This section is arranged in three parts. The first contains documents that describe/examine PRBs for multiple sites. The second section contains individual sites with PRB cleanup directed at inorganic contaminants. The third section contains individual sites with PRB cleanup directed at organic contaminants.

Multiple Sites

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Inorganics

Handbook of Groundwater Remediation Using Permeable Reactive Barriers: Applications to Radionuclides, Trace Metals, and Nutrients
Naftz, David, et al. (eds.). Academic Press, San Diego, CA. ISBN: 0125135637, 550 pp, 2002

This handbook offers numerous case studies to introduce the reader to current applications, innovations, and methods for using PRBs in the removal of inorganic contaminants from groundwater.

Mine Waste Technology Program: Permeable Treatment Wall Effectiveness Monitoring Project, Nevada Stewart Mine
McCloskey, A.L.
EPA 600-R-06-153, 100 pp (plus appendices A-F, 282 pp), 2007

This project demonstrates the effectiveness of Apatite II™ (cleaned fishbone) to remove metals (zinc, iron, manganese, lead, and cadmium) from water flowing from a mining site.

Arsenic

Field Application of a Permeable Reactive Barrier for Treatment of Arsenic in Ground Water
Wilkin, R.T., S.D. Acree, D.G. Beak, R.R. Ross, T.R. Lee, and C.J. Paul.
EPA 600-R-08-093, 81 pp, 2008

In June 2005, a pilot-scale PRB containing granular iron was installed at a former metal smelting facility near Helena, MT, to treat ground water contaminated with concentrations (>25 mg/L) of arsenite and arsenate. The barrier is 9.1 m long, 14 m deep, and 1.8 to 2.4 m wide (in the direction of ground-water flow). Within the PRB, As concentrations are 2 to <0.01 mg/L. After 2 years of operation, significant decreases in As concentrations are evident. This report covers site characterization, remedial design and implementation, and monitoring results for this pilot-scale PRB. Additional information: (Wilkin et al. 2009, Abstract)

Field Demonstration of Zerovalent Iron Treatment Technology in Parker Brothers Arroyo: Status Report
Texas Custodial Trust, El Paso, 94 pp, 2014

Environmental impacts from historical smelting operations are present within and outside the site of the former ASARCO smelter (El Paso, Texas). In Parker Brothers Arroyo, the site contractor completed construction of two in situ ZVI-based PRBs in October 2012 and the performance monitoring network in June 2013. This status report presents construction details for the PRBs with subsequent performance results. The objectives of the field demonstration are to verify the effectiveness of the ZVI PRB technology for concentrations of As, Sb, Se, and thallium above regulatory requirements at this site, initiate groundwater remediation, and provide data to support the final site-wide groundwater remedy. Additional information: Other Technical Reports.

Permeable Reactive Barriers for Treatment of As-Contaminated Groundwater (PPT)
Bain, J., David Blowes, and John Wilkens
Sudbury 2007 – Mining and the Environment

This PPT presentation discusses using basic oxygen furnace (BOF) slag as a permeable reactive barrier fill material for the treatment of arsenic. It concludes that PRBs composed of BOF slag and mixtures of ZVI with organics are effective for the treatment of arsenic in groundwater in a variety of environments.

Chromium

An In Situ Permeable Reactive Barrier for the Treatment of Hexavalent Chromium and Trichloroethylene in Ground Water
Blowes, D.W. et al.
EPA 600-R-99-095a, EPA 600-R-99-095b, and EPA 600-R-99-095c, 1999

A 46 m long, 7.3 m deep, and 0.6 m wide permeable subsurface reactive wall was installed 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 groundwater at the site, in addition to treating portions of a larger overlapping trichloroethylene (TCE) groundwater plume which had not yet been fully characterized.

• Volume 1: Design and Installation
  The site preparation, trenching installation, follow-up soil treatment, and overall project costs, using the selected reactive material and barrier configuration are described.
• Volume 2: Performance Monitoring
  This volume describes activities undertaken to monitor the barrier performance over a 2 year period. The results of the monitoring are reported.
• Volume 3: Multicomponent Reactive Transport Modeling
  Reactive transport modeling was conducted to describe the performance of the permeable reactive barrier at the U.S. Coast Guard Support Center near Elizabeth City, N.C. The multicomponent reactive transport model MIN3P was used for the simulations. The essential reactions contained in the conceptual model are aqueous complexation reactions, combined reduction-corrosion reactions between the treatment material zero-valent iron and the contaminants or other electron acceptors dissolved in the ambient groundwater and the precipitation of secondary minerals within the reactive barrier. The model results provide estimates of the potential effects of the consumption of zero-valent iron and the precipitation of secondary minerals on the long-term efficiency of the treatment system.

In Situ Permeable Reactive Barrier for Treatment of Contaminated Groundwater at the U.S. Coast Guard Support Center, Elizabeth City, North Carolina (1998)

The PRB used at this site consists of 450 tons of granular zero-valent iron keyed into an underlying low conductivity layer at a depth of approximately 22 ft bgs. The required residence time in the treatment zone has been estimated as 21 hours, based on a highest concentration scenario. The average velocity through the wall was reported as 0.2 to 0.4 ft/day. Analytical data from the first year of full-scale operation show that the cleanup goal for Cr+6 has been met, but not the goal for TCE. Several possible reasons are provided for the elevated TCE levels.

General Metals

A Permeable Reactive Barrier for Treatment of Heavy Metals
Ludwig, R. et al.
Ground Water, Vol 40, No 1 p 59-66, 2002

This paper describes a pilot application of a compost based permeable reactive barrier to treat acidic mine sulfide mineral affected groundwater (Cu, Cd, Co, Ni, and Zn). The barrier uses sulfate reducing bacteria to promote the precipitation of heavy metals as insoluble metal sulfides.

