United States	Solid Waste and	Directive:
Environmental Protection	Emergency Response	9283.1-2FS April
Agency	(OS-220)	1989
&ERA A Guide
Wmmm m m
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 beneficial
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-
ial actions will meet the following require -
ents of CERCLA:
•	Protect human health and the environ-
ment (121(b))
•	Comply with applicable or relevant and
appropriate requirements (ARARs) of Fed-
ral and State laws (121(d)(2)(A)) or warrant
a waiver under CERCLA Section 121(d)(4)
Be cost-effective (121 (a))
•	Utilize permanent solutions and altern-
ative treatment technologies or resource
recovery technologies to the maximum
extent practicable (121 (b))
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
sequence.
•	Project planning (See next
page),which includes such activities as
scoping data collection efforts, initiating
identification of ARARs, and work plan
preparation.
•	Satisfy the preference for remedies that
employ treatment that permanently and
significantly reduces the mobility, toxicity, or
volume of hazardous substances as a principal
element or provide an explanation in the ROD
for why the preference was not satisfied
(121(b)). In addition, the following provisions
of CERCLA may or may not be pertinent to
groundwater remediation, depending on
site-specific circumstances:
•	Alternate concentration limits (ACL s) from
otherwise applicable or relevant and
appropriate requirements can only be used for
determining offsite cleanup levels under special
circumstances (121 (d) (2) (B) (ii)).
Site management planning identifies the
response approaches that will be taken to
address the site problems. Two response
approaches 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
release 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.
•	Remedial actions that restore ground
water are to be federally funded until cleanup
levels are achieved or up to 10 years,
whichever comes first. However, if the
purpose of the ground-water remedial action
is to provide an alternate water supply, for
example, 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 continues to provide
adequate protection of human health and the
environment.
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
implement an operable unit as an interim
action. Interim actions may be implemented
to prevent exposure to contaminants or
prevent 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 pumping can also provide critical
information for evaluating the final remedy.
SITE MANAGEMENT PLANNING
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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
discharge 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
hydraulic properties of the aquifers and
aquitards, and to evaluate the performance and
effectiveness 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
simplify modeling. These chemicals may be
selected on the basis of toxicity, exposure,
mobility, persistence, treatability, or volume
of contaminants. 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 patterns. Note the density of
contaminants to aid in assessing their
behavior in the ground water.
Assess contaminant/soil interactions to aid in
assessing the effectiveness of a ground-water
extraction system. Laboratory analysis of
contaminant 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.
J PROJECT PLANNING ^
[	Recommended Data	j
L CollectionActivities A
Evaluation of
Plume Movement
and Response
Consider modeling the ground
water as a tool to guide the
placement of monitoring wells,
predict concentrations of
contaminants at exposure points,
estimate the effect of source control
actions, and evaluate the expected
performance of the ground-water
remedial action.
Consideration of
Technical Uncertainty
Identify sources of uncertainty, e.g., pre-
dicting the nature, extent, and movement of
contamination; determining contaminant
movement through the vadose zone;
estimating the rate and direction of the
ground-waterflow; and estimating the cost
of remedial alternatives. Assess the
magnitude of uncertainty from each of
these sources, and weigh the costs and
benefits of reducing uncertainty by
collecting additional 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 implementation
time. Consider the costs and benefits
of conducting a treatability study.
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REMEDIAL ACTION OBJECTIVES
Remedial action objectives include cleanup levels, the area of attainment, and the restoration timeframe.
Cleanup Levels
Cleanup levels will 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 safe 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 criterai 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 the 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
Figure 1
Sample Remediation Process—
Ground-Water Remedy
Contaminated
ground water
from an
Industrial
bndfWand
tar# fawn
For systemic (noncarcinogenic)
toxicants, cleanup levels should be set at
levels to which humans could be
exposed on a daily basis without
experiencing appreciable adverse effects
during their lifetimes. To determine
aggregate effects from systemic
toxicants, the hazard index is used.
For carcinogens, cleanup levels should
reflect an individual excess lifetime
cancer risk of 10~4 to 10~7; that is,
aggregate cancer risk levels should fall
within the 10~4 to 10~7 risk range. The
10"4 aggregate excess lifetime cancer risk
level is considered the starting point for
analysis, but other risk levels between
10"4 to 10"7 may be supported on the
•	Drinting water wslte
not Elected
•	No removal action
warranted
~Interim action
evaluated
•	1.1-OCE IDOOppb
PCE 650 ppb
VC 500 ppb
1,1,1-TCA 1500 ppb
TCE 1200 ppb
basis of factors related to exposure,
technical limitations, and uncertainties.
Alternate concentration limits (ACLs)
may be established in some situations
where remediation of the ground water
is not practicable. CERCLA Section
121 (d)(2)(B)(ii) places restrications 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
water. In addition, provisions for
enforceable institutional controls that
prevent access to the contaminant plume
must be made.
Bwwdy
• 3-weflpwnp
and treat
system with
continuous
pumping tor 2
years, pulsed
pumping for ,
approximately
10 years, and
tnodegradaton
'thereafter
Restoration Time Frame
The restoration time frame is defined as
the period of time required to acheive
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 frame technically
achievable. Technical limits to
extracting contaminants that will tend
to increase the restoration time frame
include contaminant/soil interactions,
the presence of dense nonaqueous phase
liquids, continued migration form
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 warranted.
Once technical limits to achieving
cleanup levels have been assessed,
restoration time frames for remedies can
be evaluted relative to this limit on the
basis ofthe following considerations:
~	Feasibility of providing an alternate
water supply - including schedule, cost,
quality, reliability, and yield. Also,
whether the alternate water supply is
itself irreplaceable should be considered.
Readily available alternate water
supplies will increase the flexibility to
select longer restoration time frames.
