A permeable reactive barrier (PRB), also referred to as a permeable reactive treatment zone (PRTZ), is a developing technology that has been recognized as being a cost-effective technology for in situ (at the site) groundwater remediation. PRBs are barriers which allow some&#;but not all&#;materials to pass through. One definition for PRBs is an in situ treatment zone that passively captures a plume of contaminants and removes or breaks down the contaminants, releasing uncontaminated water.[1] The primary removal methods include: (1) sorption and precipitation, (2) chemical reaction, and (3) reactions involving biological mechanisms.[2]

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Reactive processes

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There are a variety of ways that permeable reactive membranes can be used in order to remediate groundwater. The two main processes are immobilization (AKA sequestration) and transformation.

Immobilization

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Immobilization of the contaminant may occur through sorption to the barrier materials or precipitation from the dissolved state. Organic compounds tend to be undergo sorption due to hydrophobic expulsion from the surrounding water. Metals, however, tend to sorb through electrostatic attraction or surface complexation reactions. Sorption and precipitation are potentially reversible and may thus require removal of the reactive medium and gathered products in order to continue with remediation.[3]

Transformation

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Transformation involves taking the contaminant and transforming it to a less harmful or non-toxic form. One of the chief benefits of transformation is that it does not necessarily require removal of the reactive medium (unless the reactive medium must be replaced due to decreased effectiveness or clogging occurs). Transformation most commonly takes the form of an irreversible redox reaction. The medium may directly supply electrons for reduction or stimulate microorganisms to facilitate electron transfer.[3]

Reactive Materials

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In addition, there are several different materials which may be used. Here are the more prominent:

Zerovalent iron

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Zerovalent Iron was the first material to be used in PRBs for groundwater remediation. It continues to be the main material used in the construction of these barriers.[3] In addition to conventional scale iron, nanoscale-iron may also be used.

Biological barriers

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Sometimes material will be put into the ground to stimulate the growth of microbes that facilitate the groundwater remediation. Many environmental pollutants are highly reduced, thus, the oxidation of these pollutants to harmless compounds is thermodynamically viable. Other pollutants, such as chlorinated solvents, are highly oxidized and as such are easily reduced. Microorganisms commonly facilitate such redox reactions, exploiting contaminant degradation as a means to obtain energy and materials for cell synthesis.[3]

Oxidative biodegradation necessitates electron acceptors that microbes use to "respire" the electrons removed from target contaminants. This transfer of electrons releases energy to drive microbial life functions. Under aerobic conditions, molecular oxygen is used for this purpose. When oxygen is not present, a variety of other molecules can serve as electron acceptors. Oxygen is preferentially utilized over the anaerobic electron acceptors because using oxygen gives more energy and, as an added benefit, results in faster contaminants oxidation rates. Unfortunately, the available oxygen is often not sufficient for the contaminants in highly contaminated areas, and as a result the anaerobic electron acceptors must be utilized. Reactive barriers containing oxygen-releasing compounds have been used successfully to stimulate aerobic biodegradation of monoaromatic hydrocarbons.[3]

Surfactant-modified zeolites

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Clays, zeolites, and other natural material have a high capacity for cation exchange. They do this by creating a net negative charge by substituting lower-valent cations (e.g. Al3+) with a higher-valent cation (e.g. Si4+) within the mineral structure.[4] Adding sorbed surfactants can change the affinity for anions and nonpolar organic compounds.[3] Surfactants that have accumulated at the surface will create a hydrophobic organic coating that promotes sorption of non-polar organic compounds. Surfactant Modified Zeolites (SMZs) are promising for treating non-polar organic contaminants. However, clay's low permeability means it cannot be used in flow-through PRBs,[3] but have been proposed for use in slurry walls, landfill liners, and containment barriers.[5] Zeolites; however, have cavities to maintain hydraulic conductivity, allowing their use in PRBs.

