United States Solid Waste and EPA/500/K-93/001
Environmental Protection Emergency Response January 1993
Agency (OS-110W)
&EPA In Situ Treatment of
Contaminated Ground Water:
An Inventory of Research and
Field Demonstrations
and Strategies for Improving
Ground Water Remediation
Printed on Recycled Paper
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September 16, 1992
In Situ Treatment of Contaminated Ground Water:
An Inventory of Research and Field Demonstrations
and
Strategies for Improving Ground-Water Remediation
Technologies
Technology Innovation Office
Office for Solid Waste and Emergency Response
U.S. Environmental Protection Agency
Washington, DC
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EXECUTIVE SUMMARY
Approximately 75% of the sites on the National Priorities List (NPL) have ground-water
contamination. An analysis of the Records of Decision (RODs) for these sites shows that pump-
and-treat remediation is almost exclusively chosen as the technology to address this
contamination. However, this technology has limited success, depending on the hydrogeologic
conditions and the target contaminants. The Technology Innovation Office (TIO) investigated
the availability and development of alternate technologies which may replace or enhance pump-
and-treat remediation. This paper provides an overview of the findings of this review and
suggests strategies to bring more focus and coherence to the research, development, and
application of in situ ground-water remediation technologies.
CONCLUSIONS
• Alternate technologies to pump-and-treat remediation are extremely limited.
• At the present rate of development, alternate technologies may not be available for 3 to
5 years.
• Fifteen technologies are being developed; however, most are in the bench scale or pilot
stages.
• Avenues of development support are available in the SITE Program, EPA labs, or the
Hazardous Substance Research Centers.
• Information sharing is efficient within the EPA umbrella, but sporadic between
responsible parties and industrial interest groups.
• Information on technology development or demonstration is not easily obtained.
RECOMMENDATIONS
• The development, diversity, and information-sharing concerning ground-water remediation
technologies must be improved by all stakeholders.
• Ground-water remediation workshops, conferences, or forums should help the exchange
of ideas and experiences.
• Information and data from field demonstrations and applications should be more easily
accessible to potential users.
• Demonstration programs should be directed more toward in situ ground-water treatment.
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TABLE OF CONTENTS
ABSTRACT 1
INTRODUCTION 1
Figure 1. Occurrence of Ground-Water Contamination at NPL Sites 1
Figure 2. Treatment Specified in Ground-Water RODs 2
Figure 3. Status of Research and Demonstration Projects for Treatment 3
Figure 4. Status of Research and Demonstration Projects for Enhanced Recovery .... 4
DESCRIPTION OF TECHNIQUES 4
Contaminant Treatment: Biological/Biochemical Methods 4
Oxygen Enhancement with Hydrogen Peroxide 4
Volatilization/Oxygen Enhancement by Air Sparging 5
Treatment with Nitrate/Acetate Enhancement 5
Nitrate Enhancement 5
Bioremediation with Methanotrophic Biodegradation 6
Reductive Dechlorination 7
Oxygen Enhancement with Microbubbles 7
Contaminant Treatment: Physical/Chemical Methods 8
Dehalogenation with Metal Catalysts : 8
Enhanced Contaminant Recovery 8
Electrokinetics 8
Water or Steam Flushing 9
Hydrofracturing 10
Surfactant Mobilization 10
Altering Chemical Conditions 10
Pneumatic Fracturing 11
Solvent Mobilization 11
CONCLUSIONS 12
RECOMMENDATIONS 14
BIBLIOGRAPHY 16
u
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ABSTRACT
The mission of the U. S. Environmental Protection Agency's (EPA's) Technology Innovation
Office (TIO) is to stimulate the development and application of innovative treatment technologies
at sites contaminated from hazardous wastes and to remove impediments that inhibit the use of
such technologies. TIO has become increasingly aware of the difficulties of remediating ground
water once it has been contaminated. A recent study has shown that remediation or control of
contaminated ground water using conventional pump-and-treat technology is difficult at many
sites and, in most cases, incomplete. Consequently, there is a need for improved ground-water
remediation technologies. In response, TIO plans to promote the development and field
application of alternative technologies to increase the options available.
As a first step, TIO began developing an inventory of treatment technologies either being
researched, field tested, or actually demonstrated and used. Sources of information included
universities, government research laboratories, private laboratories, and hazardous waste sites
where the technologies are actually in use. This inventory includes chemical, biological and
physical treatment techniques that either alter the toxicity of the contamination or improve
removal. Technologies to improve the mobility of non-aqueous phase liquids are in the scope.
However, pumping techniques and the construction of physical barriers are not.
