[Federal Register Volume 85, Number 219 (Thursday, November 12, 2020)]
[Rules and Regulations]
[Pages 72506-72543]
[FR Doc No: 2020-23327]

Vol. 85

Thursday,

No. 219

November 12, 2020

Part VII

Environmental Protection Agency

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40 CFR Part 257

Hazardous and Solid Waste Management System: Disposal of CCR; A
Holistic Approach to Closure Part B: Alternate Demonstration for
Unlined Surface Impoundments; Final Rule

Federal Register / Vol. 85 , No. 219 / Thursday, November 12, 2020 /
Rules and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 257

[EPA-HQ-OLEM-2019-0173; FRL-10015-88-OLEM]
RIN 2050-AH11

Hazardous and Solid Waste Management System: Disposal of CCR; A
Holistic Approach to Closure Part B: Alternate Demonstration for
Unlined Surface Impoundments

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: On April 17, 2015, the Environmental Protection Agency (EPA or
the Agency) promulgated national minimum criteria for existing and new
coal combustion residuals (CCR) landfills and existing and new CCR
surface impoundments. On August 21, 2018, the U.S. Court of Appeals for
the D.C. Circuit issued its opinion in the case of Utility Solid Waste
Activities Group v. EPA, 901 F.3d 414 (per curiam) (USWAG). This rule
finalizes regulations proposed on March 3, 2020, including procedures
to allow facilities to request approval to operate an existing CCR
surface impoundment with an alternate liner, among other things.
Provisions from the proposed rule that are not addressed in this rule
will be addressed in a subsequent action.

DATES: This final rule is effective on December 14, 2020.

ADDRESSES: EPA has established a docket for this action under Docket
ID. No. EPA-HQ-OLEM-2019-0173. All documents in the docket are listed
on the http://www.regulations.gov website. Although listed in the
index, some information is not publicly available, e.g., CBI or other
information whose disclosure is restricted by statute. Certain other
material, such as copyrighted material, is not placed on the internet
and will be publicly available only in hard copy form. Publicly
available docket materials are available electronically through http://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT: Michelle Long, Office of Resource
Conservation and Recovery, Materials Recovery and Waste Management
Division, Environmental Protection Agency, 1200 Pennsylvania Avenue NW,
MC: 5304P, Washington, DC 20460; telephone number:<PHONE_NUMBER>;
email address<EMAIL_ADDRESS>For more information on this
rulemaking, please visit https://www.epa.gov/coalash.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. General Information
    A. Does this action apply to me?
    B. What action is the Agency taking?
    C. What is EPA's authority for taking this action?
    D. What are the incremental costs and benefits of this action?
II. Background
    A. The ``2015 CCR Rule''
    B. The 2018 USWAG Decision
    C. The March 2020 Proposed Rule
    D. Public Participation on the Proposed Rule
III. Addition of Sec.  257.71(d) To Allow for Alternate Liner
Demonstrations
    A. Factual Basis
    B. Application
    C. Alternate Liner Demonstration
    D. Procedures for Approval and Denial of Alternate Liner
Demonstration
IV. Corrections to Sec. Sec.  257.102 and 257.103
V. Rationale for 30-Day Effective Date
VI. Effect of This Final Rule on States With Approved CCR Programs
VII. The Projected Economic Impacts of This Action
    A. Introduction
    B. Affected Universe
    C. Costs, Cost Savings, and Benefits of the Final Rule
VII. Executive Orders
Regulatory Text

I. General Information

A. Does this action apply to me?

    This rule applies to all CCR generated by electric utilities and
independent power producers that fall within the North American
Industry Classification System (NAICS) code 221112 and may affect the
following entities: electric utility facilities and independent power
producers that fall under the NAICS code 221112. This discussion is not
intended to be exhaustive, but rather provides a guide for readers
regarding entities likely to be regulated by this action. This
discussion lists the types of entities that EPA is now aware could
potentially be regulated by this action. Other types of entities not
described here could also be regulated. To determine whether your
entity is regulated by this action, you should carefully examine the
applicability criteria found in Sec.  257.50 of title 40 of the Code of
Federal Regulations. If you have questions regarding the applicability
of this action to a particular entity, consult the person listed in the
FOR FURTHER INFORMATION CONTACT section.

B. What action is the Agency taking?

    EPA is revising certain provisions of the CCR regulations at 40 CFR
part 257 in response to the decision issued by the D.C. Circuit on
August 21, 2018, in Utility Solid Waste Activities Group v. EPA 901
F.3d 414 (D.C. Cir.). Specifically, the Agency is finalizing a revision
to the 2015 CCR Rule that provides procedures for facilities to request
approval to use an alternate liner for CCR surface impoundments.
    EPA is finalizing a two-step process for submittal of the necessary
documentation for the alternate liner demonstration. The first step
consists of an initial application intended to show whether a unit
meets certain minimum requirements before embarking on a comprehensive
alternate liner demonstration. These minimum requirements are designed
to ensure that it is likely that the facility will ultimately be able
to make the more extensive demonstration to support continued
operation, and that the CCR surface impoundment can operate safely over
the short term while the facility collects the data and conducts the
analyses necessary to support the demonstration. The first step
requires the facility to demonstrate that it is in full compliance with
the applicable requirements in 40 CFR part 257 subpart D; that it
possesses site characteristics that make it likely that it could
qualify for a demonstration; and that there are no constituents listed
in part 257 Appendix III that have been detected at a statistically
significant increase (SSI) above background. The second step consists
of a final demonstration intended to show whether there is a reasonable
probability that releases from the impoundment throughout its active
life may result in groundwater concentrations of constituents listed in
part 257 Appendix IV at a statistically significant level (SSL) in the
future. The purpose of this two-step approach is to ensure that units
allowed to embark on a comprehensive and time-consuming demonstration
meet the minimum requirements to ensure protectiveness throughout the
process.
    Provisions from the proposed rule that are not addressed in this
rule will be addressed in a subsequent rulemaking action. The remaining
provisions from the proposed rule are to allow the use of CCR during
closure of a CCR unit, to establish an additional closure option for
CCR units being closed by removal of CCR, and to establish requirements
for annual closure progress reports.
    EPA intends that the provisions of this rule be severable. In the
event that any individual provision or part of this rule is
invalidated, EPA intends that this would not render the entire rule
invalid, and that any individual provisions that can continue to
operate will be left in place.

C. What is EPA's authority for taking this action?

    These regulations are established under the authority of sections
1008(a), 2002(a), 4004, and 4005(a) and (d) of the Solid Waste Disposal
Act of 1970, as amended by the Resource Conservation and Recovery Act
of 1976 (RCRA), as amended by the Hazardous and Solid Waste Amendments
of 1984 (HSWA) and the Water Infrastructure Improvements for the Nation
(WIIN) Act of 2016, 42 U.S.C. 6907(a), 6912(a), 6944, and 6945(a) and
(d).

D. What are the incremental costs and benefits of this action?

    This action is expected to result in an estimated annualized net
cost savings of approximately $4.0 million per year to $8.0 million per
year when discounting at 7% and approximately $2.2 million per year to
$4.5 million per year when discounting at 3%. Further information on
the economic effects of this action can be found in Unit VII of this
preamble.

II. Background

A. The ``2015 CCR Rule''

    On April 17, 2015, EPA finalized national minimum criteria for the
disposal of CCR as a solid waste under Subtitle D of RCRA. 80 FR 21302.
The Agency refers to the April 17, 2015 rule as the ``2015 CCR Rule''
in this preamble. CCR are generated from the combustion of coal by
electric utilities and independent power producers for the generation
of electricity. CCR include fly ash, bottom ash, boiler slag, and flue
gas desulfurization materials and are commonly referred to as coal ash.
The CCR regulations are codified in subpart D of part 257 of title 40
of the CFR.
    The 2015 CCR Rule regulated existing and new CCR landfills and
existing and new CCR surface impoundments, as well as all lateral
expansions of these CCR units. The federal national minimum criteria
consist of location restrictions (siting limitations), design and
operating criteria, groundwater monitoring and corrective action
requirements, and closure and post-closure care requirements. In
addition, the 2015 CCR Rule put in place recordkeeping, notification,
and internet posting provisions that require owners and operators of
CCR units to maintain a publicly accessible internet site of rule
compliance information. The 2015 CCR Rule does not regulate CCR that
are beneficially used. It established a definition of ``beneficial use
of CCR'' to distinguish between beneficial use and disposal.
    Of particular relevance to this action, the 2015 CCR Rule required
that any existing unlined CCR surface impoundment that cause
groundwater concentrations to exceed a groundwater protection standard
(GWPS) must stop receiving waste (CCR and/or non-CCR wastestreams)
within six months of making an exceedance determination. This would
also trigger the requirement to initiate either unit retrofit or
closure activities.\1\ See Sec.  257.101(a)(1) at 80 FR 21490 (April
17, 2015). In the 2015 CCR Rule, the term ``unlined'' CCR surface
impoundment included any unit not constructed with one of the following
types of liners: (1) A composite liner; (2) an alternative composite
liner; or (3) a liner consisting of a minimum of two feet of compacted
soil with a hydraulic conductivity of no more than 1 x
10-\7\ centimeters per second. Lined CCR surface
impoundments (as defined in the CCR regulations) that impact
groundwater above the specified GWPS are not required to close and
could continue to operate while corrective action is performed, and the
source of the groundwater contamination is addressed.
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    \1\ Certain units may be eligible for the alternative closure
procedures specified in Sec.  257.103 which would change the date by
which the unit must stop receiving waste.
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    The 2015 CCR Rule was challenged by several parties, including a
coalition of regulated entities and a coalition of environmental
organizations (``Environmental Petitioners''). See USWAG v EPA, 901
F.3d 414 (DC Cir. 2018). The Environmental Petitioners raised two
challenges \2\ that are relevant to this final rule. First, they
challenged the provision that allowed existing, unlined CCR surface
impoundments to continue to operate until they cause groundwater
contamination. See Sec.  257.101(a)(1) at 80 FR 21490 (April 17, 2015).
They contended that EPA failed to show how continued operation of
unlined impoundments met RCRA's baseline requirement that any solid
waste disposal site pose ``no reasonable probability of adverse effects
on health or the environment.'' See 42 U.S.C. 6944(a). The
Environmental Petitioners also challenged the provisions that allowed
impoundments lined with two feet of clay (i.e., compacted soil) to
continue operating even when they leak, requiring only that they
remediate the resulting contamination. The petitioners pointed to
record evidence that ``clay-lined'' units are likely to leak and
contended that EPA's approach ``authorizes an endless cycle of spills
and clean-ups'' in violation of RCRA.
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    \2\ Environmental Petitioners also challenged the provisions
exempting inactive surface impoundments at inactive power plants
from regulation. The Court ruled for the Petitioners on these
claims, vacating these provisions and remanding to EPA. However, in
contrast to the other provisions addressed in this rule, additional
rulemaking is necessary to effectuate the Court's order, as the
Court's vacatur alone did not subject these units to regulation.
This aspect of the decision will be addressed in a subsequent
proposal.
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B. The 2018 USWAG Decision

    The D.C. Circuit issued its decision on USWAG v. EPA on August 21,
2018. The Court upheld most of the 2015 CCR Rule but ruled for the
Environmental Petitioners on the two claims discussed in Unit II.A of
this preamble. The Court held that EPA acted ``arbitrarily and
capriciously and contrary to RCRA'' in failing to require the closure
of unlined surface impoundments and in classifying so-called ``clay-
lined'' impoundments as lined, based on the record supporting the rule.
901 F.3d at 431-432. The Court ordered that ``the Final Rule be vacated
and remanded with respect to the provisions that permit unlined
impoundments to continue receiving coal ash unless they leak, Sec.
257.101(a), [and] classify `clay-lined' impoundments as lined, see 40
CFR 257.71(a)(1)(i).'' Id. The Court issued the mandate for this
decision on October 15, 2018. This decision is referred to as the
``USWAG decision'' in this action.

C. The March 2020 Proposed Rule

    In the March 3, 2020 rule, EPA proposed revisions to the 2015 CCR
Rule, including: Procedures to allow facilities to request approval to
use an alternate liner for CCR surface impoundments; two co-proposed
options to allow the use of CCR during unit closure; an additional
closure option for CCR units being closed by removal of CCR; and
requirements for annual closure progress reports. In this final rule,
the Agency is taking final action on the proposed procedures for
facilities to request approval to use an alternate liner for CCR
surface impoundments. Provisions from the proposed rule that are not
addressed in this rule will be addressed in a subsequent action.

D. Public Participation on the Proposed Rule

    The Agency received over 42,000 comments on the proposed rule, with
over 170 unique comments. The majority of commenters focused on the
alternate liner demonstration (ALD) provisions, as well as use of CCR
in closure. Commenters included individual electric utilities and
independent power producers, national trade associations, state
agencies, public

interest and environmental groups, and entities involved with the
beneficial use of CCR. All public comments submitted in response to the
proposal can be found in the docket for this action. EPA's responses to
comments on the proposed rule are addressed either in this preamble or
in the response to comment document available in the docket to this
final rule.
    EPA conducted two virtual public hearings on April 7, 2020, and
April 9, 2020 using an internet-based software platform. The platform
allowed hearing participants to provide oral testimony using a
microphone and speakers connected to their computers or using a phone.
It provided the ability for any person to listen to the public hearing
via their computer. On April 7, 2020, there were 38 speakers and a
total of 142 registered attendees. On April 9, 2020, there were 30
speakers and a total of 82 registered attendees. Testimony at the
public hearing focused generally on the proposed amendments of allowing
the use of alternate liner demonstrations and use of CCR in closure.
Several speakers commented on the alternate liner demonstration or the
use of CCR in closure to allow CCR to be disposed in unlined surface
impoundments indefinitely and contaminating groundwater, and the
overall risks, especially health risks, related to CCR. Many speakers
advocated for strengthening of the regulations rather than finalizing
``rollbacks.'' Many commenters were concerned that people were unable
to attend the public hearing because of the COVID-19 pandemic, and that
EPA did not extend the public comment period. Transcripts for both
virtual public hearings are included in the docket for this action.

III. Addition of Sec.  257.71(d) To Allow for Alternate Liner
Demonstrations

    The 2015 CCR Rule required that all existing unlined CCR surface
impoundments that caused groundwater concentrations to exceed
associated GWPS must stop receiving waste and either retrofit or close.
In the 2015 CCR Rule, the term ``unlined'' CCR surface impoundment
included any unit not constructed with one of the following types of
liners: (1) Composite liner; (2) alternative composite liner; or (3)
liner consisting of a minimum of two feet of compacted soil with a
hydraulic conductivity of no more than 1 x 10-\7\ cm/s.\3\
See Sec.  257.71(a). Lined CCR surface impoundments (as defined in the
CCR regulations) that impact groundwater above the specified GWPS were
not required to close and could continue operations while corrective
action was performed and the source of the groundwater contamination
was addressed.
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    \3\ The liner terms ``compacted soil'' and ``clay-lined'' are
used interchangeably in this preamble discussion.
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    On August 21, 2018, the U.S. Court of Appeals for the D.C. Circuit
found in the USWAG decision that the rulemaking record did not support
the conclusion that the 2015 CCR Rule would adequately address the
adverse effects posed by clay-lined CCR surface impoundments.
Therefore, the court vacated the provisions that treated clay-lined
surface impoundments differently than unlined impoundments. USWAG, 901
F.3d at 449. The result of the court's decision is that such units are
now required to either retrofit or close. In response to this ruling,
EPA received reports from industry groups and individual companies
claiming that the performance of some surface impoundments that would
now be required to retrofit or close is equivalent or even superior to
the liners required by the 2015 CCR Rule.\4\ These impoundments rely on
engineered liner components (e.g., manufactured geomembrane,
mechanically compacted soil) that deviate from the requirements of the
rule and/or on natural low-conductivity soil beneath the unit. EPA
agrees that it is possible for individual impoundments that are not
lined with a composite liner or an alternative composite liner (as
those terms are defined in the CCR regulations) to still be protective
of human health and the environment. This is possible if the effective
hydraulic conductivity of the engineered liner and/or naturally
occurring soil is so low that, even if leachate migrates from the unit,
the volume of leachate that can be released to the underlying aquifer
over the active life of the impoundment is so small that these releases
will not result in adverse effects at any point in the future.
Therefore, EPA proposed procedures in the March 2020 rule at Sec.
257.71(d) to allow facilities to submit to EPA an alternate liner
demonstration that would provide a sufficient record to support the
continued operation of an unlined surface impoundment that can be shown
to pose no reasonable probability of adverse effects to human health or
the environment.
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    \4\ These reports are available in the docket to this
rulemaking.
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    The current self-implementing regulations limit the ability of
owners and operators to make a site-specific demonstration that the
design of a particular CCR surface impoundment is equivalent to the
composite liner system in Sec. Sec.  257.71(c); consequently, a
regulatory revision would be necessary. However, the Agency's current
record does not support conclusions on whether any individual
impoundment has a low enough effective hydraulic conductivity to be
protective, were the unit allowed to continue operations. This would
require site-specific data, such as liner performance and surrounding
hydrogeologic characterization information. The data relied upon in the
2014 Risk Assessment were organized into distributions compiled at
various geographic scales (e.g., local, regional, national). The
resolution of these data were sufficient for identifying the potential
for risk at a national scale. However, the same data cannot be used to
draw conclusions about any individual impoundment. While reports
submitted to EPA by industry since the finalization of the 2015 CCR
Rule have provided valuable information about the characteristics of
impoundments anticipated to perform equivalent to the liner system
required by the 2015 CCR Rule, these reports generally did not include
the type or specificity of data needed to support conclusions about
individual impoundments.
    Therefore, owners and operators who believe an unlined surface
impoundment meets the RCRA Sec.  4004(a) standard and should be allowed
to continue operation as designed must provide EPA or a Participating
State Director with the site-specific data and analysis necessary to
demonstrate this fact. Based on the available groundwater monitoring
and location restriction data posted on facilities' publicly accessible
CCR internet sites, EPA believes that it is likely that only a small
fraction of non-composite lined surface impoundments currently in
operation will be able to apply successfully for this demonstration.

A. Factual Basis

    The factual record supporting the 2015 CCR Rule included a
national-scale assessment of the risks associated with disposal of CCR
in surface impoundments constructed with various liner types.\5\ As
part of the 2014 Risk Assessment, EPA modeled peak groundwater
concentrations that might occur in off-site wells up to a mile away for
a duration of up to 10,000 years. This modeling effort identified
potential risks from both unlined and clay-lined surface impoundments:
The risk that

groundwater would be contaminated at levels exceeding GWPS and the risk
arising from the exposure of human and environmental receptors to
contaminated water. It is now known that a greater fraction of
operating units are unlined than previously understood. This may shift
the national-scale risks reported for all impoundments closer to the
risks for just unlined units because a greater fraction of all
impoundments would now be modeled as unlined, but it would not
substantially alter the high-end risks already modeled for unlined
impoundments. Thus, the change in liner designation would not impact
the overall conclusions about risk drawn from the 2014 Risk Assessment.
Based on this modeling, EPA estimated that releases from up to 36.2% of
unlined impoundments and 9.1% of clay-lined surface impoundments could
ultimately contaminate off-site wells.\6\ EPA is aware that monitoring
data indicates that a higher percentage than this have exceeded GWPS.
However, monitoring wells are located at the waste boundary, which
invariably have higher concentrations than would be found up to a mile
away from the unit, and includes additional contributions from
background groundwater. In addition, a number of these impoundments are
located near water bodies, which intercept some or all of the release
before it can reach private wells on the opposite side. Therefore, EPA
does not believe that the field data that has become available since
finalization of the risk assessment conflicts with previous modeling
results.
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    \5\ U.S. EPA. 2014. ``Human and Ecological Risk Assessment of
Coal Combustion Residuals.'' Prepared by the Office of Solid Waste
and Emergency Response. Washington, DC. December.
    \6\ U.S. EPA. 2014. ``Regulatory Impact Analysis: EPA's 2015
RCRA Final Rule Regulating Coal Combustion Residual (CCR) Landfills
and Surface Impoundments at Coal-Fired Electric Utility Power
Plants.'' Prepared by the Office of Solid Waste and Emergency
Response. Washington, DC. December.
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    As explained in the proposed rule, EPA considers it to be
theoretically possible for some unlined and clay-lined units to achieve
the same level of performance as the composite liners required by the
2015 CCR Rule. In order for this to be the case, the effective
hydraulic conductivity of the engineered liner and/or naturally
occurring soil would need to be so low that, even if leachate migrates
from the unit, the volume of leachate that can be transmitted to the
underlying aquifer over time is small enough that it will not adversely
affect groundwater quality. For a unit to achieve this, it would need
to perform materially better than the clay-lined units evaluated in the
2014 Risk Assessment. Those clay-lined surface impoundments were
modeled with a fixed hydraulic conductivity of 1 x 10-\7\
cm/s and thickness of 3 feet, similar to the minimum design standard
for clay-lined units outlined in the 2015 CCR Rule. For this fixed set
of parameters, EPA identified risks slightly above the relevant risk
criteria only for lithium, one of the most mobile CCR constituents.\7\
Based on these model results, an effective hydraulic conductivity of
1x10\-8\ cm/s would be sufficient to reduce identified risks to below
levels of concern on a national-scale. However, conditions present at
individual facilities, such as the thickness of the low-conductivity
soil or the presence of a geomembrane liner, might support somewhat
higher soil conductivities on a case-by-case basis. Regardless, a
conductivity of 1 x 10-\7\ cm/s for the lowermost soil
component of the liner, whether in isolation or beneath a geomembrane
component, remains the absolute floor for any unit to even be
considered for an alternate liner demonstration.
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    \7\ Lithium had a non-cancer hazard quotient of 2.
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    EPA established the minimum liner requirements for CCR surface
impoundments in the 2015 rule based on the original municipal solid
waste landfill regulations at 40 CFR part 258. These requirements were
based on the Agency's experience with various liner materials and
reflect a uniform design that EPA expects to be reliably protective if
manufactured and constructed properly. However, EPA acknowledged in the
original 1991 rule (56 FR 51059, October 9, 1991) that alternative
designs may be able to achieve the same performance. Thus, EPA also
acknowledges that the fact that an individual unit does not meet the
liner requirements of the 2015 CCR Rule does not in and of itself
indicate that a unit will pose risk. Facilities that commented on the
proposed rule reported units that were considered unlined based on the
2015 CCR Rule definition for several reasons. Based on the available
information from these comments and the Part 258 regulatory record, EPA
identified three primary reasons that an alternately lined unit could
still be protective.
    One type of impoundment that was classified as unlined, but which
might still be demonstrated to be protective, is a unit where the soil
was not mechanically compacted to the specified depth. It is well-
established in the literature that clay-rich soils can achieve
hydraulic conductivities lower than 1 x 10-\8\ cm/s;
however, this often requires some degree of compaction to break down
any larger clumps of soil and minimize the volume of void spaces
between soil particles that allow water to flow. Reports provided by
some facilities purport that the necessary compaction of these soils
had been accomplished onsite through natural processes. One example of
the natural processes envisioned by commenters is glacial compaction,
whereby stress from the weight and flow of the glacier compressed the
naturally occurring soil. This process has been found to result in
regions of soil with conductivities lower than 1 x 10-\8\
cm/s.\8\ Soils from around the perimeter of such units, which have
historically been exposed to similar environmental conditions as the
soil beneath the unit and so are expected to have similar
characteristics, can be collected to confirm that necessary hydraulic
conductivity is present and consistent across the site. Therefore, EPA
believes the potential exists for facilities to successfully
demonstrate that naturally compacted soil can be protective.
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    \8\ United States Department of the Interior. 1998. ``National
Water-Quality Assessment of the Lake Erie-Lake St. Clair Basin,
Michigan, Indiana, Ohio, Pennsylvania, and New York Environmental
and Hydrogeologic Setting.'' Water-Resources; Investigations Report
97-4256. Prepared by the United States Geological Survey. Columbus,
OH.
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    Another type of unlined impoundment that may still be demonstrated
to be protective is one where the layer of compacted soil was not thick
enough to meet the current part 257 requirement. Based on EPA's
experience with these liner materials, two feet of soil is the minimum
thickness needed to reliably obtain adequate compaction and meet
requirements for hydraulic conductivity. This thickness is considered
necessary to minimize the number of cracks or imperfections through the
entire liner thickness that could allow leachate migration. Based on
EPA's experience, a two-foot minimum thickness is believed to be
sufficient to reliably inhibit hydraulic short-circuiting of the entire
layer. While it is possible to achieve low conductivities with a
reduced thickness, there is a far greater risk of lateral and vertical
imperfections that may arise during construction. Therefore, EPA
believes that successful demonstration is possible here only if the
facility can provide data showing the liner achieves an adequately low
hydraulic conductivity in-situ.
    The final type of unlined impoundment that may still be
demonstrated to be protective is one where the geomembrane liner used
was not thick enough to meet the current part 257 requirement. The
upper component of a composite-lined unit must consist of a minimum of
a 30-mil

geomembrane liner, or 60-mil if the liner is constructed with high
density polyethylene. Based on EPA's experience with these liner
materials, these are the minimum thicknesses necessary to ensure
adequate liner performance, including being able to withstand the
stress of construction and to ensure that adequate seams can be made.
Commenters argued that, due to improvements in welding technology and
quality control procedures since these standards were first
promulgated, concerns regarding welding thinner HDPE geomembranes have
greatly diminished. If the facility is able to document the integrity
of the liner design, then the performance of these liners will be
primarily a function of construction quality. Commenters acknowledged
that thinner liners are theoretically more susceptible to defects
during installation, but also argued that no such trends have been
identified in the literature. The 2014 Risk Assessment found that a
well-constructed geomembrane liner can remain protective, even with a
higher proportion of imperfections. Therefore, EPA believes the
potential exists for facilities to successfully demonstrate that
alternate geomembrane liners can be protective, provided that the soil
directly beneath the geomembrane has sufficiently low conductivity.
    To support the conclusion that the long-term performance of an
alternately lined CCR surface impoundment can meet the RCRA Sec.  4004
protectiveness standard, EPA would need several categories of
information. EPA proposed two categories of information that must be
provided for the demonstration step, which the Agency is finalizing as
part of this rulemaking. The first category is a characterization of
the site-specific hydrogeology surrounding the surface impoundment. The
purpose of these data is to define the variability of the soil around
the surface impoundment to determine whether preferential flow pathways
exist that effectively negate the low conductivity of the alternate
liner. The second category of data is a characterization of the
potential for infiltration through any engineered liner and/or
naturally occurring soil that control the release and transport of
leachate. These data will provide for a reasonable estimate of the rate
at which contaminants may be released and transported to groundwater
over time. Based on comments received, EPA is also finalizing a third
category of information. This additional category is documentation of
material properties and unit construction quality. The purpose of these
data is to document that the impoundment can be expected to achieve the
low conductivity specified in the unit designs. This category is
included in the application step to confirm upfront that conditions
simulated in a laboratory setting as part of the demonstration step are
a reasonable reflection of field conditions.
    Thus, EPA concludes that there is potential for some existing
unlined and clay-lined CCR surface impoundments to continue operating
without presenting unacceptable risk. However, the Agency's current
risk assessment does not support conclusions on whether any individual
surface impoundment has a low enough effective hydraulic conductivity
that operation of the unit will continue to be protective in the
future. This would require the site-specific data discussed above,
including, for example, data on the ability of the engineered liner
and/or naturally occurring soil to limit the release and transport of
leachate away from the unit. Therefore, EPA proposed procedures at
Sec.  257.71(d) to allow facilities to submit such information to EPA
to demonstrate that the engineered liner and/or naturally occurring
soil will remain protective, and consequently the continued operation
of an individual unlined surface impoundments will present no
reasonable probability of adverse effects to human health or the
environment.
    Specifically, EPA proposed a two-step process. In the first step, a
facility would be required to submit an initial application to
demonstrate that they meet certain minimum requirements before
embarking on a comprehensive alternate liner demonstration. These
minimum requirements are designed to ensure that it is likely a
facility will ultimately be able to make the more extensive
demonstration to support continued operation, and that the CCR surface
impoundment can operate safely over the near term while the facility
collects the data and conducts the analyses necessary to support the
demonstration. In the second step, the facility would be required to
submit the data and analyses necessary to support a determination that
the CCR surface impoundment can sustain its current performance and
operate safely for the remainder of its active life.
    Most industry groups and individual facilities voiced support for
the option to make this type of demonstration, stating that the
definition of a lined CCR surface impoundment in the 2015 CCR Rule is
inflexible and would result in the unnecessary closure of some unlined
CCR surface impoundments that, as designed, are as protective as lined
CCR surface impoundments. Many environmental groups and private
citizens were critical of the proposal and commented that it was
unsupportable and would lead to greater risks to human health and the
environment. Some of the same commenters noted that, while the types of
information required may be useful to differentiate non-compliant and
underperforming units, there were concerns that the amount of
information required would be difficult or impossible to collect and
review.
1. Existing Record
    Environmental groups stated the existing risk record does not
support the conclusion that alternate liners can be protective, citing
the potential risks identified for clay-lined units in the 2014 Risk
Assessment. Some of these commenters further argued that the reports
submitted by facilities to date are inadequate and similarly do not
support the continued operation of the units documented therein. These
commenters provided critiques of the individual units and concluded
that the information provided in the associated reports is not
sufficient to demonstrate whether on-site groundwater monitoring wells
are adequate in number or construction to accurately reflect upgradient
and downgradient conditions at the site. Further, commenters concluded
that some facilities have inappropriately handled monitoring data to
erroneously show that the CCR surface impoundment has not contaminated
groundwater. Commenters also critiqued a report prepared by the
Electric Power Research Institute (EPRI), which they claim shows that
clay liners cannot be equivalent to composite liners in protecting
health and the environment.
    As stated in the proposal and above, EPA agrees that neither the
2014 Risk Assessment nor the industry reports support conclusions about
any individual unlined surface impoundment. In order to draw
conclusions about the protectiveness of any individual CCR surface
impoundment, EPA needs site-specific information on the performance of
the engineered liner and/or the naturally occurring soil. This is why
EPA proposed a process for facilities to submit documentation that
would support the continued operation of an unlined surface
impoundment. At an absolute minimum, the performance of these CCR units
would need to surpass that of the clay liners previously modeled,
making them distinct from the far broader universe of clay-lined and
unlined CCR surface impoundments considered in the USWAG decision.

    Although the reports submitted to EPA by individual facilities
since finalization of the 2015 CCR Rule provide an indication on which
impoundments are most likely to seek an ALD, EPA stated in the proposal
that these reports did not include the type or specificity of data
necessary to support conclusions about these individual surface
impoundments. As a result, EPA did not rely on the conclusions of these
reports to support any provisions of this final rule. As discussed in
more detail below in Unit III.B, part of the purpose of the initial
application step is to determine whether the types of deficiencies
raised by commenters are present at a particular site, and if so, to
ensure that these facilities do not progress to the longer ALD process.
    The report submitted by EPRI considered more broadly whether
alternative liners can achieve GWPS near the CCR waste boundary. The
modeling approach in many ways mirrored that used by EPA in the 2014
Risk Assessment. Although EPRI initially made some assumptions that
would tend to overestimate risk, such as ignoring the effects of
constituent sorption onto the soil, these assumptions were later
explored in select sensitivity analyses. Ultimately, EPRI found that
even thick clay liners with a hydraulic conductivity of 1 x
10-\7\ cm/s could result in exceedances of GWPS under high-
end conditions, while thinner clay liners with a conductivity at and
above 1 x 10-\8\ cm/s did not. These results generally
comport with the conclusions drawn from the 2014 Risk Assessment and
suggest that there are plausible scenarios in which alternative liners
can be protective. Critiques of the EPRI report by commenters focused
heavily on the fact that the modeled clay liners did not perform
equivalently to composite liners, meaning that the alternative liner
could result in releases greater than a composite liner. However, after
consideration of the comments received, the Agency believes this type
of ``equivalence'' is not the appropriate standard to apply in an
alternate liner demonstration. It would be difficult for an owner or
operator to demonstrate that a clay liner of any thickness would
prevent migration just as effectively as a composite liner, which
includes a flexible membrane liner that, by design, is impermeable.
Such a standard would unnecessarily limit the ability of owners and
operators to utilize otherwise protective designs. Therefore, EPA
believes the appropriate standard for an alternate liner demonstration
is that there is no reasonable probability that releases throughout the
active life of the CCR surface impoundment will result in adverse
effects to human health or the environment. This is the standard relied
upon in the 2015 CCR Rule to determine that composite-lined units were
protective. This standard is achieved in an ALD by documenting that the
peak groundwater concentration that may result from releases over the
active life of the impoundment will not exceed GWPS at the waste
boundary.
    Therefore EPA is making revisions at Sec.  257.71(d) to specify the
owner or operator of a CCR surface impoundment constructed without a
composite liner or alternative composite liner, as defined in Sec.
257.70(b) or (c), may submit an Alternate Liner Demonstration to the
Administrator or the Participating State Director to demonstrate that
the design of the current liner system or the naturally occurring media
will remain protective of human health and the environment.
2. Potential Risks to Surface Water
    Several environmental groups expressed concern that the focus on
protection of groundwater would exclude protection of ecological
receptors in nearby surface water. In particular, commenters
highlighted the potential for some constituents to be toxic for aquatic
wildlife at lower levels than for human ingestion of groundwater. These
commenters also stated that the USWAG decision faulted EPA for not
directly addressing potential risks to ecological receptors identified
in the 2014 Risk Assessment. Another commenter pointed to the damage
cases relied upon in the 2015 CCR Rule that identified additional risks
to surface water.
    The 2014 Risk Assessment identified the potential for surface water
risks from unlined units as a whole, but the existing risk record does
not support similar concerns about units that would be able to obtain
an ALD. Releases from the base of an impoundment will migrate down to
groundwater prior to discharge into downgradient surface water. The
risk assessment explicitly modeled this pathway and found that all
surface water risks from clay-lined units fall below levels of concern
by an order of magnitude or more. If the effective hydraulic
conductivity of an alternate liner is sufficient to mitigate the
groundwater risks previously identified in the risk assessment, then it
will only further reduce downgradient releases to surface water through
groundwater discharge. Thus, by demonstrating that an alternately lined
impoundment can reliably perform better than the clay-lined units
considered in the 2014 Risk Assessment, this confirms that these
impoundments will pose no reasonable probability of adverse effects to
surface water. Although damage cases considered in the 2015 CCR Rule
identified some surface water impacts beyond those reported in the risk
assessment, these were frequently associated with scenarios not
explicitly modeled in the risk assessment, such as direct discharge of
either CCR and/or associated wastewater to surface water or disposal of
CCR in high-risk areas (e.g., within the groundwater table). These
scenarios have already been addressed under RCRA through requirements
for structural integrity and location restrictions, respectively. In
addition, EPA is finalizing a requirement as part of this rule that
facilities must remain in detection monitoring throughout both the
application and demonstration steps. Ensuring that there is no SSI of
Appendix III constituents throughout the demonstration will also ensure
that Appendix IV constituents will not migrate beyond the waste
boundary and pose risk to nearby ecological receptors while the owner
or operator prepares the necessary documentation to demonstrate both
that the facility complies with all relevant requirements of the 2015
CCR Rule and that the long-term performance of the impoundment will be
protective.
3. Continued Operation of CCR Surface Impoundments During Demonstration
    Industry groups agreed with EPA's basis for the proposed rule and
stated that the D.C. Circuit had not precluded EPA from supplementing
the existing risk record to support future decisions about individual
unlined CCR surface impoundments. However, several environmental groups
argued that the rule was in violation of the USWAG decision and
contrary to RCRA. These commenters claimed that the D.C. Circuit
decision required the closure of all unlined and clay-lined CCR surface
impoundments and so any rule that would allow additional time for
operation while the CCR surface impoundments complete a demonstration
process would violate the decision. Others contended that allowing any
additional time for operation would violate RCRA Sec.  4004(a) because
it might provide deficient units additional time to contaminate
groundwater before addressing the source.
    EPA disagrees with the suggestion that this rule is inconsistent
with the USWAG decision. The D.C. Circuit held that the rulemaking
record supporting

the 2015 CCR Rule did not support allowing clay-lined units to continue
to operate indefinitely. 901 F.3d at 431-432. The court did not find
that the statute per se prohibited such units, but that EPA had failed
to provide enough evidence to demonstrate that the statutory standard
had been met. Id. Consequently, EPA is not precluded from subsequently
developing the evidence necessary to support the continued operation of
some or all of these units. As discussed in greater detail in
subsequent Units of this preamble, the record associated with the
specific subset of impoundments that will be eligible under this rule
is very different than the record associated with all units regulated
under the 2015 CCR rule. For example, in the 2015 CCR rule the majority
of units had been operating for years without groundwater monitoring or
other regulatory requirements. The record for that rule documented that
the majority of these units had likely been contaminating groundwater
for years; EPA estimated that the contamination at these units had
spread well beyond the waste boundary. And because there was no
groundwater monitoring at these facilities, EPA was unable to
distinguish between units that did pose a risk and those that did not.
By contrast, only units that remain in detection monitoring throughout
the application and demonstration process can be approved for an ALD.
As discussed later in this preamble, EPA has also addressed the
specific faults that the court found in EPA's prior record.
    EPA further disagrees with the suggestion that this rule fails to
meet the standard in RCRA Sec.  4004(a). EPA purposefully divided the
ALD process into two steps to weed out the facilities that fail to meet
the RCRA Sec.  4004(a) standard. The initial application ensures that a
facility is in compliance with applicable requirements in 40 CFR part
257 subpart D, that the design of the monitoring network is sufficient
to identify releases, that the CCR surface impoundment is in detection
monitoring, and that the unit has the soil characteristics or
engineering quality that would make it possible to meet the ultimate
performance standard before a facility is granted any additional time
to complete the more comprehensive alternate liner demonstration. The
combination of these factors ensures that the only CCR surface
impoundments allowed to progress to the demonstration step are those
that EPA expects to remain protective during the year-long process to
complete the demonstration.
    Because the initial application phase will be completed by April
11, 2021 (the deadline for unlined surface impoundments to cease
receipt of waste pursuant to Sec.  257.101(a)(1)), this process will
grant additional time to operate only to CCR surface impoundments that
continue to show that they can operate safely during the time it will
take for the process to be completed. As discussed in more detail
below, the initial application will be due no later than November 30,
2020, and EPA will make a decision on whether the facility qualifies to
submit a demonstration no later than April 11, 2021. Consequently, all
facilities that submit an application must still be prepared to cease
receipt of waste and to begin closure in the event that the application
is ultimately rejected.
    Finally, CCR surface impoundments that are able to progress to the
demonstration step will have shown that the design of the groundwater
monitoring network is sufficient to identify releases from the unit and
that there is currently no evidence that releases have occurred or are
likely to occur while they are completing the demonstration.
    CCR surface impoundments are continuously full of water. The
resulting hydraulic head on the liner can be considerably greater than
found in landfills, which results in a greater and sustained potential
for infiltration into the subsurface. The expectation is that releases
from the unit to the subsurface would be limited primarily by the low
hydraulic conductivity of the engineered liner and/or naturally
occurring soil. Many of the surface impoundments at facilities that
commented on the proposed rule have been in operation for over a decade
and some for almost 70 years. If GWPS have not been exceeded throughout
years of operation, this indicates that some combination of low
conductivity soil, the thickness of the soil column above the aquifer,
or a geomembrane liner component is effectively limiting or entirely
preventing the release and transport of leachate. And for units such as
these, with an adequate monitoring network, the fact that they have not
triggered assessment monitoring means there is no evidence of any
release to groundwater. In addition, these units will continue routine
groundwater monitoring while preparing the demonstration to ensure that
they continue to perform as anticipated over the year-long
demonstration step. CCR units that trigger either assessment monitoring
or corrective action at any point during the process would be rendered
ineligible to proceed. Thus, any impoundment able to submit a
successful ALD would not have had any discernable impact to groundwater
quality.
    Moreover, it is highly unlikely that a unit with no prior
indication of impacts to groundwater will contaminate groundwater above
the GWPS within the relatively short timeframe permitted to complete
the demonstration. Groundwater transport is a gradual process as the
leachate migrates to and mixes with the groundwater. It is not
realistic to expect a sudden exceedance of the GWPS after years of no
detections from groundwater monitoring. Rather, one would expect to
first see the more mobile constituents in Appendix III, such as total
dissolved solids, before detecting any of the constituents of concern
in Appendix IV. If a unit is leaking but has failed to identify the
exceedance due to a deficiency with either the design or implementation
of the groundwater monitoring program, that will be identified during
the application review. Thus, there is no evidence that these units
will present a risk of contaminating groundwater above GWPS or a risk
to downgradient human or ecological receptors. Nonetheless, these units
will continue routine groundwater monitoring while preparing the
demonstration to ensure that the units continue to perform as
anticipated.
4. Potential for Future Harm
    Some environmental groups contended that it does not matter whether
an unlined unit can be shown to have no current groundwater
contamination because the existing risk record shows that it can happen
in the future. These commenters pointed specifically to the Agency's
previous finding that a certain portion of unlined and clay-lined units
are anticipated to eventually contaminate groundwater. Commenters
further stated that allowing these units to continue operation is
contrary to the USWAG decision because the risk record does not show
whether any future release could be promptly detected and, once
detected, promptly remedied before it can result in harm to human
health or the environment. Commenters also pointed out that the risk is
further compounded by the potential size of the plume from unlined
units.
    EPA disagrees with the proposition that allowing CCR surface
impoundments that meet the requirements for an ALD to continue
operation is in violation of the USWAG decision. The D.C. Circuit found
that it was contrary to RCRA Sec.  4004(a) to allow unlined and clay-
lined units to continue

operating because the rulemaking record failed to address a number of
the risks associated with these units. For example, the record did not
demonstrate that a leak from these units could be reliably contained
and addressed before it resulted in harm to human health and the
environment. 901 F.3d at 432. The D.C. Circuit specifically pointed to
several factors that EPA had failed to address that might prolong the
time required to address leaks, including the rate and extent of
contaminant release, the well sampling schedule, and the time allowed
to implement source control. Id at 42,432. However, the conditions
established as part of this rule ensure that these issues will be
sufficiently addressed for the subset of CCR surface impoundments able
to obtain and operate under an ALD.
    First, units with an ALD that enter into assessment monitoring are
required to conduct additional analyses to identify the presence and
magnitude of any trends of increasing groundwater concentrations in
downgradient wells. If these analyses show the potential exists for
releases from the impoundment to result in an exceedance of GWPS within
the timeframe needed to reliably close the unit, the facility must
retrofit or close. This provision is intended to prevent adverse
effects to groundwater and, if necessary, to expedite remedial efforts.
Use of trend analysis is appropriate to monitor for evidence of
increasing groundwater concentrations because the release and transport
of inorganic elements through the subsurface is a gradual and steady
process. The presence of low conductivity soil beneath a unit would
only further limit the speed at which contamination can spread. For
example, based on the range of anticipated hydraulic gradients and
other relevant soil properties, groundwater moving through soil with a
hydraulic conductivity of 1 x 10-\7\ cm/s would be expected
to progress less than a foot a year.\9\ In this context, there is
little concern that the time between semi-annual monitoring events
would substantially delay identification of potential
contamination.\10\
---------------------------------------------------------------------------

    \9\ The maximum hydraulic gradient considered in the 2014 Risk
Assessment was 1.0 ft/ft.
    \10\ Additionally, it is notable that the semi-annual timing
between sampling events is designed to ensure a degree of
statistical independence in assembled monitoring data. Too-frequent
sampling at a given background well can result in highly
autocorrelated, non-independent data that can reduce the accuracy of
statistical tests.
---------------------------------------------------------------------------

    Even if corrective action were triggered before closure could be
completed, this in no way prevents the concurrent implementation of
corrective measures beyond the waste boundary to contain the plume and
prevent downgradient exposures. EPA has previously documented how pump
and treat can be systematically applied to control plume migration,
even when the contaminant source has not yet been addressed.\11\
Furthermore, facilities that are able to submit a successful
demonstration will be among the most well-characterized units in the
country, which would further limit the timeframe needed to contain the
plume and the potential for unforeseen setbacks that could result in an
inadequate understanding of local hydrogeology.
---------------------------------------------------------------------------

    \11\ U.S. EPA. 2008. ``A Systematic Approach for Evaluation of
Capture Zones at Pump and Treat Systems.'' EPA 600/R-08/003.
Prepared by the Office of Research and Development. Cincinnati, OH.
January.
---------------------------------------------------------------------------

    Ultimately, EPA believes that a judgement on whether a plume can be
addressed promptly should be based on the potential for immediate and
future harm. This is consistent with the established criteria in Sec.
257.97(d) that require the development of a reasonable schedule to
implement remedial actions to be based on a number of factors, such as
the immediacy of risk to nearby receptors and the risk of contaminant
spread to other environmental media. Altogether, these factors will
help ensure that any contamination identified at the waste boundary can
be addressed before it results in risk to downgradient receptors,
regardless of the original extent of the release.
    EPA is also confident that contamination at these sites can be
successfully remediated. The inorganic constituents on Appendix IV are
not novel. Issues of impracticability at corrective action sites are
often associated with the ability to access contaminants in the
subsurface. The primary causes have been the hydrophobic behavior of
organic compounds, which is not relevant in this context, and the
presence of complex site hydrogeology.\12\ The CCR location
restrictions at Sec.  257.64 prohibit disposal in karst and other
unstable areas that might confound remedial efforts. Other highly
complex geology, such as fractured bedrock, is notoriously resistant to
modeling and unlikely to allow for a successful demonstration. Although
corrective action at the remaining sites may be technically complex, it
remains feasible. Therefore, there is little concern that corrective
action, if required, would not eventually achieve established cleanup
goals. For all these reasons, the Agency is not making any amendments
to the proposal as a result of these comments.
---------------------------------------------------------------------------

    \12\ U.S. EPA. 2012. ``Summary of Technical Impracticability
Waivers at National Priorities List Sites.'' OSWER Directive 9230.2-
24. Prepared by the Office of Solid Waste and Emergency Response.
Washington, DC. August.
---------------------------------------------------------------------------

B. Application

    In the March 2020 proposed rule, EPA proposed to establish a two-
step process: Requiring an initial application followed by the
submission of the alternate liner demonstration. The application step
is designed to ensure that a surface impoundment meets minimum
requirements before embarking on a comprehensive alternate liner
demonstration.
    The Agency proposed that in order to apply for an ALD, an owner
operator must first submit a letter to EPA declaring their intention to
submit a demonstration under the provision. EPA also proposed that
along with the letter, a facility must provide documentation showing
(1) that a facility is in compliance with all applicable requirements
in 40 CFR part 257 subpart D, including all location restrictions, and
(2) that there has not been an exceedance of any Appendix IV
constituents. EPA further proposed that, as part of this demonstration,
a facility must submit documentation to show that the existing network
of monitoring wells is sufficient to identify any releases based on
direction of flow, well location, screening depth, and other relevant
factors. EPA proposed that this could include well construction logs
and a sufficient number of diagrams to depict depth to groundwater, the
potentiometric surface, and the anticipated directions of groundwater
flow across the site. Finally, EPA proposed to require the facility to
show there is no indication from groundwater monitoring data that the
unit has or will adversely affect groundwater, in part by providing
documentation of the most recent statistical tests conducted and the
rationale for the methods used in these comparisons. Upon submission of
the application, a copy of the written demonstration and all associated
documentation must be simultaneously posted to the facility's publicly
accessible CCR internet site.
    No commenter raised concern about EPA's proposal to require the
submission of a letter or the specific requirements applicable to the
letter or the two categories of accompanying information required to be
submitted. However, some commenters broadly requested that EPA provide
greater clarity on the types of information that must be submitted for
the application to be considered complete, while other commenters asked
for greater clarity on

the specific elements necessary to satisfy the requirements of the
rule.
    EPA is finalizing much of Sec.  257.71(d)(1) as proposed--retaining
the requirement to submit a letter and accompanying information to
demonstrate that certain minimum criteria have been met. The final rule
also retains the requirements to submit documentation showing that a
facility is in compliance with all applicable requirements in 40 CFR
part 257 subpart D, including all location restrictions. However, the
final rule includes a modified provision requiring facilities to
demonstrate that there has not been a statistically significant
increase over background levels of any Appendix III constituents
throughout the application and demonstration process. EPA has also made
several modifications in response to comments requesting greater
clarity. Other changes were made to conform the procedures in this
rulemaking with the procedures recently adopted in Sec.  257.103. These
topics are discussed in further detail in the next Units of this
preamble.
1. Application Letter
    EPA proposed that the owner or operator must first submit a letter
to EPA declaring their intention to submit an alternate liner
demonstration. EPA received no comments that raised questions or
concerns about the substantive information to be included in the
letter. Consequently, the final rule adopts these requirements without
substantial revision. The final rule requires the owner or operator of
the CCR surface impoundment to submit a letter to EPA or the
Participating State Director. This letter will announce the owner or
operator's intention to submit an alternate liner demonstration. The
application must include the location of the facility and identify the
specific CCR surface impoundment for which the demonstration will be
made. The application letter must also include the information in Sec.
257.71(d)(1)(i)(A) through (D), as specified in the regulatory text,
and further described below.
2. Compliance With the CCR Regulations and Required Documentation
    Along with the letter, EPA proposed at Sec.  257.71(d)(1)(i)(A)
that the owner or operator must submit information to EPA documenting
that the facility is in compliance with the applicable requirements in
40 CFR part 257, subpart D.
    EPA continues to believe that requiring facilities to document
compliance with the subpart D of part 257 requirements is an important
part of the demonstration. Compliance with the rule provides critical
support for the determination that these units will not present the
types of risks identified in the damage cases considered in the 2015
CCR Rule. For example, some of the damage cases resulted from disposal
in high-risk areas (e.g., within the groundwater table). These issues
will be addressed through documenting that the surface impoundments
meet the requirements of the 2015 CCR Rule (e.g., location
restrictions). Similarly, documenting compliance with the groundwater
monitoring requirements shows that the design of the groundwater
monitoring network is sufficient to identify groundwater contamination
in the uppermost aquifer. This, together with the fact that the unit
remains in detection monitoring, demonstrates that there is currently
no evidence the risks modeled in the 2014 Risk Assessment are present
or will result from continued operation of the impoundment in the near
term.
    Overall, compliance with part 257, subpart D generally provides
some guarantee that the risks at the facility are properly managed and
adequately mitigated. Consequently, this determination provides
critical support for a decision to allow continued operation of the
alternately lined surface impoundment. This means that EPA must be able
to affirmatively conclude that the facility meets this criterion prior
to authorizing any continued operation of the surface impoundment. It
also means that EPA cannot grant facilities additional time to cure any
noncompliance. However, EPA's determination will be prospective only;
accordingly, for purposes of the ALD process, EPA is only interested in
the state of a facility's current compliance rather than any instances
of historic non-compliance.
    In response to commenters who requested that EPA provide greater
specificity about what constitutes a complete submission, EPA has
amended the regulatory text to identify specific documents that the
owner or operator of a CCR unit must provide to demonstrate its current
compliance with the requirements of part 257, subpart D. Most of these
documents are the same documents that EPA is requiring facilities to
provide under the recent amendments to Sec.  257.103. Further, these
documents should already exist either because they would have had to be
compiled when the unit was first constructed, or they were required to
be developed under the existing regulations.
    Consistent with the recent amendments to Sec.  257.103 (85 FR
53516, August 28, 2020), EPA has decided that a certification of
compliance and the requirement to remain in compliance with the
regulations are also necessary in this final rule. The compliance
certification is represented at Sec.  257.71(d)(1)(i)(A) to require a
certification signed by the owner or operator of the CCR unit saying it
is in full compliance with part 257, subpart D, except for the
requirement to document that the unit is constructed with either a
composite liner or alternative composite liner under Sec.
257.71(a)(1). This approach will prevent non-compliant unlined surface
impoundments from operating for an extended period of time into the
future. Requiring that only compliant surface impoundments can be
approved for an ALD provides additional support for EPA's conclusion
that this final rule meets the statutory standard.
3. Groundwater Monitoring Network Documentation
    EPA proposed at Sec.  257.71(d)(1)(i)(B) that the facility must
show in the initial application that the existing network of monitoring
wells is sufficient to identify any releases based on direction of
flow, well location, screening depth and other relevant factors,
including well construction logs and a sufficient number of diagrams to
depict depth to groundwater, the potentiometric surface, and the
anticipated direction(s) of groundwater flow across the site (multiple
diagrams may be necessary if the direction of flow is affected by
seasonal, tidal or other influences). EPA also proposed that these
diagrams should include all the water table measurements reported from
a standard datum, a map scale, and a legend of any important map
symbols. EPA proposed that facilities that have improperly placed
groundwater monitoring wells would not be eligible to apply or submit
an alternate liner demonstration.
    Many commenters requested greater specificity on the types of
information required for this part of the application. Some questioned
whether facilities will be required to gather additional groundwater
and other site-specific data in support of the application, or whether
facilities only needed to submit previously collected groundwater
monitoring data and analyses conducted for their sites. One commenter
asked whether the application required specific information, such as
representative geologic cross sections, groundwater contour maps of the
facility, or other hydrogeologic data. Another requested inclusion of a

requirement that facilities include the depth of water ponded in the
impoundment to ensure that wells intended to reflect background
conditions are not impacted by groundwater mounding. Some commenters
pointed out that some of the elements required in the application are
standard components of the annual groundwater monitoring and corrective
action reports already required by Sec.  257.90(e). Examples include
groundwater flow maps and statistical test results. These commenters
requested that the monitoring reports and other existing documentation
be allowed to substitute for some or all of the application through
citation, weblink, or other reference. Although some commenters
acknowledged that the information requested would facilitate review of
the application, others protested the additional burden of repackaging
information.
    The intent of this provision is to allow for a comprehensive review
of the existing well network to determine whether it is sufficient to
identify releases from the unit that have occurred or might occur in
the future. EPA did not intend to require the collection of any further
groundwater data or other site-specific data for the purposes of the
application. Facilities have already designed and implemented their
site groundwater monitoring programs, and EPA expects the facility
would normally have generated the information specified in Sec.
257.71(d)(1)(i)(B)(1) of this final rule, either as part of developing
or implementing the groundwater monitoring program. However, facilities
are encouraged to provide additional detailed interpretation of the
data and analyses for consideration during the review.
    EPA proposed that the application include documentation of relevant
factors considered by the owner or operator when determining the
appropriate number and placement of monitoring wells. As highlighted by
some commenters, this should include characterization of the local
hydrogeology, including the factors detailed in Sec.  257.91(b), and
the potential for groundwater mounding beneath the unit to affect
characterization of background. However, the appropriate types of data
and level of detail will depend largely on the complexity of the site.
As a consequence, EPA is not requiring every facility to incorporate
discussion of the depth of impounded water as part of the justification
for well placement. Any potential for groundwater mounding should have
been accounted for when the wells were first installed and so should be
reflected in the documentation already required. If mounding is found
to be present, then this information must be reflected in any maps of
groundwater elevation and flow direction. However, it is considered
highly unlikely that a facility with appropriately located wells and
releases substantial enough to result in groundwater mounding would
remain in detection monitoring and be eligible for an ALD.
    Because this record already exists, the facility would only be
required to provide all the data and analyses that were relied upon to
comply with the relevant standards of the CCR regulations. However,
documenting that the existing well network meets the standard in this
rule will require a level of detail and discussion beyond what is
required in a routine groundwater monitoring report. And, although such
reports contain a subset of the required information, it is likely to
be divided up among a number of different documents. This will
complicate and extend the review process because the key data and
figures will not be presented alongside the relevant discussion to
provide proper context. Thus, applications that incorporate the
required information solely through reference will be considered
incomplete.
    Because this information is already available, preparation of the
application should not require much additional work beyond compiling
information in a concise and coherent fashion. EPA discourages
facilities from sending hundreds or thousands of pages of laboratory
printouts and other raw data; instead, EPA expects the data to be
presented in a tabular or other format that has gone through a quality
control process to present the data in a concise format. The types of
data and analyses considered by facilities beyond what is required to
be presented as part of monitoring reports may appropriately vary on a
case-by-case basis.
    Therefore, EPA is finalizing the provisions at Sec.
257.71(d)(1)(i)(B)(1) with amendments to specify the documents that the
facility must provide to demonstrate how it has complied with each
requirement in Sec.  257.91. The regulatory text can provide an
effective checklist for facilities to follow. In order to review a
facility's current compliance with the requirements governing
groundwater monitoring systems, the Agency will need the following
updated list of information: (1) Map(s) of groundwater monitoring well
locations (these maps should identify the CCR units as well) that
depict the elevation of the potentiometric surface and the direction(s)
of groundwater flow across the site; (2) well construction diagrams and
drilling logs for all groundwater monitoring wells; (3) maps that
characterize the direction of groundwater flow accounting for temporal
variations; and (4) any other data and analysis the facility relied
upon when determining the number and placement of wells around the unit
compiled in a concise and readable format.
4. No Adverse Effects on Groundwater Documentation
    EPA proposed at Sec.  257.71(d)(1)(i)(C) that facilities must
demonstrate that there is no indication from groundwater monitoring
data that the unit has or will adversely affect groundwater (i.e., no
statistically significant levels (SSL) of Appendix IV constituents
above relevant GWPS), including documentation of the most recent
statistical tests conducted and the rationale for the methods used in
these comparisons. Facilities that have conducted improper statistical
analysis of groundwater monitoring results would not be eligible to
apply or submit a demonstration.
    The Agency received comments about the proposed language that a
facility must demonstrate ``there is no indication from the groundwater
monitoring data that the unit has or will adversely affect groundwater
. . .'' Commenters expressed concern that this standard was more
stringent than required by the subsequent demonstration step and may
necessitate collection of an unspecified amount of additional data,
such as sampling for Appendix IV constituents at units that had not
progressed beyond detection monitoring, which they worried would not be
possible to obtain prior to the application deadline.
    As discussed previously, EPA did not intend for facilities to
conduct additional rounds of sampling for the application beyond that
required for ongoing compliance with the CCR regulations. The
referenced preamble language was intended to convey that the monitoring
data collected to date must show that there is currently no evidence
that the unit has contaminated groundwater, as well as no evidence that
it might do so in the future. The language in question was based on the
assumption that units presently in assessment monitoring could submit
an application. However, EPA has reconsidered that position in light of
comments received. The final rule instead requires that all units must
stay in detection monitoring to remain eligible for an ALD. The fact
that a unit remains in detection monitoring

provides better evidence to demonstrate that the standard in the
proposed rule has been met (i.e., that the unit is not currently
causing adverse effects), and that such effects are not expected to
occur in the near term. EPA acknowledges, as demonstrated for
composite-lined units in the 2014 Risk Assessment, that releases can
occur from even the most well-designed units and that these
impoundments can remain protective. However, greater assurance that the
impoundment can continue to operate safely throughout the approval
process is necessary at this stage, prior to the demonstration that the
ultimate performance standard in this rule has been met.
    To reflect these changes, EPA is adopting a provision at Sec.
257.71(d)(1)(i)(B)(2) to specify that facilities must demonstrate that
the unit remains in detection monitoring as a precondition for
submitting an application. Consistent with the proposal, as part of
demonstrating that the facility remains in detection monitoring, the
owner operator must document the most recent statistical tests
conducted and the rationale for the methods used in these comparisons.
    Many industry and some state commenters requested greater
specificity on the types of information required for this part of the
application. One commenter requested clarification on the relationship
between these requirements and those found in Sec.  257.93 and Sec.
257.94. Another commenter asked whether a qualified professional
engineer's certifications that the groundwater monitoring program meets
the requirements of the 2015 CCR Rule would provide sufficient
documentation.
    The intent of this provision is to allow for a comprehensive review
of the facility's determination that a unit has not adversely affected
groundwater. Certification from a qualified professional engineer alone
would not provide the necessary documentation. EPA proposed that
facilities include documentation of the most recent statistical test
and rationale for the methods selected. Whether the results of the
statistical tests are valid depends on all the data and analyses that
underpin it. The documentation must demonstrate that the
characterization of groundwater quality is sufficient; the management
of collected monitoring data has been properly considered and addressed
non-detect data, trends, and other relevant factors that may affect
data quality; and that the statistical tests applied are appropriate.
The specific standards that the application must address are detailed
in Sec.  257.93 through Sec.  257.94.
    Therefore, EPA is finalizing Sec.  257.71(d)(1)(i)(B)(2) with
amendments to specify that the facility must document how it has
complied with each requirement in Sec. Sec.  257.93 through 257.94. The
regulatory text in these sections can provide an effective checklist
for facilities to follow. To support that demonstration, the final rule
requires facilities to provide the following: (1) Documentation of the
most recent statistical test; and (2) the rationale for the methods
used in these comparisons. As part of this rationale, the facility must
provide all data and analyses relied upon to comply with each
requirement.
5. Location Restrictions
    EPA proposed at Sec.  257.71(d)(1)(i)(D) that a unit must be in
compliance with all relevant location restrictions at Sec. Sec.  257.60
through 257.64 in order to be eligible for an ALD.
    Many industry commenters requested greater specificity on the types
of information required for this part of the application. Specifically,
commenters inquired whether facilities were expected to submit the
entire package of location restriction demonstrations, or if they can
simply certify that the CCR surface impoundment meets all location
restrictions. The documents that demonstrate a unit meets a location
restriction should already exist because they are required under the
existing regulations. Location restrictions were established to ensure
that units are constructed in suitable geographic areas. Prohibited
locations reflect areas where local conditions have the potential to
compromise the integrity of the unit or where, if contamination were to
occur, the damages could be particularly severe or difficult to
remediate. EPA still believes this is critical to the record supporting
continued operation of the unit. Consequently, facilities must submit
the entire package of location restriction demonstrations.
    Therefore, EPA maintains that documentation that the facility is in
compliance with all location restrictions must be submitted to EPA or
the Participating State Director as a requirement of the initial
application and is finalizing Sec.  257.71(d)(1)(i)(B)(3).
6. Structural Stability and Safety Factor Assessment Submission
    In order to align with the recent amendments to Sec.  257.103 (85
FR 53516, August 28, 2020)(``Part A final rule''), this final rule
specifies that a facility must submit the facility's most recent
structural stability assessment required at Sec.  257.73(d) and safety
factor assessment required at Sec.  257.73(e) at Sec.
257.71(d)(1)(i)(B)(4) and (5). EPA's intention to review these items
was discussed in the proposed rule as part of the discussion when
discussing that a unit must be in full compliance with the 2015 CCR
Rule. EPA received no comments raising concern about inclusion of this
requirement. The inclusion of this requirement also responds to
requests that EPA provide greater specificity on the documents that
must be submitted as part of the application.
    The Agency recognizes that the requirement to conduct periodic
structural stability assessments and safety factor assessments is not
applicable to all CCR surface impoundments. As specified in Sec.
257.73(b), only those impoundments with a height of five feet or more
and a storage volume of 20 acre-feet or more, or those impoundments
with a height of 20 feet or more are subject to these assessment
requirements. An owner or operator submitting an ALD application for a
unit not meeting these thresholds must include an affirmative statement
in the certification signed by the owner or operator under Sec.
257.71(d)(1)(i)(A) indicating that the impoundment is not subject to
the structural stability and safety factor assessment requirements
under Sec.  257.73(d) and (e). Similarly, EPA is aware that not all
impoundment dikes were constructed with soils that are susceptible to
liquefaction, and thus are not subject periodic safety factor
assessments showing that the calculated liquefaction factor of safety
equals or exceeds 1.20. See Sec.  257.73(e)(1)(iv). For impoundments
not constructed with soils subject to liquefaction and subject to the
safety factor assessment requirements, the owner or operator must
include an affirmative statement in the certification required under
Sec.  257.71(d)(1)(i)(A) stating that the unit is not subject to the
liquefaction factor of safety because it has been determined that the
dike(s) was not constructed with soils subject to liquefaction.
7. Documentation of Source Material and Construction Quality
    EPA noted in the proposal that geomembrane liners are not as
sensitive to the chemical composition of coal ash leachate as soil-
based liners and so performance may depend more on the frequency and
magnitude of imperfections that arise during installation. In these
instances, laboratory infiltration tests on pristine samples are
unlikely to provide representative data on field performance. EPA
discussed

construction quality reports as a type of documentation that could
support characterization of geomembrane liner performance in the field.
However, EPA did not require the submission of any particular documents
as part of the application.
    Multiple commenters indicated that historical data on the
construction of impoundments is important to understand whether a unit
can perform as intended. Commenters identified several specific factors
they believed should be part of the submission, such as the initial
saturation, compactive effort, plasticity index, subgrade water
content, and clay content of the liner. One commenter also warned that
specifications on a manufacturer's product sheet alone may not provide
adequate assurance of good performance in the field.
    EPA agrees that considerations of construction quality are equally
relevant to all types of liners. Indeed, the ability of any liner to
achieve performance objectives is predicated on the quality of both the
source materials and the construction of the surface impoundment.
Therefore, EPA concludes that information on both must be incorporated
in the application to provide evidence that the unit has the soil
characteristics or engineering quality that would make it possible for
the unit to meet the ultimate performance standard is expected to
remain protective in the near term while the comprehensive
demonstration is completed. The relevant types of information will
depend on the design of the surface impoundment. Consequently, EPA is
not specifying particular documents or data that must be submitted for
every impoundment.
    Source quality testing ensures that the materials used to construct
the liner conform with project specifications and are able to meet the
necessary standards. However, EPA has found negligible correlation
between field hydraulic conductivity and many of the common soil
characterization parameters identified by the commenter, such as
plasticity index and clay content.\13\ As a result, EPA previously
concluded that it is difficult to determine whether a particular soil
is suitable for use as a liner based solely on individual index
properties and without relevant confirmatory testing. For engineered
soils, this will involve establishing the relationship between water
content, density, and hydraulic conductivity in a laboratory setting
before construction begins to ensure the liner will be installed under
optimum conditions. For naturally-occurring soils, this will involve
testing that the pre-existing soil structure achieves a sufficiently
and consistently low hydraulic conductivity. For geomembrane liners,
this involves confirming that the material can withstand the stresses
it will be exposed to and that the seams of the liner can be reliably
welded to meet performance requirements. Altogether, this information
provides evidence that these materials can meet relevant performance
objectives during operation.
---------------------------------------------------------------------------

    \13\ U.S. EPA. 2002. ``Assessment and Recommendations for
Improving the Performance of Waste Containment Systems.'' EPA/600/R-
02/099. Prepared by the Office of Research and Development.
December.
---------------------------------------------------------------------------

    Construction quality testing ensures that surface impoundment
construction has been performed in accordance with all relevant
technical specifications before any waste is accepted. EPA stated in
the proposal that collection of in-situ data from an operating surface
impoundment will generally be impracticable because of the potential to
disrupt the integrity of the liner, and some facilities agreed in their
comments. However, laboratory testing cannot account for operational
problems during construction that result in substandard conditions,
such as desiccation, cracking, poor bonding, and inconsistent
compaction of the liner. There are no standardized laboratory tests
designed to simulate a liner that has been poorly designed or
constructed. Therefore, without contemporaneous documentation that the
surface impoundment liner was well constructed, it will be too
difficult to confirm that any data subsequently collected for the
demonstration reliably represents actual liner conditions. In
particular, for soil liners that do not meet the thickness requirement
of the rule, field testing is likely the only reliable way to ensure
that construction has achieved a sufficiently low and consistent
hydraulic conductivity. Considerable guidance exists on factors that
must be addressed to ensure the quality of a liner, such as: the proper
thickness, compaction, moisture content, and density of compacted soil;
the in-situ hydraulic conductivity of compacted soil; protection of
soil from desiccation and freezing; placement of the geomembrane liner
without excessive waves, with a goal of ensuring intimate contact
between the liner and the underlying soil; and protection of
geomembranes from puncture by adjacent materials or equipment.
Altogether, this information provides evidence that the liner is well
constructed and can be reasonably simulated in a laboratory setting.
    EPA is finalizing a new requirement at Sec.  257.71(d)(1)(i)(C)
that facilities are required to provide documentation of the design
specifications for any engineered liner components (e.g., manufactured
geomembrane, mechanically compacted soil), as well as all data and
analyses the facility relied on when determining that the materials are
suitable for use and that the construction of the liner is of good
quality and in line with proven and accepted engineering practices.
8. Additional Release Pathways
    In the proposal, EPA stated that in some instances direct
infiltration to groundwater may not be the sole mechanism by which
unpermitted release of leachate from a surface impoundment occurs. It
is possible that additional, site-specific release pathways may exist
for some impoundments. For example, there may be lateral transport from
the surface impoundment directly into the water body driven in part by
the hydrostatic head within the surface impoundment. EPA listed
proximity to a water body, construction above grade, lack of a
geomembrane liner, and the presence of low conductivity soil beneath
the unit as factors that could contribute to such releases. EPA stated
that, if such conditions are present at a site, then the demonstration
would need to address whether such releases may occur and the potential
adverse effects on health or the environment associated with these
pathways. The same types of data collected to evaluate releases to
groundwater should also support evaluation of such pathways.
    EPA received no adverse comments on this topic. One commenter
affirmed that such pathways are possible and are a concern. No
commenters identified other relevant subsurface release pathways beyond
the one contemplated in the proposal.
    Upon further consideration, EPA now believes that this type of
release is already adequately addressed by the requirements of Sec.
257.96(a). Because this issue involves compliance with an aspect of the
2015 CCR Rule, EPA believes it is most appropriately addressed as part
of the application step. As clarified in the Phase One Rule, this
provision requires a facility to commence corrective action
``immediately upon detection of a release from a CCR unit'' for any
non-groundwater releases. 83 FR 11584 (March 15, 2018). Thus, the
existence of subsurface releases directly to surface water would
trigger immediate corrective action. Further, unlike groundwater, there
is no standardized

method to monitor the progression or effects of this type of release to
confirm that the unit remains protective. Therefore, if the design of a
surface impoundment cannot be shown to reliably prevent such releases,
it would be ineligible for an ALD.
    Therefore, EPA is finalizing a requirement at Sec.
257.71(d)(1)(i)(D) that facilities with surface impoundments located on
properties adjacent to a water body must demonstrate that there is no
reasonable probability that a complete and direct transport pathway
(i.e., not mediated by groundwater) could exist between the impoundment
and any nearby water body. If the potential for such releases is
identified, then the unit would not be eligible to submit a
demonstration. If ongoing releases are identified, the owner or
operator of the CCR unit must address these releases in accordance with
Sec.  257.96(a).

C. Alternate Liner Demonstration

    EPA proposed that the ALD must present evidence to demonstrate,
with a reasonable degree of certainty, that based on the construction
of the unit and surrounding site conditions, operation of the surface
impoundment will not result in groundwater concentrations above
relevant GWPS at the waste boundary.
    EPA proposed at Sec.  257.71(d)(1)(ii) that the liner
demonstrations must be certified by a professional engineer. Some
commenters requested that the qualifications necessary to certify the
ALD be broadened beyond professional engineers to include geologists
and hydrogeologists. The commenter noted that licensed professional
geologists or hydrogeologists are trained and experienced in
investigation and analysis of groundwater and subsurface contaminant
flow and chemistry. EPA previously considered this exact request and
rationale as part of the 2015 CCR Rule. The Agency concluded there
that, while some environmental professionals (e.g., hydrologists,
geologists) may be qualified to make certain certifications, EPA was
not convinced that either hydrologists or geologists licensed by a
state are held to the same standards as a professional engineer. 80 FR
21337 (April 17, 2015). One commenter requested that EPA use the term
``qualified professional engineer'' rather than ``professional
engineer,'' as this is the term that was used in the 2015 CCR Rule. EPA
agrees with this suggestion and will be finalizing the rule requiring
that certification must be provided by a ``qualified professional
engineer''.
    The qualified professional engineer must certify that the
demonstration package presents evidence to demonstrate that there is no
reasonable probability that peak groundwater concentrations that may
result from releases throughout the active life of the surface
impoundment will exceed GWPS at the waste boundary based on the
construction of the unit and surrounding site conditions.
    EPA proposed two lines of evidence for which site-specific data
must be collected and incorporated into the demonstration. These are
the characterization of site hydrogeology and the potential for
infiltration. EPA identified these lines of evidence because the
hydraulic conductivity of the engineered liner and/or naturally
occurring soil is expected to be the primary mechanism that will limit
release and transport of contaminants from the unit. These data will be
used to model the potential for the release of contaminants and their
transport through the environment. For each line of evidence, as well
as any other data and assumptions incorporated into the determination,
EPA proposed that the facility must include documentation on how the
data were collected and why these data and assumptions are believed to
adequately reflect potential contaminant transport at and around that
specific surface impoundment.
1. Line of Evidence #1--Characterization of Site Hydrogeology
    The first line of evidence that EPA proposed at Sec.
257.71(d)(1)(ii)(A) requires characterization of the variability of the
site-specific soil and hydrogeology that surrounds the CCR surface
impoundment. Some surface impoundments are located on soils that are
expected to have extremely low hydraulic conductivity. However, there
are concerns that heterogeneity within these soils may result in
preferential flow pathways that effectively negate the low conductivity
of the remaining soil. For example, many electric utilities are located
in close proximity to bodies of water. The flow path of these water
bodies is likely to have shifted over geologic time, which could result
in complex depositional environments with interconnected lenses of
sand. Therefore, the purpose of this first line of evidence is twofold:
to define the broader connectivity of higher conductivity soils that
might act as preferential flow pathways and to characterize the
variability of the soil to guide collection of samples for the second
line of evidence.
    EPA proposed that characterization of site hydrogeology must
include all of the following: (1) Measurements of the hydraulic
conductivity in the uppermost aquifer from existing monitoring wells
and discussion of the methods used to obtain these measurements; (2)
Subsurface samples collected to characterize site hydrogeology must be
located around the perimeter of the surface impoundment at a spatial
resolution sufficient to ensure that any regions of substantially
higher conductivity have been identified; (3) Conceptual site models
with cross-sectional depictions of site stratigraphy that include the
relative location of the surface impoundment (with depth of ponded
water noted), monitoring wells (with screening depths noted), and all
other subsurface samples used in the development of the models; (4)
Narrative description of site geological history; and (5) All data used
in the conceptual site model summarized into easily readable graphs or
tables. EPA did not receive any comments relevant to Sec.
257.71(d)(1)(ii)(A)(4). Therefore, EPA is finalizing this requirement
as proposed with updated numbering to reflect changes in the other
regulatory text paragraphs. Discussion of comments on other provisions
are provided in the following Units.
a. Measurements from Existing Wells
    EPA proposed at Sec.  257.71(d)(1)(ii)(A)(1) that the demonstration
must include measurements of the hydraulic conductivity in the
uppermost aquifer measured from existing monitoring wells and
discussion of the methods used to obtain these measurements.
    One commenter stated that EPA should consider modifying or removing
the requirement that uppermost aquifer hydraulic conductivity
measurements must be measured from existing monitoring wells. They
argued that there may be additional data points and locations that may
be more representative than conductivity measurements taken from the
existing well locations. The commenter requested that locations for
these measurements be determined by the technical team preparing the
demonstration and should not be limited to these prescriptive
locations.
    The waste boundary is the point of compliance for all GWPS. These
standards apply to all units subject to the existing regulations,
including those submitting an ALD. Thus, the hydrogeologic conditions
in the vicinity of the wells used to determine compliance are highly
relevant. However, Sec.  257.71(d)(1)(ii)(A)(1) only establishes a
minimum standard for the demonstration. Facilities can collect and
incorporate additional data beyond this minimum in the demonstration,
as

warranted to further delineate hydrogeologic conditions. Therefore, EPA
made no amendment to the rule language in response to this comment.
b. Sampling at the Perimeter of a Surface Impoundment
    EPA proposed to require that subsurface samples must be collected
to characterize site hydrogeology and must be located around the
perimeter of the surface impoundment at a spatial resolution sufficient
to ensure that any regions of substantially higher conductivity have
been identified. In the proposal, EPA acknowledged that some data may
already be available from previous investigations, such as sampling or
logging done during the installation of monitoring wells or other
subsurface evaluations. However, the Agency considered it likely that
additional data would be necessary to provide adequate coverage of the
subsurface.
    Environmental groups raised concerns that it would not be feasible
for an owner or operator to collect enough site-specific data to allow
for a determination that an existing alternate liner is protective. One
commenter stated that site characterization at the necessary spatial
resolution would require multiple rounds of sampling, might necessitate
installation of additional monitoring wells, and would require far
longer than allowed by this rule. Another went further and stated that
no characterization of a site's hydrogeology and potential for
infiltration will be able to prove that a nonconductive layer is
continuous under the entire ash pond.
    EPA agrees that it is critical to adequately characterize potential
transport beneath the unit but disagrees that it is not possible to
collect sufficient data to characterize subsurface transport. For the
subset of impoundments that rely on natural soils to limit contaminant
transport, it is improbable that any high-conductivity soils present
on-site are limited entirely to within the footprint of a unit. The
long-term movement of both water bodies and glaciers tend to leave
deposits all along the migration path. This is supported by
observations across a wide range of depositional environments that
layers of sand and clay are typically found in a ``shingled'' or
``laterally offset'' fashion, rather than as a ``layer cake'' with one
stacked neatly on top of the other.\14\ Thus, collection of samples
from around the perimeter is expected to provide reliable information
about both the variability of conditions underneath the impoundment and
the potential for transport away from the impoundment. Even if isolated
lenses of sand or other high-conductivity material were located
entirely beneath the impoundment, these disconnected deposits would not
negate the low conductivity of the surrounding clay because of a lack
of connectivity. Finally, the surficial geophysical methods referenced
by one of the same commenters can provide information on soils some
distance away from the point of measurement. Depending on the specific
geometry of a unit and the methods used, the data collected around the
perimeter of the unit can also provide substantial coverage of the
soils beneath the unit. Based on these facts, EPA concludes that data
collected from around the waste boundary can also provide reasonable
estimates of the variability beneath the unit for the purposes of an
alternate liner demonstration.
---------------------------------------------------------------------------

    \14\ U.S. EPA. 2017. ``Best Practices for Environmental Site
Management: A Practical Guide for Applying Environmental Sequence
Stratigraphy to Improve Conceptual Site Models.'' EPA/600/R-17/293.
Prepared by the Office of Research and Development. Cincinnati, OH.
September.
---------------------------------------------------------------------------

    Although fieldwork may take some time, it will not begin from
scratch. Facilities allowed to progress to the demonstration step will
have already confirmed that there is adequate subsurface
characterization available to appropriately site the existing
groundwater wells. These data will inform subsequent sampling efforts.
In the proposal, EPA contemplated the potential for this line of
evidence to also identify the need for additional wells to address
previously unidentified regions of high conductivity soil. However, the
finalized application step requires documentation that the existing
network is sufficient to ensure detection of contamination in the
uppermost aquifer. Therefore, this line of evidence will not involve
the time-consuming process of installing and sampling new monitoring
wells. The standardized geophysical survey methods discussed both in
the proposal and raised by commenters can be conducted within the
required timeframe, even if more than one round of data collection is
ultimately required.
    Therefore, EPA is finalizing the requirement at Sec.
257.71(d)(1)(ii)(A)(2) without change from the proposal. The final rule
requires that measurements of the variability of subsurface soil
characteristics must be collected from around the perimeter of the
impoundment to identify any regions of substantially higher hydraulic
conductivity.
c. Sampling Methods
    In the proposal, EPA discussed that traditional geologic mapping,
that relies primarily on the Unified Soil Classification System, has
been found to underestimate the prevalence and interconnectedness of
soil deposits that may act as preferential flow pathways. EPA cited to
a practical guide on the use of environmental sequence stratigraphy and
facies models to aid in characterization of subsurface
heterogeneity.\15\ EPA noted that there are a number of methods
available that can provide useful data at the necessary spatial
resolution, such as direct-push logging (e.g., cone penetration test)
and borehole geophysical logging. However, EPA did not propose the use
any specific methods, nor did the Agency place explicit restrictions on
the types of methods available.
---------------------------------------------------------------------------

    \15\ U.S. EPA. 2017. ``Best Practices for Environmental Site
Management: A Practical Guide for Applying Environmental Sequence
Stratigraphy to Improve Conceptual Site Models.'' EPA/600/R-17/293.
Prepared by the Office of Research and Development. Cincinnati, OH.
September.
---------------------------------------------------------------------------

    Several industry commenters and one environmental group expressed
concern that the proposal unnecessarily required invasive sampling
methods to collect the necessary data on conditions below the ground
surface. Multiple commenters identified specific methods, such as
electrical-resistivity tests, as alternate methods that could provide
relevant information. One commenter further pointed to the Interstate
Technology and Regulatory Council website on advanced site
characterization tools.\16\
---------------------------------------------------------------------------

    \16\ https://asct-1.itrcweb.org/.
---------------------------------------------------------------------------

    EPA acknowledges that the language used in the proposal could be
taken to imply that invasive sampling is the only type of method
allowed for this line of evidence, but EPA did not intend to restrict
the methods available for use in this way. EPA agrees that surficial
(or non-invasive) sampling can provide useful information, though these
methods often require correlation or a combination of qualitative and
quantitative interpretation to properly interpret the data. These
surface geophysical tools tend to be most powerful when used in
combination with other methods.
    Therefore, for clarity, EPA is finalizing an amended version of
Sec.  257.71(d)(1)(ii)(A)(3). The final rule specifies that
characterization of subsurface variability must be conducted with
recognized and generally accepted methods. Facilities must document how
the combination of methods relied upon provides reliable

information at a spatial resolution necessary to adequately
characterize the variability of subsurface conditions that will control
contaminant transport.
d. Sample Depth and Spacing
    EPA discussed in the preamble of the proposed rule that samples
should extend down to the top of the natural water table or at least 20
feet beneath the bottom of the nearest water body (to identify
potential for upwelling), whichever is greater, to ensure that any
potential preferential flow pathways have been identified. EPA also
discussed that the initial soil samples collected around the perimeter
of the unit should be spaced at a distance no greater than 200 feet
apart in low-conductivity soils. This distance reflects recommendations
by the U.S. Department of Transportation (U.S. DOT) for the
characterization of unknown subsurface environments.\17\ If there is
indication from the site history, collected soil samples, or other
sources that high-conductivity deposits may be present at widths
narrower than 200 feet, then even finer sample spacing may be
warranted. EPA stated that the demonstration must substantiate why the
number and types of samples collected are sufficient to capture any
heterogeneity of the subsurface and why the data used to estimate
contaminant fate and transport through the subsurface are
representative of the variability identified. If regions of higher
conductivity are present around the site, the potential impacts of
preferential flow on groundwater concentrations will need to be
considered in the demonstration. Furthermore, if regions of
preferential flow are identified in otherwise low-conductivity soils
that are not adequately captured by the existing monitoring well
network, then re-evaluation of the placement of monitoring wells around
the waste boundary would be warranted to address these gaps.
---------------------------------------------------------------------------

    \17\ U.S. DOT. 2006. ``Geotechnical Aspects of Pavement:
Reference Manual/Participant Workbook.'' FHWA NHI-05-037. Prepared
by the Federal Highway Administration. Washington, DC. May.
---------------------------------------------------------------------------

    Many commenters argued that the depth and spacing of samples
discussed in the preamble was overly strict. No commenters raised issue
with the rationale for the proposed sample depths. However, one
commenter argued that characterization down to the groundwater table is
unnecessarily burdensome for sites with deep groundwater. This
commenter stated that if the first 100 feet of the soil overlying the
aquifer is not sufficient to prevent contamination of groundwater, then
the next 100 feet is unlikely to alter that fact. Several commenters
raised questions about the rationale for the proposed sample spacing.
One commenter pointed out that EPA has previously written that the
number of borings necessary to characterize soils is dependent on the
geological complexity, size, potential areal extent of a release, and
the importance of defining small-scale discontinuities in formation
materials.\18\ Many others pointed out that the U.S. DOT guidance
referenced in the preamble is not directly related to waste disposal
and that the guidance also states that the spacing and depth of the
borings should be based on an evaluation of available information.\19\
Most of these commenters requested further justification for the
criteria for sample spacing.
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    \18\ U.S. EPA. 1989. ``Interim Final RCRA Facility Investigation
(RFI) Guidance Volume II Of IV: Soil, Ground Water And Subsurface
Gas Releases.'' EPA 530/SW-89-031. OSWER Directive 9502.00-6D.
Prepared by the Office of Solid Waste. Washington, DC. May.
    \19\ U.S. DOT. 2006. ``Geotechnical Aspects of Pavement.'' FHWA
NHI-05-037. Prepared by the Federal Highway Administration.
Washington, DC. May.
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    EPA generally agrees with commenters that the exact depth and
spacing of samples should be informed by site conditions. The
discussion provided in the proposal was intended to define an initial
depth and spacing of samples that would ensure identification of
subsurface variability at these sites, not to impose this exact
sampling regime at every site. Instead, EPA intended for facilities to
document why the number and types of samples collected are sufficient
to capture the heterogeneity of the subsurface if sampling deviated
from these specifications. Such documentation would not provide
additional useful information if all sampling was pre-determined. EPA
believes these baseline requirements are warranted because there will
be no time for facilities to fill data gaps in the characterization of
the site if a demonstration is found to be insufficient. These
requirements also help clarify the level of documentation expected as
part of the demonstration.
    As discussed, the 200 feet spacing was based on a U.S. DOT
publication that provides a review of recommended practices for
installation of pavement from a geotechnical perspective based on
guidelines from textbooks, several state agencies, and the Federal
Highway Administration. Commenters are correct that a primary focus of
the publication is the stiffness and strength of the soil; however, it
also accounts for soil permeability and the presence of
discontinuities, fractures, and fissures of subsurface formations,
which are relevant to the demonstration. The minimum spacing was
selected from this publication based on the professional judgement of
Agency staff, who have considerable experience on this topic from work
at cleanup sites across the country. For all these reasons, EPA
continues to believe that selected minimum spacing is relevant and
appropriate. Notably, no commenters indicated that an initial 200 feet
spacing was too wide apart to effectively characterize soil, nor did
any commenters identify another standard believed to be more directly
applicable.
    In response to these comments, EPA is finalizing Sec.
257.71(d)(1)(ii)(A)(4) with amendments to make clear that facilities
must document why the specific number, depth, and spacing of samples
collected are sufficient to reflect the variability of subsurface soils
if 1) samples are advanced to a depth less than the top of the
groundwater table or 20 feet beneath the bottom of the nearest water
body, whichever is greater, or 2) samples are spaced farther apart than
200 feet around the surface impoundment perimeter.
e. Conceptual Model
    EPA proposed at Sec.  257.71(d)(1)(ii)(A)(3) that as part of the
first line of evidence, facilities must provide conceptual site models
with cross-sectional depictions of site stratigraphy that include the
relative location of the surface impoundment (with depth of ponded
water noted), monitoring wells (with screening depths noted), and all
other subsurface samples used in the development of the models.
    One commenter stated that the conceptual models should also include
``all relevant hydraulic information, including depth to saturated
zones, piezometric surface elevation, withdrawal points, recharge and
discharge areas. Based on groundwater and contaminant flow model
projections, the cross sections should extend a sufficient distance
from the surface impoundment to incorporate the influence of such
features on the site-vicinity hydrogeology.''
    EPA agrees that the depiction of site hydrology on these diagrams
is important. Although some data identified by the commenter are
already required as part of other diagrams, inclusion here allows both
an alternate view of these data (cross-sectional instead of aerial) and
a more complete understanding of the relationship between site geology
and subsurface transport. At the same time, requiring

facilities to depict the full variability of groundwater depth and flow
in these cross-sections could dramatically increase the total number of
diagrams needed without providing much additional clarity. Instead, EPA
believes it is more important for this set of diagrams to depict the
range of hydrologic conditions encountered at the site.
    Therefore, in response to these comments, EPA is finalizing Sec.
257.71(d)(1)(ii)(A)(5) with an amendment that each cross-sectional
diagram must also include demarcation of, at a minimum, (1) the upper
and lower limits of the uppermost aquifer across the site, (2) the
upper and lower limits of the depth to groundwater measured from
facility wells if the uppermost aquifer is confined, and (3) both the
location and geometry of any nearby points of groundwater discharge or
recharge (e.g., surface water bodies, wells) with potential to
influence groundwater depth and flow measured around the unit.
2. Line of Evidence #2--Potential for Infiltration
    The second line of evidence that EPA proposed at Sec.
257.71(d)(1)(ii)(B) would require evaluation of the potential for
infiltration through any liners and underlying soils that control the
release and transport of leachate by either in-situ sampling, or by
conducting an analysis of the soil-based liner and underlying soil of
the unit through laboratory testing. EPA discussed in the preamble that
the purpose of this line of evidence is to provide a reasonable
estimate of the rate at which contaminants may be released and
transported to groundwater over time. However, EPA also questioned
whether collection of in-situ data would be feasible for facilities.
    EPA received comments from multiple facilities agreeing that
collection of data from beneath the surface impoundment could be
unnecessarily onerous and may disturb the integrity of the surface
impoundment. One environmental group stated that field measurements of
hydraulic conductivity were preferable because laboratory measurements
have the potential to differ from field measurements. This commenter
stated that the hydraulic conductivity of geosynthetic clay liners can
be impacted by a variety of factors in the field that may not be
adequately addressed in the lab, citing to several studies purported to
raise concerns both that laboratory tests were unreliable and that the
leaching behavior of clays were too poorly understood to reliably
measure in the lab.
    EPA agrees with commenters who stated that in-situ analysis of
liner performance while the unit operates would be impracticable.
Installation of a leachate collection device, such as lysimeter,
beneath the impoundment to measure releases in real time risks
disruption of the liner. In addition, because the current state of the
liner cannot be directly observed or measured during operation, it is
not possible to determine whether such measurements reflect the long-
term interactions between the liner and CCR leachate. Therefore, EPA is
removing the provision that allowed for in-situ sampling of hydraulic
conductivity.
    EPA disagrees that the studies provided by the commenter raise
wider concerns about either the general reliability and reproducibility
of laboratory methods or the specific ability to accurately measure
hydraulic conductivity in a laboratory setting. The Agency's review of
the cited articles found that excerpts quoted by the commenter did not
fully reflect the context or conclusions of the studies, that the
conclusions the commenter had drawn from some studies were incorrect,
and that many of the studies cited had limited or unclear applicability
to CCR surface impoundments. Specifically:
     The first study quoted by the commenter evaluated the
precision among labs for hydraulic conductivity measurements of fine-
grained soils using Method C of ASTM D5084-10.\20\ From this study the
commenter drew the quote, ``many of the laboratories in the study did
not follow the test method precisely.'' However, the authors of this
study concluded that the variability of results between labs was not
sensitive to these deviations from protocol. Further, the authors found
that ``hydraulic conductivity can be measured within a factor of 2 for
the 10-\6\ cm/s range, a factor of 1.5 for the
10-\6\ cm/s range, and a factor of 4 for the
10-\9\ cm/s range.'' These results do not support wider
concerns about laboratory reproducibility raised by the commenter.
First, the commenter fails to acknowledge that measurement uncertainty
is an inherent part of any data collection effort and they provide no
evidence that field measurements would yield appreciably lower
variability. Second, the magnitude of variability identified in the
study is minor compared to the multiple orders of magnitude over which
soil conductivity can vary. Thus, this source of variability will
become less important in lower conductivity soils. Finally, the
commenter does not acknowledge that uncertainties can be managed within
an evaluation to ensure that long-term contaminant release and
transport are not underestimated. For example, under the requirements
of this rule, facilities are required to measure the hydraulic
conductivity of subsurface soils saturated with CCR leachate, which
will simulate the highest conductivity possible for that soil.
---------------------------------------------------------------------------

    \20\ Benson, C.H. and N. Yesiler, 2016. ``Variability of
Saturated Hydraulic Conductivity Measurements Made Using a Flexible-
Wall Permeametter,'' Geotechhnical Testing Journal. 39(3):476-491.
---------------------------------------------------------------------------

     A second study referenced by the commenter compared
concentrations in CCR leachate with two different EPA methods, the
synthetic precipitation leaching procedure (SPLP; Method 1312) and
Leaching Environmental Assessment Framework (LEAF, Method 1313).\21\
From this study the commenter pointed to the statement that ``SPLP
results were highly variable when compared to the LEAF data.'' The
commenter indicated that this was evidence that laboratory tests were
not reliable. EPA disagrees. The study authors discussed potential
causes of observed differences between the two methods, which they
attributed primarily to the different extraction acids used by the two
methods, a conclusion supported by the findings of previous studies.
This is reasonable because the two leaching tests are designed to
represent somewhat different environmental scenarios. There is no
indication that either method returned erroneous results for the
specified conditions. EPA has subjected the LEAF methods to extensive
inter-laboratory validation and has great confidence in the results of
these methods.\22\ The Agency has also emphasized that the data from
leaching tests must be considered carefully to ensure that the test
conditions provide relevant information about actual environmental
conditions. Therefore, the commenter's assertion that these results
raise concerns about the reliability of laboratory methods is
incorrect.
---------------------------------------------------------------------------

    \21\ da Silva, E.B., S. Li, L.M. de Oliveira, J. Gress, X. Dong,
A.C. Wilkie, T. Townsend, and S.Q. Ma. 2018. ``Metal Leachability
from Coal Combustion Residuals under Different pHs and Liquid/Solid
Ratios.'' Journal of Hazardous Materials. 341:66-74.
    \22\ U.S. EPA. 2012. ``Interlaboratory Validation of the
Leaching Environmental Assessment Framework (LEAF) Method 1313 and
Method 1316.'' EPA 600/R-12/623. Prepared by tthe Office of Research
and Development. September.
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     The commenter cited a number of studies as evidence that
in-situ conditions exist that cannot be reliably

measured. However, many of these studies do not directly address clay
liners or even waste disposal, focusing instead on issues such as
climate change. Others evaluated liners exposed to extreme conditions,
such as sustained operating temperatures above 100 [deg]F and high
ammonia concentrations. The commenter provides no indication beyond the
ancillary citations how these issues are germane. Nevertheless, the
commenter concluded that ``in-situ conditions are very complex and we
do not yet have enough understanding of how these complexities affect
CCR leachability to ensure that we make accurate models in the lab.''
Yet, this assertion does not comport with the available literature that
shows reasonable agreement can be achieved between field and lab
measurements when units are well constructed.\23\
---------------------------------------------------------------------------

    \23\ U.S. EPA. 2002. ``Assessment and Recommendations for
Improving the Performance of Waste Containment Systems.'' EPA/600/R-
02/099. Prepared by the Office of Research and Development.
December.
---------------------------------------------------------------------------

    EPA maintains that laboratory analysis is the preferred means to
measure hydraulic conductivity of soil for the purposes of an ALD.
Field analysis typically involves use of an infiltrometer or
permeameter to measure the rate that water infiltrates into the
uppermost layer of soil. These methods are generally not designed to
account for the complexities associated with this type of
demonstration. First, the soil to be tested may be located some
distance below the ground surface, which will be difficult to isolate
and reliably test in the field. Second, field tests are generally
designed to use water, rather than a high-ionic strength leachate. As a
result, these methods are not designed to collect the effluent needed
to track system chemistry. Third, the potentially long test run times
could make it difficult to control for environmental variables, such as
evaporation. Therefore, to ensure reliable implementation of test
methods and consistency between the various samples, EPA concludes that
all samples for hydraulic conductivity should be measured in a
controlled laboratory setting.
    Therefore, EPA is finalizing the requirement at Sec.
257.71(d)(1)(ii)(B) with an amendment that removes the option for in
situ sampling. The final rule now specifies that facilities must send
all samples of the soil-based liner components and/or naturally-
occurring soil for analysis under controlled conditions in a certified
laboratory. Samples must be analyzed using a recognized and generally
accepted methodology. Facilities must document in the demonstration how
the selected test method is designed to simulate field conditions
(e.g., hydraulic head, effective stress).
    In the proposal, EPA stressed that it is critical that laboratory
tests are designed to reflect site conditions to ensure the data
generated reflect real-world and long-term operating conditions. EPA
provided several examples of potentially relevant site conditions. EPA
received a number of comments related to several of these and other