Valkenburg, J. and J. Molin. | 48th Annual Environmental Show of the South, 15-17 May, Chattanooga, TN, 30 slides, 2019

High groundwater flow velocity caused a carbon tetrachloride (CT) groundwater plume to migrate ~2,600 ft and discharge into a creek. A permeable reactive barrier (PRB) was installed in 2005 by injecting EHC® ISCR Reagent slurry to passively treat CT. The presentation reviews geochemical parameter response and CT removal rates over time and compares them with theoretical calculations using site-specific data. Total organic carbon was monitored as a reagent indicator while oxidation-reduction potential, dissolved oxygen, nitrate, and sulfate were monitored to assess redox conditions. CT removal rates peaked 16 months after installation at >99% removal. Two years after installation, removal rates decreased to ~95% and have stabilized for >10 years. Theoretical calculations suggested that ZVI would be consumed after 2.7 years from inflowing sulfate. However, geochemical data suggest that ZVI by itself is not supporting significant sulfate reduction. The probable explanation for the long PRB life is the formation of reduced iron sulfide minerals that acts as a zone of abiotic reductive treatment. The presentation assesses long-term performance and changes to geochemical parameters since installation. https://www.tn.gov/content/dam/tn/environment/solid-waste/documents/esos/sw_esos-16_2019-05-16-1515-valkenburg.pdf More information http://www.peroxychem.com/media/121250/peroxychem-ehc-case-study-multiple-injection-prb-manufacturing-site-southeast-us.pdf