| SECTION 4.0 | ENVIRONMENTAL SETTING, IMPACTS, AND MITIGATION |
| PROPOSED PROJECT |
4.15 PALEONTOLOGICAL RESOURCES
This section is based on a paleontological resources sensitivity analysis of the Project area that includes: 1) museum repository data and paleontological collection material; and 2) a published and unpublished scientific literature survey to provide relevant environmental overview data. This paleontological resources assessment summarizes the information presented in the Paleontological Resources Technical Report prepared for the Trans Bay Cable Project (Project). The Paleontological Resources Technical Report is presented in Appendix J of this EIR.
The compiled data were used to assess paleontological resource sensitivity issues in relation to proposed Project construction, operation, and maintenance activities. The assessment is based both on known paleontological sites within the Project area, as well as extrapolated biostratigraphic information derived from rock units in adjacent areas or areas of regional context which indicate the potential for a fossil resource to occur in a particular geologic unit.
The methodology used to perform the paleontological resources analysis is as follows:
4.15.1 Environmental Setting
The following discusses the regional setting as well as the settings of the proposed Project. For a detailed description of the paleontological setting, refer to the paleontological technical report (Appendix J).
4.15.1.1 Regional Setting
The San Francisco Bay region contains a diverse record of geologic and biologic history which spans more than 100 million years, dating from the Upper Cretaceous period. Under the combined influences of regional tectonic events ranging from creation of the Sacramento Basin to uplift of the Coast Range foothill region, deposition of sedimentary sequences, and fluctuating worldwide sea level changes, fossils of marine and terrestrial organisms have accumulated to produce a significant record of prehistoric life.
Much of the paleontological interest within the Project area vicinity stems from the well known discoveries of Pleistocene age (10,000 to 1 million years ago) and fossil vertebrate faunas derived from Quaternary age units (present to 1 million years ago) in other parts of the San Francisco Bay region. Identification and scientific description of both of these diverse fossil vertebrate assemblages provides one of the best known records of Pleistocene faunas in California (Stirton, 1939, 1951; Savage, 1951; Wolf, 1971; and Jefferson, 1991). Preservation of specimens buried by river sediments and other continental volcanoclastic deposits provided favorable conditions for preserving vertebrate fossil remains in these geologic units.
Surficial sedimentary units of predominantly Pleistocene and Holocene to Recent age underlie the entire Project area. These sediments include depositions that range from continental, alluvial, fluvial, estuarine, terrace, and fan-derived sediments to subaerial floodplain to marine terrace and near-shore deposits. Lithologies include sand, gravel, silt, and clay, all of which are potentially favorable to the preservation of paleontological resources.
Rock outcrops of Miocene (13 to 25 million years ago) to Pleistocene age occur as surficial and subsurface deposits along the northeast Contra Costa County delta area. These deformed and faulted sequences of sedimentary units have been described and mapped previously by such researchers as Atwater (1982), Brabb et al. (1971), Graymer and Helley (1997), Sims et al. (1973), and Weaver, (1949). Gradual, long-term erosion and previous construction activity has removed parts of the Recent age soil cover so that these Quaternary rock units and their contained fossils are now at or near the surface in portions of the Project area. These formations or parts of the formations now exist at or near the surface with varying width across the project area terrain, but are obscured in most areas by water bodies, marsh areas, soil, vegetation, or thin deposits of surficial sediment. Thus, visual detection of fossils is possible in those areas where natural erosion or man-made excavations during road, pipeline, or building site excavation or grading operations have removed this cover.
The majority of the converter station and construction laydown areas may be overlain by imported fill material. Given this fact, the potential paleontological sensitivity of a particular site within the Project area has been determined from the distribution of known nearby fossil localities, and available mapping of the Quaternary alluvium (Qal) and Quaternary undifferentiated (Qu) outcrops. The Quaternary rock units vary in type from conglomerates to sandstones to unconsolidated siltstone and clays, all of which are either fossiliferous (fossil-bearing) or potentially fossiliferous.
