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s <br /> Date: January 28,2004 <br /> Quarter- 4`'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 LIRSNernon Elarth <br /> Consultant Project No 38466542 OL058 <br /> Primary Agency/Regulatory ID No San Joaquin Count Environmental Health Department <br /> Assembly Bill 681 Status Property Owned by Atlantic Richfield Company <br /> WORK PERFORMED THIS QUARTER (Fourth 2003): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and subnutted quarterly groundwater monitoring report. <br /> WORK PROPOSED FOR NEXT QUARTER (First 2004): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (Fourth 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 48 to 10 21 feet below ground surface <br /> Groundwater Flow and Gradient Southeast 0 0 002 feet/foot (ft/ft) <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 repotted by the <br /> laboratory <br /> DISCUSSION: <br /> Benzene and methyl tert-butyl ether (MtBE) were the only analytes reported above method detection limits in <br /> groundwater samples collected from site wells this quarter In MW-1, MtBE concentrations increased but remain <br /> well below historic concentrations In MW-2, MtBE concentrations continue to slowly increase and a low level <br /> concentration of benzene was reported for the first time since September of 2002 Groundwater elevations in site <br /> wells increased relative to the previous quarter The inferred direction of groundwater flow was to the southeast with <br /> an average gradient of 0 002 ft/ft <br /> I <br /> K NWP--ssli5 BP ARC0WW8MQ..1.,1y1A QTR 0416060 GWMR 4Q03 dm Page 1 <br />