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1
Introduction
BACKGROUND OF STUDY
Since the 1970s, hundreds of billions of dollars have been invested by
federal, state, and local government agencies as well as responsible parties
to mitigate the human health and ecological risks posed by chemicals re-
leased to the subsurface environment. Many of the contaminants common
to these hazardous waste sites, such as metals and volatile organic com-
pounds, are known or suspected to cause cancer or adverse neurological,
reproductive, or developmental conditions. Over the past 30 years, some
progress in meeting mitigation and remediation goals at hazardous waste
sites has been achieved. For example, of the 1,723 sites ever listed on the
National Priorities List (NPL), which are considered by the U.S. Environ-
mental Protection Agency (EPA) to present the most significant risks, 360
have been permanently removed from the list because EPA deemed that no
further response was needed to protect human health or the environment
(EPA, 2012). Seventy percent of the 3,747 hazardous waste sites regulated
under the Resource Conservation and Recovery Act (RCRA) corrective
action program have achieved “control of human exposure to contami-
nation,” and 686 have been designated as “corrective action completed”
(EPA, 2011a). The Underground Storage Tank (UST) program also reports
successes, including closure of over 1.7 million USTs since the program
was initiated in 1984 (EPA, 2010). The cumulative cost associated with
these national efforts underscores the importance of pollution prevention
and serves as a powerful incentive to reduce the discharge or release of
13
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14 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
hazardous substances to the environment, particularly when a groundwater
resource is threatened.
Although some of the success stories described above were challeng-
ing in terms of contaminants present and underlying hydrogeology, the
majority of sites that have been closed were relatively simple (e.g., shallow,
localized petroleum contamination from USTs) compared to the remaining
caseload. Indeed, hundreds of thousands of sites across both state and fed-
eral programs are thought to still have contamination remaining in place
at levels above those allowing for unlimited land and groundwater use
and unrestricted exposure (see Chapter 2).1 According to its most recent
assessment, EPA estimates that more than $209 billion dollars (in constant
2004 dollars) will be needed over the next 30 years to mitigate hazards at
between 235,000 to 355,000 sites (EPA, 2004). This cost estimate, however,
does not include continued expenditures at sites where remediation is al-
ready in progress, or where remediation has transitioned to long-term man-
agement.2 It is widely agreed that long-term management will be needed
at many sites for the foreseeable future, particularly for the more complex
sites that have recalcitrant contaminants, large amounts of contamina-
tion, and/or subsurface conditions known to be difficult to remediate (e.g.,
low-permeability strata, fractured media, deep contamination). Box 1-1
describes the characteristics of complex sites, where long-term management
is a likely outcome given the difficulty of remediating the groundwater to
conditions allowing for unlimited use and unrestricted exposure.
The Department of Defense (DoD) exemplifies a responsible party that
has made large financial investments to address past legacies of their indus-
trial operations. According to the most recent annual report to Congress
(OUSD, 2011), the DoD currently has almost 26,000 active sites under its
Installation Restoration Program where soil and groundwater remediation
is either planned or under way. Of these, approximately 13,000 sites are the
responsibility of the Army, the sponsor of this report. The estimated cost
to complete cleanup at all DoD sites is approximately $12.8 billion. (Note
that these estimates do not include sites containing unexploded ordnance.)
DoD has set a procedural goal for each of the Services stating that
all sites will reach the response-complete or remedy-in-place milestone by
2014. Remedy in place means that a remedial strategy has been imple-
mented and is in the performance assessment stage of the site’s life cycle,
while response complete means that remedial actions have been completed,
1 “Contamination remaining in place,” as used in this report, is consistent with the inter-
agency definition of hazardous substances, pollutants, or contaminants remaining at the site
above levels that allow for unlimited use and unrestricted exposure (UU/UE) (EPA, 2001;
DoD, 2012).
2 Long-term management is defined as requiring decades to centuries, well beyond the typi-
cal 30 years used to discount remedial costs.
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INTRODUCTION 15
although contamination at levels above those allowing for unlimited use
and unrestricted exposure may still remain on-site. In addition, the DoD
has directed 90 percent of sites at active installations to achieve response
complete by the end of FY 2018, and 95 percent by the end of FY 2021
(Conger, 2011). These goals will be extremely challenging to meet because
at many of the military’s remaining sites that have groundwater contamina-
tion, one can anticipate the need for long-term management that may take
many decades to resolve.
