meditation Hall. Those two locations were the focus of the fault study on the project site. Extensive geologic study surrounding the project site has focused on unnamed fault “C” (UNC) and unnamed fault “D” (UND). Unnamed fault “C” is located north of the project site, just south of Sierra Madre Avenue and not within a projection that could affect the project site. Unnamed fault “D” trends across a portion of the Rosedale property west of the project site as documented in investigations conducted by Lawson Geotechnical Consultants. The projection of UND in a northeast to northerly direction clips the far northwestern corner of the project site. While Earth Consultants International, Inc. recently concluded in 2014, based on the literature and examination of Lawson Geotechnical Consultants trenches, that the fault is not active according to Alquist-Priolo definitions, review of UND remains on-going. Regardless of the status of UND, the proposed improvements, most notably the proposed Organizational Housing buildings, are located over 100 feet from the projection of UND, which is sufficient separation regardless whether or not UND is ultimately determined active. Since the proposed improvements in the northwest portion of the project site near the projection of UND consist of a parking lot and landscaping, which are not subject to further Alquist-Priolo review, no significant impacts would occur from faulting in the northern portion of the project site.
Geology and Soils 4.4
Draft Environmental Impact Report 4.4-5
A photo lineament suggested a possible east – west trending fault crossing the southern portion of the project site, which could potentially impact the proposed Meditation Hall. Petra excavated and logged a 130-foot long, 23-foot deep, fault trench in the location of the Meditation Hall. The fault trench began at the edge of the Xavier Building and trended south toward East Monrovia Place. The trench was logged by Petra Geotechnical, and the results are included in Appendix D to the DEIR. The trench was examined by the City’s geotechnical consultant, RMA, and by the State Geologist. All reviewers concluded that no faulting was observed in the trench. Therefore, no significant impacts associated with faulting would impact the southern portion of the project site and the construction of the proposed Meditation Hall. While no impacts associated with active faulting are anticipated, given the location of the project site within a region of high seismicity, Mitigation Measure 4.4-A-1 is included to further minimize potential impacts. Mitigation Measure 4.4-A-1 requires that a consulting geologist be present during grading activities to observe excavations in order to document the absence or presence of active faults and to make recommendations regarding mitigation if active faults are found. Impact 4.4.A. – ii – Impacts to life and property resulting from seismically induced strong ground shaking will be less than significant with implementation of the City’s existing standards. The project site is subject to strong seismic ground shaking, as are virtually all properties in Southern California. The project site is located along the northern edge of the San Gabriel Valley, which is an alluvial filled valley bounded by the Sierra Madre Fault Zone and San Gabriel Mountains on the north, the Puente Hills on the south, the Covina and Indian Hills on the east, and by the Raymond Basin on the west. According to the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc., the type and magnitude of seismic hazards that may affect the project site are dependent on both the distance to causative faults and the intensity and duration of the seismic event. Although the probability of primary surface rupture is low, ground shaking hazards posed by earthquakes occurring along regional active faults do exist and should be taken into account in the design and construction of the proposed facilities within the project site. The proposed additions to the project site are subject to the seismic design criteria of the California Building Code (CBC). The City of Azusa adopted the 2013 CBC and included it in its Municipal Code (Section 14-51) on January 1, 2014 (Ordinance No. 13-03, § 3). The 2013 California Building Code contains seismic safety provisions with the aim of preventing building collapse during a design earthquake, so that occupants would be able to evacuate after the earthquake. A design earthquake is one with a two percent chance of exceedance in 50 years, or an average return period of 2,475 years. Adherence to these requirements will reduce the potential of building collapse during an earthquake, thereby minimizing injury and loss of life. Although structures may be damaged during earthquakes, adherence to seismic design requirements will minimize damage to property within the structure because the structure is designed not to collapse. The CBC is intended to provide minimum requirements to prevent major structural failure and loss of life. In addition, the proposed project is subject to the seismic design criteria recommendations within the Preliminary Geotechnical Report prepared by Petra Geotechnical, Inc. Adherence to the recommendations within the geotechnical report and existing regulations will reduce the risk of loss, injury, and death; impacts due to strong ground shaking will be less than significant. Impact 4.4.A – iii-iv – Impacts to life and property resulting from seismic-related ground failure, including liquefaction and landslides