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Chevron Products Company 2 Chevron Service Station#9-2033 508 West Charter Way,Stockton CA March 5,2002 Street The City of Stockton maintenance yard, located to the south, is reported to have, or have had, one or more underground storage tanks (USTs) Current and the former station features are shown on Figure 2 A brief summary of previous investigations is included in Attachment A ASSESSMENT ACTIVITIES AND FINDINGS In May 2001, SECOR supervised cone penetration testing (CPT) at four onsite locations (SB-5 through SB-8) located at each corner of the site boundary to assess soil stratigraphy and collect discrete groundwater samples (Figure 2) CPT borings advanced at each location provided continuous soil behavior and pore pressure data to the total depth explored Each CPT borings was advanced to approximately 90- to 95- feet below ground surface (bgs) Adjacent to each CPT boring, a second direct-push borehole was advanced, while water samples were collected at intervals selected through pore pressure observation in the first boring Pore pressure and lithologic information were used to target two to three depth-discrete groundwater samples in each boring Groundwater samples were analyzed for the presence of total petroleum hydrocarbons quantified as gasoline (TPHg), benzene, toluene, ethylbenzene, xylenes (BTEX) and the fuel oxygenates by Environmental Protection Agency (EPA) method 8260B Upon completion, the borings were filled with grout from the bottom up and finished to surface grade with asphalt Field and laboratory procedures are presented in Attachment B The findings of this assessment are summarized below • Subsurface Conditions. Review of the boring logs and CPT profiles suggests silty mixtures with sand/ or clay mixtures with silt to clayey silt horizons to approximately 40 feet bgs, sandy to clayey silt horizons from approximately 40 feet bgs to 50 feet bgs, sandy silt to silty horizons from approximately 50 feet bgs to 80 feet bgs, sand to clayey silt horizons were encountered below 80 feet bgs Groundwater was generally encountered at approximately 21, 43 and 81 feet bgs at each boring location CPT logs are included in Attachment C • Groundwater Analytical Results. Groundwater samples were collected from each direct-push boring from the identified water bearing zones, or at a depth - interval showing distinct pore pressure and submitted for chemical analysis Summarized groundwater analytical results are presented in Table 1 A copy of laboratory analytical reports and chain-of-custody records are presented in Attachment D ■ TPHg was detected in seven groundwater samples at concentrations ranging from 180 micrograms per liter (µg/L) in the sample collected from SB-6 at 38 feet bgs to 100,000 pg/L in the sample collected from SB-5 at 42 feet bgs I\Chevron1920331REPORTSI9-2033 SA CPT WPFA doc