Field-Scale Demonstration of In Situ Immobilization of Heavy Metals by Injecting Iron Oxide Nanoparticle Adsorption Barriers in Groundwater
Mohammadian, S., B. Krok, A. Fritzsche, C. Bianco, T. Tosco, E. Cagigal, B. Mata, V. Gonzalez, M. Diez-Ortiz, V. Ramos, D. Montalvo, E. Smolders, R. Sethi, and R.U. Meckenstock. | Journal of Contaminant Hydrology 237:103741(2021)

An in situ adsorption barrier was constructed with colloidal iron oxide nanoparticles in a very heterogeneous, contaminated aquifer. Groundwater contaminants included up to 25 mg/L Zn, 1.3 mg/L Pb, 40 mg/L Cu, 0.1 mg/L Ni and other minor heavy metal pollutants below 1 mg/L, and sediment contaminants included>900 mg/kg Zn, >2000 mg/kg Pb, and >190 mg/kg Ni About 1,500 kg of goethite nanoparticles (461±266 nm diameter) were injected at low pressure into the aquifer through nine screened injection wells. In all wells, a radius of influence of at least 2.5 m was achieved within 8 h, creating an in situ barrier of 22×3×9 m. Despite the extremely high heavy metal contamination and strong aquifer heterogeneity, successful immobilization of contaminants was observed. The contaminant concentrations were strongly reduced immediately after the injection, and the abatement of the heavy metals continued for a total post-injection monitoring period of 189 days. Iron oxide particles were found to adsorb heavy metals even at pH values between 4 and 6, where low adsorption would have been expected.

Remediation of Zinc-Contaminated Groundwater by Iron Oxide In Situ Adsorption Barriers – From Lab to the Field
Krok, B., S. Mohammadian, H.M. Noll, C. Surau, S. Markwort, A. Fritzsche, M. Nachev, B. Sures, and R.U. Meckenstock.
Science of the Total Environment [Published online 18 October 2021 prior to print]

The steps and criteria, from lab tests to field studies, are presented to implement an in situ adsorption barrier to immobilize zinc successfully. Zinc adsorption to goethite nanoparticles was studied using groundwater and sediment samples from a contaminated site in batch and flow-through systems mimicking field conditions. The goethite nanoparticles had an in situ adsorption capacity of ~23 mg Zn/g Goethite. Transport experiments in sediment columns indicated an expected radius of influence of at least 2.8 m for the injection of goethite nanoparticles. Findings were validated in a pilot-scale field study, where an in situ adsorption barrier of ca. 11 m × 6 m × 4 m was implemented in a zinc-contaminated aquifer. The injected nanoparticles were irreversibly deposited at the desired location <24 h and were not dislocated with the groundwater flow. Dissolved zinc was effectively immobilized for ca. 90 days despite a constantly increasing inflow of zinc to the barrier and the short contact time between goethite and zinc. Zinc concentrations increased slowly downstream of the barrier, though the barrier still retained most of the zinc from the inflowing groundwater. The study demonstrated the applicability of goethite nanoparticles to immobilize heavy metals in situ and highlighted the criteria for upscaling laboratory-based determinants to field-scale.

Strontium

100-NR-2 Apatite Treatability Test: High-Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization
Vermeul, V.R., B.G. Fritz, J.S. Fruchter, J.E. Szecsody, and M.D. Williams.
PNNL-19572, 134 pp, 2010

An injectable PRB technology was developed at DOE's Hanford facility to sequester Sr-90 in groundwater through the in situ formation of calcium-phosphate mineral phases, specifically apatite, which incorporates Sr-90 into the chemical structure. The 300-ft treatability-test PRB was installed in 2008 on the downgradient edge of a Sr-90 plume beneath the Hanford site to reduce Sr-90 flux discharging to the Columbia River.

• 100-NR-2 Apatite Treatability Test: An update on Barrier Performance. PNNL-20252, 70 pp, 2011
• Hanford Apatite Treatability Test Report Errata: Apatite Mass Loading Calculation. PNNL-23367 , 20 pp, 2014
• An Injectable Apatite Permeable Reactive Barrier for In Situ ⁹⁰ Sr Immobilization. Vermeul, V.R., J.E. Szecsody, B.G. Fritz, M.D. Williams, R.C. Moore, and J.S. Fruchter. Groundwater Monitoring & Remediation 34(2):28-41(2014) (Abstract)

Geochemical Characterization and Longevity Estimates of a Permeable Reactive Barrier System Remediating a ⁹⁰Sr Plume
Hoppe, Jutta, Master's thesis, University of Waterloo, Waterloo, ON, Canada, 144 pp, 2012

In 1998, a "wall and curtain" PRB containing clinoptilolite was installed at the Chalk River Laboratories in Chalk River, Ontario, to prevent the discharge of a strontium-90 plume into a nearby swamp. After nearly 14 years of operation, refined estimates of the PRB's efficiency and longevity indicate the system is highly efficient in treating an average mass flux of >17,000 Bq/m²/day and could continue to function for 80 to 100 years.

Treatment Wall for Groundwater Mitigation at the West Valley Demonstration Project (WVDP)

An 850-ft-long trench filled with 2,000 tons of a reactive medium is being used to remove radioactive Sr-90 from the groundwater at the WVDP in New York State . The contamination originated from a leak in a process line during commercial nuclear fuel reprocessing (1966-1972). The treatment wall promotes ion exchange, chiefly by means of the zeolite mineral clinoptilolite in which the divalent Sr-90 replaces the monovalent cation of potassium or sodium within the mineral's lattice structure. First conceived as a pilot in the late 1990s, full-scale installation was completed by the end of 2010 using $8M in American Recovery and Reinvestment Act funding. Resources:

• Design and Installation of a Permeable Treatment Wall at the West Valley Demonstration Project to Mitigate Expansion of Strontium-90 Contaminated Groundwater (2011)
• Evaluation of a Natural Zeolite Permeable Treatment Wall in the Removal of Strontium-90 From Groundwater: Installation to Long-Term Performance (2012)
• Natural Zeolite Permeable Treatment Wall for Removing Sr-90 from Groundwater (2013)
• West Valley Demonstration Project Annual Site Environmental Report, Calendar Year 2012 (2013)

Uranium

Design, Construction, and Monitoring of a Permeable Reactive Barrier Technology for Use at Rocky Flats Environmental Technology Site (RFETS)
Dwyer, Brian P., Sandia National Labs., Albuquerque, NM, Report No: SAND2000-2702. NTIS: DE00767720. 65 pp, 2000

This report describes the testing of three reactive media: high carbon steel iron filings, an iron-silica alloy in the form of a foam aggregate, and a pellicular humic acid based sorbent mixed with sand to remediate groundwater containing uranium, TCE, PCE, carbon tetrachloride, americium, and vinyl chloride. The iron filings were chosen and a PRB was constructed at the 903 Mound Site Plume. The treatment system began full operation in December, 1998 and despite a few problems has been operational since. Results to date show complete removal of the contaminants of concern (COCS) prior to discharge to meet project requirements.

