application of emulsified zero-valent iron: four full-scale remediation sites

REMEDIATION Winter 2011

Application of Emulsified Zero-ValentIron: Four Full-Scale Remediation Sites

James E. Huff

Emulsified zero-valent iron (EZVI) is a technology developed by the National Aeronautics and

Space Administration (NASA) that is used to remediate soil and groundwater contaminated with

chlorinated solvents. It consists of micro- and/or nano-scale iron particles suspended in a water-in-

vegetable oil emulsion. This allows EZVI to combine three remediation technologies: partitioning

of the chlorinated volatile organic compounds (CVOCs) into vegetable oil, a chemical reaction

between the CVOCs and elemental iron, and hydrogen production from the fermentation of the

vegetable oil to promote biological degradation. A description of the chemistry and biology of

this NASA technology is presented, followed by a description of four full-scale case studies where

EZVI has been applied, including post-injection results extending over three years. At each of these

sites, EZVI was determined to be the most cost-effective remedy. The sustained treatment long after

the injections resulted in contaminant reductions continuing for over three years and accelerated

remediation times compared to traditional approaches, due to the combination of technologies.

Furthermore, EZVI is consistent with US EPA’s green remediation policy. Oc 2011 Wiley Periodicals,

Inc.

INTRODUCTION

Chlorinated solvents, including perchloroethylene (PCE), trichloroethylene (TCE),1,1,1-trichloroethane (TCA), and carbon tetrachloride (CT), are present at a largenumber of sites across the United States. The US EPA Expert Panel on DNAPLRemediation (2003) estimated that there were between 15,000 and 25,000 densenonaqueous phase liquid (DNAPL) sites in the United States. The presence of DNAPLsrepresents a long-term source of groundwater contamination due to their slow dissolutioninto the aqueous phase.

Oxidation technologies have been used to address chlorinated solvent contamination;however, these contaminants are all highly oxidized, and further oxidation requires strongoxidants to succeed. Successful oxidation requires rapid contact between the oxidant andthe contaminant due to the short life expectancy of the oxidants, which makes completetreatment of DNAPLs difficult. While oxidation typically achieves a similar degree ofcontaminant reduction in the short term as other technologies, chemical oxidation siteshave a higher likelihood of rebounding three years later (McGuire, McDade, & Newell,2006). Incomplete treatment of the DNAPL phase by chemical oxidation is a likely causeof this rebound effect.

c© 2011 Wiley Periodicals, Inc.Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/rem.21303 125

Application of Emulsified Zero-Valent Iron: Four Full-Scale Remediation Sites

Sustained treatment, defined as the enhanced attenuation capacity within the targetedarea after the conclusion of the active treatment period for a given source-depletiontechnology (Adamson, McGuire, Newell, & Stroo, 2011), is being recognized as animportant concept when evaluating treatment alternatives. Enhanced bioremediation hasbeen shown to provide significant sustained treatment. Emulsified zero-valent iron (EZVI)has not been evaluated over an extended time period previously due to its limited use todate (McGuire et al., 2006); however, this article provides clear evidence of sustainedtreatment with EZVI.

Emulsified zero-valent ironhas not been evaluatedover an extended time pe-riod previously due to itslimited use to date; how-ever, this article providesclear evidence of sustainedtreatment with EZVI.

EMULSIFIED ZERO-VALENT IRON

EZVI was developed and patented by the National Aeronautics and Space Administration(NASA) in the early 2000s to address chlorinated solvent issues at its Florida facility(Quinn, 2005). The first field demonstration of this technology occurred at NASA’sLaunch Complex 34 on Cape Canaveral. The technology combines an abiotic reactionbetween nano- and/or micro-scale iron with biological reductive dechlorinationassociated with the fermentation of vegetable oil. The lipophilic nature of chlorinatedsolvents results in the chlorinated solvents preferentially partitioning into the vegetableoil, reducing the dissolution rate into the aqueous phase. This preferential partitioning wasclearly illustrated by Quinn (2005). EZVI is an emulsion of water in vegetable oil, withthe iron suspended in the water miscelles. The emulsion is stable due to a food-gradeemulsifying agent used in the formulation. The scientific theory behind EZVI is that thechlorinated solvents will partition preferentially into the oil and come into contact withthe iron suspended in the water miscelles, where the abiotic reaction will occur. Thisphase of the remediation occurs over a short time period, after which the vegetable oil andsurfactant serve as long-term electron donors and promote the anaerobic biodegradationof the chlorinated compounds.

