United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(OS-220)
Directive: 9283.1-2FS
April 1989
A Guide
On Remedial Actions For
Contaminated Ground Water
GOAL
The goal of Superfund ground-water remediation is to protect human health and the environment by restoring ground water to its benefi-
cial uses within a time frame that is reasonable, given the particular site circumstances. This fact sheet summarizes the key issues in the
development, evaluation, and selection of ground-water remedial actions at Superfund sites. For more detailed information, consult Regional
Ground-Water Forum members or the Interim Final "Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites,"
(Ground-Water Guidance) December 1988, OSWER Directive No. 9283.1-2.
REQUIREMENTS OF CERCLA
The approach outlined in this fact sheet is
designed to ensure that ground-water reme-
dial actions will meet the following require-
ments of CERCLA:
• Protect human health and the environ-
ment (12 l(b))
• Comply with applicable or relevant and
appropriate requirements (ARARs) of Fed-
eral andState laws (121(d)(2)(A)) or war-
rant a waiver under CERCLA Section
• Be cost-effective (121(a))
• Utilize permanent solutions and alterna-
tive treatment technologies or resource re-
covery technologies to the maximum extent
practicable ( 12 l(b))
• Satisfy the preference for remedies that em-
ploy treatment that permanently and signifi-
cantly reduces the mobility, toxicity, or vol-
ume of hazardous substances as a principal ele-
ment or provide an explanation in the ROD for
why the preference was not satisfied (121(b)).
In addition, the following provisions of CER-
CLA may or may not be pertinent to ground-
water remediation, depending on site-specific
circumstances:
• Alternate concentration limits (ACLs) from
otherwise applicable or relevant and appropri-
ate requirements can only be used for deter-
mining offsite cleanup levels under special
circumstances (121(d)(2)(B)(ii)).
• Remedial actions that restore ground
water are to be federally funded until cleanup
levels are achieved or up to 10 years, which-
ever comes first. However, if the purpose
of the ground-water remedial action is to
provide an alternate water supply, for ex-
ample, but not to restore ground water, then
the Federal government will pay capital
and startup costs only (104(c)(6)).
• A review must be conducted at least
every 5 years if wastes are left onsite
(121(c)) above health- or environment-
based levels to verify that the remedy con-
tinues to provide adequate protection of
human health and the environment.
SCOPING
GROUND-WATER
REMEDIAL ACTIVITIES
Before collecting any data, it is useful to
conduct two planning activities:
• Site management planning (See right),
which involves identifying the types of
analyses and actions that are appropriate to
address site problems and their optimal se-
quence.
• Projectplanning (See next page), which
includes such activities as scoping data
collection efforts, initiating identification
of ARARs, and work plan preparation.
SITE MANAGEMENT PLANNING
Site management planning identifies the re-
sponse approaches that will be taken to ad-
dress the site problems. Two response ap-
proaches can be taken to remediate ground
water at Superfund sites:
• Removal actions
• Remedial actions, which can be final, or
interim actions
Removal actions are authorized for any re-
lease that presents a threat to public health,
welfare, or the environment. CERCLA limits
Superfund-financed removal actions to
$2 million and 12 months unless the criteria
for granting an exemption to the statutory
limits are satisfied. Remedial actions are
sometimes addressed as operable units.
An operable unit is a portion of an overall
response action that, by itself, eliminates or
mitigates a release, a threat of a release, or
an exposure pathway; it may reflect the
final remediation of a defined portion of a
site. At many sites, it is appropriate to im-
plement an operable unit as an interim ac-
tion. Interim actions may be implemented
to prevent exposure to contaminants or pre-
vent further degradation of ground water
(by remediating hot spots, for example)
while the overall remedial investigation
(RI) and feasibility study (FS) are being
conducted. Interim actions involving pump-
ing can also provide critical information for
evaluating the final remedy.
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Characterization
of the Hydrogeology
Describe the geology using geophysical meth-
ods and sediment samples collected during
drilling of soil borings and monitoring wells.
