ABSTRACT

Degradative Solidification/Stabilization for Aliphatic Chlorinated Hydrocarbons

Chlorinated aliphatic hydrocarbons (CAH) are one of the main sources of sub-surface contamination in the U.S.   Available technologies such as pump-and-treat often fail to meet remedial goals for contaminated groundwater and some technologies can be very expensive. Attractive alternatives for treating sources of ground water contamination as well as other contaminated soils and sediments are to apply slower, less expensive technologies.  Natural attenuation is one example of such a remedial approach.  Other examples are chemical degradation technologies that are based on inexpensive reagents.  Chemical degradation can be combined with conventional solidification/stabilization to provide an effective method for treating soils/sediments that are contaminated by organic compounds or by combinations of organic and inorganic compounds.  This approach is called degradative solidification/stabilization (ds/s) and it is attractive, because it combines the low cost of s/s processes with the ability to destroy toxic chlorinated compounds.  A project that completed with GCHSRC funding has characterized the fundamental reactions that degrade tetrachloroethylene (PCE) and has demonstrated that the process can completely dechlorinate PCE within reasonable times.  Preliminary experiments have shown that this technology has the ability to dechlorinate other types of compounds, including chlorinated aliphatic hydrocarbons.

Current research has shown the effectiveness of the Fe(II) ds/s system for PCE and has indicated that it may be applicable to a broader range of chlorinated compounds.  However, sufficient data has not been obtained to document the effectiveness of the process for target compounds other than PCE.  In particular, additional data is needed on the ability of the process to degrade chlorinated aliphatic compounds, which are common chemicals of concern at contaminated sites.  Furthermore, the compound that is actually causing the reductive dechlorination of the target chemicals is not yet known and has not been shown to be reactive with chlorinated aliphatics.  Therefore, the goal of this project will be to develop the fundamental knowledge needed to apply the Fe(II) ds/s system to degrade chlorinated aliphatic hydrocarbons in contaminated soils and sediments.  Achieving four subordinate objectives will allow the project to reach its goal: 1) Verify analytical and experimental procedures; 2) Confirm and improve active reductant species; 3)  Characterize dechlorination rates and product formation; 4) Verify degradation in different soils/sediments.

Task 1 will develop analytical procedures for the target compounds in this research (carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dichloroethane, and 1,1,2,2-tetrachloroethane) as well as probable daughter products.  Existing reaction systems will also be demonstrated to be suitable for these compounds.  Task 2 will demonstrate that the compound identified by ongoing research as  the active reducing agent for PCE is also active toward the target CAH.  This will be accomplished by batch kinetic experiments.  Task 2 will also seek methods to improve the reactivity of the active agent by doping with cations and replacing anions in the active agent with surfactants.  Task 3 will characterize the degradation of CAH by the Fe(II)-based degradation system as affected by Fe(II) dose, pH, and concentration of target compound.  Batch kinetic experiments with slurries of the active agent or combinations of Portland cement and Fe(II) will be used.  Task 4 will confirm the ability of this ds/s system to degrade target CAH in soils solidified by Portland cement.  Batch kinetic experiments will be used to accomplish this task.