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introduced to the monitoring system to enhance natural biodegradation processes ' Ground water samples were collected routinely from the five wells installed at Site #2 during the period from April 1991 through April 1998 Ground water Ievels measured during these monitoring events are consistent with an overall south-southwest (away from the Channel) flow direction The ground water samples were analyzed for purgeable ' hydrocarbons and BTEX constituents as well as general water quality parameters Analyses during the earliest monitoring events also included organic and total lead and ethylene dibromide Tables 3-3 and 3-4 present a summary of the quarterly ground water sample results for Site #2 ' The highest concentrations of TPH and BTEX detected since the October 1993 excavation were in ground water samples collected at monitoring wells MW-1A and MW-2A Over time, the results of quarterly ground water samples collected from monitoring wells MW-1A and MW-2A have shown a steady decline in the concentrations of TPH (as gasoline and/or diesel) and BTEX in ground water During the most recent monitoring ' round (April 1998), TPH detections at MW-1A were only slightly above 1 milligram per liter (mg/1), MW-2A detections were even lower TPH detections have been at comparably low levels for the past three Mmonitoring events Analyses were run in April 1998 for fuel oxygenates (methyl tert-butyl ether, tert-amyl methyl ether, 2-methyl-2-propanol, diisopropyl ether, and ethyl tert-butyl ether) As shown in Table 3-3, with the exception of 2- ' r methyl-2-propanol, which was detected at 0 021 mg/1 in MW-1A, these fuel oxygenates were not detected at Site #2 ' Beginning in October 1996, ground water samples collected from the wells at Site #1 have been analyzed for various water quality parameters (Table 3-4) and heterotrophic plate counts to evaluate the effectiveness of the natural attenuation process The increase in heterotrophic count in the samples collected from MW-1A and MW-2A when compared to baseline results indicates that the presence of the ORC socks has enhanced ' microbial activity As presented in Table 3-4, the general water quality parameter measurements confirm that the subsurface conditions have changed from anaerobic to aerobic conditions, as evidenced by comparison of post-ORC to baseline (October 1996) conditions Furthermore, as discussed in Attachment A, pre-ORC measurements of ' certain constituents can be used to calculate the biodegradation capacity of the subsurface environment The calculations performed for Site #2 indicate that the biodegradation capacity is more than adequate to address 3-8