Peat moss

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Peat moss has a large specific surface area (>200 m2/g) and a high porosity.[6] Metals are taken up by peat through an ion exchange reaction where the metal displaces a proton if the pH is low or an existing metal if the pH is high from the anionic function group.[7] Anions, such as CrO2&#;
4 and MnO2&#;
4 are removed more effectively at pH < 3 because of the positively charged surface created by the addition of protons onto the surface functional groups, whereas cations, such as UO2+
2, Ni2+
, Cu2+
, are more effectively removed at higher pH values.[8] Peat moss seems to be an effective ion-exchange material for removing heavy metals and some anions. Removal efficiency of cations approaches 100% at low pH, but the strong dependency on pH and the initial metal ion concentration have to be considered.

Groundwater modeling

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Modeling groundwater flow is important for optimizing the design of a PRB. Most importantly, by modeling the flow, the hydraulic capture zone width (HCZW) and the residence time can be determined. The HCZW is the width of the zone of groundwater that will pass through the reactive cell or gate (for funnel-and-gate configurations). The residence time is the time that the contaminated groundwater will spend in the treatment zone for decontamination. Contamination outside the capture zone or that does not have a long enough residence time will not be properly decontaminated. Groundwater modeling can also be used for the following:

1. Determining the location of the PRB
2. Determining a suitable configuration
3. Determining the width of the reactive cell (and funnel for funnel-and gate)
4. Evaluating potential for underflow, overflow, or flow across aquifers
5. Providing knowledge of groundwater flow fluctuations (velocity and direction) for use in the design
6. Determining reactive media selection (based on hydraulic conductivity) to match the conductivity of the aquifer
7. Evaluating possibilities for flow bypass due to reduced porosity
8. Helping determine monitoring well locations and monitoring frequencies

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Configuration

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Iron barriers

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click to enlarge

The accompanying figure shows two approaches to application of iron particles for groundwater remediation: Fig. A, a conventional PRB made with mm-sized granular iron and Fig. B, a "reactive treatment zone" formed by sequential injection of nano-sized iron to form overlapping zones of particles absorbed by the grains of native aquifer material. In A, groundwater flows through the barrier and is remediated. In B, nanoparticles of iron are represented by black dots; the nanoparticles have little mobility in the porous medium. Note that reaction will only occur when contaminants, either dissolved in the groundwater or as DNAPL, come into contact with the iron surfaces.[10]

Funnel and gate

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Funnel and gate systems are used to channel the contaminant plume into a gate which contains the reactive material. The funnels are non-permeable, and the simplest design consists of a single gate with walls extending from both sides. The main advantage of the funnel and gate system is that a smaller reactive region can be used for treating the plume, resulting in a lower cost. In addition, if the reactive media needs to be replaced, it is much easier to do so because of the small gate.[11]

Implementation

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PRBs are typically installed by digging a long trench in the path of the flow of the contaminated groundwater. The trench is then filled with the reactive materials (typically iron, carbon, or limestone). Sand can be mixed with the reactive material to aid in allowing the water to flow through the materials. Sometimes, there will be a wall that directs the groundwater to the reactive parts of the barrier. After the trench has been filled with reactive material, soil will typically be used to cover the PRB, thus eliminating visibility from the surface.[12]

Sheet pile and excavation

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Sheet pile and excavation were used for the installation of earlier PRBs. This method involves containing the area of excavation using sheet piles before excavating using a trackhoe. This method may be slow (and therefore expensive) and is only viable for plumes less than 35 feet deep.[13]

Continuous trencher

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Continuous trenching involves using a large cutting chain excavator system then using the trench box and hopper to continuously back-fill the trench with reactive media. Continuous trenching can be fast and thus, inexpensive, but can only be used for trenches less than 50 feet deep. In addition, the machinery used for this technique cannot be used effectively for soil with large cobbles.[13]

Mendrel emplacement

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Mendrel technology involves vertically driving a long hollow beam deep into the ground. The beam is covered as it is driven in, and the cover is removed once the beam has been placed. Next, the hollow is filled with iron filings. The Mendrel is then vibrated as it is removed, allowing the iron to flow to the bottom, forming the PRB. The Mendrel is then moved one width over, the process is repeated, and a continuous PRB is made.[13]

