Groundwater Contamination: DOD Uses and Develops a Range of
Remediation Technologies to Clean Up Military Sites (30-JUN-05,
GAO-05-666).
To date, the Department of Defense (DOD) has identified nearly
6,000 sites at its facilities that require groundwater
remediation and has invested $20 billion over the past 10 years
to clean up these sites. In the past, DOD primarily used
"pump-and-treat" technologies to contain or eliminate hazardous
contaminants in groundwater. However, the long cleanup times and
high costs of using pump-and-treat technologies often make them
expensive and ineffective for groundwater remediation. As
directed by Public Law 108-375 and as agreed, GAO (1) described
current DOD groundwater remediation technologies and (2) examined
whether any new technologies are being used or developed outside
the department that may have potential for DOD's use and the
extent to which DOD is researching and developing new approaches
to groundwater remediation. GAO provided the Department of
Defense with a draft copy of the report for its review and
comment. DOD generally agreed with the contents stating that the
report is an accurate summary of DOD's use and field tests of
remedial technologies. DOD also provided technical clarifications
that have been incorporated, as appropriate.
-------------------------Indexing Terms-------------------------
REPORTNUM: GAO-05-666
ACCNO: A28621
TITLE: Groundwater Contamination: DOD Uses and Develops a Range
of Remediation Technologies to Clean Up Military Sites
DATE: 06/30/2005
SUBJECT: Environmental monitoring
Groundwater contamination
Hazardous substances
Military facilities
Pollution control
Technology assessment
Waste management
Water pollution
DOD Defense Environmental Restoration
Program
DOD Environmental Security Technology
Certification Program
DOD Strategic Environmental Research and
Development Program
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GAO-05-666
United States Government Accountability Office
GAO Report to Congressional Committees
June 2005
GROUNDWATER CONTAMINATION
DOD Uses and Develops a Range of Remediation Technologies to Clean Up Military
Sites
a
GAO-05-666
[IMG]
June 2005
GROUNDWATER CONTAMINATION
DOD Uses and Develops a Range of Remediation Technologies to Clean Up Military
Sites
What GAO Found
DOD has implemented or field-tested all of the 15 types of generally
accepted technologies currently available to remediate contaminated
groundwater, including several alternatives to pump-and-treat
technologies. Some of these technologies, such as bioremediation,
introduce nutrients or other materials into the subsurface to stimulate
microorganisms in the soil; these microorganisms consume the contaminant
or produce byproducts that help break down contaminants into nontoxic or
less-hazardous materials. DOD selects the most suitable technology for a
given site on the basis of several factors, such as the type of
contaminant and location in the subsurface, and the relative
cost-effectiveness of a technology for a given site. DOD has identified a
number of contaminants of concern at its facilities, each of which varies
in its susceptibility to treatment. The table below shows the technologies
DOD used to remediate contaminated groundwater.
GAO did not identify any alternative groundwater remediation technologies
being used or developed outside DOD that the department has not considered
or used. Most of the new approaches developed by commercial vendors and
available to DOD generally use novel materials applied to contaminated
sites with existing technologies. DOD actively researches and tests new
approaches to groundwater remediation largely by developing and promoting
the acceptance of innovative remediation technologies. For example, DOD's
Strategic Environmental Research and Development Program supports public
and private research on contaminants of concern to DOD and innovative
methods for their treatment.
Technologies DOD Components Used for Groundwater Remediation
Technology Air Force Army
Army Corps of Engineers
Defense
Logistics
Agency Navy
In-situ Ex-situ
Air sparging X X X X X
Bioremediation X X X X X
Enhanced recovery X X X
Chemical treatments X X X X X
Monitored natural attenuation X X X X X
Multiphase extraction X X X X X
Permeable reactive barriers X X X X X
Phytoremediation X X X X
Thermal treatments X X X X
Advanced oxidation processes X X X X
Air stripping X X X X X
Bioreactors X X X
Constructed wetlands X X X X
Ion exchange X X X X
Adsorption (mass transfer) X X X X X
Source: Department of Defense.
United States Government Accountability Office
Contents
Letter 1
Results in Brief 4
Background 5
DOD Has Implemented or Field-tested a Wide Range of Technologies
to Remediate Sites Contaminated with Groundwater 10
DOD Is Proactively Using and Developing New Approaches to
Groundwater Remediation 19
Agency Comments 24
Appendixes
Appendix I:
Appendix II:
Appendix III: Appendix IV: Appendix V:
Objectives, Scope, and Methodology
Technologies for the Remediation of Contaminated Groundwater
Ex-situ Technologies In-situ Technologies
Groundwater Remediation Experts Consulted Comments from the Department of
Defense GAO Contact and Staff Acknowledgments
26
29 29 31
39
40
41
Tables Table 1: Technologies DOD Components Used for Groundwater
Remediation 15
Table 2: Technologies Available for the Treatment of DOD's
Contaminants of Concern 17
Figures Figure 1: Example of a Site with Contaminated Groundwater 6
Figure 2: Selected Phases and Milestones in DOD's Environmental
Cleanup Process 8
Figure 3: Example of a Conventional Pump-and-Treat System 12
Contents
Abbreviations
CERCLA Comprehensive Environmental Response, Compensation, and
Liability Act DNAPL dense nonaqueous phase liquids DOD Department of
Defense EPA Environmental Protection Agency ESTCP Environmental Security
Technology Certification Program ITRC Interstate Technology and Regulatory
Council LNAPL light nonaqueous phase liquids RCRA Resource Conservation
and Recovery Act SERDP Strategic Environmental Research and Development
Program
This is a work of the U.S. government and is not subject to copyright
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separately.
A
United States Government Accountability Office Washington, D.C. 20548
June 30, 2005
The Honorable John Warner Chairman The Honorable Carl Levin Ranking
Minority Member Committee on Armed Services United States Senate
The Honorable Duncan L. Hunter Chairman The Honorable Ike Skelton Ranking
Minority Member Committee on Armed Services House of Representatives
The Department of Defense (DOD) has identified close to 6,000 sites at its
active, closing, and formerly used defense facilities where the
groundwater has been so contaminated by past defense activities and the
improper disposal of hazardous wastes that cleanup (remediation) of the
site is required.1 Groundwater-the water found beneath the earth's surface
that fills pores between soil particles, such as sand, clay, and gravel,
or that fills cracks in bedrock-accounts for about 50 percent of the
nation's municipal, domestic, and agricultural water supply. When
groundwater becomes polluted, it can endanger public health or threaten
the environment. DOD estimates that cleanup of its contaminated sites will
cost billions of dollars and may take decades to complete because of the
extent of the contamination and the complexity of groundwater systems.
DOD identifies, investigates, and cleans up contaminated groundwater
through its Defense Environmental Restoration Program. This program was
established by section 211 of the Superfund Amendments and Reauthorization
Act of 1986, which amended the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) of 1980. In fiscal year 2004, DOD
obligated approximately $1.7 billion for environmental restoration
activities, including groundwater remediation, on active, closing, and
formerly used defense facilities. Multiple DOD
1Remediation of a contaminated site involves efforts to remove, destroy,
or isolate contaminants found in the groundwater. In some cases, disposal
practices at these sites predate the enactment of relevant environmental
cleanup statutes.
entities-the Air Force, Army, Defense Logistics Agency, and Navy-are
responsible for groundwater remediation on active DOD facilities.2 In
addition, the U.S. Army Corps of Engineers (Corps) is responsible for
groundwater remediation on properties formerly owned, leased, or used by
the military.3 The Air Force has the greatest number of sites with
contaminated groundwater needing remediation, followed by the Navy, Army,
Corps, and Defense Logistics Agency.4 DOD must carry out its groundwater
remediation program in a manner consistent with section 120 of CERCLA.
Section 120 addresses the cleanup of federal facilities and, among other
things, provides for participation in cleanup decisions by the state in
which a federal facility is located. Personnel from the installation where
the contamination is located work with DOD-hired contractors; regulators
(federal, state, local, or tribal); and other stakeholders to evaluate and
select appropriate technologies to achieve cleanup goals (e.g., treatment
or containment of contaminants). DOD may use a single technology or a
combination of technologies to clean up the groundwater at a particular
site.
In the past, DOD primarily used traditional "pump-and-treat" technologies
to contain or eliminate hazardous contaminants in groundwater.
Pumpand-treat technologies extract contaminated groundwater for treatment
in above-ground (ex-situ) facilities and are often used to prevent the
further spread of contamination in the groundwater. However, according to
DOD, the Environmental Protection Agency (EPA), and groundwater
remediation experts we consulted, pump-and-treat often is expensive
because of long cleanup times, inefficiencies in removing contaminants
from the subsurface, and the costs associated with disposing of the
contaminant and treated water. Recently, DOD has begun to use alternatives
to pump-andtreat technologies that rely on a variety of biological,
chemical, or physical processes to treat the contaminated groundwater
underground (in-situ).
2The Navy oversees environmental restoration on Marine Corps facilities.
3The Corps may also participate in groundwater remediation activities on
active Army installations, some Air Force installations, and properties
that are scheduled for closure as part of the Base Realignment and Closure
Act process.
