elevations measured at monitoring wells inside Ash Pond 4 from January
1, 2016 through December 31, 2017 were on the order of 450 feet above
MSL (i.e., approximately 28 feet above the average elevation of the
CCR) centered on the central and southcentral portions of the
unit).\33\ Yet neither the approved Closure Plan nor any other document
in the record for the permit accounts for the approximately 28 feet of
groundwater present in the unit prior to closure, or describes any
engineering measures taken to eliminate the groundwater. The approved
Closure Plan states only:
---------------------------------------------------------------------------

    \33\ Tennessee Valley Authority. FY2018 Intermediate Inspection
of CCR Facilities. September 4, 2018; and Tennessee Valley
Authority. FY2017 Intermediate Inspection of CCR Facilities.
December 15, 2017.

    Final Closure of the Ash Pond 4 requires following general
tasks: . . . Begin decanting the Ash Pond 4 using pumps and existing
siphons. Discharged water will be monitored throughout decanting
operations to maintain compliance with NPDES [National Pollutant
---------------------------------------------------------------------------
Discharge Elimination System] permitted limits.

TVA Closure Plan, pp 6-7. As EPA has previously explained, Sec.
257.102(d)(2)(i) establishes a clear standard to be met: ``free liquids
must be eliminated.'' \34\ The regulation further specifies how this
standard is to be met: by ``removing liquid wastes or solidifying the
remaining wastes and waste residues.'' Id. In situations such as this,
where the waste in the unit is inundated with groundwater, the
requirement to eliminate free liquids thus obligates the facility to
take engineering measures necessary to ensure that the groundwater,
along with the other free liquids, has been permanently removed from
the unit prior to installing the final cover system. See, 40 CFR
257.102(d)(2)(i). Yet neither the Closure Plan that ADEM approved nor
the permit ADEM issued contained any such requirements.
---------------------------------------------------------------------------

    \34\ See, U.S. EPA. Denial of Alternative Closure Deadline for
General James M. Gavin Plant, Cheshire, Ohio. November 18, 2022. pp
14-42.
---------------------------------------------------------------------------

    Moreover, it is clear from the post-closure 2019-2021 Annual
Inspection Reports that whatever measures were taken as part of closure
did not actually eliminate free liquids from Ash Pond 4. These reports
document average groundwater elevations within the Ash Pond that
significantly exceed 422 above MSL. And the most recently reported
groundwater elevation measurements in 2021 reported nearly all
groundwater elevation at values of 425 to 440 ft above MSL, except for
a thin strip of lower ground water elevations near the extreme eastern
margin of the impoundment, again with a small lobe-shaped area of lower
levels (421.5 to 424.2 ft above MSL) projecting a short distance into
the central part of the unit. All of this information was available
before ADEM issued the permit in October 2022, yet the permit was
issued, essentially approving closure with CCR that will remain
saturated by groundwater, with no engineering measures to limit
groundwater from continually flowing into and out of the unit.
    A further concern is that, given the groundwater levels that
continue to be measured in the unit, it is not clear that the remaining
wastes have been stabilized sufficiently to support the final cover
system, as required by Sec.  257.102(d)(2)(ii). What is clear, however,
is that neither the approved Closure Plan nor ADEM's permit provides
any details on how this performance standard was met, given that
groundwater continues to flow into and out of the unit from the sides
and bottom. The approved Closure Plan merely summarizes the Sec.
257.102(d)(2) performance standards, and contains, for example, no
description of how, if at all, the groundwater levels would be affected
by any of the dewatering activities associated with unit closure.
Consequently, EPA is proposing to determine that the approval of the
Closure Plan, and subsequently the unit closure itself, in the absence
of such information, and the failure to include measures in the permit
requiring TVA to remedy the omission is not consistent with Sec.
257.102(d)(2)(ii).
    EPA was also unable to find any description in the ADEM approved
Closure Plan or any other permit document of engineering measures that
TVA took to ``control, minimize, or eliminate, to maximum extent
feasible'' either the post-closure infiltration of the groundwater into
the waste or the post-closure releases of CCR or leachate to the
groundwater, as a consequence of the groundwater that continues to
infiltrate into and be released from the impoundment from the sides and
bottom of the unit. 40 CFR 257.102(d)(1)(i). Based on the data and
analyses described above, groundwater continues to infiltrate into the
unit and yet the only measures described in the Closure Plan and the
permit are those taken to facilitate consolidation and cap
construction. In essence, this means the Ash Pond will continue
releasing CCR contaminants indefinitely past the waste boundary unless
TVA takes additional actions that are not required by or explained in
the permit. Given that

reasonably available engineering measures exist that can prevent, or at
least control, the flow of groundwater into the Ash Pond (and
consequently the releases out of the Ash Pond), such as physical
barriers or hydraulic containment systems, EPA cannot conclude that
TVA's Closure Plan adequately describes how the closure work will meet
the requirement to ``control, minimize or eliminate, to the maximum
extent feasible'' post-closure infiltration into the unit and post-
closure releases of CCR or leachate to the groundwater. EPA is
proposing to determine that the permit's exclusive reliance on
engineering measures related to the consolidation and cap construction
is inconsistent with Sec.  257.102(d)(1)(i).
    In addition, EPA was unable to identify any description in the
Closure Plan narrative of how TVA will ``preclude the probability of
future impoundment of water, sediment, or slurry.'' 40 CFR
257.102(d)(1)(ii). The continued presence of groundwater in the unit
constitutes the impoundment of water, and in the absence of any
engineering measures, such as a slurry wall, there are no intrinsically
obvious facts to demonstrate that this performance standard has been
met. Finally, the Closure Plan contains no discussion of how the
closure activities will minimize the need for additional maintenance of
the Ash Pond beyond a brief discussion of the final cover system. 40
CFR 257.102(d)(1)(iv).
    EPA raised these issues to ADEM in comments on the draft Colbert
permit. In response, ADEM did not dispute EPA's conclusion that CCR in
Ash Pond 4 remains saturated by groundwater. Instead ADEM stated that
EPA's comments were based on a misinterpretation of the Federal
regulations, raising three specific interpretations of the regulations
that EPA has previously rejected. First, ADEM stated that ``the Federal
CCR regulations do not require that the closure account for groundwater
levels either before or after closure.'' Rather they claim the only
requirements relevant to groundwater are the location restrictions
applicable to new or operating units in Sec.  257.60 for an operating
unit.\35\ To support this point ADEM argues that Sec.  257.102(d)(1)(i)
does not refer to groundwater. Second, ADEM argues that the Federal
standards have been met because Colbert has installed a cover system
that meets the standard in Sec.  257.102(d)(3), and the facility has
complied with all of the requirements in the general performance
standard relating to ``infiltration.'' The State supports this claim by
pointing to the absence of specific requirements for an infiltration
layer or barrier along the sides or bottom of a CCR unit, and by
defining ``infiltration'' to refer exclusively to vertical infiltration
from the surface, e.g., as rainwater entering through the cover system.
Finally, ADEM states that ``In the event that it is determined that the
closure activities conducted at Ash Disposal Area 4, as described
above, are insufficient to prevent further groundwater contamination,
additional controls or methods will be considered and addressed through
the ongoing Assessment of Corrective Measures (ACM) and selection of a
final remedy,'' that is, as part of corrective action.
---------------------------------------------------------------------------

    \35\ Letter from Stephen Cobb to Carolyn Hoskinson, Responding
to EPA Comments on Proposed Permit for the Tennessee Valley
Authority Colbert Fossil Plant. October 27, 2022. Enclosure 1, page
6.
---------------------------------------------------------------------------

    EPA has explained, at length, that a closed, unlined impoundment,
where the CCR remains in groundwater several feet deep because the
facility failed to take any reasonably available engineering measures
to prevent, or at least control, the flow of groundwater into the unit
(and consequently the releases out of the unit), does not meet the
requirements of Sec.  257.102(d).\36\ Specifically, in the final
decision denying an extension under Part A for Gavin Generating
Station, EPA expressly rejected the various interpretations of the
regulatory text that ADEM offers in its October 27 letter.
Specifically, EPA rejected the claim that the Federal closure
regulations do not require a facility to address groundwater in the
impoundment as part of closure. As noted above, based on the regulatory
terms, the structure, and context in which the terms are employed, as
well as the dictionary definitions of ``liquid,'' and the fact that
nothing in the regulatory definition limits the source of the liquid,
EPA considers groundwater to be a ``liquid'' under the existing
regulation. See, Gavin Final Denial, p, 34; Response to Comments (RTC)
on Gavin Proposed Denial, pp. 42-43, 53-58, 76.\37\ Moreover, the
source of the liquid is not important with respect to its basic and
fundamental designation as a liquid. It therefore does not matter
whether the liquid in the surface impoundment comes from the rain,
waters the facility deliberately places in the unit, floodwaters from
an adjacent river, or from groundwater--all are liquids, and once
present in the unit, they have the same potential to create leachate
(another type of liquid), as well as to contribute to hydraulic head
and drive flows driven by hydraulic gradients, and potentially
destabilize the cover system.
---------------------------------------------------------------------------

    \36\ U.S. EPA. Denial of Alternative Closure Deadline for
General James M. Gavin Plant, Cheshire, Ohio. November 18, 2022. pp
14-42.
    \37\ U.S. EPA. Denial of Alternative Closure Deadline for
General James M. Gavin Plant (Cheshire, Ohio) Response to Comments
on Proposed Denial (Docket ID No. EPA-HQ-OLEM-2021-0590). November
2022.
---------------------------------------------------------------------------

    EPA also explained its decision to rely on the plain language
meaning of ``infiltration,'' explicitly rejecting the interpretation
that the term refers only to the vertical migration of liquid through
the cover system. See, Gavin Final Denial, pp 34-38; RTC pp. 38-47.
Finally, EPA rejected the interpretation that under part 257 risks from
a CCR unit submerged in groundwater are properly addressed exclusively
as part of corrective action. Gavin Final Denial, pp. 41, RTC, pp 65-
68, 102. Accordingly, EPA is proposing to determine that ADEM's permit
approved a closure of Ash Pond 4 that is not consistent with Sec.
257.102(d).
    Because Alabama interprets its regulations to impose different
requirements than the Federal regulations in part 257, EPA must
determine that the State's requirements are ``at least as protective
as'' the Federal requirements in order to approve the program. 42
U.S.C. 6945(d)(1)(B)(ii). All the information available to EPA supports
a conclusion that the closure approved in the Colbert permit is
significantly less protective than a closure that meets the
requirements under the Federal CCR regulations. Simply put, this is
because allowing groundwater to continue flowing through the waste
indefinitely will not protect human health and the environment. As
discussed at length in 88 FR 32008-32012 (May 18, 2023), there are
several ways in which the failure to remove CCR from the water table as
part of closure can result in significantly higher risks than a
comparable closure where waste no longer remains in contact with the
water table.
    The Electric Power Research Institute (EPRI), a coal industry
analytical group, reached similar conclusions in a report issued in
2006, finding that ``[c]aps are not effective when CCP is filled below
the water table, because groundwater flowing through the CCP will
generate leachate even in the absence of vertical infiltration through
the CCP.'' 38 39

Similarly, an earlier EPRI study examined the dewatering of three
sites, two with ash situated above the water table and one with ash in
contact with groundwater. The study concluded: ``[T]he existence of
saturated ash will greatly reduce the effectiveness of any cap design
when the facility is underlain by geologic materials with high
hydraulic conductivity, because groundwater will continue to leach ash
constituents.'' \40\ The fact that coal ash is in contact with
groundwater can reduce the effectiveness of dewatering as well:
``[W]hen ash remains below the water table, dewatering may be less
effective because groundwater continues to leach constituents from the
saturated ash, particularly if the impoundment is underlain by geologic
media with relatively high rates of groundwater flow. In the case of
[the studied site], concentrations increased because groundwater
contact time with the saturated ash increased when the hydraulic
gradient of the pond was removed.''
---------------------------------------------------------------------------

    \38\ CCP means ``coal combustion product,'' another term for
CCR.
    \39\ Electric Power Research Institute. Groundwater Remediation
of Inorganic Constituents at Coal Combustion Product Management
Sites, Overview of Technologies, Focusing on Permeable Reactive
Barriers. Technical Report. 2006. 3-6.
    \40\ Electric Power Research Institute. Evaluation and Modeling
of Cap Alternatives at Three Unlined Coal Ash Impoundments.
Technical Report. 2001.1005165.
---------------------------------------------------------------------------