In this context, the Water Science and Technology Board, under aus-
pices of the National Research Council (NRC), initiated a study to assess
the future of the nation’s subsurface remediation efforts, with a particular
focus on technical, economic, and institutional challenges facing the Army
and other responsible parties as they pursue aggressive programmatic goals
for site closure. It should be noted that there is no single definition of “site
closure,” nor was the Committee able to agree on a precise consensus
definition of the term that would be applicable to all state and federal
programs. The term is often used to mean that “no further action” is re-
quired at a site (except for various institutional controls)—a connotation
that the Committee is comfortable with. However, “no further action”
does not mean that site contaminants have been reduced to levels below
those allowing for unlimited use and unrestricted exposure. Whenever pos-
sible throughout this report, the term “site closure” is replaced with the
more specific designations for success used by the various federal and state
remediation programs. Chapter 7 abandons the terms “site closure” and
“no further action” entirely and instead presents three end states, one of
which all sites will achieve: active long-term management, passive long-term
management, and achievement of unlimited use and unrestricted exposure
levels. The central theme of this report is how the nation will deal with the
complex hazardous waste sites where contamination remains in place at
levels above those allowing for unlimited use and unrestricted exposure.
REGULATORY RESPONSE TO
GROUNDWATER CONTAMINATION
The federal regulatory regime for responding to groundwater contami-
nation consists of several key statutes and regulations enforced primarily
by the EPA’s Office of Solid Waste and Emergency Response (see Box 1-2
for an overview of the major U.S. cleanup programs). Designed to address
problems related to municipal and industrial waste, RCRA was passed
in 1976 and promoted recovery methods and techniques to reduce waste
generation while also outlining environmentally sound management of
hazardous and nonhazardous wastes. In 1980, Congress passed the Su-
perfund Law (Comprehensive Environmental Response, Compensation,
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16 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
BOX 1-1
Complex Contaminated Sites
Although progress has been made in remediating many hazardous waste sites,
there remains a sizeable population of complex sites, where restoration is likely
not achievable in the next 50-100 years. Although there is no formal definition of
complexity, most remediation professionals agree that attributes include areally
extensive groundwater contamination, heterogeneous geology, large releases
and/or source zones, multiple and/or recalcitrant contaminants, heterogeneous
contaminant distribution in the subsurface, and long time frames since releases
occurred. Additional factors that contribute to complexity include restrictions on
the physical placement or operation of remedial technologies and challenging
expectations (e.g., regulatory requirements, cleanup goals, community expecta-
tions). The complexity of a site increases with the number of these characteristics
present.
Complexity is most intimately tied to limitations on the fundamental con-
taminant removal and/or destruction processes inherent to all remediation ap-
proaches, and the severity of these limitations at any given site is directly related
to geology and contaminant distribution. Thus, the more varied the geologic media
or lithology, the more complex the flow patterns of contaminants and injected so-
lutions are. The simplest geology is uniform media, like well-sorted sand (called
homogeneous), while more complex heterogeneous geology includes such varied
media as poorly sorted sand with lenses of silt and clay. Fractured media are often
considered the most heterogeneous (see Chapter 6 and NRC, 2005a, for more
details on hydrogeologic types). Heterogeneous media not only yield intricate
contaminant plumes, but also limit the effectiveness of remedial technologies that
TABLE 1-1 Relative Ease of Remediating Contaminated Aquifers
as a Function of Contaminant Chemistry and Hydrology
Contaminant Chemistry
Mobile,
Dissolved (degrades/ Mobile,
Hydrogeology volatilizes) Dissolved
Homogeneous, 1a 1-2
single layer
Homogeneous, multiple layers 1 1-2
Heterogeneous, 2 2
single layer
Heterogeneous, multiple layers 2 2
Fractured 3 3
aRelative ease of cleanup, where 1 is easiest and 4 is most difficult.
SOURCE: NRC (1994).
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INTRODUCTION 17
rely on moving fluid through the subsurface (e.g., injection of surfactants, oxidants,
or carbon sources). Heterogeneities can make these technologies less effective
due to bypass and/or limited contaminant contact time.
Complexity is also directly tied to the contaminants present at hazardous
waste sites, which can vary widely and include organics, metals, explosives, and
radionuclides. Some of the most challenging to remediate are dense nonaqueous
phase liquids (DNAPLs), including chlorinated solvents. In general, different types
of contaminants require different types of treatment and perhaps different remedial
approaches altogether. Thus, the more types of contaminants found at a site, the
more complex the site. Additionally, some contaminants are more resistant to
natural biodegradation processes than others.
NRC (1994) provided a matrix that outlined the difficulty of groundwater reme-
diation on a scale of 1 to 4 (with 4 representing the most difficult to remediate)
as a function of hydrogeology and contaminant chemistry, including contaminant
distribution in the subsurface (see Table 1-1). Ratings of 3 and 4 in Table 1-1
represent “complex sites” and include
• Sites having contamination in fractured media,
• Dissolved plumes extending more than 1000 m down-gradient of a source,
• Sites impacted by radioactive contaminants,
• Sites with DNAPL impacts extending to depths of 100 ft or greater, and
• Sites with residual NAPL that has diffused into fine-grained units.
Note that Table 1-1 does not factor in some of the topics discussed above (such
as the size of the release and regulatory expectations) that can contribute to
complexity.