INTRODUCTION
The predominance of ground-water contamination at hazardous waste sites (Figure 1) and the
dearth of methods to efficiently treat this contamination is a problem that the U.S. Environmental
Protection Agency (EPA) is examining. The contaminated ground water found at most Superfund
sites is often the limiting factor for complete site remediation.
Sites with no ground-water
contamination
Sites with ground-water
contamination *
"other media also contaminated
Figure 1. Occurrence of Ground-Water Contamination at NPL Sites
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Until recently, many believed that contaminants in surface soils were the only significant source
of ground-water contamination. Consequently, development of remediation technologies focused
mainly on this source. Ground-water management was limited to pump-and-treat containment
while in situ ground-water treatment was ignored. Technologies to remediate contaminated
ground water in situ still are not well developed, primarily because contaminated ground-water
plumes are difficult to define, contaminants can migrate in different directions simultaneously,
and, in most cases, the subsurface is unreachable for in situ physical examination.
Between 1982 and 1991, 70% (306) of all Superfund site Records of Decisions (RODs)
addressing ground-water remediation specified pump-and-treat technology for plume containment
(Figure 2). Within the past few years, regulators and researchers studying data from pump-and-
treat remediation systems have become convinced that, in addition to contaminated soils, the
source of much ground-water contamination is dense nonaqueous phase liquids (DNAPLs) and
other compounds that migrate downward into aquifers and often form pools of immiscible liquid
contaminants in the subsurface. The efficiency of contaminant removal from ground water at
sites where DNAPLs are present is contingent on the solubility of the contaminant, efficiency of
the pumping system and hydraulic characteristics of the aquifer. Unless the system is directly
removing the contaminant source, pump-and-treat systems only contain contamination. Since
most organic contaminants are, at best, sparingly soluble in water, achieving remediation goals
will be a long, inexact and expensive process. This recognition is fueling an increased interest
in improving the efficiency of pumping systems as well as in in situ treatment of contaminated
ground water and subsurface contaminant sources.
Institutional Controls,
Passive Treatment, Undetermined
In Situ or Enhanced
Pump-and-Treat
oo/ ^KflifHlpI^ Pump-and-Treat
Total = 439 RODS for FY82-91
Figure 2. Treatment Specified in Ground-Water RODs
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The purpose of this document is to describe recent research, development and application of
technologies that either treat ground-water contaminants in place or improve the solubility and
mobility of contaminants to enhance pump-and-treat remediation effectiveness. This report
discusses techniques that can be applied in situ and excludes pumping methodologies or surface
treatment systems. Figure 3 illustrates the status of research and demonstration for the treatment
techniques discussed in this report Figure 4 shows the status of research and demonstration for
enhanced recovery techniques. In addition, this publication presents conclusions based on
observations of the survey. Finally, strategies for action for stakeholders concerned with in situ
ground-water technology development are presented. This study has not defined the extent or
activities of research and development outside of EPA-supported groups.
Technique
Concept and
Bench Studies
Controlled
Field Experiments
Large Scale
Site Trials or
Scientific Reports
Accepted
Use
A. Biological/Biochemical
Treatment
Oj Enhancement with H2O2
Volatilization/O2 Enhancement by
Sparging
Treatment with Nitrate/acetate
Enhancement (CCI4only)
Nitrate Enhancement
Bioremediation w/ Methanotrophic
Biodegradation
Reductive Dechlorination
O2 Enhancement w/ Micro-bubbles
B. Physical/Chemical Treatment
Dehalogenation w/ Metal Catalyst:
Figure 3. Status of Research and Demonstration Projects for Treatment
KEY
Concept and Bench Studies: Theoretical models are developed and information searches conducted. Bench and column studies
are conducted in the laboratory. Most experimental variables (temperature, water content, contaminant concentration) are controlled.
Controlled Field Experiments: Studies are conducted on field plots and many of the variables are uncontrolled. Contaminant
concentrations, however, are usually controlled and adjusted. Data are used to calibrate generic predictive models.
Large Scale Site Trials: The technology is applied under actual site conditions with uncontrolled variables. Data collection and
analysis is comprehensive and used to refine the site predictive model.
Accepted Use: The technology is used for site cleanups and cost and performance data are being obtained A description of the
technology is included in general guidance for site cleanups. Generic predictive models are available.
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Technique
Concept and
Bench Studies
Controlled
Field Experiments
Large Scale
Site Trials or
Scientific Reports
Accepted
Use
Electrokinetics
Hot Water or Steam
Flushing
Hydrofracturing
Surfactant Mobilization!
