Draft Environmental Impact Report - East Bay Municipal Utility District

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Estates Reservoir Replacement Draft Environmental Impact ReportGeology, Soils and SeismicityRegional GeologyEstates Reservoir and Dam are located within the seismically active San Francisco Bayregion between the Pacific plate on the west and the Sierra Nevada-Central Valley(“Sierran”) microplate on the east. Geodetic data demonstrate that net motion betweenthe two plates is obliquely convergent. The oblique motion of the Sierran microplaterelative to the strike of the San Andreas and Hayward faults results in a small componentof net convergence normal to these structures, which is accommodated by both strike-slipand thrust faulting in the eastern San Francisco Bay area.The Estates Reservoir site is situated in a narrow ravine near the western edge of the EastBay Hills. The East Bay Hills region is within the central Coast Range geomorphicprovince of California and is bounded by the Hayward fault on the west and the NorthernCalaveras fault on the east.Site GeologyThe site geology in the vicinity of the Project site and dam is illustrated in Figure 3.3-1.The rock at the dam site and surrounding the reservoir appears to be blueschist-faciesmetagraywacke of the Franciscan Complex. The Franciscan bedrock units in the vicinityof the dam site include a blueschist-facies metamorphic unit, Alcatraz Terrane, Mélangeincluding Marin Headlands Terrane rocks, Novato Quarry Terrane, and undifferentiatedmélange.The Hayward Fault is located about 1,400 feet northeast of Estates Dam and is the onlyfault with demonstrated Holocene activity that has been mapped near the reservoir ordam (Lienkaemper, 1992). The Hayward Fault in this area strikes subparallel to theWarren Freeway (State Highway 13) and is located slightly east of the freeway. Thisfault marks the contact between Franciscan Complex bedrock units to the west and CoastRange ophiolite, Great Valley Group with minor Franciscan Complex rocks to the east.Several different Franciscan Complex rock units crop out west of the Hayward fault andthe strikes of their bedding, as well as the strikes of the bounding contacts, are slightlymore westerly (by about 15 to 20 degrees) than that of the Hayward fault. This bedrockstructural grain and resultant erosional contrasts may have influenced the general shapeof the hills in this area because the ridge crests trends have a similar orientation. TheFranciscan rock units west of the Hayward fault, including those in the vicinity of theEstates Dam and Reservoir, have a northeasterly dip.Fault RuptureThere is no evidence of Holocene activity in possible minor faults or shears in theFranciscan rock units at the Estates Reservoir site, either as independent faults or asstructures that exhibit co-seismic movement with earthquakes on the Hayward Fault(Lienkaemper, 1992). Therefore, no fault study trenching has been performed at the site.Accordingly, the potential for fault rupture at the dam site is judged to be very small.sb09_001.doc 3-3.2 7/22/2009
Estates Reservoir Replacement Draft Environmental Impact ReportGeology, Soils and SeismicitySource: EBMUD 2008Geologic Map of the Estates Reservoir AreaFigure 3.3-1sb09_001.doc 3-3.3 7/22/2009
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Estates Reservoir ReplacementDraft
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TABLE OF CONTENTSEstates Reservoir
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Estates Reservoir Replacement Draft
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ACRONYMS AND ABBREVIATIONSABABAGAPC
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SUMMARYS.1 IntroductionThis Draft E
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Estates Reservoir Improvements Draf
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3.6 Traffic and Circulation3.6.1 Ap
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CHAPTER 5Cumulative Impacts, Growth
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CHAPTER 6Report Preparers6.1 Lead A
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APPENDIX APublic InvolvementPublic
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APPENDIX BNotice of PreparationAUGU
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Dingee Pressure Zone Improvement Pr
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FIGURESDingee Pressure Zone Improve
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Draft Environmental Impact Report - East Bay Municipal Utility District

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