Strongly Sorbed,
Dissolved
(degrades/ Strongly Sorbed, Separate Phase Separate Phase
volatilizes) Dissolved LNAPL DNAPL
2 2-3 2-3 3
2 2-3 2-3 3
3 3 3 4
3 3 3 4
3 3 4 4
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18 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
BOX 1-2
Brief Overview of U.S. Cleanup Programs and
Regulatory Terms Found in this Report
CERCLA: The CERCLA program (established in 1980 and also known as Super-
fund) locates, investigates, and cleans up the most problematic hazardous waste
sites throughout the United States. At private sector sites, the EPA may perform
the cleanup with federal funds and seek cost reimbursement from the responsible
party or may issue orders or enter a judicially enforceable consent decree and
oversee the implementation of long-term cleanups, short-term cleanups (“removal
actions”), and other responses. At federal CERCLA sites, the federal party is pri-
marily responsible for cleanup.
RCRA Corrective Action: RCRA is the primary federal statute regulating how
wastes (solid and hazardous wastes) must be managed at facilities that treat,
store, or dispose of hazardous wastes to avoid potential threats to human health
and the environment. However, RCRA also provides corrective action order au-
thority that governs the cleanup of solid waste management units at RCRA permit-
ted facilities (including federal facilities). It is similar to CERCLA, but is primarily
implemented by the states. EPA’s policy is that the RCRA and CERCLA remedial
programs should operate consistently and result in similar environmental solutions
when faced with similar circumstances.
UST: The Underground Storage Tank program, which is part of RCRA, governs
the cleanup of the nation’s large numbers of leaking underground tanks. The sites
are individually smaller in scope than a typical site regulated under CERCLA or
RCRA corrective action. The UST program focuses on removing products (petro-
leum or industrial or dry cleaning chemicals) that have leaked out of the tanks,
removal of soil, cleanup of the groundwater, and replacement of the tanks.
Brownfields: Brownfields are defined as real properties, the expansion, rede-
velopment, or reuse of which may be complicated by the presence or potential
presence of a hazardous substance, pollutant, or contaminant. EPA’s Brownfields
program provides funds and technical assistance to states, communities, and
and Liability Act or CERCLA), which authorized broad federal authority
to respond directly to the release of hazardous substances that endanger
public health or the environment, in addition to taxing the chemical and
petroleum industries to establish the Superfund Trust Fund. The NPL of the
most contaminated sites was established under CERCLA.
Not long after CERCLA was enacted, it became clear that additional
measures would be needed to combat the nation’s burden of contaminated
sites. In 1984, Congress amended RCRA (via the Hazardous and Solid
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INTRODUCTION 19
other stakeholders in economic redevelopment to work together to assess, safely
clean up, and sustainably reuse Brownfields.
Federal Facilities Programs: A number of separate programs exist to address
hazardous waste remediation on federal facilities. These include DoD’s Military
Munitions Response Program, the Installation Restoration Program, which ad-
dresses active bases, the Base Realignment and Closure facilities, and Formerly
Used Defense Sites. The Department of Energy’s Environmental Management
program is another example (see Chapter 2). All such sites are variously regulated
under CERCLA, RCRA, UST, or state regulations.
Maximum Contaminant Level Goals (MCLGs) are the health-based drinking water
concentrations set in EPA’s Safe Drinking Water program at a one-in-one million
lifetime risk level for carcinogens and, for noncarcinogenic effects, at a concentra-
tion at which no adverse health effect are likely from long-term exposure. MCLGs
are not enforceable under the Safe Drinking Water Act.
Maximum Contaminant Levels (MCLs) are the legally enforceable drinking water
concentration limits for U.S. public drinking water supplies (i.e., supplies to more
than 25 people). They are based on a balancing of the residual risk from ingest-
ing the water, the feasibility of treatment to remove the chemical, the detection
limit, and the costs to water suppliers. MCLs are enforced under the Safe Drinking
Water Act.
Applicable or Relevant and Appropriate Requirements (ARARs) include two sepa-
rate types of requirements. Applicable Requirements are any federal or duly
promulgated state standard, requirement, criterion, or limitation under any other
federal environmental law that would legally apply to a site. Relevant and Ap-
propriate Requirements are any Federal or duly promulgated state standard,
requirement, criterion, or limitation under any other federal environmental law
that addresses problems or situations similar to the conditions at a site and that
is “well suited” to a site. MCLs promulgated under the Safe Drinking Water Act
are considered to be ARARs for sites regulated under CERCLA because of the
potential for people to ingest the groundwater derived from a contaminated aquifer.
Waste Amendments) to implement more stringent standards for hazardous
waste management, to impose restrictions that curbed the practice of land
disposal of untreated hazardous waste, and to add authority for EPA and
the states to remediate contamination on active RCRA permitted facilities.