Altering Chemical
Conditions
Pneumatic Fracturing
Solvent Mobilization
Figure 4. Status of Research and Demonstration Projects for Enhanced Recovery
Information on the innovative treatment technologies in this report was found in computerized
hazardous waste information databases such as EPA's Alternative Treatment Technologies
Information Center (ATTIC) Database, Hazardous Waste/Superfund Database, ORD Bibliographic
Database and Records of Decision System (RODS). The Ground Water Network of the National
Ground Water Information Center was also consulted. The review also included EPA research
descriptions, conference summaries, proceedings and compendiums. The survey was
supplemented with personal interviews and discussions with representatives of other federal
agencies, academic research centers and hazardous waste remediation consulting firms.
DESCRIPTION OF TECHNIQUES
Contaminant Treatment; Bioloeical/Biochemical Methods
Oxygen Enhancement with Hydrogen Peroxide. Refined petroleum can be readily biodegraded
under aerobic conditions; however, the rate of biodegradation is limited by the relatively low
solubility of oxygen in water. This problem can be overcome by injecting hydrogen peroxide.
In the most common application, a dilute solution of hydrogen peroxide is injected into
contaminated ground water.
This is an accepted technology often used in EPA's Underground Storage Tank (UST) program.
Variations, including the addition of nutrients to the hydrogen peroxide solution, are used if site
conditions permit. Field experience has shown that while the oxygen it provides is beneficial,
hydrogen peroxide itself is toxic to microorganisms. Consequently, its use must be carefully
monitored. The cost of hydrogen peroxide compared to that of oxygen must also be considered.
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Researchers from EPA's R. S. Ken Environmental Research Laboratory (RSKERL) in Ada,
Oklahoma, are in the process of obtaining performance and cost data from the Bioremediation
Performance Evaluation Project at the Champion International Superfund Site in Libby, Montana.
Another RSKERL research project that was carried out for several years in cooperation with the
Traverse Group and Rice University (National Center for Groundwater Research) at a U.S. Coast
Guard Station in Traverse City, Michigan, has produced some of the best data available on the
process. Additional research is being conducted at the EPA-sponsored Great Plains and Rocky
Mountain Hazardous Substance Research Center.1
Volatilization/Oxygen Enhancement by Air Sparging. Sparging or injection of air under
pressure through soils to below the water table can remove volatile organic chemicals (VOCs)
by creating a subsurface air stripper. Air bubbles contact dissolved/adsorbed-phase contaminants
and non-aqueous phase liquids (NAPLs) in the aquifer increasing volatilization. The volatile
organics are transported by the air bubbles into the vadose zone where they can be captured by
a vapor extraction system or, where permissible, allowed to escape to the atmosphere. As a
bonus, addition of the sparged air creates high oxygen levels in the ground water and vadose
zone and enhances natural biodegradation. This technology appears to have been taken from
concept to application without significant laboratory research. Estimates are that, at any one
time, 25 sites (mainly UST sites) use air sparging techniques.2
Ground-water aeration is reported to be a standard procedure in Germany and has been used since
1985. The "UVB technique," a method of air sparging combined with ground-water circulation,
has been used at approximately 60 sites in Germany. Contaminated ground water is stripped by
air in a below-atmospheric-pressure field. Pumps circulate ground water vertically within the
capture zone.
Treatment with Nitrate/Acetate Enhancement (CC^ only). Approximately 10 years ago,
researchers at the University of Illinois observed that complete chemical breakdown of carbon
tetrachloride occurred in columns of soils that also contained acetate and nitrate. In contrast to
reductive dechlorination, this reaction produced no chlorinated organic by-products from the
degradation of carbon tetrachloride.
Field experiments conducted at the Moffett Naval Air Station by Stanford University through the
Western Region Hazardous Substance Research Center and RSKERL have not duplicated the
laboratory results. Therefore, at this time, the usefulness of this method is undetermined. By
more thoroughly understanding the laboratory results, researchers hope to design a more effective
field study.
Nitrate Enhancement. Oxygen-enhanced bioremediation has been effective for many fuel spills.
Unfortunately, success is sometimes limited by the low solubility of oxygen. Nitrate can serve
as an electron acceptor in a reducing environment. It is more soluble and less expensive to inject
'Wilson, John. 1991. USEPA/RSKERL. Personal communication.
2Brown, Richard A., Ph.D. 1991. Groundwater Technology, Inc. Personal communication.
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into ground water. However, nitrate is subject to a drinking water standard and its release in the
subsurface must be rigorously monitored.
A field demonstration using this technology on a spill of JP-4 jet fuel was conducted in 1991 by
RSKERL at a U. S. Coast Guard Station in Traverse City, Michigan. Nitrate was mixed into
pumped ground water and reinfiltrated through a subsurface gallery. The performance of this
technology was compared with two other in situ ground-water treatment technologies at the site:
oxygen enhancement with hydrogen peroxide and bioventing by air injection in the vadose zone.
All three techniques successfully reduced benzene to below the drinking water standard.
