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concentrations of 2 6 and 0 86 mg/L, respectively, at MW-1A, MW-2A <br /> detections for TPH as gasoline and unknown TPH were 014 and 0 08 <br /> mg/L, respectively TPH detections have been at comparably low levels <br /> ' for the past four monitoring events <br /> Analyses were run in April 1998 and July 1999 for fuel oxygenates <br /> (methyl tert-butyl ether, tert-amyl methyl ether,2-methyl-2-propanol, <br /> diisopropyl ether, and ethyl Cert-butyl ether) As shown in Table 6, with <br /> the exception of 2-methyl-2-propanol (detected at 0 021 mg/1 in MW-1 A <br /> in April 1998) and methyl tert-butyl ether (detected at 0 0024 mg/L at <br /> MW-3A), these fuel oxygenates were not detected at Site #2 <br />' Samples were analyzed for 1,2-DCA in July 1999 Detections were <br /> reported in wells MW-1A through MW-4A The detected 1,2-DCA <br /> concentrations ranged from 0 00052 to 0 024 mg/L <br /> Between October 1996 and April 1998, ground water samples collected <br /> from the wells at Site #2 were analyzed for various water quality <br /> parameters (Table 7) and heterotrophic plate counts to evaluate the <br /> effectiveness of the natural attenuation process The increase in <br />' heterotrophic count in the samples collected from MW-1A and MW-2A <br /> when compared to baseline results indicates that the presence of the ORC <br /> socks enhanced microbial activity As presented in Table 7, the general <br /> water quality parameter measurements confirm that the subsurface <br /> conditions changed from anaerobic to aerobic conditions, as evidenced by <br />' comparison of post-ORC to baseline (October 1996) conditions <br /> Furthermore, as discussed in the excerpt provided in Appendix B (from <br /> December 1998 report), pre-ORC measurements of certain constituents <br />' can be used to calculate the biodegradation capacity of the subsurface <br /> environment The calculations performed for Site #2 indicate that the <br /> biodegradation capacity is more than adequate to address the low levels <br /> of TPH and BTEX constituents currently present in ground water, with or <br /> without the continued addition of ORC <br /> ERM 18 CATELI US/2996 10-10/13/99 <br />