    Finally, EPA is proposing to determine that the record fails to
support a finding that ADEM's alternative approach of relying on
corrective action to impose additional controls through the ongoing ACM
and selection of a final remedy will be as protective as the Federal
requirements. As discussed previously, data that was available at the
time of permit issuance documents that groundwater elevations remain
within the Ash Pond over three years after closure was completed, yet
the permit that ADEM issued is silent on the need to address this as
part of the corrective action process. Moreover, as discussed in the
next section, EPA has serious concerns about the protectiveness of the
corrective action at Colbert that ADEM is overseeing; for example, it
has been three years since TVA posted its initial ACM, and the facility
has still not selected a remedy. EPA is aware of no information to
support a conclusion that continuing to allow saturated CCR to remain
in Ash Pond 4 while TVA delays corrective action will protect human
health or the environment, and ADEM has offered no explanation to
support a conclusion that it is.
    Accordingly, EPA is proposing to determine that the permit for the
Colbert Plant does not require TVA to achieve compliance with either
Sec.  257.102(d) or with alternative State standards that EPA has
determined to be at least as protective.
b. Groundwater Monitoring and Corrective Action Issues
i. Summary of Federal Requirements
    The objective of a groundwater monitoring system is to characterize
groundwater to determine whether it has been contaminated by the CCR
unit being monitored. This begins in detection monitoring, by
conducting statistical comparisons between (1) The background level of
a constituent measured in one or more upgradient wells, and (2) The
level of that same constituent in a downgradient well. If the
concentration of the constituent in the downgradient well is higher
than the background concentration by a statistically significant
amount, (i.e., a statistically significant increase (SSI) over
background has been detected), this provides evidence of a potential
release from the unit. After an SSI, assessment monitoring is required
for additional constituents, and the concentrations of each of those
constituents at downgradient wells are compared to a groundwater
protection standard established for each constituent (either background
level or a regulatory limit). Prompt contaminant detection is important
in order for corrective measures to be developed to stop migration of
contaminants as soon as possible.
    To ensure detection of a release, the regulations establish a
general performance standard that all groundwater monitoring systems
must meet: all groundwater monitoring systems must consist of a
sufficient number of appropriately located wells that will yield
groundwater samples in the uppermost aquifer that represent the quality
of the background groundwater and the quality of groundwater passing
the downgradient waste boundary, monitoring all potential contaminant
pathways. 40 CFR 257.91(a)(1) and (2). Because hydrogeologic conditions
vary so widely from one site to another, the regulations do not
prescribe the exact number, location, and depth of monitoring wells
needed to achieve the general performance standard. Rather the
regulation requires installation of a minimum of one upgradient and
three downgradient wells, as well as any additional monitoring wells
necessary to achieve the general performance standard of accurately
representing the quality of the background groundwater and the
groundwater passing the downgradient waste boundary, monitoring all
potential contaminant pathways. 40 CFR 257.91(c)(1) and (2). The
number, spacing, and depths of the monitoring wells must be determined
based on a thorough characterization of the site, including a number of
specifically identified factors relating to the hydrogeology of the
site (e.g., aquifer thickness, groundwater flow rates and direction).
40 CFR 257.91(b). Groundwater elevation measurements must be obtained
around the unit(s) at sampling events over time to characterize
groundwater flow direction and identify seasonal and temporal
fluctuations. 40 CFR 257.91(b). Further, any facility that determines
that the regulatory minimum number of wells is adequate to meet the
performance standard must document the factual basis supporting that
determination. 40 CFR 257.91(f). In essence, the regulation establishes
a presumption that the minimum of one upgradient and three downgradient
wells is not sufficient, and it requires the facility to rebut the
presumption in order to install only this minimum. See, 80 FR 21399.
The number and placement of the monitoring wells is critical to proper
characterization of the groundwater.
    The Federal CCR regulations establish a phased approach to
monitoring. The first phase is detection monitoring where ``indicator''
constituents are monitored to determine whether groundwater is
potentially being contaminated. In selecting the parameters for
detection monitoring, EPA chose constituents that are present in CCR
and would rapidly move through the subsurface, and thus provide an
early indication of other contaminants that may be migrating from the
CCR units. See, 80 FR 21397. The constituents that are monitored in
detection monitoring are listed in Appendix III to 40 CFR part 257.
    After groundwater samples are collected during each monitoring
event, the samples are sent to a laboratory for analysis to determine
constituent concentrations. Once the facility has the analytical
results, it must conduct statistical analyses to determine the
background level of each constituent in upgradient groundwater for
comparison with data from downgradient compliance wells. This stage is
also critical, as even a sufficient number of properly placed wells
will not provide adequate characterization if the sampling and analysis
of data are not properly conducted. In order for upgradient groundwater
quality to be accurately characterized, the statistical approach must
be appropriate for site conditions and the data sets obtained. To this
end, the regulations require an owner or operator to select a
statistical approach and meet the performance

standards applicable to that approach when analyzing the data. 40 CFR
257.93(f)-(g).
    If a facility determines that there is an SSI over background
levels for one or more of the constituents in Appendix III at a
monitoring well at the downgradient waste boundary, there is an
opportunity to complete an alternate source demonstration (ASD) showing
that a source other than the unit (i.e., an alternate source) was the
cause of the SSI. 40 CFR 257.94(e)(2). A successful ASD must be
sufficient to rebut the presumption that the CCR unit is the source of
the SSI in a downgradient well of a properly designed groundwater
monitoring network by demonstrating that a source other than the CCR
unit is responsible for the SSI. An ASD requires conclusions that are
supported by site-specific facts and analytical data in order to rebut
the site-specific monitoring data and analysis that resulted in an SSI.
Speculative or theoretical bases for the conclusions are insufficient.
If a successful ASD for an SSI is not completed within 90 days, an
assessment monitoring program must be initiated. Id.
    In assessment monitoring, facilities are required to monitor for
additional constituents of concern, which are listed in appendix IV to
part 257. Whenever assessment monitoring results indicate a
statistically significant level (SSL) exceeding the groundwater
protection standard has been detected at a downgradient well for any of
the Appendix IV constituents, the facility must start the process for
cleaning up the contamination by characterizing the nature and extent
of the release and of site conditions that may affect the cleanup, and
by initiating an assessment of corrective measures.
    As discussed in Unit III.B of this preamble and TSD Volume III,
Alabama adopted regulations that mirror the Federal CCR regulations.
ii. TVA Colbert Groundwater Monitoring Issues
    ADEM approved the Groundwater Monitoring Plan (GWMP) dated December
10, 2021, and incorporated the approved plan into the Final Permit.\41\
Once ADEM approved and adopted TVA's GWMP into the permit, the GWMP,
rather than the referenced State regulations, became the State
requirements with which TVA is required to comply. After reviewing the
GWMP and all the materials in the permit record, EPA is proposing to
determine that the groundwater monitoring network that ADEM approved is
less protective than the Federal regulations in several regards. As
discussed below and in the technical support document, EPA identified a
number of deficiencies in the approved monitoring network.
---------------------------------------------------------------------------

    \41\ Alabama Department of Environmental Management. Colbert
Fossil Plant Coal Combustion Residual Permit. Permit No. 17-11,
October 25, 2022. Section V.A., specifying that ``The Permittee
shall install and/or maintain a groundwater monitoring system,
identified in Table 1, as specified in 335-13-15-. 06(2) and the
approved groundwater monitoring plan.''
---------------------------------------------------------------------------

    First, EPA is proposing to determine that the approved monitoring
system inappropriately includes numerous monitoring wells located
beyond the waste boundary, as well as an insufficient number of
monitoring wells at necessary locations and vertical depths to ensure
that all potential contaminant pathways have been monitored. In
addition, EPA has identified critical deficiencies in the construction
of a significant number of the bedrock monitoring wells that call into
question the accuracy of the monitoring data. As a consequence, EPA is
proposing to determine that ADEM's Final Permit fails to require TVA to
``install a groundwater monitoring system that. . .accurately
represent[s] the quality of the groundwater passing the waste boundary
of the CCR unit, [and to monitor] all potential contaminant pathways.''
40 CFR 257.91(a)(2).
(1) ADEM Issued a Final Permit That Approved the Bedrock Wells To Not
Be Installed at the Waste Boundary in Accordance With Sec.  257.91(a)
    The Federal CCR regulations require that a downgradient monitoring
system ``be installed at the waste boundary that ensures detection of
groundwater contamination in the uppermost aquifer,'' and define the
uppermost aquifer as ``the geologic formation nearest the natural
ground surface that is an aquifer, as well as lower aquifers that are
hydraulically interconnected with this aquifer within the facility's
property boundary.'' 40 CFR 257.53, 257.91(a)(2). The cross sections
and boring logs that were included as attachments to the Permit
Application confirm that the unconsolidated and underlying limestone
aquifers are hydraulically interconnected and communication via
vertical migration can occur. The hydraulic connection between the
Tuscumbia limestone aquifer, and the Tennessee River/Pickwick Reservoir
and Cane Creek, as well as the hydrogeologic continuum between the
Tuscumbia limestone and the overlying epikarst, residuum, and alluvial
units of the upper aquifer system, all indicate that the Tuscumbia is
an integral part of the composite uppermost aquifer system.
Accordingly, the entire horizontal length along the CCR unit must be
monitored in all hydrogeologic units present, alluvium, residiuum,
epikarst, and bedrock in accordance with Sec.  257.91.
    The approved GWMP includes bedrock monitoring wells COF-111BR, COF-
112BR, COF-113BR, COF-114BR, CA17B, CA30B, MC1, MC5C, and COF-108BR
(future installation), CA6 (background), and COF-116BR (background) as
part of the groundwater monitoring system. However, none of these
bedrock wells are located at the downgradient waste boundary as
expressly required by Sec.  257.91(a)(2). Instead, they are located
hundreds of feet away from this boundary. Among the wells that monitor
bedrock, only COF-111BR is located adjacent to the downgradient (east)
side of the unit and the other downgradient open-borehole bedrock wells
are located hundreds of feet to the east, and in many cases on the
other side of Cane Creek.
    Another systemic issue is that the bedrock wells were installed as
open-borehole completions with long permanently grouted surface
casings, and as a consequence have significant potential to
systemically exclude zones that have been ``cased off'' from the
monitoring well network. Permanent steel casing installations range
from 14.6 to 76.0 feet in length for in-program wells. These cased off
intervals represent potential data gaps, depending on the circumstances
and geology local to that specific region of the unit. As a highly
relevant example, well COF-111 is screened from 9-19 feet below ground
surface (bgs). The open interval for the adjacent well pair, COF-111
BR, is 76-126 ft bgs. This results in a 57-foot vertical gap at a
critical location adjacent to the unit's downgradient boundary, where
the groundwater quality is entirely unmonitored. This is significant
because the failure to monitor in the variable and significant zone of
transition from uppermost alluvium to residuum, epi-karst, and finally
to ``unweathered'' limestone would be a significant and systemic data
gap in potential contaminant pathways. Accordingly, EPA is proposing to
determine that ADEM has approved a monitoring plan with an insufficient
number of monitoring wells at necessary locations and vertical depths
to ensure that all potential contaminant pathways have been monitored.

(2) ADEM Approved Wells That Were Not Constructed in Accordance With
Sec.  257.91(e), and as a Consequence the Monitoring System Does Not
Accurately Represent the Quality of Groundwater Flowing From Ash Pond 4
    The Federal regulations provide that ``monitoring wells must be
cased in a manner that maintains the integrity of the monitoring well
borehole.'' 40 CFR 257.91(e). Integrity of the monitoring well borehole
includes all elements of the well within and including the borehole
itself. Such elements include the surface casing, generally intended to
isolate deeper geologic materials (commonly consolidated materials,
i.e., bedrock) from overlying unconsolidated materials and associated
groundwater, but also the filter pack, bentonite and grout seals,
screened intervals, riser pipe, and other constructed monitoring well
elements internal to the borehole used to isolate and ensure the
integrity of the sampling interval (e.g., screened interval). The
integrity of these elements individually and as an integrated system is
essential to meeting the performance standards in Sec.  257.91(a), (b),
and (e).
    As noted in ADEM's October 27, 2022 letter, these installations
included installation of a permanently grouted surface casing. ADEM
further indicated Rotosonic drilling methods were used to identify the
first three-to five-foot zone of unweathered material, and that a
casing was installed from this depth to the ground surface. It should
be noted that Rotosonic drilling can be a disruptive process that may
not result in full recovery of undisturbed samples of soil or bedrock.
For this reason, absent any additional information, the use of the
Rotosonic method as a tool for discriminating between weathered,
partially weathered, and unweathered bedrock, must be used with care,
particularly if sample materials are altered, pulverized, or otherwise
destroyed or obfuscated by the process of drilling as indicated by a
``no recovery'' zone or interval.\42\ In a variable zone of transition
from weathered material (residuum) to unweathered bedrock (in this case
limestone), recovered samples from each type of material would likely
be affected by the drilling process to some degree, and most competent
intervals are often preserved to a greater degree than decomposed or
partially decomposed intervals. In such a context, absent documentation
demonstrating a continuous core sample from the interval in question,
with full recovery, which penetrates and unequivocally identifies the
interface between weathered and unweathered material, it would not be
possible to confirm that any missing sample intervals did not simply
represent voids or other potentially permeable zones. The potential to
mischaracterize three-to five-foot zones as ``competent and
unweathered'' on the basis of an incomplete sequence of samples
therefore appears to be substantial. It should therefore be noted that
in this context a three-to-five-foot penetration into ``unweathered''
bedrock would generally not be considered a ``conservative'' approach,
absent additional information validating the integrity of the casing
seal and its effectiveness in isolating the ``unweathered'' bedrock
interval from the overlying materials. In such a scenario, at best, the
penetration of just a 3- to 5-foot interval of ``unweathered'' bedrock
with variably weathered materials just above introduces uncertainty
with respect to the integrity and effectiveness of the casing in
isolating the open interval from groundwater in the overlying residuum
and epikarst. Based on information provided, it is not clear how the
approach (as described) can be demonstrated to have achieved the
performance criteria outlined in Sec.  257.91(e).
---------------------------------------------------------------------------

