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01 S ECOR <br /> Second Quarter 2004, Quarterly Progress Report <br /> July 13, 2004 <br /> Page 3 <br /> 3 2 Hydrocarbon Mass Estimate <br /> The hydrocarbon mass estimates presented below are an update of results presented within the Problem <br /> Assessment Report/F1nal Remedratlon Plan (PAR/FRP) Addendum, dated June 5, 2001 Methodology <br /> ' for determining the mass of hydrocarbons adsorbed to soil and dissolved in groundwater can be found <br /> within the PAR/FRP Addendum <br /> 3 2 1 Estimated Mass of Petroleum Hydrocarbons Dissolved in Groundwater <br /> The results presented below are based on the calculation presented within the PAR/FRP Addendum and <br /> ' cumulative 2004 GWE mass removal data To conservatively estimate analyte mass remaining, <br /> historical groundwater analytical data was used This information is summarized in the following table <br /> Constituent Estimated Mass Removed Mass Remaining in Percentage <br /> Hydrocarbon Mass To Date (lbs)- Groundwater (lbs)- Removed <br /> (lbs)-July 24, 2000 2Q04 2Q04 <br /> ' TPHg 55 9 7 453 176 <br /> Benzene 42 0 2 41 8 048 <br /> . MtBE 137 85 52 620 <br /> 4.0 SUMMARY AND CONCLUSIONS <br /> • The potential for groundwater flow in the A-zone near the site appears to be radially toward <br /> extraction well EX-3, <br /> ' • The groundwater gradient in the B-zone is variable <br /> ' • Concentrations of hydrocarbons offsite are below primary and secondary maximum contaminant <br /> levels (MCLS), <br /> Concentrations of hydrocarbons dissolved in groundwater, in general, continue to decline, and <br /> ' GWET operational data indicates a decline in the rate of dissolved hydrocarbon mass removal <br /> from the subsurface <br /> ' 5,0 RECOMMENDATIONS <br /> Based on the data presented above and historical data, SECOR recommends the following <br /> 51 Groundwater Extraction <br /> SECOR recommends the continued operation of thesys em o main—ain y rau iccontro!of <br /> petroleum hydrocarbons remaining onsite <br />' 1 IChevron1957751Periodic Monitonng\Q P M200412nd Quarter-2004 QPR doe <br />