Innovations in Ground Water and Soil Cleanup From Concept to Commercialization (1997) / Chapter Skim
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3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION
3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION
Pages 80-166
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From page 80... ...
As the technology matures, it typically addresses the same range of contaminant types, but its range of application in subsurface environments becomes better defined. This evolutionary process is similar for most remediation technologies, but the rate at which new technologies are adopted varies considerably.
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From page 81... ...
1996 Innovative Treatment Technologies: Annual Status Report classifies in situ bioremediation of contaminated soils as an innovative technology, while the Air Force specifies bioventing (a type of in situ bioremediation) as the standard remedy for soils contaminated with petroleum hydrocarbons and other volatile organic compounds (DOD Environmental Technology Transfer Committee, 1994~.
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From page 82... ...
.. AVAILABILITY OF INFORMATION ON INNOVATIVE REMEDIATION TECHNOLOGIES Application of innovative remediation technologies has been slowed by lack of uniform, synthesized information about remediation technology performance.
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From page 84... ...
nology requires documentation of the technology's performance and accessibility of performance information. Often in the development of remediation technology, data collection is minimal.
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From page 85... ...
The 1995 publication Accessing Federal Data Bases for Contaminated Site Clean-Up Technologies lists 25 different data bases that could be potentially useful in evaluating remediation technologies (Federal Remediation Technologies Roundtable, 1995a) , but these data bases are not coordinated, and many of them are difficult to access (see Appendix A for a listing of data bases)
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From page 86... ...
(1992) on thermal Resorption for petroleumcontaminated soils provides a useful perspective on a particular technology application and its status of development.
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From page 87... ...
Figure 3-1 shows a conceptual diagram of where innovation is most needed to improve the performance and reduce the costs of ground water and soil remediation projects. The greatest successes in remediation to date have been in the treatment of petroleum hydrocarbon fuels gasoline, diesel, and jet fuel which are generally mobile and biologically reactive and to a lesser extent in the treatment of chlori
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From page 88... ...
At the right side, new technologies are needed to solve contamination problems that are currently intractable. nated solvents, which are generally mobile but are less readily biodegraded than petroleum hydrocarbons.
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From page 89... ...
Most such techniques have been developed for ex situ treatment of soil contaminated with heavy metals, although a few methods for in situ treatment of relatively shallow contaminated soils are in use. These processes are generally not suited for contaminants located at significant depth or for very volatile or soluble organic contaminants, although some of the methods are now being applied to a limited number of organic contaminants.
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From page 95... ...
Courtesy of Fluor Daniel GTI.
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From page 96... ...
INNOVATIONS IN GROUND WATER AND SOIL CLEANUP vast majority of the practices in this category are biological treatment methods for hydrocarbon-contaminated sites. For all other classes of chemicals, far fewer tested reactive treatment options are available.
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From page 97... ...
Table 3-2 shows the availability of the three general categories of technologies for treating different classes of contaminants. As shown in the table and in Figure 3-1, a range of treatment alternatives has been developed for the relatively mobile and biodegradable contaminants (petroleum hydrocarbons and chlorinated solvents)
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From page 99... ...
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From page 100... ...
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From page 101... ...
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From page 102... ...
6 fuel oil in fine sand (Lyman et al., 1992~. Because hydrocarbon mixtures are less dense than water, they typically accumulate in a layer on the water table when sufficient hydrocarbon has spilled or leaked to saturate the soil, allowing free-phase liquid to migrate to the water table.
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From page 103... ...
Applicable technologies include NAPL recovery, dual-phase extraction, in situ bioremediation, biopiles, land farming, SVE, bioventing, biosparging, soil washing, and soil flushing. The processes that can be applied to various sources of hydrocarbon contaminants vary considerably and are a function of the type of hydrocarbon product.
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From page 104... ...
Soil Washing and Soil Flushing. Significant quantities of petroleum hydrocarbons can be retained in soils as a residual, discontinuous NAPL phase.
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From page 105... ...
In the first approach, chemical additives (such as surfactants and cosolvents) are used to enhance the aqueous solubility of contaminants in order to more efficiently dissolve or desorb the petroleum hydrocarbons (or other organic contaminants)
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From page 106... ...
NAPL recovery is a standard remediation technology employed at almost any site having recoverable NAPL. Most applications use water table depression as the driving force for NAPL recovery.
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From page 107... ...
The purpose of the technology is to treat soil contamination below the water table so that the volatile components may be removed. The technology combines dewatering and venting.
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From page 108... ...
