ARCHIVED REPORTS_XR0006333 - Laserfiche WebLink

Home Browse Search

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) 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 2 and 3 and plotted against time in Figure 3 In contrast to previous months, concentrations were less than 1% in all wells 3.3 Hydrocarbons Eight to ten gallons of water were purged from each monitoring well before sample,, were collected During purging, the pH, temperature, conductivity, and dissolved oxygen concentrations of the extracted water were measured with a Corning meter to insw e 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 sparging wells were purged of only 1 gallon 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 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 4 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 and second quarter monitoring events The results for gasoline and BTEX are less consistent Benzene has shown a consistent decline in MW-1 and MW-5, along the margins of the plume, and the benzene plume has shown no indication of enlarging or migrating In fact, using the September data, the plume app(-ars to be smaller than it was in the quarter (Figure 4) However, none of the marginal wells is sufficiently close to an ORC infection boring to have been significantly affected by ORC, nor have they shown a consistent increase in dissolved oxygen concentrations (Figure 3), so the decrease in benzene noted in MW-1 and MW-5 is probably not attributable to oxygenation of the aquifer Relative to the second quarter, gasoline concentrations decreased in two wells (MW 5 and SW-1) and increased in four wells (MW-1, MW-2, MW-4, and SW-2) In the certer of the plume, concentrations increased significantly during the second quarter in SW 1 and remained much higher in the third quarter, while concentrations in MW-2 are presently intermediate between their first and second quarter values (Table 4 and Figure 5) At the margins of the plume, there has been a consistent improvement in MW-5 but not in MW-1 or MW-4 It is therefore evident that the infection of ORC has not resulted in dramatic improvement in groundwater quality, and it is unlikely that concentrations will decline to desired levels by the end of 1998 3