CLU-IN | Contaminants > Chromium VI > Treatment Technologies

Chromium VI

Treatment Technologies

Overview

Chromium primarily exists in nature in the trivalent and hexavalent states. Due to its widespread industrial use, it has been found in at least 120 of the 1,591 current or former NPL sites and is often found in contaminated groundwater along with complex mixtures of pollutants, which can make its remediation more difficult. Many Cr(VI) compounds are highly soluble and exist in solution as hydrochromate, chromate, and dichromate ions. The goal of remediation schemes is to reduce the carcinogenic, soluble, and mobile Cr(VI) to the less toxic and less mobile Cr(III), which forms minimally soluble precipitates. Successful removal of Cr(VI) hinges upon the formation and stability of Cr(III) precipitates.

Ex situ treatment technologies for water use commonly use chemical reduction of the Cr(VI) to Cr(III) followed by precipitation. The treated water is filtered and the chromium rich precipitates are properly disposed of.

Available in situ technologies or treatment approaches for chromate contamination use chemical reduction and fixation for remediation (e.g., geochemical fixation, permeable reactive barriers (PRBs), and reactive zones). Other types of in situ approaches under development include enhanced extraction, electrokinetics, biological processes that can be used within PRBs and reactive zones, phytoremediation, and natural attenuation.

Adapted from:

ATSDR Toxicological Profile for Chromium, Agency for Toxic Substances and Disease Registry, Sep 2000.

Cook, K.R., In Situ Treatment of Soil and Groundwater Contaminated with Chromium. Technical Resource Guide, EPA 625-R-00-005, 2000.

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Reports

General

Electrokinetic Ferric Iron Remediation and Stabilisation (FIRS) of Hexavalent Chromium Contaminated Soils: An Ex Situ Field Scale Demonstration
L. Hopkinson, A. Cundy, and R. Pollock.
CL:AIRE: Contaminated Land: Applications in Real Environments, Research Bulletin 9 (RB 9), 6 pp, 2009

A novel, low-energy, natural analog-based electrokinetic system called FIRS (ferric iron remediation and stabilization) applies a low-magnitude direct electric potential between two or more sacrificial iron-rich electrodes placed at opposing sides of a mass of contaminated soil or sediment. The electric potential generates a strong Eh/pH gradient between the two electrodes, promotes anodic dissolution, Fe(0) and Fe(2+)(aq) migration, and forces the precipitation of ferric iron oxyhydroxides, hematite, goethite, magnetite, and ZVI at near-neutral pH values at the interface of the anodic and cathodic domains. The system uses approximately one tenth of the energy requirements of most conventional electrokinetic systems. In the feasibility trial, FIRS achieved significant reduction of hexavalent chromium in the target soils and performed at least as well as in the bench-scale studies. The system currently is being developed for field-scale application to heavy-metal contaminated soils and wastes in the UK in partnership with Churngold Remediation Ltd. The bulletin is available without charge on the CL:AIRE Web site to registered users (also free).

Emerging Technologies for the Remediation of Metals in Soils:
Interstate Technology and Regulatory Council (ITRC).

Electrokinetics
MIS-4, 42 pp, 1997

Insitu Stabilization/Inplace Inactivation
MIS-3, 31 pp, 1997

Phytoremediation
MIS-5, 33 pp, 1997

Engineering Bulletin: Technology Alternatives for the Remediation of Soils Contaminated with As, Cd, Cr, Hg, and Pb
Margaret Groeber, Science Applications International Corp.
EPA 540-S-97-500, 21 pp, 1997
Contact: Michael Royer, royer.michael@epa.gov

This bulletin provides remedial project managers, on-scene coordinators, and other state or private remediation managers and their technical support personnel with information to facilitate the selection of appropriate remedial alternatives for soil contaminated with arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb).

Environmental Research Brief. Innovative Measures for Subsurface Chromium Remediation: Source Zone, Concentrated Plume, and Dilute Plume
D.A. Sabatini, R.C. Knox, E.E. Tucker, and R.W. Puls.
EPA 600-S-97-005, 16 pp, 1997
Contact: David Sabatini, sabatini@ou.edu

This environmental research brief reports on innovative measures for addressing each of these three regions. For the source zone, surfactant-enhanced chromium extraction is evaluated for expediting the removal of chromium from the source zone soils, thereby mitigating the continual feeding of the ground-water plume. For the concentrated plume, polyelectrolyte-enhanced ultrafiltration (PEUF) is evaluated as an innovative treatment process with desirable operating characteristics (less sludge production, higher quality final water, etc.). Relative to the dilute plume, the hydrogeological effectiveness of hydraulically passive, chemically reactive barrier systems is evaluated (i.e., in situ reduction of Cr(VI) to Cr(III)).

