\41\ U.S. EPA. 2022. Notes from Meeting with ProChem--April 9,
2021. DCN SE10254.
---------------------------------------------------------------------------

    In the 2020 rule, EPA stated that some of these other applications
did not show that membrane filtration was available for use on FGD
wastewater by focusing on the differences between specific
characteristics of these individual wastewaters and FGD wastewater.
Information in the 2020 record and the current record, however,
indicates that there are many similarities between FGD and the non-FGD
wastestreams where membranes have been utilized. In the 2020 rule
record, EPA discussed that cooling tower blowdown at steam electric
plants and desalination in oil and gas extraction were examples where
membrane filtration was used in full-scale applications for treating
high TDS wastewaters, a characteristic of FGD wastewater (85 FR at
64664-64665, October 13, 2020). The 2020 rule record also established
that mining wastewaters, which are high in gypsum scaling potential
(another characteristic of FGD wastewater), have been successfully
treated with membrane filtration applications. Finally, the 2020 rule
record established that despite the high variability in ash transport
water (a third characteristic of FGD wastewater), it was successfully
treated with membrane filtration. This information indicates that
membrane filtration can operate effectively on wastestreams that
contain several characteristics of FGD wastewater, including high TDS,
high gypsum scaling potential, and high variability.\42\ Thus, based on
the information gathered in both EPA's prior and current records, the
utilization of membrane technology on other wastestreams supports the
Agency's proposed conclusion that membrane filtration technology is BAT
for FGD wastewater discharges.
---------------------------------------------------------------------------

    \42\ Use of membrane filtration has since expanded into
additional applications, treating wastewaters and industries beyond
those where it was used at the time of the 2020 rule (e.g., the food
and beverage, microelectronics/semiconductors, landfills, and
automotive industries).
---------------------------------------------------------------------------

    For all the foregoing reasons, EPA proposes to find that membrane
filtration is technologically available for the control of discharges
in FGD wastewater. Moreover, membrane filtration would make reasonable
further progress toward the Act's goal of eliminating the discharge of
all pollutants because it would result in zero discharge of FGD
wastewater from steam electric power plants.
    Economic achievability of membrane filtration. EPA proposes to find
that the costs of membrane filtration for control of FGD wastewater
discharges are economically achievable. Under the CWA, BAT limitations
must be economically achievable. Courts have interpreted that
requirement as a test of whether the regulations can be ``reasonably
borne'' by the industry as a whole. Chem. Mfrs. Ass'n v. EPA, 870 F.2d
177, 262 (5th Cir. 1989); BP Exploration & Oil v. EPA, 66 F.3d 784,
799-800 (6th Cir. 1996); see also Nat'l Wildlife Fed'n v. EPA, 286 F.3d
554, 570 (D.C. Cir. 2002); CPC Int'l Inc. v. Train, 540 F.2d 1329,
1341-42 (8th Cir. 1976), cert. denied, 430 U.S. 966 (1977). ``Congress
clearly understood that achieving the CWA's goal of eliminating all
discharges would cause `some disruption in our economy,' including
plant closures and job losses.'' Chem. Mfrs. Ass'n v. EPA, 870 F.2d at
252 (citations omitted); see also id. at 252 n.337 (reviewing cases in
which courts have upheld EPA's regulations that projected up to 50
percent closure rates). Although the 2020 rule cited the increased cost
of membrane filtration as compared to the selected technology basis as
a reason for rejecting membrane filtration,\43\ the Agency did not go
so far as to find that the costs of membrane filtration were not
economically achievable at that time. EPA proposes to find that the
costs of membrane filtration for FGD wastewater are economically
achievable for the industry as a whole, as discussed further below and
in Sections VII.F and VIII of this preamble.
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    \43\ While the relative costs of technologies differ from plant
to plant, new information obtained during the 2022 information
collection confirms what was shown in the 2020 record: that, in some
cases, technologies such as membrane filtration may be less costly
than biological treatment at individual plants even where, on
average, they would be more expensive to the industry as a whole.
---------------------------------------------------------------------------

    Non-water quality environmental impacts of membrane filtration. EPA
proposes to find that the non-water quality environmental impacts of
membrane filtration are acceptable. For further discussion of these
impacts, see Sections VII.G and X of this preamble. There was one non-
water quality environmental impact that the 2020 rule found was
unacceptable. In that rule, EPA expressed concern that use of membrane
filtration would unacceptably limit the beneficial use of FA. The 2020
rule record and the current record demonstrate that the beneficial use
of FA as an admixture or to replace Portland cement in concrete
provides a substantial environmental benefit. As such, the potential
that using FA to help dispose of brine from membrane filtration would
limit this beneficial use continues to be potentially the most
substantial non-water quality environmental impact when considering
whether membrane filtration is BAT. Nevertheless, in light of the facts
and analyses described in the following paragraphs, EPA proposes to
find that these non-water quality environmental impacts are acceptable,
most importantly because EPA's record indicates that there is
sufficient FA to accommodate both FGD brine encapsulation needs
following membrane filtration of FGD wastewater and the beneficial use
market.
    At the outset, EPA notes that the 2020 rule record discusses two
uses of FA: FA fixation and brine encapsulation. FA fixation occurs
when a facility conditions its dry FA with FGD wastewater rather than
fresh makeup water.\44\ The use of FA fixation prior to the 2020 rule
is partly due to the very low costs of FA conditioning compared to
other wastewater treatment technologies for FGD wastewater, as well as
the potential to eliminate the discharge of FGD wastewater. The 2020
rule record also included discussion of brine encapsulation. Brine
encapsulation is the process of mixing raw FGD wastewater or
concentrated

FGD wastewater brine with FA and lime, which results in pozzolanic
reactions that bind additional pollutants into the final solid matrix.
Since the 2020 rule, additional facilities have evaluated FA fixation
with FGD wastewater and/or encapsulation of FGD wastewater using FA and
lime. In at least one instance, fixation/encapsulation was less costly
than biological treatment. Thus, even without a new regulation
establishing BAT limitations based on membrane filtration, the record
demonstrates that implementation of the baseline 2020 rule has resulted
in the use of some FA for fixation or encapsulation.
---------------------------------------------------------------------------

    \44\ Conditioning is required to avoid air dispersion of the
fine FA particulates.
---------------------------------------------------------------------------

    While FA fixation still may be an option for brine management, EPA
evaluated the option most discussed in the record: brine encapsulation.
Since the question in evaluating the impact of brine encapsulation is
not whether the FA needed for these processes will be disposed of, but
to what extent additional disposal curtails the FA available for
beneficial use, EPA conducted an analysis of FA availability entitled
2021 Steam Electric Supplemental Proposed Rule: Fly Ash Availability
(SE10242). This analysis shows that the amount of FA needed to dispose
of membrane filtration's byproduct would not have an unacceptable
impact on the amount of FA that is used for beneficial purposes. In
this analysis, consistent with EPA's costing methodology, the Agency
conservatively assumed that all facilities generate brine from a single
pass of a membrane filtration system, which is then encapsulated with
FA and lime.\45\ In other words, EPA conservatively assumed no further
brine concentration (e.g., additional membrane filtration, or thermal
evaporation) would be performed that would further decrease the amount
of FA needed for encapsulation.
---------------------------------------------------------------------------

    \45\ While EPA's costs assume a polishing stage RO, the brine
from that system in returned to the first stage system.
---------------------------------------------------------------------------

    The results of EPA's conservative FA availability analysis support
the finding that there is sufficient FA for the majority of the 22
plants that would be expected to make treatment upgrades to meet the
proposed limitations. Based on EPA's analysis of 2019 and 2020 EIA
data, 20 of these 22 power plants that would be expected to install
membrane filtration under proposed Option 3 have enough FA for
encapsulation before accounting for reported FA sales. For the two
remaining plants, EPA estimates there would be a combined annual FA
deficiency of approximately 240,000 tons. After accounting for reported
FA sales, and assuming these sales continue, EPA estimates that an
additional four power plants may not have enough FA available for
encapsulation--a total of six plants with a combined annual FA
deficiency of approximately 750,000 tons (or approximately one percent
of all fly ash generated). In light of the relatively small on-site FA
deficiency estimated using conservative assumptions and, as discussed
more fully below, the potential for plants to use off-site FA or
additional lime for their brine encapsulation needs or available brine
management alternatives that do not rely on FA or use less FA, EPA
proposes that its estimate of on-site FA that may no longer be
available for beneficial use after implementation of this rule does not
rise to the level of an unacceptable non-water quality environmental
impact.
    The 750,000 ton per year shortfall of FA described above is likely
an overestimate for several reasons. First, based on the 2020 EIA data,
coal-fired power plants reported more than 30 million tons of FA
generated annually. While there are increasing FA sales reported each
year, EPA identified more than 100 coal-fired power plants generating
over 9.6 million tons of unsold FA that could be redirected from
disposal towards either encapsulation or other beneficial uses.\46\
Thus, EPA estimates that there is enough FA to accommodate both FGD
brine encapsulation needs and the beneficial use market with millions
of tons still requiring disposal. In the 2020 rule record, GenOn's
plans to install membrane filtration at certain facilities did not
include use of FA from those facilities. Instead, GenOn had plans to
send the brine offsite to be mixed with other FA and lime for disposal
and continued to seek options for beneficial use of the brine.\47\ The
concepts of use of off-site FA or beneficial use of brine are not
unique to GenOn. With respect to alternate FA, the 2022 World of Coal
Ash conference included 10 sessions with abstracts discussing the
harvesting and beneficiation of previously disposed ash.\48\ This
further supports that, after accounting for FA availability across the
entire industry, the non-water quality environmental impacts of
potential FA disposal associated with membrane filtration are
acceptable.
---------------------------------------------------------------------------