In 1986, the Superfund Amendments and Reauthorization Act (SARA)
amended CERCLA to stress the importance of permanent or innovative
solutions, incorporate a more rigorous process to define the goals of reme-
diation that EPA has proposed in its regulations, provide new enforcement
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20 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
authorities and settlement tools, increase state involvement in CERCLA
activities, and increase focus on the human health impacts of hazardous
waste sites. SARA also established the Defense Environmental Restoration
Program and its regulatory underpinnings.
The early years of both programs’ implementation were marked by
site studies rather than actual remediation. In 1988, EPA released interim
measures for RCRA to allow action to be taken sooner to prevent exposure
to contamination, and the agency began focusing on completing remedy
construction, in particular pump-and-treat practices for groundwater con-
tainment and remediation. As more remediation began, it became clear that
reaching drinking water standards such as maximum contaminant levels
(MCLs), which were the applicable or relevant and appropriate require-
ments (ARARs) for many sites, was not always feasible, especially at sites
with complicated hydrogeology and/or recalcitrant contaminants (see Box
1-2 for definitions of these terms). Thus, during the 1990s EPA continued
to revisit and revise its policies for groundwater restoration. For those sites
where restoration is impracticable for the foreseeable future given site con-
ditions and the limitations of technologies, the agency created the Techni-
cal Impracticability (TI) Waiver (EPA, 1993). As specified in SARA, the TI
Waiver was one of six waiver options that allowed for alternative remedial
goals other than ARARs in specified portions of a site. For groundwater TI
waivers, this required the designation of a “TI Zone” in which a specific
ARAR (e.g., an MCL) would be waived. Outside of this zone, the original
ARARs still need to be met.
By 1999, the CERCLA program was increasingly finding success in
achieving remedy construction milestones on many of the less complex
sites. Nonetheless, a 2001 report from Resources for the Future (Probst
and Konisky, 2001) stated that most complex sites still had contamination
in place at levels above those allowing for unlimited use and unrestricted
exposure. Despite these findings, the dedicated taxes supporting the CER-
CLA program expired in 1995 and have not been reinstated, such that the
trust fund was depleted in 2003 (although appropriations to the program
continue). Other programs have fared better, such as the Brownfields pro-
gram (which allows voluntary remediation of sites to promote the rede-
velopment and reclamation of properties where hazardous substances had
been detected or are potentially present) to which $250 million per year
was authorized in 2002. RCRA’s UST program received additional support
from the 2005 Energy Policy Act. In 2009, the American Recovery and
Reinvestment Act boosted funding for all remediation-related programs
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INTRODUCTION 21
at EPA by $800 million and for other federal remediation programs by $5
billion3 (EPA, 2011b).
Today, EPA directives on groundwater remedies continue to evolve. In
June 2009, the Office of Solid Waste and Emergency Response compiled
all existing EPA groundwater policies into one singular directive (EPA,
2009). It reported that CERCLA action is only needed where groundwater
contamination exceeds drinking water standards. The directive identified
the role of institutional controls, which are non-engineered instruments
such as administrative and legal controls that help minimize the potential
for human exposure to contamination and/or protect the integrity of the
remedy, and determined they are generally not to be the sole basis for a
remedy. Classification of groundwater (i.e., whether an aquifer is a current
or potential source of drinking water) is to be conducted only by EPA unless
there is a state regulatory requirement to do so. And finally the directive
acknowledged that EPA policy on point of compliance is to restore ground-
water to the maximum extent practicable for beneficial reuse (see also Box
3-2). The report noted that in selecting remedial goals EPA is to consider
an array of criteria, including drinking water standards, site-specific risk
assessment, and land use.
THE LIFE CYCLE OF A CONTAMINATED SITE
The process for remediation of contaminated sites, from discovery to
closure, was first documented in the National Contingency Plan (40 CFR
300 et seq.) in 1980 to reflect the needs of CERCLA. Other regulatory
programs provide similar remedial guidance for active sites, including those
with underground storage tanks. The Departments of Energy and Defense
have developed their own processes that mirror the remedial process found
within CERCLA, but using different terminology, while the states imple-
ment the federal laws over which they have primacy as well as state pro-
grams that encompass additional contaminated sites.
The life-cycle components of the various federal and state remedial
programs are similar to one another and listed in Table 1-2 along with
approximate time frames for their completion. Following discovery of con-
tamination, a site must be characterized to determine the nature and extent
of the contamination, a process that can extend for years into the future for
some sites. One of the most important components of the site characteriza-
tion step is the creation of an accurate conceptual site model (discussed at
length in NRC, 2005a). If chemicals of concern are found to exceed certain
regulatory limits, and/or a risk characterization indicates that unacceptable
3
http://www.recovery.gov/Transparency/fundingoverview/Pages/contractsgrantsloans-details.
aspx#EnergyEnvironment.
