3.4 Geology/Soils/Paleontological Resources

Transcription

1 Section 3.4 Geology, Soils, and Paleontological Resources This section evaluates potential geology and soils impacts, and also paleontological impacts. The analysis is based on a preliminary geotechnical investigation that has been performed as part of the engineering technical memos prepared for the project and included as Appendix D-1 and D-2 to this EIR Regulatory Framework The California Geological Survey provides guidance on seismic hazards. Under the Seismic Hazards Mapping Act, seismic hazard zones are identified and mapped to assist local governments in land use planning. The intent is to protect the public from the effects of strong ground shaking, liquefaction, landslides, ground failure, or other hazards caused by earthquakes. In addition, 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. The Alquist Priolo Earthquake Fault Zoning Act of 1972 prohibits the construction of buildings used for human occupancy on active surface faults, which are faults that have ruptured the ground surface in the past 11,000 years (Holocene Time). New habitable building structures must maintain a minimum 50-foot setback from all known active faults. Special Publication 42 (updated 1999) from the California Geological Survey describes Alquist Priolo Earthquake Fault hazard zones in California. The project area is not within an Alquist Priolo Earthquake Fault Zone; furthermore, no habitable structures are proposed Environmental Setting Geologic Setting The project area is within the Peninsular Ranges Geomorphic Province, a group of mountain ranges which stretch approximately 900 miles from southern California in the United States, to the southern tip of Mexico's Baja California peninsula. It is underlain by fill and Santiago Peak Volcanics. Fill includes locally derived materials and imported materials that have been excavated and/or deposited on the site. Some of these materials include Santiago Peak Volcanics that were disturbed by previous pipeline construction. Page 3.4-1

2 Santiago Peak Volcanics are composed of a wide range of mildly metamorphic volcanic, volcaniclastic (derived from volcanic sources), and sedimentary rock types. The Santiago Peak Volcanics are generally hard and extremely resistant to erosion and form topographic highs. Most of the volcanic rocks are dark greenish gray where fresh, but weather to dark reddish brown (Kennedy and Peterson 1975). According to the Guidelines for Determining Significance Paleontological Resources (County of San Diego 2009), Santiago Peak Volcanics have a moderate to high potential for paleontological resources to be present. Paleontological resources are the remains and/or traces of prehistoric life, exclusive of human remains, and the geologic age they represent. These resources, or fossils, are generally regarded as older than 10,000 years and are found in geologic deposits of hard rock that has been disturbed or excavated for construction of new infrastructure or development. Soils overlay the hard rock of the Santiago Peak Volcanics. Three soil types have been identified within the project area. San Miguel-Exchequer rocky silt loams (9 to 70 percent slopes) occur within the pipeline improvements area and access road area. Redding Gravelly loam (2 to 9 percent slopes) and Redding cobbly loam (9 to 30 percent slopes) occur in the staging area (U.S. Department of Agriculture [USDA] 1973). San Miguel- Exchequer rocky silt loam soils occur on the surrounding mountainous uplands, from 400 to 3,300 feet above MSL and often have a substantial cover by rock outcrops (approximately 10 percent). Geologic Hazards The project site is located in the general proximity of a number of active and potentially active faults, as well as the regional influence of several more distant active and potentially active faults. Southern California is known to be seismically active, and geologic and seismologic data are readily available. Earthquakes originating within approximately 60 miles of the project area are capable of generating ground shaking of engineering significance. The Rose Canyon Fault Zone, located approximately 10 miles to the west of the project area, would have the most significant effect at the site from a design standpoint. Other active faults in the region that could possibly affect the project site include the Coronado Bank, San Diego Trough, and San Clemente fault zones to the west, the Elsinore and San Jacinto fault zones to the north, and the Agua Blanca and San Miguel fault zones to the south. Probable ground shaking levels at the project site could range from slight to strong depending on such factors as the magnitude of the seismic event and the distance to the epicenter. However, as noted above, the subject site is not included within an Earthquake Fault Zone created by the Alquist-Priolo Act. The state of California defines the maximum (formerly known as maximum credible) earthquake as the greatest potential ground Page 3.4-2