    \42\ See Section II.d of TSD Volume I.
---------------------------------------------------------------------------

    In addition, the boring and well construction logs that were
included in the Permit Application indicate that nearly one-half of the
groundwater wells surrounding Ash Pond 4 were constructed as open
boreholes in bedrock, with open hole intervals ranging from 45 feet up
to as much as 100 feet in length. If EPA's analysis is accurate, nearly
one half of the groundwater monitoring wells surrounding Ash Pond 4
appear to not meet the casing requirements of Sec.  257.91(e).
    One limitation of open-borehole bedrock wells of this kind is that
the entire bedrock interval serves as the monitoring zone. In effect,
the long open interval serves as a reservoir within which inputs from
various fractures intersected by the borehole are blended, resulting in
an average composition of some kind. In this situation, it is very
difficult or even impossible to monitor a specific zone because the
contaminants being monitored could be diluted to the extent of being
non-detectable. On this subject, ADEM's October 27, 2022, letter
states:

    An Interstate Technology and Regulatory Council guidance
document entitled Characterization and Remediation of Fractured Rock
discusses construction and design considerations for monitoring
wells installed in karst aquifers. Section 7.3.3 states ``Where the
bedrock has adequate strength and competency, monitoring wells may
be constructed as an open borehole.'' Because of the proven
competent nature of the Tuscumbia Limestone, there is substantial
confidence that the integrity of the monitoring well borehole will
be maintained.

    To justify their approval of long open borehole intervals, ADEM
states:

    As described above, the karst aquifer present at this site
consists of a rock matrix with distinct fractures that create
preferential pathways for groundwater flow. Studies comparing
hydraulic properties measured within different karst aquifers
indicate that conduits typically account for more than 95 percent of
the permeability of an aquifer (Rosenberry et al., 2008). Thus,
because the majority of water within the monitoring well column will
be provided by discrete fractures of the bedrock unit, the potential
for dilution in the open hole borings would be limited.

    While EPA agrees that fractured intervals in the karst limestone
aquifer are highly relevant as contaminant migration pathways as
compared to the (unfractured) rock matrix, treating all discrete
fractures that may contribute groundwater and/or contaminants to a
borehole equally would fail to ``accurately represent the quality of
the groundwater passing the downgradient waste boundary.'' 40 CFR
257.91(a)(2). The implied logical extension--that is, `the majority of
water in a large open borehole may be sampled to provide accurate and
representative groundwater samples--is simplynot correct. The technical
literature provides a many detailed examples that illustrate the
opposite conclusion. See Section II.d of TSD Volume I. A more likely
scenario is that specific fractures serve as contaminant migration
conduits and a long borehole may cross connect these fractures with
fractures containing clean and/or less contaminated groundwater. In
such a case, the water in the borehole represents in effect a blended
average of the individual contributions from the specific fractures
which it cross connects. As no information has been provided which
indicate the means or methods by which specific fractures may have been
isolated and more precisely monitored, EPA is proposing to determine
that the long-screened interval open-borehole monitoring wells yield
blended or otherwise unrepresentative samples, and thus do not comply
with the performance standards in Sec.  257.91(a)(1) and (2) and (e).
Many options are available to redevelop and reconfigure these existing
open boreholes to fully comply with the regulations, including
installing standard monitoring wells (e.g., with discrete screened
intervals) within the open boreholes with discrete

screened intervals targeted to the most important discrete fracture
zones, or a variety of specialized technologies and methods developed
to address fracture-specific sampling in fractured bedrock
environments. ADEM chose to approve the GWMP without requiring any of
them.
(3) ADEM's Permit Authorizes Intrawell Data Comparisons That Are Not
Consistent With Federal CCR Requirements
    The approach to intrawell data comparisons described in the
approved GWMP does not require TVA to achieve compliance with the
requirement in Sec.  257.91(a)(1) to establish background groundwater
quality in an upgradient well unless the criteria in Sec.
257.91(a)(1)(i) or (ii) are met. The approved GWMP contains procedures
that would allow TVA to update the background data set used in
intrawell comparisons, which would mean including data in the
background characterization that is potentially impacted by a release
from the CCR unit.\43\ See, 40 CFR 257.91(a)(1).
---------------------------------------------------------------------------

    \43\ Tennessee Valley Authority. Colbert Fossil Plant Ash Pond 4
Permit Application, December 10, 2021. Appendix C Section 2.3, p. 4
of 9 (PDF p. 469 of 603).
---------------------------------------------------------------------------

    Intrawell comparisons are not simply a statistical method; in the
CCR regulations, they are an approach to background characterization.
Intrawell data comparisons use samples taken at different times from
the same well to characterize both background groundwater quality and
downgradient compliance groundwater quality. This means downgradient
compliance wells also serve as background wells. Alternatively,
interwell data comparisons use samples taken from different wells--
upgradient or sidegradient wells characterize background groundwater
quality and downgradient wells to characterize downgradient groundwater
quality.
    The Federal CCR regulations do not mention interwell or intrawell
comparisons specifically; instead, they establish requirements for
characterizing background. Background groundwater quality is required
to be established in an upgradient well, unless a groundwater flow
gradient does not exist or it can be shown that groundwater samples
from a well that is not upgradient of the CCR unit would characterize
background groundwater quality as accurately or more accurately than
samples from an upgradient well. 40 CFR 257.91(a)(1)(i),(ii). It also
must be demonstrated that the data were gathered when the well was
known to be uncontaminated by the CCR unit. This generally means that
background data used in intrawell comparisons must be obtained prior to
placement of CCR in the unit. This also indicates a strong preference
for interwell comparison, which would necessarily be used when
background is established in any well other than a downgradient
compliance well (i.e., an upgradient or side gradient well).
    The approach to intrawell data comparisons described in the
approved GWMP includes procedures to periodically update intrawell
background data sets. Updating background data sets may be appropriate
in interwell monitoring, where background groundwater quality may
change over time due to migration of contaminants toward a CCR unit
from upgradient sources. However, in intrawell monitoring, background
data were obtained at compliance wells at the downgradient boundary of
a monitored CCR unit, prior to placement of CCR in the unit. After a
CCR unit begins operation, sampling data obtained from these
downgradient wells cannot be known to be unimpacted by leakage from the
unit.
    Samples from downgradient monitoring wells are intended to
determine whether a release could have occurred. If concentrations of
constituents monitored at the downgradient wells change, this would not
represent a change in background groundwater quality, it would
represent a release from the CCR unit. Mischaracterizing any increase
in constituent concentration at these wells over time as a change in
``background'' would result in elevating background levels and could
mask releases by preventing detection of SSLs of constituents, which
trigger corrective action requirements.
    Because the procedures for updating background levels used in
intrawell data comparisons are approved in the Final Permit, this
permit does not require Colbert to achieve compliance with either the
Federal requirements at Sec.  257.91(a)(1) or an alternative State
requirement that is equally protective.
c. TVA Colbert Permit Corrective Action Issues
    In 2018 TVA detected SSLs for cobalt and arsenic.\44\ TVA first
completed an ACM to comply with the requirements of the Federal CCR
regulations in July 2019 (``2019 ACM''). An ACM was completed in 2021
to comply with a 2018 Consent Decree issued by ADEM (``2021 CD
ACM'').\45\ The 2021 CD ACM included State requirements applicable to
units not regulated by the Federal program, as well as requirements
applicable to CCR units regulated by the Federal program.
---------------------------------------------------------------------------

    \44\ Tennessee Valley Authority. 2019 Annual Groundwater
Monitoring and Corrective Action Report, TVA Colbert. January 2020.
p. 3.
    \45\ Notice Of Electronic Filing in the Circuit Court of Colbert
County, Alabama. Alabama Department of Environmental Management v.
Tennessee Valley Aut 20-Cv-2013-900123.00. C001 Alabama Department
of Environmental Management Joint Motion for Entry of First Amended
Consent. Decree. August 15, 2018.
---------------------------------------------------------------------------

    On October 25, 2022, ADEM issued the Final Permit to TVA for Ash
Disposal Area 4 (also identified as Ash Pond 4 in the 2021 CD ACM). The
Final Permit contained only the following terms and conditions for
corrective action:

    C. Assessment of Corrective Measures. The Permittee must
initiate an assessment of corrective measures as specified in 335-
13-15-.06(7) if any constituent listed in Appendix IV of 335-13-15
has been detected at a statistically significant level exceeding the
groundwater protection standard, or immediately upon detection of a
release from the CCR unit.
    1. The permittee must continue to monitor groundwater in
accordance with the assessment monitoring program while assessing
corrective measures.
    2. Selection of Remedy. Based on the results of the corrective
measures assessment, the Permittee must select a remedy as specified
in 335-13-15-.06(8).
    3. Implementation of the Corrective Action Program. Within 90
days of selecting a remedy, the Permittee must initiate remedial
activities as specified in 335-13-15-.06(9), and shall be required
to modify the permit in accordance with Section II.E.9.

    In its Colbert Permit RTC, ADEM explains that:

    TVA submitted to the Department an initial Assessment of
Corrective Measures (ACM) in July of 2019. A revised ACM was
submitted by TVA in April 2021 and is still undergoing a detailed
review to ensure that the proposed final remedy selected by TVA
conforms to the requirements of ADEM Admin. Code r. 335-13-15-.06(7)
and (8). The proposed corrective measures will use monitored natural
attenuation (MNA) and institutional controls, interim responses, and
adaptive management. Should additional revisions be required, the
Department will review them to ensure compliance with the
requirements of ADEM Admin. Code r. 335-13-15-.06(7) and (8).
    Because an ACM has not been finalized and a final remedy has not
been selected, the permit does not include provisions for the
remediation of the groundwater at this time. However, once a final
remedy is determined complete by the Department, the permit will be
revised to include such provisions. The permit revision to include
the final remedy will include public participation.

    The Final Permit issued by ADEM merely reiterates the Alabama

regulations, which are the same as the Federal corrective action
requirements. However, incorporating the regulations verbatim in the
permit does not require TVA to achieve compliance with those
requirements. This is because ADEM did not take into account relevant
facts about the status of corrective action at Colbert, such as whether
the 2019 ACM complied with the regulatory requirements, or whether the
2021 CD ACM complied with either the Consent Decree or the regulations
or both.\46\ Most importantly, ADEM did not adjudicate what actions are
still necessary in light of those facts to achieve compliance with the
regulations and include those actions as requirements in the Final
Permit. As a consequence, EPA is proposing to determine that the permit
in essence authorizes TVA to continue to delay selection of a remedy
well beyond the required deadline, in order to pursue assessment of a
remedy that does not appear to meet the criteria in Sec.  257.97(b).
---------------------------------------------------------------------------

    \46\ The Federal CCR regulations State that an ACM is complete
when it is placed in the facility operating record. 40 CFR
257.96(d). The regulations require posting of this information to
the publicly accessible website within 30 days 40 CFR 257.107(d),
(h)(8). The 2021 Revised ACM was not posted to the TVA Colbert CCR
website at the time of EPA's review.
---------------------------------------------------------------------------

    In the Colbert Permit RTC, ADEM states that it is still reviewing
the 2021 CD ACM and has not determined whether the ACM and TVA's
preferred remedy (MNA with institutional controls but no source control
measures beyond the existing closure with waste remaining in place)
complies with the regulations. It is not clear whether ADEM provided
comments on the 2019 ACM or whether it believes that the ACM satisfies
the requirements in Sec. Sec.  257.95 and 257.96, which remain
applicable to Ash Pond 4. ADEM also states in the Colbert Permit RTC
that an ACM has not been finalized and a final remedy has not been
selected, so the permit does not include provisions for the remediation
of the groundwater. Whether or not the 2021 CD ACM meets the
requirements of the regulations is precisely the type of adjudication
required in a permitting action. What the permittee is required to do
in order to achieve compliance with the regulations must be determined
prior to final permit issuance, because the permit must contain these
requirements. This is the role of a permitting authority (i.e., ADEM).
    Under the Federal regulations, an assessment of corrective measures
that will ``prevent further releases, remediate any releases, and
restore affected areas to original conditions'' is required once
corrective action is triggered. 40 CFR 257.96. Section 257.96(c)
requires an analysis of the effectiveness of potential corrective
measures in meeting all requirements and objectives of the remedy
required by Sec.  257.97, and mandates that the analysis address at
least the criteria listed in Sec.  257.96(c)(1) through (3). Based on
the results of an ACM conducted in accordance with Sec.  257.96, a
remedy that meets the requirements of Sec.  257.97(b) must be selected
``as soon as feasible.'' 40 CFR 257.97(a).
    The full extent of corrective action requirements applicable to
Colbert are not yet known due to numerous concerns about the adequacy
of the detection and assessment groundwater monitoring system and its
ability to identify all SSLs. However, based on review of the Final
Permit, the Colbert Permit RTC, the 2019 ACM, the 2021 CD ACM, and the
January 13, 2023, Progress Report, EPA has identified a number of areas
in which it appears that neither the ACMs nor the proposed remedies are
consistent with or as protective as the Federal requirements.\47\ At a
minimum, EPA would have expected the permit to have clearly established
a deadline for submission of a final ACM and to have identified
specific corrections that must be made to address the specific
deficiencies discussed in the paragraphs below.
---------------------------------------------------------------------------