The reaction between the chlorinated ethenes and iron goes predominantly through abeta-elimination pathway—Arnold and Roberts (2000) reported reductions of 97 percentfor TCE and 87 percent for PCE. The intermediate chlorinated acetylenes(di-chloroacetylene and chloroacetylene) are also highly reactive with iron and formacetylene (Arnold & Roberts).

The properties just described make EZVI particularly suited for treatment of sourceareas, where undissolved free product is known or suspected to be present. The sustainedtreatment just mentioned is another aspect of EZVI that results in continuing contaminantreduction for an extended period of time. However, there is limited literature on thefull-scale application of EZVI and its sustained treatment benefits. Four sites where EZVIhas been applied as a full-scale remediation approach are described here, includinglonger-term monitoring to address the sustained treatment aspect.

OHIO MANUFACTURING FACILITY

This 59-acre site in Ohio was a manufacturing facility for a cleaning solvent used formimeograph machine rollers. The cleaning solvent was a mixture of PCE and naphtha.

126 Remediation DOI: 10.1002/rem c© 2011 Wiley Periodicals, Inc.


It was discovered floating on the groundwater surface, covering an area of 120 feet (ft) by200 ft and averaging 3 inches (in) in thickness. Near-surface sediments to a depth of 25 ftconsist of sand, silt, and gravel. Subsurface materials between depths of 25 and 145 ftconsist of varying ratios of sand and gravel, with very little silt and clay. Groundwateroccurs at approximately 20 ft below ground surface (bgs) and extends over 100 ft inthickness. The shallow groundwater has a velocity estimated at 180 ft per year. Through aseries of over 40 free product recovery wells, the free product was removed over a 4-yearperiod by dual phase extraction and manual bailing. These source area wells subsequentlywere used to remove contaminant from the smear zone just above the water table byemploying soil vapor extraction (SVE).

The oxidation-reductionpotential remained neg-ative in the source areamonitoring wells followingthe treatment, and con-taminant levels continue todecline 4 years after thelast EZVI injection.

Remediation Overview

Concurrent with the SVE operations, two rounds of EZVI injections from 18 to 28 ft bgswere performed in the source area. Prior to the injections of EZVI, there remained anaverage 0.22-in. floating free product on the groundwater surface across the source area.The first round, a preliminary injection of 22,455 pounds (lb) of EZVI to demonstrate thetechnology to the Ohio EPA, occurred in December 2005/March 2006 on the upgradientportion of the source area. Direct push rigs, with nitrogen gas to displace the water, wereused for the injections. Based on the success of the first round, 37,568 lb of EZVI wereinjected in the downgradient portion of the source area in December 2007. Three monthsafter the full-site injections, the downgradient monitoring well closest to the injectionswas tested for the acetylene compounds. No chloro-acetylene compounds were detected,but acetylene was detected at 0.026 milligrams per liter (mg/L), consistent with thefindings of Arnold and Roberts (2000). Subsequent testing at 9 and 12 months afterinjections did not detect any acetylene compounds. Monitoring wells furtherdowngradient, which were sampled at the same time intervals, did not detect anyacetylene compounds. From the limited results of the closest downgradient monitoringwell, it is theorized that the iron portion of the EZVI was essentially depleted between 3and 9 months after the injections.