Fry Canyon, UT, USGS Project Home Page

Three different PRBs were installed at the demonstration site in 1997, respectively containing Cercona Bone Char Phosphate, Cercona foamed ZVI pellets, and amorphous ferric oxide. The project will utilize geochemical and hydrologic approaches to assess the performance of the PRBs toward the long-term remediation of the Fry Canyon tailings site.

• Field Demonstration of Permeable Reactive Barriers to Remove Dissolved Uranium from Groundwater, Fry Canyon, Utah, September 1997 through September 1998: Interim Report
• In Situ Permeable Reactive Barriers for Contaminated Groundwater at Fry Canyon (2000)
• Selected Hydrologic Data for the Field Demonstration of Three Permeable Reactive Barriers near Fry Canyon, Utah, 1996-2000

Performance Assessment and Recommendations for Rejuvenation of a Permeable Reactive Barrier: Cotter Corporation's Canyon City, Colorado, Uranium Mill
DOE-LM/GJ816-2005, ESL-RPT-2005-02, 130 pp, 2005

A ZVI PRB was installed in 2000 to treat molybdenum and uranium at the currently operating Cotter Corporation mill site. Though the barrier eventually failed for Mo, U concentrations remained at less than 0.006 mg/L. The ZVI became clogged by mineral precipitants, and modifications (e.g., a pretreatment zone composed of coarse gravel and ZVI) were suggested. Given the conditions experienced at the PRB in 2003, Cotter evaluated the system at years' end and subsequently initiated pumping of upgradient groundwater to the site's primary impoundment.

Permeable Reactive Barrier Facility at the Bodo Canyon Disposal Cell, Durango, Colorado
U.S. DOE, Office of Legacy Management, Grand Junction, CO.

A PRB facility was constructed at the Durango, Colorado, Disposal Site in 1995 to test PRB designs for passive remediation of uranium-contaminated groundwater via treatment of contaminated tailings water (leachate) issuing from a seep into a subsurface engineered collection gallery and drained by gravity to a lined retention basin for treatment at the site's downgradient boundary. Several PRBs (ZVI, copper wool, and steel wool) were used to treat As, Mo, Se, U, V, and Zn. The ZVI barrier operated from August 1999 until June 2004, when flow ceased from the seep and remediation was no longer needed. It maintained effluent uranium concentrations of less than 0.01 mg/L, and was highly effective in treating contaminants.

Further Documentation

Permeable Reactive Barrier at the Monticello Mill Tailings Site, Monticello, Utah
U.S. DOE, Office of Legacy Management, Grand Junction, CO.

In 1999, DOE installed a ZVI-containing PRB downgradient of the former uranium milling site at Monticello, UT. The PRB has been effective in reducing concentrations of As, Se, U, and V to nondetectable levels on the PRB's downgradient side, and Mo and nitrate to near nondetect. Soil-bentonite slurry walls direct groundwater to the PRB, but some contaminated groundwater is flowing around the south slurry wall. Methods that might be used to mend the gap on the south end of the slurry wall were investigated. There has been some evidence of barrier clogging, and chemical flushing of the barrier to remedy the clogging was investigated. In 2005, a supplemental treatment cell containing a mixture of ZVI and gravel was installed at the site.

Further Documentation

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Organics

Chlorinated Solvents

A Field Study of a Novel Permeable-Reactive-Biobarrier to Remediate Chlorinated Hydrocarbons Contaminated Groundwater
Liu, C., X. Chen, S. Wang, Y. Luo, W. Du, Y. Yin, and H. Guo. Environmental Pollution 351:124042(2024)

A novel three-layer permeable reactive barrier (PRB) material incorporating Fe0 and coconut shell biochar was field-scale tested at a chlorinated hydrocarbon (CH)-contaminated site. Monitoring data revealed conditions conducive to reductive dechlorination (low oxygen levels and a relatively neutral pH in the groundwater). The engineered PRB material consistently released organic carbon and iron, fostering CH-dechlorinating bacteria proliferation. Over 250 days, the pilot-scale PRB achieved CH removal efficiencies from 21.9%-99.6% for various CH compounds. Initially, CHs were predominantly eliminated through adsorption and iron-mediated reductive dechlorination, but microbial reductive dechlorination emerged as the predominant mechanism for sustained and long-term CH removal.

A Twenty-Five-Year Examination of Zerovalent Iron for Groundwater Remediation: The Elizabeth City, NC, Case Study
Wilkin, R., T. Lee, M. Sexton, S. Acree, R. Puls, D. Blowes, C. Kalinowski, J. Tilton, and L. Woods. | Twelfth International Conference on the Remediation of Chlorinated and Recalcitrant Compounds, 22-26 May Palm Springs, CA, 19 slides, 2022

The U.S. Coast Guard Support Center site in Elizabeth City, North Carolina, provides the longest available performance record for a permeable reactive barrier (PRB) utilizing zerovalent iron (ZVI) to treat chlorinated solvents and hexavalent chromium in groundwater. For several decades, utilization of in situ groundwater treatment technologies, such as PRBs, has grown, with a related overall decrease in the selection of aboveground pump-and-treat remedies. These trends reflect acceptance and reliance on the innovative remediation approaches for site cleanup developed and implemented during the 1980s and 1990s. The PRB technology is commonly considered a potential remedy at contaminated sites, and the largest uncertainty about its use is typically related to accurately predicting longevity. Long-term datasets on remedial performance help constrain potential effectiveness; however, these data need to be relatable to site conditions. The current state-of-the-art for in situ groundwater remediation requires combining knowledge about site geochemistry and hydrology with a mechanistic understanding of specific technologies to best match sites with technologies to improve outcomes.