Present the information using geologic cross
sections and fence diagrams.
Assess the ground-water movement by using
water level measurements from wells screened
at various depths. Present a contour map of
each aquifer to determine recharge and dis-
charge and identify the direction of ground-
water flow.
Evaluate data over time to detect seasonal or
tidal fluctuations.
Aquifer tests may be used to determine the hy-
draulic properties of the aquifers and aquita-
rds, and to evaluate the performance and effec-
tiveness of the extraction system. Aquifer tests
can be used in conjunction with modeling.
Characterization of
Contamination
Consider selecting one or more chemicals for
monitoring to reduce analytical costs and sim-
plify modeling. These chemicals may be se-
lected on the basis of toxicity, exposure, mobil-
ity, persistence, treatability, or volume of con-
taminants. If appropriate, however, nontoxic
constituents or chemical classes, such as total
volatile organic compounds, could also be
monitored.
Determine the horizontal and vertical extent of
the contaminant plume through monitoring at
various locations and depths. Understand the
relationship of the source to the ground water.
Contaminant levels should be monitored over
time to identify migration and degradation pat-
terns. Note the density of contaminants to aid in
assessing their behavior in the ground water.
Assess contaminant/soil interactions to aid in as-
sessing the effectiveness of a ground-water ex-
traction system. Laboratory analysis of contami-
nant partitioning behavior in the saturated soil
may be critical to the development of the remedy
and the determination of whether ground-water
extraction is practicable.
PROJECT PLANNING
Recommended Data
Collection Activities
Evaluation of
Plume Movement
and Response
Consider modeling the ground
water as a tool to guide the place-
ment of monitoring wells, predict
concentrations of contaminants at
exposure points, estimate the ef-
fect of source control actions, and
evaluate the expected performance
of the ground-water remedial ac-
tion.
Consideration of
Technical Uncertainty
Identify sources of uncertainty, e.g., pre-
dicting the nature, extent, and movement
of contamination; determining contami-
nant movement through the vadose zone;
estimating the rate and direction of the
ground-water flow; and estimating the cost
of remedial alternatives. Assess the mag-
nitude of uncertainty from each of these
sources, and weigh the costs and benefits
of reducing uncertainty by collecting ad-
ditional information.
Assessment of Design
Parameters for
Potential Treatment
Technologies
Identify several likely remedial
technologies during scoping to
focus data collection activities.
Consider data needs for screening
out inappropriate technologies and
for designing workable systems to
provide a sound basis for selecting
a remedy and reducing implemen-
tation time. Consider the costs and
benefits of conducting a treatabil-
ity study.
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REMEDIAL ACTION OBJECTIVES
Remedial action objectives include cleanup levels, the area of attainment, and the restoration time frame.
Cleanup Levels
Cleanup levels wi 11 generally be set at health-
based levels, reflecting current and potential
use and exposure. For ground water that is
a current or potential source of drinking
water, maximum contaminant levels (MCLs)
under the Sate Drinking Water Act or more
stringent State standards devised to protect
drinking water generally are ARARs. If an
MCL or State standard does not exist for a
contaminant, then other potential ARARs
and criteria that are not ARARs but are to-
be-considered (TBC) should be identified.
The most common ARARs and TBCs are
summarized in Table 1. This is consistent
with the Ground Water Protection Strategy
which differentiates ground water on Ihe
basis of use, value, and vulnerability.
Area of Attainment
The area of attainment is the area outside the
boundary of any waste remaining in place
and up to the boundary of the contaminant
plume. Generally,the boundary of the waste
is defined by the source control remedy. If
the source is removed, the entire plume is
within the area of attainment. But. if waste
is managed onsite, the ground water directly
beneath the waste management area is not
within the area of attainment
TABLE 1
Potential ARARs
• Maximum contaminant levels (MCLs)
• Promulgated State standards
Other Potential ARARs and TBCs
• Proposed MCLs
• Risk-specific doses
• Reference doses
• Lifetime health advisories
• Maximum contaminant level goals
• Water quality criteria
For systemic (noncarcinogenic) toxicants,
cleanup teveh should be set at levels to which
humans could be exposed on a daily basis
without experiencing appreciable adverse ef-
fects during their lifetimes. To determine ag-
gregate effects from systemic toxicants, the
hazard index is used.