The use of air sparging to treat source areas requires close well spacing and moderate to high air flows. A related technology is "biosparging," which uses low air flows to minimize the amount of volatilization, so that any volatilized hydrocarbons are biodegraded in the vadose zone before being discharged to the atmosphere.
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From page 109... ...
With petroleum hydrocarbons, intrinsic remediation is a significant process. Intrinsic remediation is the reliance on natural processes, including volatilization, sorption, dilution, reactions with naturally occurring chemicals, and, most commonly, biodegradation, to decrease contaminant concentrations without human intervention other than careful monitoring.
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From page 111... ...
In the absence of sufficient O2, organisms will use alternate electron acceptors. Alternate electron acceptors become important when the dissolved O2 level drops below approximately 2 mg/liter (Salanitro, 19931.
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From page 112... ...
Research Needs While an abundance of technologies is available for cleaning up sites contaminated with petroleum hydrocarbons, some problem areas still need resolution. The main needs are technologies for treating heavy hydrocarbon mixtures and hydrocarbons in low-permeability or highly heterogeneous formations.
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From page 113... ...
Nine of the 20 most common chemicals found in ground water at Superfund sites are chlorinated solvents. TCE is the contaminant most commonly detected in ground water at Superfund sites, and PCE is third most common (National Research Council, 1994~.
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From page 114... ...
Residual-phase chlorinated solvents in the vadose zone are the easiest to treat because of the high vapor pressure of most of these solvents and because moving air through soils is easier than moving water through the saturated zone. Dissolved-phase chlorinated solvents can be treated if there are no appreciable residual-phase solvents present that is, if the dissolved plume is the result of the discharge of wash waters or low-level use of solvents.
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From page 115... ...
Table 34 provides the solubilities and vapor pressures for a number of chlorinated solvents. The aqueous solubilities are several orders of magnitude higher than drinking water standards, and thus dilution by hydrodynamic dispersion of chlorinated solvents is not a viable mechanism for managing sites contaminated with these compounds.
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From page 116... ...
Remediation Technology Options Cleaning up chlorinated solvents is significantly more difficult than cleaning up petroleum hydrocarbons. Because the neat solvent, unlike petroleum hydrocarbons, is more dense than water, it can migrate below the water table.
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From page 117... ...
The process employs an iron-filled trench (a passive reactive barrier) through which the contaminated ground water flows; the chlorinated solvents are chemically reduced upon contact with the iron (see Box
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From page 119... ...
Engineered in situ bioremediation of chlorinated solvents has been developing in two areas. The first is the continued study of aerobic cometabolic pathways, in which the bioremediation systems add toluene, natural gas, or propane to the subsurface to stimulate cometabolism of the solvent.
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From page 120... ...
Research is also needed to improve the scientific basis for designing in situ bioremediation systems for the treatment of chlorinated solvents. A number of laboratory investigations and a few field studies have shown that microbes can degrade chlorinated solvents using various cometabolic pathways and electron acceptors.
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From page 121... ...
Soil and ground water contamination problems currently exist at many former manufactured gas plants because of prior process operations and residuals management practices (Luthy et al., 1994~. Coal tar and associated PAHs are the principal contaminants of concern at these sites.
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From page 122... ...
In soils and sediments, the rate of microbial degradation of PAHs may depend on various physicochemical factors affecting the bioavailability of the target compounds to the microorganisms (see Figure 3-5~. This is a problem especially with aged and/or weathered samples, which appear to bind PAHs strongly and which often contain a resistant fraction of PAH material that is not amenable to microbial degradation (GRI, 1995; Office of Naval Research et al.,1995; Swiss Federal Institute for Environmental Science and Technology, 1994~.
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From page 123... ...
Remediation Technology Options PAH compounds are relatively persistent in the environment, being resistant to both chemical and microbial transformations. These compounds are not very soluble or volatile, and they tend to sorb to soil surfaces or remain entrapped within an organic phase.
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From page 124... ...
One area of research is the use of high concentrations of water-miscible cosolvents, which greatly enhance the solubility of hydrophobic organic contaminants, thereby increasing the mass removal per unit volume of fluid used to flush the contaminated soils (Luthy et al., 1992; Augustijin et al., 1994; Roy et al., 1995~. A pilot demonstration of in situ solvent extraction has been conducted at Hill Air Force Base in Utah using ethanol-propanol mixtures injected into gravely sand in a 3 by 5 m test cell having jet fuel as the primary contaminant.
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From page 125... ...
Another area of research is the use of surfactants that may benefit in situ soil flushing by enhancing the solubility of hydrophobic organic compounds and by lowering the interracial tension between water and NAPL, resulting in direct mobilization of the NAPL. Surfactant enhancements have been evaluated in various laboratory tests to assess physicochemical phenomena affecting the partitioning of PAH compounds in soil-water systems (Edwards et al., 1991, 1994a,b)
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From page 126... ...