Hydraulic fracture

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This methods utilizes injected fine-grained iron into fractures below the surface that were created using controlled applications of high pressure. Jets of water scour out a zone that is then filled with guar gum and iron. The guar gum holds the iron in place before degrading, leaving a permeable zone of iron (the PRB).[13]

Deep soil mixing

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Deep soil mixing adds iron to the native soil and mixing it with large augers. This process creates a series of columnar treatment zones that form a PRB when lined up. This method can treat plumes to a depth of 100 feet, but the treatment zone is relatively low in the proportion of iron.[13]

Performance assessment

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The key component for assessing the success of a PRB is whether it satisfactorily removes the contaminants. This can be done by monitoring the levels in the water immediately downstream of the PRB. If the levels are below maximum contaminant levels, then the PRB has performed its function.

Failure

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For more PRB filling medium supplyinformation, please contact us. We will provide professional answers.

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In analyzing PRBs, emphasis has been placed on losses of reactivity and permeability in the reactive well; however, flawed hydraulic characterization of the few PRB failures that have been reported. Oxidation-reduction potential, influent [pH], and influent concentrations of [alkalinity], [nitrate NO&#;
3], and [chloride Cl&#;] are the strongest predictors of possible diminished performance of PRBs. The reactivity of the media, rather than a reduction in permeability is more likely the factor that limits field PRB longevity. Because this technology is relatively new, it is still hard to predict the longevity of sites. Depending on assumptions of controlling factors, longevity estimates can differ by an order of magnitude (e.g. 10&#;100 years).[14]

Case studies

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an example of an "iron wall"

A field-scale application of PRBs in groundwater remediation consisted of a treatment zone formed by excavating an area isolated by sheet piles, refilling the hole with a mixture of granular iron and sand, and removing the sheet pile to leave an in situ, permeable, iron-bearing treatment zone. The contaminants, chlorinated ethylenes (PCE and TCE), were removed, leaving, for the most part, fully dechlorinated groundwater (little vinyl chloride was observed).

Sunnyvale, CA

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During the installation of a PRB at Sunnyvale, CA, click to enlarge

The first field-scale implementation of PRB was in Sunnyvale, California, at the site of a previously operating semi-conductor plant. At the time, the best available remediation technology was pump and treat technology. PRBs presented a more cost-effective solution to the problem at hand, being able to passively remediate the groundwater. Granular metal was chosen as the reactive media after laboratory testing using contaminated water from the site. After installation contaminants were reduced to target levels. As a result, the pump and treat machinery was able to be removed and the above ground was free to be used for commercial purposes. The savings from using the PRB as opposed to pump and treat were able to pay for the installation in about three years.[13]

Elizabeth City, NC

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In a 46 m long, 7.3 m deep, .6 m thick PRB was installed at a Coast Guard Facility near Elizabeth City, NC. The goal of this PRB was to remediate a contaminant plume of trichloroethylene (TCE) and hexavalent chromium (Cr (VI)). The PRB took only 6 hours to install using a continuous trenching technique, which simultaneously removed the pre-existing sediment while installing the reactive medium (granular iron). The PRB was configured as a continuous wall as opposed to a funnel-and-gate setup because 3D computer simulations suggested that the two would have the same effectiveness, but cost analyses showed that the continuous setup would be cheaper to install. The total cost of installation was approximately $1 million, while the U.S. Coast Guard predicts that over 20 years $4 million will be saved compared to a pump-and-treat system.[15]

Moffett Field, CA

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During the installation of a PRB at Moffett Field, CA, click to enlarge

