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E KMR Mr James L Barton April 12, 2005 Page 5 tEffectiveness of Rernediation System System effectiveness is evaluated by assessing groundwater data from monitoring wells MW-2, MW-3, MW-11, and MW-12 Concentrations of TPHg, benzene, and MTBE in groundwater samples collected from selected wells screened in Unit A or Unit B are depicted graphically on cross-sections A-A' and C-C' (Attachment E) Concentrations of TPHg, benzene, and MTBE in groundwater samples collected from selected wells screened in Unit A, Unit B and Unit D are depicted graphically on cross-section B-B' (Attachment E) Graphs of TPHg concentrations, benzene concentrations, and groundwater elevation versus time are included in Attachment G Soil vapor samples were collected from selected SVE wells and monitoring wells utilized for the SVE system Samples collected during the first quarter 2005 were submitted to Air Toxics LTD (Air Toxics) in Folsom, California for analyses of VOCs by Modified EPA Method TO-3 Historical field screening results for VOCs in soil vapor samples collected from selected wells are presented in Table 10 Recent soil vapor sampling analytical results are presented in Table 11 Copies of the laboratory analytical results with chain-of-custody documentation are included in Attachment D I • Decreasing trends in wells MW-91R, MW-10, MW-12, MW-14, MW-17, MW-18D, MW-24S, and MW-25D indicate that the AS/SVE system continues to be effective in reducing concentrations of dissolved TPHg and benzene in Unit B, Unit C and Unit D beneath the site Purge Water Waste Non-hazardous purge water generated during the first quarter 2005 groundwater sampling event and water extracted from the SVE system was stored in drums onsite temporarily until being transported to Evergreen Oil Company in Newark, California in March 2005 Discussion Groundwater analytical results for monitoring wells MW-91R, MW-10, MW-12, MW-14, MW-16, MW-17, MW-18D, MW-24S, MW-24D, and MW-25D indicate that the AS/SVE system continues to be effective at decreasing concentrations of dissolved TPHg and benzene in Unit B, Unit C and Unit D beneath the site Monitonna wells MW-2 MW-4 MW-16 and MW-25D screened in Unit B showed increases in TPHg and benzene concentrations since the fourth quarter 2004 sampling event However, overall there is a general downward concentration trend for TPHg and benzene in these wells since the fourth quarter 2003 sampling event The groundwater gradients appear similar to previous quarters The overall groundwater elevation increased approximately 1 5 feet since October 2004 • J 1Proiects10694015096-2931Workmg\Reports15098 1 st Qtr 05-QMR doc Gelenrattna 35 Years of Excellence irr Envrvonmenlal Services