    \46\ EPA also notes that the 2020 rule record failed to
acknowledge that both the American Coal Ash Association and EPA have
historically considered waste stabilization and solidification as a
category of beneficial use. See, e.g., www.acaa-usa.org/wp-content/uploads/coal-combustion-products-use/ACAA-Brochure-Web.pdf.
    \47\ Notes from Call with GenOn (SE08614).
    \48\ Session abstracts are available online at:
www.woca2022.conferencespot.org/event-data/activity.
---------------------------------------------------------------------------

    Second, the Agency notes that multiple alternatives exist for
handling the resulting brine that do not involve FA and thus would have
no impact on the beneficial use of FA in other settings. EPA evaluated
alternative scenarios including disposal of brine in a deep injection
well and crystallization to a salt for disposal. With respect to
disposal in a deep injection well, EPA has been encouraging efforts for
water reuse rather than deep well injection, particularly in arid
western climates. Most of the facilities in question here, however, are
located in the Midwest and Southern U.S., places where water reuse may
still be important when feasible, but not to the level that EPA would
find injection to be unacceptable. With respect to crystallization and
disposal of the resultant salt, none of the facilities that currently
generates brine as part of a zero discharge system elects to
encapsulate and dispose of that brine.\49\ Rather, these facilities
send the concentrated brine to a crystallizer, and these resulting salt
crystals can then be disposed of without the use of FA. The costs and
non-water quality environmental impacts of these alternatives are
presented in Alternative Brine Management Methodology (SE10243). The
2015 rule record found crystallization to have acceptable non-water
quality environmental impacts. Based on this most current analysis
along with the 2015 record, EPA proposes to find that these alternative
brine management strategies have acceptable non-water quality
environmental impacts and that, while these costs are higher, they
would be economically achievable.
---------------------------------------------------------------------------

    \49\ While these systems are thermal systems rather than
membrane systems, the brine generated would not differ substantially
in its ultimate characteristics.
---------------------------------------------------------------------------

    Third, EPA also notes that the six plants with potentially
insufficient FA may still be able to sell their FA if the brine
encapsulation were performed with additional lime use. EPA notes that
extraction, processing, and transportation associated with additional
lime use would result in some additional air emissions, but that these
emissions would be less than those associated with Portland cement, the
material that FA replaces in its most environmentally beneficial use.
    Fourth, EPA's estimates regarding non-water quality environmental
impacts associated with membrane filtration's byproduct are likely
conservative (an overestimate) because, even where encapsulation will
be the

ultimate brine management scenario, further concentration of the brine
is not only possible, but probable for at least some facilities. For
example, one utility evaluating 2020 rule VIP-compliant systems for a
specific facility discussed how it would send the membrane reject brine
to a thermal system to further reduce the volume of FGD brine to be
encapsulated. This process would result in less demand for FA due to
the decreased volume of brine.
    Finally, the 2020 record indicated that the management of FGD brine
could actually lead to new beneficial uses. At least one Chinese plant
was taking its brine down to salts and then selling its salts for an
industrial use.\50\ Where companies are ultimately able to beneficially
use some of the brine in lieu of disposal, this would be a positive
non-water quality environmental impact. Thus, both ongoing evaluation
and historical practice indicate EPA's assumptions regarding FA use to
encapsulate FGD brine is likely a conservative estimate of the amount
of ash that will be diverted from beneficial use to disposal. All of
the above information supports EPA's proposed finding that the non-
water quality environmental impacts of membrane filtration are
acceptable.
---------------------------------------------------------------------------

    \50\ Final DuPont Meeting Notes (SE08618), Notes from Vendor
Call with DuPont October 29 and December 8, 2021 (SE10245).
---------------------------------------------------------------------------

b. Other Zero Discharge Technologies
    For this proposal, EPA evaluated other zero discharge technologies
that could also eliminate the discharge of FGD wastewater. However, EPA
is not relying upon them as a basis for proposed BAT limitations
because they achieve the same pollutant reductions as the proposed BAT
technology basis (membrane filtration) but at a higher cost.
Nevertheless, EPA solicits comment on whether the Agency should
determine in a final rule that any one or more of these technologies
constitutes an additional BAT technology basis for controlling
pollutants discharged in FGD wastewater in addition to membrane
technology, or alternatively, in place of membrane technology.
    Currently, 36 coal-fired power plants in the United States operate
wet FGD systems and manage their wastewater to achieve zero
discharge.\51\ These plants achieve zero discharge using evaporation
ponds, recycling of FGD wastewater, ash fixation, thermal systems
(e.g., falling film evaporators), or SDEs. Since 2009, approximately 15
additional plants that also operated wet FGD systems and achieved zero
discharge of FGD wastewater have retired or refueled such that the FGD
wastewater has been eliminated. While some of these systems
(evaporation ponds, fixation, and recycling) may not be available at
every single site,\52\ the number of thermal and SDE systems both
domestically and internationally in use on FGD wastewater demonstrates
that they are commercially available, and thus potentially
technologically available, as technologies for treating FGD wastewater
to meet zero-discharge limitations.\53\ Specifically, at least some
steam electric power plants have used the traditional thermal systems
\54\ and SDEs \55\ to achieve zero discharge of FGD wastewater
domestically and internationally for years, and several recent electric
utility reports acknowledge this fact.56 57 58 59 EPA has
separately evaluated the costs of thermal and SDE systems. Costs per
facility have decreased over time, and due to retirements and fuel
conversions, total costs have decreased substantially. Although EPA has
not estimated potential closures associated with these technologies
using the same model it has for supporting the economic achievability
of Option 3, as discussed more in Section VIII of this preamble below,
EPA does not expect the costs associated with these technologies to
have a significant impact on industry closures. In that case, the costs
of these technologies, although higher than the costs estimated for
industrywide membrane filtration,\60\ would be reasonable for the
category as whole, and thus economically achievable.61 62
Furthermore, consistent with the findings of the 2015 rule, EPA
proposes to find no unacceptable non-water quality environmental
impacts from operation of thermal systems and proposes that SDEs have
similarly acceptable non-water quality environmental impacts.\63\
---------------------------------------------------------------------------

    \51\ A 37th project that will result in zero discharge may have
also been completed: www.woodplc.com/insights/articles/engineering-solutions-for-wastewater-treatment.
    \52\ EPA acknowledged as much in both the 2015 and 2020 rules.
    \53\ See, e.g., APEC (Asia-Pacific Economic Cooperation) Energy
Working Group. 2015. Water Energy Nexus: Coal-Based Power Generation
and Conversion--Saving Water. EWG 08/2014 A. December. Available
online at: www.apec.org/docs/default-source/Publications/2017/2/
Water-Energy-Nexus-Coal-Based-Power-Generation-and-Conversion__-
Saving-Water/217_EWG_APEC-Energy-Water-Nexus-Report-20161230-
_CPAU_010217.pdf.
    \54\ The Italian thermal systems discussed first in the 2013
proposed rule have been in operation for over a decade.
    \55\ Spray dry absorbers, effectively the same technology as the
SDE, have been in use for decades to capture the same pollutants
present in FGD wastewater.
    \56\ ``Proven technology (considered BAT for new sources by
EPA). 3+ U.S. installations and 6+ European installations by
Aquatech'' (SE07206).
    \57\ SE10234.
    \58\ SE09998.
    \59\ EPRI (Electric Power Research Institute). 2017. Thermal
Evaporation Technologies for Treating Power Plant Wastewater: A
Review of Six Technologies.<PHONE_NUMBER>02011665. (SE06971).
    \60\ The record indicates that individual utilities have found
thermal and/or SDE systems to be less expensive than membrane (and
even biological) systems in some cases.
    \61\ Thermal Evaporation Cost Methodology (SE10246).
    \62\ Spray Dryer Evaporator Cost Methodology (SE10247).
    \63\ EPA evaluated the non-water quality environmental impacts
of these technologies in Alternative Brine Management Methodology
(SE10243). EPA performed this evaluation in the context of brine
management technologies for membrane filtration, and the types of
impacts and findings would remain the same even if used as
standalone technologies.
---------------------------------------------------------------------------