Moffett Field, CA was home to a pilot scale PRB initiated by the U.S. Navy in . The Moffett Field PRB used a funnel and gate design, with the funnel being composed of interlocking steel sheet piles, while the gate consisted of granular zero-valent iron. The primary contaminants were trichloroethene (TCE), cis-1,2 dichloroethene (cDCE), and perchloroethene (PCE). Data from quarterly monitoring, tracer testing, and iron cell coring have been used to determine the effectiveness of the site. Since the first sampling event in June , concentrations of all chlorinated compounds have been reduced to either non-detect levels or below the maximum contaminant levels.[16]

Fry Canyon, UT

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The Fry Canyon site was selected in as a field demonstration site to assess the removal capabilities of PRBs for uranium. Laboratory experiments were conducted on three potential PRB materials (phosphate, zero-valent iron, and ferric iron) to determine uranium removal efficiencies and hydrologic properties. A PRB material from each class was selected for demonstration. The selected materials had satisfactory hydraulic conductivity, high U removal efficiency, and high compaction strengths. A funnel and gate design was used. The funnels channeled the groundwater into the PRB gates. During the first year, zero-valent iron had lowered U concentration by more than 99.9%, while the amount removed in both the phosphate and the ferric iron exceeded 70% for most of the measurements made. Mechanisms for removing uranium are similar to those for removing other inorganic contaminants, meaning that this study has wide applicability.[17]

Status of the technology

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In , analysts estimated that in the U.S. total cleanup costs of groundwater totaled between $500 billion and $1 trillion.[18] Until about , the majority of groundwater remediation was done using "conventional technologies" (e.g., pump-and-treat systems), which have proven costly to meet applicable cleanup standards.[19]

Notes

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Additional information on this topic may be found at the following sites:

Permeable Reactive Barriers

On this page:

Schematic

Permeable Reactive Barrier Schematic

Introduction

Many types of permeable reactive barriers (PRBs) are used to passively treat groundwater in situ. A PRB typically involves the installation of reactive media within a trench, a series of overlapping borings, or grouped injection points to create a permeable "wall" positioned perpendicular to the direction of groundwater flow, through which the contaminant plume passively flows. The media are selected to adsorb, precipitate, or chemically degrade the groundwater contaminants within, or close to, the treatment media. PRBs can leverage physical, chemical, and/or biological processes to remove contaminants of concern (COCs). This profile focuses on abiotic (physical/chemical) degradation processes while a separate biowall profile describes a similar technology focused on biodegradation processes.

Other Technology Names

Passive/Reactive Treatment Wall
Iron Wall
Funnel and Gate
Zero Valent Iron (ZVI) Curtain
ZVI Wall

Description

PRBs are installed across the flow path of a contaminated groundwater plume such that the plume is intercepted and remediated. One of the most common configurations is a continuous reactive barrier, where the treatment medium extends across the entire width and depth of the contaminant plume (NAVFAC, ). Another common configuration is the funnel-and-gate, where impermeable walls guide groundwater through one or more treatment gates (NAVFAC, ).

PRBs have evolved since their inception in from trenches filled with iron filings to include a wide range of installation methods and treatment media. The optimum installation method is site- and application-specific, based on factors such as depth and width of the PRB, type of media used, geology and hydrogeology, and existing surface and subsurface infrastructure. Installation options include:

• One-pass trencher: A one-pass trencher is a track mounted, heavy construction vehicle with an extended cutting boom (a linked chain belt with cutting teeth) similar to a chain saw. These are capable of cutting trenches 12 to 36 inches wide and 20 to 50 feet deep (though greater depths are possible with benching the excavation site). Continuous one-pass trenchers emplace the PRB media while simultaneously cutting the trench.
• Excavators: Excavators are track mounted, heavy construction vehicles with a bucket or clamshell on the end of a boom, controlled from within a cab on a rotating platform. Excavators are commonly used for depths of 45 feet and shallower, but they have the potential to trench to a depth of 200 feet below ground surface. Excavators are used to create an open trench (shored if necessary), which is backfilled with the PRB media as a granular material or a slurry.
• Soil mixing: Soil mixing using large augers of up to 30 inches in diameter can be advanced to depths up to 60 to 100 feet beneath ground surface, although the deeper portion of this range may be cost prohibitive at many sites. In this method, the PRB media are pumped as a slurry or placed as a granular material through the hollow auger stem and mixed into the soil as the auger turns and is withdrawn from the subsurface. Placement of several borings in overlapping arrays creates a continuous PRB. PRB borings can also be created using the caisson method, in which a steel cylinder up to 15 feet in diameter is driven into the ground and the soil within the cylinder is removed and replaced with the PRB media.
• Injection of aqueous phase reactants through direct injection points or permanent wells: PRB media in a carrier fluid are injected under pressure, with the goal of achieving a continuous reactive zone. This method typically results in a less continuous reactive zone than trenching or borings, because of the soil heterogeneity impacts on adequate distribution of amendments inherent with injection technologies. However, injection technics can be used at some sites where other methods are not practical. Additional guidance to inject and distribute aqueous amendments can be found here.
• Alternative, lesser used methods (ITRC, ) such as vibrating beam, direct emplacement via hydraulic and pneumatic fracturing techniques, and hydrofracturing horizontal media-packed wells (under study): These methods focus contaminated groundwater flow through preferential treatment pathways.

PRBs based on physical and/or chemical processes can be constructed using a variety of media. The selected media are based on the type of contaminants being treated and an understanding of the chemical and physical characteristics that govern how the media will remove a contaminant (ITRC, ). Some of the more commonly used media include:

• ZVI
• Zeolite and apatite to address radionuclides
• Slag
• Organophilic clays to control non-aqueous phase liquid (NAPL)
• Activated carbon to treat polycyclic aromatic hydrocarbons (PAHs) and other volatile organic compounds (VOCs)
• Mixed iron and organic substrates such as activated carbon impregnated with ZVI (ITRC, )
• Bauxite, limestone, and other mineral ores to treat a variety of metals including arsenic, cadmium, lead, and mercury (NAVFAC, )

The location of a PRB relative to the contaminant plume at a site depends on the treatment objectives and how the PRB is incorporated with other technologies in a "treatment train." PRBs can be used to reduce the mass flux from a source zone by positioning the PRB at the immediate downgradient edge of the source zone. PRBs can alternatively be installed mid-plume to reduce dissolved concentrations at a location. Key performance factors for PRBs are:

• Establish and maintain the hydraulic conditions necessary for effective treatment, including sufficient residence time for contaminated groundwater within the media and effective routing of the contaminated groundwater through the media without deflection or bypass (ITRC, ).
• Treat the target contaminant(s) to meet the remedial action objective at the specified distance downgradient of the PRB.

Development Status and Availability

The following checklist provides a summary of the development and implementation status of PRBs:

&#; At the laboratory/bench scale and shows promise

&#; In pilot studies

&#; At full scale

&#; To remediate an entire site (source and plume)

&#; To remediate a source only

&#; As part of a technology train

&#; As the final remedy at multiple sites

&#; To successfully attain cleanup goals in multiple sites

PRBs are available through the following vendors:

&#; Commercially available nationwide

&#; Commercially available through limited vendors because of licensing or specialized equipment

&#; Research organizations and academia

Applicability

Contaminant Class Applicability Rating for PRBs
(Rating codes:

&#;

Demonstrated Effectiveness, &#; Limited Effectiveness,

&#;

No Demonstrated Effectiveness,
I/D Insufficient Data, N/A Not Applicable)

Nonhalogenated VOC

Halogenated VOC

Nonhalogenated SVOC

Halogenated SVOC

Fuels

Inorganics

Radionuclides

Munitions

Emerging Contaminants

&#; &#; &#; &#; &#; &#; &#; &#; I/D

PRBs are applicable to a wide range of COCs, however the PRB media must be selected to match the contaminant. Understanding the processes by which the COCs degrade, sorb, or precipitate is crucial to choosing the PRB medium or media (ITRC, ). PRBs relying on physical and chemical processes such as sorption, reduction, or oxidation are commonly used. For instance, chlorinated compounds can be treated using PRBs constructed of ZVI or zero valent zinc. Long-lived oxidants (e.g., potassium permanganate) and sorbent materials such as activated carbon or clay can be used to remove VOCs and semi-volatile organic compounds (SVOCs), fuels, and other compounds. Depending on site conditions and the combination of COCs present, PRBs may require several types of medium applied within a single trench.