Results

Exhibit 1 presents the mean concentration of PCE and its products of anaerobicdegradation—TCE, cis-1,2-dichlroethylene (cis-DCE), and vinyl chloride (VC)—in the40-plus source area wells, based on the last samples taken before the EZVI injections andthe most recent monitoring well results. Not only was there no evidence of free product(from a pre-EZVI application average of 0.22 in across the site), but the PCE and TCEconcentrations in the source area wells were essentially below detection limits. DissolvedPCE in the source area wells averaged over 25 mg/L before the EZVI injections andaveraged 0.075 mg/L in the last monitoring event. Similar results for TCE were achieved.Cis-DCE also declined from over 40 mg/L pretreament to 3.754 mg/L post-treatment,and the VC concentration has remained low, averaging 0.653 mg/L post-treatment. Theoxidation-reduction potential remained negative in the source area monitoring wellsfollowing the treatment, and contaminant levels continue to decline 4 years after the lastEZVI injection.

c© 2011 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 127


Exhibit 1. Source area average concentration before and after EZVI

Exhibit 2 presents the groundwater results from the downgradient monitoring wellclosest to the source area, MW-7sr. This is the well where acetylene was detected 3months after the EZVI injections. PCE showed little change in concentration until 1 yearafter the first EZVI injections, and it has since declined from an average of 88 mg/L in2007 to an average of 0.705 mg/L in 2011. A similar reduction in TCE occurred.Cis-DCE, which averaged over 400 mg/L in 2006, has declined to 50 mg/L in 2011, andit continues to decline at a significant rate (from 160 mg/l in 2010 to 50 mg/L in the firsthalf of 2011). VC, not plotted in Exhibit 2 due to the larger scale on the graph, averaged3.25 mg/L in 2011, from its peak of 4.85 mg/L recorded in March 2010. Thisconcentration is relatively low considering that over 400 mg/L of cis-DCE have beendegraded. Ethene levels in MW-7sr averaged less than 0.10 mg/L prior to the EZVIinjections, increasing to a peak of 1.3 mg/L in March 2010 and subsequently declining to0.47 mg/L in June 2011. Similarly, methane concentrations prior to the EZVI injectionsin MW-7sr ranged from 0.01 to 0.06 mg/L, increasing to 0.23 mg/L in September 2006,6 months after the initial injections. Methane also peaked in March 2010 at 2.90 mg/Land declined to 1.80 mg/L in March 2011. Sustained treatment 3 years after the last EZVIinjections is apparent at this site.

With the elimination of the source area contamination, rapid improvement in thedowngradient wells was expected, and that has been the case. The sustained benefit of theEZVI injections is readily apparent from the continued improvement in groundwaterquality. The EZVI was critical in completely eliminating the source contaminants, bothabove and below the water table.



Exhibit 2. MW-7sr average annual concentrations

Costs

From the two rounds of injections, a total of 4,620 cubic yards (cu yd) of source area soil,from 2 to 3 ft above the water table to typically 8 ft into the water table, were treated.The total cost for the two rounds of EZVI injections, including design, permitting,chemical, and injections, was $269,600, which equates to a remediation cost of $58 percu yd for remediating the free product–containing source area.

LOUISIANA GRAIN TERMINAL VADOSE ZONE TREATMENT

A fumigant containing carbon disulfide dissolved in CT was used in the 1960s to the 1980sin many grain terminals. An explosion at a terminal in Louisiana in 1977 caused therelease of the fumigant, which soaked into the adjacent area. The extent of the CTcontamination was contained in an area of 60 ft by 80 ft extending to a depth of 15 ft bgs.The geology is silt with interspersed silty clay. The groundwater depth varies from nearthe surface during flood-stage conditions to 6 ft bgs during the drier part of the year.


The instability of the soil adjacent to the large silo structures precluded excavationwithout extensive shoring. In addition, the excavated soil would be classified as ahazardous waste, and exposure of the excavated soil to elevated levels of CT was an



Exhibit 3. Louisiana grain terminal contaminant reductions

Pre-EZVI, Pounds Post-EZVI, Pounds Percent Reduction

Carbon tetrachloride 3,690 46.8 98.7Chloroform 63 2.1 96.7Methylene chloride 10 0.2 98.0Total CVOCs 3,763 49.1 98.7

additional concern. After completing an evaluation of the remedial options, EZVI wasselected as the lower-cost option with the greatest chance of successfully remediating thesite. The initial mass of CT was estimated at 1,880 lb, with little biological degradationongoing due to the toxicity of the elevated concentrations. An injection grid 10 ft oncenter was laid out and injections in 2-ft zones were completed. The tight spacing wasnecessary due to the shallow depths limiting the injection pressures. Injections werecompleted in 2-ft intervals, from 4 to 15 ft bgs. A total of 23,000 lb EZVI were injectedinto 148 injection borings in July 2006.