A-Zone Aquifer ZVI Permeable Reactive Barrier Project, Hookston Station Site, Pleasant Hill, California: Final Construction Report
GeoSierra Environmental, Inc.
California Regional Water Quality Control Board, San Francisco Bay Region. 45 pp, Sep 2009

An iron PRB was installed in 2009 at an off-site location near the Hookston Station site to degrade TCE, cis-1,2-DCE, VC, and 1,1-DCE in site groundwater and limit their migration downgradient. Constructed using azimuth-controlled vertical hydrofracturing technology, the PRB consists of one continuous reactive zone of ZVI ~480 feet in length and ~32 feet in vertical height. Additional information: 2017 Status report ; CRWQCB Project Page

Allegany Ballistics Laboratory (US Navy), Mineral County, West Virginia Superfund Site

The PRB at this Superfund site consists of a wall of reactive media (zero valent iron) approximately 200 feet in length, 2 feet in width, and 17 feet in depth installed through the alluvial aquifer and keyed into the bedrock. The remedy for Site 5 (OU-2) was initiated in April 2006 and completed in June 2006. The contaminant of concern is TCE.

• The 2008 Five Year Review provides a discussion of the PRB
• General site information

Amendment Delivery Methodology for Permeable Reactive Barrier (PRB) Installation in Challenging Lithology at Shaw AFB
Simpson, G. | DCHWS East 2022 Spring Symposium, 30 March-1 April, Philadelphia, PA, 17 slides, 2022

he Shaw AFB, Environmental Restoration Program, has delivered several innovations, earning praise from the base leadership and the state regulatory agency. An innovative project was conducted when the leading edge of a TCE/PCE plume, that the main pump-treat-injection system could not contain, migrated 1.5 miles beyond the base boundary. A permeable reactive treatment barrier (PRB), 650 ft long, 20 ft wide, and ~30 ft thick, specifically designed to degrade chlorinated solvents, was installed about 100 feet below ground surface. The PRB was installed using the pre-drill technique GeoTap™, which used augers, air rotary or roto sonic techniques to total depth, a bentonite backfill, and direct push through the bentonite using direct push technology. Within the confines of the treatment barrier, BOS 100® aqueous slurries were injected into 130 temporary injection points, proactively intercepting and treating the plume's leading edge to prevent further uncontrolled impacts to downgradient parcels. The first semi-annual performance monitoring report recorded an average 38% reduction in TCE/PCE levels passing through the 20-year barrier.

An In Situ Permeable Reactive Barrier for the Treatment of Hexavalent Chromium and Trichloroethylene in Ground Water
Blowes, D.W. et al.
EPA 600-R-99-095a, EPA 600-R-99-095b, and EPA 600-R-99-095c, 1999

A 46 m long, 7.3 m deep, and 0.6 m wide permeable subsurface reactive wall was installed 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 groundwater at the site, in addition to treating portions of a larger overlapping trichloroethylene (TCE) groundwater plume which had not yet been fully characterized.

• Volume 1: Design and Installation
  The site preparation, trenching installation, follow-up soil treatment, and overall project costs, using the selected reactive material and barrier configuration are described.
• Volume 2: Performance Monitoring
  This volume describes activities undertaken to monitor the barrier performance over a 2 year period. The results of the monitoring are reported.
• Volume 3: Multicomponent Reactive Transport Modeling
  Reactive transport modeling was conducted to describe the performance of the permeable reactive barrier at the U.S. Coast Guard Support Center near Elizabeth City, N.C. The multicomponent reactive transport model MIN3P was used for the simulations. The essential reactions contained in the conceptual model are aqueous complexation reactions, combined reduction-corrosion reactions between the treatment material zero-valent iron and the contaminants or other electron acceptors dissolved in the ambient groundwater and the precipitation of secondary minerals within the reactive barrier. The model results provide estimates of the potential effects of the consumption of zero-valent iron and the precipitation of secondary minerals on the long-term efficiency of the treatment system.

Analysis of Long-Term Performance of Zero-Valent Iron Applications
Popovic, J., L. Cook, D Williamson, and R. Wilkin.
ESTCP Project ER-201589, 524 pp, 2018

The long-term performance of ZVI is detailed in this report as both a source-zone treatment and as a barrier treatment for chlorinated VOCs. The project approach consisted of desktop review and field assessment. The field assessment was conducted at two sites: (1) a ZVI PRB for dissolved-phase TCE/DCE plume control assessment at Allegany Ballistics Laboratory Site 5, and (2) ZVI introduction by soil mixing in a PCE/TCE/DCE source area at St. Louis Ordnance Plant OU1. Additional information: Executive Summary

Chlorinated Solvent Remediation at the Petro-Processors Superfund Site in Louisiana
Johnson, C., W.M. Moe, and P. Lee. ǀ Pacific Northwest National Laboratory RemPlex seminar, 72 minutes, 2022

Past practices at the Petro-Processors, Inc., Superfund site north of Baton Rouge involved the waste disposal of a mixture of liquid hydrocarbons and chlorinated organics. Multiple lines of evidence (modeling, microbial characterization, pilot-scale testing) have driven groundwater remedy decision-making and regulatory approval. This seminar presents information on remediation activities at two operable units (OUs) focusing on the characterization, remedy evaluation, microbial activity identification, and implementation of permeable reactive barriers for in situ bioremediation to provide enhanced attenuation at one of the OUs. The presentation is followed by a panel discussion that explores the use of molecular biology tools in remediation and the challenges of implementing enhanced attenuation remedies in the field.

Combined Remedy Treatment of Multi-Chemical Solvent Plume in Low Permeability Clay
Brab, B. ǀ 10th Annual AIPG Michigan Section Technical Workshop, 15-17 June, virtual, abstract only, 2021

A phased approach utilizing combined remedies was selected to remove contaminants, including halogenated solvents, methylisobutyl carbinol (MIBC), and NAPL in soil and groundwater at a former chemical plant. Remedies included 1) an off-site in-situ permeable reactive barrier utilizing Trap & Treat® BOS 100® to capture dissolved impacts and 2) shallow soil mixing using activated persulfate to mitigate unsaturated soil impacts. Trap & Treat® BOS 100® + ERD was utilized to mitigate saturated source mass soil and groundwater impacts and off-site sources during Phases 1 and 2. CAT 100 injections were also conducted in the source area. The presentation discusses the development of the CSM and the remedial action, including characterizing and injecting products into tighter units. Investigative efforts evolved to accommodate expansive clays during drilling and manage exposure to NAPL concentrations in the site source area soil. The use of a new and cutting-edge application of cometabolic synergy: granular activated carbon impregnated with metallic reactive iron coupled with an enhanced reductive chlorinating biological component is also discussed. Improved in-situ injection techniques were developed to increase effectiveness and installation throughout all planned phases. Site geology dictated multiple point installation to permit dissipation of injection pressure following completion of each injection interval.