    \47\ Tennessee Valley Authority. TVA Seventh Semi-Annual Report
on the Progress of Remedy Selection at Ash Disposal Area 4. January
13, 2023.
---------------------------------------------------------------------------

i. The Colbert Permit Does Not Require TVA To Complete an ACM That
Includes an Assessment of Source Control Measures in Accordance With 40
CFR 257.96
    40 CFR 257.97(b)(3) requires that all remedies control the source
of releases in order to reduce or eliminate, to the maximum extent
feasible, further releases of contaminants into the environment.
Neither the 2019 ACM nor the 2021 CD ACM contains any assessment of
measures to achieve this requirement (i.e., source control). Section
4.2. of the 2019 ACM states, ``Since closure of the Ash Disposal Area 4
CCR Unit serves as a source control measure, the remedial technologies
considered in the following sections are focused on addressing the area
of groundwater exhibiting arsenic and cobalt at concentrations above
the GWPS.'' The 2021 CD ACM also does not evaluate any source control
measures, focusing exclusively on three groundwater remediation
alternatives involving MNA.\48\ However, the assessment required by
Sec.  257.96 must include more than one source control measure, and
must actually assess how the various measures would perform according
to the criteria in Sec.  257.96(c). Here there is no assessment of the
one source control measure identified in the ACMs--the closure of Ash
Pond 4, which left a significant amount of CCR in contact with
groundwater--and how it would perform according to the criteria in
Sec.  257.96(c) compared to other source control alternatives, such as
clean closure or the imposition of engineering measures to control or
eliminate the groundwater that continues to flow in and out of the
impoundment.
---------------------------------------------------------------------------

    \48\ MNA refers to reliance on natural attenuation processes to
achieve corrective action objectives within a time frame that is
reasonable compared to that offered by other, more active methods.
The ``natural attenuation processes'' at work in such a remediation
approach generally include a variety of physical, chemical, or
biological processes that, under favorable conditions, act without
human intervention to reduce the mass, toxicity, mobility, volume,
or concentration of contaminants in soil or groundwater.
---------------------------------------------------------------------------

    ADEM's failure to require submission of an ACM that actually
evaluates whether the closure of the Ash Pond meets the source control
requirements in Sec.  257.97(b)(3) also undercuts their claim that they
will use the corrective action process to address any remaining
concerns with respect to the closure of the Ash Pond. In its October
27, 2022, letter to EPA regarding compliance at TVA Colbert, ADEM
states on page 7,

    In the event that it is determined that the closure activities
conducted at Ash Disposal Area 4 . . . are insufficient to prevent
further groundwater contamination, additional controls or methods
will be considered and addressed through the on-going Assessment of
Corrective Measures (ACM) and selection of a final remedy . . .

    Ash Disposal Area 4 completed closure in 2018, and groundwater
monitoring in 2022 revealed SSLs of additional constituents at wells
without prior SSLs, which indicates that the closure activities were
insufficient to prevent further groundwater contamination. Yet the
permit issued by ADEM does not require TVA to take any action to remedy
this deficiency.
ii. The Colbert Permit Does Not Require Collection of Data Needed To
Characterize Site Conditions That May Affect a Remedy To Support the
Assessments in the ACMs
    40 CFR 257.95(g)(1) requires a facility to characterize the nature
and extent of the release and any relevant site conditions that may
affect the remedy ultimately selected. The

characterization must be sufficient to support a complete and accurate
assessment of the corrective measures necessary to effectively clean up
all releases from the CCR unit pursuant to Sec.  257.96. The 2019 ACM
and 2021 CD ACM do contain information about the delineation of the
identified releases. Although, given the concerns discussed previously
about the adequacy of the downgradient wells in the groundwater
monitoring well network, EPA is concerned that additional plume
delineations may be needed, because potential contaminant pathways are
unmonitored and additional releases may have occurred.
    But critically, the reports do not include any information
collected about site conditions that would affect the efficacy of any
remedies analyzed in the 2019 and 2021 CD ACMs. Site data needed to
assess remedies vary depending on the remedy being assessed, but could
include: speciated results of constituent concentrations in groundwater
and soil, in dissolved and suspended phases; concentrations of
constituents, if present, which are necessary to complete reactions
that result in immobilization of contaminants (e.g. iron or sulfur);
and data to confirm the presence of attenuated and immobilized
contaminants in the subsurface, to demonstrate attenuation is occurring
naturally. As discussed in subsequent sections, the absence of such
data is particularly critical with respect to MNA, which is the only
remedy identified in the 2021 CD ACM. But neither ACM contains any of
these data, which would be needed to accurately assess any of the
remedies identified in the 2019 and 2021 ACMs. Yet the Final Permit
does not include terms to address these deficiencies, such as a
requirement to collect data to characterize site conditions that would
affect the corrective measures considered in either ACM, or a deadline
to submit a revised ACM that contains such data.
iii. Colbert's Permit Does Not Require an ACM That Accurately Assesses
Alternatives According to the Criteria in 40 CFR 257.96(c)
    40 CFR 257.96(c)(1) requires an assessment of how well alternative
remedies will control exposure to residual contamination. Instead, the
2019 ACM assesses potential risks from any exposure to residual
contamination that may occur. This is inconsistent with the Federal
regulations and is, in any event, a less useful metric to evaluate
control measure technologies relative to one another, particularly when
more than one alternative leaves contaminants in the environment. This
is because this alternative criterion serves as an assessment of harm
from the contaminants themselves if they are not removed from the
environment, rather than an assessment of each technology's
effectiveness at removing them. For example, in Table 6-1 in the 2019
ACM--MNA is assessed as low risk with respect to this alternative
criterion, but it would have assessed poorly according to the criterion
of how well alternative remedies will control exposure to residual
contamination. This is less an assessment of MNA's effectiveness at
meeting the requirements of Sec.  257.97(b) and more an assessment of
whether those requirements must be met, which is not the purpose of the
ACM. Moreover, this conclusion of low risk is unsupported by data or
analysis.
    The 2019 ACM also fails to consider safety impacts and cross-media
impacts. See, 40 CFR 257.96(c)(1). The 2021 CD ACM does not correct
this deficiency as it entirely fails to assess alternative remedies
with respect to this criterion at all. The Final Permit issued by ADEM
does not require any actions, by a deadline, to remedy these
deficiencies in the ACMs.
iv. The Final Permit Allows TVA To Continue To Pursue a Remedy (MNA)
That Has Not Been Demonstrated To Meet All of the Requirements in Sec.
257.97(b)
    The 2019 ACM for Colbert identified MNA as one of several potential
corrective measures to address groundwater contamination (i.e.,
hydraulic control and treatment; in-situ treatment). However, the 2021
CD ACM considers only MNA as a primary remedy, which suggests that TVA
is now largely pursuing a remedy that relies exclusively on MNA.
    MNA refers to reliance on natural attenuation processes to achieve
corrective action objectives within a time frame that is reasonable
compared to that offered by other, more active methods. The ``natural
attenuation processes'' at work in such a remediation approach could
generally include a variety of physical, chemical, or biological
processes that, under favorable conditions, act without human
intervention to reduce the mass, toxicity, mobility, volume, or
concentration of contaminants in soil or groundwater. However, mass
reduction through degradation generally is not a viable process for
most inorganic contaminants (i.e., the constituents in Appendix IV to
40 CFR part 257) in groundwater, except for radioactive decay. These
constituents are atoms, and atoms do not break down or degrade through
any naturally occurring process unless they are radioactive.
    Thus, while MNA can reduce the concentration or mobility of
inorganic contaminants in groundwater if immobilization occurs through
adsorption or absorption to subsurface soils, it does not remove the
contaminants from the environment. MNA, therefore, would not perform
well with respect to the requirement in Sec.  257.97(b)(4), which
requires that remedies ``remove from the environment as much of the
contaminated material that was released from the CCR unit as is
feasible.'' This is particularly true in this circumstance, where, as
discussed in the next sections, TVA has failed to collect the site data
needed to identify whether any naturally occurring attenuation may be
occurring on-site, as well as the mechanism by which it occurs, and to
assess whether site characteristics that control and sustain this
naturally occurring attenuation are sufficient to immobilize the entire
release. Assessments in an ACM are relative in that the expected
performance of the different technologies are compared with one another
according to how well each alternative meets each regulatory criterion.
Given both the absence of any evidence of any attenuation mechanisms
occurring at the Ash Disposal Area 4, and the conclusion in the 2020
ACM that the other alternatives such as pump and treat are feasible,
there would appear to be no basis for assessing MNA more favorably than
an alternative that unquestionably removes contaminants from the
environment. The Final Permit nevertheless allows TVA to continue to
attempt to validate MNA as a technology instead of accurately assessing
alternatives based on-site conditions and selecting a remedy that meets
the requirements in Sec.  257.97(b).
v. ADEM Issued a Final Permit That Impermissibly Allows a Remedy (MNA)
That Is Based on Unsupported Assessments
    The 2019 and 2021 ACMs assessed the performance of MNA favorably
without any supporting data that characterize site conditions that may
ultimately affect a remedy, as required by Sec.  257.95(g)(1). In order
to legitimately consider MNA as required by Sec.  257.96(c), site data
are needed to identify any naturally occurring attenuation that may be
occurring, and to assess whether site characteristics that control and
sustain this naturally occurring attenuation are sufficient to

immobilize the entire release. ``It is necessary to know what specific
mechanism (e.g., what type of sorption or reduction and oxidation
reaction) is responsible for the attenuation of inorganics so that the
stability of the mechanism can be evaluated. [. . .] Changes in a
contaminant's concentration, pH, oxidation and reduction potential
(ORP), and chemical speciation may reduce a contaminant's stability at
a site and release it into the environment.'' \49\ Determining the
existence, and demonstrating the irreversibility, of MNA mechanisms is
necessary to assess the performance, reliability, ease of
implementation, and the time required to begin and complete the remedy.
40 CFR 257.96(c)(1) and (2). This information would ultimately be
necessary to assess how well MNA meets the requirements of Sec.
257.97(b).
---------------------------------------------------------------------------

    \49\ Use of Monitored Natural Attenuation at Superfund, RCRA
Corrective Action, and Underground Storage Tank Sites, EPA OSWER
Directive 9200.4-17P. April 21, 1999. p. 8.
---------------------------------------------------------------------------

    MNA of inorganic contaminants would be assessed most favorably at
sites where immobilization is demonstrated to be in effect and the
process/mechanism is irreversible. Immobilization that is not permanent
would require ongoing monitoring in accordance with Sec.  257.98(a)(1)
as long as immobilized constituents remain in the aquifer matrix.
(1) The ACMs Do Not Include Data That Characterize Site Conditions or
Identify Any Attenuation Mechanisms Occurring at the Ash Disposal Area
4
    The site data that were collected focus only on contaminant
concentrations and trend analyses regarding the presence of
contaminants. The 2019 ACM and 2021 CD ACM do not discuss how
attenuation may be naturally occurring through any particular MNA
mechanisms (e.g., adsorption, precipitation, dispersion). EPA was not
able to find any indication in the Final Permit or supporting
documentation to confirm that the Permittee has identified the
mechanism by which MNA would occur at the site. Nor is there any
condition in the Final Permit requiring the development and submission
of such information. The Final Permit should have required collection
of groundwater data (e.g., pH or oxidation potential, speciated
concentrations of constituents of concern) as well as samples to
identify the presence of immobilized constituent in subsurface soils.
The Final Permit also should have required an amended ACM which
considered this information in the assessment of all alternatives,
including assessment of the performance of identified naturally-
occurring attenuation mechanisms (i.e., MNA).
    Determining the existence and demonstrating the irreversibility of
MNA mechanisms is necessary to evaluate the performance, reliability,
ease of implementation, and the time required to begin and complete the
remedy. See, 40 CFR 257.96(c)(1) and (2). This information would
ultimately be necessary to show that MNA meets the requirements of
Sec.  257.97(b) and would need to be supported with site-specific
characterization data and analysis. Yet the Final Permit contained no
terms or conditions requiring TVA to remedy these deficiencies.
(2) MNA Is Not a Viable Remedy Without Source Control
    From a scientific point of view, source control is necessary in
order for any MNA remedy to be effective at a particular site.\50\ In
order to properly assess MNA, first the attenuation mechanisms (for
inorganic metals, these include both chemical and physical reactions)
by which the specific constituents released may be immobilized at a
specific site must be identified. As discussed above, no mechanism was
identified in either the 2019 or 2021 ACM. After attenuation mechanisms
are identified, it is necessary to determine whether the aquifer has
the capacity (i.e., the presence of these reactants available in
sufficient amounts) to provide those reactions to attenuate the release
that has occurred. If site data are obtained verifying the localized
presence and availability of reactants, appropriate types of soil, and
other factors needed to immobilize the constituents, it must be
determined whether they are available in sufficient quantities to react
with the quantity of constituents released. This can be done using the
estimated mass of the release that was calculated in accordance with
Sec.  257.95(g)(1)(ii), as well as site data collected to determine the
presence and concentrations of the chemical and physical materials
required to complete the immobilization reactions. If there are enough
available reactants to immobilize the entire release, and the site
conditions are right for those reactions to occur, then MNA may be
effective at immobilizing a release. However, if the source of a
release has not been controlled (i.e., the CCR remains in contact with
groundwater and releases are ongoing), then it is impossible to know if
an aquifer has the capacity to attenuate the release, even if
attenuation mechanisms have been identified and site conditions are
favorable for those reactions to occur. That is because the amounts of
contaminants being released will continue over time, and releases of
new constituents could occur. Therefore, it is impossible to determine
whether the aquifer has sufficient chemical and physical materials
required to complete the immobilization reactions because the total
amount of the release is not yet known.
---------------------------------------------------------------------------