4.15.1.1.1 Cenozoic Rock Units (Present to 63 Million Years Ago). Over 100 years of fossil vertebrate collecting in the San Francisco Bay and delta region has produced one of the most extensive databases for understanding the fossil vertebrate record of northern California. The first record of a fossil vertebrate from the region was a fossil mammoth tooth from the San Pablo Bay area, as reported by Blake (1855). Stirton (1939 and 1951), Savage (1951), and Jefferson (1991) have extensively reported on fossil land-mammal assemblages found in this region. Vertebrate sites in the Hercules-Rodeo districts have yielded a significant quantity of microvertebrate material. This diverse microvertebrate fauna has been extensively studied most recently by Wolf (1971, 1973, and 1975) and consists of numerous small mammals including rabbits, rodents, insectivores and a variety of birds and lower vertebrates (frogs, lizards, and snakes). Many of the fossil specimens represent the best-preserved specimens of particular taxa found to date. The Paleontological Resources Technical Report prepared for the Project contains data from fossil mammal assemblages collected from the San Francisco Bay and delta region (see UCMP 1359,1363 V3719, and V79073 site records).
Sandstone, silt, and clay lithologies of both geologic units are favorable for exceptional preservation of vertebrate and microvertebrate fossil resources.
4.15.1.1.2 Quaternary Age Sediments (Qal) (Present to 1 Million Years Ago). Quaternary alluvium deposits of Pleistocene age occur locally within the active stream portions of the Project area. Usage of the Qal geologic symbol designation on available geologic maps is highly variable. Geologic units ranging from Quaternary age stream, terrace, fluvial, and alluvial fan and floodplain deposits have been lumped under this designation, particularly where geologic data have been scarce (see Helley and Harwood, 1985; and Wagner and Jennings, 1981).
Sandstone, silt, and clay lithologies of both geologic units are favorable for exceptional preservation of vertebrate and microvertebrate fossil resources. Several Pittsburg vertebrate sites outside the Project area have been assigned to the Pleistocene age Quaternary alluvium unit (Qal) by museum scientists and are not further differentiated geologically.
4.15.1.1.3 Holocene and Post-Holocene Age Sediments (Present to 10,000 Years Ago). Sediments of probable Holocene or post-Holocene age that form the thin, surficial cover are considered of limited paleontological interest and thus considered inconsequential.
4.15.1.2 Project Area Setting
No vertebrate paleontological sites are known to exist within the Project area. However, paleontological sites do occur in similar age rock units outside the specific Project area but within the San Francisco Bay - Sacramento region. These contain scientifically important vertebrate fossils of elephant, camel, sloth, bison, and rodent terrestrial mammalian taxa.
When describing the Project area setting, three categories of paleontological potential are used in this report. Rating categories are considered to be interpretive and are subject to change as new information is obtained. High potential, moderate potential, and low potential ratings are defined as follows:
4.15.1.2.1 High Potential Rating. Rock units with a high potential for significant paleontological resources are known to have yielded vertebrate fossils within the Project area or region. This does not necessarily imply that vertebrate fossils will always be recovered from high potential rated rock units, but only that there are recorded occurrences within the unit. Additional factors that are considered pertain to inferred depositional environment and lithology.
4.15.1.2.2 Moderate Potential Rating. Rock units possessing some degree of potential, such as favorable depositional environment for resource preservation or lithologically similar rock units in the region have yielded vertebrate fossils. All moderate potential-rated rock units are recommended for field survey and construction monitoring.
4.15.1.2.3 Low Potential Rating. Rock units containing lithologies that do not commonly preserve significant fossil resources (i.e., coarse conglomerates, welded or ignimbrite volcanic ash deposits) are rated as low potential. Igneous plutonic rocks, such as the granite or gabbro, are precluded from preservation of paleontological resources, due to their genesis within a magmatic environment. In addition, sediments of subHolocene or Recent age are usually considered too young in geologic time to preserve fossils.
4.15.1.3 San Francisco HWC Converter Station
No fossil localities have been identified within the footprints of these Project components. The proposed San Francisco HWC Converter Station site and its associated onshore AC/DC cable route are assigned a high sensitivity rating, since excavations have the potential to penetrate into undisturbed Qal sediments which could contain significant fossil resources (refer to Figure 4.15-1). The proposed laydown area is assigned a low sensitivity rating, as use of this area is not expected to penetrate into undisturbed Qal sediments. The alternative laydown area is located outside of fossil bearing sediments.
