Directive 9234,2-25
September 1993
Guidance for the
Technical of
Ground-Water
Interim Final
Office of Solid and Emergency Response
U.S. Environmental Protection Agency
Washington, DC 20460
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Notice
The policies set out in this document are intended solely as guidance to U.S, Environmental Protection Agency
(EPA) personnel; they are not final EPA actons and do not constitute rulemaking. These policies are not intended,
nor can they be relied upon, to create any rights enforceable by any party in litigation with the United States, EPA
officials may decide to follow the guidance provided in this document, or to act at variance with the guidance, based
on an analysis of specific site circumstances. EPA also reserves the right to change this guidance at any time with-
out public notice.
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Contents
1.0 Introduction ., , 1
1.1 Background 1
1.2 Purpose of the Guidance 2
2.0 Ground Water Remedy Decision Framework ..............2
2.1 Use of the Phased Approach ...2
2.2 Documenting Ground-Water Remedy Decisions Under CERCLA 4
2.2,1 Removal Actions ..,..,.....,., ,,,...,,,,,.,,.,,,,,4
2.2.2 Interim RODs 5
2.2,3 Final RODs ...5
2.2,4 ROD Contingency Remedies and Contingency Language ......5
2.3 Documenting Ground-Water Remedy Decisions under RCRA 6
2.3.1 Permits/Orders Addressing Stabilization...,., ., 6
2.3.2 Permits/Orders Addressing Final Remedies ..6
3.0 Remedial Strategy for DNAPL Sites ................................6
4.0 TI Decisions and Supporting Information ....... 9
4.1 Regulatory Framework for H Decisions 9
4.1.1 Superfund ...............9
4.1.2 RCRA ..............................10
4.2 Timing of TI Evaluations..... .10
4.3 TI Evaluation Components ., .,11
4.4 Supporting Information for TI Evaluations ..11
4.4.1 Specific ARARs or Media Cleanup Standards ..12
4.4.2 Spatial Extent of TI Decisions .............12
4,4.3 Development and Purpose of the Site Conceptual Model 13
4.4,4 Evaluation of Restoration Potential . .13
4.4.4.1 Source Control Measures 13
4.4.4.2 Remedial Action Performance Appraisal 16
4.4.4.3 Restoration Timeframe Analysis 16
4.4.4.4 Other Applicable Technologies 18
4.4.4.5 Additional Considerations , ..18
4.4.5 Cost Estimate ..„.. 19
5,0 Alternative Remedial Strategies., „.......„. 19
5.1 Options and Objectives for Alternative Strategies 19
5.1.1 Exposure Control .19
5,1.2 Source Control , , ,,19
5.1.3 Aqueous Plume Remediation .,..,......,„...,....,....,.„...,....,.„ .............20
5.2 Alternative Remedy Selection .......21
5.2.1 Superfund 21
5.2.2 RCRA 21
5,2.3 Additional Remedy Selection Considerations .,....,. , ..22
5.2.4 Relation to Alternate Concentration Limits ..,.,..„.„„..„ 22
6,0 Administrative Issues 23
6.1 TI Review and Decision Process...... 23
6.1,1 Superfund .......23
6.1.2 RC1A ..24
6.1.3 Technical Review and Support , 25
6.2 Duration of TI Decisions , 25
7.0 References •. 26
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1.0 Introduction
1,1 Background
Restoration1 of contaminated ground waters is one of
the primary objectives of both the Superfund and
RCRA Corrective Action programs. Ground-water
contamination problems are pervasive hi both pro-
grams; over 85 percent of Superfund National Priori-
ties List (NPL) sites and a substantial portion of
RCRA facilities have some degree of ground-water
contamination. The Superfund and RCRA Corrective
Action programs share the common purposes of pro-
tecting human health and the environment from con-
taminated ground waters and restoring those waters
to a quality consistent with their current, or reason-
ably expected future, uses.
The National Contingency Plan (NCP), which pro-
vides the regulatory framework for the Superfund
program, states that*
"EPA expects to return usable ground waters to
their beneficial uses wherever practicable,
within a time frame that is reasonable given the
particular circumstances of the site"
(NCP
Generally, restoration cleanup levels in the Superfund
program are established by applicable or relevant and
appropriate requirements (ARARs), such as the use of
Federal or State standards for drinking water quality.
Cleanup levels protective of human health and the en-
vironment are identified by EPA where no ARARs for
particular contaminants exist (see Section 4.1.1).
The RCRA Corrective Action program for releases
from solid waste management facilities (see 40 CFR
264.101)2 requires a facility owner/operalor to:
"...institute corrective action as necessary to pro-
tect human health and the environment for all
releases of hazardous waste or constituents from
any solid waste management unit..."
The goal of proteetiveness is further clarified in the
Preamble to ihe Proposed Subpart S to 40 CFR 264:
"Potentially drinkable ground water would be
cleaned up to levels safe for drinking throughout
the contaminated plume, regardless of whether the
water was in fact being consumed... Alternative
levels protective of the environment and safe for
other uses could be established for ground water
that is not an actual or reasonably expected source
of drinking water."3
While both programs have had a great deal of success
reducing the immediate threats posed by contami-
nated ground waters, experience over the past decade
has shown that restoration to drinking water quality
(or more stringent levels where required) may not al-
ways be achievable due to the limitations of available
remediation technologies (EPA 1989b, 1992d). EPA,
therefore, must evaluate whether ground-water resto-
ration at Superfund and RCRA ground-water cleanup
sites is attainable from an engineering perspective.
This document outlines EPA's approach to evalu-
ating the technical impracticability of attaining re-
quired ground-water cleanup levels and establish-
ing alternative, protective remedial strategies
where restoration is deter mined to be technically
impracticable.
Many factors can inhibit ground-water restoration.
These factors may be grouped under three general
categories;
• Hydrogeologic factors;
• Contaminant-related factors; and
« Remediation system design inadequacies.
Hydrogeologic limitations to aquifer remediation in-
clude conditions such as complex sedimentary depos-
its; aquifers of very low permeability; certain types of
1 For this guidance, "restoration" refers to the reduction of contaminant concentrations to levels required under the Superfund
or RCRA Corrective Action programs. For ground water currently or potentially used for drinking water purposes, these lev-
els may be Maximum Contaminant Levels (MCLs) or non-zero Maximum Contaminant Levels Goals (MCLGs) established
under the Safe Drinking Water Act; State MCLs or other cleanup requirements; or risk-baaed levels for compounds not cov-
ered by specific State or Federal MCLs or MCLGs. Other cleanup levels may be appropriate for" pound waters used for non-
drinking water purposes.
2 At this time, this guidance is not applicable to corrective actions for releases from Snbpart F regulated units (hat are subject to
corrective actions under 40 CM 264 J1 -264.100.
3 "Corrective Acton for Solid Waste Management Units (SWMUs) at Hazardous Waste Management Facilities," 55 Fjl 30798-
30884, My 27,1990, Proposed Rnles, is currently used as guidance in the RCRA Corrective Action program. When final
regulations under Subpart S are promulgated, certain aspects of this guidance pertaining to the RCRA program may need to be
revised to reflect new regulatory requirements.
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characterization should be designed to provide infor-
mation necessary for the next phase of characteriza-
tion. Likewise, site remediation activities can be con-
ducted in phases to achieve interim goals at the out-
set, white developing a more accurate understanding
of the restoration potential of the contaminated aqui-
fer. An example of how fliis approach might be ap-
plied at a site is provided below in Section 4.4,3,
The timing of phased cleanup actions (early, interim,
final) should reflect the relative urgency of the action
and the degree to which the site has been character-
ized. Early actions should focus on reducing the risk
posed by site contamination (e.g., removal of con-
tamination sources) and may be carried out before de-
tailed site characterization studies have been com-
pleted. Interim remedial actions may abate the
spread of contamination or limit exposure but do not
fully address the final cleanup levels for the site. In-
terim actions generaly will require a greater degree
of site characterization than early actions. However,
implementation of interim actions still may be appro-
priate prior to completion of site characterization
studies, such as the Remedial Investigation/Feasibil-
ity Study (Rl/FS) or RCRA Facility Investigation
(RFI) and Corrective Measures Study (CMS), Final
remedial actions must address the cleanup levels and
other remediation requirements for the site and, there-
fore, must be based on completed characterization re-
pods. Information from early and interim actions
also should be factored into these reports and final
remedy decisions.
Phasing of activities generally should not delay or
prolong site characterization or remediation. In fact,
such an approach may accelerate the implementation
of interim risk reduction actions and lead more
quickly to the development of achievable final reme-
diation levels and strategies, A phased approach
should be considered when there is uncertainty re-
garding the ultimate restoration potential of the site
but also a need to quickly control risk of exposure to,
or limit further migration of, the contamination.
It is critical that the performance of phased remedial
actions (e.g., control of plume migration) be monitored
carefully as part of the ongoing effort to characterize
the site and assess its restoration potential. Data collec-
tion activities during such actions not only should be
designed to evaluate performance with respect to the
action's specific objectives but also contribute to the
overall understanding of the site. In this manner,
actions implemented early in the site remediation
process can achieve significant risk reduction and
lead to development of technically sound, final rem-
edy decisions,
2.2 Documenting Ground-Water Remedy
Decisions Under CERCLA
The phased approach to site characterization and
remediation can be employed using the existing deci-
sion document options within the Superfund program.
2,2,1 Removal Actions
Removal authority can be used for early actions as
part of a phased approach to ground-water cleanup
and decision making and should be considered
where early response to ground-water contamination
is advantageous or necessary. Within the context of
ground-water actions, removals are appropriate
where contamination poses an actual or potential
threat to drinking water supplies or threatens sensi-
tive ecosystems. Examples of actions that might
qualify for use of removal authority include removal
of surface sources (e.g., drums or highly contami-
nated soils), removal of subsurface sources (e.g.,
NAPL accumulations, highly contaminated soils, or
other buried waste), and containment of migrating
ground-water contamination "hot spots" (zones of
high contaminant concentration) or plumes to protect
current or potential drinking water supplies.
Removals of subsurface sources most likely will be
non-time-critical actions, although time-critical ac-
tions may be appropriate for removal of NAPL ac-
cumulations or other sources, depending on the ur-
gency of the threat Documentation requirements
for removal actions include a Removal Action
Memorandum and, for non-time critical actions, an
Engineering Evaluation/Cost Analysis report.4
Removal actions must attain ARARs to the extent
practicable, considering the exigencies of the
situation, "flie urgency of the situation and the scope
of the removal action may be considered when
determining the practicability of attaining ARARs
(NCP §300.415®), Stendards or regulations typically
used to establish ground-water cleanup levels for final
actions (e.g., MCLs/MCLGs) may not be ARARs,
depending on the scope of the removal. Further
See "Guidance on Conducting Nan-Time Critical Removal Actions under CERCLA," OSWBR Publication 9360.0-32,
August 1993 (EPA 1993b).
