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BENCH STUDY SET-UP

Flow-through column systems (Figure 1) were set up alongside a control. Each system consisted of an 800-mL column filled with a soil/EHC mixture, followed by a 2-L jar containing soil only. The soil-only jar simulates further contaminant reduction downstream of an EHC zone, since EHC will release dissolved organic carbon and low redox conditions downstream. Two systems were set up; one with EHC and one with EHC-A. An application rate of 2% of EHC to soil mass was used.

For each column system, groundwater impacted with CT was pumped from a Tedlar® bag through the column in an up-flow manner at approximately 150 mL/day. This results in a contact time of 2.7 days within the columns and 5.0 days within the downgradient jar (assumes 50% porosity).

RESULTS

After some acclimatization time, both the EHC and EHC-A systems performed very well with CT and all daughter products below the detection limit in the effluent water. The effluent water was sampled both after the column and the following soil jar. Figure 2 shows the concentration of CT in the influent and effluent water for the two systems. In addition the soil control system is presented. As shown, the CT started to break through in the effluent water for the EHC-A system following 355 days of continuous operation at room temperature. This would indicate that the EHC-A was consumed and had to be rejuvenated.

Figures 3 and 4 shows the effect on CT and daughter products over time for the EHC-A system after the column and soil jar respectively. As shown, the EHC-A removed the CT without generation of daughter products. Breakthrough occurred for CF after approximately 230 days in the column and after approximately 270 days following the soil jar.