Pilot testing of in situ chemical reduction to treat carbon tetrachloride at a former grain storage facility in Missouri
At a former grain storage facility in Missouri, EVS has initiated a pilot test of an innovative treatment using amended zero-valent iron to achieve in situ chemical reduction of carbon tetrachloride contamination. Carbon tetrachloride concentrations above regulatory levels in soil and groundwater (at 8-89 ft below ground level [BGL]) are confined to a small area of the former facility, on property that is now a county fairground. At present, the contamination poses no known risks to fairgrounds workers or visitors. The deep bedrock aquifers in the area are at minimal risk of contamination.
The areas targeted for treatment in the pilot test are localized contaminant “hot spots” that have characteristics of contaminant source areas. The EHC™ material being tested is a proprietary mixture of slow-release, food-grade organic carbon and zero-valent iron, marketed by FMC Environmental Solutions. EHC promotes the degradation of carbon tetrachloride through chemical processes and by the action of naturally occurring bacteria in the subsurface. The material is harmless and biodegradable.
The EHC material was injected in November-December 2012 at 15-35 ft BGL at 34 “shallow” locations (typically in 5 discrete vertical zones) and at 15-60 ft BGL at 65 “deep” locations (typically in 8-9 vertical zones). Roughly 40 tons of the EHC material, mixed with water to form a slurry, was injected through the use of direct-push equipment.
Pre-treatment baseline testing involved groundwater sampling immediately before injection, with analysis for volatile organic compounds (VOCs), cations, anions, and additional parameters including temperature, conductivity, pH, oxidation-reduction potential, dissolved oxygen, and reduced iron. Approximately a month after injection, Argonne‘s cone penetrometer vehicle was used to collect soil cores for visual examination and VOCs analysis, and groundwater samples were collected from monitoring wells. After additional groundwater sampling at intervals for a year, the results will be evaluated, and further monitoring might be proposed.
In 2007, EVS initiated another pilot test of the EHC material at a similar site in Kansas. Carbon tetrachloride concentrations there have decreased dramatically, and the effects of the EHC material have persisted for five years. The work at both sites is sponsored by the Commodity Credit Corporation of the U.S. Department of Agriculture, which operated numerous grain storage facilities from the late 1940s to the early 1970s, during the period when carbon tetrachloride was a common constituent of commercial grain fumigants. The work at the two sites is under the regulatory purview of the respective states.