For carcinogens, cleanup levels should re-
flect m individual excess lifetime cancer risk
of IO4 to IO-7; that is, aggregate cancer risk
levels should fall within the 10* to 10-' risk
range. The 10* aggregate excess lifetime
cancer risk level is considered the starting
point for analysis, but other risk levels be-
tween 10^* to IO7 may be supported on the
basis of factors related to exposure, technical
limitations, and uncertainties.
Alternate concentration limits (ACLs) may be
established in some situations where remedia-
tion of the ground water is not practicable.
CFJtCLA Section l21(dX2XBXii) places
restrictions on the use of ACLs: The ground
water must discharge to nearby surface water
and cause no statistically significant increase
of contaminants in the surface witter. In addi-
tion, provisions for enforceable institutional
controls that prevent access to the contaminant
plume must be made.
Restoration Time Frame
The restoration time frame is defined as the
period of time required (o achieve cleanup
levels in the ground water at all locations
within the area of attainment For drinkable
ground water, at least one alternative should
reach cleanup levels in the minimum time
frarnelechnicaUyachievable. Technical limits
to extracting contaminants that will tend to
increase the restoration time frame include
contaminant/soil interactions, the presence of
dense nonaqueous phase liqokfs, continued
migration from sources, widely spread
plumes, and poorly transmissive aquifers.
Because these conditions are not generally
addressed in plume migration models, aquifer
testing or saturated soil core analysis may be
FIGURE 1
Sample Remediation Process--
Ground-Water Remedy
• Prevent BipOKire • Preurt ccrtumatCTidJoepiiquifec • Restore ground water to drlnBna wattrgmOy \
Patent*! Hemdto • Natural laanmnnwBi moototna • ran reaonfen «* ertacfcn |
• Drinking water well
not affected
warranted
• Interim adion
evaluated
•1.1-DCE ISOOppo
PCE 650 pf*
VC 500ppt»
1.1,1-TCA iSOOppb
TCE 1200 ppb
DM
CoiUctton
•Well and
tteepand
shdoiD
aquifers
• Contaminant
concentrations
andTOC
• Aquifer Kit
toesttmao
hydraulic
conductivity
degradation
__^ .^.
-*•
taMUM
Helton
Otjecttwi
•A/we* .
attainment:
entire plume
• Restoration
lime frame:
appr
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GENERAL RESPONSE ACTIONS
After developing remedial action objectives,
general response actions are identified. Gen-
eral response actions for contaminated
ground water include active restoration,
plume containment through hydraulic con-
trol, and limited or no active response,
combined, if appropriate, with institutional
controls to protect human health. These are
discussed below.
Active restoration is useful when there are
mobile contaminants, moderate to high hy-
draulic conductivities in the contaminated
aquifer, and effective treatment technolo-
gies available for the contaminants in the
ground water. Innovative technologies for
active restoration may include biorestora-
tion, soil flushing, in situ stream stripping,
soil vapor extraction, in situ vitrification, and
others.
Plume containment seeks to minimize the
spread of a plume through hydraulic gradient
control, which can be either active or passive.
Containment is appropriate where active
restoraton is not practicable or where the bene-
ficial uses of the ground water do not warrant
it. In addition, plume containment may be
combined with active restoration or natural
attenuation to achieve cleanup levels.
