Draft Technical Protocol for Characterizing Natural Attenuation of Chlorinated Solvent Ground-Water Plumes Discharging into Wetlands.

摘要

The U.S. Environmental Protection Agency (USEPA) has defined natural attenuation processes as a variety of physical, chemical, or biological processes that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil and ground water. These in-situ processes include biodegradation, dispersion, dilution, sorption, volatilization, and chemical or biological stabilization, transformation, or destruction of contaminants (Wiedemeier and others, 1998). Monitored natural attenuation (MNA) as a remedial action alternative for contaminants dissolved in ground water has gained considerable acceptance in recent years, particularly with respect to dissolved petroleum hydrocarbons (Stauffer and others, 1993; Wiedemeier and others, 1994, 1996, 1998; National Research Council, 2000). In aquifers, trichloroethene (TCE) and other chlorinated solvents tend to be relatively resistant to transformations, either biotic or abiotic, compared to the biodegradation potential of petroleum hydrocarbons. Reductive dechlorination is the most important biodegradation process for the more heavily chlorinated ethenes such as TCE and tetrachloroethene (PCE). In reductive dechlorination, the chlorinated solvent acts as an electron acceptor and is sequentially reduced to lower chlorinated compounds. Reductive dechlorination of PCE and TCE occurs primarily by sequential hydrogenolysis to 1,2- dichloroethene (12DCE), vinyl chloride (VC), and ethene (Vogel and McCarty, 1985; Freedman and Gossett, 1989; Bouwer, 1994). This biodegradation process can result in accumulation of toxic chlorinated intermediates and relies on an adequate supply of other organic substrates as electron donors, therefore, natural attenuation generally is considered a less favorable remediation technology for chlorinated solvents than for petroleum hydrocarbons (National Research Council, 2000).