Additional EPA-sponsored lab and field-testing is also being conducted at the Western Region
Hazardous Substance Research Center.
Bioremediation with Methanotrophic Biodegradation. Chlorinated solvents and their
transformation products are the most prevalent priority contaminants found in ground water at
Superfund sites. They include trichloroethylene (TCE); 1,1-dichloroethylene (1,1-DCE); 21,1,1-
trichloroethane (TCA); 1,2-dichloroethane (DCA); and vinyl chloride (VC). These chemicals are
characterized by their relatively high mobility in ground water and their resistance to biological
degradation. However, in recent years biodegradation of chlorinated solvents with concentrations
less than 100 parts per million has been demonstrated both in the presence and absence of
oxygen. (Higher concentrations of chlorinated solvents seem to be toxic to the microorganisms.)
However, when certain microorganisms are provided with methane for energy and growth, these
methanotrophic organisms produce enzymes that transform chlorinated compounds. Patented by
a RSKERL scientist in 1985, the process of providing one chemical to the microorganisms to
facilitate transformation of another, called cometabolism, offers new possibilities for
environmental restoration.
Laboratory studies on this technique have been conducted through RSKERL, the Northeast
Hazardous Substance Research Center, the Western Region Hazardous Substance Research Center
and the Biosystems Technology Development Program. A successful field demonstration was
conducted by the Western Region Hazardous Substance Research Center at Moffett Naval Air
Station, in Mountain View, California. In 1990, the Center also conducted an initial feasibility
study for full-scale application at the Allied Signal Corporation Superfund site in St. Joseph,
Michigan. (The results of the latter study showed that concentrations of TCE were too high to
support methanotrophic organisms and, instead, biodegradation using indigenous microorganisms
will be studied.)
ABB Environmental Services, Inc., will demonstrate this technology in the SITE Emerging
Technology Program. They propose to treat a mixture of chlorinated and non-chlorinated organic
solvents in ground water by applying an in situ two-zone plume interception treatment system.
The first zone is anaerobic where growth of methanogenic bacteria is stimulated. This zone
promotes the reductive dechlorination of chlorinated solvents from highly chlorinated forms such
as tetrachloroethylene (PCE), TCE and TCA to less chlorinated forms such as DCE, VC and
DCA. The second zone is made aerobic by introducing oxygen. Here the methanotrophs
growing on injected methane are expected to oxidize the partiaUy-dechlorinated products from
the first zone.
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Reductive Dechlorination. Researchers have been studying the isolation and stimulation of
indigenous microorganisms capable of dechlorinating polychlorinated biphenyls (PCBs) and other
chlorinated hydrocarbons. They have found that changing the environment of the contaminated
zone from anaerobic to aerobic is productive. The heavily-chlorinated compounds are
dechlorinated in an anaerobic environment and the less heavily-chlorinated compounds can be
degraded in aerobic conditions. Theoretically, oxygen-rich water can be pumped into
contaminated ground water that is naturally anaerobic. Researchers at some institutions have
found, however, that making the system aerobic stimulates the degradation of the less chlorinated
daughter products, but also stops the reductive dechlorination of the original, more chlorinated,
compounds. EPA is also sponsoring research to develop engineered microorganisms capable of
anaerobic reductive dehalogenation.
The feasibility of sequential anaerobic-aerobic treatment of PCB-contaminated sediments is being
investigated at the University of Michigan. So far, successful batch experiments have illustrated
the potential of the process for in situ PCB degradation. With support from the Great Lakes and
Mid-Atlantic Hazardous Substance Research Center and General Electric, a large river model will
be used to demonstrate the feasibility of the sequential process in a bench-scale study that
simulates natural conditions.
An aerobic PCB biodegradation experiment was conducted by General Electric at Fort Edwards,
New York, on the Hudson River. General Electric is also planning an anaerobic dechlorination
field study on river and pond sediments contaminated with PCBs. Results of the first test will
be available in early 1992; data from the second in 1993.3
ABB Environmental Services, Inc., proposes to use reductive dechlorination with methanogenic
bacteria in a passive ground-water remediation project in the SITE Emerging Technology
Program.
Oxygen Enhancement with Microbubbles. This technology is designed to carry oxygen and
other nutrients to subsurface microorganisms to stimulate in situ bioremediation of organic
contaminants in ground water. Oxygen is mixed with an inexpensive, biodegradable surfactant
to produce highly stable microbubbles in the 40-per-micron size range. Bubbles this size can
remain dispersed in a coarse sand matrix in the saturated zone without significant coalescence.
