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SECOR AR/MW-9A, AR/MW-12A, AR/MW-23A, TONT-2, TO/MW-1, TO/R-3, TO/R-5, TS-4, TS-8, TS-10, TS/M-2, TS/MW-1A). Due to the presence of SPH, SECOR installed SoakeaseTm liquid phase petroleum removal socks in wells AR/MW-12A, TO/MW-1, TS-4, and TS/M-2 on September 20, 2002. The absorbent socks have been effective in removing SPH in those wells. SPH has ng in as declined in the majority of these wells with the most consistent presence of SPH occurri zone wells TS-4 and TS/M-2. Wells TS-4 and AR/MW-11A contained a visible sheen during the first quarter 2006. None of the wells gauged during the first quarter 2006 contained measurable SPH thicknesses (Table 2) Historical SPH thickness measurements are included in Appendix E. Dissolved TPHg, TPHd, benzene, and MTBE concentrations in the "A" zone were within historical ranges during the first quarter 2006 with the following exceptions: • In the first quarter 2006, samples from the following wells contained historically high concentrations at the indicated levels: o Well TONT-8 contained benzene at a concentration of 2,300 pg/L (historically ranged from 170 pg/L to 1,500 Ng/L) and contained TPHg at 10,000 pg/L (historically ranged from 660 pg/L to 7,100 pg/L). o Well TS-1 contained benzene at a concentration of 13 pg/L (historically ranged from <0.50 to 6.8 pg/L). o Well TS-5 contained benzene at a concentration of 540 pg/L (historically ranged from <0.50 pg/L to 48 pg/L) and contained TPHg at a concentration of 1,600 pg/L • (historically ranged from <50 pg/L to 540 pg/L). o Well TS-9 contained TPHg at a concentration of 220 pg/L (historically ranged from <50 pg/L to 170 pg/L). o Well TS/M-2 contained MTBE at a concentration of 16 pg/L. It must be noted that this well has historically contained a visible sheen and has only been sampled three times including the first quarter 2006 sampling event. The lab results from the two historical events indicated that MTBE was not present in the well above elevated MRLs of 25 Ng/L and 100 pg/L, respectively. • In the first quarter 2006, samples form the following wells contained historically low concentrations at the indicated levels: o Well TS-1 contained TPHd at a concentration of 130 Ng/L (historically ranged from <500 pg/L to 20,000 pg/L). o Well TS/M-2 contained benzene at a concentration of 5,400 pg/L (historically 11,000 pg/L to 16,000 pg/L), TPHg at a concentration of 19,000 pg/L (historically ranged from 29,000 pg/L to 44,000 pg/L), and TPHd at a concentration of 26,000 pg/L (historically ranged from 37,000 pg/L to 690,000 pg/L). It must be noted that this well has historically contained visible sheen and has only been sampled three times including the first quarter 2006 sampling event. The concentration ranges listed above represent the results from the two historical sampling events. o Well TS/MW-1A contained MTBE at a concentration of 23 pg/L (historically ranged from 34 pg/L to 19,000 pg/L). Generally, dissolved chemical concentrations at the site are affected by seasonal groundwater • fluctuations. Dissolved hydrocarbon concentrations tend to increase during times of higher groundwater elevations, and decrease during times of lower groundwater elevations. STTC 1Q06 Final Report 7 May 1, 2006 770T.43673.12.0002