4.15.1.4 Pittsburg Standard Oil Converter Station
No fossil localities have been identified within the footprints of these Project components. The proposed Pittsburg Standard Oil Converter Station and its associated onshore AC/DC cable route and proposed access road are assigned a high sensitivity rating, since excavations have the potential to penetrate into undisturbed Qal sediments which could contain significant fossil resources (refer to Figure 4.15-2). The proposed laydown area is assigned a low sensitivity rating, as use of this area is not expected to penetrate into undisturbed Qal sediments.
No fossil localities have been identified within the footprint of the alternative Standard Oil Converter Station access road or alternative laydown area. The alternative access road and laydown area are assigned a low sensitivity rating, since use of the road and laydown area are not expected to penetrate into undisturbed Qal sediments, which could contain significant fossil resources.
4.15.1.5 Offshore DC Cable Route
No fossil localities have been identified within the footprint of this project component. The proposed offshore route is assigned a low sensitivity rating, since excavations are not expected to penetrate into undisturbed Qal sediments where there would be a potential for paleontological resources.
4.15.2 Regulatory Setting
4.15.2.1 Federal
Paleontological resources are classified as a non-renewable scientific-cultural resource and are protected most notably by the 1906 Federal Antiquities Act and other subsequent federal legislation and policies. Significant paleontological resources are defined in this analysis to include the interpretation outlined by the Society of Vertebrate Paleontology (SVP) (1994), wherein vertebrate fossils are considered significant.
4.15.2.2 State
Appendix G of CEQA Guidelines provides a checklist of questions that a lead agency will normally address if relevant to a project's environmental impacts. Section (V) (c) of the CEQA Guidelines asks if the project will directly or indirectly destroy a unique paleontological resource, site, or unique geological feature.
4.15.2.3 Local
No local regulations pertaining to paleontological resources were identified.
4.15.3 Environmental Impacts
This section evaluates potential impacts from Project implementation on paleontological resources. Where applicable, mitigation measures are recommended to reduce potential impacts to a less-than-significant level.
4.15.3.1 Thresholds of Significance
The threshold of significance for impacts to paleontological resources for purposes of the analysis in this EIR utilized guidelines established by the SVP (1994) and CEQA.
SVP significance thresholds use the following criteria for vertebrate paleontological resources:
The CEQA threshold for a significant impact to a paleontological resource is reached when the project would directly or indirectly destroy a unique paleontological resource, site, or unique geological feature.
4.15.3.2 San Francisco HWC Converter Station
4.15.3.2.1 Construction-related Impacts. Although no paleontological resources are known in the Project vicinity, Qal sediments underly the Project vicinity. Soils of the Qal series are known to contain paleontological remains.
Impact PALEO-1: Disturbance of Fossil Resources. There are no known significant fossil resources at this location. However, excavations associated with construction have the potential to penetrate into undisturbed Qal sediments, which could contain significant fossil resources. This impact would be considered potentially significant.
Mitigation Measure PALEO-1: Potential Fossil Resources Protection. The following measures shall be implemented:
Implementation Responsibility: Project proponent/construction contractor
Requirements and Timing: A professional paleontologist shall be retained prior to Project implementation to conduct monitoring in geological units designated with a potentially moderate or high sensitivity rating during onshore Project construction activities involving ground disturbance
Monitoring Requirements: The City of Pittsburg to monitor and ensure compliance
Resulting Level of Significance. Mitigation Measure PALEO-1 would reduce Impact PALEO-1 to a less-than-significant level.
4.15.3.2.2 Operations-related Impacts. No impacts have been identified with the operational phase of the Project.
4.15.3.3 Pittsburg Standard Oil Converter Station
4.15.3.3.1 Construction-related Impacts. There are no known significant fossil resources at this location. However, excavations associated with construction of the proposed Pittsburg Standard Oil Converter Station, proposed access road, and onshore cable routes have the potential to penetrate into undisturbed Qal sediments, which could contain significant fossil resources.
Impact PALEO-1: Disturbance of Fossil Resources. The disturbance of fossil resources impact (Impact PALEO-1) described in Section 4.15.3.2.1 applies to the Pittsburg Standard Oil Converter Station site.
Mitigation Measure PALEO-1: Potential Fossil Resources Protection. Mitigation Measure PALEO-1 described in Section 4.15.3.2 would be implemented at the Pittsburg Standard Oil Converter Station site.