will be less than significant. A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. There are five categories of landslide movement types: slide, flow, fall, topple, and spread. According to the Landslide Inventory Map of the Azusa 7.5-minute quadrangle, no landslide activity has been documented on the project site.2 Impacts related to landslides will be less than significant. As discussed herein, liquefaction is a phenomenon that occurs when soil undergoes transformation from a solid state to a liquefied condition due to the effects of increased pore-water pressure. This typically occurs where susceptible soils (particularly the medium sand to silt range) are located over a high (less than 50 feet from the surface) groundwater table. Affected soils lose all strength during liquefaction and foundation failure can occur. According to the Seismic
Geology and Soils 4.4
4.4-6 Dhammakaya International Meditation Center
Hazards Zone Map for the Azusa 7.5-minute quadrangle, the southern and northwestern portions of the project site lie within an area that has been mapped as being potentially susceptible to earthquake-induced liquefaction.3 According to the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc., groundwater was encountered at the bedrock contact in several of the borings drilled in the southern portion of the project site. This occurrence is likely the result of surface waters which have percolated down to the relatively impermeable bedrock surface. A groundwater surface at a depth of approximately 20 feet was established within the alluvial sediments to the south of the project site. Saturated alluvial soils were encountered at depths of 15 feet below preexisting grades during the grading for Rosedale Avenue adjacent to the northwest property line. Compressible materials must be removed below the proposed buildings and either bedrock or dense alluvial soils should be exposed. In the northern portion of the site in the vicinity of the Organizational Housing, removals on the order of 5 feet are anticipated. In the southern portion of the site, in the vicinity of the Meditation Hall, low density artificial fill and alluvial soils were encountered to depths of 15 feet and greater below surface. These materials exhibit low density and are therefore considered unsuitable to support the proposed structures and will be excavated and re-compacted as part of remedial grading operations. All earthwork and grading will be performed in accordance with all applicable requirements of the grading and excavation codes of the City of Azusa and is subject to CBC standards including requirements for excavation, fill, footings, retaining walls, and pier and pile foundations. Typical design features required by the CBC are ground improvement or foundational design. Ground improvement includes removal and recompaction of low-density soils and removal of excess groundwater. Given that the site is relatively flat, and that all loose compressible soils will be removed during remedial grading activities in compliance with CBC requirements, liquefaction is not considered a potential hazard with respect to the project site. Impacts related to life and property resulting from seismic-related ground failure, including liquefaction and landslides will be less than significant Impact 4.4.B – Impacts related to a geologic unit or soil that is unstable or that would become unstable as a result of the project will be less than significant with implementation of the City’s existing standards and regulations. Landslides and Liquefaction. Impacts related to landslides and liquefaction are discussed in impacts 4.4.A.iii-iv herein. Impacts related to landslides and liquefaction will be less than significant. Lateral Spreading. Lateral spreading of the ground surface during a seismic activity usually occurs along the weak shear zones within a liquefiable soil layer and has been observed to generally take place toward a free face (i.e. retaining wall, slope, or channel) and to lesser extent on ground surfaces with a very gentle slope. Due to the absence of any channel within or near the project site and the required excavation and re-compaction of the artificial fill materials and loose natural soils (alluvium) underlying portions of the project site, the potential for lateral spread occurring on the project site is considered to be negligible. The project is required to be constructed in accordance with the CBC. The CBC includes a requirement that any City-approved recommendations contained in the soils report be made conditions of the building permit. All earthwork and grading will be performed in accordance with all applicable requirements of the grading and excavation codes of the City of Azusa and in compliance with all applicable provisions of the 2013 CBC. Compliance with existing CBC regulations would limit hazard impacts arising from unstable soils to less than significant levels. Collapse and Subsidence. Subsurface investigations found that the project site is underlain by artificial fill (af/Caf), alluvium (Qal), and bedrock of the Topanga Formation (Tt). As mentioned herein, artifical fill (af/Caf) is non-engineered fill material that was placed on the project site as part of original site development. These materials were derived from near site sources and consist of a varied admixture of sand, silt, and clay. The fill materials, where encountered, were found to be dry to moist and loose to medium dense and varied in depth from a few feet to 5+ feet.