4For the purposes of this report, we have defined a "site" as a specific
area of contamination and a "facility" as a geographically contiguous area
under DOD's ownership or control within which a contaminated site or sites
are located. A single DOD facility may contain multiple sites requiring
cleanup.
GAO Definition of Groundwater Remediation Technology
For this report, we define a technology as a distinct technical method or
approach for containing, treating, or removing contaminants found in
groundwater.
Any modifications or enhancements to a technology, such as variations in
the material or equipment used during treatment, are not considered to be
a separate technology.
As directed by Public Law 108-375,5 and as agreed with your offices, this
report (1) describes the groundwater remediation technologies that DOD is
currently using or field-testing and (2) examines whether any new
groundwater remediation technologies are being used outside the department
or are being developed by commercial vendors that may have potential for
DOD's use, and the extent to which DOD is researching and developing new
approaches to groundwater remediation. In addition, this report provides
limited information on the key characteristics, benefits, and limitations
of selected groundwater remediation technologies in appendix II.
To determine the range of groundwater remediation technologies DOD is
currently using or field-testing, we developed a questionnaire that we
sent to the DOD components responsible for DOD's groundwater cleanup
efforts-the Air Force, Army, Corps, Defense Logistics Agency, and Navy. In
the questionnaire, we listed 15 technologies that are currently available
for the treatment of contaminated groundwater and asked the DOD components
to indicate which of the technologies they have used and to provide
examples of specific groundwater remediation projects.6 We developed this
list of technologies by reviewing existing lists developed by the National
Research Council, EPA, and others, as well as by working with a
groundwater remediation consulting firm and five nationally recognized
groundwater remediation experts. To identify DOD components involved with
groundwater remediation activities, we met with department officials
responsible for developing policy on groundwater remediation and for
researching and developing groundwater remediation technologies. We
reviewed documents, reports, and guidance on groundwater remediation from
DOD, EPA, and the National Academy of Sciences; and visited an Air Force
groundwater remediation project and a facility DOD uses to test innovative
groundwater remediation technologies. In addition, we attended a national
groundwater remediation conference, and spoke with a number of commercial
vendors of groundwater remediation technologies about their products and
efforts to develop innovative approaches to groundwater remediation.
Information presented in this report is based on publicly available
documents and information provided by government officials, independent
consultants, and experts. We did not review
5Ronald W. Reagan National Defense Authorization Act for Fiscal Year 2000,
Pub. L. No. 108375, S: 316, 118 Stat. 1811, 1843 (Oct. 28, 2004).
6See appendix II for more information on each of the 15 technologies.
nonpublic research and development activities that may be ongoing in
private laboratories. A more detailed description of our scope and
methodology is presented in appendix I. We performed our work from January
2005 through May 2005, in accordance with generally accepted government
auditing standards.
Results in Brief DOD has implemented or field-tested all of the 15 types
of generally accepted technologies currently available to remediate
groundwater. These various remediation technologies include both in-situ
and ex-situ treatments, each of which relies on biological, chemical, or
physical processes to clean up groundwater. Of these 15 types of
technologies, the Navy reported that it has used all 15 and the Air Force,
Army, and Corps have used 14 each. The Defense Logistics Agency, which has
significantly fewer sites to clean up than the other DOD components,
reported using 9 of the 15 technologies. According to department
officials, DOD selects the most suitable technology for a given site on
the basis of a number of factors, such as the type of contaminant and its
location in the subsurface, and the relative cost-effectiveness of a
technology for a given site. DOD has identified a number of contaminants
of concern at its facilities, each of which varies in its behavior and
susceptibility to treatment by the various technologies. Some of the
contaminants, such as chlorinated solvents, can potentially be treated
using 14 of the 15 technologies, while others, such as metals, can only be
treated effectively with 7 of the 15 technologies. According to analyses
conducted by groups such as EPA and the Federal Remediation Technologies
Roundtable, the cost-effectiveness and performance of each technology can
vary significantly depending, in part, on site-specific conditions. A more
detailed description of each of the technologies we identified for
cleaning up groundwater is presented in appendix II.
We did not identify any alternative technologies for groundwater
remediation being used or developed outside of DOD that it has not
considered or employed. However, we did identify a number of new
approaches to groundwater remediation being developed by commercial
vendors-most of which are also being explored or used by DOD-that are
based on modifications of or enhancements to existing technologies. Most
of the new approaches involve the use of novel materials applied to
contaminated sites using existing technologies. For example, DOD has
recently used molasses and vegetable oils at several bioremediation
projects to stimulate microorganisms in the subsurface to biodegrade
contaminants. Other alternative approaches being developed by
commercial vendors usually involve modifying the design of existing
technologies. For example, DOD is exploring the use of nanoscale rather
than granular sized metals to clean up sites contaminated by chlorinated
solvents. In addition, we found that DOD is actively involved in
researching and testing new approaches to groundwater remediation, largely
through its efforts to develop and promote the acceptance of innovative
technologies. For example, DOD maintains several programs-such as the
Strategic Environmental Research and Development Program-to support the
research, development, and testing of innovative cleanup approaches. This
program, a DOD-funded basic and applied research program, supports public
and private research on contaminants of concern to DOD and innovative
methods for their treatment, as well as a variety of other activities. DOD
also pursues innovative solutions to groundwater remediation through its
Environmental Security Technology Certification Program. This program
field-tests and validates promising innovative environmental technologies
and transfers these technologies to the commercial sector. DOD also works
with various stakeholders, including the regulatory community, to promote
understanding and acceptance of innovative remediation approaches. For
example, DOD participates in the Interstate Technology and Regulatory
Council, a state-led coalition that works with the private sector,
regulators, and other stakeholders to increase the regulatory acceptance
of new environmental technologies.
Background DOD sites that require cleanup are often contaminated by many
different types of hazardous materials, have contamination in more than
one medium (e.g., soil, surface water, or groundwater), and may encompass
several acres or even square miles. Groundwater stored in subsurface
formations called aquifers can become contaminated in a number of ways.
For example, contamination can occur when a liquid hazardous substance
soaks down through the soil. Often, groundwater contamination is difficult
to address because of the complexity of groundwater systems. The
subsurface environment can be composed of numerous layers of diverse types
of material-such as sand, gravel, clay, and solid rock-and fractured
layers through which groundwater flows. These variations in the subsurface
often affect how groundwater flows through a contaminated site and can
influence how contaminants are spread and accumulate in the subsurface.
Chemical properties of the contaminant also influence its distribution in
the subsurface. Typically, contaminated sites consist of a source zone
where the bulk of the contaminant is concentrated and a plume of
contamination that develops beyond the source of contamination
as a result of groundwater flowing through the contaminated site. See
figure 1 for an illustration of a site with contaminated groundwater.
Figure 1: Example of a Site with Contaminated Groundwater
According to DOD, the Air Force has identified more than 2,500 sites on
its active and closing installations with contaminated groundwater; the
Navy has identified more than 2,000 sites; the Army has identified about
800 sites; and the Defense Logistics Agency has identified 16 sites. In
addition, DOD has identified more than 500 contaminated groundwater sites
on formerly used defense sites for which the Corps is responsible for
cleanup. Contamination on DOD facilities can pose a threat to military
personnel, the public, and the sustainability of DOD's training and
testing ranges. DOD first initiated its environmental restoration efforts
in 1975. Over the last 10 years, DOD has invested approximately $20
billion for the environmental restoration of contaminated sites, including
remediation of contaminated groundwater on and around active, closing, and
formerly used defense facilities.7
Source: Adapted from EPA, Fact Flash #5, Groundwater.
DOD Facilities Can Have Significant Groundwater Contamination
7Some of DOD's sites are considered megasites-defined by EPA as sites
requiring investments of over $50 million to achieve cleanup.
DOD Cleanup Activities Generally Follow the CERCLA Process
DOD's policies for administering cleanup programs are outlined in its
guidance for managing its environmental restoration program and generally
follow the CERCLA process for identifying, investigating, and remediating
sites contaminated by hazardous materials.8 According to DOD's guidance,
department officials are required to involve EPA, relevant state and local
government officials, and the public, among others, at specified points in
the cleanup process. See figure 2 for more information on the phases of
DOD's environmental cleanup process.
8DOD carries out some groundwater remediation as corrective action under
the Resource Conservation and Recovery Act of 1976 (RCRA). According to
DOD, while RCRA and CERCLA contain somewhat different procedural
requirements, these differences do not substantively affect the outcome of
remedial activities.
Figure 2: Selected Phases and Milestones in DOD's Environmental Cleanup
Process
Source: Department of Defense, Defense Environmental Programs, Annual
Report to Congress, Fiscal Year 2004.
Note: These phases may overlap or occur simultaneously, but cleanup
activities at DOD facilities generally occur in the order shown.
Once DOD identifies potential contamination on one of its facilities, it
initiates a preliminary assessment to gather data on the contaminated
site. If DOD finds evidence that the site needs remediation, it consults
with EPA to determine whether the site qualifies for inclusion on the
National Priorities List.9 If EPA places a DOD facility on the National
Priorities List, CERCLA requires DOD to begin the next phase of cleanup
within 6 months. During this next phase, called a remedial
investigation/feasibility study, DOD characterizes the nature and extent
of contamination and evaluates the technical options available for
cleaning up the site.