Implementation Responsibility: Project proponent/construction contractor
Requirements and Timing: A professional paleontologist shall be retained prior to Project implementation to conduct monitoring in geological units designated with a potentially moderate or high sensitivity rating during onshore Project construction activities involving ground disturbance
Monitoring Requirements: City of Pittsburg to monitor and ensure compliance
Resulting Level of Significance. Implementation of Mitigation Measure PALEO-1 would reduce Impact PALEO-1 to a less-than-significant level.
4.15.3.3.2 Operations-related Impacts. No impacts have been identified for the operation of the Project.
4.15.3.4 Offshore DC Cable Route
No fossil localities have been identified within the footprint of this Project component. Excavations and operational aspects are not expected to penetrate into undisturbed Qal sediments where there would be a potential for significant paleontological resources.
4.15.4 References
Atwater, B.F. 1982. Geologic Maps of the Sacramento-San Joaquin Delta, California, U.S. Geological Survey, Miscellaneous Field Studies Map MF-1401 15 p., Scale 1:24,000., 21 sheets.
Blake, W. P. 1855. Remains of the Mammoth and Mastodon in California, Amer. Jour. Sci. Arts, Series 2, Vol. 19, No. 55, 133p.
Brabb, E.E., Sonneman, H.S., and Switzer, J.R., Jr. 1971. Preliminary Geologic Map of the Mt. Diablo - Byron area, Contra Costa, Alameda, and San Joaquin Counties, California, U.S. Geological Survey, Open-File Report 71-53. Scale 1:62,500, 2 sheets.
Graymer, R.W., Helley, E.J. 1997. Quaternary Geology Map of Contra Costa County and Surrounding Parts of Sonoma, Solano, Sacramento, and San Joaquin Counties, California: A Digital Database, U.S. Geological Survey, Open-File Report 97-98. Scale 1:75,000.
Helley, E. J. and Harwood, D. S. 1985. Geologic Map of the Late Cenozoic Deposits of the Sacramento Valley and Northern Sierran Foothills Region, California. U.S. Geological Survey, Miscellaneous Field Studies Map MF-574. Scale 1:62,500.
Jefferson, G.T. 1991. A Catalogue of Late Quaternary Vertebrates From California: Part One, Nonmarine Lower Vertebrates and Avian Taxa, Natural History Museum of Los Angeles County, Technical Report No. 5, 60 p.
Savage, D.E. 1951. Late Cenozoic Vertebrates of the San Francisco Bay Region. Univ. Calif. Public. Geol. Sci., Vol. 28, No. 10, pp.215-314, 51 figs.
Sims, J.D., Fox, K.F., Jr., Bartow, J.A., and Helley, E.J. 1973. Preliminary Geologic Map of Solano County and parts of Napa, Contra Costa, Marin, and Yolo Counties, California. U. S. Geological Survey, Miscellaneous Field Studies Map MF-484. Scale 1:62,500, 5 sheets.
Society of Vertebrate Paleontology. 1994. Mitigation and Monitoring Guidelines Vertebrate Paleontological Resources. Memorandum.
Stirton, R.A. 1939. Late Cenozoic Vertebrates of the San Francisco Bay Region. Univ. Calif. Public. Geol. Sci., Vol. 24, pp.339-410, 95 figs.
1951. Prehistoric Land Mammals of the San Francisco Bay Region. In - Geologic Guidebook of the San Francisco Bay Counties, Calif. Div. Mines Geol., Regional Map Series, Bulletin 154, pp.177-186.
Wagner, D. L., and Jennings, C.W. 1981. Geologic Map of the San Francisco Sheet, California, California Division of Mines and Geology - Regional Map Series. Map scale 1:250,000.
Weaver, C.E. 1949. Geology of the Coast Ranges - North San Francisco Bay Region. Geol. Soc. Amer. Memoir 35, 242 p.
Wolf, R.G. 1971. Paleoecology of a Late Pleistocene (Rancholabrean) Vertebrate Fauna from Rodeo, California, Ph.D. dissertation, University of California, Berkeley, 136 p., unpublished.
1973. Hydrodynamic Sorting and Ecology of Late Pleistocene Mammalian Assemblage from California (USA). Paleogeog., Paleoclimatol., Paleoecol., Vol. 13, pp. 91-102.
1975. Sampling and Sample Size in Ecological Analyses of Fossil Mammals, Paleobiology, Vol. 1, No. 2, pp. 195-202.
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