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h Date: October 20,2003 Quarter- 3`d Quarter,2003 ARCO QUARTERLY GROUNDWATER MONITORING REPORT Facility No 2168 Address 411 Charter W a , Stockton, CA IL-13 -0-J4 -c2 ARCO Environmental Engineer Kyle Christie Consulting Co/Contact Person URS/Vernon Elarth Consultant Project No 38466297 OL058 Primary Regulatory Agency San Joaquin County Environmental Health Department WORK PERFORMED THIS QUARTER (Third 2003): 1 Performed quarterly groundwater monitoring and sampling 2 Prepared and submitted quarterly groundwater monitoring report WORK PROPOSED FOR NEXT QUARTER (Fourth 2003): 1 Perform quarterly groundwater monitoring and sampling 2 Prepare and submit quarterly groundwater monitoring report QUARTERLY RESULTS SUMMARY (Third 2003): Current Phase of Project Monitoring Frequency of Groundwater Sampling MW-1, MW-1 B, MW-1 C, MW-2, MW-3, MW-4, MW-5, MW-6, MW-7, MW-8, MW-813, MW-8C Sampled Quarter) Frequency of Groundwater Monitoring Quarterly Is Free Product (FP) Present on Site No Current Remediation Techniques Natural attenuation Approximate Depth to Groundwater 20 81 to 25 21 Groundwater Flow and Gradient East to Northeast @ 0 0015 ft/ft ANALYTICAL DATA REVIEW: Based on the review of the analytical and hardcopy data (chain-of-custody records, blanks, dilutions,holding times, LCS/LCSD results,MSIMSD results,and surrogate recoveries),the data are acceptable as reported by the laboratory with the following hrrutations • The reported results for total petroleum hydrocarbons as gasoline (TPHg) in samples MW-1, MW-2, MW-3, MW-4, and MW-5 are due to a discrete peak in the C5-C6 range • The reported result for I,2-dichloroethane(1,2-DCA) in sample MW-IC may be biased high as demonstrated by a high surrogate recovery due to matrix interference DISCUSSION: Total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, total xylenes (BTEX), methyl tert-butyl ether (MtBE), and 1,2-dichloroethane (1,2-DCA) were reported above method detection limits in groundwater samples collected from site wells this quarter Analyte concentrations were generally consistent with historical data with the following exception Benzene and ethylbenzene concentrations in MW-4 increased relative to the previous sampling event but are within historic ranges Groundwater elevations across the site decreased K\Wpr cess%13F ARCO=168\Qnanerly\3 QTR 0312168 GWMR 3Q03 doc Page 1