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Chevron Products Company Page 2 Chevron Service Station 201761 1103 South Main Street Manteca California Aril] 2002 encountered groundwater. The field and laboratory procedures followed during the performance of the work are summarized in Attachment A. The findings of this assessment are summarized below. ' • Subsurface Conditions. Review of the boring logs"suggests the site stratigraphy is comprised of sand to an approximate depth of 15 feet bgs, silty sands from 15 feet bgs to 30 feet bgs, and clayey silty sands from 30 feet bgs to the bottom of each boring. Groundwater was generally encountered at approximately 21 feet bgs. Boring logs and well construction details are included in Attachment B. 4 i • Soil Analytical Results. Soil samples were collected at 5-foot intervals and delivered under chain-of-custody procedures to a Califormar state-certified laboratory for analysis for total petroleum hydrocarbons quantified. as gasoline (TPHg), benzene, toluene, ethylbenzene, xylenes (BTEX), and methyl tertiary butyl ether (MtBE). A copy of the laboratory analytical report and chain-of-custody record for the soil samples is presented in Attachment C. TPHg, BTEX, and MtBE were not detected i above the laboratory detection limits in any of the soil samples submitted for chemical analysis. i 0 Well Surveying and Groundwater Gradient Interpretation. A state-licensed surveyor surveyed the newly installed wells to known! vertical and horizontal datum. Depth to groundwater measurements were collected prior to sampling activities and utilized for interpretation of groundwater flow and gradient beneath the site. The interpreted groundwater flow direction was to the north at a gradient of 0.13 foot/foot (Figure 3). Based on this interpretation, groundwater appears to flow away from the municipal drinking water supply well. i F 9� • Monitoring Well Development and Sampling. The wells were developed and sampled on October 22, 2001. Field data sheets for the development and sampling of the wells are included in Attachment D. Groundwater samples were collected and sent under standard chain-of-custody procedures to a California state-certified a l laboratory and analyzed for TPHg, BTEX, and MtBE. The laboratory analytical report and chain-of-custody record for the groundwater samples are presented in Attachment C. TPHg, BTEX, and MtBE were not ipcietected above the laboratory detection limits in any of the groundwater samples collected. E� DISCUSSION OF FINDINGS Based on the results of this assessment, this site does not appear to present a threat to the nearby municipal drinking water supply well, as no petroleum'hydrocarbons were detected in soil or groundwater samples analyzed and groundwater flow; appears to be away from the municipal drinking water supply well. The SJCPHS concur-red with this conclusion during a telephone conversation between Mr. Bill Brasher of SECOR and Mr. Sam Savig of the SJCPHS on November 8, 2001. Therefore, SECOR has not,',and does not pian to, perform the additional investigation activities proposed in the September 19, 2001 work plan. Additionally, SECOR proposes to destroy the monitoring webs according to the procedures described below. ` `4 I:1Chevron12017611Reports1201761 SA Report 2001.doc