3 shaking event that appears capable of occurring under the presently understood tectonic framework. Other seismic hazards include soil lurching, liquefaction, and landslides. Soil lurching refers to the rolling motion on the ground surface by the passage of seismic surface waves. Effects of this action are likely to be significant where the thickness of soft sediments (such as loose or saturated alluvium) vary appreciably under structures and at the interface of sediments of varying densities. Liquefaction is the conversion of soil into a fluid-like mass during seismic-related ground failure. The soils at risk of liquefaction are typically uniform, granular, and saturated with groundwater. Any structures founded on or buried in such soils, including pipelines, can experience large differential settlement, causing major damage. A landslide is the down slope movement of a large amount of soil due to gravity. These typically occur when the side of a hill or mountain becomes unstable to external factors, such as erosion, moisture, or seismic events Thresholds for Determining Significance Thresholds used to evaluate potential geology, soils, and paleontological resources impacts are based on applicable criteria in the state CEQA Guidelines (California Code of Regulations [CCR] ), Appendix G. A significant impact would occur if the project would: 1) Expose people or structures to potential substantial adverse effects, including the risk of injury or death involving; a) 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, such as Division of Mines and Geology Special Publication 42; b) Strong seismic ground shaking; c) Seismic-related ground failure, including liquefaction; or, d) Landslides; 2) Result in substantial soil erosion or the loss of topsoil; 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; Page 3.4-3

4 4) Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), or other soil characteristics that may result in a substantial risk to failure of the aqueduct system (i.e., corrosive soils), and thereby have a substantial effect on life or property; or 5) Directly or indirectly destroy a unique paleontological resource or site or unique geologic feature Impact Analysis The potential for rockfall or other geologic hazards due to controlled blasting activities required for this project are addressed in Section 3.6, Hazards and Hazardous Materials Analysis of Project Effects Threshold 1: Exposure to Seismic-related Hazards Would the project expose people or structures to potential substantial adverse effects, including the risk of 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, such as Division of Mines and Geology Special Publication 42? Strong seismic ground shaking? Seismic-related ground failure, including liquefaction? Landslides? PIPELINE IMPROVEMENTS (BOTH ALTERNATIVES) Seismic-related hazards have the potential to impact both the pipelines and workers during construction activities. Analysis of the potential impacts to the pipelines during and after construction is included below. The Water Authority has numerous requirements to address safety concerns for the workers for both tunneling and open trench construction methods. These related requirements have been incorporated into features of the project design and are detailed in Chapter 2, Project Description. As an example, the Water Authority has standard specifications for tunnel support systems, including appropriate materials and loading, rock reinforcement, and structural calculations. When a construction alternative is selected, additional detailed engineering and construction requirements would be required to be implemented prior to construction. Thus, contract specifications incorporated into the project design will ensure that potential impacts associated with seismic-related hazards during construction would be less than significant. Page 3.4-4

5 Fault Rupture: The pipeline improvements area is not within a mapped Alquist-Priolo Fault Zone, and there are no known or mapped faults that traverse this area. Impacts associated with rupture of a known earthquake fault would be less than significant. Seismic Ground Shaking: As discussed above, the project area is located within a seismically active region. Based on recorded earthquake magnitudes and locations, the area may be vulnerable to moderate- to high-seismic ground shaking during the design life of the project. The Rose Canyon Fault Zone would have the most significant affect at the site from a design standpoint. Peak ground acceleration is expressed in g (i.e., the acceleration due to Earth's gravity, equivalent to g-force). The maximum earthquake event is expected to produce peak horizontal ground acceleration at the site of 0.17g. This represents a low seismic hazard over the next 50 years. The Water Authority s pipelines have been designed to resist damage from ground-shaking induced by an earthquake of this magnitude. Project plans will be reviewed to ensure compatibility with geotechnical conclusions, and applicable field activities (e.g., seismic loading requirements) will be reviewed and appropriately modified by the geotechnical engineer. Soil Lurching: The potential for damage to the replacement pipelines due to soil lurching is low, since a relatively large differential fill/alluvial thickness will not exist below the majority of the pipeline alignment, except at the extreme northern end of the alignment. Since the soils have a relatively moderate seismic velocity and the anticipated peak horizontal ground acceleration is relatively low, the potential for soil lurching would be less than significant. Liquefaction: Based on the site characteristics encountered within the pipeline improvements area, the potential for liquefaction is very low since there is no nearsurface groundwater table and the site materials (Santiago Peak Volcanics) are extremely hard. Landslides: The site is underlain by hard rock materials with a low potential for slope instability. Accordingly, the potential for large-scale landslides in the pipeline improvements area is low. Overall, the replacement pipelines have been designed to withstand damage from potential seismic events. The contractor would be required to verify that the geotechnical specifications are met. Thus, the pipeline improvements component of the project would not expose structures or people to potential substantial adverse seismic effects. Impacts would be less than significant. ACCESS ROAD Potential geological hazard impacts are associated with the operation of the access road after construction is finished. The access road would be unmanned during the Page 3.4-5

