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Date December 20,2002 <br /> Quarter 3rd Quarter,2002 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 6020 <br /> Address 1711 E Yosemite Ave , Manteca, CA <br /> ARCO Environmental Engineer Paul Supple <br /> Consulting Co/Contact Person URSNernon Elarth <br /> Consultant Project No 38465974 00436 <br /> Primary Agency/Regulatory ID No San Joaquin County Public Health Services (SJCPHS) _ <br /> Assembly Bill 681 Status _Proper owned by Atlantic Richfield Company <br /> WORK PERFORMED THIS QUARTER (Third 2002): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (Fourth 2002): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (Third 2002): <br /> . Current Phase of Project Monitoring <br /> Frequency of Groundwater MW-5 through MW-10 sampled quarterly <br /> Sampling <br /> Frequency of Groundwater Quarterly <br /> Is Free Product (FP) Present Onsite No <br /> Current Remediation Techniques Natural attenuation <br /> Approximate Depth to Groundwater 20 8-22 6 ft <br /> Groundwater Flow and Gradient North'@ 0 003 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 laboratory <br /> with the following Iimitations <br /> • Elevated reporting limits were due to dilutions performed by the laboratory <br /> • The results for tent-butyl alcohol and tert-amyl methyl ether in sample MW-8 may be biased low due to <br /> continuing calibration verification falling outside acceptance criteria <br /> DISCUSSION: <br /> Total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total xylenes (BTEX), and <br /> methyl tert-butyl ether (MtBE) were reported as nondetectable in all wells with the exception of MW-6 MW-6 <br /> contained 770 ppb MtBE Chemical concentrations were consistent with historical analytical data On average, <br /> K U5 SP ARC0\06020tQaanerly\3Q1 R 02%020 GWMR3Q02 doc Page 1 <br />