DOD also pursues a remedial investigation/feasibility study for sites that
do not qualify for the National Priorities List but require
decontamination. Data collected during the remedial investigation
influences DOD's development of cleanup goals and evaluation of
remediation alternatives. During the feasibility study, often conducted
concurrently with the remedial investigation, DOD identifies applicable
regulations and determines cleanup standards that will govern its cleanup
efforts. CERCLA requires that sites covered by the statute be cleaned up
to the extent necessary to protect both human health and the environment.
In addition, cleanups must comply with requirements under federal
environmental laws that are legally "applicable" or "relevant and
appropriate" as well as with state environmental requirements that are
more stringent than the federal standards. Furthermore, CERCLA cleanups
must at least attain goals and criteria established under the Safe
Drinking Water Act and the Clean Water Act, where such standards are
relevant and appropriate under the circumstances.
Once cleanup standards have been established, DOD considers the merits of
various actions to attain cleanup goals. Cleanup actions fall into two
broad categories: removal actions and remedial actions. Removal actions
are usually short term and are designed to stabilize or clean up a
hazardous site that poses an immediate threat to human health or the
environment. Remedial actions, which are generally longer term and usually
costlier, are
9This list represents EPA's highest priorities for cleanup nationwide,
including public and private sites considered by EPA to present the most
serious threats to human health and the environment. To make its
determination, EPA uses a hazard-ranking system to evaluate the severity
of the contamination by examining the nature of the contaminants, the
pathways through which they can move (such as soil, water, or air), and
the likelihood that they may come into contact with a receptor-for
example, a person living nearby. According to DOD's Defense Environmental
Programs, Annual Report to Congress, Fiscal Year 2004, DOD has 152
facilities that are listed or proposed for listing on the National
Priorities List.
aimed at implementing a permanent remedy. Such a remedy may, for example,
include the use of groundwater remediation technologies. Also during the
feasibility study, DOD identifies and screens various groundwater
remediation technologies based on their effectiveness, feasibility, and
cost. At the conclusion of the remedial investigation/feasibility study,
DOD selects a final plan of action-called a remedial action-and develops a
Record of Decision that documents the cleanup objectives, the technologies
to be used during cleanup, and the analysis that led to the selection. If
EPA and DOD fail to reach mutual agreement on the selection of the
remedial action, then EPA selects the remedy. If the cleanup selected
leaves any hazardous substances, pollutants, or contaminants at the site,
DOD must review the action every 5 years after the initiation of the
cleanup.10 According to DOD policy, this may include determining if an
alternative technology or approach is more appropriate than the one in
place. DOD continues remediation efforts at a site until the cleanup
objectives stated in the Record of Decision are met, a milestone referred
to as "response complete." Even if DOD meets the cleanup objectives for a
site, in some cases the site may require long-term management and
monitoring to ensure that it does not become contaminated from residual
sources of pollution.
DOD Has Implemented or Field-tested a Wide Range of Technologies to
Remediate Sites Contaminated with Groundwater
DOD has implemented or field-tested all of the 15 types of generally
accepted technologies currently available to remediate groundwater. These
15 technologies include 6 ex-situ and 9 in-situ technologies, each of
which can be used to treat a variety of contaminants. All of these
groundwater remediation technologies rely on a variety of biological,
chemical, or physical processes to treat or extract the contaminant. DOD
guidance directs department officials to consider cost-effectiveness and
performance when selecting technologies for cleanup.
1042 U.S.C. S: 9621(c). The applicable EPA regulation differs from the
statute: It requires the five-year reports only if contaminants will
remain at the site "above levels that allow for unlimited use and
unrestricted exposure." 40 C.F.R. S: 300.430(f)(4)(ii).
Fifteen Ex-situ and In-situ Technologies Are Currently Available for
Groundwater Cleanup
We identified a range of ex-situ and in-situ technologies that DOD can
employ to clean up a contaminated groundwater site. Ex-situ technologies
rely on a pump-and-treat system to bring the contaminated water above
ground so that it can be treated and the contaminants removed. Some exsitu
technologies destroy the contaminant, while others remove the contaminant
from the groundwater, which is subsequently disposed of in an approved
manner. The decontaminated water can be discharged to surface water, used
as part of a public drinking water supply, injected back into the ground,
or discharged to a municipal sewage plant. We identified 6 categories of
ex-situ technologies:
o Advanced oxidation processes often use ultraviolet radiation with
oxidizing agents-such as ozone or hydrogen peroxide-to destroy
contaminants in water pumped into an above-ground treatment tank.
o Air stripping separates volatile contaminants from water by exposing
the water to large volumes of air, thus forcing the contaminants to
undergo a physical transformation from liquid to vapor (volatilization).
There is no destruction of the contaminant; therefore, the contaminant
must be removed and disposed of properly.
o Bioreactors areabove-ground biochemical-processing systems designed to
degrade contaminants in water using various microorganisms, an approach
similar to that used at a conventional wastewater treatment facility.
Contaminated groundwater flows into a tank or basin where it interacts
with microorganisms that degrade the contaminant.
o Constructed wetlands are artificially built wetland ecosystems that
contain organic materials, plants, microbial fauna, and algae that filter
or degrade contaminants from the water that is pumped into the wetland.
o Ion exchange involves passing contaminated water through a bed of resin
media or membrane that exchanges ions in the contaminants, thus
neutralizing them into nonhazardous substances.
o Adsorption (mass transfer) involves circulating contaminated water
through an above-ground treatment vessel containing a sorbent
material-such as activated carbon-that removes the contaminant from the
water.
(See app. II for more information on key characteristics of these ex-situ
technologies.)
Figure 3: Example of a Conventional Pump-and-Treat System
Source: Federal Remediation Technologies Roundtable Treatment Technologies
Screening Matrix, 2002.
Similarly, we identified nine in-situ technologies that can be used to
remediate contaminated groundwater. In contrast to ex-situ technologies,
in-situ technologies treat contaminants within the subsurface. Some
in-situ technologies-such as bioremediation and chemical treatment-destroy
the contaminant within the subsurface by altering the contaminant's
chemical structure and converting the toxic chemical to a nontoxic form
(e.g., benzene to carbon dioxide). Other in-situ technologies-such as
multiphase extraction and enhanced recovery using surfactant flushing-
facilitate the removal of the contaminant from the subsurface for
treatment above ground. Still other technologies-such as air
sparging-combine insitu treatments with extraction techniques.
o Air sparging introduces air or other gases into the subsurface to
remove the contamination from the groundwater through volatilization
(converting a solid or liquid into a gas or vapor that may be treated at
the surface), and in some configurations may also introduce oxygen into
the contaminated area to stimulate in-situ biological breakdown (i.e.,
bioremediation) or ozone to achieve chemical oxidation of the contaminant.
o Bioremediation relies on microorganisms living in the subsurface to
biologically degrade groundwater contaminants through a process called
biodegradation. Bioremediation may be engineered and accomplished in two
general ways: (1) stimulating native microorganisms by adding nutrients,
oxygen, or other electron acceptors (a process a called biostimulation) or
(2) providing supplementary pregrown microorganisms to the contaminated
site to augment naturally occurring microorganisms (a process called
bioaugmentation).
o Enhanced recovery using surfactant flushing involves the injection of
active agents known as surfactants11 into contaminated aquifers to flush
the contaminated groundwater toward a pump, which removes the contaminated
water and surfactant solution to the surface for treatment and disposal of
the contaminants.
o Chemical treatments inject various substances into the groundwater that
can chemically oxidize or reduce contaminants into less-toxic or
nonhazardous materials.
o Monitored natural attenuation involves using wells and monitoring
equipment in and around a contaminated site to track the natural physical,
chemical, and biological degradation of the contaminants. Although not
necessarily considered a treatment technology, this approach is often used
to monitor contaminant concentrations to ensure that human health and the
environment are not threatened.
o Multiphase extraction uses a series of pumps and vacuums to
simultaneously remove from the subsurface combinations of contaminated
groundwater, free product (i.e., liquid contaminants floating on top of
groundwater), and hazardous vapors. This technology can be used to remove
contaminants from above and below the
11Surfactants, or surface active agents, are molecules with two structural
units: one with an affinity for water and one with an aversion to water.
This molecular combination is useful for dissolving some contaminants and
enhancing their mobility by lowering the interfacial tension between the
contaminant and the water.
groundwater table, thereby exposing more of the subsurface for treatment.
o Permeable reactive barriers are vertical walls or trenches built into
the subsurface that contain a reactive material to intercept and remediate
a contaminant plume as the groundwater passes through the barrier.
o Phytoremediation relies on the natural hydraulic and metabolic
processes of selected vegetation to remove, contain, or reduce the
toxicity of environmental contaminants in the groundwater.
o Thermal treatments involve either pumping steam into the aquifer or
heating groundwater to vaporize or destroy groundwater contaminants.
Vaporized contaminants are often removed for treatment using a vacuum
extraction system.
(See app. II for more information on key characteristics of these in-situ
technologies.)
