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r <br /> Date January 25,2001 <br /> • Quarter 4Q00 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No 4493 Address 205 North Center Street, Stockton,CA <br /> ARCO Environmental Engineer Paul Supple <br /> Consulting Co/Contact Person SECOR International Incorporated/Rusty Benkosky <br /> Consultant Project No 077 41907 704 <br /> Primary Agency/Regulatory ID No San Joaquin County Environmental Health Department <br /> Assembly Bill 681 Status Property Owned by City of Stockton <br /> WORK PERFORMED THIS QUARTER (Fourth Quarter—2000): <br /> 1 Conducted quarterly groundwater momtonng and sampling <br /> 2 Prepared and submitted quarterly groundwater monitoring report <br /> 3 Prepared and submitted work plan for additional site assessment,"Work Plan for the Installation of Multi- <br /> Completion Wells",(SECOR,November 16,2000)and"Addendum to Work Plan for the Installation of <br /> Multi-Completion Wells",(SECOR,December 20,2000) <br /> WORK PROPOSED FOR NEXT QUARTER (First Quarter—2001): <br /> . 1 Conduct quarterly groundwater monitoring and sampling <br /> 2 Prepare and submit quarterly groundwater monitoring report <br /> 3 Install multi-completion wells <br /> QUARTERLY RESULTS SUMMARY <br /> Current Phase of Protect Monitonng/Assessment <br /> Frequency of Groundwater Sampling MW-I through MW-7 are sampled quarterly <br /> Frequency of Groundwater Monitoring Quarterly <br /> Is Free Product(FP)Present On-Site No <br /> Current Remediation Techniques Natural Attenuation <br /> Approximate Depth to Groundwater 13 %to 16 feet <br /> Groundwater Gradient East 0 0 005 ft/ft <br /> DISCUSSION: <br /> TPHg was reported in four of the seven groundwater morutonng wells sampled this quarter at concentrations ranging <br /> from 81 1 ppb(MW-3)to 3,640 ppb(MW-4) Benzene was reported in four of the seven wells sampled this quarter at <br /> concentrations ranging from 0 674 ppb(MW-3)to 219 ppb(MW-4) MtBE(EPA Method 8260) was reported in four <br /> wells sampled this quarter at concentrations ranging from 2 34 ppb(MW-7) to 427 ppb(MW-4) Trichloroethene <br /> (TCE) was reported in four of the seven wells sampled this quarter at concentrations ranging from 2 72 ppb(MW-5)to <br /> 189 ppb(MW-1) Cis-1,2-Dichloroethene was reported in five of the seven wells sampled at concentrations ranging <br /> from 2 98(MW-5)to 308 ppb(MW-1) Groundwater elevations across the site decreased by an average of 1 35 feet <br /> this quarter Groundwater flow was to the east with a hydraulic gradient of approximately 0 005 ft/ft,groundwater flow <br /> is consistent with previous groundwater gradients <br />