Limited or no active response includes two re-
medial scenarios: (1) a natural attenuation al-
ternative thateventually achieves cleanup levels
throughout the area of attainment and includes
monitoring and institutional controls; and
FORMULATING REMEDIAL ALTERNATIVES
A range of remedial technologies can be
combined under a particular general response
action. Process options for extraction in-
clude: extraction wells, extraction/injection
systems, and interceptor drains and trenches.
Treatment options include biological, chemi-
cal, physical, thermal, or in situ methods.
Treated ground water can be discharged to
surface water or a publicly-owned treatment
works, reinjected to the aquifer, or used as a
(2) wellhead treatment or provision of an al-
ternate water supply with institutional con-
trols, when complete restoration to cleanup
levels is not practicable.
Factors that may cause active restoration to
be impracticable or not cost-effective in-
clude:
• Widespread plumes such as at industrial
areas, mining sites, and pesticide sites
• Hydrogeological constraints such as with
fractured bedrock, or where the transmissiv-
ity is less than 50 square feet per day
• Contaminant-related factors such as the
presence of dense nonaqueous phase liquids
• Physical/chemical factors such as parti-
tioning to soil or organic matter.
drinking water supply. Finally, there are
various options for containment, monitoring
effectiveness, and institutional controls. Al-
ternatives are developed by combining these
various process options into a comprehen-
sive response approach.
DETAILED ANALYSIS OF ALTERNATIVES
AND SELECTION OF REMEDY
CRITERIA AND BALANCING
The analysis of remedial actions for ground
water is made on the basis of the following
evaluation criteria. Considerations that are
unique to ground water are noted.
Threshold criteria
• Overall protection of human health and
the environment: Will the remedy achieve
and maintain clean-up levels? Are all expo-
sure pathways controlled; e.g., discharge
points, points of use?
• Compliance with ARARs: Will the rem-
edy attain MCLs or state standards in poten-
tially drinkable ground water or justify a
technical impracticability waiver? Are
ARARs met for the treated ground water
and any treatment residials that are gener-
ated?
Balancing criteria
• Long term effectiveness and permanence:
Remedies that achieve the cleanup levels
will be comparable with respect to this cri-
teria. For remedies that will not restore
ground water, how reliable are the engineer-
ing or institutional controls used to prevent
exposure?
• Reduction of mobility, toxicity, and volume:
What reductions are achieved through treat-
ment in any phase of the remediation process?
This includes initial treatment of ground water
and subsequent treatment of resulting residu-
als. Special note should be given to remedies
that transfer contaminants from ground water
to air without treatment of the air releases,
especially if risk through the air pathway ex-
ceeds 10'6.
• Short-term effectiveness: What is the resto-
ration time frame? What cross-media impacts
occur as a result of ground-water treatment or
construction of a containment facility? How
much farther will the plume spread before the
remedy is completed?
• Implementability: What permitting require-
ments must be met for discharge of treated
ground water? Are there access problems with
installation of the remedy—e.g., extraction wells
and slurry walls-in terms of resources re-
quired? Are there capacity limitations on
POTWs receiving discharge waters? What
uncertainties exist with the treatment process
considered?
• Cost
Modifying critera:
• State Acceptance
• Community Acceptance
If the alternatives will achieve the same long
term goals, the primary balancing criteria
will be implementability, cost and short term
effectiveness.
DOCUMENTATION
In addition to the standard documentation, a
ROD for a ground-water action should in-
clude the following components:
• Remedial action objectives defined in the
FS for each alternative: i.e., the cleanup lev-
els, the area of attainment, and the restoration
time frame.
• A description of the technical aspects of
the selected remedy that will form the basis of
design for the system, such as the following:
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(Detailed A nalysis-- Continued from pre-
vious page)
- Number of extraction wells
- Treatment process
- Control of cross-media impacts
- Expected pumping and flow rates
- Management of residuals
- Gradient control system
- Type of institutional controls and the
implementing authority
Since performance of remedies for restoring
contaminated ground water can often be evalu-
ated only after the remedy has been imple-
mented and monitored for a period of time,
remedial action objectives should be presented
as ranges to accommodate reasonable degrees
of change during design and implementation.