    \50\ Id.
---------------------------------------------------------------------------

    At TVA Colbert, source control has not been achieved. As discussed
above, the closure of Ash Pond 4 has resulted in continuing releases
from the closed unit, i.e., a continual source of groundwater
contamination from the unit. Therefore, based on the current record,
MNA is not a viable remedy for Ash Pond 4. This should have been
addressed prior to permit issuance during the permit application review
stage or by some other means, such as a schedule of compliance in the
final permit, e.g., by requiring TVA to submit a revised ACM that
accurately assesses MNA and includes a corrective measure which
achieves source control in each alternative assessed.
(3) The Assessment of Cross-Media Impacts in the ACMs Is Inaccurate and
Not Supported by Data
    The table in the 2019 ACM, which summarizes TVA's assessment of
groundwater corrective measures, states that MNA poses a low risk of
cross-media impacts. The reason given is that ``all work activities
occur in-situ.'' This conclusion is only accurate if natural
attenuation through immobilization is occurring on-site, but no such
showing has been made. In fact, in the absence of any information to
the contrary, it is more likely that MNA through dilution and
dispersion would occur, that is, by mixing with clean groundwater as it
migrates from the unit, ultimately transferring the contamination from
groundwater to surface water. But the transfer of contamination from
groundwater to surface water is a cross-media impact and it only occurs
in-situ until the groundwater reaches the surface water. The assessment
of low risk of cross-media impacts is therefore not supported by facts
and site data. See, 40 CFR 257.95(g)(1).
    A similar table (6-1) in the 2021 CD ACM assesses ``potential
adverse impacts'' as low. Its assessment of the first alternative, MNA
with no institutional controls or adaptive management, is favorable
even though it is noted that there would be no protection of surface
water in the short term. In fact, because all three

alternatives rely on MNA and do not include active remediation or
containment, none of them would protect surface water in the short
term. It is unclear why this concern is not noted in all the
alternatives. There is also no discussion of long-term impacts to
surface water. Accordingly, EPA is proposing to determine that the
assessment of these potential remedies as low risk is not supported by
any evidence, and that the assessment of the third alternative does not
meet the requirements of Sec.  257.96(c)(1) because it does not
consider impacts to surface water (i.e., cross-media impacts).
    The lack of data to support the assessments in both ACMs means they
may not accurately reflect MNA's ``effectiveness of potential
corrective measures in meeting all of the requirements and objectives''
in Sec.  257.97(b). 40 CFR 257.96(c) Conclusions without a supporting
assessment or data do not constitute ``an analysis of the effectiveness
of potential corrective measures.'' 40 CFR 257.96(c) (emphasis added).
In addition, inaccurate assessments in an ACM can ultimately result in
selection of a remedy that will not meet the requirements of Sec.
257.97(b). The Final Permit issued by ADEM in October 2022 does not
require TVA to take any actions to remedy the deficiencies in either
the earlier 2019 ACM or subsequent 2021 CD ACM.
(4) The 2021 CD ACM Is More Deficient Than the 2019 ACM
    Even though the 2021 CD ACM was developed in response to comments
from ADEM, it not only fails to remedy the deficiencies in the 2019
ACM, but also contains provisions that raise additional concerns.
First, the remedial objectives in section 1.3 of the 2021 CD ACM do not
address the requirements in Sec.  257.97(b)(3) or (4) relating to
source control or the removal of the release from the environment--
rather, they only consider off-site impacts of groundwater
contamination.
    It is unclear whether the 2021 ACM was intended to replace or to
supplement the 2019 ACM. But assessed on its own merits, the 2021 CD
ACM failed to assess two remedies included in the 2019 ACM: hydraulic
control and treatment and enhanced in-situ treatment as primary
corrective measures. Only three alternatives are considered in the 2021
CD ACM, which all rely on MNA as the primary corrective measure. The
only consideration of active corrective measures is in alternative
three, as part of an adaptive management strategy if MNA does not meet
the remedial objectives on its own. Therefore, EPA is proposing to
determine that the 2021 CD ACM does not meet the requirement in Sec.
257.96(a) to assess corrective measures ``to prevent further releases,
to remediate any releases and to restore affected area to original
conditions,'' because the alternatives, limited to MNA without
additional source control, would not meet any of these requirements at
the Colbert Plant.
(5) The Ongoing Data Collection and Model Development Are Not Necessary
To Select a Remedy
    According to the January 13, 2023 Progress Report, the facility has
delayed selection of a remedy by, among other tasks, continuing to
monitor the migration of the release and developing a computer model to
predict groundwater behavior. It is not necessary to delay completion
of an ACM or selection of a remedy until a model can be developed and
refined; the Federal regulations do not require development of a
groundwater model to complete an ACM or to select a remedy. Since
actual site monitoring data-- rather than an estimate from a model-- is
required to characterize the release sufficiently to assess corrective
measures-- the primary use of a model in this stage of CCR corrective
action would be to estimate the amount of time needed to complete a
remedy. But this estimate may be accomplished through other methods
(e.g., calculation of the mass of the release, groundwater flow
velocity, hydraulic conductivity, and the attenuation capacity of the
downgradient subsurface where MNA mechanisms have been identified and
can be quantified). Nor is such delay consistent with the requirements
of Sec.  257.95(g), which only requires characterization ``sufficient
to support a complete and accurate assessment of the corrective
measures necessary to effectively clean up all releases from the CCR
unit pursuant to Sec.  257.96.'' In order to support the assessment in
the ACM, this characterization must be complete prior to the deadline
to complete the ACM.
    Based on all of the above, EPA is proposing to determine that the
permit fails to require the Permittee to select its remedy ``as soon as
feasible,'' as required by Sec.  257.97(a). Section 5.C.2 of the
permit, entitled ``Selection of Remedy,'' only reiterates the
regulatory requirement that the Permittee must select a remedy as soon
as feasible. It has been three years since the 2019 ACM for the Ash
Pond was placed in the facility's operating record, and it is not clear
why the facility has not selected a remedy.\51\ The 2021 CD ACM does
not reflect progress toward selection of a remedy, as it does not
address any of the deficiencies in the 2019 ACM. For example, even
though the 2021 CD ACM focuses exclusively on MNA, it still fails to
identify any attenuation mechanism, or to include any of the supporting
data that characterize site conditions that may ultimately affect a
remedy, as required by Sec.  257.95(g)(1). For all the reasons
discussed above, EPA is proposing to determine that neither the 2019
ACM, the 2021 CD ACM, or the two ACMs taken together meet the
requirements of Sec.  257.96 or Sec.  257.97 or support selection of a
compliant remedy. By failing to require TVA to obtain the necessary
data and submit a revised ACM by a date certain, the Final Permit
appears to authorize the permittee to continue to indefinitely delay
selecting a remedy, while the permittee continues to conduct the same
sampling it has conducted since 2019, that is likely to be insufficient
to support the selection of that alternative as a remedy. Accordingly,
EPA is proposing to determine that the permit does not require
compliance with the Federal requirements and, because it allows the
facility to continue to delay corrective action, the alternative State
requirement is less protective.
---------------------------------------------------------------------------

    \51\ Tenessee Valley Authority. 2019 Assessment of Corrective
Measures Report for the Ash Pond TVA Colbert Fossil Plant,
Tuscumbia, Alabama. July 15, 2019.
---------------------------------------------------------------------------

2. Plant Gadsden
    EPA reviewed the Final Determination Initial Permit And Variance
for the Alabama Power Company, Gadsden Steam Plant (Plant Gadsden
Permit), issued by ADEM under Permit No. 28-09 on December 18,
2020.\52\ The permit summary on Page 1 says:
---------------------------------------------------------------------------

    \52\ Alabama Department of Environmental Management. Final
Determination Initial Permit And Variance for the Alabama Power
Company, Gadsden Steam Plant, issued under Permit No. 28-09.
December 18, 2020.

[t]he Plant Gadsden Ash Pond is a CCR surface impoundment located in
Section 2, Township 12 South, Range 6 East in Etowah County, Alabama
consisting of approximately 130.22 acres with a disposal area that
consists of approximately 58.73 acres. The permit requires the
Permittee to manage CCR in accordance with the conditions of the
permit, ADEM Admin. Code r. 335-13-15, . . . and the approved permit
application.
. . .
The Permittee must comply with all conditions of the permit except
to the extent and for the duration such noncompliance is authorized
by a variance granted by ADEM. The first variance requests to
exclude boron as an Appendix IV assessment monitoring

constituent. The second variance requests groundwater protection
standards of 6 micrograms per liter ([micro]g/L) for cobalt; 15
[micro]g/L for lead; 40 [micro]g/L for lithium; and 100 [micro]g/L
for molybdenum. The third variance requests the final grade of the
cover system be less than 5 percent and greater than 25 percent. The
fourth variance being requested is from 335-13-15-.03(6) requiring a
100 foot buffer from the perimeter of the facility boundary.
a. Plant Gadsden Closure Issues
    Section VII.B.1 of Plant Gadsden Permit contains the following
terms and conditions:

    A. Closure Timeframe and Notifications. The Permittee shall
close their CCR units as specified in 335-13-15-07(2), this permit
and the Application.
    B. Criteria for Closure.
    1. Cover. Closure of a CCR landfill, surface impoundment, or any
lateral expansion of a CCR unit must be completed by either leaving
the CCR in place and installing a final cover system or through
removal of the CCR and decontamination of the CCR unit, as described
in 335-13-15-.07(3)(b) through (j). The minimum and maximum final
grade of the final cover system may be less than 5 percent and
greater than 25 percent, as specified in the Permit Application.
(See Section IX.C.)
    2. Written Closure Plan. The written closure plan, as part of
the Application, must include, at a minimum, the information
specified in 335-13-15-.07(3)(b) 1.(i) through (vi).