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22 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
TABLE 1-2 Components and Approximate Time Frames in the Life Cycle
of a Remediation Program
conditions exist, then several activities are possible. Interim responses may
be necessary to reduce immediate threats. Once these are in place, remedial
action objectives are set, and then remedial alternatives are evaluated and a
remedy selected that will meet those objectives within a “reasonable”4 time
4 The definition of “reasonable” has been debated for many years at EPA and in state regu-
latory agencies. There are no statutory or regulatory definitions of this term in the context of
soil and groundwater cleanup. EPA explicitly adopted no single definition for all sites because
a “timeframe of 100 years may be reasonable for some sites and excessively long for others”
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INTRODUCTION 23
frame. Once the remedy has been designed and installed, monitoring of the
impacted media and performance assessment of the remedial technology
commence. Information from the monitoring program is used to inform
future decision making, including the decision to continue remediation or
transition to more passive management. From here, actions can lead to
either site closure (including no further action required) or to long-term
management. If residual contamination persists at levels above those allow-
ing for unlimited use and unrestricted exposure, engineering and/or institu-
tional controls will be needed. For example, institutional controls like deed
restrictions are often necessary for long-term management at sites where
physical or hydraulic containment of the contamination is a component of
the final solution. Whether long-term management sites will ever attain con-
tamination levels below those allowing for unlimited use and unrestricted
exposure is often uncertain; at many sites, perpetual management may be
necessary, particularly those with recalcitrant contaminants.
In practice, the process of moving a site from investigation to closure
has been much more complex than implied in Table 1-2, and virtually all
phases of remediation take more time and resources than originally contem-
plated. At NPL sites the time lapse from discovery to remedy implementa-
tion can exceed two decades. For example, two sites at Letterkenny Army
Depot were listed on the NPL in 1987 and 1989, but as of 2011 neither
had reached the point of having a final remedy selected (although interim
actions have been taken to reduce risk including provision of alternative
water supplies). There are numerous reasons for the long time lags between
site discovery and closure, including the fact that remedial systems often
require modification during implementation due to uncertainties in tech-
nology performance. Limited and shrinking resources (particularly at the
state level) have also increased the time period between site discovery and
eventual remediation.
Some states have proposed changes to their remediation programs
in order to expedite moving sites through the system. For example, in
2009 New Jersey created a Licensed Site Remediation Professional (LSRP)
Program to address a backlog of relatively simple sites that were not yet
closed. Modeled after a similar program in Massachusetts, the New Jersey
program transfers responsibility for remediation from the state Department
of Environmental Protection (NJDEP) to private contractors licensed by
the state in order to reduce the backlog of cases that need to be reviewed
and approved by NJDEP. As of July 2010, a total of 392 LSRPs had been
(EPA, 1996). Because “reasonable” includes not just scientific judgments, but also values, risk
tolerances, and preferences for discounting effects on future generations, definitions can vary
by individual (Weitzman, 2001). The Committee, therefore, does not provide its own defini-
tion of “reasonable.”
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26 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
BOX 1-3
Select NRC Studies Relevant to Groundwater
Remediation at Sites with Persistent Contamination
The following five NRC reports have particular relevance to this report, as they
address the feasibility of subsurface remediation from various perspectives:
Alternatives for Groundwater Cleanupa (NRC, 1994) reviewed extensive data from
77 pump-and-treat sites and found that ease of remediation depended on the na-
ture of the contamination present and the site hydrogeology. Only two of 77 sites
were rated as easy to clean up, and only eight of the 77 sites reached remedial
goals, like obtaining MCLs in groundwater. The report suggested that an infeasi-
bility fee be charged to potentially responsible parties (PRPs) to further research
and development of new technologies to remediate such sites.
Groundwater and Soil Cleanup: Improving Management of Persistent Contami-
nants (NRC, 1999) provided a comprehensive review of groundwater and soil
remediation technologies, focusing on three classes of contaminants that have
proven very difficult to treat once released to the subsurface: metals, radionu-
clides, and DNAPLs, such as chlorinated solvents. The report concluded that
“removing all sources of groundwater contamination, particularly DNAPLs, will
be technically impracticable at many Department of Energy sites, and long-term
containment systems will be necessary for these sites."
Natural Attenuation for Groundwater Remediation (NRC, 2000) focused on moni-
tored natural attenuation (MNA) and considered when and where MNA will work.
Prompted by the increasing use of MNA as a remedy at hazardous waste sites
(from less than 5 percent of Records of Decision in 1985 to more than 25 percent
in 1995), it evaluated the likelihood of success of MNA for many contaminant
classes. The report found that the likelihood of MNA success for most compounds
is low, despite the increase in its use at Superfund facilities. None of the 14
protocols reviewed in the report was completely adequate in its treatment of the
important scientific and technological, implementation, and community concerns
inherent to MNA. Thus, EPA was advised to provide new guidance on protocols.
and its distribution (sometimes referred to as “source zone architecture”6)
and due to the diversity of opinions on the anticipated cost, effectiveness,
and robustness of various remediation technologies.