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infomiition on removal actions may be found in
other EPA guidances (EPA I990b, 1991d).
2 3.2 interim RODs
Interim RODs may be appropriate where there is a
moderate to high degree of uncertainty regarding at-
tainment of ARARs or other protective cleanup lev-
els. As mentioned before, an interim action may be
used to minimize further contaminant migration and
reduce the risk of exposure to contaminated ground
water. Interim actions include containment of the
leading edge of a plume to prevent further contami-
nation of unaffected portions of an aquifer, removal
of source material, remediation of ground-water hot
spots, and in some cases, installation of physical
barriers or caps to contain releases from source ma-
terials. Interim actions should be monitored care-
fully to collect detailed information regarding aqui-
fer response to remediation, which should be used to
augment and update previous site characterization
efforts. This information then can be used at a later
date to develop final remediation goals and cleanup
levels that more accurately reflect the particular con-
ditions of the site,
It is important to note that for interim actions,
ARARs must be attained only if they are within the
scope of that action. For example, where an interim
action will manage or contain migration of an aque-
ous contaminant plume, MCLs and MCLOs would
not be ARARs, since the objective of the action is
containment, not cleanup (although requirements
such as those related to discharge of the treated water
still would be ARARs, since they address the disposi-
tion of treated waste).
Furthermore, a requirement that is an ARAR for an
interim action may be waived under certain circum-
stances. An "interim action" ARAR waiver may be
invoked where an interim action that does not attain
an ARAR is part of, or will be followed by, a final
action that does (NCP §300.430{f)(l)(ii){C)). For ex-
ample, where an interim action seeks to reduce con-
tamination levels in a ground-water hot spot, MCLs/
MCLGs may be ARARs since the action is cleaning
up a portion of the contaminated ground water. If,
however, this interim action is expected to be fol-
lowed by a final, ARAR-compliant action that ad-
dresses the entire contaminated ground-water zone,
an interim action ARAR waiver may be invoked.
5 At sites where a IT ARAR waiver is invoked in the ROD, preparation of the pre-refenral negotiation package ("mini-lit" pack-
age) must include analysis of the model Consent Degree language to ensure that appropriate consideration of the waiver's im-
pact is incorporated.
233 Final RODs
Where site characterization is very thorough and
there is a moderate to high degree of certainty that
cleanup levels can be achieved, a final decision docu-
ment should be developed that adopts those levels.
Conversely, in cases where there is a high degree of
certainly that cleanup levels cannot be achieved, a final
ROD that invokes a Tl ARAR waiver and establishes
an alternative remedial strategy may be the most appro-
priate option,5 Note that for ROD-stage waivers, site
characterization generally should be sufficiently de-
tailed to address the data and analysis requirements for
Tl determinations set forth in this guidance,
2,2.4 ROD Contingency Remedies and
Contingency Language
Where a moderate degree of uncertainty exists re-
garding the ability to achieve cleanup levels, a final
ARAR-compliant ROD generally still is appropriate.
However, the ROD may include contingency lan-
guage that addresses actions to be taken m the event
the selected remedy is unable to achieve the required
cleanup levels (EPA 1990a, 1991a). The contingency
language may include requirements to enhance or
augment the planned remediation system as well as
an alternative remedial technology to be employed if
modifications to the planned system fail to signifi-
cantly improve its performance. Use of language in
final remedy decision documents that addresses the
uncertainty in achieving required cleanup levels also
is appropriate in certain cases. However, language
that identifies a TI decision (e,g., an ARAR
waiver) as a future contingency of the remedy
should be avoided. Such language is not necessary,
as a TI evaluation may be performed (and a decision
made) by EPA at any site regardless of whether such
a contingency is provided to the decision document.
Note that in cases of existing RODs that already
include a contingency for invoking a TI ARAR
waiver, the conditions under which the ARAR
may he waived should be consistent with, and as
stringent as, those presented in this guidance or a
future update.
Furthermore, the fact that such contingency lan-
guage has been included in an existing ROD does
not alter the need to enhance or augment a rem-
edy to improve its ability to attain ARARs before
concluding that a waiver can be granted. It also
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should be noted that remediation must be conducted
for a sufficient period of time before its ability to re-
store contaminated ground water can be evaluated.
This minimum time period will be determined by
EPA on a site-specific basis,
2.3 Documenting Ground-Water Remedy
Decisions under RCRA
The instruments used for implementing the RCRA
Corrective Action program (permits and orders) also
are amenable to a phased approach to remedy selec-
tion and facility remediation. The RCRA program
can uie permits or orders to compel both interim
measures and final remedies.
2.3,1, Permits!Orders Addressing Stabilization
RCRA permits or orders can require the stabilization
of releases from solid waste management units
(SWMUi) at the facility. The Stabilization Initiative
focuses on taking Interim actions to pevent the fur-
ther spread of existing contamination and reduce
risks. Examples of measures used for stabilization
include capping, excavation, and plume containment.
Since the long-term or final cleanup of the facility is
not the objective of stabilization (although stabiliza-
tion should be consistent with the final remedy), TI
decisions are not applicable at this early stage. Infor-
mation gained during stabilization should be used to
help determine the restoration potential of the facility
and the objectives of the final remedy.
232. Permits/Orders Addressing Final Rem&Mes
Where achieving ground-water cleanup standards is
determined by EPA to be technically impracticable,
the permit or order addressing final remedies should
include practicable and protective alternative reme-
dial measures, EPA's decision to make a TI determi-
nation will be based on clear and convincing infor-
mation provided by the owner/operator. EPA gener-
ally will seek public comment on TI determinations
prior to implementation. EPA's preliminary TJ deter-
minations and justification for these determinations
should be documented in a Statement of Basis. As
discussed above, uncertainty in the ability to restore
an aquifer should be reduced through phased charac-
terization and the use of interim remedial measures,
where appropriate.
Peimits and orders that address "final" remedies should
specify Ihe remediation cleanup levels selected by the
implementing Agency. Such permits and orders, how-
ever, generally should not incorporate contingency TI
language. The permit or order will need to be modified
to document the TI determination and to specify, as
appropriate, alternative cleanup levels and alternative
remedial measures that have been determined to be
technically practicable and protective of human health
and the environment,
3.0 Remedial Strategy for
DNAPL Sites
Many of the subsurface contaminants present at Su-
perfond sites and RCRA facilities are organic com-
pounds that are either lighter-than-water NAPLs
(LNAPLs) or DNAPLs. As mentioned in Section 1.1,
the presence of NAPL contamination, and in particu-
lar DNAPL contamination, may have a significant
impact on site investigations and the ability to restore
contaminated portions of the subsurface to required
cleanup levels. Furthermore, DNAPL contamination
may be a relatively widespread problem. A recent
EPA study (EPA 1993a) concluded that up to 60 per-
cent of National Priorities List (NPL) sites may have
DNAPL contamination in the subsurface; a signifi-
cant percentage of RCRA Corrective Action facilities
also are thought to be affected by DNAPLs, As
proven technologies for the removal of certain types
of DNAPL contamination do not exist yet, DNAPL
sites are more likely to require TI evaluations than
sites with other types of contamination. Although
this guidance pertains to TI evaluations at all site
types, EPA believes the significance of the DNAPL
contamination problem warrants the following brief
discussion of DNAPL contamination and recom-
mended site management strategies,
DNAPLs comprise a broad class of compounds, in-
cluding creosote and coal tars, polychlorinated biphe-
nyls (PCBs), certain pesticides, and chlorinated or-
ganic solvents such as uichloroethylene (TCE) and
tetrachloroethylene (PCE), The term "DNAPL" re-
fers only to liquids immiscible in, and denser than,
water and not to chemicals that are dissolved in water
that originally may have been derived from a DNAPL
source. DNAPLs may occur as "free-phase" or "re-
sidual" contamination. Free-phase DNAPL is an im-
miscible liquid in the subsurface that is under positive
pressure; that is, the DNAPL is capable of flowing
into a well or migrating laterally or vertically through
an aquifer. Where vertically migrating free-phase
DNAPL encounters a rock or soil layer of relatively
low permeability (e.g., clay or other fine-grained layer),
a DNAPL accumulation or "pool" may form. Residual
DNAPL is immiscible liquid held by capillary forces
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wilhin the pores or fractures in soil or rock layers;
residual DNAPL, therefore, generally is not capable
of migrating or being displaced by normal ground-
water flow, Bolh free-phase and residual DNAPL,
however, can slowly dissolve in ground water and
produce "plumes" of aqueous-phase contamination.
DNAPLs also can produce subsurface vapors capable
of migrating through the unsaturaled zone and con-
taminating ground water (EPA 1992e). Figure 2 de-
picts the various types of contamination ihat may be
encountered at a DNAPL site,
The three areas ihat should be delineated at a
DNAPL site are the DNAPL entry location, the
DNAPL zone, and the aqueous contaminant plume.
The entry locations are those areas where DNAPL
was released and likely is present in the subsurface,
Entry locations include waste disposal lagoons, drum
burial sites, or any other area where DNAPL was al-
lowed to infiltrate into the subsurface. The DNAPL
zone is defined by that portion of the subsurface con-
taining free-phase or residual DNAPL. Thus, the
DNAPL zone includes all portions of the subsurface
where the immiscible-phase contamination has come
to be located. The DNAPL zone may occur wilhin
both the saturated zone (below the water table) and
the unsaturaled zone (above the water table). The
DNAPL zone also may contain vapor and aqueous-
phase contamination derived from the DNAPL. The
DNAPL zone may include areas at relatively great
depths and lateral distances from the entry locations,
depending on the subsurface geology and the volume
of DNAPL released. The aqueous contaminant
plume contains organic chemicals in the dissolved
phase. The plume originates from the DNAPL zone
and may extend hundreds or thousands of feet
downgradient (in the direction of ground-water flow).
Figure 3 illustrates the various components of &
DNAPL site.
Since each DNAPL site component may require a
different remediation strategy, it is important to char-
acterize these components to the extent practicable.
Thus, the properties and behavior of DNAPL con-
tamination require consideration when planning and
conducting both site investigation and remediation.
The potential for DNAPL occurrence at the site
should be evaluated as early as possible in the site in-
vestigation. Recent publications such as "Estimating
Potential for DNAPL Occurrence at Superfund Sites"
(EPA 1992c) and "DNAPL Site Evaluation" (Cohen
and Mercer, 1993) provide detailed guidance on
these topics. At sites where DNAPL disposal is
known or suspected to have occurred, likely DNAPL
entry locations should be identified from available
historical waste-management information and sub-
surface chemistry date. This information can assist
in the delineation of the DNAPL zone.