Contamination Movement around a Permeable Reactive Barrier at Solid Waste Management Unit 12, Naval Weapons Station Charleston, North Charleston, South Carolina, 2009
Vroblesky, D.A., M.D. Petkewich, and K.J. Conlon.
U.S. Geological Survey Scientific Investigations Report 2010-5086, 84 pp, 2010

Chlorinated VOC (PCE, 1,1,1-TCA, TCE, cDCE, VC, 1,1-DCE, 1,2-DCA, and 1,1-DCA) groundwater contamination SWMU 12 at the Naval Weapons Station Charleston, SC, is being addressed in part by a ZVI PRB 130 ft long and 3 ft wide installed in December 2002. In early 2004, groundwater contaminants began moving around the southern end of the PRB. USGS is monitoring and documenting the interaction of PRB and groundwater. Additional information: 2004-2006 Report; 2006-2007 Report; 2008 Report

Design, Construction and Monitoring of a Permeable Reactive Barrier Technology for Use at Rocky Flats Environmental Technology Site (RFETS)
Dwyer, Brian P., Sandia National Labs., Albuquerque, NM, Report No: SAND2000-2702. NTIS: DE00767720. 65 pp, 2000

This report describes the testing of three reactive media: high carbon steel iron filings, an iron-silica alloy in the form of a foam aggregate, and a pellicular humic acid based sorbent mixed with sand to remediate groundwater containing uranium, TCE, PCE, carbon tetrachloride, americium, and vinyl chloride. The iron filings were chosen and a PRB was constructed at the 903 Mound Site Plume. The treatment system began full operation in December, 1998 and despite a few problems has been operational since. Results to date show complete removal of the contaminants of concern (COCS) prior to discharge to meet project requirements.

Design, Construction, and Monitoring of the Permeable Reactive Barrier in Area 5 at Dover Air Force Base
Gavaskar, Arun; Neeraj Gupta; Bruce Sass; Woong-Sang Yoon; Robert Janosy, Battelle, Columbus, OH. Report No: AFRL-ML-WP-TR-2000-4546. NTIS: ADA380005. 399 pp, 2000

The primary objective of this project was to test the performance of two different reactive media in the same aquifer. The PRB was installed in Area 5 at Dover Air Force Base, DE in December 1997 to treat a PCE plume and was monitored over 18 months of operation. The PRB is a funnel-and-gate system with two gates. Both gates contain granular iron as the reactive medium and were installed with the use of caissons. Gate 1 had a pretreatment zone (PTZ) consisting of 10% iron and sand, and Gate 2 had a PTZ consisting of 10% pyrite and sand. The PTZs were designed to remove dissolved oxygen before it entered the 100% iron reactive cell. The pyrite PTZ had the proposed benefit of pH control. However, monitoring showed that the reduced pH in the pyrite PTZ could not be sustained in the 100% iron reactive cell. The PRB is functioning as designed in terms of chlorinated solvent reduction, hydraulic performance, and geochemistry. The use of caissons was found to be a viable method for installing a PRB in the midst of several utility lines and in a relatively deep aquifer.

Emulsified Oil Bio-Barrier to Remediate TCE in the Distal Portion of a Groundwater Plume
Killeen, T., J. Ross, A. Willey, and K. Adams.
WM2020: Annual Waste Management Conference, 8-12 March, Phoenix, AZ, 23 slides, 2020

A non-time-critical removal action was designed at the Savannah River Site (SRS) to inject an emulsified oil mixture with a bioaugmentation culture to prevent TCE from discharging to surface water above maximum contaminant levels. The emulsified oil mixture is expected to sequester and then break down TCE through microbial biodegradation. At 15 locations, 8,290 L (2,190 gals) of an oil mixture, buffer, and chase water were injected into the subsurface creating two biobarriers. At each location, half of the oil mixture was injected, followed by 2 L (0.528 gals) of an enriched bioaugmentation culture, then the second half of the oil mixture was injected. Lastly, 151 L (40 gals) of buffer mixed with 575 L (200 gals) of dilution water was injected, followed by 1,135 L (300 gals) of chase water. SRS estimates the two emulsified oil barriers measure 73 m (240 ft) long, ~3 m (10 ft) high, and 4.9 m (16 ft) wide in the subsurface. Additional information: Slides

Ensuring the Continued Success of a Mulch Biowall at a Trichloroethylene-Contaminated Superfund Site: Lessons Learned
Ghandehari, S.S., S.-H. Cheng, C.J. Hapeman, A. Torrents, and B.V. Kjellerup. | Remediation [published online 3 August 2023 before print]

A biowall was installed at a TCE-contaminated landfill in Maryland in 2013 to promote the bioremediation of TCE and its degradation products. Six-year monitoring data indicated a steady removal of >99% TCE in groundwater at the wall, however, a concurrent buildup of intermediate byproducts was observed downgradient of the wall. The background of the site, remediation plan, and installation were assessed to identify the cause of the biowall’s inefficiency. Monitoring data, including the concentration of TCE and its degradation byproducts, and geochemical and physical characteristics were evaluated to understand project conditions and challenges and possible options to improve biowall efficacy. Additional information: 2023 Five Year Review

Evaluating Long-Term Impacts of Soil-Mixing Source-Zone Treatment Using Cryogenic Core Collection
Olson, M., W. Clayton, T. Sale, S. De Long, M. Irianni-Renno, and R. Johnson.
ESTCP Project ER-201587, 232 pp, 2017

This project focused on DNAPL source zone remediation using soil mixing with ZVI and bentonite, a technology referred to as ZVI-clay soil mixing. In November 2012, the soil mixing technology was implemented in a TCE DNAPL source zone at Site 17, Naval Support Facility Indian Head, MD. Four years of remediation performance data indicate that TCE concentrations in soil and groundwater within the treated-soil zone had been reduced by up to four and five orders of magnitude, respectively. Groundwater concentrations in portions of the former-DNAPL source-zone approached MCLs within four years of soil-mixing completion. To assess post-remediation potential for TCE concentrations to rebound, as well as effects of remediation on natural fate and transport processes, high-resolution data representing both high-permeability and low-permeability soil strata were collected using cryogenic core collection.

