The Regional Superfund Ground Water Forum is a group of EPA professionals, representing EPA's Regional Superfund Offices, committed to the identification and the resolution of ground water issues impacting the remediation of Superfund sites. The Forum is supported by and advises the Superfund Technical Support Project. Remediation of trichloroethylenecontaminated soils and ground waters is an issue identified by the Forum as a concern of Superfund decision-makers. For further information contact Hugh H. Russell (FTS-7432444), John E. Matthews (FTS-743-2408), or Guy W. Sewell (FTS-743-2232).

AbstractHeavy metal contamination of soil resulting from anthropogenic sources poses a significant challenge in many industrialized societies. The current technologies employed for removal of heavy metals often involve expensive ex‐situ processes requiring sophisticated equipment and removal, transportation, and purification of the soil. Generally, in‐situ remedial technologies are favored to ex‐situ methods for detoxification, neutralization, degradation, or immobilization of contaminants. In‐situ bioremediation is increasingly favored because of its effectiveness and low cost. A new type of bioremediation, known as vegetative remediation or “phytoremediation,” uses metal‐tolerant hyperaccumulator plants to take up metal ions from soils and store them in their aboveground parts. To select the appropriate phytoremediation technology, one must understand the technical feasibility, cost effectiveness, and availability of the suitable plant species. Equally important is determining whether the site's soil conditions are optimal to enhance or restore the soil biological activity. Before phytoremediation can be exploited on a contaminated site, greenhouse‐scale confirmatory testing is necessary to measure plant uptake and correlate shoot metal concentrations to available soil metals. These tests also validate that the harvesting and subsequent disposal of metal‐containing plant tissues are environmentally safe and manageable.

Soils contaminated with wood preserving wastes, including pentachlo‐rophenol (PCP) and creosote, are treated at field‐scale in an engineered prepared‐bed system consisting of two one‐acre land treatment units (LTUs). The concentration of selected indicator compounds of treatment performance included PCP, pyrene, and total carcinogenic polycyclic aromatic hydrocarbons (TCPAHs) was monitored in the soil by taking both composited soil samples at multiple points in time, and discrete soil samples at two points in time. The mean concentration of the indicator compounds and the 95‐percent confidence interval (CI) of the composite and discrete samples agreed relatively well, and first‐order degradation rate kinetics satisfactorily represented the mean chemical concentration loss of indicator compounds in the LTU. Toxicity of the soil, as measured by Microtox TM assay of the soil extracts, indicated that toxicity reduction corresponded with indicator compound disappearance. No toxicity effects were observed with time in treated layers of soil (lifts) buried beneath highly contaminated lifts of newly applied soil. This indicated that vertical migration of soluble contaminants from such lifts had little effect on the microbial activity in the underlying treated soil.

AbstractWidespread use of trichloroethylene (TCE) in the U.S. has resulted in its frequent detection in soil and groundwater. TCE can become a health hazard after being processed in the human liver; or reductive dehalogenation in the environment may result in production of vinyl chloride, a known carcinogen. This has generated a high degree of interest in efficient and cost‐effective technologies that can be used to remediate soil and ground‐water contaminated with TCE. The purpose of this paper is to present and discuss relevant physicochemical properties and reactive mechanisms of TCE, and to delineate and discuss promising remediation methodologies that have been proposed and/or demonstrated for restoring contaminated subsurface environments. The information in this article has been funded wholly or in part by the U.S. EPA under contract No. 68–C8–0058 to Dynamac Corporation; it has been subjected to the Agency's peer and administrative review process and approved for publication.

Biological processes, including microbial degradation, have been identified as critical mechanisms for attenuating organic contaminants during transit through the vadose zone to the groundwater. On-site soil remedial measures using biological processes can reduce or eliminate groundwater contamination, thus reducing the need for extensive groundwater monitoring and treatment requirements. On-site remedial systems that utilize the soil as the treatment system accomplish treatment by using naturally occurring microorganisms to treat the contaminants. Treatment often may be enhanced by a variety of physical/chemical methods, such as fertilization, tilling, soil pH adjustment, moisture control, etc. The development of a bioremediation program for a specific contaminated soil system includes: (1) a thorough site/soil/waste characterization; (2) treatability studies; and (3) design and implementation of the bioremediation plan. Biological remediation of soils contaminated with organic chemicals has been demonstrated to be an alternative treatment technology that can often meet the goal of achieving a permanent clean-up remedy at hazardous waste sites.

Biological transformation and detoxification of 7,12-dimethylbenz(a)anathracene (DMBA) were studied in a nonacclimated sandy loam soil. Parent 14C DMBA biodegraded extensively (62% to 20%), accompanying an increase of metabolite 14C fraction (4% to 53%). Incorporation of DMBA into non extractable soil residue ,4C increased from 12 to 17%, but the increase was not statistically significant. DMBA was transformed into several metabolic products in the soil system, including 4-hydroxy-, 5-hydroxy-, and 10-hydroxy-DMBA and 7,12-dihydro 12-methyl-7-methylene-benz(a)anthracene-12-ol. High polarity transformation products of DMBA demonstrated a negative mu tagenic response with the Ames mutagenicity assay, strain TA 100, for both low and neutral pH soils. Moderate and low polar metabolites, however, induced mutagenicity for both soil samples. The mutagenicity of these metabolites decreased with incubation time in the soil, suggesting detoxification and assimilation of this polyaromatic hydrocarbon in soil systems. Mutagenic responses for the metabolites formed from low and neutral pH soil were similar. J. Water Pollut. Control Fed. 60, 1822 (1988).

Land treatment is categorized in the Resource Conservation and Recovery Act of 1976 (RCRA) as one of the land disposal options for managing hazardous wastes. Land treatment relies on detoxification, degradation, and immobilization of hazardous waste constituents within the defined treatment zone to ensure protection of surface water, groundwater, and air. Under the authority of Subtitle C of RCRA, the U.S. Environmental Protection Agency has promulgated regulations governing the treatment of hazardous wastes in land treatment units (40 CRF, Part 264, Subpart M, July, 1982). This paper describes the land treatment practices used by petroleum waste land treatment facilities in the U.S. Information obtained for thirteen full-scale land treatment facilities included types of waste land treated, characterization of land treated wastes, waste application rates (loading rates), waste application frequencies, and management practices used at the treatment units. Engineering design matrices which illustrate the relationships among waste application rate, application frequency, and waste degradation rate, and the effect of these parameters on stabilized concentrations during the active life a unit were developed. Waste degradation half-life and waste application frequency were observed to have greater influence in determining the stabilized weight percentage of oil in the treatment soil than waste application rate. A three-dimensional graph was developed as an example of how design matrices can be used as engineering/management aids for petroleum land treatment site design and operation.