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Date October 29,2003 <br /> Quarter Yd Quarter,2003 <br />• ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 6080 <br /> Address 85 Louise Avenue_, Lathrop, CA <br /> ARCO Environmental Engineer Paul Supple — <br /> Consulting Co/Contact Person URSNernon Elarth <br /> Consultant Project No 38466249 OL058 <br /> Primary Agency/Regulatory ID No San Joaquin County Environmental Health Department <br /> Assembly Bill 681 Status Property Owned by Atlantic Richfield Company <br /> WORK PERFORMED THIS QUARTER (Third 2003): <br /> I Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report. <br /> WORK PROPOSED FOR NEXT QUARTER (Fourth 2003): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (Third 2003): <br /> Current Phase of Project Monitoring <br /> Frequency of Groundwater Sampling MW-1 through MW-3 sampled quarterly <br /> Frequency of Groundwater Monitoring Quarterly <br /> Is Free Product (FP) Present Onsite No <br /> Current Remediation Techniques Natural attenuation <br /> Approximate Depth to Groundwater 9 71 to 10 47 feet below ground surface <br /> Groundwater Flow and Gradient Southeast @ 0 002 feet/foot <br /> ANALYTICAL DATA REVIEW: <br /> Based on the review of the analytical and hardcopy data (chain-of-custody records, blanks, dilutions, holding times, <br /> LCS/LCSD results, MS/MSD results, and surrogate recoveries), the data are acceptable as reported by the <br /> laboratory <br />- —-- - - DISCUSSION:--- - - - - - -- - - -- - -- --- - — --- - --- <br /> Methyl tent-butyl ether(MtBE) was the only analyte reported above method detection limits in groundwater samples <br /> collected from site wells this quarter In MW-I, MtBE was reported as below method detection limits for the first <br /> time historically In MW-2, MtBE concentrations slightly increased this quarter but remain well below historic high <br /> concentrations Groundwater elevations in site wells increased relative to the previous quarter The inferred <br /> direction of groundwater flow was to the southeast with an average gradient of 0 002 ft/ft <br /> K\Wpruc sW5 RP ARC010W80\Quw1ey1y�3 QTR 03YW80 GWMR 3Q03 duc Page 1 <br />