6 operational phases, except during routine, biweekly maintenance activities conducted by Water Authority personnel. Fault Rupture: The access road area is not within a mapped Alquist-Priolo Fault Zone, and there are no known or mapped faults that traverse this area. Impacts associated with rupture of a known earthquake fault would be less than significant. Seismic Ground Shaking: As discussed above, the project area is located within a seismically active region. The access road has been designed to resist damage from ground-shaking induced by a maximum earthquake event. Project plans will be reviewed to ensure compatibility with geotechnical conclusions, and applicable field activities (e.g. seismic loading requirements) will be reviewed and appropriately modified by the geotechnical engineer. Soil lurching: Similar to the pipeline improvements area, because the soils have a relatively moderate seismic velocity and the anticipated peak horizontal ground acceleration is relatively low, the potential for soil lurching would be less than significant. Liquefaction: Based on the site characteristics encountered along the access road area, the potential for liquefaction exists at the low point of the alignment adjacent to the drainage. The final design and construction of the access road would be required to meet all Water Authority specifications for design and construction. For example, unsuitable subgrade material would be replaced with compacted native material or crushed aggregate base. Other requirements and project design features will be reviewed prior to construction to ensure compatibility with final geotechnical conclusions. Applicable field activities (e.g., manufactured slope conditions, excavations, and fill placement) will be reviewed and appropriately modified by the geotechnical engineer. Landslides: The site is underlain by hard rock materials with a low potential for slope instability. Accordingly, the potential for large-scale landslides in the access road area is low. Thus, the access road component of the project would not expose structures or people to potential substantial adverse seismic effects. Impacts would be less than significant. STAGING AREA Construction staging would be temporary and would not involve the construction of any structures. Rock crushing would take place using temporary equipment that would be removed at completion of the pipeline improvements. Impacts would be less than significant. Threshold 2: Soil Erosion/Loss of Topsoil Would the project result in substantial soil erosion or the loss of topsoil? Page 3.4-6

7 PIPELINE IMPROVEMENTS (BOTH ALTERNATIVES) Both construction alternatives for the pipeline improvements would involve grading; however, the activities would be temporary and the excavated area would be filled, recontoured, and revegetated (as necessary) after construction is completed. During construction activities under either alternative, the project contractor would implement the Water Authority s standard erosion and sediment control, slope stability design features, and associated BMPs (see Section 3.7, Hydrology and Water Quality). These typically include the use of erosion stabilizing measures in appropriate areas (including disturbed areas), such as geotextiles, mats, fiber rolls, or soil binders. Thus, impacts associated with the substantial loss of topsoil and soil erosion during construction activities would be less than significant due to implementation of the project design features described above. ACCESS ROAD The access road component of the project would involve widening and paving of unpaved areas within the Water Authority ROW on soils with erodibility and runoff potential. Therefore, the potential for soil erosion or the loss of topsoil is high. However, substantial soil erosion or loss of topsoil would be avoided by implementation of BMPs incorporated into the specifications and project design features. This includes measures described above for the pipeline improvements area, as well as other measures immediately following clearing operations in the following locations: within the pipeline ROW immediately upstream of all natural channels; at the lowest end of areas disturbed by construction before runoff from storms can reach natural streams; and at additional location as required by the Storm Water Pollution Prevention Plan (SWPPP), detailed in Section 3.6, Hydrology and Water Quality. Through implementation of the required SWPPP, project design features, and standard contract specifications, impacts associated with erosion and the substantial loss of topsoil would be less than significant. STAGING AREA Substantial clearing or grading activities would not be required for temporary equipment staging. As detailed in Chapter 2, Project Description, the staging area has been previously cleared. Heavy construction equipment, including a rock crusher, would be stored in the cleared portion of the staging area, thus increasing the potential for erosion. To protect the surrounding areas from erosion, measures such as silt fences, sandbag dikes, or stabilized construction entrances would be used in the staging area. Additional erosion control BMPs developed for the SWPPP would be implemented through specifications and project design features. Thus, impacts would be less than significant. Page 3.4-7

