Fountaingrove Environmental Impact Report - City of Santa Rosa ...

3.6 GEOLOGY, SOILS, AND SEISMICITY
analysis was acceptable for a preliminary evaluation and for assessing overall geotechnical
feasibility of landslide mitigation and project development (Kleinfelder, 2008b).
Supplemental recommendations for site preparation, grading and foundation design criteria
should be provided based on the results of additional site exploration and analysis of the
conditions encountered (Giblin, 2008b).
Mitigation Measure 3.6-3: Incorporate site-specific slope stability analysis into Project
design.
AdditionalThe site-specific investigations and analyses will be performed during final
design by the Applicant. The investigations will include drilling soil borings and recovering
soil samples within and outside the boundaries of the proposed development site. The
investigation will also include identification and characterization of the horizontal and
vertical (depth) extents of slope instability. The findings will be incorporated in the analyses
that will evaluate slope stability, including landslides and soil creep, and various slope
stability measures. Depending on the findings, slope stabilization measures may consist of
regrading slopes, providing surface and subsurface drainages, and constructing slope
strengthening elements such as toe buttresses and secant walls. analyses will be performed
and the findings of the analyses The results of these studies may limit the proposed
development design, and they will be incorporated into the design of Project components
prior to approval of the Improvement Plan. If the studies result in a significant redesign of
the Project, then recirculation of the EIR may be required.
After Mitigation: Less than significant
Impact 3.6-4: The Project could result in exposure of people or structures to loss, injury, or
death due to liquefaction and other forms of seismic-induced ground failure, including
seismic slope instability and ground cracking.
Analysis: Significant
Seismic-induced ground failure has the potential to distress, displace, and/or destroy
Project buildings and facilities. Portions of the Project site that are susceptible to slope
instability hazards may also be susceptible to slope failure as a result of strong seismic
ground shaking.
Mitigation Measure 3.6-4: Incorporate the results of geologic and geotechnical
investigations and site-specific seismic analysis into Project design.
As part of a design-level geologic and geotechnical investigations, site-specific seismic and
geologic hazard analyses will be performed to collect data and to assess the potential for
seismic-induced ground failure in soil and rock materials adjacent to and underlying Project
components. The study will include assessments of seismic-induced geologic hazard
potential at the Project site, such as liquefaction, slope failure during earthquakes, and loss
of bearing capacity of foundation soils. If such potentially problematic soils and/or slopes
are found, the effects of these seismic-induced geologic hazards to the performance of
Project components will be evaluated and incorporated into the design.
Mitigation measures may include excavation of potentially liquefiable soils during
construction and replacement with engineered backfill, in-situ ground-treatment (such as
compaction grouting, deep soil mixing, and jet grouting) to prevent occurrence of
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