    EPA solicits comment on whether the Agency should identify, in any
final rule, one or more of the technologies of evaporation ponds,
recycling of FGD wastewater, ash fixation, thermal systems (e.g.,
falling film evaporators), or SDEs as a BAT technology basis for
control of FGD wastewater discharges, in addition to membrane
filtration technology. EPA solicits comment on whether such additional
BAT basis or bases would be technologically available and economically
achievable, and whether they would have acceptable non-water quality
environmental impacts. EPA also solicits comment on whether any one or
more of these alternative zero discharge technologies should be the BAT
technology basis for control of FGD wastewater discharges in lieu of
chemical precipitation plus membrane filtration.
c. EPA Proposes To Reject as BAT Less Stringent Technologies Than
Membrane Filtration
    Except for the early adopter subcategory discussed in Section
VII.C.4 of this preamble, EPA is not proposing to base BAT on chemical
precipitation followed by a low hydraulic residence time biological
treatment including ultrafiltration, the technology which EPA
determined to be BAT in the 2020 rule. Under CWA section 301(b)(2)(A),
BAT is supposed to result in ``reasonable further progress toward the
national goal of eliminating the discharge of all pollutants'' and
``shall require the elimination of discharges of all pollutants if the
Administrator finds . . . that such elimination is technologically and
economically achievable'' as determined in accordance with CWA section
304(b)(2)(B). The record shows that the 2020 rule industrywide BAT
technology

basis for FGD wastewater removes fewer pollutants than the BAT basis of
chemical precipitation plus membrane filtration identified in this
proposal. Similarly, except for the permanent cessation of coal
combustion subcategory discussed in Section VII.C.3 of this preamble,
EPA is not identifying the less stringent (and previously rejected)
technologies of surface impoundments or chemical precipitation, as
these technologies too will remove fewer pollutants than the BAT in
this proposal.
2. BA Transport Water
    EPA is proposing dry handling or closed-loop systems as the
technology basis for establishing BAT limitations to control pollutants
discharged in BA transport water. EPA proposes to find that these
technologies are technologically available, are economically
achievable, and have acceptable non-water quality environmental impacts
after evaluating the factors specified in CWA section 304(b)(2)(B).
Specifically, dry handling systems include mechanical drag systems
(e.g., submerged chain conveyors), submerged grind conveyors (e.g.,
compact submerged conveyors), air-cooled conveyor systems, and
pneumatic systems. Closed-loop systems consist of remote mechanical
drag systems paired with any necessary storage tanks, chemical addition
systems, and/or RO treatment necessary to fully recycle BA transport
water.\64\
---------------------------------------------------------------------------

    \64\ In addition to remote MDSs, non-BAT technologies include
many dewatering bins (also known as hydrobins), and surface
impoundments may also have the flexibility to operate as closed-loop
systems. Like remote MDSs, the latter systems may need to install
chemical addition systems (acid, caustic, and/or flocculants), RO
systems, and/or additional storage tanks to operate as fully closed
loop.
---------------------------------------------------------------------------

    In the 2020 rule, EPA rejected dry handling or closed-loop systems
as the BAT technology basis in favor of high recycle rate systems due
to process changes plants made to comply with the CCR rule (i.e., re-
routing non-CCR wastes to their wet BA handling systems to avoid
sending them to their unlined surface impoundments, as the CCR rule's
cease-receipt-of-waste date approached), as well as the additional
costs of dry handling or closed-loop systems. EPA also stated in 2020
that many plants may not, as a technical matter, be able to fully close
their BA handling systems to operate without discharge. Upon further
careful consideration of the record and the CCR rule, EPA does not
think that plants need a purge allowance to comply with the CCR rule.
While in some cases plants may incur additional costs to achieve zero
discharge by making process changes, the widespread use of dry handling
or closed-loop systems supports the view that these technologies are
available. As explained below, EPA proposes to find that the
technologies are available and economically achievable, and they have
acceptable non-water quality environmental impacts. Thus, EPA is
proposing dry handling or closed-loop systems as the BAT technology
basis for BA transport water.
    In the first subsection immediately below, EPA discusses its
rationale for proposing dry handling or closed-loop systems as BAT for
BA transport water. In the following subsection, EPA discusses why it
is not proposing less stringent technologies than dry handling or
closed-loop systems. In the final subsection, EPA solicits comment on
issues associated with a BA transport water purge allowance and bottom
ash contact water.
a. Dry Handling or Closed-Loop Systems
    Availability of dry handling or closed-loop systems. Based on the
record, EPA proposes to find that dry handling or closed-loop systems
are technologically available. At the time of the 2020 rule, EPA
estimated that more than 75 percent of plants already employed dry
handling systems or wet sluicing systems in a closed-loop manner, or
had announced plans to switch to such systems in the near future. The
high percentage of plants already employing these systems indicates
that they are technologically available. Some of these systems have
been in use since the 1970s, and today, most facilities have installed
one or more such systems.\65\
---------------------------------------------------------------------------

    \65\ One vendor estimates that only seven ash conversions remain
in the entire industry.
---------------------------------------------------------------------------

    In the 2015 and 2020 rule preambles, EPA discussed the widespread
use of dry handling systems for control of BA transport water servicing
approximately 200 EGUs at over 100 plants. In the 2020 rule, EPA also
discussed advances in dry BA handling systems. Specifically, the Agency
discussed a newer technology called submerged grind conveyors (one
example of which is called a compact submerged conveyor). At the time,
compact submerged conveyors were known to be installed and in operation
at two plants. EPA has since learned that about 12 compact submerged
conveyors have been installed.66 67 Partly due to the
increased use of compact submerged conveyors, more dry handling systems
are currently in place than EPA originally forecasted. For example, as
indicated in the 2020 rule record, one utility commented that it had
space constraints at a facility that would preclude the installation of
a compact submerged conveyor, and EPA thus projected that this facility
would employ a high recycle rate system under the 2020 rule. Since the
2020 rule, however, that utility ultimately proceeded to install a
different dry handling system, which highlights the broad array of dry
handling options available for coal-fired power plants, regardless of
their configuration. Even where space constraints may prohibit certain
dry systems, a plant could use a pneumatic system, albeit at a somewhat
greater cost. The 2020 rule record included information on 50 pneumatic
installations from as early as 1992. Given that BAT is to reflect the
best performing plant in the field Kennecott v. EPA, 780 F.2d at 447,
and the facts in the record support the use of dry handling technology
to achieve zero discharge of BA transport water, EPA could propose to
identify dry handling as the sole technology basis for control of BA
transport water. Nonetheless, as it did in the 2015 rule, EPA is
proposing to also identify closed-loop systems as a BAT technology
basis for controlling discharges of BA transport water, given that a
limited number of plants may find that option to be more attractive due
to space constraints and lower costs when compared to a pneumatic
system.
---------------------------------------------------------------------------

    \66\ Some utilities have even suggested that the discussion of
compact submerged conveyors in the final 2020 rule preamble and
additional compliance timeframes have led them to consider these
newer dry systems rather than a previously contemplated high recycle
rate/closed-loop system.
    \67\ Final Burns & McDonnell Meeting Notes (SE10248).
---------------------------------------------------------------------------

    After the 2015 rule and throughout the 2020 rulemaking, certain
industry representatives argued that there are challenges to operating
a closed-loop BA handling system in a truly zero discharge manner. They
argued that closed-loop systems, including remote MDS and dewatering
bins, cannot maintain fully closed-loop operations due to chemistry
issues or water imbalances in the system, such as those that might
occur from unexpected maintenance or large precipitation events.
However, even accounting for these issues, the 2020 rule did not find
that closed-loop systems are not technologically available. Information
in EPA's 2020 rule record indicated that plants can operate their
closed-loop systems to achieve zero discharge, although this could
require some process changes and their resulting costs. The 2020 record
found that industry could achieve complete recycle

at an additional cost of $63 million per year in after-tax costs
(beyond the costs of the systems themselves) over the 2015 rule's
estimates. Moreover, EPA's cost estimates at the time were admittedly
conservative, as the Agency assumed the need to treat 10 percent of the
BA handling system's volume using RO for every facility with a closed-
loop system. See Section VIII of this preamble for a further discussion
of costs associated with the proposed closed-loop system technology
basis.
    In the 2020 rule record, EPA discussed four potential challenges
with maintaining closed-loop systems: (1) managing non-BA transport
water inflows, (2) managing precipitation-related inflows, (3) managing
unexpected maintenance events, and (4) maintaining water system
chemistry. As further discussed below, based on the current record,
none of these previously discussed challenges provide a reasoned basis
for finding closed-loop systems not to be technologically available,
although these issues may in certain circumstances require a plant to
incur additional costs.
    First, in 2020, EPA stated that managing non-BA transport water
inflows had the potential to result in water imbalances within a
closed-loop system. With respect to the inflow of other wastestreams
into the BA handling system, EPA's record in the 2015 and 2020 rules
indicates that closed-loop systems (i.e., remote MDSs) can be sized to
handle these additional wastestreams.\68\ To ensure effective
operations when designing and procuring closed-loop systems, facilities
should seek to size these systems for all wastestreams the system would
handle. Moreover, there is no evidence in the record that unanticipated
inflows cannot be addressed with reasonable steps.\69\ EPA solicits
comment on whether the best performing remote MDSs have documented non-
BA transport water inflows regularly exceeding the ability of the
systems to reuse their wastewater. EPA solicits comment providing data
from any remote MDS that would suggest whether a purge allowance is or
is not appropriate due to the technological availability of the system.
---------------------------------------------------------------------------

    \68\ For example, the Belews Creek remote MDS discussed during
the 2020 rulemaking also accepts economizer ash and pyrites
(SE07137).
    \69\ Even including dewatering bins, which are not the basis for
either the 2015 BAT for BA transport water or this proposed BAT, the
2020 record included only a single facility where the water inflows
to its dewatering bin system were too great to be recycled due to
the presence of other wastewaters.
---------------------------------------------------------------------------