Partially supported by EPA and the Air Force, researchers at Virginia Polytechnic Institute and
State University (Virginia Tech) in Blacksburg, Virginia, have taken the lead in developing this
technology. In proposed field tests, microbubbles will be added to the soil either through a
laminated interceptor trench perpendicular to the ground-water flow, or through a series of
injection wells. As the ground water passes by or through the injected microbubbles, oxygen will
slowly dissolve in the water, delivering oxygen to support bacterial activity. Numerous pilot
scale studies have been conducted and the developer will perform additional laboratory studies
prior to field testing.4
3Abramowitz, Dan. 1991. General Electric. Personal communication.
4Michelsen, Don. 1991. Virginia Polytechnic Institute. Personal communication.
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Contaminant Treatment; Physical/Chemical Methods
Physical/chemical methods of contaminant treatment have not been studied as extensively as
biological methods. There has been little field testing to date. Many physical/chemical treatment
techniques lend themselves to use in above-ground reactors but few to in situ use because of the
difficulties in achieving effective contact of a catalyst with contaminants.
Dehalogenation with Metal Catalysts. Researchers are studying the use of metal catalysts in
the degradation of halogenated organic compounds in aqueous solutions. Based on batch and
column tests, the catalyst performs two functions: (1) it produces highly reducing conditions, and
(2) it participates in the degradation process. The catalysts have been effective in degrading a
range of halogenated methanes, ethanes and ethenes.
Investigators conducted a small-scale field test using iron filings as the treatment catalyst at the
Waterloo Center for Groundwater Research in Ontario. They placed permeable walls containing
the catalyst underground perpendicular to the flow of contaminated ground water. The system
is entirely passive and cost effective—the catalyst is even an industrial waste product Seventy
percent of the organic compounds present (trichloroethylene and carbon tetrachloride) were
removed. The lack of complete degradation was believed to be the result of cutting oil residue
on the iron filings. The Waterloo Center continues to conduct laboratory work on this
technique.5
The University of Michigan has developed chemical model systems to study the extent to which
transition metal-organic catalysts influence the rate of dechlorination of chlorinated aliphatic
compounds.
Enhanced Contaminant Recovery
The terms "removal by pumping" and "pump-and-treat" refer to the extraction of contaminated
ground water and subsequent treatment of the extracted ground water at the surface. Extraction
is accomplished through the use of extraction (pumping) wells operated at specific locations and
depths to optimize contaminant recovery. Injection wells may be installed to enhance recovery
by flushing contaminants toward extraction wells. This technology is best suited for managing
mobile chemicals found in relatively permeable and homogeneous hydrogeologic settings. The
techniques described below are designed to improve the effectiveness of pump-and-treat systems.
Electrokinetics. When an electric field is applied to a porous material containing a liquid (soil,
for example), movement of charged molecules and of the liquid itself is induced. The
phenomenon is known as "electroosmosis." As the electric field pulls positively charged ions
toward the cathode, the water in the pores is also drawn toward the cathode due to "viscous
drag." Consequently, positively-charged organic or inorganic contaminants can be made to
migrate in the electric field to a collection point for removal by pumping.
5Gillham, Robert. 1991. University of Waterloo. Personal communication.
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Two major laboratory efforts are providing information on this technology. Research at the
University of Colorado is currently funded by the Electric Power Research Institute and has been
funded in the past by the U.S. Air Force. Experimental results show elevated concentrations of
contamination in water adjacent to the electrodes. Researchers at Massachusetts Institute of
Technology (MIT) have been studying electrode emplacement geometries and electric field
strengths under a grant from the Northeast Hazardous Substance Research Center.Commercial
application of electromigration in Europe has been led by a company called Geokinetics in
Rotterdam, The Netherlands. Some of their laboratory and field tests report a wide range in the
removal levels of heavy metal. Success appears contingent on hydraulic conductivity. The
highest degree of removal, over 90%, was achieved in clayey soils, whereas in porous soils only
65% was removed.
In the United States, Electrokinetics, Inc., will conduct studies under the SITE Emerging
Technology Program. Bench-scale laboratory studies investigating the removal of heavy metals,
radionuclides and organic contaminants will be completed by the end of 1991. Field studies
investigating removal of radionuclides will be completed in late 1992. The technology will be
available for full-scale implementation upon completion of the pilot-scale studies.
Hot Water or Steam Flushing. This process removes volatile and semi-volatile organic
compounds such as TCE, TCA and dichlorobenzene (DCS) above and below the water table.
Steam is forced into the aquifer by injection wells and the vaporized volatile components are
removed by vacuum extraction. The technology uses readily-available components, such as
extraction and monitoring wells, manifold piping and vacuum pumps. Hot water injection may
be particularly useful at oil refineries, which often have oil-contaminated ground water and waste
heat that can be used in the recovery process.