126 INNOVATIONS IN GROUND WATER AND SOIL CLEANUP reduction of total PAHs by 86 percent from initial values of 2,460 mg/kg, with the greatest reduction (more than 98 percent) for 2- and 3-ring PAHs and lower removal rates (72 percent)
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From page 127... ...
Courtesy of Remediation Technologies, Inc.
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From page 128... ...
The treatment achieved remediation objectives for the compounds, including benzene and benzo~a~pyrene, that were used as indicators of overall contamination. Research Needs Additional data are needed to assess thermal treatment processes for PAHs.
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From page 129... ...
Various factors remain to be resolved for practical implementation of soil washing and flushing systems that use cosolvents or surfactants for remediation of PAHs. Although laboratory work has been performed to advance the basic science of soil washing and flushing, experience with pilot- or field-scale demonstrations is very limited.
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From page 130... ...
Therefore, containment or stabilization processes are effective for managing PCB-contaminated soils, but separation processes (thermal treatments or chemical extractions) require significant energy inputs.
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From page 131... ...
Operation of thermal desorption systems may create up to eight process residual streams requiring attention (Lightly et al., 1993~. Soil Washing and Soil Flushing.
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From page 132... ...
provide a description of a process using methoxyethanol and potassium hydroxide. Results of high-temperature substitution processes in field trials with PCB-contaminated soils or sediments are described by Vorum (1991)
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From page 133... ...
Problems with soil washing or flushing include the generation and treatment of large volumes of water; uneven treatment in soil flushing due to nonhomogeneous conditions, including the presence of NAPLs; and the need for improved control of pumped fluids. Problems with surfactant-aided technologies include assessing surfactant losses by degradation or sorption and evaluating surfactant recovery and reuse.
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From page 134... ...
Radioactive elements are also found in nature, but naturally occurring concentrations pose ecological or human health risks in few cases. Although metallic and radioactive contaminants can occur at modest scales, many of the sources of these contaminants, such as iThe term "metals" is used in this text to refer to transition metals, heavy metals, and radioactive metals and metalloids.
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From page 135... ...
Both nitrate and tritium migrate essentially unretarded in ground water. Nitrate can be treated by osmosis or can serve as an electron acceptor in microbial processes.
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From page 136... ...
The inability to eliminate inorganic contaminants by biological or chemical reactions and the strong effect of geochemistry on inorganic contaminant mobility present major challenges in the cleanup of sites containing these contaminants. For two primary reasons, relatively few metals are soluble and mobile enough to form significant plumes of contamination in typical ground water environments.
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From page 137... ...
, such as chromium and technetium, are typically relatively mobile in oxic water but form stable precipitates under reducing conditions. Some inorganic contaminants, such as arsenic and mercury, form complexes with organic compounds.
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From page 138... ...
Because inorganic contaminants cannot be destroyed, innovative technologies focus on either stabilizing the contaminants by decreasing contaminant mobility and toxicity or separating the contaminants from the soil or ground water. Solidification, Stabilization, and Containment Techniques In Situ Precipitation and Coprecipitation.
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From page 139... ...
The approach is to develop reducing conditions in situ such that mobile metals precipitate or coprecipitate as relatively insoluble solid phases; unlike the acidic mine drainage schemes, shifting pH is not a priority for these technologies. Treatment by generating reducing conditions abiotically in a permeable wall containing zero-valent iron is currently being tested at the pilot scale at a site with a plume of chromate-contaminated water from an electroplating facility (Blowes and Ptacek, 1992; Puts et al., 1995; Blowes et al., 1995; Powell et al., 1995~.
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From page 140... ...
The Big Five Tunnel wetland removes heavy metals from the sulfur-containing water primarily as sulfide precipitates in the anaerobic portion of the wetland (Wildeman et al., 1994~. Passive treatment by constructed wetlands is projected to be cost effective relative to lime precipitation for some sites (Gusak, 1995)
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From page 141... ...
The reactions can be used to stabilize the metals in situ, or the contaminants can be removed in a concentrated form from the water or process solution surrounding the electrode. Proposed applications focus on ex situ water treatment and in situ or ex situ treatment of fine-grained soils that are difficult to flush because of low permeability.
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From page 142... ...
. For some highly radioactive contaminated soils, viable disposal locations may not exist.
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From page 143... ...
. For inorganic contaminants, soil flushing is not as well developed
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From page 144... ...
Smith et al., 1995~. Research Needs Radioactive isotopes and mixtures of heavy metals having different chemistries present major challenges in treatment of inorganic contaminants.