Geology and Soils 4.4
Draft Environmental Impact Report 4.4-7
Compacted/engineered fill (Caf) has been placed in the southeast portion of the site and along the north, east and south property boundaries. These materials were placed as part of the grading construction of the Rosedale Development and consist primarily of silty sand and sand that is moist and dense. The placement of these fill sections was observed and tested by the geotechnical consultant for the Rosedale project. Review of grading reports indicates that these materials were compacted and moisture conditioned to generally accepted industry standards. Alluvium (Qal)/older Alluvium (Qol) are alluvial soils that were deposited in tributary canyons by streams and/or surface flow have been mapped in the southern, western and eastern portions of the project site. Based on the boring logs and grading exposures, alluvium consists of loose to medium dense, dry to saturated sand and silty sands with occasional gravel and cobble sized material. Alluvial thicknesses vary from a few feet to as much as 35+ feet in the southern portion of the property. Older alluvium was observed in the recently excavated trench. These materials are similar to the younger alluvial soils but are dense and well consolidated. The artificial fill materials and alluvium exhibit low density and are therefore considered unsuitable to support the proposed structures and will be excavated and re-compacted as part of remedial grading operations. All earthwork and grading will be performed in accordance with all applicable requirements of the grading and excavation codes of the City of Azusa and in compliance with all applicable provisions of the 2013 CBC. Given that all loose compressible soils will be removed during remedial grading activities in compliance with CBC requirements, collapse and subsidence are not considered potential hazards with respect to the project site. Impacts will be less than significant.
Mitigation Measures 4.4-A-1 During site grading activities, the consulting geologist must observe excavations to document the
absence or presence of active faults; and to make recommendations regarding mitigation of active faults if found.
Level of Significance with Mitigation Incorporation Impact 4.4.A.i will be less than significant with the incorporation of Mitigation Measures 4.4.A-1. Impacts 4.4.A.iii-iv and Impact 4.4.B will be less than significant without the need for mitigation incorporation.
References 1 California Department of Conservation. California Geological Survey. Earthquake Zones of Required Investigation. Earthquake
Fault Zones. Azusa Quadrangle. Released November 6, 2014. 2 California Department of Conservation. California Geological Survey. Landslide Inventory Map of the Azusa Quadrangle. J.A.
Treiman and C.J. Wills. December 2007. 3 California Department of Conservation. California Geological Survey. Earthquake Zones of Required Investigation. Seismic Hazard
Zones. Azusa Quadrangle. Released March 25, 1999.
Draft Environmental Impact Report 4.4-8
Geology and Soils 4.4
Geology and Soils 4.4
The geology and soils analysis is based on the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc. (see Appendix E) and discusses potential impacts due to rupture of a known earthquake fault, strong seismic ground shaking, liquefaction, landslides, and unstable geologic units or soil. As analyzed in the Initial Study, the proposed project will not result in substantial erosion or loss of topsoil, be located on expansive soils, or include the use of septic tanks or alternative waste water disposal systems. Therefore, this DEIR does not further analyze these topics. No comments regarding geology and soils were submitted during circulation of the Notice of Preparation (NOP).
Existing Conditions
TOPOGRAPHY The southern portion of the site is relatively flat with a slight gradient to the north. Elevations begin to rise just south of the MacNeil Mansion. Several small retaining walls within the lower garden area are used to gain elevation. The site continues to gain elevation north of the MacNeil Mansion with additional retaining walls. Slopes ascend in the northern portion of the site and continue onto the adjacent properties as graded fill slopes. Elevations range from 680 feet above sea level (asl) in the southeast corner of the project site to 760 feet asl along the northern property boundary.
REGIONAL GEOLOGY The project site is located along the northern edge of the San Gabriel Valley, which is an alluvial filled valley bounded by the Sierra Madre Fault Zone and San Gabriel Mountains to the north, the Puente Hills on the south, the Covina and Indian Hills on the east, and by the Raymond Basin on the west. The project area is located in the foreland slopes at the foot of the San Gabriel Mountains. This foreland area is characterized by shallow to moderately steep slope flanks that are underlain by fan deposits that have been shed from the proto-mountains, which in turn mantle sedimentary bedrock. Surficial deposits including alluvial soils in the canyon bottoms, slopewash/mass wasted materials on the ridge flanks, weathered soils and artificial fill also mantle portions of the foreland area on and adjacent to the project site.
