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Chevron Products Company Page 2 Chevron Station #9-3232 8660 Lower Sacramento Road Stockton California October 23. 2001 monitored continuously for soil behavior and pore pressure to approximately 55 feet below ground surface (bgs) . Based on pore pressure and on lithologic information collected from the CPT logs, one depth-discrete groundwater sample was collected from each of the direct- push borings. Groundwater samples were analyzed for the presence total petroleum hydrocarbons quantified as gasoline (TPHg), benzene, toluene, ethylbenzene, xylenes (BTEX), and the fuel oxygenates methyl tertiary butyl ether (MtBE), di-isopropyl ether (DIPE), tertiary amyl methyl ether (TAME), ethyl tertiary butyl ether (EtBE), tertiary butyl alcohol (TBA), ethyl dibromide (EDB), and 1 ,2 dichloroethane ( 1 ,2-DCA) by EPA Method 8260B . Upon completion , the borings were filled with grout from the bottom up and finished to surface grade with either asphalt or concrete depending on the preexisting surface material . Field and laboratory procedures are presented in Attachment B . The findings of this assessment are summarized below : • Subsurface Conditions. Review of the CPT logs suggests clay mixtures with silt and/or silt mixtures with clay comprise most of the stratigraphy to an approximate depth of 55 feet bgs at each CPT location. Multiple thin sand layers were encountered in most of the borings, however, groundwater was not observed within the sand layers encountered near the surface (approximately 15 feet bgs) . Groundwater was expected to be encountered at approximately 33 feet bgs based on recent groundwater monitoring events , however, groundwater was observed in a sand layer at approximately 50 feet bgs at most of the boring locations. CPT logs are included as Attachment C. • Groundwater Analytical Results. Groundwater samples were submitted to a California state-certified laboratory and analyzed for the presence of TPHg, BTEX, and the fuel oxygenates MtBE, DIPE, TAME, EtBE, TBA, EDB, and 1 ,2-DCA. One depth-discrete groundwater sample was collected from each of the borings in the identified water-bearing zone at approximately 49 to 53 feet bgs and submitted for chemical analysis. Groundwater analytical results are presented in Table 1 . Groundwater analytical data are presented graphically in Figure 2. Certified analytical reports and chain-of-custody documentation are presented as Attachment D. TPHg was detected in two groundwater samples at concentrations of 0.24 micrograms per liter (µg/1) in CPT-3 and 0.056 µg/1 in CPT-6. TBA was detected in four groundwater samples at concentrations ranging from 5.4 µg/1 in CPT-3 to 21 µg/1 in CPT- 1 . 1 ,2-DCA was detected in four groundwater samples at concentrations ranging from 4.6 µg/1 in CPT-3 to 10 µg/1 in CPT-1 . None of the other chemicals for which the samples were analyzed were detected above their respective method detection limits. Well Search On June 4, 2001 , SECOR personnel performed a water well search to identify the location of documented water supply wells within a one-mile radius of the site. The water well search consisted of examining the files of the California Department of Water Resources (DWR). 1:\Chevron\93232\REP0R7'S\93232 CPT SA 2001 .doc