Characterization and delineation of the DNAPL zone
is critical for remedy design and evaluation of the
restoration potential of the site. At many sites, a sub-
surface investigation strategy that begins outside of
the suspected DNAPL zone may be appropriate
("outside-in" strategy), in part to minimize the possi-
bility of inadvertent mobilization of DNAPLs to
Figure 2. Types of Contamination and Contaminant Zones at
DNAPL Sites (Cross-sectional view)
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Figure 3. Components of DNAPL sites
DNAPL Z0IM
contains free-phase DNAPL in pools
or ienaes mnHor residual DNAPL DNAPL Errtty Location
sudn as a termer waste pond
Ground-Water Flow
lower aquifers. Delineation of the extent of the
DNAPL zone may be difficult at certain sites due to
complex geology or waste disposal practices. In such
cases, the extent of the DNAPL zone may need to be
inferred from geologic information (e.g., thickness,
extent, structure, and permeability of soil or rock
units) or from interpretation of the aqueous concen-
tration of contaminants derived from DNAPL
sources. At some sites, however, geologic complex-
ity and inadequate information on waste disposal may
make the delineation of the DNAPL zone difficult.
A phased approach, as discussed in Section 2.1, is
recommended for DNAPL sites; such an approach
may facilitate identification of appropriate short- and
long-term site remediation objectives. Note also that
technical approaches appropriate for the DNAPL
lone (e.g., free-phase DNAPL removal, vapor extrac-
tion, excavation, and slurry walls aided by limited
pump-and-treat) may differ significantly from those
appropriate for the aqueous contaminant plume (typi-
cally pump-and-treat).
Short-term remediation objectives generally should
include prevention of exposure to contaminated
ground water and containment of the aqueous con-
taminant plume. Where sufficient information is
available, early removal of DNAPL sources also is
recommended. Information gathered during these
actions should be used to help characterize the site and
identify practicable options for further remediation.
The long-term remediation objectives for a DNAPL
zone should be to remove the free-phase, residual,
and vapor phase DNAPL to the extent practicable and
contain DNAPL sources that cannot be removed.
EPA recognizes that it may be difficult ID locate and
remove all of the subsurface DNAPL within a
DNAPL zone. Removal of DNAPL mass should be
pursued wherever practicable and, in general, where
significant reduction of current or future risk will re-
sult,6 Where it is technically impracticable to remove
subsurface DNAPLs, EPA expects to contain the
DNAPL zone to minimize further release of contami-
nants to the surrounding ground water, wherever
practicable.7
Where it is technically practicable to contain the
long-term sources of contamination, such as the
DNAPL zone, EPA expects to restore the aqueous
contaminant plume outside the DNAPL zone to re-
quired cleanup levels. Effective containment of the
DNAPL zone generally will be required to achieve
this long-term objective because ground-water ex-
traction remedies (e.g., pump-and-treat) or in situ
treatment technologies are effective for plume resto-
ration only where source areas have been contained
or removed.
6 DNAPL mass removal ata> must satisfy the Swperfund or RCRA Corrective Action remedy selection criteria, as appropriate.
7 As DNAPLs may be lemobttized during drilling or ground-water pumping, caution should be exercised where such activities
are proposed for DNAPL zone characterization, remediation, or containment.
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Monitoring and assessing the performance of
DNAPL zone containment and aquifer restoration
systems, iheiefore, are critical to maintaining remedy
protectiveness and evaluating the need for remedy
enhancements or application of new technologies,
EPA recognizes, however, that there are technical
limitations to ground-water remediation technologies
unrelated to the presence of a DNAPL source zone.
These limitations, which include contaminant-related
factors (e.g., slow desorpbon of contaminants from
aquifer materials) and hydrogeologic factors (e.g.,
heterogeneity of soil or rock properties), should be
considered when evaluating the technical practicabil-
ity of restoring the aqueous plume.
EPA encourages consideration of innovative technolo-
gies at DNAPL sites, particularly where containment
of a DNAPL lone may require costly periodic mainte-
nance (and perhaps replacement). Innovative technolo-
gies, therefore, should be considered where DNAPL
zone containment could be enhanced or where such a
technology could clean up the DNAPL lone,
4.0 TI Decisions and Supporting
Information
4.1 Regulatory Framework for Ti Decisions
The bases for 11 decisions discussed in this guidance
are provided in CERCLA and the NCP for the Super-
fond program and in the Proposed Subpart S rule for
the RCRA program, White the processes the two pro-
grams use to establish cleanup levels differ (e.g., the
ARAR concept is not used in RCRA), the primary con-
siderations for determining the technical impracticabil-
ity of achieving those levels are identical:
* Engineering feasibility; and
* Reliability.
A brief summary of the regulatory basis for establish-
ing cleanup levels and making TI determinations at
Superfund and RCRA sites is provided below.
4J.1 Superfund
Remedial alternatives at Superfund sites must satisfy
two "threshold" criteria specified in the NCP to be
eligible for selection: 1) the remedy must be protec-
tive of human health and the environment; and 2) the
remedy must meet (or provide the basis for waiving)
the ARARs identified for the action,8 There generally
are several different types of ARARs associated widi
ground-water remedies at Superfund sites, such as re-
quirements for discharge of treated water to surface
water bodies or other receptors, limitations on rein-
jeetion of treated water into the subsurface, and
cleanup levels for contaminants in the ground water,
ARARs used to establish cleanup levels for current or
potentially drinkable ground water typically are
MCLs or non-zero MCLOs established under the
Federal Safe Drinking Water Act, or in some cases,
more stringent State requirements. For compounds
for which there are no ARARs, cleanup levels gener-
ally are chosen to protect users or receptors from un-
acceptable cancer and non-cancer health risks or ad-
verse environmental effects. Such levels generally
are established to fall within the range of 104 to 10*
lifetime cancer risk or below a hazard index of one
for non-carcinogens, as appropriate.
ARARs may be waived by EPA for any of the six
reasons specified by CERCLA and the NCP (High-
light 1), including technical impracticability from
an engineering perspective. TI waivers generally
will be applicable only for ARARs thit aie used to
establish cleanup performance standards or levels,
such as chemical-specific MCLs or Stale ground-wa-
ter quality criteria.
Highlight 1.
CERCLA ARAR Waivers
The six ARAR waivers provided by CERCLA
§121(d)(4)are:
1. Interim Action Waiver;
2, Equivalent Standard of Performance Waiver,
3. Greater Risk to Health and the Environment
Waiver;
4. Technical Impracticability Waiver;
5, Inconsistent Application of S tate Standard
Waiver; and
6. Fund Balancing Waiver.
8 NCP §300.430(f)(l)(l). For a detailed discussion of the Superfund remedy selection process, see also EPA 1988a .and 198Sb.
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Use of the term "engineering perspective" implies lhat
a TI determination should primarily focus on the tech-
nical capability of achieving the cleanup level, with
cost pkying a subordinate role. The NCP Preamble
states that Tl determinations should be based on:
"...engineering feasibility and reliability, with
cost generally not a major factor unless compli-
ance would be inordinately costly."9
4J.2 RCRA
The Proposed Subpart S rule specifies that the correc-
tive action for contaminated ground water include at-
tainment of "media cleanup standards," which gener-
ally are Federal or State MCLs, contaminant levels
within the range of 10"* to W* lifetime cancer risk, or
hazard index of less than one for non-carcinogens, as
appropriate. The proposed rule also specifies three
conditions under which attainment of media cleanup
standards may not be required: 1) remediation of the re-
lease would provide no significant reduction in risks to
actual or potential receptors; 2) the release does not oc-
cur in, or threaten, ground waters that are current or po-
tential sources of drinking water, and 3) remediation
of the release to media cleanup standards is tech-
nically impracticable.10
Further clarification of TI determinations is provided
in the preamble to the proposed rule. The determina-
tion involves a consideration of the "engineering
feasibility and reliability" of attaining media
cleanup standards, as well as situations where reme-
diation may be "technically possible," but the "scale
of the operations required might be of such a magni-
tude and complexity that the alternative would be
impracticable" (emphasis added}.11
The basis for a RCRA Subpart S TI decision (engineer-
ing feasibility, reliability, and the magnitude and com-
plexity of the action) therefore is consistent with that
provided for the Superfund program in the NCP, In the
context of remedy selection, both programs consider
the notion of technical feasibility along with reliability
and economic considerations; however, the rote of cost
(or scale) of the action is subordinate to tbe goal of
remedy protectiveness,
4.2 Timing of Tl Decisions
TI decisions may be made either when a final site
decision document is being developed (e.g., RCRA
Statement of Basis and Response to Comments or
Superfund ROD) or after the remedy has been
implemented and monitored for a period of time.
EPA believes that, in many cases, TI decisions should
be made only ate interim or full-scale aquifer
remediation systems are implemented because often it
is difficult to predict the effectiveness of remedies
based on limited site characterization data alone.
However, in some cases, TI decisions may be made
prior to remedy implementation. These pre-
implementation or "front-end" TI decisions must be
supported adequately by detailed site characterization
and data analysis. Front-end TJ evaluations should
focus on those data and analyses that define the most
critical limitations to ground-water restoration.
Data and analysis requirements for front-end deci-
sions should be considered carefully. Generally, in-
formation regarding the nature and extent of contami-
nation sources is more critical to assessing restoration
potential than are other types of characterization data
This often is the case, as currently available technolo-
gies generally are more effective for remediating and
restoring eonlaminatied aquifers affected only by dis-
solved, or aqueous, contamination. However, certain
types of source contamination are resistant to extraction
by these technologies and can continue to dissolve
slowly into ground water for indefinite periods of time.
Examples of this type of source constraint include cer-
tain occurrences of NAPLs, such as where the quantity,
distribution, or properties of the NAPL render its re-
moval from, or destruction within, the subsurface infea-
sible or inordinately costly (See Section 3.0).
Geologic constraints, such as aquifer heterogeneity
(e.g., interlayering of coarse and fine-grained strata),
also may critically limit the ability to restore an aquifer.
However, it generally is more difficult to accurately de-
termine the impact of such constraints prior to imple-
mentation and monitoring of partial or full-scale aqui-
fer remediation efforts. Some geologic constraints,
however, may be defined sufficiently during site
characterization so that their impacts on restoration
potential are known with a relatively high degree of
certainty. An example of this type of constraint in-
cludes complex fracturing of bedrock aquifers,
which makes recovery of contaminated ground wa-
ter or DNAPLs extremely difficult.
It should be noted, however, thit the presence of
known remediation constraints, such as DNAPL,
9 See NCP Preamble, 55 JRR. 8748, March 8,1990.
10 Technical impracticability is discussed in Sections 264,52S(d)(2) and 264.531 of ihe Proposed SubpaitS rule.
11 Proposed Subpart S; 55 FR 30830, July 27,1990.
10
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fractured bedrock, or other condition, are not by
themselves sufficient to justify a TI determination.
Adequate site characterization data must be presented
to demonstrate, not only that the constraint exists, but
that the effect of the constraint on contaminant distri-
bution and recovery potential poses a critical limita-
tion to the effectiveness of available technologies,
4.3 TI Evaluation Components12
Determinations of technical impracticability will be
made by EPA based on site-specific characterization
and, where appropriate, remedy performance data.
These data should be collected, analyzed, and pre-
sented so that the engineering feasibility and reliabil-
ity of ground-water restoration are fully addressed in
a concise and logical manner.
The TI evaluation may be prepared by the owner/op-
erator of a RCRA facility, by a PRP at an enforce-
ment-lead Superfund site, or by EPA or the State at
Fund- or State-lead sites, as appropriate. The evalu-
ation generally should include the following com-
ponents, based on site-specific information and
analyses:
1. Specific ARARs or media cleanup standards for
which TI determinations are sought (See Section
4.4,1),
2. Spatial area over which the TI decision will apply
(See Section 4.4.2).
3. Conceptual model that describes site geology, hy-
drology, ground-water contamination sources,
transport, and fate (See Section 4,4.3).
4. An evaluation of the restoration potential of the site,
including data and analyses that support any
assertion that attainment of ARARs or media
cleanup standards is technically impracticable from
an engineering perspective (See Section 4,4.4). At a
minimum, this generally should include:
a, A demonstration that contamination sources
have been identified and have been, or will be,
removed and contained to the extent practicable;
b. An analysis of the performance of any ongo-
ing or completed remedial actions;
c. Predictive analyses of the timeftames to attain
required cleanup levels using available tech- >
nologies; and
d, A demonstration that no other remedial tech-
nologies (conventional or innovative) could
reliably, logically, or feasibly attain the
cleanup levels at the site within a reasonable
tuneframe.
5, Estimates of the cost of the existing or pro-
posed remedy options, including construction,
operation, and maintenance costs (See Section
4,4.5).
6. Any additional information or analyses that
EPA deems necessary for the TI evaluation.
The data and analyses needed to address each of
these components of a TI evaluation should be de-
termined on a site-specific basis. Where outside
parties are preparing the TI evaluation, its contents
generally should be identified and discussed prior to
submittal of the evaluation to EPA. Early agreement
between EPA and PRPs or owner/operators on the type
and quantity of data and analyses required for TI deci-
sions will promote efficient review of TI evaluations.
References to other documents in the administrative
record, such as the RI/FS and RFI, likely will be nee-
essary to produce a concise evaluation; however,
these references should be as explicit as possible
(e,g,, cite specific page or table numbers). Technical
discussions and conclusions should be supported by
data compilations, statistical analyses, or other types
of data reduction included in the evaluation,
4.4 Supporting Information for TI Evaluations
Most, if not all, of the information needed to evaluate
TI could be obtained during a thorough site investiga-
tion and, where appropriate, remedy performance
monitoring efforts. At some sites, however, addi-
tional analysis of existing data or new information
may be required before EPA can determine accu-
rately the technical practicability of the restoration
goals. Not all of the data or analyses outlined in this
guidance will be required at all sites; specific infor-
mation needs will depend on site conditions and any
ongoing remediation efforts.
12 For this guidance a "TI evaluation" comprises the data and analyses necessary to make a TI determination. The TI evaluation
may be perfomed by PRPs at enforcement-lead Superfund sites, or by State or other Federal agencies, where appropriate.
Similarly, owner/opgrattas at RCRA facilities may perform TI evaluations. However, the actual TI "deternunaiion," or "deci-
sion," will be made by EPA (or other lead agency, as appropriate).
11
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The data and analyses identified and discussed below
address the Tl evaluation components provided in
Section 4,3.
4,4,1. Specific ARARs or Media Cleanup
Standards
The TI evaluation should identify the specific
ARARs or media cleanup standards (i.e., the specific
contaminants) for which the determination is sought
Such contaminants generally should include only
those for which attainment of the required cleanup
levels Is technically impracticable. Factors EPA
will consider when evaluating contaminants lhat
may be included in the TI decision include; 1) the
technical feasibility of restoring some of the con-
taminants present in the ground water; and 2) the
potential advantages of attaining cleanup levels for
some of the contaminants.
For example, consider a Saperfund site with a DNAPL
contamination problem (e.g,, TCE), including a wide-
spread subsurface DNAPL source area for which con-
tainment or restoration are technically impracticable.
The aqueous plume also contains inorganic contamina-
tion (e,g,, chromium) from on-sile sources. Although it
would be feasible to reduce chromium coneentrationi
to the required cleanup level within a reasonable time-
frame, TCE concentrations would remain above
cleanup levels much longer due to the continued pres-
ence of the DNAPL or slow desorption of TCE from
aquifer materials. However, in such cases, EPA may
choose to limit the TI ARAR waiver to TCE alone,
while requiring cleanup of the chromium.13
Two situations would favor use of this approach.
The first would be where attaining chromium cleanup
levels in the ground water will make future ex situ
treatment of the (TCE-contaminated) pound water
less complex and less expensive. This may be advan-
tageous where a community wishes to extract the
TCE-contarninated water, perform ex situ treatment,
and put the treated water to beneficial use, A related
consideration is whether removal of the chromium
wiD facilitate future subsurface remediation using a
newly developed technology. The second situation
favoring this approach is where one of the contami-
nants (e.g., TCE) is being naturally biodegraded and
the other (e.g., chromium) is not. Therefore, cleanup
of the chromium may result in more rapid attainment
of the long-term cleanup goals at the site.
Where the balance of conditions at such a site do not
indicate that it is practicable to attain the cleanup
levels for only some of the contaminants present,
EPA may conclude that cleanup levels for the re-
maining contaminants need not be attained, depend-
ing on the circumstances of the site. As discussed
further in Section 5.0, however, this decision does
not preclude EPA from selecting (or continuing op-
eration of) a remedy that includes active measures
(e.g., pump-and-treat) along with measures to pre-
vent exposure (e.g., institutional controls) needed to
address site risks.
4.4,2 Spatial Extent of TI Decisions
The TI evaluation should specify the horizontal and
vertical extent of the area for which the TI determina-
tion is sought. Where EPA determines that ground-
water restoration is technically impracticable, the
area over which the decision applies (the "Tl zone")
generally will include all portions of the contami-
nated ground water that do not meet the required
cleanup levels (contaminated ground-water 2one), un-
less the TI zone is otherwise defined by BPA.
In certain cases, EPA may restrict the extent of the
TI zone to a portion or subarea within the contami-
nated ground-water zone. For example, consider a
DNAPL site where it is technically impracticable to
remove the residual DNAPLs from the subsurface
but it is feasible and practicable to: 1) limit further
migration of contaminated ground-water using a
containment system; and 2) reitore that portion of
the aqueous plume outside of the containment area.
The TI zone in this case should be restricted to that
portion of the site that lies within the containment
area. Outside of the Tl zone, ARARs or media
cleanup standards still would apply. The potential
to spatially restrict the TI zone, therefore, will de-
pend on the ability to delineate and contain non-re-
movable subsurface contamination sources and re-
store those portions of the aqueous plume outside of
the containment area. The spatial extent of the TI
zone should be limited to as small an area as pos-
sible, given the circumstances of the site,
A TI zone should be delineated spatially, both in area
and depth. Depth of a TI zone may be defined in ab-
solute terms (e.g., feet above mean sea level) or in
relative terms (e.g., with respect to various aquifers
within multi-aquifer systems), as appropriate. Where
13 The extracted ground water would likely need to be treated for both TCE end chromium to satisfy treatment and waste dis-
posal ARARs.
12
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the TI zone will be restricted to a portion of the con-
taminated ground-water zone, the limits of the TI
zone should be delineated clearly on site maps and
geologic cross-sections. Delineation of the TT zone
based on the location of a particular mapped contami-
nant concentration contour interval (e.g,» the 200 part
per billion isoconcenttation line) generally should be
avoided. This is because the location of such mapped
contours often is highly interpretive, and their posi-
tion may change with lime. While concentration data
may be appropriate to consider when determining the
size of a containment area or the extent of a TI zone,
the limits of that TI zone should be fixed in space,
both horizontally and vertically.
4.4.3 Development and Purpose of the Site
Conceptual Model
Decisions regarding the technical practicability of
ground-water restoration must be based on a thor-
ough characterization of the physical and chemical
aspects of the site. Characterization data should de-
scribe site geology and hydrology; contamination
sources, properties, and distribution; release mecha-
nisms and rates; fate and transport processes; current
or potential receptors; and other elements that define
the contamination problem and facilitate analysis of
site restoration potential. While the elements of such
a model may vary from site to site, some generaliza-
tions can be made about what such a model would
contain. Examples of these elements are provided in
Figure 4. The site conceptual model synthesizes data
acquired from historical research, site characteriza-
tion, and remediation system operation.
The site conceptual model typically is presented as a
summary or specific component of a site investigation
report. The model is based on, and should be sup-
ported by, inierprelive graphics, reduced and analyzed
data, subsurface investigation logs, and other pertinent
characterization information. The site conceptual
model is not a mathematical or computer model, al-
though these may be used to assist in developing and
testing the validity of a conceptual model or evaluating
the restoration potential of the site. The conceptual
model, like any theoiy or hypothesis, is a dynamic tool
that should be tested and refined throughout the life of
the project. As illustrated in Figure 5, the model should
evolve in stages as information is gathered during the
various phases of site remediation. This iterative pro-
cess allows data collection efforts to be designed so
that key model hypotheses may be tested and revised to
reflect new information.
The conceptual model serves as the foundation for
evaluating the restoration potential of the site and,
thereby, technical impracticability as well. The TI
determination must consider how site conditions im-
pact the potential for achieving remediation goals and
whether remediation performance, cost-effectiveness,
and timeframe meet EPA requirements or expecta-
tions. As theee determinations rely on professional
judgment, the clarity of the conceptual model (and
supporting information) is critical to the decision-
making process.
4,4.4 Evaluation of Restoration Potential
4.4.4.1 Source Control Measures, Remediation of
contamination sources is critical to the success of
aquifer restoration efforts. Continued releases of
contamination from source materials to ground water
can peatly reduce the effectiveness of aquifer resto-
ration technologies, such as pump-and-treat, which
generally are effective only for removing dissolved
contaminants (EPA 1989b; 1992d), EPA considers
subsurface NAPLs to be source materials because
they are capable of releasing significant quantities of
dissolved contamination ID ground water over long
periods of time.
A demonstration that pound-water restoration is
technically impracticable generally should be accom-
panied by a demonstration that contamination sources
have been, or will be, identified and removed or
treated to the extent practicable. EPA recognizes that
locating and remediating subsurface sources can be
difficult. For example, locating DNAPLs in certain
complex geologic environments may be impracti-
cable. BPA expects, however, that all reasonable ef-
forts will be made to identify the location of source
areas through historical information searches and site
characterization efforts.
Source removal and remediation may be difficult,
even where source locations are known. The appro-
priate level of effort for source removal and remedia-
tion must be evaluated on a site-specific basis, con-
sidering the degree of risk reduction and any other
potential benefits that would result from such an ac-
tion. Even partial removal of contamination sources
can greatly reduce the long-term reliance on both ac-
tive and passive ground-waler remediation.
Where complete source removal or treatment is im-
practicable, use of migration control or containment
measures should be considered. Physical and hy-
draulic barriers are proven technologies that are ca-
pable of limiting or preventing further contaminant
13
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Figure 4. Elements of Site Conceptual Model
The data and analysis required for TI evaluations will be determined by EPA on a site-specific basis. This infor-
mation should be presented in formats conducive to analysis and in sufficient detail to define the key site condi-
tions and mechanisms that limit restoration potential. Types of information and analysis that may be needed for
conceptual model development are illustrated below.
Background information
Location of water supply wells.
Ground-water Classification.
Nearby wellhead protection areas or sole-source aquifers.
Location of potential environmental receptors.
Geologic and Hydrologlc Information
Description of regional and site geology.
Physical properties of subsurface materials
(e.g., texture, porosity, bulk density).
Stratigraphy, including thickness, lateral extant, contin-
uity of units, and presence of depositions! features,
such as channel deposits, that may provide preferential
pathways for, or barriers to, contaminant transport.
Geologic structures that may form preferential pathways
for NAPL migration or zones of accumulation.
Depth to ground water.
Hydraulic gradients (horizontal and vertical).
Hydraulic properties of subsurface materials (e.g.,
hydraulic conductivity, storage coefficient, effective
porosity) and their directional variability (anisotropy).
Spatial distribution of soil or bedrock physical/hydraulic
properties (degree of heterogeneity).
Characterization of secondary porosity features
(e.g., fractures, karst features) to the extent practicable.
Temporal variability In rtydrologb conditions.
Ground-water recharge and discharge information.
Ground -water/surface water interactions.
Contaminant Source and Release Information
• Location, nature, and history of previous
contaminant releases or sources,
' Locations and characterizations of continuing
refeases or sources.
• Locations of subsurface sources (e.g., NAPLs),
Contaminant Distribution, Transport, and Fate Parameters
Phase distribution of each contaminant (gaseous, aqueous, sorted, free-phase NAPL, or residual NAPL)
in the unsaturated and saturated zones.
Spatial distribution of subsurface contaminants In each phase in the unsaturated and saturated zones.
Estimates of subsurface contaminant mass.
Temporal trends in contaminant concentrations in each phase.
Sorption information, including contaminant retardation factors.
Contaminant transformation processes and rate estimates.
Contaminant migration rates.
Assessment of facilitated transport mechanisms (e.g., colloidal transport).
Properties of NAPLs that affect transport (e.g., composition, effective constituent solubilities, density, viscosity).
Geochemical characteristics of subsurface media that affect contaminant transport and fate.
Other characteristics that effect distribution, transport, and fate {e.g., vapor transport properties).
14
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Figure 5. Evolution of the Site Conceptual Model
Site Background and History
Preliminary Site Investigations
Likely Sources arid
• Receptors identified -
Conceptual Model
Provides Basis for:
Early Action/Removal of
Near-Surface Materials
Site Characterization Studies
(RI/PS.RFI)
Removal of Subsurface Sources
(e.g,, free-phase NAPLs)
V
Conceptual Model
Provides Basis for:
Pilot Studies
Interim Ground-Water Actions
Conceptual Model
Provides Basis for:
* Evaluation of Restoration Potential
(orTI)
• Full-Scale Treatment System
Design and Implementation
• Performance Monitoring and
Evaluations
• Enhancement or Augmentation of
Remediation System, if Required
« Future Evaluation of TI, if
Required (See Figure 6)
Drum and Soil
Removal
Excavation and
Capping of Lagoon
installation of
Subsurface
Monitoring Systems
Pilot
Stu
Interim Action
Hydraulic
Containment
15
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migration from a source area under the right circum-
stances. While these containment measures are not
capable of restoring source areas to required cleanup
levels (i.e., a TI decision may be necessary for the
source area), they may enable restoration of portions
of the aquifer ouiside the containment zone,
4.4.4,2 Remedial Action Performance Analysis.
The suitability and performance of any completed or
ongoing ground-water remedial actions should be
evaluated with respect to the objectives of those ac-
tions. Examples of remedy performance data are pro-
vided in Figure 6". The perfomiince analysis should;
1. Demonstrate that the ground-water monitoring pro-
gram within and outside of the aqueous contaminant
plume is of sufficient quality and detail to fully
evaluate remedial action performance (e,g., to ana-
lyze plume migration or containment and identify
concentration trends within the remediation zone),14
2, Demonstrate that the existing remedy has been ef-
fectively operated and adequately maintained,
3, Describe and evaluate the effectiveness of any
remedy rnodiRcations (whether variations in op-
eration, physical changes, or augmentations to the
system) designed to enhance its performance,
4. Evaluate trends in subsurface contaminant concen-
trations. Consider such factors as whether the aque-
ous plume hai been contained, whether the area! ex-
tent of the plume is being reduced, and the rates of
contaminant concentration decline and contaminant
mass removal. Further considerations include
whether aqueous-phase concentrations rebound
when the system is shut down, whether dilution or
oiher natural attenuation processes are responsible
for observed trends, and whether contaminated soils
on site are contaminating the ground water.
Analysis of aqueous-phase concentration data should
be performed with caution. Contaminant concentra-
tions plotted as a function of time, pore volumes of
flushed fluids, or other appropriate variables may be
useful in evaluating dominant contaminant fate and
transport processes, evaluating remedial system design,
and predicting future remedial system performance.
Sampling methodologies, locations, and strategies,
however, should be analyzed to determine the impact
they may have had on observed concentration trends.
For example, studies of ground-water extraction sys-
tems indicate that some systems show rapid initial
decreases in aquifer concentration, followed by less
dramatic decreases that eventually approach an as-
ymptotic concentration level (EPA 1989b, 1992d).
This "leveling off* effect may represent either a
physical limitation to further remediation (e.g(> con-
taminant diffusion from low permeability units) or an
artifact of the system design or monitoring program.
Professional judgment must be applied carefully
when drawing conclusions concerning restoration po-
tential from this information.
In certain cases, EPA may determine that lack of
progress in achieving the required cleanup levels has
resulted from system design inadequacies, poor sys-
tem operation, or unsuitability of the technology for
site conditions. Such system-related constraints are
not sufficient grounds for determining that ground-
water restoration is technically impracticable. In
such instances, EPA generally will require that the
existing remedy be enhanced, augmented, or replaced
by a different technology. Furthermore, EPA may re-
quire modification or replacement of an existing rem-
edy to ensure protectiveness, regardless of whether or
not attainment of required cleanup levels is techni-
cally impracticable.
4.4.4,3 Restoration Timeframe Analysis. Estimates
of the timeframe required to achieve ground-water
restoration may be considered in TI evaluations.
While restoration timeftames may be an important
consideration in remedy selection, no single
timeframe can be specified during which restoration
must be achieved to be considered technically practi-
cable. However, very long restoration limeframes
(e.g., longer than 100 years) may be indicative of
hydrogeologic or contaminant-related constraints to
remediation. While predictions of restoration
timeframes may be useful in illustrating the effects of
such constrains, EPA will base n decisions on an
overall demonstration of the extent of such physical
constraints at a site, not on restoration timeframe
analyses alone. Such demonstrations should be based
on detailed and accurate site conceptual models that
also can provide the bases for meaningful predictions
of restoration timeframes.
14 Further guidance on design of performance monitoring for remedial actions at ground-water sites is provided in "General
Methods for Remedial Operations Performance Evaluations," EPA Office of Research and Development Publication EPA/
60Q/R-92/002, January 1992 (EPA 1992e).
16
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Figure 6. Remedy Performance Analysis
Remedy design and performance daia requirements should be specific to technologies employed and site conditions.
The categories of requited infoimation normally necessary to evaluate performance are provided below with some
examples of specific daia elements. These data should be reported to EPA in formats conducive to analysis and in-
terpretation. Simple data compilations are insufficient for this purpose.
Remedy Design and Operational Information
Design and as-built construction information,
including locations of extraction or in a'ttu treat-
ment points with respect to the contamination.
Supporting design calculations (e.g., calculation of
well spacing).
Operating information pertinent to remedy (e.g.,
records of the quantity and quality of extracted or
injected fluids).
Percent downtime and other maintenance
problems.
Ground-water
Extraction/Injection
and Performance
Monitoring Systems
Enhancements to Original Remedial Design
Information concerning operational modifications,
such as variations in pumping, injection rates, or
locations.
Rationale, design, and as-built construction
information for system enhancements.
Monitoring data and analyses that illustrate the
effect these modifications have had on system
performance.
Hydraulic
/Containment and
^ Performance
Monitoring Systems
DNAPL
Recovery
System
Source Removal or Control
Source removal information (e.g., results of soil
excavations, removal of lagoon sediments, NAPL
removal activities).
Source control information (e.g., results of NAPL
containment, capping of former waste manage-
ment units).
Performance Monitoring Information
Design and as-built construction information for
performance monitoring systems.
Hydraulic gradients and other information
demonstrating plume containment or changes in
area! extent or volume.
Trends in subsurface contaminant concentrations
determined at several/many appropriate locations
in the subsurface. Trends should be displayed as
a function of time, a function of pore volumes of
flushed fluids, or other appropriate measures.
Information on types and quantities of
contaminant mass removed and removal rates.
17
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A further consideration regarding the usefulness of
restoration timeftame predictions in 11 evaluations is
the uncertainty inherent In such analyses. Restora-
tion timeframea generally are estimated using math-
ematical models that simulate the behavior of subsur-
face hydrologic processes. Models range from those
with relatively limited Input data requirements that
perform basic simulations of ground-water flow only,
to those with extensive data requirements that are ca*
pable of simulating multi-phase flow (e.g,, water,
NAPL, vapor) or other processes such as contaminant
adsorption to, and desorplion from, aquifer materials.
Model input parameters generally are a combination
of values measured during site characterization stud-
ies and values assumed based on scientific literature
or professional judgment. The input parameter selec-
tion process, as well as the simplifying assumptions
of the mathematical model itself, result in uncertainty
of the accuracy of the output. Restoration timeframes
predicted using even the most sophisticated modeling
tools and data, therefore, will have some degree of
uncertainty associated with them.
Restoration timeframe analyses, therefore, generally
are weir suited for comparing two or more remedia-
tion design alternatives to determine the most appro-
priate strategy for a particular site. Where em-
ployed for such purposes, restoration timeframe
analyses should be accompanied by a thorough dis-
cussion of all assumptions, including a list of mea-
sured or assumed parameters and a quantitative
analysis, where appropriate, of the degree of uncer-
tainty in those parameters and in the resulting time-
frame predictions. The uncertainty in the predic-
tions should be factored into the weight they are
given in the remedy decision process.
4,4.4.4 Other Applicable Technologies. TheTI
evaluation should include a demonstration that no
other remedial technologies or strategies would be
capable of achieving ground-water restoration at the
site.15 The type of demonstration required will de-
pend on the circumstances of the site and the state of
ground-water remediation science at the time such an
evaluation is made. In general, EPA expects that
such a demonstration should consist of; 1) a review
of the technical literature to identify candidate tech-
nologies; 2) a screening of the candidate technologies
based on general site conditions to identify poten-
tially applicable technologies; and 3) an analysis, us-
ing site hydrogeologic and chemical dala, of the ca-
pability of any of the applicable technologies to
achieve the required cleanup standards. Analysis of
the potentially applicable technologies generally can
be performed as a "paper study," EPA, however, may
reserve the right to require treatability or pilot testing
demonstrations to determine the actual effectiveness
of a technology at a particular site,
Treatability and pilot testing should be conducted
with rigorous controls and mass balance constraints.
Information required by EPA for evaluation of pilot
tests will be similar to that required for evaluation of
existing remediation systems (e.g., detailed design
and performance data),
4.4.4,5 Additional Considerations, Techniques
used for evaluation of ground-water restoration
potential are still evolving. The results of such
evaluations generally will have some level of
uncertainty associated with them. Interpretation of
the results of restoration potential evaluations,
therefore, will require the use of professional
judgment. The use of mathematical models and
calculations of mass removal rates are two examples of
techniques that require particular caution.
Ground-water Flow and Contaminant Transport/Fate
Modeling. Simulation of subsurface systems through
mathematical modeling can be useful for designing
remediation systems or predicting design perfor-
mance. However, the limitations of predictive mod-
eling must bo considered when evaluating site resto-
ration potential. As discussed in Section 4.4.4,3,
ground-water models are sensitive to initial assump-
tions and the choice of parameters, such as contami-
nant source locations, leachability, and hydraulic con-
ductivity. Predictions such as the magnitude and dis-
tribution of subsurface contaminant concentrations,
therefore, will involve uncertainty. The source and
degree of this uncertainty should be described, quanti-
fied, and evaluated wherever possible so the reviewer
understands the level of confidence that should be
placed in the predicted concentration values or other
outputs. Predictive modeling may be most valuable in
providing insight into processes that dominate contami-
nant transport and fate at the site and evaluating the
relative effectiveness of different remedial alternatives.
Further guidance and information on the use of
ground-water models is provided in Anderson and
Woessner (1992), EPA (19921), and EPA (1992g),
Contaminant Mass Removal Estimates. Evaluation of
contaminant mass removal may be useful at some sites
15 See discussions in (he NCP (55 ER 8748, March 8,1990} and Subpart S (55 £& 30838, July 27,1990).
18
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with existing remediation systems. These measures
may include evaluation of mass removal rates,
comparison of removal rates to in situ mass esti-
mates, changes in the size of the contaminated area,
comparison of mass removal rates with pumping rates,
and comparison of such measures with associated
costs. Mass removal and balance estimates should be
used with caution, as there often is a high degree of
uncertainty associated with estimates of the initial mass
released and the mass remaining in situ. This uncer-
tainty results from inaccuracy of historical site waste-
management records, subsurface heterogeneities, and
the difficulty in delineating the severity and extent of
subsurface contamination,
4,4*5 Cost Estimate
Estimates of the cost of remedy alternatives should
be provided in the TI evaluation. The estimates
should include the present worth of construction, op-
eration, and maintenance costs. Estimates should be
provided for the continued operation of the existing
remedy (if the evaluation is conducted following
implementation of the remedy) or for any proposed
alternative remedial strategies.
As discussed in Section 4.4.1, a Superfund remedy
alternative may be determined to be technically im-
practicable if the cost of attaining ARARs would be
inordinately high. The role of cost, however, is sub-
ordinate to that of ensuring protectiveness. The point
at which the cost of ARAR compliance becomes in-
ordinate must be determined based on the particular
circumstances of the site. As with long restoration
timeframes, relatively high restoration costs may be
appropriate in certain cases, depending on the nature
of the contamination problem and considerations
such as the current and likely future use of the ground
water. Compliance with ARARs is not subject to a
cost-benefit analysis, however.16
5.0 Alternative Remedial Strategies
5,1 Options and Objectives for Alternative
Strategies17
EPA's goal of restoring contaminated ground water
within a reasonable timeframe at Superfund or RCRA
16 A Fund-Balancing ARAR waiver may be invoked at Fund-lead Superfund sites where meeting an ARAR would entail such
cost in relation to the added degree of protection or reduction of risk that remedial actions at other sites would be jeopardized
(BPA1989c).
17 These recommendations we consistent with those made in Section 3.0 concerning DNAPL sites, but are applicable for any
site where restoration is technically impracticable,
18 PRPs or owner/operators may propose and analyze alternative remedid strategies. However, only EPA (or designated lead
agency, where appropriate) has remedy selection authority.
sites will be modified where complete restoration is
found to be technically impracticable. In such cases,
EPA will select an alternative remedial strategy that
is technically practicable, protective of human heallh
and the environment, and satisfies the statutory and
regulatory requirements of the Superfund or RCRA
programs, as appropriate.1*
Where a TI decision is made at the "front end" of the
site remediation process (before a final remedy has
been identified and implemented), the alternative
strategy should be incorporated into a final remedy
decision document, such as a Superfund ROD or
RCRA permit or enforcement order. Where the TI
decision is made after the final decision document
has been signed (i.e., after a remedy has been imple-
mented and its performance evaluated), the alterna-
tive remedial strategy should be incorporated in a
modified final remedy decision document, such as a
ROD amendment or RCRA permil/order modifica-
tion (see Section 6.0).
Alternative remedial strategies typically will address
three types of problems at contaminated pound-wa-
ter sites: prevention of exposure to contaminated
ground water; remediation of contamination sources;
and remediation of aqueous contaminant plumes.
Recommended objectives and options for addressing
these three problems are discussed below. Note that
combinations of two or more options may be appro-
priate at any given site, depending on the size and
complexity of the contamination problem or other
site circumstances.
5.1.1 Exposure Control
Since the primary objective of any remedial strategy
is overall proiectiveness, exposure prevention may
play a significant role in an alternative remedial strat-
egy. Exposure control may be provided using institu-
tional controls, such as deed notifications and restric-
tions on water-supply well construction and use. The
remedy should provide assurance that these measures
are enforceable and consistent with Stale or local
laws and ordinances.
5,1.2 Source Control
Source remediation and control should be considered
when developing an alternative remedial strategy.
19
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Sources should be located and treated or removed
where feasible and where significant risk reduction will
result, regardless of whether EPA has determined that
ground-water restoration is technically impracticable.
In some cases, however, the mobility to remove or
treat sources will be a major factor in a H decision.
Where sources cannot be completely treated or re-
moved, effective source containment may be critical
to the long-term effectiveness and reliability of an al-
ternative ground-water remedy. Options currently
available for source containment usually involve ei-
ther a physical barrier system (such as a slurry wall)
or a hydraulic containment system (typically apump-
and-treat system) (EPA 1992b).
Applicability and effectiveness of containment sys-
tems are influenced by several hydrogeologic factors,
however, For example, the effectiveness of a slurry
wall generally depends on whether a continuous, low
permeability layer exists at a relatively shallow depth
beneath the site.
Source containment has several benefits. First,
source containment will contribute to the long-term
management of contaminant migration by limiting
the further contamination of ground water and spread
of potentially mobile sources, such as NAPLs. Sec-
ond, effective source containment may permit resto-
ration of that portion of the aqueous plume that lies
outside of the containment area. Third, effective
containment may facilitate the future use of new
source removal technologies, as some of these tech-
nologies (e.g., surfactants, steam injection, radio fre-
quency heating) may Increase the mobility of residual
and tree-phase NAPLs, RemQbflizatiQn of NAPLs,
particularly DNAPLs, often presents a significant risk
unless the source area can be reliably contained.
J./.3 Aqueous Plume Remediation
Remediation of the aqueous plume is the third major
technical concern of an alternative remedial strategy.
Where the technical constraints to restoration include
the inability to remove contamination sources, the
ability to effectively contain those sources will be
critical to establishing the objectives of plume
remediation. Where sources can be effectively con-
tained, the portion of the aqueous plume outside of
the containment area generally should be restored to
the required cleanup levels.
Inability to contain the sources, or other technical
constraints, may render plume restoration technically
impracticable. There are several options for alterna-
tive remedial strategies in such cases. These include
hydraulic containment of the leading edge of the
aqueous plume, establishing a less-stringent cleanup
level that would be actively sought throughout the
plume (at Superfund sites), and natural attenuation or
natural gradient flushing of the plume.
Containment of the aqueous plume usually requires
the pumping and treating of contaminated ground wa-
ter, but usually involves fewer wells and smaller
quantities of water than does a full plume restoration
effort. Plume containment offers the potential advan-
tages of preventing further spreading of the contami-
nated ground water, thereby limiting the size of the
plume, and preventing the plume from encroaching
on water-supply wells or discharging to ecologically
sensitive areas.
At certain Superfund sites, it may be feasible to re-
store the contaminated plume (outside of arty source
containment area) to a site-specific cleanup level that
is less stringent than that originally identified. EPA
may establish such a level as the cleanup level within
the TI zone, where appropriate. The site-specific
level may consider the targeted risk level for site
cleanup and other factors. Site-specific cleanup lev-
els offer the advantage of providing a clear goal
against which to measure the progress of the alterna-
tive remedial strategy. However, where site-specific
cleanup levels exceed the acceptable risk range for
human or environmental exposure, the remedy gener-
ally must include other measures (e,g., institutional
controls) to ensure protectiveness.
At some Superfund sites, a less-stringent ARAR than
the one determined to be unattainable may have to be
complied with. For example, it may be technically
impracticable to attain the most stringent ARAR at a
site (e.g., a State requirement to restore ground water
to background concentration levels). However, the
next most stringent ARAR (e.g., Federal MCL) for the
same compound may be attainable. In such cases, the
next most stringent ARAR generally must be attained.
In certain situations where restoration is technically
impracticables EPA may choose natural attenuation
as a component of the remedy for the aqueous
plume,19 Natural attenuation generally will result in
19 Technical impracticability of restoration is not a precondition for the use of natural attenuation in a ground-water remedy, however.
20
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attainment of the desired cleanup levels, but may take
longer to meet them lhan active remediation. This
approach is most likely to be appropriate where the
affected ground water is not a current or reasonably
expected future source of drinking water, and ground-
water discharge does not significantly impact surface
water or ecologic resources. Sufficient technical in-
formation and supporting data must be presented to
demonstrate the effectiveness of this strategy, along
with assurances that any institutional controls re-
quired to prevent exposure will be reliable and en-
forceable. Contingencies for additional or more ac-
tive remediation also should be incorporated into the
remedy, to be triggered by specific contaminant con-
centration levels in the site ground-water monitoring
network, or other criteria as appropriate,
5.2 Alternative Remedy Selection
The alternative remedial strategy options discussed
above represent a range of responses for addressing the
various aspects of a ground-water contamination site.
Selection of the options appropriate for a particular site
must not only consider die desired remediation objec-
tives, as discussed above, but also the statutory and
regulatory requirements applicable to the program un-
der which the action is being taken. These require-
ments are discussed briefly below. Further information
and guidance on these requirements can be obtained
from publications referenced hi this section,
52,1. Superfund
The selection of an alternative remedy at a Superfund
site should follow the remedy selection process pro-
vided in NCP §300.430(1). Regardless of whether
ARARs are waived at the site, the alternative remedy
still must satisfy the two threshold remedy selection
criteria (protect human health and the environment
and comply with all ARARs that have not been
waived); be cost effective; and utilize permanent so-
lutions and treatment to the maximum extent practi-
cable. This last finding is satisfied by identifying the
alternative that best balances the trade-offs with re-
spect to the remaining balancing and modifying crite-
ria, taking into account the demonstrated technical
limitations (see Highlight 2),20
Where ground-water ARARs are waived at a Super-
fund site due to technical impracticability, EPA's
general expectations are to prevent further migration
of the contaminated ground-water plume, prevent ex-
posure to the contaminated ground water, and evalu-
ate further risk reduction measures as appropriate,
(NCP §3QO,43Q(a)(lXiii)(F)). These expectations
should be evaluated along with the nine remedy se-
lection criteria to determine ihe most appropriate re-
medial strategy for the site.
Highlight 2,
Superfund Remedy Selection Criteria
Threshold Criteria
• Overall protection of human health and
the environment
« Compliance with (or justification for a waiver
of) ARARs
Balancing Criteria
« Long-term effectiveness and permanence
* Redaction of mobility, toxicity, or volume
» Short-term effectiveness
• Implementability
• Cost
Modifying Criteria
• State acceptance
» Community acceptance
5.2.2 RCRA
At RCRA facilities where pound-water restoration is
technically impracticable, the permit or order sched-
ule of compliance may be modified by establishing;
1) further measures that may be required of the per-
mittee to control exposure to residual contamination,
as necessary to protect human health and the environ-
ment; and 2) alternate levels or measures for cleaning
up contaminated media.21
Criteria for establishing an alternative remedial strat-
egy under RCRA are presented in Highlight 3, In ad-
dition to satisfying the general standards for rem-
edies, the alternative remedial strategy at a RCRA fa-
cility also should provide the best balance of trade-offs
among the five remedy selection decision factors.22
20 For further guidance on the Superfund remedy selection process, see NCP PQQ.430(f) and "Guidance for Conducting Reme-
dial Investigations and Feasibility Studies wider CERCLA," (EPA 1988a).
21 Proposed Subpart S Rule, |264.531(b).
22 Farther guidance on remedy selection at RCRA facilities is provided in the proposed Subpait S Rule (55 PR 30823-30824.
My 27,1990),
21
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Highlights.
RCRA Remedy Standards and
- Selection Factors
General Standard! for Remedies
1. Overall protection of hyman health and the
environment
2. Attainment of media cleanup standards
3, Source control
4. Compliance with waste management standards
Remedy Selection Decision Factors
1. Long-torn effectiveness
2, Reduction of waste todeity»mobility, or volume
3. Short-term effectiveness
4. hnplementability
5, Cost
5JJ Additional Remedy Selection
Considerations
The choice among available remedial strategy options
may involve a consideration of the aggressiveness of
the remedy, a concept thai includes both the choice of
remedial technologies as well as the relative intensity
of how that technology is applied at the site. For ex-
ample, consider a site where source area restoration is
technically impracticable but source containment is
both feasible and practicable. With the contaminant
source contained, restoration of the portion of the
plume outside of the containment area may be fea-
sible. However, as discussed earlier, there are several
options for attaining cleanup levels within the aque-
ous plume: active pump-and-treat throughout the
aqueous plume; natural gradient flushing of (he
plume towards a pump-and-treat capture system lo-
cated at the leading edge of the plume; and natural at-
tenuation (dilution, dispersion, and any natural degra-
dation processes active within the affected aquifer).
Each alternative will attain the required cleanup lev-
els, bat the choice involves a trade-off among several
factors, including: I) remediation timeframe (longer
with less aggressive strategies); 2) cost (lower with less
aggressive strategies); and 3) potential risk of exposure
(may increase wilh less aggressive strategies).23
Conditions favoring more aggressive strategies (i.e.,
active pump-and-treat throughout the aqueous plume)
include the following;
1) The aggressive strategy clearly will result In a
significantly shorter restoration timeframe than
other available options. This will depend on site
hydrogeologic and contaminant-related factors, in-
cluding the complexity of the aquifer system, natural
rate of pound-water flow, quantity of sorbed con-
taminant mass in the aquifer (and its rate of desorp-
tion), and other factors,
2) A shorter remediation timeframe is desired to
reduce the potential for human exposure. This
generally is the case where there is current or reason-
ably expected near-term future use of the ground wa-
ter. Factors that may be useful in evaluating the like-
lihood of exposure include the State (or Federal, as
appropriate) classification of the ground water; avail-
ability of alternate supplies, such as municipal hook-
ups or other water supply aquifers; interconnections
of die contaminated aquifer wiih other surface or
ground waters; and the ability of institutional controls
to limit exposure.
3} A shorter remediation timeframe is desired to
reduce ongoing or potential impacts to environ-
mental receptors. Such impacts may be caused by
discharges to surface waters, sensitive ecologic areas
(e.g., wetlands), or sole-source aquifers.
EPA will evaluate and determine the objectives and
relative aggressiveness of the alternative remedy on a
site-specific basis, based on the applicable regulatory
requirements and considering the factors discussed
throughout this section. Where conditions favoring
more aggressive strategies do not exist, EPA is more
likely to choose a less aggressive strategy to achieve
the desired remediation objectives, EPA recognizes
that, at some sites, remedies may need to be in opera-
tion for very long time periods. Adequate monitoring
and priodic evaluation of remedy performance
should be conducted to ensure protectiveness and to
evaluate the need for remedy enhancements or the
use of new or different remediation technologies.
5.2.4 Relation to Alternate Concentration
Limits
Site-specific cleanup levels established as part of an al-
ternative remedial strategy at a Superfund site should
not be confused with CERCLA Alternate Concentra-
tion Limits (ACLs). To qualify for use of a CERCLA
ACL, the site must meet the following three require-
ments: 1) there are known points of entry of ihe con-
taminated ground water into surface water; 2) there
23 The long-term reliability of a remedy also is an important consideration for alternative remedial strategy selection. In this ex-
ample, long-term reliability is primarily a function of the design and integrity of the source containment system.
22
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will be rid statistically significant increases of the
contaminant concentrations in the surface water or
contaminant accumulations in downstream sedi-
ments; and 3) enforceable measures can be put into
place to prevent exposure to the contaminated ground
water (see CERCLA §l21(d)(2)(B)(ii)). In addition,
EPA generally considers ACLs appropriate only
where cleanup to ARARs is impracticable, based on
an analysis using the Superfund remedy selection
"balancing" and "modifying" criteria shown in High-
light 2, Where an ACL is established, an A! AR
waiver is not necessary. Conversely, where an
ARAR is waived due to technical impracticability,
there is no need to establish a CERCLA ACL. For
further guidance on CERCLA ACLs, refer to the
NCP Preamble (55 Fg. 8754, March 1990).
Site-specific cleanup levels established in response to
a TI determination at a RCRA facility also should not
be confused with ACLs established as part of the
ground-water monitoring program for regulated units
under 40 CFR 264.94. ACLs established under
§264.94(a)(3) represent concentrations that EPA de-
termines will not pose a substantial hazard to human
or environmental receptors. (If the ACL is exceeded,
then corrective action responsibilities for the regulated
unit are triggered.) A TI determination generally will
not satisfy the criteria for an ACL under this authority.
6.0 Administrative Issues
6.1 TI Review and Decision Process
A TI decision must be incorporated into a site deci-
sion document (Superfund ROD or RCRA permit or
enforcement order) or be incorporated into a modifi-
cation or amendment to an original document. In-
formation and analyses supporting the TI decision
must be incorporated into the site administrative
record, either as part of a Feasibility Study or Cor-
rective Measures Study (for a "Grant-end*1 TI determi-
nation) or remedy rjerformance evaluation or other
technical report or evaluation (for a post-remedy imple-
mentation determination).
The first step in EPA's review process for a n determi-
nation will be to assess the completeness and adequacy
of the TI evaluation. TI evaluations that do not ad-
equately address the considerations identified in this
guidance likely will have to be revised or augmented to
address the inadequacies identified by EPA. or the re-
sponsible agency. Early consultation with EPA by
PRPs or owner/operators is encouraged to help identify
appropriate data and analysis for the evaluation. While
a TI evaluation is underway, remediation efforts under-
way at a site shall continue until the State or Federal
official responsible for the decision determines that the
existing remedy should be altered. Requirements spe-
cific to the Superfund and RCRA programs are dis-
cussed further below.
6,1,1 Superfund
As discussed in Section 4.2, TI decisions may be
made either in the ROD (front-end decisions) or after
the remedy has been implemented and monitored
(post-implemenlation decisions), depending on the
circumstances of the site.
TI decisions at Superftind sites generally will be
made by the EPA Regional Administrator who, upon
review of a TI evaluation, will determine whether
ground-water restoration is technically impracticable
and will identify further remedial actions to be taken
at the site. TI determinations at Superfund sites may
require consultation with headquarters program man-
agement Regional personnel should refer to the
most recent OERR Remedy Delegation Memoran-
dum for current consultation requirements,24
Where a Superfund ROD will invoke a TI ARAR
waiver (front-end decision), EPA (or the lead
agency) must provide notice of its intent to waive the
ARAR in the Proposed Plan for the site and respond
to any State (or Federal) agency or public comments
concerning the waiver. The requirements for State
and community involvement are provided in NCP
§300,500-515 and §300.430, respectively. In gen-
eral, State and community involvement in the deci-
sion to waive an ARAR based on technical impracti-
cability will be the same as for other site remedy de-
cisions. Since TI decisions may affect the potential
future uses of ground water, interest in TI ARAR
waivers may be high. Therefore, it is EPA's intent to
coordinate and consult with States and the public re-
garding TI ARAR waiver issues as early as possible
in the remedy decision process.
24 The types of Superfund site remedy decisions that require consultation with headquarters program management are identified
in the periodically updated OERR Remedy Delegation Memorandum. The most recent version available at the rime of publi-
cation of this guidance was the "Twenty Fourth Remedy Delegation Report - FY 1993," dated February 18,1993.
23
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State concurrence should be sought, but Is not re-
quired, for all remedy decisions in which EPA in-
vokes an ARAR waiver. Where the ARAR to be
waived is a State ARAR, EPA must notify the State
of this when submitting the RI/FS to the State or
when responding to a State-lead RI/FS (NCP
§300.515(d)(3)), EPA must provide the State with an
explanation of any waiver of a State standard
(CERCLA §l21(f)(l)(O)).
For remedial actions under CERCLA §106 that will
waive an ARAR, the State must be notified at least
30 days prior to the date on which any Consent De-
cree will be entered If the State wishes the action to
conform to (and not waive) those standards, the State
may intervene in the action before the Consent De-
cree is entered (see §121(f)(2) and (f)(3)).
At certain State-lead sites, the State may make the fi-
nal remedy decision, including a decision to invoke
an ARAR waiver. This situation is restricted to sites
where the State has been assigned the lead role for
the response action, the action is being taken under
State law, and the State is not receiving funding for
the action from the Trust Fund, In such situations,
the State may seek, but is not required to obtain, EPA
concurrence on the remedy decision. For further
guidance on this and other issues regarding the State
role in remedy selection, see "Questions and Answers
About the State Role in Remedy Selection at Non-
Fund-Financed Enforcement Sites" (EPA 1991c).
Post-remedy-implementation TI decisions may be
made in cases where an outside party or agency sub-
mits comments requesting a TI determination or EPA
determines on its own initiative that a waiver is war-
ranted. The information considered in making such
decisions should include the same types of informa-
tion and analyses discussed for front-end determina-
tions, except that remedy performance data and
analysis also should be provided. This information
must be entered into the site administrative record be-
fore the TI decision can be made and an ARAR
waiver invoked. There are limitations, however, to
the requirement that EPA open the administrative
record to new comments, such as an outside party's
request for a TI determination. EPA is not required
to consider comments on the selected remedy unless
the comments contain "significant information not
contained elsewhere in the administrative record file
which substantially supports the need to significantly
alter the response action" (see NCP §300.825). The
type and amount of information necessary to meet
this requirement (e.g., the length of time a remedy
must be operated prior to a TI evaluation) will be de-
termined by EPA on a site-specific basis.
A modification to a signed ROD invoking a TI
ARAR waiver generally will require a ROD amend-
ment, since a waiver usually will constitute a funda-
mental change in the remedy. A public comment pe-
riod of 30 days is required for an amendment to a
ROD; this period may be extended to 60 days upon
request.25 A public meeting also should be granted
if requested. In the exceptional case where an BSD
is used to invoke a TI ARAR waiver, public notice
and opportunity for comment also should be pro-
vided. Further guidance on ROD amendments is
provided in "Guide to Addressing Pre-ROD and
Post-RQD Changes" (EPA 199 Ib) and upcoming re-
visions to "Guidance on Preparing Superfund Deci-
sion Documents" (expected Fall 1993).
6,1.2 RCRA
TI decisions at RCRA Corrective Action facilities
will be made either by the EPA Regional Administra-
tor or by the appropriate State agency, depending on
the RCRA program authorization status of ihe State,
EPA's goal in the RCRA corrective action program is
to work cooperatively with individual States, regard-
less of their authorization status, to promote consis-
tent TI decisions. As in the Superfund program, it is
recommended that the State and EPA notify and con-
sult each other as early as possible regarding sites
where TI determinations may be made. This notifica-
tion and consultation process may be outlined in the
State/EPA Memorandum of Understanding,
For States authorized for Hazardous and Solid Waste
Amendments (HSWA) Corrective Action, the State
will have primary authority for remedy decisions, in-
cluding TI decisions. EPA will retain authority for
TI determinations in States that are not authorized for
HSWA corrective action,
At RCRA permitted facilities, implementation of aTI
determination generally would require a Class 3 permit
modification for the purpose of specifying (alternative)
corrective measures. This process requires a 45-day
notice and comment period, response to comments, and
25 Public notice and opportunity for comment should be provided before an ARAR waiver is granted, regardless of whether an
Explanation of Significant Differences (BSD) or ROD miendineiu is used to invoke the waiver.
24
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public hearing, if requested. At RCRA facilities
conducting corrective action under an order, II de-
terminations generally are implemented through the
negotiation of a new order or an amendment to an
existing order. This process generally includes a
30- to 45-day pubic comment period and public
hearing, if requested.
6,1,3 Technical Renew and Support
Technical support for the TI evaluation should be
sought as early in the process as possible, preferably
during the initial scoping of the content of the TI
evaluation, TI determinations usually will require
expertise from several disciplines, including hydro-
geology, engineering, and risk assessment,
Technical staff within the Regions representing these
disciplines should be part of the TI review team.
EPA's Office of Research and Development (ORD)
technical liaisons and scientists based in the Regions
also may provide assistance to program staff. Further
assistance and review may be obtained from the ORD
laboratories involved in the Technical Support
Project, including the R,S. Keir Environmental
Research Laboratory (Ada, OK), the Risk Reduction
and Engineering Laboratory (Cincinnati, OH), the
Environmental Research Laboratory (Athens, OA),
and the Environmental Monitoring Systems
Laboratory (Las Vegas, NY). The directory of ORD
technical services may be consulted for further
information (EPA 1993c).
General assistance and site-specific consultation on
technical impracticability issues also is available
from EPA headquarters staff. Inquiries should be di-
rected to the appropriate OSWER program office.
6.2 Duration of Tl Decisions
A determination that ground-water restoration is tech-
nically impracticable and the subsequent selection of
an alternative remedial strategy will be subject to fu-
ture review by EPA,
At Superfund sites, an alternative remedial strategy
implemented under a CERCLA TI waiver remains in
effect so long as that strategy remains protective of
human health and the environment. Protectiveness in
this context encompasses long-term reliability of the
remedy. If the conditions of protectiveness or reliabil-
ity conditions cease to be met, EPA will determine
what additional remedial actions must be imple-
mented to enhance or augment the existing remedy.
EPA shall conduct a full assessment of the protective-
ness of the alternative remedy at least every five
years at any site where contamination remains above
levels that allow for unrestricted use, as required un-
der NCP §300.430(f)(4)(ii).
RCRA TI decisions will be incorporated into facility
permits or enforcement orders and therefore will be
subject to continual oversight and review. Condi-
tions of the permit or order involving the TI decision
or the alternative strategy may be revisited on a peri-
odic basis to ensure protectiveness. It may be neces-
sary to modify permits or orders to reflect new infor-
mation that becomes available during the remedy
implementation and monitoring period.26 Additional
measures may be required by EPA to ensure the on-
going protectiveness and reliability of the remedy.
Further, owner/operators of RCRA facilities may be
required by EPA to undertake additional remedial
measures in the future if subsequent advances in re-
mediation technology make attainment of media
cleanup standards technically practicable,
The protectiveness of an alternative remedial strategy
at a Superfund site or RCRA facility must be ensured
through a monitoring program designed to detect re-
leases from containment areas, migration of contami-
nants to water supply wells, or other releases that
would indicate a possible failure of one of the remedy
components. EPA may decide to take any further re-
sponse actions necessary to ensure protectiveness at
any time based upon whether the alternative remedy
is achieving its required performance standards.
Monitoring data, therefore, must be provided to EPA
on a regular basis to ensure adequate performance of
the alternative remedy. The format, content, and re-
porting schedule of the monitoring program will be
determined by EPA as part of the TI determination
and alternative remedy selection process.
26 RCRA Corrective Action Orders that incorporate TI decisions should contain language chat retains EPA's authority to review
these decisions and complete additional site remediation, as necessary.
25
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7.0 References
Anderson, Mf. and W.W. Woessner, 1992, Applied.
Oroundwater Modeling. Academic Press, San
Diego.
Cohen, R.M. andJ.W, Mercer, 1993. DNAPLSite
Evaluation. C.K. Smoley, Boca Raton, FL.
EPA, 1988a, "Guidance for Conducting Remedial
Invesiiptions and Feasibility Studies Under
CERCLA, Interim Final," QSWER Dkective
9355.3-01, EPA/540/G-89/004.
EPA, I988b. "Guidance on Remedial Actions for
Contaminated Ground Water at Superfund Sites,"
EPA/540/G-88/QQ3.
EPA, 1989a. "Considerations in Ground Water
Remediation at Superfund Sites," OSWER
Directive 9355.4-03.
EPA, 1989b. "Evaluation of Ground-Water Extraction
Remedies," EPA/540/2-89/<054, Vols. 1-3.
EPA, 1989c. "Overview of ARARs, Focus on ARAR
Waivers," OSWER Publication 9234.2-03/FS,
EPA, 1990s. "Suggested ROD Language for Various
Ground Water Remediation Options," OSWER
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EPA, 1990b. "Superfund Removal Procedures - Action
Memorandum Guidance," OSWER Directive
9360.3-01, EPA/54Q/P-90/004.
EPA, 1991a "ARARs Q's & A's: General Policy,
RCRA, CWA, SDWA, Post-ROD Information, and
Contingent Waiveis," QSWER Publication 9234.2-
OWFS-A.
EPA, I991b. "Guide to Addressing Pre-ROD and
Post-ROD Changes" OSWER Publication
9355.3-02/FS4. i
EPA, 1991c. "Questions and Answers About the Slate
Role in Remedy Selection at Non-Fund-Financed
Enforcement Sites," OSWER Directive 9831,9.
EPA, 1991d. "Superfund Removal Procedures -
Guidance on the Consideration of ARARs During
Removal Actions," OSWER Publication 9380.3-02.
EPA, 1992a, "Considerations in Ground-Water
Remediation at Superfund Sites and RCRA
Facilities-Update," OSWER Dkective 9283.1-06.
EPA, 1992b. "Dense Nonaqueous Phase Liquids - A
Workshop Summary, Dallas, Texas, April 16-18,
1991," Office of Research and Development,
EPA/60Q/R-92/G30.
EPA, 1992c. "Estimating Potential for Occurrence of
DNAPL at Superfund Sites," OSWER Publication
9355,4-07/FS.
EPA, 1992d. "Evaluation of Ground-WaDer Extraction
Remedies, Phase II," OSWER Publication 9355.4-
05,Vokl-2.
EPA, 1992e. "General Methods for Remedial
Operations Performance Evaluations," Office of
Research and Development, EPA/60Q/R-92/OG2,
EPA,1992f. "Ground Water Issue; Fundamentals of
Ground-Water Modeling," EPA/S40/S-92/Q05.
EPA,1992g, "Ground-Water Modeling
Compendium," EPA/5QO/B-92/QG6.
EPA, 1993a. "Evaluation of the Likelihood of DNAPL
Presence at NPL Sites," OSWER Publication
9355.4-13, EPA/540/R-93/Q73.
EPA, 1993b. "Guidance on Conducting Non-Time-
Critical Removal Actions Under CERCLA,"
OSWER Directive 9360.0-32, EPA/540/R-93/057.
EPA, 1993c. "Technical Assistance Directory," Center
forEnvtonmenlal Research Information, Office of
Research and Development," EPA/600/K-93/006.
Federal Register. Volume 55, No. 46, March 8,1990.
"National Oil and Hazardous Subsiances Pollution
Contingency Plan; Final Rule."
Federal Register. Volume 55, No, 145, July 27,1990.
"Corrective Action for Solid Waste Management
Units at Hazardous Waste Management Facilities;
Proposed Rule."
26
*ILS. G.P.a.:W3-3QO-574:82091
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