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l•' <br /> Date .Tune 6,2001 <br /> Quarter 2Q01 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 4932 Address 16 East Harding Way,Stockton,CA <br /> ARCO Environmental Engineer Paul Supple <br /> Consulting Co/Contact Person SECOR International Incorporated/Rusty Benkosky <br /> Consultant Project No 077 43285 702 <br /> Primary Agency/Regulatory ID No San Joaquin County Environmental Health Services <br /> Assembly Bill 681 Status Property Owned by Atlantic Richfield Company <br /> WORK PERFORMED THIS QUARTER (Second Quarter—2001): <br /> 1 Conducted quarterly groundwater monitoring and sampling <br /> 2 Prepared and subrmtted quarterly groundwater monitoring report <br /> 3 Prepared and submitted interim remediation/feasibility testing report <br /> WORK PROPOSED FOR NEXT QUARTER (Third Quarter—2001): <br /> 1 Conduct quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> • 3 Perform additional site assessment including the installation of five groundwater monrtonng wells and the <br /> drilling of two soil borings <br /> QUARTERLY RESULTS SUMMARY <br /> Current Phase of Project Monitoring <br /> Frequency of Groundwater Sampling MW-I through MW-4 and SVE-1 are sampled quarterly <br /> Frequency of Groundwater Momtonng Quarterly <br /> Is Free Product(FP)Present On-Site No <br /> Current Remediation Techniques Natural Attenuation <br /> Approximate Depth to Groundwater 26 to 2732 feet <br /> Groundwater Gradient Northeast @ 0 004 ft/ft <br /> DISCUSSION: <br /> Total petroleum hydrocarbons as gasoline(TPHg) were reported to four of the five groundwater monitoring wells <br /> sampled this quarter at concentrations ranging from 600 ppb(MW-1) to 149,000 ppb (MW-4) Benzene was reported <br /> to four of the five wells sampled this quarter at concentrations ranging from 78 I ppb(MW-1)to 9,660 ppb(MW-4) <br /> MtBE(analyzed using EPA Method 8260A)was reported in each well sampled this quarter at concentrations ranging <br /> from 3 98 ppb(MW-3)to 500,000 ppb(MW-4) Tert-amyl methyl ether(TAME)was reported in well MW-1 at a <br /> concentration of 10 3 1,2-Dichloroethane(1,2-DCA)was reported to well MW-1 at a concentration of 79 4 ppb The <br /> average groundwater elevation increased by 0 37 feet from the previous quarter Groundwater flow was to the <br /> northeast with a hydraulic gradient of approximately 0 004 ft/ft <br />