Udell Technologies, Inc., completed a successful demonstration of steam-enhanced extraction in
1988 and the technology is now scheduled to be demonstrated under the SITE Demonstration
Program at the McClellan Air Force Base in Sacramento, California. The site is contaminated
by waste oils mixed with VOCs, semi-volatile organic chemicals and metals.
A case study will be performed by the Department of Energy to remediate a gasoline spill to
depths of 137 feet at the Lawrence Livermore National Laboratory in Livermore, California. The
Naval Civil Engineering Laboratory, in Port Hueneme, California, and EPA's Risk Reduction
Engineering Laboratory (RREL) in Cincinnati are also considering a demonstration at the
LeMoore Naval Air Station.
A similar use of thermal technology can be used to recover oily wastes by adapting a technology
presently used for secondary petroleum recovery and for primary production of heavy oil and tar-
sand bitumen. Steam is injected below the oily wastes and condenses to cause rising hot water
that dislodges the oils upward into more permeable soil regions. Hot water can then be injected
adjacent to the now-floating oil bank to move the oil to extraction wells as it is contained and
moved by barriers of hot water. In situ biological treatment may follow the displacement. It can
be applied to manufactured gas plants, wood treating sites and other sites with saturated soils
containing organic liquids such as coal tars, pentachlorophenols, creosotes and petroleum by-
products. The Western Research Institute (WRI) has tested this technology in the laboratory and
in a field study under the SITE Emerging Technology Program. In the SITE Demonstration
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Program, WRI will conduct additional studies at the Pennsylvania Power and Light Brodhead
Creek Site in Stroudsburg, Pennsylvania. In addition to the SITE Program demonstration, the
technology is now being demonstrated at a wood treatment site in Minnesota.
Hydrofracturing. Hydrofracturing involves the cracking of low permeability and over-
consolidated sediments using pressurized water injected through wells. The resulting cracks are
filled with a porous medium such as a sand/gel mixture that props open the cracks to form sand-
filled lenses that serve either as avenues for bioremediation or to improve pumping efficiency.
Three hydrofracturing field demonstrations on VOCs in the unsaturated zone have been conducted
by RREL—two combined with vapor extraction and one with bioremediation. The developers
believe that it can be used in the saturated zone as long as the sediments can be fractured. RREL
is ready to apply the technology to any site that meets the geologic criteria.
Surfactant Mobilization. Surfactants increase contaminant mobility in two ways. The first is
by increasing the solubility of the contaminant in water. This speeds up the removal of sorbed
contaminants by increasing their concentration in solution. The second is by reducing interfacial
tension of nonaqueous phased liquids (NAPLs). This requires greater surfactant concentrations
than those required for increasing solubility, but results in direct mobilization of the NAPL,
which may allow it to be extracted more efficiently. Although the successful application of
surfactants to enhance oil recovery has been demonstrated, transferring the knowledge to
problems of aquifer remediation is not direct Incorrect formulation and application can
exacerbate remediation by making the NAPL more mobile thereby increasing its potential to
reach larger populations as it flows in the subsurface.
Surfactants can effectively complex and exchange with metal ions. Investigators in the
laboratories at the University of Oklahoma have demonstrated the use of cationic surfactant
polymers for separation of anionic contaminants such as chromate from aqueous solution through
selective binding. Laboratory studies at RSKERL have shown that anionic surfactants increase
the removal efficiency of adsorbed chromate from aquifer sediments. Researchers at the Great
Lakes and Mid-Atlantic Hazardous Substance Research Center have developed computer and
physical models of surfactant mobilization systems. The Western Region Hazardous Substance
Research Center is studying the use of surfactants to improve biodegradation. Researchers at the
State University of New York-Buffalo are conducting field tests on surfactant mobilization of
PCE at the Borden Canadian Forces Base (with scientists from the Waterloo Center) and of
carbon tetrachloride at the Dupont Chemical Plant in Corpus Christi. Studies will continue until
mid-1992. Researchers at Rice University (National Center for Groundwater Research) are
studying methods to increase the amount of natural surfactant produced in situ by subsurface
microbial populations. Much of the research conducted has been concerned with the efficiency
of surfactants to solubilize, but little has been done concerning the fate and behavior of these
compounds.
Altering Chemical Conditions. Changing the redox conditions in aquifers theoretically can
change the valence state of a metal contaminant in ground water. This can reduce its mobility
or make it less toxic, such as in the transformation of hexavalent chromium to trivalent
chromium. Scientists at the Western Region Hazardous Substance Research Center and EPA's
Environmental Research Laboratory in Athens, Georgia (AERL) have conducted laboratory tests
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on reducing hexavalent chromium in aquifer materials. AERL researchers are now ready to study
this technology in a field test
Shifting the equilibrium solubility of solids and solid/solution systems can change the aqueous
concentrations of some contaminants. The Oregon Graduate Institute is exploring chemical
enhancement with barium sulfate for a pump-and-treat operation at a chromium-contaminated site.
