Environmental Impact Statement - Sonoma Land Trust

California Department of Fish and Game
U.S. Fish and Wildlife Service
Section 3.1. Geology, Soils, and Paleontology
Permit. The existing levees are outdated and were not constructed to USACE
flood control standards (WWR 2005b). The surrounding agricultural land is
therefore at risk of flooding due to potential levee failure. Levees would continue
to be maintained by CDFG at reduced levels. Soil subsidence would likely
continue in the diked baylands portion of the site due to soil decomposition, wind
erosion, and compaction of organic matter. Existing levels of risk related to
seismic and landslide hazards would also continue in effect.
Conclusion: No Impact.
Action Alternatives
Impact GEO-1: Potential Damage to Proposed Facilities
Resulting from Strong Seismic Ground Shaking,
Liquefaction, or Other Types of Seismic-Related Ground
Failure
Proposed Project
Implementation of the Project would involve the construction of a levee south of
the SMART rail line, one or more bridges and/or boardwalks north of the rail
line, a possible grade-separated crossing underneath the SMART rail line , and
modifications to an existing undercrossing beneath Highway 37. The project site
is likely to experience ground shaking from a major earthquake in the next 70
years. Because the project site is underlain by unconsolidated Bay mud deposits
south of the SMART rail line and Bay mud deposits overlain by artificial fill in
the area between the rail line and Highway 37, ground shaking likely would be
more intense and/or prolonged at the project site than in adjacent areas underlain
by bedrock. The site is also potentially subject to ground failure related to
liquefaction. Earthquake-induced ground shaking and associated liquefaction
could damage the proposed facilities, including the levee, any bridges and/or
boardwalks, and the modified highway undercrossing. Specific seismic- and
soils-related impacts associated with the above features are discussed below.
Flood Control Levee
As mentioned above, the levee could be subject to strong seismic groundshaking
and ground failure related to liquefaction. This could result in damage to any or
all of the levee’s structural components, including the core levee, geotechnical
stability berm, and erosion /habitat leveesslopes. Damage to the proposed levee
could lead to tidal flooding of the agricultural lands north of the SMART line,
Reclamation Road, and other areas to the north. However, the new levee would
be designed and constructed to meet or exceed relevant standards of the U.S.
Army Corps of Engineers and thus would be expected to perform better in a
seismic event than the existing agriculturalperimeter levee. As discussed abovein
Chapter 2, design would be supported by detailed site-specific geotechnical
investigations consistent with the current standard of care. Although no levee is
earthquake proof, overall risks of tidal inundation as a result of earthquake-
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
3.1-14
April 2012