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Date- December 10,2002 <br /> Quarter 3rd Quarter,2002 <br /> • <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 6080 <br /> Address 85 Louise Avenue, Lathrop, CA <br /> ARCO Environmental Engineer Paul Su le <br /> Consulting Co/Contact Person URSNernon Elarth <br /> Consultant Project No 38465981 00436 <br /> Primary Agency/Regulatory ID No San Joacliuin County Public Health Services <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 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 2 to 10 0 ft below ground surface <br /> Groundwater Flow and Gradient Southeast @ 0 0009 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 /> Total petroleum hydrocarbons as gasoline(TPHg),benzene,ethylbenzene,and xylenes(total) (BTEX) were reported <br /> in groundwater samples collected this quarter at concentrations consistent with previous quarters Fuel oxygenates, <br /> including methyl tert-butyl ether (MtBE), tert-butyl alcohol (TBA), and 1,2 Dichloroethane (1,2 DCA) were also <br /> reported The concentration of MtBE decreased in MW-1 The concentrations of TBA and MtBE increased in <br /> MW-2, relative to previous quarters Groundwater elevations across the site decreased, relative to the previous <br /> quarter The calculated groundwater flow direction was to the southeast at an average gradient of 0 0009 ft/ft <br /> This report is based on data, site conditions, and other information that are generally applicable as of the date of the <br /> report,and the conclusions and recommendations herein are therefore applicable only to that time frame <br /> K us BP ARc010608MQunnarW-QTR 02"90 G WMR3QO2 d4c Page 1 <br />