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Date January 30,2002 <br /> Quarter 4Q01 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 6020 Address 1711 E Yosemite Ave,Manteca,CA <br /> Environmental Engineer Paul Supple <br /> Consulting Co/Contact Person SECOR/Rusty Benkosky <br /> Consultant Project No 077 43345 704 <br /> Primary Agency/Regulatory ID No San Joaquin County Public Health Services(SJCPHS) <br /> Assembly Bill 681 Status Property owned by Atlantic Richfield Company <br /> WORK PERFORMED TMS QUARTER (Fourth Quarter - 2001): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> WORK PROPOSED FOR NEXT QUARTER (First Quarter - 2002): <br /> 1 Perform quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> • QUARTERLY RESULTS SUMMARY <br /> Current Phase of Project Monitoring <br /> Frequency of Groundwater Sampling MW-5 through MW-10 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 201/4-221/4 ft <br /> Groundwater Flow and Gradient Northeast @ 0 004 ft/ft <br /> DISCUSSION: <br /> Groundwater monitoring well MW-7 was inaccessible during the fourth quarter sampling event Total petroleum <br /> hydrocarbons as gasoline(TPHg),benzene,toluene,ethylbenzene, and xylenes(total) were reported as <br /> nondetectable in all five wells sampled this quarter Methyl tert-butyl ether(MtBE),analyzed using EPA Method <br /> 8260B,was reported in two of five wells at concentrations of 2 6 ppb(MW-8)and 2,400 ppb (MW-6) Chemical <br /> concentrations were consistent with historical analytical data with the exception of well MW-8, which contained <br /> levels of MtBE slightly higher than the laboratory reporting Imut Groundwater elevations across the site increased <br /> by an average of 0 27 ft Groundwater flow was to the northeast at an approximate gradient of 0 004 ft/ft <br /> . This report presents our understanding of existing conditions at the subject site The conclusions contained herein <br /> are based on the analytical results,and professional judgment in accordance with current standards of professional <br /> practice,no other warranty is expressed or implied SECOR assumes no responsibility for exploratory borings or <br />