In Situ Treatment of Soil and Groundwater Contaminated with Chromium. Technical Resource Guide
K.R. Cook, Science Applications International Corp., San Diego, CA.
EPA 625-R-00-005, NTIS: PB2001-103721, 2000
Contact: Douglas W. Grosse, grosse.douglas@epa.gov

This report brings together information pertaining to chromium contamination and its in situ treatment and control in groundwater and/or soil, and addresses developed and developing technologies. The report contains a description of each technology, with advantages and disadvantages, status, and performance and cost data.

Intrinsic Remediation of a Chromium Contaminated Wetland by Biogeochemical Stabilization
G.A. Icopini, D.T. Long, R.J. Ellis and T.L. Marsh
Proceedings of the 10th International Conference on Environmental Science and Technology
Kos island, Greece, 5 - 7 September 2007,A-520

This article discusses the conditions necessary to leave chromium contaminated soil in place.

Low-Level Hexavalent Chromium Treatment Options: Bench-Scale Evaluation
P. Brandhuber, M. Frey, M. McGuire, P.F. Chao, C. Seidel, G. Amy, J. Yoon, L. McNeill, and K. Banerjee.
IWA Pub., London. AwwaRF Report 91042F, ISBN: 1843399245, 212 pp, 2005.

Researchers investigated nearly all of the potential methods of controlling Cr(VI), via either technologies that remove it directly (adsorption, anion exchange, membrane filtration) or those that remove Cr(III), the reduced form of chromium (precipitation with membranes or coagulation and precipitation with conventional or membrane filters).

Metals in Soils 1998 Technology Status Report: Soil Washing and the Emerging Technologies of Phytoremediation, Electrokinetics, In-Situ Stabilization/Inplace Inactivation
Interstate Technology and Regulatory Council (ITRC), MIS-6, 46 pp., 1999

Pollution Prevention and Control Technologies for Plating Operations, Section 6 - Wastewater Treatment, 6.2 CONVENTIONAL TREATMENT TECHNOLOGIES, 6.2.2 Chromium Reduction
National Metal Finishing Resource Center

This section provides a discussion of the advantages and limitations of different reduction techniques for the ex situ treatment of wastewater contaminated with hexavalent chromium.

Recent Developments for In Situ Treatment of Metal Contaminated Soils
U.S. Environmental Protection Agency, Technology Innovation Office.
EPA 542-R-97-004, 1997
Contact: John Kingscott, kingscott.john@epa.gov

This report presents an overview of four commercial applications of technologies for in situ soil treatment: electrokinetics, phytoremediation, soil flushing, and in situ solidification/ stabilization.

Remediation of Metals-Contaminated Soils and Groundwater. Technology Evaluation Report
Cynthia R. Evanko and David A. Dzombak, Carnegie Mellon Univ., Pittsburgh, PA.
Ground-Water Remediation Technologies Analysis Center (GWRTAC), TE-97-01, 61 pp, 1997

General overview of in situ and ex situ treatment technologies.

Site Characterization to Support Use of Monitored Natural Attenuation for Remediation of Inorganic Contaminants in Ground Water
R.G. Ford, R.T. Wilkin, and S. Acree.
EPA 600-R-08-114, 16 pp, 2008

This Issue Paper highlights at what stage of the process solid-phase characterization techniques need to be implemented during site characterization and describes two case studies (one site affected by arsenic, lead, and chromium, and the other by uranium) where the results of these techniques were critical to evaluation of MNA as a potential component of ground-water cleanup.

Bioremediation

Bioremediation of Arsenic, Chromium, Lead, and Mercury
2004

This document was prepared by Adebowale Adeniji, a National Network of Environmental Management studies grantee, under a fellowship from the U.S. Environmental Protection Agency. This paper addresses the status of the application of biological treatment to clean up hazardous metals from the earth's subsurface.

