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< Date April 21,2004 <br /> Quarter 151 Quarter,2004 <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 URSNemon Elarth <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 (First 2004): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (Second 2004): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (First 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 Onsite No <br /> Current Remediation Techniques Natural attenuation <br /> Approximate Depth to Groundwater 9 07 to 9 81 feet below ground surface _ <br /> Groundwater Flow and Gradient Northeast @1 0 001 feet/foot (ft/ft) <br /> ANALYTICAL DATA REVIEW: <br /> Please note that during 2003, the laboratory has changed Total Petroleum Hydrocarbons as Gasoline (TPHg) to <br /> Gasoline Range Organics (GRO) The resulting data may be impacted by the potential inclusion of non-TPHg <br /> analytes within the requested carbon range resulting in a higher concentration being reported Where the resulting <br /> GRO concentration is based on a single analyte (i e, a non-TPHg analyte or a single TPHg analyte),the analyte will <br /> be identified if possible <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 reported above method detection limits in groundwater samples <br /> collected from site monitoring wells MW-1 and MW-2 this quarter The MtBE concentrations in MW-land MW-2 <br /> decreased relative to the previous monitoring event <br /> Y\WP-9:ssV5 ar ARC01DW9(KQufta&r1yl1 QTR 04WBO GWMR iQoa as Page 1 <br />