At sites with extensive chromium contamination, a large fraction of the chromium appears to be
precipitated in a solid barium chromate phase from which it slowly dissolves into ground water.
The slow rate of dissolution limits the rate at which the chromium can be pumped from the
aquifer. Adding barium sulfate will increase the solubility of the chromate by substituting sulfate
for chromate in the solid phase. This technology is still at the laboratory bench-scale stage.
Pneumatic Fracturing. This process requires the injection of highly pressurized air into the
subsurface contaminated zone to extend existing fractures and create a secondary network of
fissures and channels. This enhanced fracture network increases the permeability of the soil to
liquids and vapors and accelerates the removal of contaminants, particularly by vapor extraction,
biodegradation and thermal treatment
The New Jersey Institute of Technology (NJIT), with support from the Northeast Hazardous
Substance Research Center, conducted studies of pneumatic fracturing as part of the SITE
Emerging Technology Program beginning in 1988. Four field demonstrations all showed an
improved permeability in relatively impermeable soils and rock. To date, most of the work on
this technology has been in the unsaturated zone but the NJIT developers believe that the removal
of contaminated ground water can also be enhanced by pneumatic fracturing.
In 1990, this technology (integrated with a surface treatment system) was accepted in the SITE
Demonstration Program. Accutech Remediation Systems, Inc., will begin then- demonstration in
1992 at a TCE-contaminated site in New Jersey.
Solvent Mobilization. The rate of removal of organic contaminants is often limited by their low
solubility in water. Many of these contaminants are much more soluble in solvents other than
water. Although theoretical models suggest that the injection of solvents into a contaminated
zone can improve mobility of several organic compounds, complications in the field include
complex and unpredictable transport behavior, biofouling of the aquifer and reductive dissolution
of iron and manganese oxides that clog wells.
Laboratory experiments on solvent mobilization have been conducted by researchers at the
Northeast Hazardous Substance Research Center, but no field studies have been completed.
Researchers at RSKERL are conducting laboratory tests and, in cooperation with the U.S. Coast
Guard, expect to begin a small-scale field test of solvent flushing at Traverse City in 1992.
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CONCLUSIONS
Research Coordination
1) EPA has provided avenues for development of in situ ground-water remediation
technologies through the SITE Program, the Hazardous Substance Research Centers
(HSRCs) or directly through the EPA labs.
EPA's Office of Research and Development (ORD) has established programs to support the
laboratory development and field testing of emerging technologies. Of the IS technologies
examined, five are being studied by researchers at either RSKERL, RREL, or AERL. One
patent for in situ ground-water treatment has been awarded to a RSKERL scientist Four of
the HSRCs are supporting studies on eight technologies. Two Centers (the Great Lakes/Mid-
Atlantic and the Western Region Centers) have committed approximately one third of their
grant budget to in situ ground-water remediation.
The Superfund Innovative Technology Evaluation (SITE) Program has accepted five
technologies for demonstration and testing—three in the Emerging Technology Program and
two in the Demonstration Program. Technology developers may not be aware of these
avenues or may choose not to use them. Major stakeholders (refineries, wood treating
facilities, electric power generators, etc.) may be supporting development, but information
and data from these findings may not be freely distributed.
2) Communication and information-sharing among EPA-sponsored researchers appears
to be efficient.
Although the scope of this project did not include process analyses, we observed that the
researchers, in most cases, were very familiar with die work of their colleagues. The ORD
laboratories, HSRCs and other university-based research centers seem to be the focal points
for ground-water research. While EPA researchers are individually informed on their
colleagues' work in other federal agencies, there is no centralized sharing or formal
networking of research information. Our interviews and literature reviews rarely led to work
being supported by responsible parties or industrial interest groups. Communication could
be improved between these parties and EPA.
3) There are no major mechanisms available to collect and distribute information from
field demonstrations and applications. The exception are projects involved in the SITE
program.
We found very little cost and performance data on the two technologies that have reached
the stage of "accepted use" (oxygen enhancement by air sparging and hydrogen peroxide
injection). Users of these technologies (mostly in the UST Program) explained successes and
failures when interviewed, but there is no systematic effort to collect, organize and distribute
the data. Six Superfund Records of Decision (RODs) include in situ ground-water
remediation (five specify nitrate enhancement), but plans to collect data and exchange
information concerning experiences during these applications must be developed.
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Communications could be improved among managers of Superfund sites that are using
similar technologies. We located a developer using the same technology as specified in two
RODs on a State-lead cleanup through a chance conversation at a technical conference. The
experiences of these developers should be shared among themselves as well as with potential
future users.
Technology Status
1) The alternatives to pump-and-treat remediation are extremely limited.
