Remediating Explosive-Contaminated Groundwater by in situ Redox Manipulation (ISRM) of Aquifer Sediments

In situ chemical reduction of clays and iron oxides in subsurface environments is an emerging technology for treatment of contaminated groundwater. Our objective was to determine the efficacy of dithionite-reduced sediments from the perched Pantex Aquifer (Amarillo, TX) to abiotically degrade the explosives RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), HMX (octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine), and TNT (2,4,6-trinitrotoluene). The effects of dithionite/buffer concentrations, sediments-solution ratios, and the contribution of Fe(II) were evaluated in batch experiments. Results showed that reduced Pantex sediments were highly effective in degrading all three high explosives. Degradation rates increased with increasing dithionite/buffer concentrations and soil to solution ratios (1:80–1:10 w/v). When Fe(II) was partially removed from the reduced sediments by washing (citrate-bicarbonate buffer), RDX degradation slowed, but degradation efficiency could be restored by adding Fe(II) back to the treated sediments and maintaining an alkaline pH. These data support in situ redox manipulation as a remedial option for treating explosive-contaminated groundwater at the Pantex site

HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes