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

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Chromium VI

Treatment Technologies


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, 2012.

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

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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).

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

MIS-4, 42 pp, 1997

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

MIS-5, 33 pp, 1997

Adobe PDF LogoEngineering 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,

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).

Adobe PDF LogoEnvironmental 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,

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)).

Adobe PDF LogoField, Laboratory and Modeling Evidence for Strong Attenuation of a Cr(VI) Plume in a Mudstone Aquifer Due to Matrix Diffusion and Reaction Processes
Chapman, S., B. Parker, T. Al, R. Wilkin, D. Cutt, K. Mishkin, and S. Nelson.
Soil Systems 5(18)(2021)

Both conventional and high-resolution field and laboratory methods were used to investigate processes that attenuate a Cr(VI) plume in sedimentary bedrock. Cr(VI) concentrations in the plume at a former industrial facility declined by more than three orders of magnitude over 900 m downgradient. Internal plume concentrations generally are stable or declining due to diffusive and reactive transport in the low-permeability matrix as fluxes from the source dissipate due to natural depletion and active remediation. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates. Field characterization data for the fracture network and matrix properties were used to inform 2-D numerical model simulations that quantify attenuation due to diffusion and reaction processes. The field, laboratory, and modeling evidence demonstrate effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer.

Adobe PDF LogoHexavalent Chromium Removal: Research Project Report to the California Department of Public Health
City of Glendale, California, Dept. of Water and Power, 161 pp, 2013

In spring 2010, the city of Glendale, CA, constructed two demonstration facilities consisting of a 425 gpm treatment using weak-base ion exchange (WBA) and a 100 gpm system using reduction/coagulation/filtration (RCF). The WBA resin converts Cr(VI) to Cr(III), retains Cr(III) on the resin, and can achieve levels <1 ppb Cr(VI), although breakthrough is relatively quick, and total Cr effluent concentrations exceed 1 ppb within a short timeframe. Testing also revealed that the resin can leach formaldehyde at startup (requiring pretreatment) and accumulate uranium. The RCF coagulation and filtration processes are similar to conventional water treatment, but ferrous sulfate (rather than ferric iron) is used to reduce Cr(VI) to Cr(III), in the process producing iron floc with which the Cr(III) adsorbs or coprecipitates. The RCF process with granular media filtration can reliably achieve Cr(VI) concentrations <1 ppb and total Cr concentrations <5 ppb. Due to the multiple treatment process steps, RCF is relatively labor intensive. Both systems achieved the target chromium level of 5 ppb. The RCF was shut down in July 2012, and the WBA continues to operate. Additional information: Supporting documents

Adobe PDF LogoIn-Situ Chromium Treatability Study Results Report, Nevada Environmental Response Trust Site, Henderson, Nevada: Revision 1
Nevada Environmental Response Trust, Chicago, IL. 1139 pp, 2018

For the biological reduction treatability study (Nov. 2016-Oct. 2017) in the Central Retention Basin, three separate injection events of carbon substrates—EOSPRO®, industrial sugar wastewater, granular sugar and/or molasses—were conducted to promote in situ biological reduction of Cr(VI). For the chemical reduction study conducted August 7-8, 2017, the injection and monitoring wells installed as part of the Ammonium Perchlorate Area Up and Down Flushing Treatability Study were used for a single chemical injection event of a total of 600 gal of a calcium polysulfide solution.

In Situ 'Deliverability' Trials Using Calcium Polysulphide to Treat Chromium Contamination at Shawfield, Glasgow
Bewley, R. and G. Sojka.
CL:AIRE (Contaminated Land: Applications in Real Environments), Technology Demonstration Project Bulletin TDP30, 8 pp, 2013

Following earlier field trials that indicated the effectiveness of calcium polysulfide (CaSx) application in reducing Cr(VI) associated with chromite ore processing residue, another field trial was conducted in 2009 to identify the most effective CaSx delivery mechanism into the subsurface. The methods investigated for CaSx delivery were (1) a groundwater recirculation system (which also achieved situ flushing of contaminated soil); (2) direct-push injection using close grid spacing; and (3) soil mixing. All three trials provided evidence of total Cr mobilization as a combination of chemical-physical action. [NOTE: The bulletin is available without charge on the CL:AIRE website to registered users (also free) at]

Adobe PDF LogoIn 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,

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.

Adobe PDF LogoIntrinsic 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.

Adobe PDF LogoInvestigation and Remediation of Plating Facilities
Bekele, T., C. Bucklin, K. Burger, S. Martinez, L. Parnass, B. Renzi, E. Rodriguez, M. Schum, and P. Wong.
CalEPA, Department of Toxic Substances Control (DTSC). 139 pp, 2011

This document is a reference text for corrective action and cleanup at sites in California affected by releases from plating operations, particularly impacts from Cr(VI), other heavy metals, and VOCs. This guide provides recommendations for characterizing contamination nature and extent, developing a conceptual site model, and collecting data needed to support the cleanup alternatives. It also discusses characterizing risk and establishing cleanup goals; applying proven technologies and identifying other likely technologies for addressing Cr(VI) in soil and Cr(VI) and VOCs in groundwater; considerations for controlling site conditions, cleanup, and closure; and potentially applicable long-term stewardship requirements.

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).

Adobe PDF LogoMetals 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

Adobe PDF LogoPG&E Topock Compressor Station, Needles, California: Revised Groundwater Corrective Measures Implementation/Remedial Design Work Plan for SWMU 1/AOC 1 and AOC 10
Pacific Gas and Electric Company, 312 pp, Nov 2011

The selected remedy for Cr(VI) in groundwater at SWMU 1/AOC 1 and AOC 10 near the Compressor Station combines in situ reduction with fresh-water flushing in an in situ reactive zone with injection of an organic carbon source to promote biological reduction of Cr(VI) to Cr(III). Fresh and carbon-amended water will be injected alternately upgradient of the plume to mobilize Cr from soil and provide nutrients to the treatment zone. MNA will provide a long-term component for any residual Cr. This well-documented project has a large dedicated website.

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.

Adobe PDF LogoProven Technologies and Remedies Guidance: Remediation of Metals in Soil
Burger, K., P. Carpenter, M. Finch, H. Muniz-Ghazi, D. Oudiz, K. Shaddy, and J. Sotelo.
California Department of Toxic Substances Control, 420 pp, 2008

This guidance streamlines the cleanup process by (1) limiting the number of evaluated technologies to excavation/disposal and containment/capping; (2) facilitating remedy implementation; and (3) facilitating documentation and administrative processes. The focus is on commonly encountered metal contaminants: arsenic, chromium, lead, and mercury. This approach is not intended to replace the evaluation of innovative and new technologies.

Adobe PDF LogoRecent Developments for In Situ Treatment of Metal Contaminated Soils
U.S. Environmental Protection Agency, Technology Innovation Office.
EPA 542-R-97-004, 1997

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.

Adobe PDF LogoRemediation 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.

Adobe PDF LogoSite 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.

Adobe PDF LogoSmalley Piper NPL Site
Annual Legislative Report for July 1, 2012 - June 30, 2013. Tennessee Department of Environment and Conservation, Division of Remediation, p 7, 2013

Industrial activities conducted at the Smalley-Piper site (~9 acres in size) included the manufacture of magnesium battery casings utilizing caustic soda, acetic acid, and chromium acid, which contaminated soil, surface water pathways, and groundwater with Cr(VI). All on-site operations ceased in 2007. An amended Superfund State Contract (SSC) addresses the previously performed soil remedy of excavation and ex situ stabilization/solidification as specified in the 2008 RODAdobe PDF Logo and adds a soil flushing component. The original SSC addressing soil remedial action was performed at a cost of $1,982,915. The amended SSC has a total current estimated cost of $7,781,970, with a state 10% match of $778,197. The intent of the in situ flushing remedy is to reduce remaining Cr(VI) subsurface soil concentrations that might leach into groundwater. Water will be extracted by on-site recovery wells; treated by chemical reduction, precipitation, and ion-exchange treatment modules; and then re-injected into the former source area via an infiltration gallery. The system is expected to operate for one year. Construction of the treatment plant building is scheduled for December 2014, followed by the installation of the treatment equipment in January 2015 and system startup in March 2015. Additional information: EPA Region 4.

Adobe PDF LogoTechnology Performance Review: Selecting and Using Solidification/Stabilization Treatment for Site Remediation
U.S. EPA, National Risk Management Research Laboratory, Cincinnati, OH.
EPA 600-R-09-148, 28 pp, 2009

Solidification/stabilization (S/S) is used to prevent migration of contaminants from contaminated soil, sludge, and sediment. Solidification refers to a process that binds a contaminated medium with a reagent, such as Portland cement, changing its physical properties. Stabilization involves a chemical reaction that reduces the leachability of a waste. The effectiveness of S/S has been demonstrated for non-volatile metals (e.g., arsenic, chromium), radioactive materials, halogenated semivolatiles, non-halogenated nonvolatiles and semivolatiles, PCBs, and pesticides, and potentially dioxins/furans. For treating organic contaminants (e.g., creosote), the use of certain materials such as organophilic clay and activated carbon, either as a pretreatment or as additives in cement, can improve contaminant immobilization. This review addresses important factors to consider in the selection of S/S treatment and discusses its implementation at seven sites.

Adobe PDF LogoTreatability Study Work Plan: In Situ Soil Flushing Pilot, Nevada Environmental Response Trust Site, Henderson, Nevada. Revision 2
Nevada Division of Environmental Protection (NDEP), 190 pp, 2014

A groundwater extraction and treatment system (GWETS) has removed chromate since 1986 and perchlorate since 1998 from the site's groundwater under NDEP oversight. Collected groundwater is first treated to reduce chromate to Cr( III ) through a ferrous sulfate treatment system, and then the perchlorate is addressed in a series of fluidized bed reactors that contain perchlorate-reducing bacteria. Following treatment, groundwater is discharged to the Las Vegas Wash. This Work Plan details the pilot test conceptual design, preliminary lab-scale evaluations, and preliminary field work necessary for conducting an in situ soil flushing pilot test at the site. The proposed pilot testing continues and builds on a preliminary evaluation of soil flushing technology conducted in 2010. The testing program will evaluate the performance of alternative flushing liquids ( Lake Mead water versus GWETS effluent) and the potential for the technology to stimulate biodegradation of perchlorate in situ, prior to implementation at the field scale. Additional information: Other Reports.

Adobe PDF LogoTreatment of Cr(VI)-Containing Wastes in the South African Ferrochrome Industry: A Review of Currently Applied Methods
Beukes, J.P., P.G. van Zyl, and M. Ras.
Journal of the Southern African Institute of Mining and Metallurgy 112:347-352(2012)

This paper describes current Cr(VI) treatment strategies as investigated through a literature review and a questionnaire survey of South African ferrochrome producers. Although different treatment strategies are available to deal with Cr(VI)-containing waste, the most commonly implemented treatment strategy is the aqueous reduction of Cr(VI) with ferrous iron. The advantages and correct application of this strategy are covered alongside the disadvantages and pitfalls.


Adobe PDF LogoBioremediation of Arsenic, Chromium, Lead, and Mercury

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.

