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The rest Pof the analysis showed that there was an increase in DO downgradient of the barer and a change in BTEX concentrations. Upon ORC' addition, there was evidence of dispersion of oxygen downgradtent by Day 9. There was also a marked decrease in the size of the BT-Ex plume. It was apparent ' from the contour plots that the plume was retreating and was in the process of being `cut-off" from any further downgradient migration. The BTEX levels showed an initial drop until Day 20. This was followed by an increase in BTEX ' levels until Day 75 The iruaal decrease was during a penod of a rising ground water table and the increase of BTEX concentrations was during a period of a falling ground water. The water table elevations for monitor well SH-5, located ' I rn upgradient of the barer are shown in Figure 2 The results of the analysis, presented as nonnahzed mass curves for DO and BTEX, for the areal analysis over a one-year period are summarized in Figure 3. ' Cross-Sectional Analysis The same methods used for determinin the volumes s of DO and BTEX for the areal analysis were used for the crass-sectional analysis. ' Contour plots were made of the DO and BTEX concentrations in a cross-section across the face of each of the barriers ' The average DO background concentration was 1.4 mg/L and 1 8 mg/L for the long bares and the short barer, respectively The results of the data analysis indicated there was an increase of DO above background levels during the first ' nine days. The average concentration for DO reached a maximum of 13.1 mg/L and 14 8 mg/L on Day 9 for each of the barriers. Individual maximum levels grater than 20 mg/L DO were achieved at the long barrier and there was a general decrease in DO after the initial increase. Levels of DO were maintained greater than background levels (1 to 2 mg/L) for more than 200 days after the emplacement of the ORC' The ORC' was replaced in half of the source wells 275 days a-fter initial emplacement DO levels in the vicinity of the wells where the ORC` was replaced again increased to above 10 mg/L. The levels in the vidrury of wells that did not have the ORC' replaced were still above background ' levels at 365 days after initial emplacement. The analysis of the BTEX data showed an overall decrease in BTEX levels across the bamer Average background BTEX concentrations were 2 3 mg/L and 14 mgfL for the long and short bare=s, respectively. There was a slight increase in the average. BTEX concentrations to 2.6 mglL and 2.1 mg./L on Day 3. There ' was an overall decrease in BTEX concentrations through Day 93. There was a slight increase in BTEX concentrations measured on Day 47 and just before the parnal replacement of the OAC' on Day i90 There was an overall decrease ' following the partial replacement. The results of the analysis, presented as normalized mass curves for DO and BTEX, for the two barriers over a one-year period are summarized in Figure 4 and ' Figure 5. 1 1 LO ' d d0E = 90 66-fi1 -tea0