6 Source zone architecture refers to the distribution of DNAPL as either residual saturation
(immobile ganglia and blobs) in more permeable media or as pools on tops of low-permea-
bility layers. Residual DNAPL has a higher surface area, which provides greater exposure to
flowing groundwater, contributing significantly to downgradient contaminant mass flux. In
contrast, pools usually contain more DNAPL mass but have lower surface area exposed to
clean groundwater and a correspondingly lower contribution to mass flux. See Figure 1-1.
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INTRODUCTION 27
Environmental Cleanup of Navy Facilities: Adaptive Site Management (NRC,
2003) developed the concept of adaptive site management (ASM) to deal with
sites where remedial goals have not been reached after some significant amount
of time operating the remedy (the so-called asymptote effect). The hallmark of
ASM is doing things while a remedy is ongoing that will inform the process if the
remedy fails. The report describes several management decision points at which
new information from parallel activities could be incorporated to allow site rem-
edies to be reconsidered over time.
Contaminants in the Subsurface (NRC, 2005a) responded to another trend in
hazardous waste remediation—the use of aggressive source removal. Source
removal via such technologies as in situ chemical oxidation, thermal treatment,
and surfactant-enhanced flushing was often attempted without a clear understand-
ing of whether those actions would in fact remove mass or lead to substantial
changes in contaminant concentration in groundwater. The report defined five
hydrogeologic settings, based on the degree of heterogeneity and permeability
found in subsurface soils. In addition, it created a table for each source remedia-
tion technology discussing the extent to which that technology could meet five
different goals in each of the five hydrogeologic settings. The goals included mass
removal, concentration reduction, mass flux reduction, reduction of source migra-
tion potential, and a change in toxicity. The report concluded that available data
from field studies do not demonstrate what effect source remediation is likely to
have on water quality.
a Although sometimes used synonymously, there is an important difference between the
terms remediation and cleanup. Remediation is the “removal of pollutants or contaminants
from environmental media such as soil, groundwater, sediment, or surface water for the gen-
eral protection of human health and the environment” (http://sis.nlm.nih.gov/enviro/iupacglos-
sary/glossaryr.html); it does not imply removal or destruction of all contaminants. Cleanup is
the restoration of the affected site to a condition allowing for UU/UE which generally implies
meeting drinking water standards in the case of contaminated groundwater. This report pri-
marily uses the term remediation to avoid confusion.
Key Challenges for Subsurface Remediation at DoD Facilities
The DoD has invested over $30 billion to address contamination of
the soil and groundwater at military bases in the United States and abroad
(OUSD, 2011). Under the Installation Restoration Program, many indi-
vidual sites have been closed with no further action required. However, at
complex sites characterized by multiple contaminant sources, large past
releases of chemicals, or highly complex geologic environments, meeting
the DoD’s ambitious programmatic goals for remedy in place/response
complete seems unlikely and site closure almost an impossibility. The recent
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28 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
FIGURE 1-1 Hypothetical DNAPL release site. In addition to residual and pooled
DNAPL sources, the figure depicts vapor-phase contaminants in the unsaturated
zone and a plume of dissolved and sorbed contamination in the saturated zone
downgradient of the DNAPL. Note that1-1 residual DNAPL is more likely to occur
Figure the
Bitmapped
in sparse pools and fingers, rather than in the massive bodies inferred in the picture.
SOURCE: NRC (2005a); adapted from Cohen et al. (1993).
FIGURE 1-2 Schematic of possible post-remediation trajectories for plume behavior.
The y axis could be any decision variable used to measure the remedial objective
(e.g., the contaminant concentration at a point of compliance).
Figure 1-2
bitmapped
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INTRODUCTION 29
policy memorandum from the Air Force (Yonkers, 2011) regarding the
new milestone of accelerated site completion does not appear to clarify or
simplify military remediation requirements.
An example of the array of challenges faced by the DoD is provided by
the Anniston Army Depot, where groundwater is contaminated with chlo-
rinated solvents (as much as 27 million pounds of TCE [ATSDR, 2008])
and inorganic compounds. TCE and other contaminants are thought to
be migrating vertically and horizontally from the source areas, affecting
groundwater downgradient of the base including the potable water supply
to the City of Anniston, Alabama. The interim Record of Decision called
for a groundwater extraction and treatment system, which has resulted in
the removal of TCE in extracted water to levels below drinking water stan-
dards. Because the treatment system is not significantly reducing the extent
or mobility of the groundwater contaminants in the subsurface, the current
interim remedy is considered “not protective.” Therefore, additional efforts
have been made to remove greater quantities of TCE from the subsurface,
and no end is in sight. Modeling studies suggest that the time to reach the
TCE MCL in the groundwater beneath the source areas ranges from 1,200
to 10,000 years, and that partial source removal will shorten those times
to 830–7,900 years (Tetra Tech, 2011). Although Anniston is a strong can-
didate for a TI wavier, DoD officials have struggled to convince regulators
of the need for alternative remedial objectives (at this and other complex
military sites).
