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
erodible surface soils assigned to the Diablo series and underlain by the Petaluma
Formation. Creation of cuts and fill embankments to support the proposed trail
alignments in these areas could lead to a risk of localized slope failure if the
slopes are improperly designed or implemented. This impact would be less than
significant because the new levee that would be utilized for the proposed trail
alignments would be designed and constructed to meet or exceed relevant
standards of the U.S. Army Corps of Engineers and would therefore be built to an
appropriate engineering standard of care. All earthwork required to construct the
proposed trails, including levee top and upland trails, would conform with
applicable codes and design standards. Furthermore, all trail designs would
incorporate any additional recommendations identified in site-specific
geotechnical evaluations completed during detailed design. As such, impacts are
considered less than significant, and no mitigation is required.
Conclusion: Less than Significant.
Full-Tidal Alternative
The potential for the Full-Tidal Alternative to contribute to increased exposure of
persons or structures to landslide hazards would be the same as for the Project.
Impacts are considered less than significant, and no mitigation is required.
Conclusion: Less than Significant.
Impact GEO- 4: Potential Short-Term Increase in Erosion
and Sedimentation Rates during Construction 4
Proposed Project
Many of the activities that would be conducted during the construction of the
Project would result in disturbances to soil and the existing vegetation that
stabilizes it. These activities include breaching the existing levee, construction of
the new levee, and dredging, removal and replacement of culverts, construction
of the detention basins, internal features, excavation of pilot channels, and
construction of access and maintenance roads, trails, bridges, and/or boardwalks,
and/or undercrossings. This would be a particular concern in areas of the project
site where the soil erosion hazard is high, such as uplands where loose and highly
erodible soils are found. Depending upon the nature of the soil at a given site, site
grading, and other construction-related disturbances could expose bare soil to
erosion by water and wind and could increase erosion and sedimentation rates
above pre-construction levels. Impacts could be significant.
4 Sedimentation issues associated with dredging and the placement of dredged material and levee construction are
addressed in the Water Quality section of this chapter.
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
3.1-17
April 2012