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Date- March 14,2005 <br /> Quarter 1"Quarter 2005 <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 38466530 OA143 <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 2005): <br /> 1 Performed quarterly groundwater morutoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (Second 2005): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> QUARTERLY RESULTS SUMMARY (First 2005): <br /> iCurrent Phase of Project Monitoring <br /> Frequency of Groundwater Sampling MW-5 through MW-12, and MW-13D 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 20 72 to 23 19 feet below ground surface (bgs) <br /> Groundwater Flow and Gradient Northwest to Northeast 0 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 groundwater <br /> samples collected from site monitoring wells MW-6 and MW-13D this quarter MtBE concentrations in MW-6 and <br /> MW-13D were generally consistent with the previous quarter No other analytes were detected above laboratory <br /> reporting limits in groundwater samples collected from site monitoring wells this quarter <br /> Groundwater elevations increased relative to the previous quarter The inferred direction of groundwater flow <br /> generally ranged from the northwest to the northeast at an average hydraulic gradient of 0 002 ft/ft <br /> K XWproceWJ5 BP ARC0V)W2000uarer1y1200511 QTR 05%MO GWMR IQ05 Bloc Page 1 <br />