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I trough to the low permeability of the pavement, which was previously thought to 1),. the cause of the trough 3.2 Dissolved Oxygen A portable dissolved oxygen sensor was used to measure the concentration in percent DO and in milligrams per liter (mg/1) during purging The dissolved oxygen data are shown in Appendix A, and final readings at the conclusion of purging are tabulated in Tables 2 and 3 and plotted against time in Figure 4 Concentrations were less than 1% in most we Its in November, and were 0% in all wells except VW-1 in December This indicates that CRC is no longer releasing oxygen to the groundwater 3.3 Hydrocarbons Eight to ten gallons of water were purged from each monitoring well before sample., were collected in December During purging, the pH, temperature, conductivity, and dis,,-)lved oxygen concentrations of the extracted water were measured with a Corning meter to insure that water samples would be representative of unaltered groundwater (Appendix A) To prevent cross-contamination from MW-2 to the more distant wells, MW-2 was purge d and sampled last The water purged from the wells was stored on site in a 55-gallon drum The sparging wells were purged of only 2 gallons before they went dry Gasoline odors were noted in MW-2 and in the vapor extraction and sparging wells Samples were collected from all ten wells using dedicated disposable bailers We noted that the bailers in MW-2 and SW-1 have become discolored over the past several month,,, as a result of being in contact with contamtnted groundwater in these wells The samples were poured into sterilized vials, labeled,placed in a cooled ice chest, and transported to Sc quota Analytical Laboratories for hydrocarbon analysis Laboratory data are summarized in fable 4 The full laboratory report is included in Appendix B The laboratory irntially reported that MTBE was detected at a concentration of 15 ppb in MW-1 Because this sample was the first one analyzed by the laboratory, and because no MTBE or other oxygenates had previously been detected in any of the wells, Upgradient requested the laboratory to re-run this sample As suspected, no MTBE was detected in the re-run sample, implying that the initial detection was due to carryover from a previous sample and incomplete cleaning of laboratory equipment (Appendix B) None of the oxygenates were detected in any of the other wells There has been little change in the concentration of gasoline in MW-2 since ORC ink,etion � (Table 4) The concentration has fluctuated between 37,000 and 27,000 ppb throughcut the 30 year On the other hand, benzene and toluene have declined noticeably, while ethylbeiizene and xylene have risen This could indicate that benzene and toluene have degraded , somewhat, leading to the production of less volatile compounds like xylene Sim,larly, gasoline concentrations have remained high in SW-1, and have even increased (Figure 5), while benzene concentrations have declined significantly (Figure 6) 16 3