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Date: February 11, 2003 <br /> Quarter 4'" Quarter, 2002 <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 38466093 00436 <br /> Primary Agency/Regulatory ID No San Joaquin County _ <br /> WORK PERFORMED THIS QUARTER (Fourth 2002): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (First 2003): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> I <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> i <br /> QUARTERLY RESULTS SUMMARY (Fourth 2002): <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 79 to 10 59 feet below ground surface <br /> Groundwater Flow and Gradient East-Northeast @ 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 laboratory <br /> with the following limitations <br /> • Elevated reporting limits were due to dilutions performed by the laboratory in order to quantitate a <br /> target analyte <br /> • In the total petroleum hydrocarbons as gasoline (TPHg) analysis of sample MW-2 the hydrocarbon <br /> pattern present(probably methyl tert-butyl ether(MtBE)) is due to a discrete peak at C6-C7 <br /> • The tert-butyl alcohol (TBA) results for MWA may be biased low due to the associated continuing <br /> calibration verification(CCV) falling outside acceptance criteria <br /> DISCUSSION: <br /> TPHg and the fuel oxygenate MtBE were reported in groundwater samples collected from site wells this quarter <br /> • Analyte concentrations were generally consistent with historic data All other analytes were reported as below <br /> K V5 SP ARC0\W801Quar1er1yU-QTR 0216080 GWMR4Q02 doe Page 1 <br />