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w 3.2 Hydrocarbons On July 6, eight to ten gallons of water were purged from each monitoring well before samples were collected During purging, the pH, temperature, and conductivity 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 purged and sampled last The water purged from the wells was stored on site in a 55-gallon drum The vapor extraction and sparging wells were purged of only 2 to 5 gallons prior to sampling because of their slower recharge rates Strong sewer odors were noted in S W-1 and SW-2, and the water was gray in color, suggesting that water from a buried sewer line is tapped by these wells Strong gasoline odors were also noted in SW-1 and MW-2 Samples were collected from all ten wells in sterilized vials, labeled, placed in a cooled ice chest, and transported to Sequoia Analytical Laboratories for hydrocarbon analysis Laboratory data are summarized in Table 2 The full laboratory report is included in Appendix B None of the five gasoline oxygenates were detected in any of the wells, confirming the results obtained during the first quarter monitoring in April Concentrations of gasoline and BTEX were lower in all wells except SW-1, which showed an increase in TPH-g from 13,800 to 59,700 despite decreases in concentrations of all aromatic compounds (benzene, etc ) Concentrations of all analytes decreased significantly in MW-2, and for the first time, concentrations in MW-2 have declined below those in SW-I Figure 4 is a benzene isocontour map for the samples collected on July 6 Comparing this map to the map prepared by the Clearwater Group prior to ORC injection(see Upgradient's First Quarter Report) ,the plume is smaller and more elongate than it was in 1997 The third quarterly monitoring and sampling event will take place in late September 3.3 Dissolved Oxygen Dissolved oxygen concentrations were measured on June 10 and again on July 6 in conjunction with quarterly monitoring A portable dissolved oxygen sensor was used to measure the concentration in percent DO and in milligrams per liter (mg/1) at 2-gallon intervals during purging The dissolved oxygen data are shown in Appendix A, and final readings at the conclusion of purging are tabulated in Tables 3 and 4 and plotted against time in Figure 5 In contrast to previous months, concentrations did not decrease during purging, indicating that standing water in the wells was no more oxygenated than water from deeper in the formation Concentrations were slightly higher in seven of the ten wells on June 10 than they had been on May 8, and were significantly higher in four of the ten on July 6 Only one well (VW-1) 3