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Updated Site Conceptual Model and Fourth Quarter 2002 Monitoring and Remediation Report Cleanup and Abatement Order No 5-00-707 T_ EAI Project No 1232 10A, 0 56 Pg/L and MW-14A, 7 4 pg/L) The highest Unit B benzene concentration was in monitoring well MW-3 at 2,700 ug/L (see Figure 13) 5.5 Analytical Testing Results Hydrocarbon concentrations in ground water were generally lower during the fourth quarter ' 2002 sampling event than during the third quarter 2002 5 5 1 Units A and B Wells For Units A and B, similar or lower hydrocarbon concentrations were generally observed during this sampling event when compared to the prior quarters data with the exception of wells MW-3, MW-4 MW-6, and AS-26 In general, these wells had slightly higher testing results Figure 14 summarizes the TPH-G, BTEX, and MTBE concentrations in ground water for the December 2002 ground water sampling event No TBA, DIPE, ETBE, TAME, or EDB above laboratory reporting Iimits were detected in any of the ground water samples MTBE was detected in one ground water sample at a concentration of 4 4 ug/L (MW-13) 5 5 2 Units C and D Wells (MW-813. MW-23S/D, and MW-24S/D) Similar or lower hydrocarbon concentrations were generally observed during this sampling event when compared to the prior quarters data The exceptions were wells MW-23S and MW- 23D where slightly higher concentrations of hydrocarbons were observed (see Table 1) Spargfng of Units C and D will not be conducted at this time It is EAFs opinion that with time oxygen injected into Units A and B will diffuse downward to remediate the deeper zones 5 5 3 Well MW-9 and Other Perimeter Wells Generally, hydrocarbon concentrations in lateral and down gradient wells MW-5, MW-7, MW- 13, MW-14, MW-15, MW-16, MW-18, and MW-27 are at or below the laboratory detection limit One down gradient perimeter well, well MW-9, frequently contains low hydrocarbon concentrations In December 2002, down gradient well MW-9 contained TPH-G and benzene at concentrations of 80 pg/L and 9 7 pg/L, respectively These data indicate that well MW-9 is at or near the down gradient extent of the hydrocarbon plume s BHM WORD 1232Ro2DI -9- ENVIRONMENTAL AUDIT, INC