Although most in-situ technologies have the advantage of treating a
contaminant in place, these technologies may afford less certainty about
the extent and uniformity of treatment in contaminated areas when compared
with some ex-situ technologies. For example, enhanced recovery using
surfactant flushing has not been used extensively and has limited data on
its remediation effectiveness, whereas air stripping has been widely used
for several decades to remove certain contaminants, and its benefits and
limitations as a water treatment technology are wellunderstood. In some
cases, a combination of in-situ and ex-situ technologies may be used
(either concurrently or successively) to clean up a site if a single
technology cannot effectively remediate an entire site with its range of
contaminants and subsurface characteristics. According to the National
Research Council, integration of technologies is most effective when the
weakness of one technology is mitigated by the strength of another
technology, thus producing a more efficient and cost-effective solution.12
12For more information, see National Research Council, Water Science and
Technology Board, Contaminants in the Subsurface: Source Zone Assessment
and Remediation (Washington, D.C., 2004).
DOD Has Used the Full Range of Groundwater Remediation Technologies
Identified
As shown in table 1, the DOD components involved in groundwater
remediation activities reported using the full range of technologies that
we identified as currently available for groundwater remediation.
Specifically, the Navy reported that it has used all 15 of the currently
available technologies; the Air Force, Army, and Corps reported using 14
each. The Defense Logistics Agency has used 9 of the available
technologies for the cleanup of the limited number of contaminated
groundwater sites for which it is responsible.
Table 1: Technologies DOD Components Used for Groundwater Remediation
Defense Army Corps Logistics Technology Air Force Army of Engineers Agency
Navy
In-situ
Air sparginga X X X X X
Bioremediationb X X X X X
Enhanced recovery/surfactant flushingc X X X
Chemical treatmentsd X X X X X
Monitored natural attenuation X X X X X
Multiphase extractione X X X X X
Permeable reactive barriersf X X X X X
Phytoremediationg X X X X
Thermal treatmentsh X X X X
Ex-situ
Advanced oxidation processesi X X X X
Air stripping X X X X X
Bioreactors X X X
Constructed wetlands X X X X
Ion exchangej X X X X
Adsorption (mass transfer) X X X X X
Source: Department of Defense responses to GAO data collection instrument.
Notes: This table focuses on technologies used to treat contaminants found
in groundwater. It excludes technologies used (1) to treat and dispose of
the byproducts of groundwater remediation-such as emissions of potentially
harmful volatile gases; (2) exclusively to treat contaminated soil (such
as soil washing or excavation), although soil remediation is often
conducted in conjunction with groundwater remediation; and (3) primarily
to physically contain a contaminant-such as soil capping. See appendix II
for more information on the key characteristics, benefits, and limitations
of each of these technologies.
aIncludes related remedial approaches and technologies, such as
co-metabolic air sparging, oxygen and ozone sparging, in-well air
stripping, and soil vapor extraction. Soil vapor extraction, although not
technically a groundwater remediation technology, is often used with air
sparging to extract or capture emissions that result from treating
contaminated groundwater.
bIncludes related bioremedial approaches, such as bioaugmentation,
biostimulation, co-metabolic treatment, enhanced aerobic biodegradation,
enhanced anaerobic biodegradation, and biobarriers.
cIncludes related remedial approaches that use co-solvents to improve the
solubility of surfactants in the subsurface, and other technologies, such
as hydrofracturing and pneumatic fracturing, that attempt to increase the
permeability of the subsurface.
dIncludes various remedial approaches and technologies that chemically
oxidize or reduce contaminants in-situ, as well as the in-situ
immobilization and stabilization of soluble metals.
eIncludes the related technologies of bioslurping and dual-phase
extraction.
fIncludes both biotic and abiotic passive and reactive treatment barriers.
gIncludes the related technologies of phytostabilization,
phytoaccumulation, phytoextraction, rhizofiltration, phytodegradation,
rhizosphere degradation, organic pumps, and phytovolatization.
hIncludes related heating technologies, such as steam flushing, conductive
heating, and electrical resistance heating.
iIncludes the related technologies of ultraviolet oxidation, ultraviolet
photolysis, and photocatalysis.
jIncludes technologies that use ion exchange resins or membranes to remove
contaminants from groundwater, including dissolved metals and nitrates.
According to department officials, DOD selects the most suitable
technology to clean up a contaminated site based on a number of factors,
including the type of contaminant, its location and concentration at
different levels in the subsurface, and its chemical and physical
composition.13 These officials identified a number of contaminants of
concern, such as federally regulated chlorinated solvents (commonly found
in metal degreasers) and fuels used for military aircraft and vehicles.
DOD officials also consider some other hazardous materials that are not
regulated by the federal government-such as the rocket propellant
perchlorate-to be contaminants of concern because they are regulated by
some states, such as California, where DOD has active, closing, or
formerly used defense sites that need groundwater remediation.
According to the groundwater remediation experts we consulted, some of
DOD's contaminants of concern, such as chlorinated solvents, can
potentially be treated using 14 of the 15 technologies, while others, such
as metals, can be treated with only 7 of the 15 technologies. For example,
many chlorinated solvents do not readily dissolve in water; and because
they are often more dense (heavier) than water, they migrate downward and
pool at the bottom of aquifers, thereby limiting the number of
technologies that can treat them. Alternatively, some contaminants
13A contaminant may exist in aqueous (dissolved in water), nonaqueous,
solid (sorbed), or gaseous form.
composed of petroleum hydrocarbons (e.g., jet fuel, diesel fuel, and motor
gasoline) float on top of the water table because they are less dense
(lighter) than water, and technologies such as air sparging or multiphase
extraction can often effectively treat or extract them through processes
such as volatilization or free product recovery. See table 2 for
information on which of the 15 technologies can potentially treat each of
DOD's contaminants of concern.
Table 2: Technologies Available for the Treatment of DOD's Contaminants of
Concern
Chlorinated Technology solventsa Explosivesb Fuelsc Metalsd Oxygenatese
Propellantsf In-situ Ex-situ
Air sparging X X X
Bioremediation X X X X X X
Enhanced recovery/surfactant flushing X X X
Chemical treatments X X X X X X
Monitored natural attenuation X X X X X X
Multiphase extraction X X X
Permeable reactive barriers X X X X X X
Phytoremediation X X X X X
Thermal treatments X X X
Advanced oxidation processes X X X X
Air stripping X X X
Bioreactors X X X X X
Constructed wetlands X X X X X X
Ion exchange X X
Adsorption (mass transfer) X X X X X
Sources: Department of Defense and several groundwater remediation
experts.
Notes: This table presents the contaminants of concern to DOD. Depending
on their concentrations, these contaminants can pose health risks to
humans. The ability for any one technology to effectively treat a
contaminant is greatly influenced by site-specific conditions. Some
technologies are generally less effective or currently less utilized to
treat contaminants.
aIncludes, but is not limited to, perchloroethene (PCE), trichloroethene
(TCE), dichloroethene (DCE), vinyl chloride (VC), and chloroform (CF).
bIncludes, but is not limited to, trinitrotoluene (TNT); dinitrotoluene
(DNT); cyclotrimethylene trinitramine, cyclonite, and hexogen (RDX); and
octogen and cyclotetramethylene-tetranitramine (HMX).
cIncludes gasoline, diesel fuel, jet fuel, and BTEX. BTEX is an acronym
for benzene, toluene, ethylbenzene, and xylene-a group of volatile organic
compounds commonly found in petroleum hydrocarbons, such as gasoline.
dIncludes, but is not limited to, arsenic, barium, cadmium, chromium,
copper, lead, mercury, selenium, silver, and zinc.
eIncludes, but is not limited to, oxygen-bearing chemicals that can be
added to fuel to bring additional oxygen to the combustion process. These
include ethers such as methyl tertiary butyl ether (MTBE) and its related
compounds.
fIncludes, but is not limited to, materials such as ammonium perchlorate
and potassium perchlorate that are used in the manufacturing and testing
of solid rocket propellants and other munitions such as flares.
Technology Selection Is Also Influenced by Cost and Performance
According to DOD guidance on groundwater remediation, department officials
should consider cost-effectiveness and performance of various groundwater
remediation options when selecting the most suitable cleanup technology. A
number of factors influence total cleanup costs for a given site, such as
how long the cleanup is expected to take and the horizontal and vertical
extent of the contamination. In addition, according to the National
Research Council, actual cleanup costs associated with each technology
depend on site-specific hydrogeologic, geochemical, and contaminant
conditions.14 Thus, a particular technology may be the most cost-effective
solution for one site and not necessarily for another similarly
contaminated site. The National Research Council and others have also
found that performance of most technologies, including time for total
cleanup, also depends on complexities within the site's subsurface (i.e.,
site heterogeneities) as well as contaminant characteristics. For example,
the effectiveness of certain in-situ technologies-such as air sparging-
decrease as site heterogeneity increases because the air will naturally
follow certain pathways that may bypass the contaminant. Similarly, the
effectiveness of many in-situ technologies may be limited by the presence
of some chlorinated solvents that, if heavier than water, can migrate into
inaccessible zones in the subsurface. Alternatively, in-situ thermal
treatments that use conductors to heat the soil are not as sensitive to
heterogeneity in the subsurface and contaminant characteristics because
thermal conductivity varies little with the properties of subsurface
materials and certain contaminants are more easily volatilized at elevated
temperatures. However, equipment and energy costs may make this approach
more costly than other in-situ technologies.