SUBSURFACE CONDITIONS The Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc. included a comprehensive evaluation of the seismic setting and focused on interpreted fault lineaments in the southern portion of the project site. The study included a review of existing published and unpublished reports and studies conducted on the adjacent properties. On-site subsurface investigations included seven bucket auger borings ranging from 11 to 36 feet deep, two Cone Penetrometer soundings to depths of 25 and 36 feet deep and the excavation and logging of an approximately 130 foot long, 15 to 20 foot deep trench. The trench was excavated across an interpreted fault lineament. Subsurface investigations found that the project site is underlain by artificial fill (af/Caf), alluvium (Qal), and bedrock of the Topanga Formation (Tt). Artifical fill (af/Caf) is non-engineered fill material (af). Artificial fill was placed on the project site as part of original site development. These materials were derived from near site sources and consist of a varied admixture of sand, silt, and clay. The fill materials, where encountered, were found to be dry to moist and loose to medium dense and varied in depth from a few feet to 5+ feet. Compacted/engineered fill (Caf) has been placed in the southeast portion of the site and along the north, east and south property boundaries. These materials were placed as part of the grading construction of the Rosedale Development and consist primarily of silty sand and sand that is moist and dense. The placement of these fill sections was observed and tested by the geotechnical consultant for the Rosedale project. Review of grading reports indicates that these materials were compacted and moisture conditioned to generally accepted industry standards. Alluvium (Qal)/older Alluvium (Qol) are alluvial soils that were deposited in tributary canyons by streams and/or surface flow. These materials have been mapped in the southern, western and eastern portions of the project site. Based on the boring logs and grading exposures, alluvium consists of loose to medium dense, dry to saturated sand and silty sands with occasional gravel and cobble sized material. Alluvial thicknesses vary from a few feet to as much as 35+ feet in the
Geology and Soils 4.4
4.4-2 Dhammakaya International Meditation Center
southern portion of the property. Older alluvium was observed in the recently excavated trench. These materials are similar to the younger alluvial soils but are dense and well consolidated. The Topanga Formation (Tt) underlies the site and is mantled by alluvium and fill deposits. Based on the trench exposure, this bedrock unit consists of thick bedded sandstone layers with thin clay and siltstone interbeds. The sandstone is weathered in the upper 1 to 2 feet and moderately to well indurated.
GEOLOGIC HAZARDS Various types of ground failure can occur as a result of earthquakes shaking and can cause substantial damage to the built environment. Ground failure types include settlement, collapse, subsidence, liquefaction, and slope failure.
SETTLEMENT Differential seismic settlement occurs when seismic ground shaking causes one type of soil or rock to settle more than another type. Settlement is more likely to occur in areas of alluvium. Settling can damage structures and infrastructure by unevenly depressing soils underlying building foundations. COLLAPSE Collapsible soils consist of loose, dry, low-density materials that collapse and densify with the addition of water or excessive loading. Such soils are typical in areas of young alluvial fans, debris flow sediments, and aeolian (wind-blown) deposits. Collapse occurs when subsurface soils are excessively saturated at levels deeper than those reached by an average rainfall and the clay bonds holding the soil grains together are weakened. Collapse can result in cracked foundations, floors, and walls.
SUBSIDENCE Land subsidence is a gradual settling or sudden sinking of the Earth’s surface due to subsurface movement of earth materials. More than 80 percent of the identified subsidence in the United States is caused through overdrafting of groundwater. Drainage of organic soils, undergrounding mining, natural compaction, and thawing of permafrost can also cause subsidence. Similar to collapse and settlement, subsidence causes large areas of land to sink, thereby potentially damaging foundations, walls, and floors.
LATERAL SPREAD Lateral spreading is the downslope movement of surface sediment due to liquefaction in a subsurface layer. The downslope movement is due to gravity and earthquake shaking combined. Such movement can occur on slope gradients of as little as one degree. Lateral spreading typically damages pipelines, utilities, bridges, and structures.
