A Six Year Field Test of Emulsified Zerovalent Iron to Treat Source Zone Chlorinated Solvents at a Superfund Site

Groundwater contamination by dense non-aqueous phase liquids (DNAPL) dominated by tetrachloroethene (PCE) occurred from a 1994 spill at the Marine Corps Recruit Depot (MCRD), Parris Island, South Carolina, Superfund site. Containment and treatment of the source zone was critical in controlling the migration of the contaminant plume. Emulsified zerovalent iron (EZVI) technology was chosen due to its previous success.

EZVI was injected into the treatment areas in October 2006, and performance monitoring was conducted until October 2012 to establish long-term post-demonstration conditions. The demonstration consisted of two side-by-side treatment areas to evaluate the performance of EZVI to remediate a shallow (<20 ft) PCE DNAPL source area and to evaluate two injection technologies for EZVI, pneumatic injection and direct injection. In the pneumatic injection plot, 2180 liters of EZVI containing 225 kg of iron (Toda RNIP-10DS), 856 kg of corn oil, and 22.5 kg of surfactant were injected to remedy an estimated 38 kg of CVOCs. In the direct injection plot, 572 liters of EZVI were injected to treat an estimated 0.155 kg of CVOCs. Soil samples were analyzed to evaluate contaminant mass changes.

Significant reductions in PCE and trichloroethene (TCE) concentrations were observed in downgradient wells with corresponding increases in degradation products including significant increases in ethene. In the pneumatic injection plot, there were significant reductions in the downgradient groundwater mass flux values for chlorinated ethenes (>58%) and a significant increase in the mass flux of ethene (628%). There were significant reductions in total CVOC mass (78%); an estimated reduction of 23% in the sorbed and dissolved phases and 95% reduction in the PCE DNAPL mass. There are uncertainties in these estimates because DNAPL may have been mobilized during and after injection. Significant increases in dissolved sulfide, volatile fatty acids (VFA), and total organic carbon (TOC) were observed and dissolved sulfate and pH decreased in many wells. The apparent effective remediation seems to have been accomplished by a combination of abiotic dechlorination by nanoiron and biological reductive dechlorination stimulated by the oil in the emulsion.