With the exception of oxygen enhancement by sparging and hydrogen peroxide injection, no
technology has adequate field demonstration or actual application data to be considered as
an alternative to pump-and-treat remediation. Cumulatively, the UST, CERCLA and RCRA
programs estimate that 100,000 to 200,000 sites have ground-water contamination. However,
only IS technologies are being developed to supplement or improve pump-and-treat
remediation.
2) At the present rate of development and field demonstration, alternative technologies to
pump-and-treat remediation may not be available for application for at least 3 to 5
years.
Most of the technologies are approaching, or are in, the "controlled field experiment" stage
of development At this stage, studies are conducted in a natural environment but many
factors, such as contaminant concentration and homogeneity, are controlled and adjusted.
Laboratory and bench-scale studies provide qualitative information (what and why).
However, field studies provide quantitative information (how much and how long). These
time-controlled studies may take months or years to provide data to advance the technology
to large-scale site trials.
3) There is a lack of emerging technologies to treat inorganic contaminants.
All of the treatment technologies reviewed are designed to treat organic contaminants and
only two recovery technologies are specifically designed toward solubilizing or mobilizing
inorganic compounds. However, approximately 20% of Superfund sites have ground-water
contaminated by lead, arsenic or chromium. Therefore, only two technologies are being
developed to address hundreds of sites contaminated with inorganics.
4) The development of delivery systems is as important as the development of the
technology.
Techniques to deliver in situ treatments to contaminated ground water are complicated and
underdeveloped. While some researchers are developing technologies along with the
necessary delivery systems, others are relying on existing delivery systems such as well
injection or trench infiltration. Incompatibility between technology and delivery systems can
cause technical problems that decrease efficiency. Consequently, the success of a technology
is partially contingent on its compatibility with the delivery system.
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RECOMMENDATIONS
1) All major stakeholders should take a lead in improving the development and diversity
of ground-water remediation technologies. Information-sharing among all parties needs
to be improved as well.
All stakeholders involved in ground-water remediation would benefit if more technologies
were available. Site conditions and contaminant characteristics are unique. Consequently, a
standardized cleanup technology (pump-and-treat) cannot meet all the requirements for
efficient remediation. For example, the technologies required to clean up an aquifer
contaminated with TCE in a fractured rock matrix are not the same as those to clean up an
aquifer contaminated with hexavalent chromium in a coarse sand matrix. A variety of
treatment technologies and delivery systems are needed to accommodate the complexities of
each site. The few technologies now being developed cannot effectively meet the needs of
the tens of thousands of ground-water remediation projects in the CERCLA, RCRA and UST
programs. EPA, DOE, and DOD, as well as other stakeholders, should take a lead in
improving the development, diversity, and information-sharing of ground-water remediation
technologies.
2) Stakeholders involved in ground-water remediation should be convened to exchange
ideas and experiences for improving the state of technology.
Activities and opinions from the private sector may not have been adequately defined during
this survey. Most of the information was obtained from scientists and databases either
partially or wholly supported by the government However, there may be advances
developed by research supported by private industry. A continuing forum of industry
representatives, government and private researchers, regulators, consultants and contractors
who are involved in ground-water remediation should be held. The purpose would be to
discuss successes and failures, barriers to using more efficient ground-water remediation
methods and courses of action which could be taken to increase the diversity of available
technologies.
3) Information and data from field demonstrations and applications should be stored and
managed in an accessible manner.
Specifically, the location of and contact person for each project, as well as a brief description
of the technology used, should be easily accessible. Some of this information is already
captured in the RODS database and the Bioremediation Field Initiative databases, but
additional information could be obtained from the Underground Storage Tank (UST)
Program, RCRA corrective action sites and other remediation projects regulated by the states.
Improving communication between technology practitioners and users will decrease the risk
of making uninformed decisions.
4) The adequacy of delivery systems for in situ technologies should be examined.
Some researchers are developing delivery systems concurrent with a technology. We suspect,
however, that many systems are being planned and constructed in the field without benefit
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of the normal developmental phases. Documentation of this trial-and-error process may help
other users apply the technology more efficiently.
5) Demonstration projects could be directed more towards in situ ground-water treatment.
In the SITE program, there are two in situ ground-water technologies in the 78 proposed or
existing demonstrations and four in situ ground-water technologies in the 44 emerging
technologies. Ground-water contamination is found at approximately 75% of NPL sites.
Clearly, the percentage of projects directed at the problem is disproportionately low. Other
Federal agencies should evaluate the activities in their demonstration programs to further
support in situ ground-water technologies.
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BIBLIOGRAPHY
Publications
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Environmental Protection, Vienna, Austria, 1990.
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Sci. and Tech., 23(6), 1989.
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