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F �- S ECOR Second Quarter 2004, Quarterly Progress Report July 13, 2004 Page 3 c. 3.2 Hydrocarbon Mass Estimate The hydrocarbon mass estimates presented below are an update of results presented within the Problem Assessment Report / Final Remediation Plan (PAR/FRP) Addendum, dated June 5, 2001. Methodology for determining the mass of hydrocarbons adsorbed to soil and dissolved in groundwater can be found within the PAR/FRP Addendum. 3.2.1 Estimated Mass of Petroleum Hydrocarbons Dissolved in Groundwater The results presented below are based on the calculation presented within the PAR/FRP Addendum and cumulative 2Q04 GWE mass removal data. To conservatively estimate analyte mass remaining, historical groundwater analytical data was used. This information is summarized in the following table: Constituent Estimated Mass Removed Mass Remaining in Percentage Hydrocarbon Mass To Date (lbs)- Groundwater (lbs)- Removed (lbs)- July 24, 2000 2Q04 2Q04 TP H 1 55 9.7 45.3 17.6 �` Benzene 42 0.2 41.8 0.48 MtBE 137 85 52 62.0 4.0 SUMMARY AND CONCLUSIONS • The potential for groundwater flow in the A -zone near the site appears to be radially toward extraction well EX -3; • The groundwater gradient in the B -zone is variable. • Concentrations of hydrocarbons offsite are below primary and secondary maximum contaminant levels (MCLs); • Concentrations of hydrocarbons dissolved in groundwater, in general, continue to decline, and GWET operational data indicates a decline in the rate of dissolved hydrocarbon mass removal from the subsurface. k 5.0 RECOMMENDATIONS } Based on the data presented above and historical data, SECOR recommends the following: r. 5.1 Groundwater Extraction JCI�VK recurnmenas ine continued operation of the GWET system -10 ma petroleum hydrocarbons remaining onsite. I` F . 1:IChevron1957751Periodic MonitoringlQ P R1200412nd Quarter -2004 QPR.doc k M -;