    Second, in 2020, EPA stated that managing precipitation-related
inflows had the potential to result in water imbalances in the BA
handling system. However, EPA's record shows that precipitation-related
inflows can be adequately managed with design improvements, including
the use of roofing where appropriate. The 2015 BAT technology basis and
2020 rule remote MDS technology designs included and costed for covers
to avoid collecting precipitation.\70\ There is no record evidence that
this previously discussed precipitation-related challenge cannot be
overcome with reasonable steps and, therefore, this concern does not
provide a basis for rejecting closed-loop systems as BAT. EPA solicits
comment on whether the best performing remote MDSs have documented
precipitation inflows that have exceeded the ability of the systems to
reuse or store their wastewater, or whether the technology issue can be
addressed by undertaking measures at a reasonable additional cost. EPA
solicits comment providing data from such systems that would suggest
whether a purge allowance is or is not warranted. EPA solicits comment
on allowing for unlimited one-time purges due to large precipitation
events exceeding a 10-year storm event of 24-hour or longer duration
(e.g., a 30-day storm event) where drains or other precipitation-
collection components may not be amenable to roofs or other covers,
including any necessary reporting or recordkeeping requirements. Due to
the increasing storm severity associated with climate change, EPA also
solicits comment on whether a different type of storm event would be
more appropriate. Should EPA allow such discharges, the Agency solicits
comment on whether to require facilities to submit information when
they discharge, such as why the discharge was necessary, how much was
discharged, or any other specific information (e.g., meteorological
information) that would be helpful to the permitting authority or
public at large.
---------------------------------------------------------------------------

    \70\ 2020 Supplemental TDD (EPA-821-R-20-001).
---------------------------------------------------------------------------

    A third previously discussed challenge mentioned in the 2020 rule
to operating a remote MDS as a closed-loop system is the possibility of
infrequent maintenance events that might fall outside the 2015 rule
exemption of ``minor maintenance'' and ``leaks'' from the definition of
BA transport water. EPRI (2018) listed several such maintenance events;
most were expected to occur less than annually. EPRI provided
information about the estimated frequency and volume of water
associated with each maintenance event; however, EPRI did not provide
information about a specific remote MDS unable to manage these
maintenance events with existing maintenance tanks. Furthermore, even
where maintenance wastewater volumes are too large to be managed in
existing maintenance tanks, utilities can, at additional cost, lease
storage tanks for short-term maintenance where these infrequent
maintenance events are foreseeable.\71\ There is no record evidence
that infrequent maintenance events cannot be overcome with reasonable
steps and, therefore, this concern does not provide a basis for
rejecting closed-loop systems as BAT. EPA solicits comment on whether
data from such systems would suggest a purge allowance is or is not
warranted, as well as on the underlying data. EPA also solicits comment
on whether the Agency should expand the existing ``minor maintenance
event'' exemption from the definition of BA transport water in Sec.
423.11(p). One example of such a potential expansion could include
changing the current language that excludes ``minor maintenance events
(e.g., replacement of valves or pipe section)'' to instead state
``minor maintenance (e.g., replacement of valves or pipe sections) or
infrequent (i.e., occurring less than annually) maintenance events.''
Another example would be to delete the term ``minor'' and associated
parenthetical and merely say ``maintenance events.'' To the extent that
EPA expands this exemption in 40 CFR 423.11(p), the Agency also
solicits comment on any appropriate reporting or recordkeeping
requirements. For example, EPA is interested in commenters' views on
whether, when a facility discharges due to a maintenance event,
facilities should submit information about why it was necessary to
discharge, how much was discharged, or any other specific information
that would be helpful to the permitting authority or broader public.
Furthermore, EPA solicits comment on whether implementation of such a
change to the definition of BA transport water should require, for
example, a demonstration that the maintenance water could not be
managed within the system.
---------------------------------------------------------------------------

    \71\ In contrast, if the maintenance discharge is caused by an
unforeseeable upset condition, the plant would have an affirmative
defense to an enforcement action if the requirements of 40 CFR
122.41(n) are met.
---------------------------------------------------------------------------

    The final engineering challenge discussed in the 2020 rule record
as a reason for selecting high recycle rate systems rather than closed-
loop systems was the need to maintain water system chemistry. The 2020
rule discussed

potentially problematic system chemistries, such as extreme acidic
conditions, high scaling potential, and the buildup of fine
particulates that could clog pumps and other equipment. The 2015
closed-loop system BAT design basis included a chemical addition system
to manage these system chemistries. In particular, corrosivity could be
managed through pH adjustment, scaling could be managed with acid and/
or antiscalants, and fines could be further settled out with polymers
and other coagulants. EPRI \72\ documented that some systems went
slightly further, pairing the chemical addition systems with changes in
operations such as higher flow rates or longer contact time. Even where
all else fails, the same slipstream of purge allowed under the 2020
rule could be treated with RO and recycled back in as clean makeup
water. While it is possible that addressing these issues could entail
additional costs, there is no record evidence that this chemistry-
related challenge cannot be overcome with reasonable steps and,
therefore, this concern does not provide a basis for rejecting closed-
loop systems as BAT. EPA solicits comment on the extent to which any
plant using a remote MDS has tried all the processes described above
and still failed to adequately control system chemistry. EPA solicits
comment on whether data from such systems would suggest a purge is or
is not warranted, as well as on the underlying data.
---------------------------------------------------------------------------

    \72\ SE08927.
---------------------------------------------------------------------------

    For all the foregoing reasons, EPA proposes to find that the record
indicates that dry handling or closed-loop systems are technologically
available for control of discharges in BA transport water. Moreover,
dry handling or closed-loop systems would result in reasonable further
progress toward the Act's goal of eliminating the discharge of all
pollutants, as the limitations based on this technology would require
zero discharge of BA transport water from the steam electric industry.
    Economic achievability of dry handling or closed-loop systems. EPA
proposes to find that the costs of dry handling or closed-loop systems
are economically achievable for the industry as a whole. In the 2020
rule, EPA cited the additional costs of closed-loop systems as part of
its basis for selecting high recycle rate systems. In the 2020 rule
record, EPA noted that it had ``conservatively'' estimated costs of $63
million per year based on all facilities using a remote MDS needing a
10 percent purge to be treated with RO in order to achieve complete
recycle (i.e., zero discharge operations). However, EPA never found
that the additional costs to achieve zero discharge were not
economically achievable. Moreover, the 2020 rule record never
demonstrated that a full 10 percent purge at all facilities was a
realistic costing assumption. The primary basis for the 2020 rule purge
allowance was a 2016 report from EPRI that involved continuous purges,
the majority of which were well under one percent. Thus, in the 2020
rule record, EPA presented a sensitivity analysis with costs for a two
percent purge treatment, which may better reflect actual operations.
    Even using the more conservative cost estimates in the baseline IPM
analysis for the 2020 rule (i.e., full implementation of the 2015
rule),\73\ the record demonstrated minimal changes in coal combustion
and in steam electric power plant retirements. After updating these
conservative cost estimates to $45 million per year pre-tax in proposed
Option 3, the IPM analysis performed for this proposed rule continues
to demonstrate that, after including the costs of treating all
wastestreams--including achieving zero discharge for BA transport
water--the proposed rule would result in minimal economic impacts. (For
further information, see Sections VII.F and VIII of this preamble).
Because EPA is required to consider whether the cost of BAT can be
reasonably borne by the industry and confers on EPA discretion in
consideration of the BAT factors, see, e.g., Chem. Mfrs. Ass'n v. EPA,
870 F.2d at 262; Weyerhaeuser v. Costle, 590 F.2d at 1045, EPA proposes
to find that these additional costs are economically achievable as that
term is used in the CWA.
---------------------------------------------------------------------------

    \73\ The 2020 rule analysis had a baseline of zero discharge
under the 2015 rule.
---------------------------------------------------------------------------

    Non-water quality environmental impacts of dry handling or closed-
loop systems. EPA proposes to find that the non-water quality
environmental impacts associated with dry handling or closed-loop
systems for controlling BA transport water discharges are acceptable.
See Sections VII.G and X of this preamble below for more details.
    Process changes associated with dry handling or closed-loop
systems. EPA also rejected closed-loop systems in the 2020 rule due to
process changes happening at steam electric facilities as they move
toward compliance with the CCR rule. EPA stated that as plants close
their surface impoundments under the CCR rule, they may choose to send
certain non-CCR wastewaters to their BA handling system. This could
complicate their efforts to fully close their BA handling systems due
to increased scaling, corrosivity, or plugging of equipment.
Alternatively, EPA mentioned that a closed-loop requirement might
incentivize plants to discharge their non-CCR wastes rather than send
them to their BA handling systems for control, in which case they would
be subject to less stringent requirements governing low-volume wastes.
EPA also suggested that requiring limitations based on closed-loop
systems could result in plants using their surface impoundments longer,
assuming plants cannot build alternative storage capacity and need to
continue to send their non-CCR wastes to unlined impoundments.
    The rationale in the 2020 rule is not persuasive under the
timeframe of any final ELG rule because by the time any BA transport
water requirement would be implemented in NPDES permits, the CCR rule
ash pond cease receipt of waste dates will have long since passed, or
this rule's proposed subcategories could address any remaining CCR
coordination issue. The CCR Part A rule required plants to cease
receipt of waste in unlined surface impoundments by April 11, 2021.\74\
This date has already passed, with most facilities having completed
conversions from leaking, unlined surface impoundment BA handling
systems to a CCR rule-compliant BA handling system (i.e., systems that
do not rely on unlined CCR surface impoundments). Of the remaining
unlined surface impoundments, those operating under CCR Part A
flexibility found in Sec.  257.103(f)(2) are permanently ceasing coal
combustion, and EPA proposes to continue to treat them differently
under the subcategory for EGUs permanently ceasing coal combustion by
2028. This leaves only the unlined surface impoundments where
alternative capacity is technically infeasible, a CCR Part A
flexibility with maximum timeframes of October 15, 2023, and October
15, 2024, to cease receipt of waste.\75\ These later dates require EPA
approval.\76\ Even with extensions, nearly every facility will have
completed its conversion to a CCR rule-compliant BA handling method by
2024, the year in which EPA intends to promulgate any final ELG
following this proposal. Since EPA expects that all facilities would
comply with the CCR

rule cease-receipt-of-waste provisions and have alternative BA handling
systems or compliant surface impoundments by then, there are no looming
deadlines and tight timeframes that would justify continued
flexibility. Instead, with the work to meet these CCR deadlines
completed, facilities with high recycle rate systems would be free to
focus on transitioning those high recycle rate systems to closed-loop
operations.\77\ Thus, EPA proposes that there are no ``process change''
reasons related to the CCR rule that undermine EPA's proposed BAT basis
of dry handling or closed-loop systems for control of BA transport
water discharges.
---------------------------------------------------------------------------