While overall conclusions on the cost-effectiveness of each groundwater
remediation technology are difficult to reach, a few groups have attempted
14For more information, see National Research Council, Contaminants in the
Subsurface: Source Zone Assessment and Remediation (Washington, D.C.,
2005).
to estimate costs for various technologies. For example, EPA has developed
a technology cost compendium for several technologies based on cost data
from various public and private remediation projects.15 Similarly, the
Federal Remediation Technologies Roundtable-a federal consortium of
representatives from DOD, EPA, and other federal agencies-has attempted to
evaluate the relative overall cost and performance of selected remediation
technologies in general terms.16 However, according to DOD officials and
other experts we consulted, these efforts to compare technologies are of
only limited utility because of the site-specific nature of technology
decisions.
DOD Is Proactively Using and Developing New Approaches to Groundwater
Remediation
We did not identify any alternative groundwater remediation technologies
being used outside the department that DOD has not already either employed
or tested on some scale (laboratory or pilot). However, we did identify a
number of new approaches to groundwater remediation being developed by
commercial vendors, but these approaches are based on modifications of or
enhancements to existing technologies. Most of these new approaches are
being used or field-tested by DOD and involve novel materials that are
applied to contaminated sites using existing technologies. In addition, we
found that DOD is generally aware of new approaches to groundwater
remediation, in part through its efforts to develop remediation
technologies with the commercial sector. DOD also works with various
stakeholders, including the regulatory community, to promote understanding
and acceptance of innovative remediation approaches. Some DOD officials
and groundwater remediation experts believe additional resources may be
needed in order to develop and advance DOD's process for selecting the
most appropriate technology at a site.
15For more information, see EPA, Office of Solid Waste and Emergency
Response, Remediation Technology Cost Compendium-Year 2000 (Washington,
D.C., 2001).
16For additional information, see the online version of the Federal
Remediation Technologies Roundtable Treatment Technologies Screening
Matrix at http://www.frtr.gov/scrntools.htm.
Most New Approaches Employ Novel Materials or Modifications to Existing
Technologies
Most of the new remediation approaches commercial vendors have developed
and made available to DOD use existing technologies to apply novel
materials to contaminated sites. These materials typically accelerate the
breakdown of contaminants through biological or chemical processes. In
particular, multiple commercial vendors have developed proprietary
compounds used during bioremediation to stimulate microorganisms in the
subsurface to biodegrade contaminants. Some of these compounds are
designed to slowly release oxygen or other nutrients into the subsurface
in an effort to prolong their availability, which microorganisms need to
biodegrade the contaminants. DOD has also field-tested several novel
compounds for bioremediation that are derived from food-grade materials
such as molasses or vegetable oils. These compounds can be injected into
the contaminated site using pre-existing wells or other existing
techniques such as direct push injection:
o The Army used a compound developed by a commercial vendor to stimulate
the bioremediation of chlorinated solvents at a contaminated site at its
Rocky Mountain Arsenal. This compound reacted with the contaminated
groundwater to produce lactic acid, which native microorganisms used to
produce the hydrogen that ultimately led to the biological degradation of
the contaminants. In addition, the Air Force reported using
oxygen-releasing compounds to stimulate aerobic biodegradation at several
of its cleanup sites, including a site in Florida contaminated by spilled
fuel.
o DOD has also field-tested the use of molasses during bioremediation to
treat chlorinated solvents at Vandenberg and Hanscom Air Force bases. In
addition, DOD reported using vegetable oils to stimulate microorganisms in
order to treat groundwater contaminated by chlorinated solvents and
perchlorate at a variety of locations, including naval facilities in
Massachusetts, Rhode Island, and South Carolina.
Commercial vendors have also developed innovative approaches for
chemically treating contaminants in the subsurface. For example, several
vendors have developed proprietary approaches for delivering oxidants,
such as molecular oxygen and ozone with or without hydrogen peroxide, into
the subsurface to achieve in-situ chemical oxidation of a variety of
contaminants, including fuels and chlorinated solvents. These oxidants are
often delivered underground using variations of existing air sparging
technologies and a variety of injection technologies. In addition to
achieving in-situ chemical oxidation of target contaminants, the use of
ozone with or without hydrogen peroxide can enhance the aerobic
biodegradation of contaminants because it increases oxygen levels in the
subsurface. Commercial vendors have also developed approaches to directly
injecting other chemicals that are oxidizing agents, such as persulfate
and permanganate, into the subsurface using existing technologies such as
injection wells and direct push-probe technologies.
DOD is exploring with the commercial sector other innovative approaches to
groundwater remediation that involve modifying the engineering, design, or
application of existing technologies. For example, DOD is currently
working with the commercial sector to explore innovative uses of nanoscale
metallic materials-such as zero-valent iron and palladium impregnated
iron-to improve the efficacy of in-situ chemical treatments of chlorinated
solvents commonly found on DOD facilities.17 In the past, DOD used
metallic materials, such as zero-valent iron in granular form, to fill
trenches dug into the ground (a form of a permeable reactive barrier) to
chemically reduce chlorinated solvent plumes. The iron reacts with
chlorinated solvents, transforming them into benign products, such as
ethane and ethene. Treating contaminant plumes located deep within the
subsurface is often difficult, costly, and technically impossible using
this approach. Because of their size, nanoscale particles can be mixed
with other materials-such as vegetable oil and water-and injected deep
into the subsurface using existing technologies to treat contaminant
sources or plumes. Furthermore, nanoscale particles have high surface
areas relative to their volume (i.e., more metal is available to contact
and react with the contaminants), which will lead to increased rates of
reaction and more effective treatment.
DOD Supports the Development of New Technologies with the Commercial
Sector through Several Programs
We found that DOD is actively involved in researching and testing new
approaches to groundwater remediation, largely through its efforts to
develop and promote the acceptance of innovative groundwater remediation
technologies. According to the National Research Council, research on
innovative remediation technologies is sponsored almost exclusively by
federal agencies such as DOD and, in some circumstances, by individual
companies and industry groups that have joined with federal
17Nanoscale refers to miniscule particles that measure less than 100
nanometers in diameter. In comparison, an average human hair typically
measures 10,000 nanometers in diameter.
agencies in seeking more cost-effective solutions to common problems.18 In
particular, the DOD-funded Strategic Environmental Research and
Development Program (SERDP) supports public and private research on
contaminants of concern to DOD and innovative methods for their treatment,
among other activities. Created in 1990, the program primarily focuses on
issues of concern to DOD, although it is jointly managed by DOD, EPA, and
the Department of Energy.19 In fiscal year 2004, SERDP spent about $49
million to fund and manage projects in a variety of areas, including 27
projects related to groundwater remediation.
In response to technology needs and requirements generated by each of the
DOD components, SERDP funds research projects in private, public, and
academic settings on the fundamentals of contaminant behavior,
environmental toxicity, and the advanced development of cost-effective
innovative groundwater remediation technologies, among other things. For
example, SERDP has funded research projects to examine such issues as the
innovative use of vegetable oils for bioremediation; zero-valent iron
based bioremediation of explosives; and the behavior of, and treatment
options for, several emerging groundwater contaminants not yet regulated
by the federal government, such as 1,4-Dioxane (found in solvents),
N-Nitrosodimethylamine (found in rocket fuel), and trichloropropane (used
as a degreaser and paint stripper). In addition, SERDP holds workshops
with the scientific, engineering, academic, regulatory, and DOD-user
communities to discuss DOD's issues and identify needs for future
research, development, and testing of groundwater remediation techniques.
DOD also pursues innovative solutions to groundwater remediation through
its Environmental Security Technology Certification Program (ESTCP). This
program, founded in 1995, field-tests and validates promising innovative
environmental technologies that attempt to address DOD's highest-priority
environmental requirements, including groundwater
18See National Research Council, Water Science and Technology Board,
Environmental Cleanup at Naval Facilities: Adaptive Site Management
(Washington, D.C., 2003).
19SERDP's goals include supporting basic and applied research and
development of environmental technologies; providing information and data
on environmental research and development activities to other governmental
and private organizations in an effort to promote the transfer of
innovative technologies; and identifying technologies developed by the
private sector that are useful for DOD's and DOE's environmental
restoration activities.
remediation.20 Using a process similar to that of SERDP, ESTCP solicits
proposals from public and private researchers to field-test
laboratoryproven remediation technologies that have broad DOD and market
application. Once ESTCP accepts a proposal, it identifies a military
partner, which provides a site on a DOD installation where the researcher
can fieldtest the technology and document the technology's cost,
performance, and reliability. In fiscal year 2004, ESTCP spent about $35
million to fund and manage its program, including 36 projects on
groundwater remediation. These projects include the demonstration of an
enhanced recovery technology using innovative surfactants, emulsified
zero-valent nanoscale iron to treat chlorinated solvents, and an ion
exchange technology for the removal and destruction of perchlorate. ESTCP
and SERDP have colocated offices and, according to DOD officials, the two
programs work together to pursue the development of innovative groundwater
remediation technologies from basic research through advanced
field-testing and validation. ESTCP often funds the demonstration of
technologies that were developed by private or public researchers with
financial support from SERDP.
