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Jun 6 1995 4 18PM 1 E G TEHtIGL^1JIE No 2616 P 12/34 95-VVP 103 05 An average TCE reduction of greater than 60% occurred in the monitoring wells which have data . available prior to system startup and are within the treatment zone (Table 1) Mass Removals - The Mus Balance The mass of VOCs removed from the graundwater was estimated by comparing the UVB well groundwater influent concentrations to the effiuent groundwater concentrations The concentration of VOCs removed multiplied by the average water flow through the stripping reactor (based on the pump performance) resulted in an average removal rate for TCE from the groundwater to be on the order of 10 grams per day The mass of VOCs collected in the air stream was determined by multiplying the air sample concentrations by the average air flow rate, assuming that all the air flow was from the ambiem air intake pipe and no air flow was from the vadose zone This resulted in an average removal rate for TCE, as collected m the air stream, to be on the order of 0 1 grams per day This mass balance estimate shows at least an order-0f=-magnitude difference between the water and the air side of the mass balance equation. That is, the mass balance estimate shows that the amount of TCE entering and not leaving the UVB system through the water side, can not be accounted for by detailed monitoring of the TCE being removed on the air side of the system- The assumption associated with this analysis is that there are only two comps to the mass balance. Based on these results, it is suspected that the simple two-compartment conceptual model for TCE removal by air stripping as the primary treatment mechanism may be overly simplified and should be further evaluated CONCLUSIONS • An 18-month demonstration project of the UVB Vacuum Vaporizer Well tr&chnology has been completed at Site 31, March AFB The primary objective of the study was to evaluate the feasibility of the LJVB system for removal of chlorinated hydrocarbons from the groundwater The monitoring and sampling program designed to generate data necessary for evaluating the system effectiveness consisted of soil sampling, baseline groundwater sampling, air monitoring and sampling, and treatment and perimeter groundwater monitoring well sampling Conclusions derived from analysis of the data are as follows_ • Except for the scheduled maintenances, the system operated without interruption for the entire 18 months • During normal operating conditions, TCE removal of greater than 95% was achieved- Effluent chievedEffluent TCE concentrations were below the Federal MCL in 85% of the samples • Final perimeter well TCE concentrations for those wells within the treatment zone are lower than their initial concentrations • Perimeter well TCE concentrations for those wells within the treatment zone showed a marked increase in the fust few months of operation. These results are attributed to mobilization of contaminants from the pore spaces, particularly in the capillary fringe. • Capture zone evaluation using Herrling's model estimated the radius of the treatment cell at approximately 110 feet. • Perimeter well results validated the calculated treatment cell size The calculated mass of wntaminants removed from the groundwater and from the air samples is at least an order-of-magnitude off It is suspected that additional treatment mechanisms other than air stnppmg may be performing a significant role in TCE removal. 10