    \74\ 40 CFR 257.101(a)(1).
    \75\ 40 CFR 257.103(f)(1)(vi).
    \76\ Further information on the implementation of these Part A
applications is available on EPA's website at: www.epa.gov/coalash/coal-combustion-residuals-ccr-part-implementation.
    \77\ Although EPA estimates that fully closing the loop would be
less expensive than converting to dry handling, nothing would
preclude a facility with a high recycle rate system from installing
one of the technologically available and economically achievable dry
handling systems.
---------------------------------------------------------------------------

b. EPA Proposes To Reject as BAT Less Stringent Technologies Than Dry
Handling or Closed-Loop Systems
    Except for the early adopter subcategory, EPA is not proposing to
base BAT on high recycle rate systems. In the 2020 rule, EPA reversed
its decision from the 2015 rule and determined that closed-loop systems
were not BAT. As a result, EPA established a volumetric purge allowance
(with a maximum of 10 percent of the system volume) to be determined on
a case-by-case basis by the permitting authority, which required a
permitting authority's BPJ analysis to determine whether that purge
required further control. As discussed above, the technological issues
can be resolved, albeit at potentially additional costs, which EPA now
proposes are economically achievable. Furthermore, a dewatering bin or
remote MDS with a purge removes fewer pollutants than the proposed BAT
basis of dry handling or closed-loop systems, which the Agency proposes
to find are technologically available, are economically achievable, and
have acceptable non-water quality environmental impacts. Under CWA
section 301(b)(2)(A), BAT is supposed to result in ``reasonable further
progress toward the national goal of eliminating the discharge of all
pollutants'' and ``shall require the elimination of discharges of all
pollutants if the Administrator finds . . . that such elimination is
technologically and economically achievable'' as determined in
accordance with CWA section 304(b)(2)(B). Because high rate recycle
systems achieve fewer pollutant removals than the dry handling or
closed-loop systems EPA has proposed as BAT, such less stringent
technologies would not result in reasonable further progress toward the
CWA's goal of eliminating the discharge of pollutants.
    Except for the permanent cessation of coal combustion subcategory,
EPA is also not identifying the less stringent (and previously
rejected) technology of surface impoundments as the technology basis
for BAT, as this technology would also remove fewer pollutants than the
proposed BAT basis of dry handling or closed-loop systems, which EPA
proposes are technologically available, are economically achievable,
and have acceptable non-water quality environmental impacts.
c. Solicitation of Comment on Additional BPJ-Based Permitting
Constraints and Issues Related to BA Contact Water
    Despite the preceding discussion, if EPA were to maintain the 2020
rule's purge allowance, the Agency solicits comment on whether it
should establish constraints and additional requirements on where and
how a purge may be allowed on a case-by-case basis. All the instances
EPA is aware of involving requests by plants to purge BA transport
water under the 2020 rule have included a request for a full 10 percent
purge. The limitation EPA established in the 2020 rule was, however, a
site-specific purge allowance with a maximum 10 percent threshold. In
practice, this flexibility has resulted in a situation where BA
handling systems either achieve zero discharge or purge the maximum 10
percent. EPA notes that all the chemistry-related purges discussed in
EPRI (2016) were one percent or less of system volume, and it solicits
comment on whether, if a final rule were to include allowance for any
purge, the Agency should constrain the purge allowance to reflect the
smaller continuous purge volumes in EPRI (2016). EPA also solicits
comment on whether, in the event of allowance of any purge, the
permittee should provide further analysis and justification to the
permitting authority or if EPA should place further constraints on the
permitting authority in allowing purges. For example, EPA solicits
comment on whether permittees should be required to complete an
engineering study, starting with closed-loop operations and slowly
increasing purge as necessary after demonstrating that the system
cannot be operated with the existing level of purge (e.g., by using
chemical addition systems, changing flows, or residence time).
    Moreover, if EPA elects to retain a high recycle rate system as BAT
for BA transport water, the Agency is interested in whether there
should be any additional constraints on the purge allowance to ensure
that the pollutant reductions achieved are consistent with the
reductions expected from the BAT technology basis. In particular, EPA
has become aware of system operations that recycle a high percent of
water, but in practice may not achieve pollutant removals as high as
those of the remote mechanical drag chain and dewatering bin systems
described in the 2020 rule preamble, which were the bases for the
following findings:
    Based on actual, measured purge rates in EPRI (2016), however, the
agency estimates that actual purge rates necessary on a day-to-day
basis may be less than one percent of the system's volume, with higher
purges necessary at less frequent intervals due to precipitation and
maintenance. Furthermore, while surface impoundments can cover dozens
of acres and contain volumes in the billions of gallons, typical high
recycle rate systems have volumes closer to one-half million gallons
(\1/2\ million). Thus, even assuming the proposed maximum allowable
purge of 10 percent is necessary for a unit, the average gallons per
day released by high recycle rate systems will be two percent of the
average gallons per day released by surface impoundments, and therefore
will also be 1.5 percent of the pollutant releases expected from
surface impoundments. Industry-wide, EPA estimates this combination of
reduced volume and increased recycling reduces discharges by 366
million lb/year of pollutants, and thus makes reasonable further
progress toward the CWA goal to eliminate the discharge of pollutants.
See 33 U.S.C. 1251(a), 1311(b)(2)(A). Therefore, it is the combination
of the reduced system volume and high capacity to recycle BA transport
water that supports EPA's basis for high recycle rate systems as BAT.
(Emphasis added.)
    As an example of such a system, following the 2020 rule, EPA became
aware of one plant that intentionally constructed a concrete basin
system intended to recycle only 90 percent of BA transport water (Smith
et al., 2022).\78\ Due to the size of this system, the 10 percent purge
generated results in a much greater volume of discharged wastewater
than the 2020 rule contemplated. This facility is not unique in its use
of large, concrete basins. The APS Four Corners power

plant recently submitted a request for a 10 percent purge of BA
transport water \79\ where the claimed system volume of over 4.5
million gallons would result in a BA transport water purge of nearly
one-half MGD, a volume greater than the entirety of the purges claimed
for the Duke Energy coal fleet.\80\ While the facility employs
dewatering bins as the primary BA handling mechanism, part of this high
volume discharge request appears to stem from the large concrete
basins, or ``tanks,'' that APS has installed. EPA solicits comment on
other facilities that have installed concrete basin systems or tanks
and any facts describing the size, flows, and other operational
parameters of such systems. Furthermore, should EPA ultimately elect to
retain a purge allowance for BA transport water, the Agency solicits
comment on whether the total volume (not just the percent) of purge
should also be limited to ensure that the system achieves the pollutant
removals of a true high recycle rate system (i.e., a remote MDS).
---------------------------------------------------------------------------

    \78\ See www.woca2022.conferencespot.org/event-data/pdf/catalyst_activity_28074/catalyst_activity_paper_20220329020324138_a6f09dfc_ad86_4183_9ecb_a71e88b48245.
    \79\ An updated submission made to EPA has since reduced this
request to between two and 2.5 percent of system volume and is
currently being evaluated by the Agency.
    \80\ In contrast, the purge requests from Duke Energy estimated
a 10 percent purge of between approximately 50,000 and 100,000
gallons per day at each of the company's five plants with such
systems.
---------------------------------------------------------------------------

    While EPA is concerned that the site-specific purge in the 2020
rule may be unnecessary or not adequately justified, the Agency also
notes that ``dry handling'' systems often are not completely dry. EPRI
(2014) included information about an MDS with purge of 270 gpm from an
under-boiler ``dry handling'' system. EPA has received additional flow
diagrams in the most recent information collection that show purges
from additional MDS systems.\81\ Thus, while many facilities have
installed pneumatic and air-cooled drag chain systems, many EGUs with
``dry handling'' due to under-boiler MDS or compact submerged conveyor
systems still rely on wet hoppers that catch and cool hot (in some
cases molten) BA in quench water. EPA has not considered this BA
contact water to be transport water (instead considering it within the
catch-all category of low volume wastewater), because, as explained in
the 2015 rule, the water is not used to transport the BA, resulting in
decreased contact times (and thus decreased pollutant concentrations)
from the BA. While overall pollutant concentrations may be lower,
leaching data in the 2015 CCR rule record indicate that some
constituents wash out due to their high solubility.\82\ For these
pollutants, there may be little difference in concentration between
transport water and contact water. In the absence of data from actual
under-boiler purges, EPA solicits comment providing data and purge
examples from existing dry handling systems. EPA solicits comment on
whether limiting or removing the ability to purge from a high recycle
rate system but not from a ``dry'' under-boiler system may result in
unwarranted disparate treatment or perverse incentives. EPA solicits
comment on whether there is a potential unwarranted disparity and how
the Agency might address this disparity to avoid potentially
encouraging larger discharges. For example, EPA solicits comment on
whether it should continue to allow (or alternatively not allow,
through a zero-discharge requirement) a purge for both contact water
and transport water. Since contact water is not covered by the
definition of transport water in 40 CFR 423.11(p), EPA solicits comment
on whether the purge of such water should nevertheless be included as
``bottom ash purge water'' under Sec.  423.11(cc) and thus subject to a
BPJ analysis by the permitting authority.
---------------------------------------------------------------------------

