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a r1 y Date October 15,2004 <br /> Quarter 3`o Quarter,2004 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 6080 <br /> Address 85 E Louise Avenue, Lathrop, CA <br /> ARCO Environmental Engineer Paul Supple <br /> Consulting Co/Contact Person URS/Jeffrey Brooks <br /> Consultant Project No 38466542 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 2004): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (Fourth 2004): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (Third 2004)- <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 Onstte No <br /> Current Remediation Techniques Natural attenuation <br /> Approximate Depth to Groundwater 9 91 to 10 68 feet below ground surface (bgs) <br /> Groundwater Flow and Gradient Southeast @ 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 reported by the <br /> laboratory <br /> —DISCUSSION: <br /> Methyl tert-butyl ether (MtBE) was the only analyte detected above laboratory reporting limits in the groundwater <br /> sample collected from site monitoring well MW-2 this quarter MtBE concentrations decreased in MW-2 relative to <br /> the previous quarter No other analytes were detected above laboratory reporting limits in groundwater samples <br /> collected from site wells <br /> Groundwater elevations in site wells decreased relative to the previous quarter The inferred direction of <br /> groundwater flow was to the southeast with an average hydraulic gradient of 0 002 ft/ft <br /> K%Wpm eWJ5 BP ARC010WWQuanerW00413 QTR 04WBO GWMR 3Q04 d— Page 1 <br />