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' Report of Findings Frontier Transportation ' 03-28-98 March 28, 1998 In January of 1998, BEI, Inc. advanced four(4) groundwater monitoring wells (MW-4 through MW-7) to assess the extent of subsurface contamination beneath the site (See Figure 4, ' 1997 Site Layout Map). Results of this investigation are presented in Section 4.0 in this report. 3.0) SITE GEOLOGY/HYDROGEOLOGY ' The site is located on the boundary ry of the Sacramento V lley and the San Joaquin Valley within the west-central portion of the Great Valley Geomorphic province of California. The ' Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age. These sedimentary units, in turn, overlay a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks. The shallow subsurface geology in the site vicinity is a heterogeneous mix of gravel, sand, silt, and clay (Reference; Site Characterizalign Report, Twining Laboratories, October 16, 1996). BEI, Inc. encountered clay and a heterogeneous mix of clay from 0' to 25' bg. Boring logs are ' presented as Appendix A. l ie First subsurface water was encountered at depths from I P to 12' bg during tank removal and monitoring well installation at this site in 1995 and 1996. The flow direction for this subsurface water was identified as northwesterly with a shallow gradient of 0.002 feet per foot ' (Reference; Site Characterizalign Report, Twining Laboratories, October 16, 1996). BEI, Inc. encountered first subsurface water between 10' and 16'bg. The groundwater gradient flows to the south beneath the site as determined by data collected in March of 1998 (See Figure 5, ' Groundwater Gradient Map). 4.0) MONITORING WELL INSTALLATION On January 13 and 14, 1998, four (4) 2" diameter groundwater monitoring wells (MW-4 through MW-7)were installed to 20' bg (MW-4 was advanced to 26' bg)to assess the extent of ' contamination as identified by monitoring wells MW-1, MW-2, and MW-3. Groundwater--- samples were subsequently collected from all monitoring wells (MW-1"through MW-7) on March 4, 1998. ' A hollow stem auger was used to provide the soil borings for well installation. The hollow stem auger was 8-inches outside diameter and 4Y.,-inches inside diameter. All well materials were installed through the hollow stem to allow maximum control during placement. ' Each well consisted of a central section composed of riser, screen and sump. The annular space around the sump and screen was filled with sand to 4' bg_ This was overlain with a 5' seal 4 1