An option is to include two possible scenarios
in the remedy, e.g., ground-water extraction
until cleanup levels are attained, or ground-
water extraction until an equilibrium is
reached and contaminant mass is no longer
being removed at significant rates, at which
time portions of the plume that remain above
cleanup levels should be monitored and insti-
tutional controls established to prevent ac-
cess to contaminated ground water.
EVALUATING PERFORMANCE AND MODIFYING
REMEDIAL ACTIONS
Performance evaluations of the full-scale
remedial action are conducted periodically
to compare actual performance to expected
performance. Conducting performance
evaluations and modifying remedial actions
is part of a flexible approach to attaining
remedial action objectives.
Figure 2 represents a decrease in contami-
nant concentration over time for three
ground-water remedial actions of varying
effectiveness. Line A represents a reme-
dial action that is meeting design expecta-
tions, and the desired cleanup levels are
predicted to be reached within the antici-
pated time. Line B represents a remedial
action that is predicted to achieve the cleanup
levels, but the action will have to be oper-
ated longer than anticipated. LineC repre-
sents a remedial action that will not achieve
the desired cleanup levels for a long time, if
ever, without modifying the remedial ac-
tion.
After evaluating whether cleanup levels
have or will be achieved in the desired
time frame, the following options should
be considered:
• Discontinue operation
• Upgrade or replace the remedial ac-
tion to achieve the original remedial
action objectives or modified remedial
action objectives
• Modify the remedial action objec-
tives and continue remediation, if appro-
priate.
Performance monitoring should ensure
that residual contamination has been
removed. This will generally require
monitoring ground-water concentrations
after active measures have been com-
pleted to allow contaminant concentra-
tions in the soil and ground water to re-
equilibrate.
FIGURE 2
Predicting Remedial Action Performance
Actual ; Predicted
Performance . Performance
Contaminant
Concentration
Time
MULTIPLE SOURCES STRATEGY
At sites where there are multiple sources of
ground-water contamination, some of which
are Superfund sites, it may be appropriate to
implement a multiple-source strategy. The
Superfund program should work coopera-
tively with other responsible entities to
achieve comprehensive remedies, and may
accept primary responsibility for coordinat-
ing all involved parties during the source
identification phase of work.
The Superfund program should coordinate
an initial scoping plan for source identifica-
tion that would include limited sampling.
Locations of possible sources may be deter-
mined through two surveys: (1) a survey of
contributors to and users of the affected
ground water (termed a "contributor/user
assessment") that will help identify the other
parties that must be involved in the formula-
tion of an effective remedy; and (2) a survey
of potential sources such as solvent storage
facilities located at or upgradient of the area of
contamination.
Superfund will implement appropriate reme-
dial actions related to National Priorities List
sites once an RI/FS is initiated. At this point,
the Regional Administrator, in consultation
with the Assistant Administrator of OSWER,
should evaluate the appropriateness of the
Superfund program retaining primary respon-
sibility for coordinating the ground-water re-
sponse action for all sources. This decision
may be determined by factors such as the
contribution of Superfund sources relative to
other sources, as well as the availability and
willingness of other involved parties to initiate
action.
Response actions generally fall into three cate-
gories: provision of alternate water supply,
source control measures, and ground-water
remedies. Superfund resources may be used to
provide an alternate water supply if an NPL
site is a significant contributer to the plume
and if the need to alleviate the public health
threat does not allow for identification and
involvement of other parties at that time.
Actions to prevent or minimize spread of
contaminants from the source are often
implemented at multiple source ground-
water sites before completing plume char-
acterization, which can be lengthy and com-
plicated at these sites.
The amount of Superfund resources used to
address ground-water contamination will
derive primarily from the extent to which
the overall contamination can be attributed
to the Superfund site. It will also depend on
the willingness and capability of the other
involved parties to take actions to address
the contamination for which they are re-
sponsible.
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