In Situ Long-Term Reductive Bioimmobilization of Cr(VI) in Groundwater Using Hydrogen Release Compound
B. Faybishenko, T.C. Hazen, P.E. Long, et al.
LBNL-1799E, 21 pp, 2009

A field experiment at Hanford is testing the effectiveness of long-term, in situ bioimmobilization of toxic and soluble Cr(VI) in groundwater using HRC, a slow-release glycerol polylactate. A single HRC injection into groundwater stimulated an increase in biomass, a depletion of the terminal electron acceptors (nitrate, dissolved oxygen, and sulfate), and an increase in iron, resulting in a significant decrease in soluble Cr(VI). The Cr(VI) concentration has remained below the background concentration in the downgradient pumping/monitoring well, and below the detection limit in the injection well for more than 3 years after the HRC injection. The degree of sustainability is under study.

Low temperature reduction of hexavalent chromium by a microbial enrichment consortium and a novel strain of Arthrobacter aurescens
Rene' Horton, William Apel, Vicki Thompson, and Peter Sheridan
BMC Microbiol, v.6; 2006

This paper describes laboratory tests to determine the effectiveness of microbial reduction of hexavalent chromium at the DOE Hanford facility. The article concludes that A. aurescens, indigenous to the subsurface, has the potential to be a predominant metal reducer in enhanced, in situ subsurface bioremediation efforts involving Cr(VI).

Mechanism of hexavalent chromium detoxification by microorganisms and bioremediation application potential: A review
K.H. Cheunga and Ji-Dong Gu
International Biodeterioration & Biodegradation Volume 59, Issue 1, January 2007, pp 8-15

A review of aerobic and anaerobic microbes that are capable of reducing Cr(VI) to Cr(III).

Reduction of chromate by cell-free extract of Brucella sp. isolated from Cr(VI) contaminated sites
Urvashi Thackera, Rasesh Parikhb, Yogesh Shoucheb and Datta Madamwara
Bioresource Technology Volume 98, Issue 8, May 2007, pp 1541-1547

This article discusses the potential use of Brucella sp to reduce hexavalent chromium to trivalent. Results indicate 100 percent reduction at 50 mg/L and approximately 42 percent at 300 mg/L.

Stimulation of in situ bioprecipitation for the removal of hexavalent chromium from contaminated groundwater
K. Vanbroekhoven, Y. Vermoortel, L. Diels, and J. Gemoets
IMWA Symposium 2007: Water in Mining Environments, 27th - 31st May 2007, Cagliari, Italy

This article describes a pilot study to determine the best carbon source for biostimulation to produce reducing conditions that transform hexavalent chromium to trivalent with a resulting precipitation of Cr(OH)3. Lactate was found to be the most efficient carbon source.

Study of CR(VI) Detoxification by Basalt Inhabiting Bacteria Using NAA and ESR Methods
N. Ya. Tsivakhashvili, T. L. Kalabegishvili. E. I. Kirkesali, L. M. Mosulishvili, M. V. Frontasyeva, S. S. Pavlov, N.G. Aksenova, and H.-Y. N. Holman
Proceedings of the 2nd Environmental Physics Conference, 18-22 Feb. 2006, Alexandria, Egypt

A well pronounced correlation is discussed of ability of the bacteria (Arthrobacter oxydans isolated from Columbia basalts) to accumulate Cr(VI) and to reduce Cr(V) to Cr(III) observed in our experiments.

Study of Microbial Chromium(VI) Reduction by Electron Energy
T.L. Daulton, B.J. Little, and J.M. Jones-Meehan.
2002 NRL Review, NRL/PU/5211-02-442, p. 115-117, May 2002

This article demonstrates the application of electron energy loss spectroscopy for the determination of metal oxidation state in studies of microbial reduction.

Ex Situ Treatment

Acid Extraction Treatment System for Treatment of Metal Contaminated Soils
Stephen W. Paff, Brian Bosilovich, and Nicholas J. Kardos, Center for Hazardous Materials Research
Pittsburgh, PA. EPA 540-R-94-513, 58 pp, 1994

This Superfund Innovative Technologies Evaluation report evaluates the effectiveness of an ex situ soil washing technology for the removal of heavy metals from soils.

San Fernando Valley Superfund Sites, Area 1: North Hollywood and Burbank, California
U.S. EPA Region 9 Web site.