LIQUEFACTION Liquefaction is a phenomenon that occurs when soil undergoes transformation from a solid state to a liquefied condition due to the effects of increased pore-water pressure. This typically occurs where susceptible soils (particularly the medium sand to silt range) are located over a high (less than 50 feet from the surface) groundwater table. Affected soils lose all strength during liquefaction and foundation failure can occur.
Regulatory Setting
SEISMIC HAZARDS MAPPING ACT The California Geological Survey (CGS) provides guidance with regard to seismic hazards under the Seismic Hazards Mapping Act. Seismic hazard zones are identified and mapped by the CGS to assist local governments in land use planning. The intent of the Act is to protect the public from the effects of strong groundshaking, liquefaction, landslides, ground failure, or other hazards caused by earthquakes. In addition, CGS Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California, provides guidance for the evaluation and mitigation of earthquake-related hazards for projects within designated zones of required investigations.
Geology and Soils 4.4
Draft Environmental Impact Report 4.4-3
CALIFORNIA BUILDING CODE The California Building Standards Law states that every local agency enforcing building regulations must adopt the provisions of the California Building Code (CBC) within 180 days of its publication; however, each jurisdiction can require more stringent regulations issued as amendments to the CBC. The publication date of the CBC is established by the California Building Standards Commission and the code is known as Title 24 of the California Code of Regulations. In the past, the CBC was modeled on the Uniform Building Code (UBC); however, beginning with the 2007 version, the CBC is now modeled after the International Building Code (IBC). It should be emphasized that the building codes provide minimum requirements to prevent major structural failure and loss of life. The City of Azusa adopted the 2013 CBC through Chapter 14-1 (Codes Adopted) of the Municipal Code. The 2013 CBC bases its seismic design criteria on maximum considered ground motion through maps prepared by the USGS for the National Seismic Hazard Mapping Program (see Section 1613). Pursuant to the CBC, soils reports are required to be submitted prior to issuance of grading permits.
CITY OF AZUSA GENERAL PLAN The Azusa General Plan includes the following goals and policies related to geological hazards: Goal 1 Ensure the continued functioning of essential (critical, sensitive, and high occupancy) facilities following a
disaster; help prevent loss of life from the failure of critical and sensitive facilities in an earthquake; and help prevent major problems for post-disaster response, such as difficult or hazardous evacuations or rescues, numerous injuries, and major cleanup or decontamination of hazardous materials.
Goal 2 Minimize to the greatest extent feasible the loss of life, serious injuries, and major social and economic
disruption caused by the collapse of, or severe damage to, vulnerable structures (e.g., buildings, bridges, water storage facilities, key railroad components) resulting from an earthquake.
Goal 5 Encourage the preparation of a plan to facilitate the rapid and effective recovery of the city following an
earthquake. Identify alternative financing sources for the repair and reconstruction of disaster related damage.
Thresholds of Significance Significant impacts related to geology and soils would result from implementation of the proposed project if the project would:
A. 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;
ii. Strong seismic ground shaking; iii. Seismic-related ground failure, including liquefaction; iv. Landslides
B. 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
Geology and Soils 4.4
4.4-4 Dhammakaya International Meditation Center
Environmental Impacts Impact 4.4.A. – i – Impacts to life and property resulting from the rupture of a known earthquake fault as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map will be less than significant with mitigation incorporated. As stated within the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc., the project site is located within a zone requiring investigation as defined by the Alquist-Priolo Earthquake Fault Zoning Act based on the Earthquake Fault Zones map for the Azusa 7.5-minute quadrangle (released on November 6, 2014)1 (See Exhibit 4.4- 1,Earthquake Fault Zones & Seismic Hazard Zones). The Alquist-Priolo Earthquake Fault Zoning Act defines an active fault as one that “has had surface displacement within Holocene time (about the last 11,000 years).” The main objective of the Alquist Priolo Act is to prevent the construction of dwellings on top of active faults that could displace the ground surface resulting in loss of life and property. The Act sets forth standards of investigation and analysis that must be met in site studies. As a result, Petra Geotechnical, Inc. completed a comprehensive Fault Investigation and Evaluation (Appendix C of the Preliminary Geotechnical Review) for the project site including conclusions concerning the structural setting of the site, surrounding environs, and the possible existence of fault traces. The study included a review