Because of the wide variety of installation methods, PRBs are applicable at a relatively wide range of sites. Continuous wall and trenched PRBs are most applicable to sites with treatment zones 40 feet deep or less, with minimal subsurface and overhead obstructions (utilities), and substantial access for construction equipment at the surface. PRBs can be constructed to greater depths using caissons, auger soil mixing, or pneumatic or hydraulic fracturing, or caisson technologies. PRBs constructed by injecting various amendments can be installed with a smaller surface footprint required for the construction equipment, and with the ability to work around some surface and subsurface infrastructure (see case studies included in Appendix A of ITRC, ).

Cost

Cost drivers for PRBs include the type and quantity of media required, and the emplacement methods needed. As with all in situ technologies, application costs vary according to site conditions and contaminants. Major cost drivers include:

Upfront Costs

• Area and depth of contaminants. Extent of contamination impacts the length and depth of the PRB, and therefore the quantity of media required and the emplacement methods that can be selected.
• Groundwater flow rate. The mass flux of the contaminants through the PRB is a key design factor that impacts the thickness of the PRB necessary to achieve the required residence time, and therefore the quantity of PRB media required.
• Nature of the contaminants and degradation pathways. Determines the type of PRB media required (e.g., oxidants, reductants, sorptive) and impacts the longevity of the media.
• Construction requirements. PRB construction requires the use of heavy equipment to install the system. Installation activities include monitoring well installation, trenching and/or drilling, reactive media emplacement, and transportation of materials. Drill rigs, continuous trenchers, backhoes, delivery trucks, and other large equipment are usually required. Fracturing and media injection require pumping and/or high pressures, often using substantial amounts of water and/or gases.
• Type of media required.
• Investigation-derived waste (IDW). Costs to dispose of IDW generated during drilling and/or excavation activities.
• Number and depth of injection points. At some sites, PRBs may be installed by injecting media through a series of injection points or wells. The number and depth of the points/wells can have a significant impact on cost.
• Remedial goals. More stringent remedial goals may require a greater biobarrier thickness, and hence greater material and construction cost, to ensure sufficient residence time.

Operation and Maintenance Costs

• Longevity of media. Short-lived media may require frequent replacement/replenishment. Longevity is impacted by media properties, types of COCs, contaminant concentrations, groundwater geochemistry, groundwater flow and other aquifer characteristics.
• Performance criteria. Performance criteria can impact the frequency that the biobarrier must be replenished with additional amendments to ensure proper operation.
• Changes in hydraulic conductivity. Periodic testing of hydraulic conductivity may be required to ensure that the barrier is not adversely impacting groundwater flow. Fouling could cause a portion of the contaminated groundwater to flow around the barrier requiring mitigation that could include the application of anti-fouling agents, replacement of material, or extending the PRB, among others.

The list above highlights those cost dependencies specific to PRBs and does not consider the dependencies that are general to most in situ remediation technologies. Click here for a general discussion on costing which includes definitions and repetitive costs for remediation technologies. A project-specific cost estimate can be obtained using an integrated cost-estimating application such as RACER® or consulting with a subject matter expert.

Duration

PRBs are passive in nature and typically require longer times to achieve cleanup goals than do other more aggressive remedial technologies. If PRBs are employed at a site where an aggressive technology is used to treat a source area, the duration needed for the PRB may be shorter. Also, in many cases, PRBs are used with monitored natural attenuation, in which case the duration that the PRB is operated will increase. The longevity of PRBs is dependent on many factors, including the following conditions.