Enhanced Biostimulation Coupled with a Dynamic Groundwater Recirculation System for Cr(Vi) Removal from Groundwater: A Field-Scale Study (Abstract)
Song, X., Q. Wang, P. Jin, X. Chen, S. Tang, C. Wei, K. Li, X. Ding, Z. Tang, and H. Fu.
Science of The Total Environment 772:145495(2021)

Enhanced bioremediation of Cr(VI) was conducted in situ by coupling organic carbon (ethanol) with a dynamic groundwater recirculation (DGR)-based system in a field-scale study. The DGR system was applied to remove Cr(VI) from groundwater via enhanced flushing by the recirculation system and deliver the biostimulant to the heterogeneous subsurface environment, including a sand/cobble aquifer and a fractured bedrock aquifer. The combined extraction and bioreduction reduced Cr(VI) concentrations from 1,000-2,000 mg/L to below the clean-up goal of 0.1 mg/L within 52 days. The study evaluated bioremediation effectiveness and the relationship between microbial communities and geochemical parameters. Multiple-line of evidence demonstrated that introducing ethanol significantly stimulated various bacteria, including those responsible for denitrification, sulfate reduction, and Cr(VI) reduction, which contributed to establishing reducing conditions in both aquifers. Cr(VI) was removed from groundwater via combined physical removal mechanisms through the DGR system, and the bioreduction of Cr(VI) followed by precipitation. Competitive growth among Cr(VI)-reducing bacteria was induced by ethanol injection.

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.

Adobe PDF LogoStimulation 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.

Adobe PDF LogoStudy 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

Adobe PDF LogoAcid 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.

Adobe PDF LogoGroundwater Remediation at the 100-HR-3 Operable Unit, Hanford Site, Washington, USA
Smoot, J.L., F.H. Biebesheimer, J.A. Eluskie, T. Simpkin, A. Spiliotopoulos, M.J. Tonkin
CHPRC-01149-FP, Rev 0, 10 pp, Jan 2011 [Prepared for WM2011: Waste Management Conference, 27 February - 3 March, 2011, Phoenix, Arizona

The hexavalent chromium plume at the 100-HR-3 Groundwater Operable Unit at the Hanford Site is the largest plume of its type in the state of Washington, covering an area of approximately 2.7 sq mi. Concentrations range from 60,000 µg/L near the former dichromate transfer station in the 100-D Area to large areas of 20 to 100 µg/L across much of the plume area. Groundwater extraction and ion exchange treatment operations began in 1997 and continued into 2010 at a limited scale of ~200 gal/min. Remediation of groundwater has been fairly successful in reaching remedial action objectives (RAOs) of 20 µg/L over a limited region. In 2000, an in situ redox manipulation (ISRM) barrier was installed downgradient of a hotspot as a second remedy. Both pump and treat and the ISRM continue to operate, but the RAOs are still being exceeded over a large portion of the area. Following a 2008 remedial process optimization study, 1,400 gal/min of expanded treatment capacity is being installed to meet 2012 and 2020 target milestones for protection of the Columbia River and cleanup of the groundwater plumes.

First Five-Year Review Report for Valley Wood Preserving, Inc., Superfund Site, Turlock, CA
U.S. EPA Region 9, 91 pp, Sep 2009

The selected groundwater remedy for a migrating Cr(VI) plume in the 1991 ROD was electrochemical treatment in conjunction with existing pump and treat. During a 33-month (1998-2000) pilot study, extracted groundwater was treated via the existing electrochemical precipitation system, with addition of calcium polysulfide to the treated water prior to reinjection. The calcium polysulfide reacted with the Cr(VI) in situ, reducing it to Cr(III). The pilot essentially eliminated the Cr(VI) plume from most of the wells on site and all of the wells off site. Pursuant to ROD Amendment 2, in situ treatment for an arsenic groundwater plume was completed in October 2007 using injections of ViroBind(tm) F Blend reagent slurry to immobilize and incorporate arsenic permanently into ferrous iron minerals and to continue reduction of residual Cr(VI) to Cr(III). Arsenic concentrations fell by as much as 2 orders of magnitude after the treatment.

Remediation of a Hexavalent Chromium Release to Groundwater Using Ion-Specific Resins
Milkey, N.E., Tighe & Bond, Inc., Westfield, MA.
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy, Vol 15, Article 7, 12 pp, 2010

In March 1986, a chrome rinse line was pierced by an auger during installation of a monitoring well at an industrial electroplating facility, releasing Cr(VI) to the groundwater. A 2006 pilot test confirmed that ion-specific exchange filters were appropriate for the removal of Cr(VI) and nickel. Three Cr(VI)-specific resins and two nickel-specific resins were installed in 2008 in a remediation building at the site.