The groundwater beneath the San Fernando Valley Area 1 is contaminated with TCE and PCE. In addition, EPA has detected Cr(VI) and 1,4-dioxane, which the existing groundwater VOCs treatment system is not designed to address. The 2009 Second Interim Remedy adds wellhead treatment systems to remove hexavalent chromium and 1,4-dioxane. The treatment technology for 1,4-dioxane is a UV light and hydrogen peroxide advanced oxidation process. The 2009 Focused Feasibility Study identifies the preferred technology for Cr(VI) as ferrous iron reduction with microfiltration. Alternatively, an anion-exchange-based treatment process could be installed if pilot test results expected from the groundwater operable unit in 2010 demonstrate that the process is effective and does not produce other problematic organic compounds. The Area 1 page provides access to the technical reports, and the San Fernando Valley (All Areas) page contains additional monitoring data and the presentations from the March 10, 2008, San Fernando Valley Chromium Workshop.

Sol-Gel Stabilization of Heavy Metal Waste
Donald Cropek, P. Kemme, J. Day, J. Barrios, Construction Engineering Research Lab (Army), Champaign, IL.
Report No: CERL-TR-00-6, NTIS: ADA375073, 22 pp, Feb 2000
Contact: Donald Cropek, Donald.M.Cropek@erdc.usace.army.mil

Sol-gel chemistry is a low-temperature means to make glass that chemically incorporates heavy metals in a glass matrix rather than merely encapsulating them. This report contains a recipe formulated for immobilizing lead in glass by the sol-gel process and discusses the merits of the process. Test results showed that sol-gel processing stabilized some lead from solutions and encapsulated other metals (including chromium) in a glass matrix. The testers found sol-gel was found to be too sensitive to chemistry, too limited in application, and too expensive to compete with current S/S processes.

In Situ Injection

The California Regional Water Quality Control Board, Los Angeles Region in ORDER NO. R4-2007-0019 provides a Table of chemicals that can be used to reduce hexavalent chromium to trivalent chromium.

100-D Area In Situ Redox Treatability Test for Chromate-Contaminated Groundwater
M.D. Williams, V.R. Vermeul, J.E. Szecsody, J.S. Fruchter. Pacific Northwest National Lab., Richland, WA.
PNNL-13349, 173 pp., Oct 2000
Contact: Mark Williams, mark.d.williams@pnl.gov

A treatability test was conducted to determine the effectiveness of In Situ Redox Manipulation (ISRM) technology on dissolved chromate [Cr(VI)] in groundwater at the 100 D Area of DOE's Hanford Site in southeastern Washington State. ISRM technology involves creating a permeable subsurface treatment zone by injecting aqueous sodium dithionite into the aquifer and then withdrawing the reaction products, thereby reducing ferric iron [Fe(III)] to ferrous iron [Fe(II)] within the aquifer sediments. The treatment zone reduces mobile chromate in groundwater to an insoluble form.

Calcium polysulfide remediation of hexavalent chromium contamination from chromite ore processing residue
Margaret C. Graham, John G. Farmer, Peter Anderson, Edward Paterson, Stephen Hillier, David G. Lumsdon and Richard J.F. Bewley

This article discusses laboratory column studies that show when ferrous sulfate fails to reduce chromate, calcium polysulfide (CaS_x) may be a better choice.

Development and validation of a model of bio-barriers for remediation of Cr(VI) contaminated aquifers using laboratory column experiments
T. Shashidhar, S. Murty Bhallamudi, Ligy Philip
Journal of Hazardous Materials 2007 Jul 16;145(3):437-52

Column experiments were performed to demonstrate the effectiveness of a biobarrier (molasses) in reducing Cr(VI) to Cr(III).

FY2003 Annual Summary Report for the In Situ Redox Manipulation Operations
R.F. Raidl and G.G. Kelty.
DOE/RL-2004-06, OSTI: DE00825446, 85 pp., May 2004.

This is the fourth annual progress and performance report (October 2002 through September 2003) to discuss the In Situ Redox Manipulation (ISRM) interim remedial action to address a hexavalent chromium plume at the Hanford 100-HR-3 Operable Unit. Implementation of the ISRM technology involves creating a permeable subsurface treatment zone by injecting sodium dithionite into the aquifer, which creates a chemically reduced environment. Hexavalent chromium passing through the treatment zone is reduced to less toxic and less mobile trivalent chromium.

