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Jun 6 199 A 1 "M [EG TECHNOLOGIES No 2616 P 10/31 95-VtP 1 a3 05 then stabilized at low concentrations between 13 to 75 7 gg/cu m after approximately one month of operation. The chlorinated compounds chloroethane, chloromethane,dichloromethane,PCE, 1,1,1-TCA,and TCE were detected in the groundwater and in the airstream • The overall concentrations of VOCs vnth in the air stream are much lower than was calculated based upon anticipated removal rates from the groundwater • The highest VOC concentrations were from BTEX compounds which are not thought to be associated with the groundwater at Site 31 Since the treatment well is located near an active runway, the elevated BTEX concentrations most likely reflect ambient conditions. • Sample ports VI and V2 showed consistent results for sampling rounds where both samples were collected, indicating that samples collected from either sample port are indicative of the air concentrations being extracted from the UVB well Operational Monitoring - Treatment Well Groundwater Sampling The TCE analytical results for groundwater sampling performed at the UVB treatment well are plotted on Figure 6 Samples from well Wl are representative of the groundwater conditions in the lower, or influent well screen, and samples from well W3 are representative of treated groundwater exiting the UVB well in the upper well screen • Influent TCE concentrations, as measured at well W1, have vaned between non-detect and 324 µg/1 throughout the pilot study The highest tnfluent concentrations, as well as the highest variability in influent concentrations, occurred during the fust five months of operation This time frame corresponds to the highest concentrations m the adjacent monitoring wells The influent concentration peaks observed during the 19-month pilot study probably reflect the inhomogeneity in the distribution of TCE entering the treatment cell from upgradient areas For the most part, the effluent concentrations, as measured at well W3, have vaned between non-detect and 15 µg,11 throughout the study Eight anomalous peaks in the effluent concentrations are exceptions (Figure 6) These peaks to the effluent concentrations are explained as follows • Peaks 1, 2, and 3 are single sample occurrences corresponding to low concentrations in monitoring well W1 It is suspected that the samples collected during these sample rounds were inadvertently switched between wells W1 and W3 • Peaks 4 and 5 are suspected to be a response to system maintenance performed pnor to those sampling events This interpretation is based solely on the eommdent occurrence of the maintenances and anomalous peaks, and not on a predicted theoretical, basis Unlike the single sample anomalies discussed above, the concentration data for these two peaks are comprised of several sampling rounds conducted over 1-2 weeks • Peaks 6 and 7 occurred following the development of a Mole in one of the buoyancy tanks of the UVB system This occurrence caused the system to ride lower in the water thereby reducing, or eliminating, intake air flow and subsequent air stripping Based on the groundwater sample data 8