In addition to funding the development of innovative technologies, DOD
works with various stakeholders, including the regulatory community, to
promote the understanding and acceptance of these technologies. For
example, DOD participates in the Interstate Technology and Regulatory
Council (ITRC), a state-led coalition that works with the private sector,
regulators, and other stakeholders to increase the regulatory acceptance
of new environmental technologies. ITRC develops guidance on innovative
environmental technologies and sponsors training for regulators and others
on technical and regulatory issues related to environmental cleanup
technologies and innovative groundwater remediation approaches. According
to ITRC, these efforts are designed to help regulators streamline their
review process and enable wider acceptance of innovative environmental
technologies across state boundaries. In 2004, ITRC and DOD signed a
memorandum of understanding on the relationship between the two
organizations. As a result of the agreement, DOD now provides several
liaisons to the ITRC's board of advisers and helps the group develop
materials and training courses on innovative groundwater remediation
technologies. According to a DOD official, the department's partnership
20According to ESTCP, the program "provides an independent, unbiased
evaluation of the cost, performance, and market potential of
state-of-the-art environmental technologies based on field demonstrations
conducted under DOD operational conditions."
with ITRC has led to enhanced cooperation among state regulators, DOD
personnel, and community stakeholders and increased the deployment of
innovative technologies at DOD cleanup sites.
Although DOD is actively involved in the research and development of
innovative technologies, some groundwater remediation experts and some DOD
officials with whom we consulted believe that additional resources may be
needed to develop and advance DOD's process for selecting the most
appropriate technology at a site. These individuals believe that a better
understanding of the nature and extent of contamination at a site is
critical for selecting appropriate technologies for cleanup. Furthermore,
these experts and some DOD officials believe that additional resources may
be appropriate for examining and improving methods and engineering
approaches for optimizing the performance of the 15 types of groundwater
remediation technologies that are currently available. Other groundwater
remediation experts and some DOD officials suggested that more resources
may be needed to further develop innovative approaches to emerging
groundwater remediation issues, and to educate DOD personnel and
regulators on these approaches.
Agency Comments DOD generally agreed with the content of the report,
stating that the report is an accurate summary of DOD's use and field
tests of remedial technologies; DOD also provided technical clarifications
that we have incorporated, as appropriate.
We are sending copies of this report to appropriate congressional
committees; the Secretary of Defense; the Administrator of EPA; and other
interested parties. We will also make copies available to others upon
request. In addition, the report will be available at no charge on GAO's
Web site at http://www.gao.gov.
If you or your staff have any questions about this report, please contact
me at (202) 512-3841 or [email protected]. Contact points for our Offices of
Congressional Relations and Public Affairs may be found on the last page
of this report. GAO staff who made major contributions to this report are
listed in appendix V.
Anu K. Mittal Director, Natural Resources and Environment
Appendix I
Objectives, Scope, and Methodology
This report (1) describes the groundwater remediation technologies that
the Department of Defense (DOD) is currently using or field-testing and
(2) examines whether any new groundwater remediation technologies are
being used outside the department or are being developed by commercial
vendors that may have potential for DOD's use, and the extent to which DOD
is researching and developing new approaches to groundwater remediation.
In addition, this report provides limited information on the key
characteristics, benefits, and limitations of selected groundwater
remediation technologies.
To address the first objective, we developed a questionnaire that we sent
to the DOD components responsible for DOD's groundwater cleanup
efforts-the Air Force, Army, U.S. Army Corps of Engineers, Defense
Logistics Agency, and Navy. In the questionnaire, we listed groundwater
remediation technologies and asked these DOD components to indicate which
technologies they have implemented and still currently use. We also asked
the components to provide examples of specific groundwater remediation
projects. We developed the list of technologies based on a review of
reports and existing lists developed by the National Research Council,
Environmental Protection Agency (EPA), Federal Remediation Technology
Roundtable, and others, as well as through discussions with a groundwater
remediation consulting firm and several nationally recognized groundwater
remediation experts. To better understand DOD's processes for
environmental cleanup and technology development, we met with officials
from the offices of the Deputy Undersecretaries of Defense for
Installations and Environment and for Science and Technology. We also
reviewed documents, reports, and guidance on groundwater remediation from
the Office of the Secretary of Defense and the various DOD components
involved in groundwater remediation. To obtain information on how DOD uses
groundwater remediation technologies to treat contaminants of concern, we
toured several bioremediation projects at Dover Air Force Base and spoke
with a groundwater remediation program manager for the Air Force.
To address our second objective, we contracted with consultants from the
Washington, D.C., office of Malcolm Pirnie Inc. to gather information from
commercial vendors on the range of currently available groundwater
remediation technologies. We also attended a national groundwater
remediation conference, where we spoke with a number of vendors of
groundwater remediation technologies about their products, efforts to
develop innovative approaches to groundwater remediation, and remediation
work they may have performed for DOD. In addition, we
Appendix I
Objectives, Scope, and Methodology
collected and reviewed reports and studies from these vendors to better
understand the range of technologies available to DOD. We also consulted
with four nationally recognized groundwater remediation experts-two from
academia and two from industry-to provide information on innovative
remediation technologies currently available or under development by the
commercial sector. We selected these experts on the basis of their
independence, knowledge of and experience with groundwater remediation
technologies, and recommendations from the National Academy of Sciences
and others. In addition, we consulted with a senior groundwater
remediation official from EPA's Groundwater and Ecosystem Restoration
Division, who is an expert on technologies used for groundwater
remediation.
Through these sources, we identified 15 technologies that are currently
available commercially for the treatment of contaminated groundwater. For
the purposes of this report, we defined a technology as a distinct
technical method or approach for treating or removing contaminants found
in groundwater. We did not consider any modifications or enhancements to a
technology, such as variations in the material or equipment used during
treatment, to be a separate technology. To determine whether there were
any technologies currently being used outside of DOD, we compared the list
of 15 currently available technologies with information provided to us by
DOD officials on technologies currently used by DOD for groundwater
remediation.
To identify the extent to which DOD supports the research and development
of new approaches to groundwater remediation, we interviewed officials
from the Strategic Environmental Research and Development Program and the
Environmental Security Technology Certification Program. We reviewed
reports, project portfolios, and other documents developed by these two
programs. To gain a better understanding of DOD's efforts to field-test
innovative approaches to groundwater remediation, we visited a DOD
National Environmental Technology Test Site, located in Delaware, where
private and public researchers can test innovative groundwater remediation
technologies. We observed several ongoing research projects and
interviewed an official responsible for managing the test facility. To
gain a better understanding of DOD's relationship with the Interstate
Technology and Regulatory Council, we reviewed a memorandum of
understanding between the two organizations and interviewed an official
that serves as DOD's liaison to the council.
Appendix I
Objectives, Scope, and Methodology
Information presented in this report is based on publicly available
documents and information provided by government officials, independent
consultants, and experts. We did not review nonpublic research and
development activities that may be under way in private laboratories. We
reviewed data for accuracy and consistency, and corroborated DODprovided
data to the extent possible. We assessed the reliability of the
DOD-provided data by reviewing related documentation, including DOD's
annual reports to Congress on its Defense Environmental Restoration
Program and information provided by consultants.
We performed our work from January 2005 through May 2005, in accordance
with generally accepted government auditing standards.
Appendix II
Technologies for the Remediation of Contaminated Groundwater
Ex-situ Technologies 1.
2.
3.
Advanced oxidation processes often use ultraviolet light irradiation with
oxidizers such as ozone or hydrogen peroxide to produce free radicals,
which break down and destroy chlorinated solvents, fuels, and explosive
contaminants as water flows through a treatment reactor tank. Depending on
the design of the system, the final products of this treatment can be
carbon dioxide, water, and salts. An advantage of advanced oxidation
processes is that it destroys the contaminant, unlike some other
technologies, which only shift the phase of the contaminant into something
more easily handled and removed. There are some limitations to these
processes; for instance, maintenance of the treatment equipment can be a
problem if certain substances-such as insoluble oil or grease-are allowed
into the system. Also, the handling and storage of oxidizers can require
special safety precautions. The cost of this type of remediation is
largely dependent on the volume and flow rate of groundwater to be
treated, energy requirements, and chemicals utilized. Operations and
maintenance costs are also a factor in the overall cost of this approach.
For the purposes of this report, advanced oxidation processes also include
the related technologies of phyotolysis and photocatalysis.
Air stripping involves the mass transfer of volatile contaminants from
water to air by exposing contaminated water to large volumes of air, so
that the contaminants, such as chemical solvents, undergo a physical
transformation from liquid to vapor. In a typical air stripper setup,
called a packed tower, a spray nozzle at the top of a tower pours
contaminated water over packing media or perforated trays within the
tower. At the bottom of the tower, a fan forces air up through the tower
countercurrent to the water flow, thus stripping the contaminants from the
water. The contaminants in the air leaving the tower must then be removed
and disposed of properly. Air strippers can be combined with other
technologies for treatment of groundwater. Advantages of this technology
include its potential to effectively remove the majority of the volatile
organic contaminants of concern. Moreover, this mature technology is
relatively simple and design practices are standardized and
well-documented, and, in comparison with other approaches, this technology
is often less expensive. However, maintenance can be an issue with this
technology if inorganic or biological material clogs or fouls the
equipment, and process energy costs can be high.
Bioreactors are biochemical-processing systems designed to degrade
contaminants in groundwater using microorganisms, through a process
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
similar to that used at a conventional wastewater treatment facility.