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From page 145... ...
Higher contaminant concentrations in ground water and soil result from point sources of pesticides, rather than from nonpoint sources. Proximity to a pesticide formulator, dealer, or applicator has been correlated with high frequency of pesticide detections (Holder et al., 1992~.
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From page 146... ...
As the water solution passes through the soil, some of the dissolved pesticide may sorb to and contaminate the soil. This contaminated soil can then become a longterm source of ground water contamination as the pesticide slowly redissolves.
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From page 147... ...
Volatile losses are significant primarily for pesticides with very high vapor pressures, low aqueous solubilities, and a very low tendency for sorption. Migration of the pesticide into the subsurface significantly decreases losses due to volatilization.
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From page 148... ...
In summary, pesticide transport properties are extremely complex, perhaps among the most complex of all contaminant groups, and highly variable depending on the type of pesticide, how it entered the environment, and the environmental conditions at the contaminated site. Remediation Technology Options The options appropriate for treating pesticide-contaminated soil depend on the nature of the pesticide and the way in which the pesticide was released to the environment.
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From page 149... ...
. Two companies2 are developing coupled anaerobic/aerobic bioremediation as a two-step process for ex situ treatment of pesticide-contaminated soils.
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From page 150... ...
. Composting is conducted by mixing highly contaminated soil with organic matter in piles and providing aeration.
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From page 151... ...
Applicable in situ technologies include soil flushing, SVE, air sparging, steam extraction, and radio frequency heating. These in situ technologies are less frequently applied than ex situ techniques such as those discussed above and thermal Resorption (discussed below)
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From page 152... ...
Considerable research is also needed to understand the potential for in situ bioremediation of various classes of pesticides. While recent research has demonstrated the potential for intrinsic remediation of pesticides, this research needs to be expanded before the potential for intrinsic remediation to achieve regulatory goals can be accurately predicted.
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From page 153... ...
Effort is needed to organize pesticides into groups of like compounds that can be treated with similar types of remediation technologies. CONCLUSIONS From a national perspective, there is little field experience with innovative technologies for treating contaminants other than petroleum hydrocarbons and, to a lesser extent, chlorinated solvents in relatively homogeneous geologic settings.
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From page 154... ...
The EPA, in collaboration with other stakeholders, should increase the scope and compatibility of data bases containing remediation technology performance information and should make these data bases available on the Internet, with a single World Wide Web page including links to all of the data bases. Improvements in information collection, assessment, and dissemination are needed to speed development and commercialization of remediation technologies.
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From page 155... ...
Treatment of mixtures including radioactive contaminants poses a special challenge that needs to be addressed. · Factors controlling the bioavailability of hydrophobic organic compounds (especially residual contamination from petroleum hydrocarbons, chlorinated solvents, PAHs, PCBs, and pesticides)
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From page 156... ...
Physical, chemical, and biological processes affecting the rate of intrinsic bioremediation. As for engineered bioremediation processes, current scientific knowledge is inadequate to provide accurate predictions of the rate and extent of intrinsic bioremediation, especially for contaminants other than easily degradable petroleum hydrocarbons.
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From page 157... ...
1995. Assessment of in situ solvent extraction for remediation of coal tar sites: Process modeling.
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From page 158... ...
Presented at First International Symposium on In Situ Air Sparging for Site Remediation, Las Vegas, Nevada, October 26-27, 1996. Bedard, D
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From page 159... ...
Vol. 4 of Innovative Site Remediation Technology, W
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From page 160... ...
1994b. Status Reports on In Situ Remediation Technologies for Ground Water and Soils at Hazardous Waste Sites: Surfactant Enhancements (Draft)
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From page 161... ...
:250-253. GWRTAC (Ground-Water Remediation Technologies Analysis Center)
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From page 162... ...
1995. C2 Chlorinated Solvents (www-cmrc.sru.com/CIN/mar-apr95/ article10.html)
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From page 163... ...
Paper presented at Conference on Intrinsic Remediation of Chlorinated Solvents, Airport Hilton, Salt Lake City, Utah, April 2, 1996. McCarty, P
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From page 164... ...
1995. In situ remediation of ground water contaminated with chromate and chlorinated solvents using zero-valent iron: A field study.
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From page 165... ...
Technology Evaluation Report TE-96-01. Pittsburgh, Pa.: Ground Water Remediation Technologies Analysis Center.
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From page 166... ...
Presented at Conference on Intrinsic Remediation of Chlorinated Solvents, Airport Hilton, Salt Lake City, Utah, April 2, 1996. Wildeman, T
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