A Hydrogen Recirculation System For The Treatment Of Tce-Impacted Groundwater
ABSTRACT: To speed the rate of reductive dechlorination of trichloroethylene (TCE)-impacted groundwater at the Old Jet Engine Test Site (OJETS), Offutt AFB, Nebraska, an in situ pilot-scale dissolved hydrogen addition system was installed. The test area consisted of an injection well, a recovery well, and five monitoring wells within an 8.5 m x 4.3 m (28 ft x 14 ft) test plot. Groundwater was pumped from the recovery well at a flow rate of 1.5 L/min (0.4 gpm), amended with hydrogen at 20 mL/min, and injected into the injection well, thereby creating a recirculation system. The results of the first 6 months of operation are presented in this paper. After 6 months of operation, the oxidation-reduction potential and dissolved oxygen of the groundwater decreased. Despite background sulfate levels of 280 mg/L, the mean TCE concentration declined 63% from 2.9 μmol/L to 1.07 μmol/L. Significant production of cis-1,2-dichloroethene (cDCE) was observed within the test area (i.e., 0.7 to 3.0 μmol/L), indicating that the hydrogen was promoting reductive dechlorination. The cDCE:TCE ratio increased more than ten fold from 0.25 to 2.8, despite decreasing groundwater temperatures. In summary, the dissolved hydrogen recirculation system was effective in removing TCE from groundwater without significant vinyl chloride production.