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J u n 6 1996 A I8F1}j [EG TECHIIOLOJIES No 2616 P 11/34 95-WP 103 05 and air flow data, the hole developed sometime following the maintenance conducted on January . 10/11, 1994, but prior to the February 3, 1994 sample round The damaged buoyancy tank was discovered and replaced on 17 May 1995 • Peak 8 occurred in early November 1994, following the system being shut down from October 26, 1994 to November 3, 1994 to allow for dialling beneath the power lines Disregarding the data from these anomalous peaks in the effluent concentrations, a comparison of influent TCE concentrations to the effluent TCE concentrations for the stripper unit indicates that a TCE removal percentage of greater than 90% was achieved in 95% of the sample rounds and a TCE removal percentage of greater than 95%was achieved in approximately 77% of the sample rounds It is evident from this data that the UVB vacuum vaponaation well is effectively treating the groundwater (removing TCE) across the system The UVB system effluent TCE concentzations as measured at monitoring well W3 were below the Federal MCL of 5 99/1 in 85% of the samples Operational Monitoring - Perimeter WcUs Groundwater Sampling Results of the groundwaxr TCE analyses for bath the treatment and petimetear monitoring welts are shown on Figure 7 For monitoring wells PW 1 through PW6, data generated by PRC Environmental Management, Inc is also plotted PRC was retained by the EPA SITE Program to perform field sampling and technical analysis for this project. Several important trends are evident from review of the TCE plots and the summary concentration data on Table 1 • The final TCE concentrations ui wells that are both within the treatment cell, and have sufficient data available to establish a trend, are lower than their init,al concentzanons These wells include PW1, PW2, PW4, PW5, 4MW14, and 31OW1 • The concentrations in wells considered most affected by the UVB (PW 1, PW2, PW4, PW5, 4MW14, and 31OW1) showed a marked increase following startup, followed by decrease after several months of operation. Similar trends have been observed in previous UVB groundwater remediation programs and have been attributed to mobilization of contaminants from the pore spaces, particularly m the capillary fringe (Herrling et al, 199 1) The increase and subsequent decrease is delayed from PW1 to PW4 (and from PW2 to PW5) which reflects the increased travel time as the treatment cell expands over time • Wells screened deeper than the treatment interval (PW3, PW6, and 31MW1) do not appear to be affected by the UVB • Well 31MW4 is considered laterally outside of the capture zone as evident by fairly consistent TCE concentrations • The monitoring well data is generally consistent with the capture zone model computation results Based on a comparison of Figures 4 and 7, it is evident that monitoring wells PW 1, PW2, PW4, • PW5, PW7, PWB, 4MW14, 31PW1, and 310W1 are located within the treatment zone Monitonng wells PW3, PW6, and 31MW1, are screened below the treatment interval Monitonng well 31MW4 is laterally outside of the treatment zone 9