Contaminated groundwater flows into a tank or basin, where it interacts
with microorganisms that grow and reproduce while degrading the
contaminant. The excess biomass produced is then separated from the
treated water and disposed of as a biosolids waste. This technology can be
used to treat, among other things, chlorinated solvents, propellants, and
fuels. Potential advantages of bioreactors include relatively low
operations and maintenance costs and the destruction, rather than mass
transfer of, the contaminants. Moreover, regulators and other stakeholders
generally accept bioreactor technology as a proven approach for
remediation. Nonetheless, there are some limitations to the use of
bioreactors, including decreases in effectiveness if contaminant
concentrations in the influent water are too high or too low to support
microorganism growth and if nuisance microorganisms enter the system.
Additionally, the sludge produced at the end of the process may need
further treatment or specialized disposal. Bioreactor cost is influenced
by the upfront capital needed for installation, setup, and start-up, as
well as the operations and maintenance costs associated with longer-term
treatment.
4. Constructed wetlands use artificial wetland ecosystems (organic
materials, microbial fauna, and algae) to remove metals, explosives, and
other contaminants from inflowing water. The contaminated water flows into
the wetland and is processed by wetland plants and microorganisms to break
down and remove the contaminants. Wetlands, intended to be a long-term
remediation approach, can be created with readily available equipment and
generally can operate with low maintenance costs. Furthermore, because
this technology provides a new ecosystem for plant and animal life, it is
generally popular with the public. However, this approach is often more
suitable for groundwater that is ultimately discharged to the surface
rather than reinjected into the ground. Also, the long-term effectiveness
of this treatment is not well-known, as aging wetlands may lose their
ability to process certain contaminants over time. Temperature, climate,
and water flow rate may negatively impact the processes that break down
the contaminants. Applicability and costs associated with constructed
wetlands vary depending on site conditions, such as groundwater flow rate,
contaminant properties, landscape, topography, soil permeability, and
climate.
5. Ion exchange involves passing contaminated water through a bed of resin
media or membrane (specific to the particular contaminant) that
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
exchanges ions in the contaminants' molecular structure, thus neutralizing
them. This approach can be useful for dissolved metals (e.g., hexavalent
chromium) and can be used to treat propellants such as perchlorate. Once
the ion exchange resin has been filled to capacity, it can be cleaned and
reused (following a process called resin regeneration). Ion exchange is
usually a short-to medium-term remediation technology. This technology
allows contaminated water to be treated at a high flow rate and can
completely remove the contaminants from the water. However, some
substances-such as oxidants or suspended solids-in the incoming water may
diminish the effectiveness of the ion exchange resins. Furthermore,
different resin types can be needed for different contaminants. Among the
factors influencing costs are discharge requirements, the volume of water
to be treated, contaminant concentration (as well as the presence of other
contaminants), and resin regeneration. For the purposes of this report,
ion exchange includes technologies that use ion exchange resins or reverse
osmosis membranes to remove contaminants from groundwater, including
dissolved metals and nitrates.
6. Adsorption (mass transfer) technologies involve passing contaminated
water through a sorbent material-such as activated carbon-that will
capture the contaminants (through either adsorption or absorption), thus
removing or lessening the level of contaminants in the water. The
contaminated water is pumped from the aquifer and passed through the
treatment vessel containing the sorbent material. As the contaminated
water comes into contact with the sorbent surface, it attaches itself to
that surface and is removed from the water. Benefits of this technology
include its ability to treat contaminated water to nondetectable levels
and its potential for treating low to high groundwater flow rates as well
as multiple contaminants simultaneously. However, some contaminants may
not be sorbed well or the sorbent unit may require disposal as hazardous
waste. Furthermore, this approach is impractical if the contaminant levels
are high due to higher costs resulting from frequent changing of the
sorbent unit. If the concentrations of contaminants are low or flow rates
for treatment can be kept low, then adsorption technology may be a
costeffective approach.
In-situ Technologies 1. Air sparging introduces air or other gases into a
contaminated aquifer to reduce concentrations of contaminants such as fuel
or chlorinated solvents. The injected air creates an underground air
stripper that
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
removes contaminants by volatilization (a process similar to evaporation
that converts a liquid or solid into a gas or vapor). This injected air
helps to transport the contaminants up into the unsaturated zone (the soil
above the water table, where pores are partially filled with air), where a
soil vapor extraction system is usually implemented to collect the vapors
produced through this process. This technology has the added benefit of
often stimulating aerobic biodegradation (bioremediation) of certain
contaminants because of the increased amount of oxygen introduced into the
subsurface. Typically, air sparging equipment is readily available and
easily installed with minimal disturbance to site operations. However,
this technology cannot be used if the contaminated site contains
contaminants that don't vaporize or are not biodegradable. In some cases,
this technology may not be suitable for sites with free product (e.g., a
pool of fuel floating on the water table) because air sparging may cause
the free product to migrate and spread contamination. Also, this
technology is less effective in highly stratified or heterogeneous soils
since injected air tends to travel along paths of least resistance in the
subsurface, potentially bypassing areas of contamination. This technology
can be less costly than ex-situ technologies because it does not require
the removal, treatment, storage, or discharge of groundwater. For the
purposes of this report, air sparging includes the related remedial
approaches of co-metabolic sparging, sparging using other gases, and
in-well air stripping.
2. Bioremediation relies on microorganisms to biologically degrade
groundwater contaminants through a process called biodegradation. It may
be engineered and accomplished in two general ways: (1) stimulating native
microorganisms by adding nutrients, oxygen, or other electron acceptors (a
process called biostimulation); or (2) providing supplementary pregrown
microorganisms to the contaminated site to augment naturally occurring
microorganisms (a process called bioaugmentation). This technology mainly
focuses on remediating organic chemicals such as fuels and chlorinated
solvents. One approach, aerobic bioremediation, involves the delivery of
oxygen (and potentially other nutrients) to the aquifer to help native
microorganisms reproduce and degrade the contaminant. Another approach,
anaerobic bioremediation, circulates electron donor materials-for example,
food-grade carbohydrates such as edible oils, molasses, lactic acid, and
cheese whey-in the absence of oxygen throughout the contaminated zone to
stimulate microorganisms to consume the contaminant. In some cases,
pregrown microbes may be
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
injected into the contaminated area to help supplement existing
microorganisms and enhance the degradation of the contaminant, a process
known as bioaugmentation. A potential advantage of bioremediation is its
ability to treat the contaminated groundwater in place with naturally
occurring microorganisms, rather than bringing contaminants to the
surface. By using native microorganisms, rather than injecting additional
ones, cleanup can be more cost-effective at some sites. However,
heterogeneous subsurfaces can make delivering nutrient/oxygen solutions to
the contaminated zone difficult by trapping or affecting movement of both
contaminants and groundwater.1 Also, nutrients to stimulate the
microorganisms can be consumed rapidly near the injection well, thereby
limiting the microorganisms' contact with the contaminants, or stimulating
biological growth at the injection site. In summary, this technology
avoids the costs associated with bringing water to the surface for
treatment; instead, the main costs associated with bioremediation include:
delivery of the amendments to the subsurface (which varies depending on
the depth of contamination), the cost of the amendments themselves, and
monitoring of the treatment. For the purposes of this report,
bioremediation includes the related bioremedial approaches of
bioaugmentation, biostimulation, co-metabolic treatment, enhanced aerobic
biodegradation, enhanced anaerobic biodegradation, and biobarriers.
3. Enhanced recovery using surfactant flushing speeds contaminant removal
in conventional pump-and-treat systems by injecting surfactants2 into
contaminated aquifers or soil to flush the contaminant toward a pump in
the subsurface (some distance away from the injection point); this pump
removes the contaminated water and surfactant solution to the surface for
treatment and disposal of contaminants. Surfactants are substances that
associate with organic compounds such as fuels and chlorinated solvents
and significantly
1Heterogeneities can cause wide variability in hydraulic properties such
as hydraulic conductivity-a measure of the volume of water that will pass
through an area at a given time. These changes in hydraulic properties
enhance the dispersion of a dissolved contaminant spread. Heterogeneities
can also create preferential pathways for contaminant migration.
2Surfactants are molecules with two structural units: one with an affinity
for water and one with an aversion to water. Surfactants are especially
useful for dissolving some contaminants and enhancing their mobility by
lowering the interfacial tension between the contaminant and water.
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
increase their solubility, which aids cleanup of contaminated aquifers
with less flushing water and pumping time. This technology is applicable
to both dense and light nonaqueous phase liquids (DNAPL and LNAPL).3
Benefits of enhanced recovery approaches include the rapid removal of
contaminants, which may significantly reduce cleanup times. However,
regulatory issues may require special attention due to extra scrutiny for
obtaining approvals to inject surfactant solutions; a greater degree of
site characterization is often required to satisfy both technical and
regulatory requirements. In addition, subsurface heterogeneities and low
permeability can interfere with the effective delivery and recovery of the
surfactant solution. Furthermore, to the extent that mobilization of
organic liquid contaminants is achieved, this approach may be better for
LNAPLs than DNAPLs, as LNAPLs tend to migrate upward and DNAPLs downward,
possibly trapping them in previously uncontaminated subsurface areas. In
addition to the high cost of surfactant solutions, another factor
influencing the overall cost of this approach may be the treatment of the
surfactant solution that is pumped out of the aquifer. For the purposes of
this report, this technology includes related remedial approaches that use
co-solvents such as ethanol to improve the solubility of surfactants in
the subsurface.