of earlier investigations, thus providing a regional context for the fault investigation and a review of published articles covering the regional geology. The subsurface evaluation consisted of seven bucket auger borings ranging from 11 to 36 feet deep, two Cone Penetrometer soundings to depths of 25 and 36 feet deep, and excavation and logging of a 130-foot long, 23-foot deep fault trench within the southern portion of the project site (See Exhibit 4.4-2, Fault Trench Profile). Alquist-Priolo-level fault investigations are not intended to assess the intensity and hence effects of ground motions on the proposed structures. The investigation is solely intended to avoid placement of habitable structures on active faults as defined by the State of California. Based on the results of the Fault Investigation and Evaluation, Petra Geotechnical, Inc. determined that the project site is within a tectonically active area characterized by the active and well located Sierra Madre fault and the less active and less well located Duarte fault (See Exhibit 4.4-1). As demonstrated by earlier investigations by consultants such as Earth Consultants International, Inc., Richard Mills and Associates, and Pacific Soils Engineering, faults located on the project site are not active per Alquist-Priolo requirements; that is, they have been documented not to displace Holocene sediments. According to the Fault Investigation and Evaluation, a review of stereo-paired aerial photographs identified two potential lineaments crossing the project site; one mapped in the northwestern portion of the project site in the vicinity of the Organizational Housing buildings and one mapped in the southern portion of the site, through the proposed Meditation Hall. Those two locations were the focus of the fault study on the project site. Extensive geologic study surrounding the project site has focused on unnamed fault “C” (UNC) and unnamed fault “D” (UND). Unnamed fault “C” is located north of the project site, just south of Sierra Madre Avenue and not within a projection that could affect the project site. Unnamed fault “D” trends across a portion of the Rosedale property west of the project site as documented in investigations conducted by Lawson Geotechnical Consultants. The projection of UND in a northeast to northerly direction clips the far northwestern corner of the project site. While Earth Consultants International, Inc. recently concluded in 2014, based on the literature and examination of Lawson Geotechnical Consultants trenches, that the fault is not active according to Alquist-Priolo definitions, review of UND remains on-going. Regardless of the status of UND, the proposed improvements, most notably the proposed Organizational Housing buildings, are located over 100 feet from the projection of UND, which is sufficient separation regardless whether or not UND is ultimately determined active. Since the proposed improvements in the northwest portion of the project site near the projection of UND consist of a parking lot and landscaping, which are not subject to further Alquist-Priolo review, no significant impacts would occur from faulting in the northern portion of the project site.
Geology and Soils 4.4
Draft Environmental Impact Report 4.4-5
A photo lineament suggested a possible east – west trending fault crossing the southern portion of the project site, which could potentially impact the proposed Meditation Hall. Petra excavated and logged a 130-foot long, 23-foot deep, fault trench in the location of the Meditation Hall. The fault trench began at the edge of the Xavier Building and trended south toward East Monrovia Place. The trench was logged by Petra Geotechnical, and the results are included in Appendix D to the DEIR. The trench was examined by the City’s geotechnical consultant, RMA, and by the State Geologist. All reviewers concluded that no faulting was observed in the trench. Therefore, no significant impacts associated with faulting would impact the southern portion of the project site and the construction of the proposed Meditation Hall. While no impacts associated with active faulting are anticipated, given the location of the project site within a region of high seismicity, Mitigation Measure 4.4-A-1 is included to further minimize potential impacts. Mitigation Measure 4.4-A-1 requires that a consulting geologist be present during grading activities to observe excavations in order to document the absence or presence of active faults and to make recommendations regarding mitigation if active faults are found. Impact 4.4.A. – ii – Impacts to life and property resulting from seismically induced strong ground shaking will be less than significant with implementation of the City’s existing standards. The project site is subject to strong seismic ground shaking, as are virtually all properties in Southern California. The project site is located along the northern edge of the San Gabriel Valley, which is an alluvial filled valley bounded by the Sierra Madre Fault Zone and San Gabriel Mountains on the north, the Puente Hills on the south, the Covina and Indian Hills on the east, and by the Raymond Basin on the west. According to the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc., the type and magnitude of seismic hazards