    \81\ These flow diagrams did not include flow rates or pollutant
concentrations. (SE09754 and SE09724.)
    \82\ U.S. EPA (Environmental Protection Agency). 2014. Human
Health and Ecological Risk Assessment of Coal Combustion Residuals.
2050-AE81. December. Available online at www.regulations.gov.
Document ID#: EPA-HQ-OLEM-2019-0173-0008.
---------------------------------------------------------------------------

3. Combustion Residual Leachate (CRL)
    EPA is proposing chemical precipitation as the technology basis for
establishing BAT limitations to control pollutants discharged in CRL.
After evaluating the factors specified in CWA section 304(b)(2)(B), EPA
proposes that this technology is available, is economically achievable,
and has acceptable non-water quality environmental impacts.
Specifically, the proposed BAT basis consists of chemical
precipitation/coprecipitation employing the combination of hydroxide
precipitation, iron coprecipitation, and sulfide precipitation.
    In the subsection immediately below, EPA discusses its rationale
for proposing chemical precipitation as BAT for control of leachate. In
the following subsection, EPA solicits comment on whether it should
base BAT for CRL on more stringent technologies, such as chemical
precipitation plus biological treatment, chemical precipitation plus
membrane filtration, or chemical precipitation plus thermal treatment,
and whether these technologies are technologically available, are
economically achievable, and have acceptable non-water quality
environmental impacts, as discussed below. In the third subsection, EPA
discusses why it is not proposing to establish BAT for control of
pollutants in CRL based on surface impoundments. In the fourth
subsection below, EPA solicits comment on additional options related to
co-treatment of FGD and CRL wastewater, a potential grandfathering
provision, co-treatment of CRL and stormwater, and potential
differences in leachate associated with pre- and post-close of
landfills. Finally, in the last subsection below, EPA solicits comment
on EPA's estimates of potential costs and loads of pollutant discharges
through groundwater, treatment differences, and potential
subcategorization related to discharges through groundwater.
a. Chemical Precipitation
    Technological availability of chemical precipitation. EPA proposes
to find that chemical precipitation is technologically available for
control of CRL discharges. In the 2015 rule record, EPA found that
chemical precipitation systems are technologically available for
treating CRL, capable of achieving low effluent concentrations of
various metals, and effective at removing many of the pollutants of
concern present in CRL discharges to surface waters. The Agency also
found that the pollutants of concern in CRL are the same pollutants
that are present in, and in many cases are also pollutants of concern
for, FGD wastewater, FA transport wastewater, BA transport water, and
other CCR solids. This proposed finding is consistent with the findings
of this technology as the basis for the 2015 rule's NSPS and PSNS for
CRL.\83\
---------------------------------------------------------------------------

    \83\ In establishing chemical precipitation as the basis for
NSPS, the Agency stated that chemical precipitation is a well-
demonstrated technology for removing metals and other pollutants
from a variety of industrial wastewaters. 80 FR 67859.
---------------------------------------------------------------------------

    EPA is basing the proposed effluent limitations on the chemical
precipitation system for treating FGD wastewater as described in the
2015 rule record because the record indicates that CRL wastewater is
similar to FGD wastewater, which the record demonstrates can be
effectively treated using chemical precipitation. Specifically, the
system serving as the BAT technology basis employs equalization,
hydroxide and organosulfide precipitation, iron coprecipitation, and
removal of suspended and precipitated solids. As discussed in Section
VI of this preamble above, EPA asked eight utilities to

voluntarily perform CRL sampling at CCR landfills the Agency believed
were new CCR rule-compliant landfills and/or expansions. EPA ultimately
received supplemental CRL sampling data covering 25 landfills. EPA
analyzed these data in the CRL Analytical Data Evaluation (SE10249) and
found that CRL has a similar wastewater characterization to FGD
wastewater. Chemical precipitation would make reasonable further
progress toward the Act's goal of eliminating the discharge of all
pollutants, as the limitations based on this technology would eliminate
substantial amounts of arsenic, mercury, and other toxic pollutants
from CRL discharges by the steam electric industry.
    Economic achievability of chemical precipitation. EPA proposes to
find that the costs of chemical precipitation for control of CRL
discharges are economically achievable. This proposal includes IPM
modeling of the preferred option (Option 3) which includes chemical
precipitation costs for CRL. The results of the analysis show small
changes in coal utilization and only one incremental retirement of a
facility out of 871 steam electric power plants in the steam electric
power generation industrial category. Furthermore, that plant already
operates at a low capacity utilization rating. This is well within the
economic impact estimated for other BAT rules and has been upheld by
courts. Chem. Mfrs. Ass'n v. EPA, 870 F.2d at 252. As a result of this
analysis, EPA proposes to find that chemical precipitation is
economically achievable.\84\ For further discussion of the economic
analysis, see Sections VII.F and VIII of this preamble below.
---------------------------------------------------------------------------

    \84\ EPA notes that the 2015 rule record indicated that the
costs of treating CRL based on chemical precipitation were only
marginally higher than the total costs in the selected option, which
was found to result in minimal economic impacts. Furthermore, the
cost screening in 2015 found that only a small portion of the plants
and parent entities would experience costs greater than one percent
or three percent of revenue, even with chemical precipitation
treatment of CRL. While these thresholds do not necessarily equate
to what is economically achievable, they may serve as a screening
analysis to find that the costs do not raise economic achievability
concerns.
---------------------------------------------------------------------------

    Non-water quality environmental impacts of chemical precipitation.
EPA proposes to find that the non-water quality environmental impacts
associated with chemical precipitation to control CRL discharges are
acceptable. See discussion below in Section VII.G and Section X of this
preamble.
b. More Stringent Technologies Than Chemical Precipitation
    EPA solicits comment on whether the technology basis for BAT
limitations to control discharges of pollutants in CRL should be based
on more stringent technology, such as biological treatment, spray dry
evaporation, thermal systems, or membrane filtration. The record
includes plants that have successfully treated a combination of CRL and
FGD wastewater with chemical precipitation as pretreatment for
biological or thermal systems. This successful treatment history may
further support the availability of chemical precipitation either alone
or as pretreatment for more advanced systems. EPA solicits comment and
additional data about these systems treating CRL beyond chemical
precipitation and further solicits comment on whether and to what
extent it should instead, or in addition, base BAT limitations
applicable to CRL on these technologies.
    With respect to biological treatment, EPA solicits comment on
whether it should base BAT limitations applicable to CRL on chemical
precipitation plus biological treatment. In the 2015 rule record, EPA
found that chemical precipitation plus biological treatment was
technologically available and in use domestically to treat a mix of FGD
wastewater and CRL. Given the data cited above showing the similarity
of FGD and CRL wastewater, EPA solicits comment on transferring the FGD
wastewater technology basis and BAT limitations from the 2020 rule as
the technology basis and BAT limitations for CRL as well.
    With respect to thermal treatment, the 2020 rule record included a
facility that co-treated its FGD wastewater and CRL with a thermal
system to achieve zero discharge. At least four vendors have conducted
thermal system pilots on CRL, and there has been one full-scale thermal
system installation for the treatment of CRL. EPA has identified four
vendors that have conducted successful thermal system pilots, and each
of these vendors has installed multiple full-scale thermal systems at
non-power plant landfills. Thus, EPA solicits comment on finalizing a
zero-discharge requirement for CRL based on chemical precipitation plus
thermal treatment systems and/or SDE treatment systems, or
alternatively on transferring the chemical precipitation plus thermal
treatment-based BAT limitations established for the FGD wastewater NSPS
in the 2015 rule.
    With respect to membrane treatment, as discussed above under FGD
wastewater, the record is also replete with the use of membrane
filtration for a variety of wastestreams with characteristics like high
TDS, high scaling potential, and high variability, both within the
steam electric sector and in other industries. Furthermore, one
midwestern facility conducted a successful pilot of a membrane
filtration system on CRL.\85\ EPA solicits comment on establishing zero
discharge BAT limitations for CRL based on chemical precipitation plus
membrane filtration, or alternatively on transferring the membrane
filtration limitations established in the VIP for FGD wastewater in the
2020 rule.
---------------------------------------------------------------------------

    \85\ This utility declined to provide the pilot in response to a
voluntary request from EPA.
---------------------------------------------------------------------------

    EPA also solicits comment on establishing limitations based on any
combination of chemical precipitation plus membrane filtration,
chemical precipitation plus thermal, and/or SDE treatment. To
facilitate comments on a zero discharge option, EPA has provided memos
to the record evaluating the costs of achieving zero discharge of CRL
and the associated pollutant reductions.\86\ Should EPA finalize BAT
limitations based on more stringent technologies than chemical
precipitation, EPA also solicits comment on the appropriateness of
revising NSPS and PSNS for CRL based on a more stringent technology
than the NSPS basis selected in the 2015 rule (chemical precipitation).
---------------------------------------------------------------------------