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.

Adobe PDF LogoSol-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,

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 TableAdobe PDF Logo of chemicals that can be used to reduce hexavalent chromium to trivalent chromium.

Adobe PDF Logo100-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,

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 (Abstract)
Margaret C. Graham, John G. Farmer, Peter Anderson, Edward Paterson, Stephen Hillier, David G. Lumsdon and Richard J.F. Bewley
Science of The Total Environment, Volume 364, Issues 1-3, 1 July 2006, Pages 32-44

This article discusses laboratory column studies that show when ferrous sulfate fails to reduce chromate, calcium polysulfide (CaSx) 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).

Adobe PDF LogoFY2003 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.

Adobe PDF LogoIn 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

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.

Adobe PDF LogoIn 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,

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

Adobe PDF LogoIn 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)Adobe PDF Logo; 5-Year Review (2008)Adobe PDF Logo; 2018 Close-Out ReportAdobe PDF Logo.

Adobe PDF LogoNO. 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.

Adobe PDF LogoPrecision National Plating Services, Inc.: Response Action Plan
U.S. EPA Region 3, 101 pp, July 2012

Precision National Plating Services, Inc. operated a chrome plating facility from 1958 to 1999 in Clarks Summit, PA. This response action plan gives the site background and describes the strategy for continued in situ chemical reduction (ISCR) of Cr(VI) in the site's overburden and bedrock. Following previous successful ISCR activities completed from 2008 through 2011, the proposed supplemental bedrock injections of calcium polysulfide (CaSx) are designed to treat the remaining Cr(VI) in the overburden and shallow bedrock beneath the former building slab and downgradient areas of the site. The final cleanup is expected to take several years. Additional information: Precision National Plating website

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).

Adobe PDF LogoSecond 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.

Adobe PDF LogoSuccessful 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.

Adobe PDF LogoThird Five-Year Review Report for Boomsnub/Airco Superfund Site, Hazel Dell, Washington
U.S. EPA Region 10, 141 pp, 2013

Cr(VI) and TCE were released to soil and groundwater at this Superfund site during historical commercial chrome plating (Boomsnub) and compressed gas production (Airco). In September 2006, a toe-of-plume pilot study was initiated for in situ reduction of residual contamination in an area believed to be located in the low-permeability silt layer at a depth of ~80-90 ft bgs. EHC-M™, a combination of controlled-release carbon and ZVI particles, was injected into the alluvial aquifer to stimulate reductive dechlorination of TCE and chemical reduction-precipitation of chromium. Post-remediation monitoring indicates EHC-M was effective at reducing TCE and chromium concentrations below cleanup levels. Additional information: Work plan for in situ treatment of areas of residual contaminationAdobe PDF Logo

Adobe PDF LogoVoluntary Cleanup Report: Cross Manufacturing, Inc., Lewis, Kansas
Kansas Dept. of Health and Environment, Bureau of Environmental Remediation, 215 pp, 2015

Past operations at the Cross plant included chrome plating. A voluntary cleanup in situ Cr reduction and fixation remedy was completed at the site between 2012 and 2015 to reduce the toxic, soluble, and mobile Cr(VI) species to the much less toxic and mobile Cr(III) species. The remedy was completed by delivering the reducing agent calcium polysulfide (CPS) by direct injection and through amendment infiltration galleries, with treatments performed in October 2014 and May 2015. This report describes the completed in situ Cr reduction and fixation remedy, performance monitoring, and site restoration activities.

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.

Adobe PDF LogoDevelopment of HumasorbTM—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,

HumasorbTM 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,
Adobe PDF LogoVolume 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.

Adobe PDF LogoPermeable 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,

Adobe PDF LogoSurface-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,

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.