that may affect the project site are dependent on both the distance to causative faults and the intensity and duration of the seismic event. Although the probability of primary surface rupture is low, ground shaking hazards posed by earthquakes occurring along regional active faults do exist and should be taken into account in the design and construction of the proposed facilities within the project site. The proposed additions to the project site are subject to the seismic design criteria of the California Building Code (CBC). The City of Azusa adopted the 2013 CBC and included it in its Municipal Code (Section 14-51) on January 1, 2014 (Ordinance No. 13-03, § 3). The 2013 California Building Code contains seismic safety provisions with the aim of preventing building collapse during a design earthquake, so that occupants would be able to evacuate after the earthquake. A design earthquake is one with a two percent chance of exceedance in 50 years, or an average return period of 2,475 years. Adherence to these requirements will reduce the potential of building collapse during an earthquake, thereby minimizing injury and loss of life. Although structures may be damaged during earthquakes, adherence to seismic design requirements will minimize damage to property within the structure because the structure is designed not to collapse. The CBC is intended to provide minimum requirements to prevent major structural failure and loss of life. In addition, the proposed project is subject to the seismic design criteria recommendations within the Preliminary Geotechnical Report prepared by Petra Geotechnical, Inc. Adherence to the recommendations within the geotechnical report and existing regulations will reduce the risk of loss, injury, and death; impacts due to strong ground shaking will be less than significant. Impact 4.4.A – iii-iv – Impacts to life and property resulting from seismic-related ground failure, including liquefaction and landslides will be less than significant. A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. There are five categories of landslide movement types: slide, flow, fall, topple, and spread. According to the Landslide Inventory Map of the Azusa 7.5-minute quadrangle, no landslide activity has been documented on the project site.2 Impacts related to landslides will be less than significant. As discussed herein, liquefaction is a phenomenon that occurs when soil undergoes transformation from a solid state to a liquefied condition due to the effects of increased pore-water pressure. This typically occurs where susceptible soils (particularly the medium sand to silt range) are located over a high (less than 50 feet from the surface) groundwater table. Affected soils lose all strength during liquefaction and foundation failure can occur. According to the Seismic
Geology and Soils 4.4
4.4-6 Dhammakaya International Meditation Center
Hazards Zone Map for the Azusa 7.5-minute quadrangle, the southern and northwestern portions of the project site lie within an area that has been mapped as being potentially susceptible to earthquake-induced liquefaction.3 According to the Preliminary Geotechnical Review prepared by Petra Geotechnical, Inc., groundwater was encountered at the bedrock contact in several of the borings drilled in the southern portion of the project site. This occurrence is likely the result of surface waters which have percolated down to the relatively impermeable bedrock surface. A groundwater surface at a depth of approximately 20 feet was established within the alluvial sediments to the south of the project site. Saturated alluvial soils were encountered at depths of 15 feet below preexisting grades during the grading for Rosedale Avenue adjacent to the northwest property line. Compressible materials must be removed below the proposed buildings and either bedrock or dense alluvial soils should be exposed. In the northern portion of the site in the vicinity of the Organizational Housing, removals on the order of 5 feet are anticipated. In the southern portion of the site, in the vicinity of the Meditation Hall, low density artificial fill and alluvial soils were encountered to depths of 15 feet and greater below surface. These materials exhibit low density and are therefore considered unsuitable to support the proposed structures and will be excavated and re-compacted as part of remedial grading operations. All earthwork and grading will be performed in accordance with all applicable requirements of the grading and excavation codes of the City of Azusa and is subject to CBC standards including requirements for excavation, fill, footings, retaining walls, and pier and pile foundations. Typical design features required by the CBC are ground improvement or foundational design. Ground improvement includes removal and recompaction of low-density soils and removal of excess groundwater. Given that the site is relatively flat, and that all loose compressible soils will be removed during remedial grading activities in compliance with CBC requirements, liquefaction is not considered a potential hazard with respect to the project site. Impacts related to life and property resulting from seismic-related ground failure, including liquefaction and landslides will be less than significant Impact 4.4.B – Impacts related to a geologic unit or soil that is unstable or that would become unstable as a result of the project will be less than significant with implementation of the City’s existing standards and regulations. Landslides and Liquefaction. Impacts related to landslides and liquefaction are discussed in impacts 4.4.A.iii-iv herein. Impacts related to landslides and liquefaction will be less than significant. Lateral Spreading. Lateral spreading of the ground surface during a seismic activity usually occurs along the weak shear zones within a liquefiable soil layer and has been observed to generally take place toward a free face (i.e. retaining wall, slope, or channel) and to lesser extent on ground surfaces with a very gentle slope. Due to the absence of any channel within or near the project site and the required excavation and re-compaction of the artificial fill materials and loose natural soils (alluvium) underlying portions of the project site, the potential for lateral spread occurring on the project site is considered to be negligible. The project is required to be constructed in accordance with the CBC. The CBC includes a requirement that any City-approved recommendations contained in the soils report be made conditions of the building permit. All earthwork and grading will be performed in accordance with all applicable requirements of the grading and excavation codes of the City of Azusa and in compliance with all applicable provisions of the 2013 CBC. Compliance with existing CBC regulations would limit hazard impacts arising from unstable soils to less than significant levels. Collapse and Subsidence. Subsurface investigations found that the project site is underlain by artificial fill (af/Caf), alluvium (Qal), and bedrock of the Topanga Formation (Tt). As mentioned herein, artifical fill (af/Caf) is non-engineered fill material that was placed on the project site as part of original site development. These materials were derived from near site sources and consist of a varied admixture of sand, silt, and clay. The fill materials, where encountered, were found to be dry to moist and loose to medium dense and varied in depth from a few feet to 5+ feet.
Geology and Soils 4.4
Draft Environmental Impact Report 4.4-7
Compacted/engineered fill (Caf) has been placed in the southeast portion of the site and along the north, east and south property boundaries. These materials were placed as part of the grading construction of the Rosedale Development and consist primarily of silty sand and sand that is moist and dense. The placement of these fill sections was observed and tested by the geotechnical consultant for the Rosedale project. Review of grading reports indicates that these materials were compacted and moisture conditioned to generally accepted industry standards. Alluvium (Qal)/older Alluvium (Qol) are alluvial soils that were deposited in tributary canyons by streams and/or surface flow have been mapped in the southern, western and eastern portions of the project site. Based on the boring logs and grading exposures, alluvium consists of loose to medium dense, dry to saturated sand and silty sands with occasional gravel and cobble sized material. Alluvial thicknesses vary from a few feet to as much as 35+ feet in the southern portion of the property. Older alluvium was observed in the recently excavated trench. These materials are similar to the younger alluvial soils but are dense and well consolidated. The artificial fill materials and alluvium exhibit low density and are therefore considered unsuitable to support the proposed structures and will be excavated and re-compacted as part of remedial grading operations. All earthwork and grading will be performed in accordance with all applicable requirements of the grading and excavation codes of the City of Azusa and in compliance with all applicable provisions of the 2013 CBC. Given that all loose compressible soils will be removed during remedial grading activities in compliance with CBC requirements, collapse and subsidence are not considered potential hazards with respect to the project site. Impacts will be less than significant.
Mitigation Measures 4.4-A-1 During site grading activities, the consulting geologist must observe excavations to document the
absence or presence of active faults; and to make recommendations regarding mitigation of active faults if found.
Level of Significance with Mitigation Incorporation Impact 4.4.A.i will be less than significant with the incorporation of Mitigation Measures 4.4.A-1. Impacts 4.4.A.iii-iv and Impact 4.4.B will be less than significant without the need for mitigation incorporation.
References 1 California Department of Conservation. California Geological Survey. Earthquake Zones of Required Investigation. Earthquake
Fault Zones. Azusa Quadrangle. Released November 6, 2014. 2 California Department of Conservation. California Geological Survey. Landslide Inventory Map of the Azusa Quadrangle. J.A.
Treiman and C.J. Wills. December 2007. 3 California Department of Conservation. California Geological Survey. Earthquake Zones of Required Investigation. Seismic Hazard
Zones. Azusa Quadrangle. Released March 25, 1999.
Draft Environmental Impact Report 4.4-8
Geology and Soils 4.4
Geology and Soils 4.4