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
Upper Tertiary mudstone and shale, and sandstone (Tu-md), although both of
these lithologic units also extend to the gentle to moderately steep hillslopes
south of Highway 37. As with the areas north of Highway 37, the southern
hillslopes are characterized by generally erodible surface soils assigned to the
Diablo series and underlain by the Petaluma Formation. A 2003 Draft Geologic
and Geotechnical Feasibility Report (Geocon Consultants 2003) on the area
extending from Highway 37 south to the SMART line noted that although the
upland Diablo clays are known to be prone to slippage, the slopes in that
particular portion should not be steep enough to induce landslides. A 2003
Environmental Constraints Analysis of most of the site by CH2M Hill (CH2M
Hill 2003a) contradicts that conclusion, however, stating that “even shallow cuts
[in the Petaluma Formation, or the Diablo clays] may induce slope instability.”
Evaluation of Engineering Materials and
Identification of Methods for Minimizing Structural
Damage During Seismic Events
As described in Chapter 2, as part of the project design process, SLT will be
retaining qualified professionals to conduct site-specific geotechnical
investigations consistent with all applicable standards and the current standard of
care for professional engineering geologic and geotechnical practice. The
purpose of the investigations will be to provide a geologic basis for the
development of appropriate project design. Investigations will address bedrock
and Quaternary geology; geologic structure, including primary and secondary
seismic hazards as defined by the State of California; soils; landslide,
liquefaction, and expansive soils hazards; earthwork recommendations; substrate
and foundation design for all project features; engineering properties of materials
used in levee construction; and any other topics identified by USFWS/CDFG,
design engineer(s), geotechnical engineer, or project engineering geologist as
relevant.
Environmental Consequences and Mitigation
Measures
Approach and Methods
Geology, Seismicity, and Soils
Potential impacts related to geology, seismicity, and soils were analyzed
qualitatively, based on a review of available existing data for the project area,
including information contained above in the existing conditions section.
Analysis focused on the Project’s potential to increase the risk of damage to
property, including but not limited to project facilities such as levees, as a result
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
3.1-10
April 2012