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S E C O R Fourth Quarter 2003, Quarterly Progress Report January 14, 2004 Page 3 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 4Q03 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 Hydrocarbon Mass (lbs)- July 24, 2000 TPHg 55 Benzene 42 MtBE 137 Mass Removed Mass Remaining in Percentage To Date (lbs)- Groundwater (lbs)- Removed 4003 4003 9.4 45.6 17.1 0.2 41.8 0.48 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 continue to decline, and GWET operational data indicates a decline in dissolved hydrocarbon mass removal from the subsurface. 5.0 RECOMMENDATIONS Based on the data presented above and historical data, SECOR recommends the following: 5.1 Groundwater Extraction SECOR recommends the continued operation of the GWET system to maintain hydraulic control of petroleum hydrocarbons remaining onsite. 5.2 Assessment Activities SECOR recommends no additional assessment activities. I:1Chevron%957751Peri0di0 Monitoring\Q P R1200314th Quarter -2003 QPR.doc