In Situ Gaseous Reduction Pilot Demonstration ? Final Report
E.C. Thornton, J.T. Giblin, T.J Gilmore, K.B. Olsen, J.M. Phelan, and R.D. Miller, Pacific Northwest National Laboratory, Richland, WA.
PNNL-12121, 95 pp., 1999
Contact: Edward Thornton, edward.thornton@pnl.gov

This report discusses the use of dilute hydrogen sulfide to treat hexavalent chromium in the vadose zone. Final performance assessment of the demonstration is presented herein based on the analysis of the post treatment characterization samples for Cr(VI) and comparison of the results to the pretreatment data. This information indicates that 70% of the Cr(VI) was reduced. In particular, the zone of highest Cr(VI) concentration, located at a depth of 4 to 10 & was nearly completely treated, with Cr(VI) concentrations of soil samples decreasing from an average of 8.1 mg/kg before treatment to 1.14 mg/kg after treatment. However, a zone of lower contamination (from 10 to 16 ft) was largely unaffected. It is concluded that the treatment gas mixture was largely channeled through the upper zone and bypassed the less-permeable, lower zone. .Treatment of the lower zone could probably be completed, if necessary, through injection of gas into the zone through a borehole specifically screened over this interval.

In Situ Gaseous Reduction System. Innovative Technology Summary Report
U.S. DOE, Office of Science and Technology. DOE/EM-0521, 24 pp, Apr 2000
Contact: Edward Thornton, edward.thornton@pnl.gov

Summary report on using dilute hydrogen sulfide gas to treat hexavalent chromium in the vadose zone.

In Situ Groundwater MOP-UP
Biopraxis, Inc., for U.S. DOE, Federal Energy Technology Center, Morgantown, WV.
DOE/MC/33090-1, 92 pp., 1998

This report describes feasibility tests that showed MOP-UP^® able to remove all detectable traces of a wide variety of metals, such as Hg, Pb, Cd, Cu, Cr(VI), As, Ba, Zn, and Al, and take U into the low parts per trillions, in heavily polluted groundwater, with little effort needed to optimize the reagent formulation.

In Situ Redox Manipulation Permeable Reactive Barrier Emplacement: Final Report, Frontier Hard Chrome Superfund Site, Vancouver, WA
V.R. Vermeul, M.L. Rockhold, B.N. Bjornstad, J.E. Szecsody, C.J. Murray, M.D. Williams, D.R. Newcomer, and Y. Xie.
PNWD-3361, 107 pp + separate appendices, 2004

This report documents results from the emplacement of an in situ redox manipulation (ISRM) treatment zone for the remediation of chromate-contaminated ground water. Additional information: Groundwater Monitoring Network Optimization (2007); 5-Year Review (2008).

NO. R4-2007-0019, Revised General Waste Discharge Requirements for Groundwater Remediation at Petroleum Hydrocarbon Fuel, Volatile Organic Compound and/or Hexavalent Chromium Impacted Sites (FILE NO. 01-116)
State of California, California Regional Water Quality Control Board, Los Angeles Region

Provides, among other things, a discussion of materials that can be used for in-situ remediation of hexavalent chromium.

Reductive immobilization of chromate in water and soil using stabilized iron nanoparticles
Yinhui Xu and Dongye Zhao
Water Research Volume 41, Issue 10, May 2007, Pages 2101-2108

This article discusses laboratory batch and column experiments using zero-valent iron (ZVI) nanoparticles for in situ reductive immobilization of Cr(VI) in water and a sandy loam soil. The treatment reduced the TCLP leachability of Cr(VI) in the soil by 90%.

Removal of hexavalent chromium from aqueous solution by iron nanoparticles
Shao-feng Niu, Yong Liu, Xin-hua Xu, and Zhang-hua Lou
J Zhejiang Univ Sci B. 2005 October; 6(10): 1022-1027

This article discusses delivery solutions for zerovalent iron and comes to the conclusion that the order of reactivity was starch-stabilized Fe⁰ nanoparticles>Fe⁰ nanoparticles>Fe⁰ powder>Fe⁰ filings. The starch treatment slows down the initial high reactivity, and prevents rapid agglomeration that results in the formation of numerous large particles and rapid loss in reactivity. Electrochemical analysis of the reaction process led to the conclusion that Cr(OH)3 should be the final product of Cr(VI).