Borings in July 2007, one year after the injections, revealed significant progress butalso identified several areas where the EZVI did not penetrate. Thus, a secondmobilization was completed in 2009, with spot injections of 7,600 lb additional EZVIinjected into 56 points. In 2010, final closure borings were completed.

Results

The results are summarized in Exhibit 3. The overall mass of CT in the vadose zone wasreduced from 3,690 lb to 46.8 lb, a reduction of 98.7 percent. Overall chlorinatedvolatile organic compound (CVOC) reduction was also 98.7 percent, leaving only 49.1 lbin the 2,600-cu yd area. The average remaining CVOC concentration was less than 6 mgper kilogram (kg), compared to an initial average concentration of 480 mg/kg.

For the two rounds of EZVI injections and two rounds of soil borings, the total costwas $103 per cu yd treated within the vadose zone, or $72 per lb contaminant destroyed.The injection costs were higher due to the shallow depths injected, which necessitated atighter injection grid. EZVI thus proved effective in remediating chlorinated solventswithin the vadose zone.

TEXAS GRAIN TERMINAL

A fumigant containing CT was used at this grain elevator from 1965 to 1986. CT wasdiscovered in the groundwater and just above the groundwater adjacent to the grainelevator where the fumigant was likely stored. Initial concentrations were high enoughthat undissolved free product both above and below the water table was suspected.Groundwater is approximately 25 ft bgs and flows north toward the adjacent river. Sourcearea CT levels were as high at 153 mg/L. The top 25 ft of the subsurface soils arepredominantly brown and gray clays, with silty sand between 26 and 30 ft bgs, which is



the upper water-bearing zone. The hydraulic conductivity within this saturation zoneranges from 10–3 to 10–4 centimeters per second.


Biological anaerobic dechlorination was not considered at this site due to the extremelyhigh CT concentrations, which inhibit bacteria growth. The suspected undissolved freeproduct made EZVI the cost-effective remediation choice, as the free product wouldpartition into the vegetable oil and then react with the suspended iron, providing asignificant reduction in CT concentrations (and toxicity) before the biological degradationbegan.

In July 2006, a total of 58 borings were used to inject a total of 8,750 lb EZVIbetween 18 ft and 33 ft bgs as a demonstration step. The borings were drilled on 10-ftcenters. This was followed by the injection of 35,400 lb EZVI in June 2010, through 70injection borings, also on 10-ft centers, treating 3,765 cu y of l above and below thegroundwater table. Exhibit 4 depicts the initial injections within the source area.

Results

Exhibit 5 depicts the annual average concentrations in source area monitoring wellMW-205. Immediately after the first injection round, the CT concentration declinedfrom over 150 mg/L to less than 30 mg/L. Chloroform (CF) increased from 12 mg/Land peaked at 60 mg/L in 2008 before declining. Methylene chloride (MeCl) increased to8 mg/L and began declining in 2010. However, the CT steadily increased to 80 mg/Lafter the initial decline, before the second round of EZVI was initiated.

After the second EZVI round in June 2011, CT in MW-205 declined rapidly to 0.646mg/L. Prior to the second round of injections in June 2011, CF also declined rapidly from43 mg/L to 0.629 mg/L. As depicted in Exhibit 5, MeCl increased after the injections to32.5 mg/L by March 2011, only to decline to 2.48 mg/L in June 2011. After the firstround of injections, the CT began to increase after 6 months, suggesting that not all of theDNAPL was depleted. After the second round, no evidence of rebounding has beenobserved, and the trend remains downward, suggesting that the DNAPL has beeneffectively captured and destroyed.

In the first downgradient monitoring well from the source area, MW-102, the CTdeclined steadily after the first EZVI injections. The CT concentration started toincrease in late 2009, as presented in Exhibit 6. The second round of EZVI created atemporary increase in CT to 5.9 mg/L in September 2010, with a subsequent decline to0.835 mg/L in June 2011.