~	Potential use and value of the ground
water - including the timing of
anticipated demand, the magnitude of
the demand, the need (drinking,
irrigation), and the availability of other
water sources. If there is a high demand
for the ground water, shorter time frames
are warranted.
~	Effectiveness and reliability of
institutional controls - effective
controls restricting use or access to
contam inated ground water may increase
the flexibility to select a remedy with a
longer restoration time frame. Examples
of institutional controls include
licensing of well drillers, well
construction permits, well quality
certification, and regulations of new
development and property transactions.
~	Ability to monitor and control
contaminant movement - complex flow
patterns, for example in fractured
bedrock or karst areas, and unusual
distributions of contaminants may
increase the benefits of shorter
restoration time frames.

Response OfcJecOm
• Prevent Expc«jre » Piwent contaawMiioflpt deep aquifer • Restore ground water to drtnMnq water qua%
• Natural atenuafon w#i monitoring
• Active restoration will extraction
•	Sol vapor
exfraciion
•	Low-rate
ground-water
pumping
Atatrfpping
Twtedf
ground
Granular
actuated
Data
CoQietfon
•	Wafts and
piezometers In
deep and
shaflow
aquifers
•	Contaminant
concentrations
endTOC
•	Aquifer test
to estimate
hydraulic
conductivity
•	Contaminant
degradation
FtHMdM
tetton
Objective*
•	Area of
attainment:
entire piume
•	Restoration
timeframe:
approximately
12 years
•	Cleanup
levets: MCLs
andheaWi-
based criteria
Marin
Action
•	Sol vapor
effraction
•	Low-rate
ground-water
pumping
<— SCOPING 	>
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GENERAL RESPONSE ACTIONS
After developing remedial action objectives,
general response actions are identified.
General response actions for contaminated
ground water include active restoration,
plume containment through hydraulic
control, 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
hydraulic conductivities in the contaminated
aquifer, and effective treatment technologies
available for the contaminants in the ground
water. Innovative technologies for active
restoration may include biorestoration, 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
beneficial 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
remedial scenarios: (1) a natural attenuation
alternative that eventually achieves cleanup
levels throughout the area of attainment and
includes monitoring and institutional
controls; and (2) wellhead treatment or
provision of an alternate water supply with
institutional controls, when complete
restoration to cleanup levels is not
practicable.
Factors that may cause active restoration to
be impracticable or not cost-effective include:
•	Widespread plumes such as at industrial
areas, mining sites, and pesticide sites
•	Hydrogeological constraints such as
with fractured bedrock, or where the
transmissivity 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
partitioning to soil or organic matter.
FORMULATING REMEDIAL ALTERNATIVES
A range of remedial technologies can be
combined under a particular general
response action. Process options for
extraction include: extraction wells,
extraction/injection systems, and
interceptor drains and trenches.
Treatment options include biological,
chemical, 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
drinking water supply. Finally, there are
various options for containment,
monitoring effectiveness, and institutional
controls. Alternatives are developed by
combining these various process options
into a comprehensive 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
exposure pathwayscontrolled;e.g.,discharge
points, points of use?
•	Compliance with ARARs: Will the
remedy attain MCLs or state standards in
potentially drinkable ground water or justify
a technical impracticability waiver? Are
ARARs met for the treated ground water and
any treatment residuals that are generated?
Balancing criteria
•	Long term effectiveness and
permanence: Remedies that achieve the
cleanup levels will be comparable with
respect to this criteria. For remedies that will
not restore ground water, how reliable are the
engineering or institutional controls used to
prevent exposure?
•	Reduction of mobility, toxicity, and
volume: What reductions are achieved
through treatment in any phase of the
remediation process? This includes initial
treatment of ground water and subsequent
treatment of resulting residuals. 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
exceeds 10"6.
•	Short-term effectiveness'. What is the
restoration 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
requirements 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 required? Are there capacity
limitations on POTWs receiving discharge
waters? What uncertainties exist with the
treatment process considered?
•	Cost
Modifying criteria
•	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
include the following components:
•	Remedial action obj ectives defined in the
FS for each alternative: i.e., the cleanup
levels, 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 Analysis— 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
eval-uated only after the remedy has been
implemented 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 groundwater extraction until an
equilibriumis 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
institutional controls established to prevent
access 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 contaminant
concentration over time for three
ground-water remedial actions of varying
effectiveness. Line A represents a remedial
action that is meeting design expectations,
and the desired cleanup levels are predicted
to be reached within the anticipated time. Line
B represents a remedial action that is
predicted to achieve the cleanup levels, but
the action will have to be operated longer
than anticipated. Line C represents a remedial
action that will not achieve the desired
cleanup levels for a long time, if ever, without
modifying the remedial action.
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 action
to achieve the original remedial action
objectives or modified remedial action
objectives
•	Modify the remedial action objectives
and continue remediation, if appropriate.
Performance monitoring should ensure that
residual contamination has been removed.
This will generally require monitoring
ground-water concentrations after active
measures have been completed to allow
contaminant concentrations in the soil and
ground water to re-equilibrate.
FIGURE 2
Predicting Remedial Action Performance
Artoaf PfwMtd
Perf or jnanc* Parioriranc*
Contaminant
Restoration
TlfM Frama
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
cooperatively with otherresponsible entities
to achieve comprehensive remedies, and may
acceptprimary responsibility for coordinating
all involved parties during the source
identification phase of work.
The Superfund program should coordinate an
initial scoping plan for source identification
that would include limited sampling.
Locations of possible sources may be
determined through two survey s: (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
formulation 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
remedial 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 responsibility for
coordinating the ground-water response
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
categories: 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
contributor 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 groundwater sites before completing
plume characterization, which can be lengthy
and complicated 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
responsible.
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