    The Ash Pond was closed by removing CCR from the southern portion
of the Lower Pond (the area of the western expansions in the 1970s) and
consolidating the ash in the Lower Pond to about 30 acres in the
northern portion of the Lower Pond. The CCR in the Upper Pond (original
ash pond prior to expansions) was regraded to achieve a minimum 3%
slope, and a cover system was constructed over the re-graded Upper Pond
and consolidated ash in the Lower Pond.\53\
---------------------------------------------------------------------------

    \53\ Alabama Power. Revised Closure Permit Application for the
Plant Gadsden Ash Pond. April 30, 2020. Appendix 6.
---------------------------------------------------------------------------

    Closure construction activities for the Ash Pond were certified as
completed in October 2018, and a certification of completion of closure
activities was later submitted in April 2020, and approved by ADEM on
June 9, 2022.54 55
---------------------------------------------------------------------------

    \54\ Alabama Power. Plant Gadsden 2020 Notice of Closure
Completion Plant Gadsden Ash Pond Alabama Power Company.
    \55\ Alabama Power. Plant Gadsden 2022 Closure Inspection
Gadsden Steam Plant Permit No. 28-09.
---------------------------------------------------------------------------

i. Base of the Impoundment
    Plant Gadsden is located in Gadsden, Alabama, south of the Coosa
River. The Ash Pond is located on the north side of and adjacent to the
Coosa River. The Permit Application states that the Ash Pond was
initially constructed in 1949 and subsequently expanded to the west in
1976 and 1978.\56\ The Permit Application states that the fully
constructed Ash Pond was 75 acres. Id. at Appendix 8. Alabama Power
closed the Ash Pond by consolidating CCR to a smaller area within the
impoundment footprint. Id. at Appendix 6. As a result, the consolidated
closed footprint of Ash Pond 4 decreased to approximately 59 acres. Id.
at Appendix 2.
---------------------------------------------------------------------------

    \56\ Alabama Power. Revised Closure Permit Application for the
Plant Gadsden Ash Pond. April 30, 2020. Appendix 3.
---------------------------------------------------------------------------

    EPA was unable to locate information in the Permit Application or
other publicly available documents that characterizes the bottom
elevation of the Ash Pond across its entire footprint. Nonetheless,
similar to the review for the permit for Plant Colbert, EPA estimates
the average bottom elevation of the impoundment for purposes of
calculating the volume of CCR that remains saturated by groundwater.
EPA is estimating that the average bottom elevation of the closed Ash
Pond is 510 ft above MSL.\57\ This estimate is based on consideration
of the information available in the Permit Application. Specifically,
EPA considered the following information: (1) the original ground
surface contours shown on construction drawings for areas that were
closed by leaving CCR in place; (2) information showing that the bottom
of the impoundment was lower than the original ground surface contours
at some locations while the unit was in operation; and (3) closure-
related drawings portraying an estimated waste bottom.
---------------------------------------------------------------------------

    \57\ USEPA. Volume I: Technical Support Document for the
Proposed Notice to Deny Alabama's Coal Combustion Residuals Permit
Program, Supplemental Analyses of Technical Issues with ADEM
Permits. August 2023. Section III.a.
---------------------------------------------------------------------------

    EPA's estimate recognizes that the original ground surface contours
for most of the impoundment footprint (both the initial footprint and
western expansions) range between 505 to 515 ft above MSL, or an
average elevation of 510 ft above MSL. In addition, certain closure
drawings show that current surface elevations in the upper northern
part of the unit are actually lower in 2016 than the original ground
surface elevations depicted on the 1978 expansion drawing. This means
that the original ground surface elevations shown on the 1949, 1976,
and 1978 drawings do not necessarily reflect the bottom of the
impoundment at closure at all locations within the unit footprint. The
2016 drawing shows the bottom elevation at this upper northern part of
the unit to be no higher than 505 to 510 ft above MSL, which is lower
than the original ground contours at this location that ranged from 510
to 515 ft above MSL. Finally, the four cross-sections provided in the
Gadsden Permit Application depict the impoundment bottom appearing to
range between 495 to 510 ft above MSL, but these cross-sections are
annotated with a note that the bottom elevations have not been
verified. Based on the available information, EPA's estimated average
bottom elevation of 510 ft above MSL is a reasonable reconciliation of
the available information.
ii. Characterization of Groundwater Elevations
    The CCR program groundwater monitoring network installed at the
unit consists of fifteen downgradient monitoring wells (GSD-AP-MW-1
through MW-12 and GSD-AP-PZ-1, PZ-5, and PZ-6). The following
evaluation of groundwater elevation data for the unit focuses on the
twelve monitoring wells that are immediately adjacent to the waste
boundary (i.e., MW-1 through MW-12). Monitoring wells PZ-1, PZ-5 and
PZ-6 are located hundreds of feet from the waste boundary and thus were
not considered. Also, three ``upgradient'' monitoring wells (MW-14, -
16, and -17) are located to the southeast on the other side of the
Coosa River and are not considered with respect to groundwater
elevations within the unit. Based on the single groundwater flow map
included in the Permit Application,\58\ based on August 19, 2019, data,
groundwater elevations in monitoring wells surrounding the unit ranged
from a high of 512.03 ft above MSL along the northeastern boundary of
the unit (GSD-AP-MW-3) to 506.95 ft above MSL along the western
boundary (GSD-AP-MW-7). The potentiometric surface contour map
presented for August 19, 2019, reveals a somewhat radial flow pattern,
with highest groundwater elevation values recorded along the
northeastern boundary of the facility. Between monitoring wells GSD-AP-
MW-1 and GSD-AP-MW-4 along the northeastern boundary of the unit,
groundwater elevation values are similar, approximately 512 ft above
MSL, resulting in a northwest to southeast trending ridge-like region
of relatively high groundwater elevations.
---------------------------------------------------------------------------

    \58\ Alabama Power. Revised Closure Permit Application for the
Plant Gadsden Ash Pond. April 30, 2020, Appendix 7, Plant Gadsden
Ash Pond Groundwater Monitoring Plan, Figure 6.
---------------------------------------------------------------------------

    Groundwater elevations drop to the north, northeast, northwest,
west and to

the south and southwest from this central axis which is mapped as a
groundwater divide just east of the unit boundary on the August 19,
2019, map. There are no data in the Permit Application that can enable
a determination of groundwater flow directions to the east and
southeast of the unit, thus the possibility of unmonitored flow in
these directions has not been ruled out. These uncertainties
notwithstanding (see Unit IV.C.2.b of this preamble for additional
assessment of uncertainties associated with the groundwater monitoring
network), the available information indicates that groundwater from the
Ash Pond generally flows toward the surface water features represented
by the main stem of the Coosa River as well as toward the tributary
stream segments to the north and northwest of the unit. Groundwater
elevations within the unit appear to be primarily controlled by the
consistently higher elevations along the northeastern boundary of the
unit as well as the lower elevations associated with the Coosa River to
the northwest, west, and southwest. On August 19, 2019, the elevation
of the Coosa River was reported to be approximately 508 ft above
MSL.\59\
---------------------------------------------------------------------------

    \59\ Volume I: Technical Support Document for the Proposed
Notice to Deny Alabama's Coal Combustion Residuals Permit Program,
EPA Analysis of Alabama CCR Permits. U.S. Environmental Protection
Agency, Office of Land and Emergency Management (5304T), 1200
Pennsylvania Avenue NW, Washington, DC 20460. August 2023. Section
III.b.i.
---------------------------------------------------------------------------

    It is important to note that the groundwater elevations reported on
August 19, 2019, represent a relatively low condition, on balance, and
groundwater elevation values measured at the unit are observed to
oscillate over several feet on average in response to seasonal rainfall
or other variations, with individual wells immediately adjacent to the
Ash Pond (i.e., GSD-AP-MW-1 through MW-12) varying over a range of
approximately 3.9 to 8.5 feet between 2018 and 2022,\60\ which covers
the period after closure construction activities for the Ash Pond were
certified as completed in October 2018. Similarly, the Coosa River
levels show considerable variation, ranging from 503.3 to 512.6 ft
above MSL between 2018 and 2022 as monitored by a gauge located
approximately 900 feet upstream of GSD-AP-MW-11. Given these
fluctuations, EPA considered additional groundwater elevation data from
documents included on Alabama Power's CCR website. Groundwater
elevation data from measurement events since August 19, 2019, were
initially evaluated to illustrate the range of groundwater elevation
fluctuations at the site, as summarized in Table III. The recorded
elevations of the Coosa River on the corresponding dates are also
included on the table.
---------------------------------------------------------------------------

    \60\ Id at Section III.c.iii.

    Table III--Groundwater Elevation Fluctuations at the Ash Pond and Corresponding Coosa River Elevations a
----------------------------------------------------------------------------------------------------------------
                                                           Groundwater elevation  (ft     Coosa River elevation
                                                                   above MSL)               (ft above MSL) \b\
                          Date                          --------------------------------------------------------
                                                                                Range Over 24-Hour
                                                             Maximum         Minimum              Period
----------------------------------------------------------------------------------------------------------------
8/19/2019..............................................          512.03          506.95              507.6-507.8
4/13/2020..............................................          517.91          508.71              507.9-510.3
8/24/2020..............................................          512.57          507.64                507.8-508
3/15/2021..............................................          516.98          507.18                507-507.4
10/4/2021..............................................          513.76          508.03              507.9-508.1
1/11/2022..............................................          515.65          508.01              507.8-508.2
5/5/2022...............................................          516.18          507.97              507.6-508.1
10/24/2022.............................................          510.86          506.64         \c\ 507.5-507.7
----------------------------------------------------------------------------------------------------------------
\a\ Measured at groundwater monitoring wells GSD-AP-MW-1 through GSD-AP-MW-12.
\b\ Source: U.S. Geological Survey (USGS). See Section III.b.i of TSD Volume I for further details.
\c\ These data are provisional and may be revised by the USGS.

    As shown here, groundwater levels are variable, and are generally
higher during spring monitoring events (March, April) as compared to
late summer/fall events (August, October). In consideration of the 15
groundwater elevation monitoring events from October 4, 2018, through
October 24, 2022, EPA calculated average minimum, average maximum, and
overall average groundwater elevations within the unit over the four-
year period, as follows:

Groundwater Elevation (overall average): 511 ft above MSL
Groundwater Elevation (average maximum): 514.6 ft above MSL
Groundwater Elevation (average minimum): 508.6 ft above MSL

    The average range of fluctuation between maximum and minimum values
at a particular monitoring well location over this same period of
interest was 5.9 feet.
    These values were used in conjunction with the estimates for the
bottom-of-waste elevation to calculate estimated volumes of saturated
waste, as presented in the following section.
iii. Volumes of Saturated Ash Estimates
    Based on available information and the averages discussed above,
EPA estimated the volume of CCR in the Ash Pond that, on average, would
continue to be saturated with approximately 1 to 4.6 feet of
groundwater.\61\ Because both the base elevation of the waste and the
groundwater elevations vary, those estimates both overstate and
underestimate the degree of saturation. For example, at its lowest
point, the base of the impoundment measures 505 ft above MSL, and the
highest elevation of groundwater was measured at 519.26 ft above MSL
(GSD-AP-MW-1 on February 25, 2019). However, the data show that even
during the periodically dry conditions in summer when the groundwater
elevations can decline to values approaching Coosa River surface
levels, significant volumes of saturated waste may still be present
because of uncertainties with the waste bottom elevation. If areas of
waste are present below the elevation of the Coosa River, as some
information suggests, these areas of waste are expected to remain
saturated because, absent any information to the contrary, it is
presumed that a hydraulic connection between the uppermost aquifer and
the river exists due to the close proximity of the Ash Pond to the
river. In any case,

the regular and significant oscillation in waters levels in the CCR
indicate that significant volumes of saturated CCR persist routinely
despite closure efforts to date. Moreover, evaluation of water level
elevations over time show that water levels are higher than the bottom
of the impoundment under most conditions, and there is no indication
from available information that this situation will change absent
additional engineering controls.
---------------------------------------------------------------------------

    \61\ Id at Section III.c.iv.
---------------------------------------------------------------------------

    EPA's analysis shows that substantial volumes of saturated CCR
currently remain in the closed impoundment under conditions where
groundwater elevations were at the overall average or maximum average
levels, ranging from approximately 95,000 to 436,000 CY, respectively.
Furthermore, these saturated volume estimates equate to approximately
8% to 36% of the total volume of CCR in the Ash Pond with an average
thickness of CCR over the entire footprint between approximately 1 to
4.6 feet of statured CCR within the unit. These estimates are further
explained in Section III.c of the TSD Volume I. Table IV summarizes the
volumes and areas of saturated CCR calculated under both conditions.

     Table IV--Estimates of Saturated CCR at Plant Gadsden Ash Pond
------------------------------------------------------------------------
                                              Overall         Maximum
     Groundwater elevation condition          average         average
------------------------------------------------------------------------
Groundwater elevation (ft above MSL)....             511           514.6
Average waste bottom (ft above MSL).....             510             510
Saturated CCR thickness (feet)..........               1             4.6
Total CCR in Ash Pond (cubic yards).....       1,200,000       1,200,000
Area of Ash Pond (acres)................           58.73           58.73
Area of Ash Pond (square yards).........         284,253         284,253
Volume of saturated CCR (cubic yards)...          94,751         435,855
Fraction of total CCR saturated (%).....             7.9            36.3
------------------------------------------------------------------------

    Based on EPA's estimates, the closure of the Plant Gadsden Ash
Pond, authorized and approved by ADEM, does not meet the requirements
of Sec.  257.102(d). Overall, the closure of the Gadsden Ash Pond
presents the same issues as the closure of the Colbert Ash Pond 4
discussed in the previous section. The post-closure groundwater
monitoring data from 2019 through 2021 show that groundwater is still
infiltrating into the Ash Pond. The average groundwater elevations
measured at monitoring wells surrounding the Ash Pond from 2018 through
2022 were on the order of 514 ft MSL (i.e., approximately 4 feet above
the average bottom elevation of the CCR). Yet neither the approved
Closure Plan nor any other document in the record for the permit
accounts for the levels of groundwater present in the unit prior to
closure or describe any engineering measures taken to meet each of the
Federal CCR closure-in-place performance standards in Sec.
257.102(d)(1) and (2) in light of the groundwater present in the unit.
Nor based on the post-closure groundwater elevation data from
piezometer wells from 2019-2021, did the approved closure address the
groundwater that continues to saturate the CCR in the closed unit. EPA
is therefore proposing to determine that the permit for Plant Gadsden
does not require Alabama Power to achieve compliance with either Sec.
257.102(d) or with alternative State standards that EPA has determined
to be at least as protective. EPA is therefore, proposing to determine
that Alabama's CCR permit program does not satisfy the statutory
requirement in RCRA section 4005(d)(1)(A) or (B).
    As previously explained, in situations such as this, where the
waste in the unit is continually saturated with groundwater, the
requirement to eliminate free liquids obligates the facility to take
engineering measures to ensure that the groundwater, along with the
other free liquids, has been permanently removed from the unit prior to
installing the final cover system. See, 40 CFR 257.102(d)(2)(i). Yet
neither the Closure Plan that ADEM-approved nor the permit ADEM issued
contained any such requirements.
    While the approved Closure Plans for the Ash Pond at Plant Gadsden
discuss dewatering techniques employed before and during closure, it
appears the facility at most eliminated only the ``free water'' ponded
above the CCR, and only dewatered the CCR and sediment ``to the extent
necessary to provide a stable working surface for earthwork equipment''
as provided in the closure and post-closure for the Ash Pond:

2.2 DEWATERING FOR CLOSURE
    Free water in the clear pool will be removed through pumping,
maintaining compliance with the NPDES discharge limits. The saturated
ash will be dewatered to the extent necessary to allow a stable working
surface for earthwork equipment. Interstitial water '' removal. All
water will be sent to an onsite water treatment system prior to
discharge to ensure compliance with the NPDES discharge limits.\62\
---------------------------------------------------------------------------

    \62\ Alabama Power. Revised Closure Permit Application for the
Plant Gadsden Ash Pond. April 30, 2020. Appendix 8, p 2.
---------------------------------------------------------------------------

    The ``free water'' referenced above is only a subset of the ``free
liquids'' that must be eliminated; and that standard (``eliminated'')
applies equally to the pore water intermingled with the CCR. See, 40
CFR 257.102(d)(2)(i). The Closure Plans do not acknowledge the
groundwater within the consolidated footprint that continues to
routinely flow into the base of the impoundment and saturate the CCR or
describe any engineering measures to eliminate those free liquids,
despite the continued saturation. Moreover, it is clear from the post-
closure 2019-2022 monitoring data that the measures that were taken
during closure did not actually eliminate the free liquids from Ash
Pond.
    A further concern is that, given the failure to eliminate the free
liquids from the saturated CCR underlying the consolidated unit, it is
not at all clear that the remaining wastes have been stabilized
sufficiently to support the final cover system, as required by Sec.
257.102(d)(2)(ii). Creating a stable working surface for earthwork
equipment while the cover system is being installed is not the same as
ensuring that the unit has been sufficiently dewatered prior to
installation of the cover system and that over the long term there will
be no differential settlement of the CCR in the closed unit that would
disrupt the integrity of the cover system and allow

liquids to infiltrate into the closed unit. Neither the approved
Closure Plan nor ADEM's permit provides any details of engineering
measures that were taken to address the groundwater that continues to
flow into and out of the unit from the sides and bottom. In the absence
of such measures, EPA has no basis for concluding that the standard in
Sec.  257.102(d)(2) has been met.
    EPA was also unable to find any description in the ADEM approved
Closure Plan or any other permit document of engineering measures that
Alabama Power took to ``control, minimize, or eliminate, to maximum
extent feasible'' either the post-closure infiltration of the
groundwater into the waste or the post-closure releases of CCR or
leachate to the groundwater, resulting from the groundwater that
continues to infiltrate into the impoundment from the sides and bottom
of the unit. 40 CFR 257.102(d)(1)(i). Based on the data and analyses
described above, groundwater continues to infiltrate into the unit and
yet the only measures described in the Closure Plan and the permit are
those taken to facilitate consolidation and cap construction.\63\ In
essence, this means the Ash Pond will continue releasing CCR
contaminants indefinitely unless Alabama Power is taking additional
actions that are not required by or explained in the permit.
---------------------------------------------------------------------------

    \63\ Id at Appendix B (Infiltration Equivalency Demonstration)
in Appendix 8.
---------------------------------------------------------------------------

    The absence of such measures from the closure approved by ADEM is
consistent with the State's interpretation of its closure requirements,
but as discussed above, it is neither consistent with, nor as
protective as, the Federal regulations. As with the TVA Colbert Plant
Permit, EPA is proposing to determine that the record does not support
a finding that ADEM's alternative approach of relying on the existing
corrective action process will be as protective as the Federal
requirements. As discussed in a subsequent section, EPA has serious
concerns about the protectiveness of the corrective action at Gadsden
that ADEM is overseeing.
    All of this information was available before ADEM issued the permit
in December 2020, and again when ADEM approved the completion of
closure on June 9, 2022. Yet the permit continues to authorize the
closure of the unit with no engineering measures to limit the
groundwater from continually flowing into and out of the CCR in the
unit, and with no permit terms on the need to address this as part of
the corrective action process.
    Accordingly, EPA is proposing to determine that the permit for
Plant Gadsden does not require Alabama Power to achieve compliance with
either Sec.  257.102(d) or with alternative State standards that EPA
has determined to be at least as protective.
b. Plant Gadsden Groundwater Monitoring Issues
    The Plant Gadsden Permit says on page 1,
    Groundwater monitoring and corrective action requirements in the
permit establish a groundwater monitoring system of wells that provides
an accurate representation of the groundwater quality underlying the
unit and a groundwater monitoring plan to establish appropriate
sampling and analysis of the system to detect the presence of CCR
constituents.
    In addition, Section V of the Plant Gadsden Permit incorporates the
GWMP submitted with the Permit Application, and directed Alabama Power
to comply with the State regulations and the approved plan:

Section V. Groundwater Monitoring and Corrective Action Requirements.
A. Groundwater Monitoring System. The Permittee shall install and/or
maintain a groundwater monitoring system, identified in Table 1, as
specified in 335- 13- 15-. 06(2) and the approved groundwater
monitoring plan.
Once ADEM approved and adopted the GWMP into the permit, the GWMP,
rather than the referenced State regulations, became the State
requirements with which the facility is required to comply.
    Based on EPA's review of the approved groundwater monitoring plan,
EPA is proposing to determine that the groundwater monitoring well
network ADEM approved does not meet the performance standards in Sec.
257.91(a) or (b). As discussed in more detail below, EPA is proposing
to determine that the approved groundwater monitoring system is not
based on a thorough characterization of the elements listed in Sec.
257.91(b). EPA is also proposing to determine that the groundwater
monitoring system does not ``yield groundwater samples from the
uppermost aquifer,'' but has been screened instead in only a portion of
the aquifer. 40 CFR 257.91(a). Further, it appears that the background
wells were not installed in locations hydraulically upgradient of the
Ash Pond, and EPA was unable to locate sufficient information in the
permitting record demonstrating that the standard for such wells in
Sec.  257.91(a)(1)(i) or (ii) was met. In addition, based on the
documentation provided in the Permit Application, it appears that the
downgradient compliance wells are spaced too far apart and/or are
screened too deeply and/or shallow to accurately represent the quality
of groundwater passing the waste boundary and to monitor all potential
contaminant pathways in the uppermost aquifer. See, 40 CFR
257.91(a)(2). Therefore, EPA is proposing to determine that ADEM's
Final Permit fails to require Alabama Power to achieve compliance with
either the Federal regulations or with an equally protective State
requirement.
i. Failure To Delineate the ``Uppermost Aquifer'' and To Base the
System on Thorough Characterization of Site Data
    The Federal CCR regulations require that a groundwater monitoring
system sample ``the uppermost aquifer,'' which is defined as ``the
geologic formation nearest the natural ground surface that is an
aquifer, as well as lower aquifers that are hydraulically
interconnected with this aquifer within the facility's property
boundary.'' 40 CFR 257.53, 257.91(a). The design of the monitoring
systems must be based on a thorough characterization of, among other
things, the ``aquifer thickness, groundwater flow rate, groundwater
flow direction including seasonal and temporal fluctuations in
groundwater flow; and saturated and unsaturated geologic units and fill
materials overlying the uppermost aquifer, materials comprising the
uppermost aquifer, and materials comprising the confining unit defining
the lower boundary of the uppermost aquifer.'' 40 CFR 257.91(b)(1) and
(2). EPA is proposing to determine that ADEM approved a groundwater
monitoring plan that does not meet these requirements.
    Based on the limited information in the permit record, it appears
the facility failed to fully define the limits of the uppermost
aquifer, particularly its lower boundary. The GWMP provided in the
Permit Application provides only limited characterization of the
geologic units beneath the Ash Pond. In addition, the technical
information provided in the Permit Application is insufficient to
support a determination of the lateral and vertical limits of the
entire uppermost aquifer; for example, EPA found only limited data on
the ``saturated and unsaturated geologic units and fill materials
overlying the uppermost aquifer and materials comprising the uppermost
aquifer.'' 40 CFR 257.91(b)(2). And EPA was unable to find adequate
information about the ``materials comprising the confining unit
defining the lower boundary of the uppermost aquifer.'' Because the
information in the Permit Application

was inadequate, EPA also consulted information available on Alabama
Power's CCR website to understand the hydrogeology of the site. EPA is
proposing to determine that neither the information in the Permit
Application nor the additional information available on Alabama Power's
CCR website constitutes ``a thorough characterization of . . . aquifer
thickness, groundwater flow rate, groundwater flow direction including
seasonal and temporal fluctuations in groundwater flow; and saturated
and unsaturated geologic units and fill materials overlying the
uppermost aquifer, materials comprising the uppermost aquifer, and
materials comprising the confining unit defining the lower boundary of
the uppermost aquifer.'' 40 CFR 257.91(b)(1) and (2).
    A generalized visual representation of the various lithologies
composing the uppermost aquifer beneath the Ash Pond can be found in
the cross sections in Figures 5A and 5B (included on pages 142 and 143)
in the Permit Application and in other places, such as Figures 4A, 4B,
9, and 10 from the 2021 Semi-Annual Groundwater Monitoring and
Corrective Action (GWMCA) Report for Plant Gadsden.\64\ Based on EPA's
assessment of the available information, the uppermost aquifer, which
has not yet been fully identified and characterized, is a composite
layered system consisting of unconsolidated deposits of alluvial origin
on top of a predominantly mudstone bedrock. The unconsolidated alluvial
deposits consist of interlayered deposits of silt, sand, gravel, and
clay material. These unconsolidated alluvial deposits unconformably
overlay a variably fractured and weathered bedrock material,
predominantly mudstones of the Conasauga formation. The three-
dimensional surface represented by the contact between the uppermost
portion of the (consolidated) bedrock and the overlying alluvium
(unconsolidated), which can also be described as the top-of-rock
surface, is a distinct hydraulically relevant zone of interest. These
points are illustrated (in part) in the geologic cross-sections on
Figures 5A and 5B (included on pages 142 and 143) in the Permit
Application, which show the uppermost aquifer consisting of layers of
sand, silt, gravel, as well as the underlying Conasauga bedrock
formation. The elevation of this contact zone changes laterally across
the unit, depending on location, and these differences in elevation are
important with respect to the siting of appropriate monitoring well
location and depths.
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    \64\ Southern Company Services. 2022 Semi-Annual Groundwater
Monitoring and Corrective Action Report, Alabama Power Company Plant
Gadsden Ash Pond. Prepared for Alabama Power Company. January 31,
2022.
---------------------------------------------------------------------------

    Immediately located beneath the unconsolidated alluvial materials
is a zone of degraded bedrock (typically referred to as ``weathered
bedrock'') in the uppermost portion of the Conasauga bedrock. This
weathered bedrock material consists primarily of variably weathered
mudstones which have been degraded by naturally occuring processes. The
weathered rock zones vary in thickness laterally and vertically. This
interface between the unconsolidated alluvial materials and the
underlying bedrock constitutes an irregular geologic contact, which
varies spatially in terms of the thickness and degree of the weathered
bedrock material, that is sandwiched between alluvial deposits above,
and lightly weathered or unweathered bedrock below. The contact can be
thick and gradational in some areas, and abrupt and thin in other
areas. This variability demands additional characterization as it
creates the potential for preferential pathways which may exploit the
weathered interval. While limited information has been collected from
this interval, a few monitoring wells are partially screened across the
bedrock/overburden contact, and thus monitor the weathered bedrock
interval to some degree at those locations. However, the variable
nature of the bedrock/overburden contact was not sufficiently
characterized to meet the performance standards in Sec.  257.91(a) or
(b), as discussed in more detail below.
    Beneath the uppermost veneer of weathered bedrock are rocks of the
Conasauga group, which consists of varying amounts of limestone,
dolomite, and shale, with chert and siltstone horizons present locally.
The 2021 Semi-Annual GWMCA Report states, ``The Limited core logs from
the Site indicate the Conasauga [beneath the Ash Pond] to be a medium
to dark gray mudstone or shale with noticeable calcite veining.'' \65\
While the Report goes on to State, ``The Conasauga Formation is not
considered to be a water-bearing aquifer at the Site,'' this statement
conflicts with boring logs and other information which indicate that
the mudstones of the Conasauga Formation are locally fractured,
weathered and hydraulically connected to the alluvium and weathered
bedrock deposits lying above. The lower limits of the hydraulically
connected portions of the bedrock, however, have not yet been
established, and reporting is not consistent on this. Both the Permit
Application and the 2021 Semi-Annual GWMCA Report generally describe
the aquifer similarly. For example, the 2021 Semi-Annual GWMCA Report
\66\ states,
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    \65\ Id.
    \66\ Id.

The uppermost aquifer beneath the Site corresponds to a coarse and more
permeable fraction of alluvial overburden soils and weathered or
fractured rock near the soil-rock interface. The uppermost aquifer is
typically located at depths between 15 and 50 feet below ground surface
(BGS). Soils are generally poorly graded sands with layers of clay and
well-graded gravels that overlay a mudstone or shale bedrock,''
See also Permit Application at section 3 of the GWMP. As shown on
Figures 5A and 5B in the Permit Application, bedrock intervals are not
included in the represented monitoring wells and little
characterization appears to have penetrated the bedrock beyond the
uppermost intervals.
    But elsewhere the 2021 Semi-Annual GWMCA Report states that,

Vertical delineation wells targeted more permeable/fractured water-
bearing zones within the Conasauga formation in the upper 50 feet of
bedrock.
    A further inconsistency appears on the geologic cross sections
included in the 2021 Semi-Annual GWMCA Report (see Figures 4A, 4B, 9,
and 10), which indicate the connection of the alluvial and bedrock
zones to depths of over 100 feet into the mudstone bedrock. These cross
sections and the associated boring logs, some of which were included in
the Permit Application and some of which were included in the 2021
Semi-Annual GWMCA Report, confirm that this group of geologic layers
and formations are hydraulically interconnected to depths of over 100
feet into the bedrock. The totality of this information forces the
conclusions that the lower limits of the uppermost aquifer have not
been determined and the uppermost aquifer and hydraulically connected
underlying intervals extends at least 100 feet into the bedrock.
    In other words, based on the available information, the uppermost
aquifer consists of the alluvial aquifer nearest the ground surface and
at least the uppermost 100 feet of the hydraulically connected bedrock
beneath it. See, 40 CFR 257.53 (definition of uppermost aquifer). As
such the materials presented in the Permit Application do not present a
complete or accurate representation of the uppermost aquifer and
hydraulically connected aquifer zones beneath it.
    In addition, the top-of-bedrock surface has not been adequately
resolved in all

areas of the site because some boring logs lack reliable confirmatory
data. According to the boring logs that were included in the Permit
Application, there are multiple missing intervals of ``no recovery''
from numerous borings advanced into bedrock, which indicate a large
potential for hydraulically significant zones that are currently
insufficiently characterized. As a consequence, EPA is proposing to
determine that the thickness, variability, nature, and hydrogeologic
significance of the transitional zone of weathering in the uppermost
part of bedrock has not been established, as required by Sec.
257.91(b).
    Furthermore, a hydraulic divide, generally located along the
northeastern boundary of the unit, indicates the groundwater hydraulics
are more complex than the current coarse monitoring network can
adequately evaluate. Additional monitoring points are needed laterally
(and vertically) in this area to provide the ``thorough
characterization of groundwater flow rate [and] groundwater flow
directions, including seasonal and temporal fluctuations in groundwater
flow'' required to support the design of the groundwater monitoring
system pursuant to Sec.  257.91(b)(1). There are also insufficient data
to allow for the determination of groundwater flow directions at the
eastern limits of the Ash Pond. While GSD-AP-MW-12 is downgradient of
GSD-AP-MW-1, there are no wells or piezometers that would serve as
hydraulic control points to the east of the Ash Pond to fully
characterize the groundwater flow directions at the eastern waste
boundary. Furthermore, GSD-AP-MW-1 consistently has one of the highest
groundwater elevations, and the possibility of eastward flow beyond the
eastern boundary cannot be ruled out without additional data.
Additional groundwater monitoring wells are needed to the northeast,
east, and southeast of the easternmost boundary of the Ash Pond. In
summary, EPA is proposing to determine that significant numbers of
additional characterization borings and monitoring wells are needed to
effectively characterize the alluvial aquifer nearest the ground
surface and hydraulically connected zones within the weathered bedrock
and upper portion of the bedrock intervals. See, 40 CFR 257.91(b).
ii. ADEM Issued a Final Permit With Background Wells That Do Not Meet
the Sec.  257.91(a)(1) Performance Standard
    The Federal CCR regulations require that a groundwater monitoring
system consist of a sufficient number of wells at appropriate locations
and depths to yield samples from the uppermost aquifer that accurately
represent the quality of the background groundwater that has not been
affected by leakage from a CCR unit. 40 CFR 257.91(a)(1). The
regulations also specify that background wells must normally be
hydraulically upgradient of the CCR unit, unless specific showings have
been made. See, Id. EPA is proposing to determine that the approved
GWMP fails to document either that the background wells are upgradient
of the CCR unit or that the wells meet the performance standards in
Sec.  257.91(a)(1)(i) or (ii). EPA is also proposing to determine that
the background wells in the approved groundwater monitoring system do
not ``accurately represent the quality of the background groundwater''
because of differences in the lithology between the background wells
and the majority of the wells in the downgradient groundwater
monitoring network, which is discussed in detail below.
    At the time of permit issuance, the approved groundwater monitoring
network installed at the unit consisted of three ``background''
monitoring wells (GSD-AP-MW-14, -16, and -17). According to the single
groundwater flow map included in the Permit Application,\67\
groundwater predominantly flows toward the main stem of the Coosa River
from both the southern and northern sides of the river. The Coosa River
acts as a hydraulic divide between the Ash Pond and the region to the
south of the river where the background wells are located.
Consequently, the Plant Gadsden background wells, which are all located
on the southern side of the river, are hydraulically disconnected from
the Ash Pond, rather than ``upgradient'' of the Ash Pond. In addition,
they are in a different flow system and therefore cannot accurately
represent the quality of the background groundwater at the Ash Pond.
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    \67\ Alabama Power. Revised Closure Permit Application for the
Plant Gadsden Ash Pond. April 30, 2020. Appendix 7, Plant Gadsden
Ash Pond Groundwater Monitoring Plan, Figure 6.
---------------------------------------------------------------------------

    The Federal regulations specify that wells that are not
hydraulically upgradient of the CCR unit can only serve as background
wells if one of two showings have been made: (1) that hydrogeologic
conditions do not allow the owner or operator to determine whether
wells are hydraulically upgradient; or (2) sampling at other wells will
be as representative or more representative of background groundwater
quality than that provided by the upgradient wells. 40 CFR
257.91(a)(1)(i), (ii).
    EPA found nothing in the Permit Application or on the facility's
CCR website to indicate that site conditions made it infeasible to
determine whether background wells could be installed at locations that
are hydraulically upgradient on the same side of the river. For
example, while on-site access may be limited due to conditions near the
Ash Pond, there is no discussion about other access points offsite to
the north, northeast, or east of the unit that may provide adequate
background samples. In addition, there are site-specific geologic
conditions identified in the Permit Application that indicate that
sampling at the current background wells will not ``accurately
represent the quality background groundwater'' quality at the Ash Pond.
40 CFR 257.91(a)(1). For example, based on the boring logs presented in
the Permit Application, background monitoring well GSD-AP-MW-17 is
screened in limestone but nearly all of the bedrock groundwater
monitoring wells surrounding the Ash Pond are screened in a different
rock type (i.e., mudstone). In addition, background monitoring well
GSD-AP-MW-16 is screened in sand and gravel alluvial materials and
based on a note included within the boring log, it is partially
screened into approximately four feet of limestone bedrock, whereas
numerous wells in the shallow downgradient compliance monitoring
network surrounding the Ash Pond are screened just above or across the
interface between mudstone and overlying overburden materials.
Limestone and mudstone are different rock types and, based on the
boring logs presented in the Permit Application, limestone substrates
do not appear to have been penetrated by monitoring wells installed for
the unit's downgradient compliance monitoring network on the northern
side of the river.
    Due to fundamental differences between limestone and mudstone
mineralogy and chemical composition, it is not clear that ambient
geochemical conditions in the limestone-hosted aquifer would be
representative of an environment where mudstone predominates, and site-
specific comparative analysis of both the geology and geochemistry for
the two distinct geochemical environments and flow systems is necessary
to determine whether the wells across the river are in fact
sufficiently representative of conditions within the uppermost aquifer
to serve as representative background wells. Although the Groundwater
Monitoring Plan included a limited

narrative at Section 4.2.2, entitled ``Groundwater Geochemistry,'' the
narrative did not address any known differences in geology, lithology,
or mineralogy between the two aquifers that are located on opposite
sides of the river. ADEM nevertheless approved the plan without
requiring the facility to resolve these issues.
iii. The Gadsden Final Permit Allows Insufficient Locations and Depths
of Downgradient Compliance Wells To Monitor the Uppermost Aquifer
    As previously discussed, the Federal regulations specify that a
groundwater monitoring system must ``consist[ ] of a sufficient number
of wells, installed at appropriate locations and depths, that . . .
accurately represent the quality of the groundwater passing the waste
boundary of the CCR unit.'' 40 CFR 257.91(a)(2). The regulations
further specify that ``[a]ll potential contaminant pathways must be
monitored.'' Id. But as discussed in more detail below, EPA is
proposing to determine that ADEM approved a GWMP with an insufficient
number of wells laterally along the downgradient perimeter of the unit
to monitor all potential contaminant pathways. EPA is also proposing to
determine that monitoring wells in the approved plan were not installed
at appropriate depths to ensure that all potential contaminant pathways
were monitored. Finally, EPA is proposing to determine that the
approved groundwater monitoring system fails to account for
preferential pathways beneath the Ash Pond.
(1) Insufficient Lateral Spacing of Compliance Wells To Monitor All
Potential Contaminant Pathways
    At the time of permit issuance, the approved groundwater monitoring
network installed at the unit consisted of only fifteen compliance
monitoring wells (GSD-AP-MW-1 through GSD-AP-MW-12 and GSD-AP-PZ-1,
GSD-AP-PZ-5 and GSD-AP-PZ-6), at an impoundment with a perimeter of
approximately 7,500 feet.
    Most of the groundwater monitoring wells that parallel the river
for the Plant Gadsden Ash Pond unit are spaced approximately 400 to 900
feet apart, and lateral distribution of wells is somewhat uniform with
downgradient monitoring wells surrounding the waste boundary at an
average lateral spacing of 630 feet.\68\ These large lateral well
spacings are particularly problematic to the north, northwest, west,
and to the southwest where groundwater discharges to the Coosa River.
Given the propensity for groundwater to flow within the preferential
pathways that exist at the site and the close proximity of the Coosa
River to the unit, one would expect to see a detailed rationale
explaining why these well locations at large lateral distances were
sufficient to monitor all potential contaminant pathways. However,
EPA's review of the approved GWMP did not identify any such
explanation. Therefore, given the proximity to the Coosa River, the
large well spacings make it likely that all potential contaminant
pathways--such as the gravel and other coarse material in the alluvium
and fractures, or the dissolution features at or below the weathered
bedrock surface that may be causing groundwater to surface water
discharges immediately adjacent to the Ash Pond--are not currently
monitored.
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    \68\ Southern Company Services 2022 Annual Groundwater
Monitoring and Corrective Action Report, Alabama Power Company Plant
Gorgas Ash Pond. Prepared for Alabama Power Company. February 1,
2023.
---------------------------------------------------------------------------

(2) Insufficient Number of Downgradient Compliance Wells Installed at
Appropriate Depths To Monitor the Entire Aquifer (Inadequate Vertical
Spacing)
    EPA is also proposing to determine that ADEM approved a GWMP that
lacked ``a sufficient number of wells, installed at appropriate
locations and depths'' to ensure that all potential contaminant
pathways in the entire uppermost aquifer are monitored. As stated
previously, the uppermost aquifer is a composite layered system
consisting of unconsolidated deposits of alluvial origin on top of
mudstone bedrock. The unconsolidated alluvial deposits consist of
interlayered deposits of silt, sand, gravel, and clay material. These
unconsolidated alluvial deposits overlay a variably fractured and
weathered bedrock material, predominantly mudstones of the Conasauga
formation. The contact between the uppermost portion of the
(consolidated) bedrock and the overlying (unconsolidated) alluvium,
which can also be described as the top-of-rock surface, is a distinct
hydraulically relevant zone of interest, and many ``downgradient''
compliance monitoring wells in the approved network are screened across
this interface, as is appropriate. However, although the lower limits
of the hydraulically connected portions of the bedrock have not yet
been established, as previously discussed, the available information
supports the conclusion that this group of geologic layers and
formations are hydraulically interconnected to depths of 100 feet or
more into the bedrock. Consequently, EPA is proposing to determine that
the entire group of geologic layers and formations should have been
more comprehensively monitored. See, 40 CFR 257.53 (definition of
uppermost aquifer).
    The downgradient well network ADEM approved is focused on a narrow
subset of the uppermost geologic layers associated with river
deposition. These unconsolidated materials occur in terrace deposits at