8 Threshold 3: Soil Stability Would the project 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? PIPELINE IMPROVEMENTS (BOTH ALTERNATIVES) As previously discussed, the pipeline improvements would not be located on an unstable geologic unit or soil, nor would the soil become unstable as a result of the project. The site is underlain by hard rock materials with a low potential for slope instability. The project contractor would implement the Water Authority s standard erosion and sediment control BMPs, slope stability design features, and associated BMPs. Following completion of construction, the ground surface would be recontoured and restored to its existing condition. Impacts would be less than significant. ACCESS ROAD As detailed under the first threshold, the access road may be subject to liquefiable soils near the low point/drainage. As previously detailed, the final design and construction of the access road would be required to meet all referenced Water Authority specifications. This includes specifications on grading, preparation of subgrade, furnishing/installation of base materials, and installation of wearing surface for permanent access road construction. Applicable field activities (e.g., manufactured slope conditions, excavations, and fill placement) would be reviewed and appropriately modified by the geotechnical engineer. Compliance with these specifications would ensure that impacts associated with soil stability would be less than significant. STAGING AREA As detailed under the previous threshold, heavy construction equipment, including a rock crusher, would be stored in the cleared portion of the staging area. The project would incorporate features such as stabilized construction entrances and other BMPs developed for the SWPPP, which would be implemented through project specifications. Thus, soil stability impacts would be less than significant. Threshold 4: Expansive Soils/Other Soil Characteristics Would the project be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), or other soil characteristics that may result in a substantial risk to failure of the aqueduct system (i.e., corrosive soils), and thereby have a substantial effect on life or property? Page 3.4-8

9 ALL PROJECT COMPONENTS Expansive soils are clay- or adobe-based soils that absorb large quantities of water and, as a result, expand. This expansion can cause building slabs to crack and buckle. As noted above, the pipeline and road alignments would be located in materials (Santiago Peak Volcanics) that are extremely hard. Santiago Peak Volcanics are not considered an expansive soil. In addition, the pipeline and road would be excavated and backfilled with appropriate materials. The staging area would not involve the construction of structures, nor are expansive soils present. No impacts related to expansive soils would occur. The pipeline improvements area is underlain by soils that are considered very corrosive. Project development would conform to applicable industry standards (i.e., Water Authority standards) regarding corrosive soils within the pipeline improvements area. A site-specific investigation of potential corrosion hazards would be conducted in areas deemed appropriate by a qualified corrosion engineer prior to construction. The results of this analysis would be checked against the final project design, as appropriate, to address potential corrosion impacts, and would include design features such as excavation (or overexcavation) and treatment, and/or removal and replacement (i.e., with engineered fill) of corrosive soil materials; and use of non-corrosive and/or corrosion-resistant building materials and coatings in appropriate locations and installation of cathodic protection systems, such as cathodic test stations and anodes. Accordingly, conformance with applicable industry standards and project design features that would be confirmed prior to construction would ensure that impacts related to corrosive soils in the pipeline improvement area would be less than significant. Threshold 5: Paleontological Resources Would the project directly or indirectly destroy a unique paleontological resource or site or unique geologic feature? PIPELINE IMPROVEMENTS (BOTH ALTERNATIVES) AND ACCESS ROAD As previously detailed, the project area is underlain by Santiago Peak Volcanics, a geologic formation which, in the Mira Mesa/Scripps Ranch area, is considered to have a moderate to high paleontological resource potential. Both the pipeline improvements and access road areas have been previously disturbed due to installation of the original pipelines 3, 4, and 4A. However, grading and excavation activities have the potential to extend to depths previously undisturbed within the Santiago Peak Volcanics. Thus, potential impacts to paleontological resources would be considered significant. Page 3.4-9

10 Analysis of Cumulative Effects The geographic scope of the cumulative impact analysis for geology is limited to the immediate area of the potential geologic constraints associated with development, with the exception of some geologic impacts that are regional, such as earthquake risk. Threshold 1: Exposure to Seismic-related Hazards Potential seismic-related hazards affect all development activities within southern California. These hazards are typically reduced through conformance with existing regulations, such as the California Building Code (CBC), Seismic Hazards Mapping Act, and Alquist Priolo Earthquake Fault Zoning Act. All potential project-related seismic hazard impacts would be avoided or reduced below identified thresholds for determining significance through conformance with geotechnical recommendations and established regulatory requirements as part of the project design. As with the project, cumulative area projects would be required to implement similar site-specific measures to address potential impacts to seismic hazards. Because of the site-specific nature of these potential hazards and the measures to address them, there would be no connection to similar potential issues or cumulative effects to or from other properties. The project, in combination with other cumulative projects, would result in a less than significant contribution to a cumulatively considerable impact. Threshold 2: Soil Erosion/Loss of Topsoil Project-related impacts related to erosion are less than significant due to erosion control measures and conformance with current Water Authority standards and specifications. Based on the strict requirements identified in the listed National Pollutant Discharge Elimination System (NPDES) permits and the fact that other planned and proposed developments in the project vicinity would be required to implement similar controls, the project in combination with other cumulative projects, would result in a less than significant contribution to a cumulatively considerable impact. Threshold 3: Soil Stability Potential soil stability impacts would be reduced or avoided altogether through implementation of the Water Authority s standard erosion and sediment control BMPs, slope stability design features, and associated BMPs. Other development projects in the area would be required to comply with similar regulations concerning soil stability, such as the CBC, and would have to demonstrate compliance during environmental review. Cumulative project compliance with existing regulations would ensure that a significant cumulative impact would not occur. The project, in combination with other cumulative projects, would result in a less than significant contribution to a cumulatively considerable impact. Page