F.E. Warren Air Force Base, Cheyenne, Wyoming Superfund Site

As part of the groundwater remedy at this Superfund site, a three-section PRB wall was designed for the upper 15 feet of the aquifer at SS7 to minimize the TCE concentrations reaching Diamond Creek. Construction of the PRB wall was completed in September 1999 and included installation of an array of monitoring wells upgradient, within and downgradient of the PRB. Monitoring of the groundwater in these wells has been ongoing and indicates that the PRB wall has reduced the concentration of TCE in groundwater on the downgradient side of the PRB.

• The 2010 Five Year Review provides a discussion of the PRB
• General site information

Geochemical and Isotope Study of Trichloroethene Degradation in a Zero-Valent Iron Permeable Reactive Barrier: A Twenty-Two-Year Performance Evaluation
Wilkin, R.T., T.R. Lee, M.R. Sexton, S.D. Acree, R.W. Puls, D.W. Blowes, C. Kalinowski, J.M. Tilton, and L.L. Woods.
Environmental Science & Technology 53(1):296-306(2019)

This study provides a 22-yr record of in situ degradation of chlorinated organics by a granular iron PRB. Groundwater concentrations of TCE entering the PRB were as high as 10670 µg/L. Treatment efficiency ranged from 81 to >99%, and TCE concentrations from <1 µg/L to 165 µg/L were detected within and hydraulically down-gradient of the PRB. After 18 years, effluent TCE concentrations remained above the MCL along segments of the PRB exhibiting upward trending influent TCE. Methanogenesis is a sink for inorganic carbon in ZVI PRBs that competes with carbonate mineralization, and this process is important for understanding pore-space clogging and longevity of iron-based PRBs.

Improved Assessment and Performance Monitoring of a Biowall at a Chlorinated Solvent Site Using High-Resolution Passive Sampling
Garza-Rubalcava, U. P.B.Hatzinger, D. Schanzle, G. Lavorgna, P. Hedman, and W.A. Jackson.
Journal of Contaminant Hydrology 246:103962(2022)

High-resolution passive sampling and traditional groundwater monitoring wells (GWMW) were used to characterize a chlorinated solvent site and assess the effectiveness of a biowall (mulch, compost and sand) installed to remediate TCE. High-resolution passive profilers (HRPPs) were direct-driven upgradient, within, and downgradient of the biowall and near existing GWMWs. Compared with upgradient locations, the biowall was highly reducing, as higher densities of bacteria/genes capable of reductive dechlorination were present. While GWMW data indicated that TCE reductive transformation was incomplete as indicated by cis-DCE detected within and downgradient of the biowall, HRPP data indicated that the biowall completely transformed TCE to ethene in all areas except within a high-velocity groundwater interval where concentrations were reduced, but cis-DCE breakthrough was apparent. TCE concentrations upgradient of the biowall increased with depth where a low permeability zone exists that will likely remain as a long-term source. Although low concentrations of cis-DCE were present downgradient of the biowall, surfacing into a downgradient stream was not detected.

In Situ Chemical Reduction (ISCR) Technologies: Significance of Low eH Reactions
Dolfing, J., M. Van Eekert, A. Seech, J. Vogan, and J. Muellers.
Soil & Sediment Contamination, Vol 17 No 1, p 63-74, Jan 2008

In March 2005, 22,000 kg of ISCR reagent was injected to form an 82-m PRB across a plume of dissolved-phase carbon tetrachloride (CT) about 150 m downgradient of the suspected source area. The ISCR reagent slurry was injected at 126 injection points advanced via direct push. By August 2006, CT concentrations had decreased from > 1,600 ppb to < 5 ppb, achieving > 99% removal.

In Situ Treatment of BTEX And CVOC Under a Large Car Manufacturing Industrial Plant
Carboni, M., G. Leonard, and K. Maerten.
RemTech Europe 2020: European Conference on Remediation Market and Technologies, 21-25 September, virtual, 20 minutes, 2020

Following a successful pilot-scale injection at a contaminated area beneath an active automobile manufacturing plant, a full-scale barrier injection of Plumestop^® and Oxygen Release Compound to stimulate and maintain aerobic biodegradation of sorbed BTEX and consequential regeneration of the activated carbon barrier. The goal was to stop offsite migration of the plume. Implementation did not interrupt manufacturing operations. Reinjections were not needed due to the self-regenerating capability of the carbon through biodegradation, minimizing costs. Additional information: Slides; Case Study

Lessons Learned from One of the Largest "Traditional" ZVI PRBs Installed in North America
Sweet, B. ǀ SMART Remediation 31 March, Toronto, ON, 17 slides, 2022

This presentation shares lessons learned from the installation of one of the largest "traditional" zero-valent iron (ZVI) permeable reactive barriers (PRBs) in North America. The site is a former industrial facility with legacy chlorinated solvent issues, mainly TCE and daughter products. Managing off-site migration was critical to facilitating site redevelopment. Risk mitigation measures included installing a 400 m, ZVI-based PRB system to control plume migration. The site conditions necessitated the creative use of multiple installation procedures; the wall was installed via a blended approach utilizing direct push injection and trenching techniques to address the complex plume structure. Over 400,000 kgs of ZVI were installed across 335 m of linear injection points and 65 m of trenching to complete the PRB installation to depths of up to 9 m. The focus of this case study asks: How does a contractor install a PRB? What techniques are being used in the field and why? How can creative problem-solving be used to address technical and logistical challenges?