In part, the delays and transaction costs experienced at complex sites
have led to the use of alternative contracting mechanisms for site remedia-
tion within the DoD, including performance-based contracting. In some
cases, this has involved requesting guaranteed fixed-price proposals to
achieve certain milestones within specified schedule deadlines. The intent
of these contracting procedures is to accelerate remediation and reduce the
overall life-cycle costs (Army, 2010). Anecdotal stories suggest that this
process has indeed accelerated transition of sites to the status of remedy in
place, but not to site closure.
It appears that future liabilities for the DoD are unknown because of
the uncertain time frames to achieve remedial action objectives at the more
complex sites. It is probable that these sites will require significantly longer
remediation times than mandated, and thus, continued financial demands
for monitoring, maintenance, and reporting. In addition, the tension be-
tween remedial strategies involving long-term containment compared to
contaminant removal from the subsurface will likely continue, with a lack
of efficient protocols that could potentially reduce overall life-cycle costs.
Finally, consistent with DoD goals of achieving a greater level of environ-
mental sustainability in all environmental programs (DoD, 2009), increased
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30 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
incorporation of sustainability metrics in remedial decision making appears
likely.
STATEMENT OF TASK AND REPORT ROADMAP
Although technologies capable of removing substantial amounts of
contaminants from groundwater have evolved significantly over the last
40 years, our ability to predict remediation performance, and its associ-
ated groundwater quality improvement, with adequate certainty is limited.
Additional questions must be answered before management of sites can
proceed in a way that is protective in an era of limited financial resources.
The following questions guided the work of this NRC committee.
1. Size of the Problem
t how many sites does residual contamination remain such that site
A
closure is not yet possible? At what percentage of these sites does re-
sidual contamination in groundwater threaten public water systems?
2. Current Capabilities to Remove Contamination
hat is technically feasible in terms of removing a certain percentage
W
of the total contaminant mass? What percent removal would be needed
to reach unrestricted use or to be able to extract and treat groundwa-
ter for potable reuse? What should be the definition of “to the extent
practicable” when discussing contaminant mass removal?
3. Correlating Source Removal with Risks
ow can progress of source remediation be measured to best cor-
H
relate with site-specific risks? Recognizing the long-term nature of
many problems, what near-term endpoints for remediation might be
established? Are there regulatory barriers that make it impossible to
close sites even when the site-specific risk is negligible and can they be
overcome?
4. The Future of Treatment Technologies
he intractable nature of subsurface contamination suggests the need
T
to discourage future contaminant releases, encourage the use of innova-
tive and multiple technologies, modify remedies when new information
becomes available, and clean up sites sustainably. What progress has
been made in these areas and what additional research is needed?
5. Better Decision Making
an adaptive site management lead to better decisions about how to
C
spend limited resources while taking into consideration the concerns of
stakeholders? Should life-cycle assessment become a standard compo-
nent of the decision process? How can a greater understanding of the
limited current (but not necessarily future) potential to restore ground-
water be communicated to the public?
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INTRODUCTION 31
Although the focus of the study was on military sites, particularly those of
the U.S. Army, the conclusions and recommendations are relevant to both
public and private hazardous waste sites.
The study was intended to focus on those recalcitrant contaminants
occurring most frequently at the most complex sites, in particular organic
compounds present as DNAPLs. In addition, groundwater cleanup, as op-
posed to soil remediation, poses the greatest remediation challenge and
was thus the primary focus of this study. Other topics relevant to the na-
tion’s subsurface remediation efforts that are not reviewed here include
the impacts of agricultural activities on groundwater quality, abandoned
mine sites, and impacts from municipal and solid waste landfills. Finally,
although Department of Energy sites also illustrate the challenges of recal-
citrant contamination requiring long-term management, because a number
of NRC reports have reviewed sites with radioactive contaminants (NRC,
2005b, 2007, 2009) they are not discussed further here.
The questions in the statement of task are addressed variously through-
out the report. Thus, Chapter 2 attempts to bound the size of the prob-
lem (first task item), including federal sites under the jurisdiction of EPA
(CERCLA, RCRA, and UST programs), the military, the Department of
Energy, and state remediation programs. For all programs, the Committee
sought information on the total number of sites, the costs expended to date
and to clean up remaining sites, and the number of sites affecting a drinking
water supply. Chapter 2 (and Appendix C) also discusses sites that have
been “closed” and characterized as successes to illustrate the point that
many “closed” sites are still contaminated (though they are protective of
human health and the environment).
