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Date March 20,2003 <br /> Quarter- 1"Quarter 2003 <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 38466092 00436 <br /> Primary Agency/Regulatory ID No San Joaquin County _ <br /> Assembly Bill 681 Status Property owned by Atlantic Richfield Company <br /> WORK PERFORMED THIS QUARTER (First 2003): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (Second 2003): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (First 2003): <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 23 to 22 11 feet below ground surface <br /> Groundwater Flow and Gradient Northeast 0 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 limitations <br /> • Elevated reporting trouts were due to dilutions performed by the laboratory to order to quantitate a <br /> target analyte <br /> DISCUSSION: <br /> Methyl tert-but I ether MtBE was reported in one site well MW-6 at 340 micrograms per liter u this <br /> Y Y ( ) p ( g P � P�-D) <br /> reporting period No other analytes were reported above detection Itnuts to site wells Groundwater elevations to <br /> site wells generally decreased relative to the previous quarter The inferred direction of groundwater flow was to the <br /> northwest and northeast at an average hydraulic gradient of 0 003 feet/foot,which is consistent with historic data <br /> K U5 BP ARC010W201Quaner1ylt QTR 0316020 GWMRIQ03 dm Page 1 <br />