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Cobb Environmental & Technical Services <br /> r <br /> 31 <br /> QUARTERLY GROUNDWATER MONITORING REPORT <br /> FOURTH QUARTER 1997 <br /> E-Z Serve#100966, 2537 Waterloo Road, Stockton, CA <br /> BACKGROUND <br /> All underground storage tanks were removed in March, 1990 A total of eight monitoring wells (MW-1 <br /> through MW-8) and two vapor extraction wells(VE-1 and VE-2) have been installed, eight on-site(MW-1 <br /> through MW-5, MW-07, VE-1 and VE-2)and two off-srte(MW-6 and MW-8) The extent of groundwater <br /> contarmnatlon has been delineated <br /> GROUNDWATER MONITORING FIELD ACTIVITIES <br /> Date of Field Activities 11/19/97 <br /> Wells Monitored/Sampled MW-3, VW-1,2 and 3 <br /> Analytes Tested TPHg,BTEX and MTBE <br /> Analytical Methods EPA Methods 8015/8020(modified) <br /> Laboratory Entech Analytical Labs,Inc <br /> Remarks All wells sampled were properly purged <br /> GROUNDWATER MONITORING RESULTS <br /> Depth to Water 57 69 to 58 61 feet below grade <br /> Flow Direction/Gradient Radial at 0 0048 ft/ft <br /> SPH- wells/thicknesses Not Detected <br /> TPHg concentration range 11Oppb(VW-3) to 72,000ppb(VW-1) <br /> Benzene concentration range 0 76ppb(MW-3) to 28,000ppb(VW-1) <br /> MTBE concentration range <5 Oppb(MW-3,VW-I and VW-2)to 9 Ippb(VW-3) <br /> ' Remarks Groundwater flow is radial with a mounding effect over the tank pit <br /> area Groundwater depth is consistent with previous quarters <br /> Groundwater is above all well screens Due to this condition all wells <br /> will be purged during the third quarter sampling <br /> PROJECT STATUS <br /> The next quarter monitoring will utilize the purge technique for sampling all wells Appropriate future <br /> courses of action are being evaluated <br /> ATTACHMENTS <br /> • Groundwater Elevation Contour Map <br /> • Groundwater Elevations and Analytical Results(Table 1) <br /> • Laboratory Report and Cham-of-Custody form <br /> • Groundwater Monitoring and Sampling Protocols <br /> • Gauge/Purge Calculations and Well Purging Date Sheets <br /> • Purge vs No-Purge Protocol <br />•I <br /> Y O Box 1602 o Tupelo, Mississippi 38802-1602 <br /> 601-841-0995 (phone) e 601-841-0810 (fix) <br />