chlorinated solvents

Chlorinated solvents such as trichloroethene (TCE, C2HCl3) and carbon tetrachloride (CT, CCl4) are priority groundwater contaminants at many EPA field sites.

Green rust (GR) minerals are important corrosion products of zerovalent iron (Fe0) that has been used in permeable reactive barrier (PRB) technologies to remediate groundwater contaminants.

Green rusts also occur naturally and are found in certain soils and sediments.

The ozonation of model systems and several natural waters was examined in bench-scale batch experiments. In addition to measuring the concentration of ozone (03), the rate of depletion of an in situ hydroxyl radical probe compound was monitored, thus providing information on the transient steady-state concentration of hydroxyl radials (*OH).

A new parameter, Rct, representing the ratio of the *OH-exposure to the O3-exposure was calculated as a function of reaction time.

A new analytical solution has been developed for simulating the transient effects of groundwater source and plume remediation.

This development was performed as part of a Strategic Environmental Research and Development Program (SERDP) research project, which was a joint effort between the US EPA, Clemson University, Purdue University, the University of Florida, and the Air Force Institute of Technology, focused on defining the benefits of partial DNAPL source remediation.

The analytical model is called REMChlor (for Remediation Evaluation Model for Chlorinated Solvents).

Abstract: Iron and sulfur reducing conditions are generally created in permeable reactive barrier (PRB) systems constructed for groundwater treatment, which usually leads to formation of iron sulfide phases.

Iron sulfides have been shown to play an important role in degrading chlorinated solvents and removing metals in these engineered systems.

This study uses acid volatile sulfide (AVS) and chromium reducible sulfur (CRS) as probes to investigate iron sulfide formation and transformation in a column and PRB field study dealing with TCE degradation.

Historical disposal practices of chlorinated solvents have resulted in the widespread contamination of ground-water resources.

These ground-water contaminants exist in the subsurface as free products, residual and vapor phases, and in solution.

The remediation of these contaminates often require a sequenced train of treatments, the success of which is ultimately dependent on the hydraulic control of local flow regimes.

In the past ten years, passive reactive barriers (PRBs) have found widespread application to treat chlorinated solvent contamination in ground water.

The traditional PRB commonly uses granular zero-valent iron and/or iron alloys as filling materials for treatment of chlorinated solvents.

In recent years, there has been a surge in the price of iron. The higher price for iron makes alterative matrix materials for the PRBs more attractive.

One alternative for iron is shredded plant mulch.

Disposal of the chlorinated solvents PCE and TCE at the Twin Cities Army Ammunition Plant (TCAAP) resulted in the contamination of groundwater in a shallow, unconsolidated sand aquifer.

The resulting plume had moved over 1000 feet from the disposal source area and had impacted private wells adjacent to the TCAAP property.

When the contamination was discovered in the late 1980s, the U.S. Army installed a recovery well and a system of containment wells, preventing further downgradient contamination of the aquifer.