11 Threshold 4: Expansive Soils/Other Soil Characteristics No expansive soils were found within the project area; nor are they expected to occur due to the extremely hard geological formation that underlies the area (Santiago Peak Volcanics). Corrosive soils are present within the pipeline improvements area; however, conformance with applicable industry standards would reduce impacts to less than significant. Other development projects in the area would be similarly required to comply with applicable industry standards and regulations, and would have to demonstrate compliance during environmental review. Compliance with existing regulations would ensure that a significant cumulative impact associated with expansive soils would not occur. The project, in combination with other cumulative projects, would result in a less than significant contribution to a cumulatively considerable impact. Threshold 5: Paleontological Resources Projects within the cumulative study area have the potential to result in disturbance of geologic formations with moderate to high paleontological resource potential. At the sitespecific level, paleontological surveys would be required to determine the resource value for impacted areas. A qualified paleontological monitor would also be a requirement in all those areas where grading would occur in formations of moderate to high resource potential and would reduce any cumulative impacts to regional paleontological resources to a less than significant level Mitigation Measures Threshold 5: Paleontological Resources PIPELINE IMPROVEMENTS (BOTH ALTERNATIVES) AND ACCESS ROAD Significant impacts to paleontological resources would be mitigated by the implementation of a monitoring program carried out under the supervision of a qualified paleontologist. MM-PALEO-1: 1. Prior to start of construction, the qualified paleontologist (Paleontological Monitor) shall conduct a site-specific records search from the San Diego Natural History Museum. 2. Prior to the start of any grading and excavation, the Paleontological Monitor shall submit an exhibit based on the final construction documents that shall identify the areas to be monitored, including the delineation of grading/excavation limits. The exhibit shall be based on the results of a site-specific records search, existing known soil conditions (native or formation), and the depth to which grading/excavation activities would occur. Prior to the start of any work, the Paleontological Monitor shall Page

12 also develop a monitoring schedule consistent with the construction schedule, indicating when and where monitoring will occur. 3. During construction, in the event of a discovery, grading/trenching activities in the area of discovery will be temporarily diverted. The Paleontological Monitor shall evaluate the significance of the resource. The determination of significance for fossil discoveries shall be at the discretion of the Paleontological Monitor. a. If the resource is significant, a Paleontological Recovery Program shall then be submitted to the Water Authority. Impacts to significant resources must be mitigated before ground disturbing activities in the area of discovery shall be allowed to resume. The Paleontological Monitor shall also: Notify the Water Authority that fossil resources will be collected, curated, and documented. Ensure that all fossil remains collected are cleaned and catalogued. Ensure that all fossil remains are analyzed to identify function and chronology as they relate to the geologic history of the area, that faunal material is identified as to species, and that specialty studies are completed, as appropriate. Ensure that all fossil remains associated with the monitoring for this project are permanently curated with an appropriate institution. b. If the resource is not significant (e.g., small pieces of broken common shell fragments or other scattered common fossils), the Paleontological Monitor shall note in the monitoring reports and notify the Construction Manager that a nonsignificant discovery has been made, and work can continue. 4. Following construction, the Paleontological Monitor shall submit a Monitoring Report to the Water Authority that describes the results, analysis, and conclusions of all phases of the Paleontological Monitoring Program. If significant paleontological resources are encountered during monitoring, the Paleontological Recovery Program shall be included in the Monitoring Report. A copy of the final Monitoring Report shall be submitted to the San Diego Natural History Museum Significance after Mitigation Implementation of mitigation measure MM-PALEO-1 would reduce impacts to less than significant. Page