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Chevron Products Company Page 3 Chevron Service Station 9 4275 2905 Benjamin Holt Drive Stockton Califorrna May 20 2002 lithologic Interpretation formation pore pressure collected from the CPT logs, three to four depth-discrete groundwater samples were collected from each of the borings Groundwater • samples were analyzed for the presence of total petroleum hydrocarbons quantified as gasoline (TPHg), benzene, toluene, ethylbenzene, xylenes (BTEX), and fuel oxygenates including methyl tertiary butyl ether (MtBE) Upon completion, the borings were filled with grout from the bottom up and finished to surface grade with cement Field and laboratory procedures are included in Attachment C • Municipal Well No 10 Sampling April to August 2001, SECOR conducted monthly sampling of Municipal Well No 10 A City of Stockton Public Works Department representative activated the well pump Approximately 300 gallons of groundwater was purged from municipal well No 10 prior to sample collection Samples were submitted to a California certified Laboratory and analyzed for the presence of TPHg, BTEX, and MtBE Municipal Well No 10 analytical results are presented in Table 2 ASSESSMENT FINDINGS The findings of this assessment are summarized below Lithology and Stratigraphy Review of the boring logs and CPT profiles suggests silt mixtures with clay and/or clay mixtures with silt comprise the sediments to an approximate depth of 100 feet bgs at each CPT location Multiple thin sand layers were encountered in most of the borings, producing groundwater as shallow as 10 bgs CPT data interpretations, in Attachment D, appear generally consistent with stratigraphy shown on the Water Well Drillers report (Attachment B), suggesting a predominantly clay stratigraphic column interbedded with multiple, thin, sandy horizons A soil horizon with character ranging from sandy to stiff, fine-grained was encountered from 62- to 80-feet bgs Fine-grained (i a silt and clay) sediments were encountered from 80- to 100- feet bgs This stratum may be equivalent to the top of the clay unit reported on the Water Well Drillers report from 80- to 146- feet in depth Hydrogeology The presence of shallow groundwater in the CPT report is consistent with routine groundwater monitoring data for the 1"quarter 2002 Quarterly Monitoring Report (Attachment E) In general, shallow groundwater flows from the Chevron site to the northeast contrasted to the easterly position of Municipal Well No 10 Potentiometric pressure along each CPT profile appears to increase linearly with depth, an underlying confined or semi-confined groundwater regime is not evident from inspection of the CPT profiles, this trend suggest hydraulic communication exists between shallow groundwater and groundwater in the deeper interval s I IChevron1942751REPORTS12001 CPT SA and Muni sampling Rev A doe