4. Chemical treatments include remediation technologies that chemically
oxidize or reduce contaminants when reactive chemicals are injected into
the groundwater. This approach converts contaminants such as fuels and
explosives into nonhazardous or less-toxic compounds. Depending on the
extent of contamination, this process involves injecting chemicals into
the groundwater and generally takes a few days to a few months to observe
results in rapid and extensive reactions with various contaminants of
concern. Additionally, this technology can be tailored to the site and
does not require rare or complex equipment, which may help reduce costs.
Generally, there are no unusual operations and maintenance costs; however,
in-situ chemical treatment may require intensive capital investment for
large contaminant plumes or zones where repeated applications or large
volumes of reactive chemicals may be required; major costs are
3Nonaqueous-phase liquids are liquids that do not mix with, or dissolve
in, water. Dense nonaqueous-phase liquids (DNAPL) fall to the bottom of a
body of water; chlorinated solvents are typical examples. Conversely,
light nonaqueous-phase liquids (LNAPL) gather on top of the water.
Gasoline and fuel oil are examples of LNAPLs.
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
associated with injection-well installation (cost influenced by well
depth), procurement of the reactive chemicals, and monitoring.
Additionally, site characterization is important for the effective
delivery of reactive chemicals, as subsurface heterogeneities may result
in uneven distribution of the reactive chemicals. For the purposes of this
report, chemical treatment also includes various remedial approaches and
technologies that chemically oxidize or reduce contaminants insitu, as
well as those that result in the in-situ immobilization and stabilization
of soluble metals.
5. Monitored natural attenuation is a relatively passive strategy for
insitu remediation that relies on the naturally occurring physical,
chemical, and biological processes that can lessen concentrations of
certain contaminants in groundwater sufficiently to protect human health
and the environment. The changes in contaminant concentrations are
observed through various wells that are placed throughout the contaminated
groundwater zone to monitor the level of contamination over time and its
migration from its initial location in the subsurface. Some chlorinated
solvents and explosives may be resistant to natural attenuation; however,
it can still be used in cases of nonhalogenated chlorinated solvents and
some inorganic compounds. If appropriate for a given site, natural
attenuation can often be less costly than other forms of remediation
because it requires less infrastructure, construction, and maintenance.
Furthermore, it is less intrusive because fewer surface structures are
necessary and it may be used in all or selected parts of a contaminated
site, alone or in conjunction with other types of remediation. However,
compared with active techniques, natural attenuation often requires longer
time frames to achieve remediation objectives.
6. Multiphase extraction uses a series of pumps and vacuums to remove free
product,4 contaminated groundwater, and vapors from the subsurface, treat
them, and then either dispose or reinject the treated groundwater.
Specifically, one or more vacuum extraction wells are installed at the
contaminated site to simultaneously pull liquid and gas from the
groundwater and unsaturated soil directly above it. This type of vacuum
extraction well removes contaminants from above and below the groundwater
table, and can expose more of the subsurface for treatment, notably in low
permeability or heterogeneous
4Free products are liquid contaminants floating on top of groundwater.
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
formations. The contaminant vapors are collected in the extraction wells
and taken above ground for treatment. This approach can be used to treat
organic contaminants-such as chlorinated solvents and fuels-and can be
combined with other technologies, particularly above-ground liquid/vapor
treatment, as well as other methods of insitu remediation such as
bioremediation, air sparging, or bioventing. Potential advantages of this
technology include its applicability to groundwater cleanup in low
permeability and heterogeneous formations and its minimal disturbance to
site-specific conditions. However, the system requires complex monitoring
and specialized equipment, and it may be difficult or problematic to
implement the most effective number of pumps. A major contributor to this
technology's cost is operations and maintenance, which may run from 6
months to 5 years, depending on site-specific factors. For the purposes of
this report, multiphase extraction includes the related technologies of
bioslurping and dual-phase extraction.
7. Permeable reactive barriers are vertical walls or trenches built into
the subsurface that contain a reactive material to intercept and remediate
a contaminant plume as the groundwater passes through the barrier. This
technology can be used to treat a wide range of contaminants and is
commonly used to treat chlorinated solvents and heavy metals. Reactive
barriers usually do not require above-ground structures or treatment,
allowing the site to be used while it is being treated. However, its use
is limited by the size of the plume since larger contaminant plumes are
often more difficult to intercept for treatment. Moreover, the barrier may
lose effectiveness over time as microorganisms or chemicals build up on
the barrier, making rehabilitation or media replacement necessary. The
depth of the contaminated groundwater zone and the required barrier may
also present some technical challenges. Underground utility lines, rocks,
or other obstacles can increase the difficulty of installing a barrier and
drive up capital costs. Additionally, because permeable reactive barriers
do not treat the contaminant source, but simply the plume, treatment may
be required for extended time periods, thus increasing overall cleanup
costs. For the purposes of this report, permeable reactive barriers
include biotic and abiotic, as well as passive and active treatment
barriers.
8. Phytoremediation is the use of selected vegetation to reduce, remove,
and contain the toxicity of environmental contaminants, such as metals and
chlorinated solvents. There are several approaches to
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
phytoremediation that rely on different plant system processes and
interactions with groundwater and contaminants. One approach to
phytoremediation is phytostabilization, which uses plants to reduce
contaminant mobility by binding contaminants into the soil or
incorporating contaminants into plant roots. Another approach is
phytoaccumulation, where specific species of plants are used to absorb
unusually large amounts of metals from the soil; the plants are later
harvested from the growing area and disposed of in an approved manner. A
similar process is called rhizofiltration, where contaminated water moves
into mature root systems and is circulated through their water supply.
Another process can remove contaminants by evaporating or volatilizing the
contaminants from the leaf surface once it has traveled through the
plant's system. Phytoremediation offers the benefit of only minimally
disturbing the environment and can be used for the treatment of a wide
range of contaminants. However, specific plant species required for
particular contaminants may be unable to adapt to site conditions due to
weather and climate, and phytoremediation may not be an effective approach
for deep contamination. While maintenance costs, including cultivation,
harvesting, and disposal of the plants, are substantial for this
technology, phytoremediation typically has lower costs than alternative
approaches. For the purposes of this report, phytoremediation includes
phytostabilization, phytoaccumulation, phytoextraction, rhizofiltration,
phytodegredation, rhizosphere degredation, organic pumps, and
phytovolitilization.
9. Thermal treatments involves either pumping steam into the aquifer or
heating groundwater in order to vaporize chlorinated solvents or fuels
from the groundwater. The vaporized contaminant then rises into the
unsaturated zone and can be removed via vacuum extraction for treatment.
There are three main approaches for heating the groundwater in-situ. The
first, radio frequency heating, uses the electromagnetic energy found in
radio frequencies to rapidly heat the soil in a process analogous to
microwave cooking. The second, electromagnetic heating, uses an
alternating current to heat the soil and may include hot water or steam
flushing to mobilize contaminants. The third uses heating elements in
wells to heat the soil. Thermal treatments may be applied to a wide range
of organic contaminants and sites with larger volumes of LNAPLs or DNAPLs
as well as sites with low permeability and heterogeneous formations.
However, the presence of metal and subsurface heterogeneities in the
contaminated site may interfere with this process. The heating and vapor
collection
Appendix II
Technologies for the Remediation of
Contaminated Groundwater
systems must be designed and operated to contain mobilized contaminants,
to avoid their spread to clean areas. The major costs incurred for thermal
treatments are for moving specialized equipment to the site, developing
infrastructure to provide power, and providing energy to run the system.
For the purposes of this report, thermal treatments include related
soil-heating technologies, such as steam flushing, conductive heating, and
electrical resistance heating.
Appendix III
Groundwater Remediation Experts Consulted
Dr. John Fountain Professor and Head, Department of Marine, Earth and
Atmospheric Sciences North Carolina State University Raleigh, North
Carolina
Dr. Robert E. Hinchee
Principal Civil and Environmental Engineer
Integrated Science and Technology Inc.
Panacea, Florida
Dr. Michael C. Kavanaugh
Vice President
National Science and Technology Leader
Malcolm Pirnie Inc.
Emeryville, California
Dr. Robert L. Siegrist
Professor and Division Director
Environmental Science and Engineering Division
Colorado School of Mines
Golden, Colorado
Dr. John T. Wilson
Senior Research Microbiologist
Ground Water and Ecosystems Restoration Division, National Risk
Management Research Laboratory Office of Research and Development U.S.
Environmental Protection Agency Ada, Oklahoma
Appendix IV
Comments from the Department of Defense
Appendix V
GAO Contact and Staff Acknowledgments
GAO Contact Anu K. Mittal, (202) 512-3841
Staff In addition to the contact above, Richard Hung, Lynn Musser,
Jonathan G. Nash, Omari Norman, and Diane B. Raynes made key contributions
to this
Acknowledgments report. Jessica A. Evans, Katherine M. Raheb, and Carol
Herrnstadt Shulman also made important contributions to this report.
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