• Groundwater flowrate and mass flux of contaminants
• Native and anthropogenic electron acceptor demand impacting the media use rate
• Iron and sulfate availability and usage (determines biogeochemical transformation process rates)
• Initial quantity and reactivity of the media used in the PRB

Coarse-grained ZVI can persist for several decades. Solid carbon-based substrates have demonstrated 5 to 15 years of productivity before replacement was warranted. Injectable substrates derived from solid carbon are intended to perform for 5 to 10 years before replenishment is needed. The longevity of potassium permanganate or other chemical treatments used in PRBs is similar to that for other in situ chemical oxidation (ISCO) configurations. ISCO is described in a separate profile.

Implementability Considerations

The following are key considerations associated with implementing PRBs:

• Performance may decrease over time.
• Proximity of the plume to site boundaries or receptors.
• Depth and width of the contaminant plume.
• Need for treatability testing. Batch jar or column tests may be performed. Results may be used to calculate reaction rates and residence time required to estimate mass of media needed and thickness of the barrier.
• Cost of treatment media.
• Size of the treatment media. Finer particles have greater surface area and therefore exhibit greater reactivity than larger particles; however, they may be expended faster.
• Fine particles result in reduced hydraulic conductivity, which can impact groundwater flow and treatment effectiveness. Larger particles, comprised of inert materials (e.g., sand), may be combined with the reactive media to improve conductivity.
• PRBs will not treat residual plumes present downgradient of the barrier. Secondary treatment may be necessary to address residual contamination. Multiple parallel PRBs may be installed at specific intervals within the contaminated plume to facilitate complete treatment.
• Longevity of reactive media.
• Deed restrictions for groundwater use may be required if the upgradient source area is not remediated or until COCs are adequately treated.
• Generation of precipitates may limit the permeability of the treatment barrier.
• Nearby dynamic loading (future pile driving, dewatering, excavation) can compromise the structure of the PRB media.
• For excavated trenches, care is needed to assure stability of the trench walls prior to amendment placement, or there is a risk of trench wall collapse and the creation of a "hole" through which groundwater could pass through untreated.

Resources

EPA. Clu-In Technology Focus on Permeable Reactive Barriers, Permeable Treatment Zones, and Application of Zero-Valent Iron
This EPA website provides an overview of PRB technologies, with links to additional resources.

ITRC. PRB Technology Technical Update (July ) (PDF) (234 pp, 7.58 MB)
Most recent update to four previous ITRC guidance documents on PRBs.

ITRC. PRB Reference Documents
ITRC web page providing PDF downloads of all five ITRC documents regarding PRBs.

NAVFAC. Permeable Reactive Barrier Cost and Performance Report () (PDF) (85 pp, 3.40 MB)
This report provides an evaluation of cost and performance conducted for three full-scale PRBs representing a range of installation technologies, reactive media, and targeted contaminants. Injection media used ranged from ZVI that stimulates abiotic transformation of chlorinated solvents, to organic materials (e.g., mulch; vegetable oil) that treat perchlorate and enhance reductive dechlorination of chlorinated solvents.

NAVFAC. Permeable Reactive Barrier Technology Transfer Tool ()
A PRB is a trench built across the flow path of a groundwater plume. The trench is filled with a suitable reactive or adsorptive medium that removes the contamination from the groundwater. This tool is designed to assist in the development and implementation of effective PRB applications.

SERDP-ESTCP. Evaluation of Performance and Longevity at DoD Permeable Reactive Barrier Site (October ) (PDF) (328 pp, 18.9 MB)
A study coordinated with companion studies through EPA and DOE to assess the long-term performance of PRBs.

SERDP-ESTCP. Remediation of TNT and RDX in Groundwater Using Zero-Valent Iron Permeable Reactive Barriers and Zero-Valent Iron In Situ Treatment Wells (May ) (PDF) (123 pp, 3.84 MB)
Two demonstration studies, one replacing traditional well sand pack with coarse granular iron to treat munitions constituents, and a second using a ZVI barrier wall.

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