Long-Term Evaluation of Mulch Biowall Performance to Treat Chlorinated Solvents
Walker Jr., K.L., T.M. McGuire, D.T. Adamson, R.H. Anderson.
Groundwater Monitoring & Remediation [Published online 9 January 2020 prior to print]

Seven mulch biowalls were installed Altus Air Force Base to degrade CVOCs in site groundwater and limit their migration downgradient. Microbial sampling indicated high reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content of the mulch, elevated total organic carbon content in groundwater and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon for continued degradation. See longer abstract

Moffett Field

Permeable Reactive Barrier Cost and Performance Report
Naval Facilities Engineering Service Center.
TR-NAVFAC-ESC-EV-1207, 85 pp, 2012

A cost and performance evaluation of three full-scale PRBs installed at Navy sites also considered the remedy footprint for each PRB, using SiteWise(tm) to assess energy consumption, water consumption, generation of criteria air pollutants, and other metrics. The PRBs represent a range of installation techniques, reactive media, and target contaminants: (1) Granular-scale ZVI trench placement at NWIRP Dallas, Texas, for TCE and Cr(VI); (2) Mulch/vegetable oil biowall rock trencher installation at NWIRP McGregor, Texas, for perchlorate and TCE; and (3) Micro-scale ZVI pneumatic fracturing injection at Hunters Point Naval Shipyard, San Francisco, for chloroform and TCE.

Permeable Reactive Barrier Downgradient of the Southern Source Area, Former Tecumseh Products Company Site, Tecumseh, Michigan: Construction Documentation Report
U.S. EPA Region 5, 148 pp, 2012

The PRB was installed in May 2011. Site COCs include chlorinated VOCs (mainly TCE, TCA, and daughter products), SVOCs, 1,4-dioxane, metals, cyanide, and PCBs. Where the target treatment zone is relatively shallow, the design called for in situ soil blending to deliver DARAMEND(r) (a pelletized form of controlled-release carbon and ZVI) to the subsurface. The design included the use of injections to deliver ABC(r)+ (a patented mixture of ethyl lactate and glycerin, plus ZVI) to portions of the PRB farther beneath ground surface. ABC(r)+ also was used for shallow injections around an existing sewer pipe. Additional resources: Tecumseh website .

Permeable Reactive Wall Remediation of Chlorinated Hydrocarbons in Groundwater: ESTCP Cost and Performance Report (CU-9604)
1999, ESTCP

This document provides a brief account of the technology evaluation of a pilot-scale permeable reactive barrier that was installed at Moffett Field in April 1996. The objective was to capture and treat a small portion of the West Side Plume that contains chlorinated volatile organic compound (CVOC) contaminants, primarily trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), and perchloroethene (PCE). The reactive cell in the funnel-and-gate type barrier is composed of granular zero-valent iron. The flowthrough thickness of the reactive cell is 6 ft and it is lined on either side by 2 ft of pea gravel. The reactive cell and pea gravel comprise the gate, which is 10 ft-long and is flanked on each side by 20-foot long funnel walls. There were no indications during the 16 months of operation of any decline in the reactivity or hydraulic performance of the barrier.

Remediation of Benzene and 1,2-Dichloroethylene in Groundwater by Funnel and Gate Permeable Reactive Barrier (FGPRB): A Case Study
Gao, C., Q. Song, X. Li, L. Wang, Y. Zhai, X. Du, and W. Yin. ǀ Water 13:3336(2021)

A pilot test using a FGPRB was established downstream of a petrochemical site to clarify the impact on groundwater dynamic conditions. Results showed that groundwater concentrations of 1,2-DCE and benzene decreased to below the detection limit. Numerical simulation results indicated that both point source and area source pollution achieved a delay effect, extending the response time after establishing FGPRB from ~27 d to ~65 d. Changing the thickness and permeability coefficient had no obvious impact on the delay effect. A tracer test showed the average permeability coefficient of the medium from the injection well to the monitoring well decreased from 77.0 m/d to 31.2 m/d, and the average seepage velocity from the injection well to the monitoring well decreased from 0.19 m/d to 0.078 m/d. The max concentration time from the injection well to the monitoring well increased from ~10 d (before construction) to ~27 days (after construction). Results confirmed that the FGPRB changed the hydrodynamic conditions of groundwater and delayed the response time of pollutants in the monitoring well.

Remediation of Contaminated Groundwater Using Permeable Reactive Barriers (RESET)
Tuominen, S., T. Nysten, and J. Reinikainen.
Finnish Environment Institute website, 2014

The long-term performance of a pilot-scale PRB installed at the Orivesi (Finland) field site has been monitored since summer 2006 to evaluate the performance of the granular iron barrier in addressing chlorinated solvents (PCE, TCE, and their degradation products) released to the subsurface by a dry cleaner. The system has a funnel-and-gate configuration with an additional control well. Traditional open pit and cleat-supported excavation techniques were essentially the only available earthwork methods for barrier installation. The fracture zones in bedrock were filled with injection material to eliminate contaminated groundwater bypass below the PRB.

Report for Full-Scale Mulch Wall Treatment of Chlorinated Hydrocarbon-Impacted Groundwater: Offutt Air Force Base, Nebraska Building 301
Groundwater Services, Inc., Houston, TX. DTIC: ADA422621, 97 pp, 2004.

This report describes the construction of a mulch barrier wall to treat chlorinated solvents (e.g., TCE). The report also describes performance monitoring results and concludes the wall is functioning as designed. There also is a recommendations and lessons learned section

The Biogeochemical Reductive Dehalogenation Groundwater Treatment Process: Commercialization Status at Bench, Pilot and Full Scale
Studer, J.E.
Abstracts of the 21 st Annual Florida Remediation Conference, Orlando, October 8-9, 2015

A novel in situ remediation technology that combines biological and abiotic processes has been commercialized as the BiRD biogeochemical reductive dehalogenation treatment process. The technology generates amorphous and crystalline forms of iron sulfide (referred to as FexSy) in situ, which can dehalogenate compounds such as PCE, TCE, and other chlorinated aliphatics at significant rates. The FexSy reactive zone is created rapidly and can treat passing groundwater over a relatively long period of time. The process can be applied via direct injection or trenching techniques using inexpensive nontoxic reactants that are readily available in either liquid or solid form. The technology is compatible with enhanced bioremediation and zero-valent iron treatments. Additional information: Presentations to the California State Water Resources Control Board .