The rebound observed af-ter the first injections clearlydemonstrated the need toprovide sufficient EZVI tocompletely destroy the freeproduct within the sourcearea.

The chloride concentration in the source area well, MW-205, increased from 332mg/L before the first EZVI injection in 2008 to 738 mg/L. This increase of 406 mg/L inchloride equates to the complete destruction of 437 mg/L CT, far more than what wasdetected in the monitoring well. This is clear evidence of undissolved free product beingdestroyed by EZVI. A similar spike in chlorides after the second round occurred, from693 mg/L to 1,880 mg/L, equivalent to the complete destruction of 1,287 mg/L CT, anorder of magnitude higher than what was dissolved in the groundwater. The reboundobserved after the first injections clearly demonstrated the need to provide sufficient EZVIto completely destroy the free product within the source area.



Exhibit 4. Layout of Texas initial injection grid and key monitoring

wells

The total cost for the two rounds of EZVI, including design, the EZVI product,injections, and oversight, was $292,600 for treating the 3,765 cu y. This equates to a costof $77.70 per cu y of source area (with DNAPL present) treated.

ILLINOIS BROWNFIELD SITE VADOSE ZONE REMEDIATION

During the site investigation of a 33-acre brownfield redevelopment along the Fox Riverin Illinois, an area impacted by PCE was discovered adjacent to the former heating plant ina railroad maintenance yard. PCE contamination, and its products of degradation,



Exhibit 5. MW-205 average annual concentrations

Exhibit 6. MW-102 average annual concentrations

extended from varying depths 4 to 18 ft bgs and extended over an area approximately 40ft by 70 ft. The total volume of PCE affected soil was 850 cu yd.

Remediation

EZVI was selected as the low-cost remediation option to treat the PCE contamination inthe vadose zone. In August 2008, a total of 9,834 lb EZVI were injected through 15pneumatic fracturing borings, with an average of 3 fractures/injections per boring.



Exhibit 7. VOC results—Illinois Brownfield Site.

Average Concentration Across Remediation Area, mg/kg

Analyte Initial 10 Months After Pneumatic Fracturing 8 Months After Soil Mixing

PCE 352.44 111.64 0.70TCE 9.90 2.82 0.05c-DCE 16.66 9.40 0.21VC 12.26 0.56 0.08

Refusal was encountered over approximately 25 percent of the remediation area at 1.5feet bgs, and the injection pattern was adjusted around this area.

In November 2008, a backhoe was mobilized to the site, and the source of refusal, aconcrete floor, was removed. A basement that had been backfilled with sand wasdiscovered, along with a dry well that had been backfilled with sand/soil and wassaturated with PCE. To address this concentrated PCE area, 1,200 lb EZVI were broughtto the site and mixed with the saturated soil within the dry well.

In June 2009, progress borings were completed that showed a significant reduction inPCE and its daughter products. PCE concentrations showed an approximate 66 percentreduction in concentration.

A second round of EZVI was mixed in with a backhoe, saturating the soil with waterduring mixing. A total of 7,100 lb EZVI were applied to the remaining hot spots, some ofwhich were beneath the former foundation and inaccessible to the earlier pneumaticfracturing.

Results

A total of 18,134 lb EZVI were applied to the estimated 850 cu yd impacted soil. In May2010, closure borings were conducted to assess the effectiveness of the EZVI treatments,and the results after both the initial and final EZVI applications are summarized inExhibit 7.

Overall mass destruction within the vadose zone during the 21-month remediationperiod was 99.7 percent. In December 2010, the Illinois EPA issued a No FurtherRemediation letter for the site.

Costs

The remediation cost for the EZVI, pneumatic fracturing contractor, excavator, andengineering oversight was $93,500, or $110 per cu yd. Given the small volumeremediated (850 cu yd), this was a cost-effective remediation, completed in under 2 years.

SUMMARY

Source area remediation with EZVI combines abiotic and biotic processes to overcome thelimitations of individual processes in the following ways:



� The delivery of iron within EZVI to the subsurface is more efficient than whenattempting to place iron alone within the subsurface. EZVI comes to the site ready toinject, so there is no supplemental mixing equipment and associated labor commonwhen injecting iron using a guar suspension or fluidizing the iron in a high-pressuregas injection.