Chapter 3 discusses elements primarily from the third task item but also
from the second and fourth. With regards to the third task item, it outlines
common remedial objectives (stemming from regulatory programs) includ-
ing the use of MCLs and other risk-based objectives. It demonstrates the
flexibility inherent in CERCLA for defining measurable remedial objectives
that protect human health and the environment and prevent the spread of
contamination, in the most cost-efficient way. It also discusses a suite of
alternative remedial objectives that could be considered for sites slated for
long-term management and the barriers that prevent more frequent use of
these alternatives. The chapter introduces the concept of sustainability in
remediation and its role as a remedial objective (from the fourth task item),
and it provides the regulatory definition of “maximum extent practicable”
(from the second task item).
Chapter 4 focuses on the current capabilities of technologies to remove
or contain subsurface contamination (the second task item). For the major
classes of removal technologies, including extraction, thermal, chemical,
and biological technologies, as well as containment, the chapter updates the
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32 MANAGING THE NATION’S CONTAMINATED GROUNDWATER SITES
NRC (2005a) report in addressing what is technically feasible in terms of
removing contaminant mass. Case studies for the technologies are included
both within the chapter and in Appendix B to illustrate the capabilities of
existing technologies for removing mass from the subsurface. It should be
noted that the percent contaminant removal that would be needed to reach
unrestricted use, or to be able to extract and treat groundwater for potable
reuse, can only be determined on a site-specific basis and is not addressed
further in this report. It depends on knowing the amount of contamination
present at a site as well as the removal capabilities of the chosen well-head
treatment technologies.
Although not explicitly called for in the statement of task, the risks
of leaving residual contamination in place in the subsurface are discussed
comprehensively in Chapter 5. These include technological risks such as the
failure of hydraulic containment or barrier technologies, or the inability of
current treatment and containment systems to handle unregulated and un-
anticipated contaminants. Chapter 5 also discusses institutional issues that
arise when contamination remains in place, such as economic and litiga-
tion risks like possible natural resource damage and trespass suits and the
failure of institutional controls. The consequences of leaving contamination
in place for water utilities and domestic wells are discussed.
Chapter 6 focuses on the future of treatment technologies (fourth task
item). It provides a targeted discussion of those areas of technology devel-
opment relevant to the problem of leaving contamination in place, but is
not meant to be a comprehensive cataloging of remediation technologies
(see Chapter 4). In addition to remediation technologies, it speaks to ad-
vances in our understanding of hydrogeology and contaminant transport
pathways, improved diagnostics and new geophysical methods, and the use
of sensors for monitoring long-term management. It should be noted that
the report does not comprehensively discuss the need to discourage future
contaminant releases, as significant progress has been made in this area.
That is, it is now so expensive to manage contaminated sites that potentially
responsible parties will go to great lengths to avoid causing groundwater
contamination.
The report ends with a chapter on how better decision making can
help manage sites with residual contamination (addressing the fifth task
item, as well as the call for near-term endpoints in the third task item). This
includes the introduction of several important decision points and a transi-
tion assessment to help move sites to one of three end states. The transition
assessment is akin to the adaptive site management concept first developed
in NRC (2003), but focuses specifically on complex sites where long-term
management is likely needed. The chapter discusses the economic, risk
assessment, and risk communication implications of this transition assess-
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INTRODUCTION 33
ment. Life-cycle assessment is not discussed further because it goes beyond
the issues presented by groundwater sites with residual contamination.
The Committee reached consensus on all conclusions and recommen-
dations in the report except regarding a proposal for a public/private
partnership that could be established to manage portfolios of sites in a
manner similar to initiatives undertaken by private responsible parties
(e.g., separate companies to manage legacy sites) or public agencies (e.g.,
Minnesota Pollution Control Agency’s Closed Landfill Program). In these
entities, liability and long-term responsibility for contaminated sites are
transferred from the responsible party to a new entity. In the case of the
Minnesota Pollution Control Agency, owners of sanitary landfills pay a fee
to the program in exchange for transfer of all future liability and manage-
ment costs. The Committee considered the concept of an industry/govern-
ment/public organization that could be formed to assume management
for a portfolio of sites, called the “environmental liability management
organization (ELMO).” PRPs would pay ELMO to assume liability and
site management, and the payment would cover expected damages and
management costs for as long as the contamination remains above levels
allowing for unlimited use and unrestricted exposure. The Committee could
not agree on the details of such a proposed entity, but all members agreed
that future consideration of such an organization could potentially provide
a number of advantages to all parties, especially in the context of long-term
management of sites.
Throughout the report are case studies of complex sites where it is
most likely that contamination will remain in place after remedy opera-
tion. These sites are the most important to the Army in terms of being
able to reach its 2014 goal of remedy in place/response complete and the
updated goals of DoD, and in determining its future remediation liability.
A list of the complex sites studied in depth by the Committee is found in
Appendix B.
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INTRODUCTION 35
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