Second Five-Year Review Report for the Odessa Chromium I Superfund Site Odessa, Ector County, Texas, September 2006
U.S. EPA Region 6

This review describes the progress of using FeSO₄ and MRC™ for the remediation of a hexavalent chromium plume.

Successful Implementation of the In Situ Gaseous Reduction Approach for Vadose Zone Remediation
Edward C. Thornton, Tyler J Gilmore, Khris B. Olsen, and Ronald Schalla

This paper describes the use of dilute hydrogen sulfide gas to reduce hexavalent chromium to trivalent chromium in the vadose zone.

Permeable Reactive Barriers

Biosorption of hexavalent chromium using tamarind (Tamarindus indica) fruit shell-a comparative study
Srinivasa Rao Popuri, Ajithapriya Jammala, Kachireddy Venkata Naga Suresh Reddy, Krishnaiah Abburi
Electronic Journal of Biotechnology, Vol. 10 No. 3, Issue of July 15, 2007

Laboratory study that shows that tamarind shells are a viable media for sorbing hexavalent chromium from solution.

Development of Humasorb^TM—a Coal Derived Humic Acid for Removal of Metals and Organic Contaminants from Groundwater
H.G. Sanjay, A.K. Fataftah, D.S. Walia, K.C. Srivastava, ARCTECH, Inc., Chantilly, VA.
DE-AR21-95MC32114-10, 119 pp, May 2000
Contact: H. G. Sanjay, envrtech@arctech.com

Humasorb^TM is designed for use in situ in permeable reactive barriers, though mobile treatment systems containing it have been tested.

In Situ Permeable Reactive Barrier for the Treatment of Hexavalent Chromium and Trichloroethylene in Ground Water:
Contact: David W. Blowes, blowes@sciborg.uwaterloo.ca
Volume 1. Design and Installation, EPA 600-R-99-095A, 128 pp., 1999
Volume 2. Performance Monitoring, EPA 600-R-99-095B, 240 pp., 1999
Volume 3. Multicomponent Reactive Transport Modeling, EPA 600-R-99-095C, 52 pp., 1999
D.W. Blowes, R.W. Gillham, C.J. Ptacek, R.W. Puls, T.A. Bennett.

This report describes the installation and performance of a 46 m long, 7.3 m deep, and 0.6 m wide permeable subsurface reactive wall at the U.S. Coast Guard (USCG) Support Center, near Elizabeth City, North Carolina, in June 1996. The reactive wall was designed to remediate hexavalent chromium [Cr(VI)] contaminated ground water at the site, in addition to treating portions of a larger overlapping trichloroethylene (TCE) ground-water plume which has not yet been fully characterized. The wall was installed in approximately 6 hours using a continuous trenching technique, which simultaneously removed aquifer sediments and installed the porous reactive medium. The reactive medium was composed entirely of granular iron, with an average grain size (d50) of 0.4 mm.

Permeable Reactive Subsurface Barriers for the Interception and Remediation of Chlorinated Hydrocarbon and Chromium(VI) Plumes in Ground Water
EPA 600-F-97-008, July 1997
Contact: Robert W. Puls, puls.robert@epa.gov

Surface-Altered Zeolites as Permeable Barriers for In Situ Treatment of Contaminated Groundwater
R.S. Bowman, Z. Li, S.J. Roy, T. Burt, T.L. Johnson, R.L. Johnson.
DE-AR21-95MC32108-02, 61 pp, 1999
Contact: Robert S. Bowman, bowman@nmt.edu

This report describes two pilot-scale tests of surfactant-modified zeolite (SMZ) permeable barriers conducted at the Large Experimental Aquifer Facility of the Oregon Graduate Institute on groundwater contaminated with chromate and PCE.

Federal Remediation Technology Roundtable Technology Cost and Performance Reports

Federal Remediation Technology Roundtable Technology Cost and Performance Reports

Literature References

Technology Innovation News Survey Archives
The Technology Innovation News Survey archive contains resources gathered from published material and gray literature relevant to the research, development, testing, and application of innovative technologies for the remediation of hazardous waste sites. The collected abstracts date from 1998 to the present, and the archive is updated twice each month.

U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

Chromium VI

Treatment Technologies