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f <br /> Date January 3,2002 <br /> r <br /> Quarter 4Q01 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 4932 Address 16 E Harding Way,Stockton,CA <br /> ARCO Environmental Engineer Paul Supple <br /> Consulting Co/Contact Person SECOR/Rusty Benkosky <br /> Consultant Project No 077 43285 704 <br /> Primary Agency/Regulatory ID No San JoNum County Public Health Services(SJCPHS) <br /> Assembly Bill 681 Status Property owned by ARCO <br /> WORD PERFORMED THIS QUARTER (Fourth Quarter - 2001): <br /> 1 Performed quarterly groundwater monitoring and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> 3 Submitted report documenting additional site assessment <br /> 4 Began weekly SPH bailing from wells MW-4 and SVE-1 <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 /> 3 Continue weekly SPH bailing from wells MW-4 and SVE-1 <br /> 4 Submit workplan for additional site assessment and aquifer feasibility testing <br /> QUARTERLY RESULTS SUMMARY <br /> Current Phase of Project Monitoring <br /> Frequency of Groundwater Sampling MW-1 through MW-9 and SVE-1 sampled quarter/ <br /> Frequency of Groundwater Monitoring quarterly <br /> Is Free Product(FP)Present Onsite Yes <br /> Current Remediation Techniques Natural attenuation <br /> Approximate Depth to Groundwater 28 i/z- 30 i/s ft <br /> Groundwater Flow and Gradient Northeast @ 0 002 ft/ft <br /> i <br /> DISCUSSION: <br /> Free product was present in MW-4 and SVE-1 at thicknesses of 0 46 ft and 0 01 ft,respectively This is the second <br /> time that free product has been measured at the site,last quarter SPH was first discovered in these wells Total <br /> petroleum hydrocarbons as gasoline(TPHg) were reported in five of the eight wells sampled this quarter with <br /> concentrations ranging from 120 ppb(MW-7)to 1,500 ppb(MW-2) Benzene was reported in five of the eight wells <br /> with concentrations ranging from 3 3 ppb(MW-9)to 50 ppb (MW-1) Methyl tert-butyl ether(MtBE),analyzed using <br /> EPA Method 8260B,was reported in three of the eight wells at concentrations ranging from 1,600 ppb(MW-1 and <br /> MW-2)to 82,000 ppb(MW-6) 1,2-Dichloroethane(1,2-DCA)was reported in two of the eight wells with <br /> concentrations of 2 5 ppb(MW-5) and 16 ppb(MW-9) Chemical concentrations are generally consistent with / <br /> historical data Groundwater elevations across the site decreased by an average of 190 ft Groundwater flow was to <br /> the northeast at an approximate gradient of 0 002 ft/ft,which is generally consistent with historical data <br />