Zero-Valent Iron Permeable Reactive Barrier to Remediate Volatile Organic Compounds in Groundwater
Willey, A., J. Ross, M. Amidon, M. Rabin, and P. Prater.
WM2020: Annual Waste Management Conference, 8-12 March, Phoenix, AZ, 21 slides, 2020

A non-time-critical removal action was performed at the P-Area Groundwater Operable Unit at the Savannah River Site (SRS) to reduce the mass and downgradient transport of TCE in a groundwater plume. Contaminated groundwater discharge to Steel Creek within the SRS boundaries resulted in TCE contamination over an area of ~6.9 hectares with concentrations as high as 7.7 mg/L. The non-time critical removal action involved installing a zero-valent iron (ZVI) permeable reactive barrier (PRB) within the neck area of the TCE groundwater plume perpendicular to groundwater flow direction. A pre-design investigation and probabilistic modeling were conducted using field and laboratory data to determine the expected performance of the ZVI PRB. The final design was a 10.2-cm thick barrier that will extend 80.5 linear meters in a "zig-zag" orientation to best transect the TCE plume and account for varying groundwater flow, the base of which is "keyed" into a low permeability zone. A total of ~689 metric tons of ZVI will be injected using guar to suspend the ZVI. The ZVI was sized to have a hydraulic conductivity greater than the natural subsurface, thus promoting groundwater flow through the barrier. Performance will be monitored using three upgradient monitoring well clusters, six downgradient monitoring well clusters, and four in-wall monitoring wells. The in-wall monitoring wells will indicate immediate reduction of TCE mass in the groundwater for analyses of PRB health. Additional information: Slides

Creosote

Moss-American Site, Milwaukee, Wisconsin Superfund Site

The Moss-American Site, located in Milwaukee, Wisconsin, is approximately 88 acres in size, and consists of a former wood preserving facility, portions of the Little Menomonee River, and adjacent flood plain soils. The biotreatment funnel and gate system consists of six treatment gates, with Waterloo sheet piling located on both sides of the gates to direct groundwater flow. Operation of the system began in October 2000, with the injection of air, followed by the addition of nutrients in Gate 1 in June 2001. In addition, sumps are being used to collect any free product prior to its entering the treatment gate.

The 2005 five-year review noted that very good contaminant removal efficiency was occurring at upgradient treatment gates within the funnel and gate system (TG 1 and TG2). However, the 2005 review found that little beneficial treatment was occurring at two or more downgradient pairs of treatment gates (TG3 and TG4). It concluded that there was a pocket of contaminatlon downgradient of the first pair of treatment gates where flow conditions were nearly stagnant. The 2010 Five Year Review concludes that the downgradient funnel and gate systerm may not be optimally operating.

• The 2005 Five Year Review provides a discussion of the PRB
• The 2010 Five Year Review provides a discussion of the PRB
• General site information
• Cost and Performance Case Studies from the Federal Remediation Technologies Roundtable
  Biotreatment Funnel and Gate at the Moss-American Site, Milwaukee, Wisconsin (2004)

Explosives

Passive Biobarrier for Treating Co-mingled Perchlorate and RDX in Groundwater at an Active Range
Hatzinger, P.B. and M.E. Fuller.
ESTCP Project ER-201028, 225 pp, 2016

A field demonstration was undertaken to investigate the performance of a passive emulsified oil biobarrier (EOS 550LS plus CoBupH, a slow-release buffering agent) to remediate commingled perchlorate, RDX, and HMX in the naturally acidic groundwater at the Naval Surface Warfare Center, Dahlgren (Virginia). Perchlorate degraded most quickly and HMX most slowly. After the second injection of emulsified oil, concentrations of RDX, HMX, and perchlorate fell by ≥92% in the centerline of monitoring wells extending 40 ft downgradient of the biobarrier. Accumulation of nitroso- degradation products from RDX was minimal. The biobarrier required no O&M other than injection/reinjection of oil substrate and had no impact on range activities. Additional information: ESTCP Cost and Performance Report

Remediation of TNT and RDX in Groundwater Using Zero-Valent Iron Permeable Reactive Barriers: Cost and Performance Report
ESTCP, Project ER-0223, 66 pp, 2008

A mixed iron/sand PRB was installed to remove TNT and RDX contamination from groundwater at the Cornhusker Army Ammunition Plant near Grand Island, Nebraska. Performance was evaluated over a 20-month period. Installation costs for the pilot-scale barrier (50 ft long by 15 ft deep by 3 ft thick) were $138,000, ~$180 per square ft.

Treatment of RDX & HMX Plumes Using Mulch Biowalls
Newell, C. ESTCP Project ER-0426, 77 pp, 2008

The field demonstration conducted at the Pueblo Chemical Depot in Colorado represents the first ever application of mulch PRBs for the treatment of explosives contamination in groundwater. The state-mandated, site-specific cleanup criteria of 0.55 ppb RDX and 602 ppb HMX was used as the project goal. A pilot-scale organic mulch/pea gravel biowall 100 ft long and 2 ft thick was installed using one-pass trenching. The PRB was in place by November 16, 2005, and all performance objectives were met by June 2006, when the system appeared to have reached a pseudo steady state. See also the ESTCP Cost and Performance Report

MTBE

In Situ Bioremediation of MTBE in Groundwater
Johnson, P., C. Bruce, and K. Miller.
TR-2222-ENV, 118 pp, 2003

A biologically reactive ground-water flow-through barrier (a 'biobarrier') was established at the Naval Base Ventura County, Port Hueneme, CA, to prevent further contamination of ground water by MTBE leaching from gasoline-contaminated soils. The biobarrier was installed downgradient of a gasoline-spill source zone. Ground water containing dissolved MTBE flowed to and through the biobarrier, and the microorganisms in the treatment zone converted MTBE to carbon dioxide and water. Gas injection wells were installed to introduce oxygen into the treatment zone.

Petroleum Products

Case Study: New Delivery Method to Inject Remedial Amendments Into a Difficult Aquifer
Feeney, G. | Smart Remediation, 23 January, Toronto, Ontario, Canada, 45 slides, 2020

A case study of a former fueling station site in Canada where two different in situ remediation techniques to treat PHCs failed is presented. Potential reasons for the failed remedial efforts are proposed, and insights are offered on avoiding failure and maximizing success for in situ remediation. The presentation highlights the collection of additional site data for selection and application of a different in situ remediation approach. Risk management measures were used so remediation of the source area was not required. However, an injected permeable reactive barrier was installed to prevent the continued offsite migration of the PHC plume at a busy downgradient barrier.

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