� In source areas, the concentrations of the chlorinated solvents are so high thatbiological inhibition is a serious impediment to remediation. With EZVI, the con-taminants partition preferentially into the vegetable oil, where contaminants contactiron particles suspended in the water miscelles. This results in a dramatic reductionin contaminant concentration prior to establishing anaerobic biological conditions.

� With iron alone and many substrates, there is no driving force for DNAPL to migratetoward the material being used. With EZVI, the vegetable oil will wick in DNAPL,dramatically retarding the dissolution into the groundwater, so rapid groundwaterquality improvements occur.

� EZVI provides sustained treatment for several years after injections, resulting incontinued declines in contaminant levels.

EZVI is delivered in a formthat is ready to inject andcan be injected using a vari-ety of conventional deliverytechnologies.

EZVI is delivered in a form that is ready to inject and can be injected using a variety ofconventional delivery technologies. The case studies presented herein have beensuccessful in remediating soil and groundwater with free product to essentiallynondetectable levels, with the cost for remediating source areas ranging from $58.35 to$110 per cu yd, based on site-specific conditions and volume of soil to be treated. There isa trade-off between the quantity of EZVI injected per unit volume and remediation time.Lower dosages result in more of the contaminants being reduced via the biologicaldechlorination pathway, with more of the daughter products initially produced.However, with the sustained treatment effect, lower dosages can be successful over alonger period of time. Higher dosages result in faster remediation, which is attributed tothe abiotic reaction, resulting in lower levels of daughter products being produced. Theretardation of the dissolution of the chlorinated solvents results in significant groundwaterimprovements in a relatively short period of time.

In November 2009, US EPA Region 5 issued its Greener Cleanup Interim Policy(US EPA, 2009). This policy outlines the practices that are deemed Greener CleanupPractices, and include practices that:

� minimize the production and/or use of pollutants;� utilize water conservation;� reduce emissions of greenhouse gases and other air pollutants; and� conserve natural resources and energy.

EZVI meets all of these criteria. EZVI uses food-grade vegetable oil and iron, whichare essentially nontoxic, renewable resources. The associated energy consumption isminimal, primarily that associated with the EZVI production, shipping, and injectiontechnology. There is no ongoing post-treatment energy consumption associated with thistechnology other than that used for monitoring. Overall, the technology generatesminimal greenhouse gases and other air pollutants. When the life cycle costs are factoredin, including ongoing monitoring costs, EZVI is a cost-effective, green remediationtechnology that provides sustained treatment for several years after application.



REFERENCES

Adamson, D. T., McGuire, T. M., Newell, C. J., & Stroo, H. (2011). Sustained treatment: Implications for

treatment timescales associated with source-depletion technologies. Remediation Journal, 21(2), 27–50.

Arnold, W. A., & Roberts, A. L. (2000). Pathways and kinetics of chlorinated ethylene and chlorinated

acetylene reaction with Fe(0) particles. Environmental Science & Technology, 34(9), 1794–1805.

McGuire, T. M., McDade, J. M., & Newell, C. J. (2006). Performance of DNAPL source depletion technologies

at 59 chlorinated solvent-impacted sites. Ground Water Monitoring & Remediation, 26(1), 73–84.

Quinn, J. (2005). Field demonstration of DNAPL dehalogenation using emulsified zero-valent iron.

Environmental Science & Technology, 39(5), 1309–1318.

U.S. Environmental Protection Agency, EPA Expert Panel on DNAPL Remediation. (2003). The DNAPL

remediation challenge: Is there a case for source depletion? (EPA/600/R-03/143): Washington, DC: U.S.

Government Printing Office.

James E. Huff, P.E., is senior vice president at Huff & Huff, Inc., a 35-person environmental engineering firm

in Oak Brook, Illinois, and license holder for EZVI manufacturing, distribution, and use. Mr. Huff has 40 years of

environmental experience and has conducted remediation projects across the country, including six sites where

EZVI was the primary remediation technology employed.


application of emulsified zero-valent iron: four full-scale remediation sites

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