specs

Geotechnical Investigation South River Place, Gasser Drive, Napa 29 December 2010
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The groundwater conditions are highly variable at the site. Groundwater was encountered in the
recent borings at elevations ranging from -6.0 to +11.5 feet at the time of drilling. Groundwater
levels during previous investigations ranged from elevations of 0 to +9.0. Fluctuations in the
groundwater table will likely occur with variations in seasonal rainfall and fluctuations in the
nearby retention basin, and the Napa River.
A more thorough description and stratification of the soils encountered along with the results of
the recent laboratory tests are presented on the respective “Logs of Test Borings” in Appendix A.
The approximate locations of the recent borings are shown on Figure 4, “Site Plan.”
Site Geology
According to the Geologic Map of the Napa 7.5’ Quadrangle 2 , a portion of which is included as
Figure 3 in the Appendix, the geologic deposits underlying the site consist of Holocene-aged
Stream terraces. These terraces were deposited as point bar and overbank deposits along the
Napa River. The deposits are composed of moderately-sorted clayey sand and sandy clay with
gravel. The subsurface deposits encountered during our investigation generally correlate with
previous mapping.
Geo-Hazards
Seismicity
The site is not located within an Alquist-Priolo Earthquake Fault Zone 3 . There are no known
active or inactive faults crossing the site as mapped and/or recognized by the State of California.
Earthquake related ground shaking should be expected during the design life of the structures at
the site. The California Geological Survey (CGS) has defined an active fault as one that has had
surface displacement in the last 11,000 years, or has experienced earthquakes in recorded history.
Based on our review of the Fault Activity Map of California 4 and the USGS Fault Database 5 , the
nearest active faults are the West Napa, Green Valley, Cordelia, Rodgers Creek and Hunting
Creek-Berryessa, located approximately 1.4 miles west, 5.1 miles east, 7.0 miles east, 11.8 miles
southwest and 17.3 miles northeast of the site, respectively.
2 Clahan, K.B., Wagner, D.L., Saucedo, G.J., Randolph-Loar, C.E., and Sowers, J.M., 2004, Geologic Map of the
Napa 7.5’ Quadrangle, Napa County, California, California Geological Survey, Version 1.0
3 Hart, E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, Alquist-Priolo Earthquake Fault
Zoning Act with Index to Earthquake Fault Zones Maps, California Department of Conservation, Division of Mines
and Geology, Special Publication 42, Revised 1997, Supplements 1 and 2 added 1999.
4 Jennings, Charles W., 1994, Fault Activity Map of California and Adjacent Areas, California Division of Mines
and Geology Geologic Map Data Series, Map No. 6.
5 U.S. Geological Survey and California Geological Survey, 2006, Quaternary Fault and Fold Database for the
United States, accessed 9 March 2009, from USGS web site: http://earthquake.usgs.gov/regional/qfaults/.
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