    \86\ Evaluation of Zero Discharge Options for CRL (SE10257).
---------------------------------------------------------------------------

c. Less Stringent Technologies Than Chemical Precipitation
    EPA is not proposing to base BAT limitations for control of CRL on
surface impoundments because there are other technologies (like
chemical precipitation) that achieve greater reductions in pollutant
discharges, which EPA proposes are available and economically
achievable, with acceptable non-water quality environmental impacts.
Surface impoundments would not make reasonable further progress toward
the national goal of eliminating the discharge of pollutants.
d. Solicitation of Comment on Additional Options Related to Co-
Treatment of FGD and CRL Wastewater, Potential Grandfathering
Provision, Co-Treatment of CRL and Stormwater, and Potential
Differences in Discharges Associated With Pre- and Post-Closure of
Landfills
    EPA also solicits comment on whether EPA should create a

subcategory allowing facilities that co-treat their FGD and CRL
wastewater to meet BAT limitations based on a different technology
basis than the one used by facilities treating CRL alone. EPA solicits
comment on whether there are engineering obstacles to such co-treatment
based on proximity of the landfill or other factors. EPA also solicits
comment on whether it would be appropriate to establish either a
grandfathering provision that would allow such facilities a limited
payback period to recover costs on the CRL treatment investments
already made before having to comply with any new limitations or
another provision that would account for the potentially unique
circumstances of these facilities, in light of the factors specified
under CWA section 304(b).
    In developing the current record, EPA received information about
systems that collect leachate and stormwater in the same system. For
example, one type of system involves the use of chimneys that route
stormwater straight through a landfill into the leachate collection
system to minimize percolation through the CCR solids. Thus, EPA also
solicits comment on flexibilities that might be warranted for such
systems. For example, EPA solicits comment on whether such systems
should be subcategorized, or whether either the definition of CRL or
the applicability of the CRL limitations should exclude discharges when
stormwater exceeds specific storm events, such as events used as the
basis of the BA transport water purge allowance in the 2020 rule.
    EPA also discussed the differences between pre- and post-closure
landfill operations with several stakeholders. For example, post-
closure, the CCR rule requires landfills and surface impoundments
closing with waste in place to have a cap that is graded to minimize
infiltration into the CCR solids. This will result in volumes of CRL
decreasing significantly post-closure. EPA solicits comment on specific
information that would suggest whether different limitations should
apply to the same landfill or surface impoundment pre- and post-
closure. The change in flows also means the amount of capital
expenditure on treatment systems (larger flows lead to larger treatment
systems) might be disparate for landfills and surface impoundments
nearing closure when compared to those with many operating years
remaining or to those that have already closed under the CCR rule.
Thus, EPA solicits comment on whether there should be flexibility for
landfills and surface impoundments nearing closure such that
limitations could be postponed until after closure to avoid
construction of a larger, more expensive system that would operate for
only a relatively short period of time. EPA also solicits comment on
whether CRL generated by already closed landfills and surface
impoundments should be subcategorized, as well as information
demonstrating whether subcategorization is warranted.
e. Solicitation of Comment on EPA Estimates of Potential Costs and
Loads of Pollutant Discharges Through Groundwater, Treatment
Differences, and Potential Subcategorization
    EPA also notes that unlined landfills and surface impoundments
potentially discharge CRL through groundwater before entering surface
water.\87\ EPA, through this action, is not addressing the definition
of any terms in the CWA (such as ``point source'' or ``discharge of a
pollutant'') that govern when a discharge is subject to NPDES
permitting requirements or when a discharge to WOTUS through
groundwater is a functional equivalent of a discharge and thus subject
to the Act's NPDES permitting requirement. See County of Maui v. Hawaii
Wildlife Fund, 140 S. Ct. 1462 (2020). Those issues are outside the
scope of this rulemaking. EPA proposes that any discharge through
groundwater that is the functional equivalent of a direct discharge
under the Maui decision would be subject to the same BAT limitations as
discharges that occur at the end of pipe. To evaluate the potential
costs and loads of such discharges, EPA conducted Evaluation of
Potential CRL in Groundwater (SE10250). EPA solicits comment on the
appropriateness of the Agency's proposed BAT findings and their
application to any discharges of CRL via groundwater that permitting
authorities ultimately determine are subject to NPDES permitting. EPA
also solicits comment on the extent to which CRL discharges through
groundwater might be different than other discharges potentially
subject to any final rule, including specific facts demonstrating that
the chemical makeup, treatment effectiveness, or other factors differ
from end-of-pipe discharges of CRL. EPA solicits comment on whether
such discharges of CRL through groundwater should be defined as a
separate wastestream or subcategorized and how, including whether these
discharges should be subject to BAT limitations on a case-by-case, BPJ
basis. Should EPA reserve these limitations such that permitting
authorities' BPJ would apply, section 304(b) of the CWA, 33 U.S.C.
1314(b), and 40 CFR 125.3 specify factors the permitting authority
would consider when establishing BPJ-based effluent limitations for
CRL. Furthermore, EPA solicits comment on whether the Agency should
explicitly set BAT equal to BPJ in the regulation and include
additional constraints (e.g., one or more presumptive standards) that
are specific to this wastestream in this industry.
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    \87\ Three panels in the 2022 World of Coal Ash conference
included discharges through groundwater as a topic in their
abstracts, and one abstract stated that surface impoundments are
located so close to surface waters that the groundwater underlying
the surface impoundment ``is often in hydraulic communication with
surface water.'' DeJournett et al., 2022. Available online at:
www.woca2022.conferencespot.org/event-data/pdf/catalyst_activity_28060/catalyst_activity_paper_20220124235416545_8aa3636e_85c7_4a17_bcca_a3119e01a5f9.
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4. Legacy Wastewater
    EPA proposes not to establish a nationwide BAT basis for legacy
wastewater at this time and instead to continue to reserve these
limitations for determination by the permitting authority, using its
BPJ for what is technologically available, economically achievable, and
has acceptable non-water quality environmental impacts. This potential
case-by-case outcome was explicitly identified by the Court in
Southwestern Elec. Power Company v. EPA, 920 F.3d at 1021, as an
alternative EPA should have considered.
    In the first subsection immediately below, EPA discusses its
rationale for BPJ-based BAT limitations to control legacy wastewater.
In the second subsection, EPA discusses why it is not proposing less
stringent technologies as BAT for legacy wastewater. In the last
subsection, EPA discusses why it is not selecting more stringent
technologies as BAT for legacy wastewater and is soliciting comment on
potentially different limitations for a subset of legacy wastewater.
a. BPJ-Based BAT Limitations
    After evaluating the factors specified in CWA section 304(b)(2)(B),
EPA is proposing to find that no single technology is technologically
available and economically achievable on a nationwide basis for control
of pollutants in legacy wastewater. Because of process changes
happening at plants in the form of ongoing and soon-to-be-completed
rapid surface impoundment closures under the CCR rule, EPA proposes
that a nationwide BAT limitation for legacy wastewater that would be
finalized mid-closure could be infeasible. The statute requires BAT to
reflect what is technologically available, is economically achievable,

and has acceptable non-water quality environmental impacts based on
consideration of several factors, including ``process changes'' and
``such other factors'' as the Administrator deems appropriate. Because
many facilities with surface impoundments are or will be in the process
of closing their surface impoundments under the CCR rule, the
technology that represents BAT for legacy wastewater treatment is
likely to vary at any given site depending on several factors. These
factors include, but are not limited to, the types of wastes and
wastewaters present, the characteristics of the legacy wastewater in
each layer of a surface impoundment, the amount of legacy wastewater
remaining to be treated in a surface impoundment, the treatment option
costs, the extent to which CWA requirements could interfere with
closure timeframes required under the CCR rule, and the potential for
increased discharges through groundwater. While there is no typical
site given the dynamic and changing nature of this wastestream at this
time, given the CCR rule's closure requirements, permitting authorities
should seriously consider treatment beyond that afforded by surface
impoundments, which the Fifth Circuit found to be arbitrary,
capricious, and inconsistent with the ``technology-forcing mandate of
the CWA.'' Southwestern Elec. Power Company v. EPA, 920 F.3d at 1017.
The effect of finalizing this proposal would be for permitting
authorities to continue to establish site-specific technology-based
effluent limitations using their BPJ. Because the limitations would be
derived on a site-specific basis, taking into account the requisite
statutory factors and applying them to the circumstances of a given
plant, EPA proposes that these case-by-case limitations would be
technologically available and economically achievable and have
acceptable non-water quality environmental impacts.
    As part of this proposal, EPA is proposing to segregate legacy
wastewater into two main categories of separately regulated discharges,
which would each be subject to separate case-by-case technology-based
effluent limitations established by the permitting authority (after
considering the statutory factors). Legacy wastewater was defined in
the 2015 rule preamble as:

``. . . FGD wastewater, fly ash transport water, bottom ash
transport water, FGMC wastewater, or gasification wastewater
generated prior to the date determined by the permitting authority
that is as soon as possible . . .'' \88\
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    \88\ 80 FR 67854. CRL does not appear in this list because, in
2015, EPA did not establish more stringent limitations for this
wastewater than the previously applicable BPT limitations.
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    In practice, there are two distinct categories of legacy
wastewater: (1) wastewater that is continuously or intermittently
generated and discharged to a pond after the issuance of the first
permit implementing the 2015 or 2020 rule but before the compliance
date specified in the permit (the ``as soon as possible'' date required
by the rule), and (2) wastewater that was discharged to the pond
previously and will be discharged when the pond is dewatered for
closure.
    By segregating wastewaters continuously or intermittently generated
and discharged after permit issuance from those already accumulated in
closing surface impoundments, permitting authorities could justify more
stringent BAT requirements on a BPJ basis for one or both categories of
legacy wastewater. The first category is continuously or intermittently
generated and discharged and may be able to be more easily transmitted
to other treatment systems at the facility. The second type is
typically treated with modular, leased systems for a shorter period,
making treatment more affordable.
    For example, regarding FGD wastewater generated after permit
issuance but before the ``as soon as possible'' date determined by the
permitting authority, a facility installing the 2020 BAT technology
basis of chemical precipitation plus biological treatment and
ultrafiltration may be able to operate the chemical precipitation
module before the date the permitting authority determines is the
soonest date that the more stringent limitations apply pursuant to
Sec.  423.11(t). In such a scenario, it would be reasonable for a
permitting authority to establish BAT limitations for legacy FGD
wastewater using a BPJ approach that would transfer mercury and arsenic
limitations with a date corresponding to the operability of that
chemical precipitation module. Since permitting authorities already
determine the ``as soon as possible'' date, it is reasonable that the
same information could be used for a BPJ analysis.
    The state of Pennsylvania recently implemented a similar approach
in an NPDES permit issued to Homer City. In the Homer City NPDES Permit
Fact Sheet Addendum 3,\89\ the state found the plant had ``voluntarily
committed'' to a more stringent technology than BAT. The state further
found that the plant needed time ``to plan, design, procure, and
install equipment'' that would ``bring about a result that is more
desirable under the Clean Water Act than a treated discharge--the
elimination of a discharge.'' While the permit limits for this legacy
wastewater were not as stringent as the 2020 rule FGD wastewater BAT
limitations, the state permit required the discharger to meet interim
effluent limits based on a chemical precipitation and aerobic
biological treatment system that was available to this facility but may
not be to other facilities, as the facility already had this technology
in place before the completion of upgrades to achieve zero discharge.
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    \89\ Available online at: www.files.dep.state.pa.us/water/wastewater%20management/EDMRPortalFiles/Permits/PA0005037_FACT_SHEET_20210819_DRAFT_V2.pdf.
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    The second category of legacy wastewater is wastewater accumulated
over years in a surface impoundment that is later drained during the
closure of that surface impoundment. Such wastewater consists of:
     surficial water located above the CCR solids (hereafter
referred to as ``surface impoundment (SI) decant wastewater''); and
     pore water in the saturated CCR layer at levels beyond
that needed for conditioning (hereafter referred to as ``surface
impoundment (SI) dewatering wastewater'')
    EPA also notes that there would necessarily be an interstitial zone
where there may be some disturbed CCR solids. In this case, the water
may not necessarily be pore water from CCR solids but would
sufficiently mix with the CCR solids such that it presents similarly
elevated pollutant concentrations. Hence, while it is not pore water
per se, this interstitial zone water should be similarly situated with
the pore water layer from a regulatory perspective. For this reason,
EPA is proposing, and soliciting comment on, the following set of
definitions and proposing to require a separate BAT/BPJ analysis for
this category of legacy wastewater:
     The term ``surface impoundment'' means a natural
topographic depression, man-made excavation, or diked area that is
designed to hold an accumulation of coal combustion residuals and
liquids, and the unit treats, stores, or disposes of coal combustion
residuals.\90\
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    \90\ EPA has always sought to harmonize the CCR rule and this
ELG. Therefore, this definition, and terms therein (e.g., unit), was
taken from 40 CFR 257.53 to match the definition under the CCR rule.
---------------------------------------------------------------------------

     The term ``surface impoundment decant wastewater'' means
the layer of

a closing surface impoundment's wastewater that is located from the
water surface down to the level sufficiently above any coal combustion
residuals that, when drained, does not resuspend the coal combustion
residuals.
     The term ``surface impoundment dewatering wastewater''
means the layer of a closing surface impoundment's wastewater that is
located below surface impoundment decant water due to its contact with
either stationary or resuspended coal combustion residuals.
    EPA also proposes a clarifying change to the definition of ``tank''
to ensure that there would be no structure that would qualify as both a
tank and a surface impoundment. By separating these legacy wastewaters
as distinct wastestreams from the legacy wastewater definition
discussed above, EPA is proposing that the treatment of SI decant and
dewatering wastewaters can, and in many cases should, be subject to
different limitations from the first category of continuously or
intermittently generated and discharged legacy wastewater. For example,
a permitting authority conducting a BPJ analysis for a plant with the
first type of legacy wastewater discussed above (e.g., a continuously
or intermittently discharged FGD wastewater) may determine that BAT
limitations based on chemical precipitation are appropriate for the
plant's legacy FGD wastewater discharged before its ``as soon as
possible'' date, and that BAT limitations based on chemical
precipitation plus biological treatment are appropriate thereafter. At
the same time, the same plant may have the second type of legacy
wastewater--SI decant and/or dewatering wastewater. For example, the
plant may be dewatering one or more surface impoundments with
historically generated FA and BA transport water, which the permitting
authority could determine should be subject to different BAT effluent
limitations after performing a BPJ analysis. These limitations could be
more or less stringent than the FGD-specific chemical precipitation
limitations derived for discharges before the ``as soon as possible''
date.
    Factors the permitting authority must consider when establishing
BPJ-based BAT effluent limitations for these two types of legacy
wastewater are specified in section 304(b) of the CWA, 33 U.S.C.
1314(b), and 40 CFR 125.3(d). EPA solicits comment on whether the
Agency should explicitly promulgate specific elements related to these
factors, which are particular to this wastewater in this industry, in
regulatory text. For example, such specific elements could include: (1)
technologies available at the site, (2) the characteristics of the
legacy wastewater, (3) amount of remaining legacy wastewater, (4) the
treatment option costs, (5) the extent to which CWA requirements would
interfere with surface impoundment closure required under the CCR rule,
(6) the completed stage of closure for each surface impoundment, or (7)
the closure deadline under the CCR rule.
    EPA notes that some permitting authorities have actively sought to
regulate these SI decant and dewatering wastewaters (typically through
water quality-based effluent limitations). For example, the state of
North Carolina considered SI decant and dewatering wastewaters in
issuing several permits to Duke Energy. These permits generally limited
SI decant wastewater to a maximum elevation change (e.g., one foot per
day), applied controls to stop decanting if TSS or dissolved pollutants
exceeded some fraction of the discharge limitations (e.g., 50 percent
of TSS, 85 percent of arsenic), and would not drop the water level
below some threshold (e.g., three feet above the CCRs).\91\ These
performance restrictions were also paired with monitoring and reporting
requirements. EPA discussed these permits with North Carolina
regulators who found that this set of restrictions in the uppermost
layer (i.e., SI decant water) have been sufficient to protect receiving
water quality.\92\ EPA also notes that this approach is consistent with
the approach EPRI presents in section 4 of Coal Combustion Residuals
Pond Closure: Guidance for Dewatering and Capping.93 These
same North Carolina permits place water quality-based effluent
limitations on several pollutants that apply once the lower water
levels (i.e., SI dewatering wastewater) are reached. These pollutants
differ for each permit, but generally have led to the inclusion of
physical settling, chemical precipitation, and (for at least one
facility) ZVI treatment \94\ to remove TSS, metals, and selenium/
nutrients, respectively. This makes these systems a potential basis for
BAT for the newly defined SI decant and dewatering wastewaters. In
response to a voluntary information request from EPA, Duke Energy
declined to provide additional data on these systems.\95\ EPA solicits
comment on the costs and performance of all the systems discussed above
and whether any of these systems could be used as a basis for a
nationwide BAT limitations for SI decant and dewatering wastewaters.
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    \91\ Requirements differ by permit. Permits are available online
at: www.deq.nc.gov/about/divisions/water-resources/duke-energy-npdes-wastewater-permitting.
    \92\ Notes from Meeting with NC DEQ--December 13, 2021
(SE10258).
    \93\ EPRI (Electric Power Research Institute). 2014. Coal
Combustion Residuals Pond Closure: Guidance for Dewatering and
Capping. Palo Alto, CA.<PHONE_NUMBER>. March.
    \94\ Duke Energy Site Visit Notes--November 2021 (SE10259).
    \95\ Although Duke declined to provide this information on claim
that it was proprietary information of the vendors, EPA has already
discussed some of these systems with the vendors and notes that the
Agency can protect proprietary information as CBI.
---------------------------------------------------------------------------

    EPA also learned that Minnesota Power has commissioned an SDE for
its Boswell Energy Center.\96\ On October 4, 2020, the plant also
provided a notice of intent to close its unit 4 surface impoundment
under the CCR rule.\97\ EPA has learned that the SDE is currently used
to evaporate SI decant and dewatering wastewater as part of its closure
process. Once this impoundment is drained, the SDE will treat FGD
blowdown and other plant wastewater such as bottom ash blowdown, pond
water, and cooling tower blowdown. EPA solicits comment on this
system's use, as well as cost and performance data related to this
system. EPA solicits comment on whether an SDE might serve as a
technology basis for BAT for SI decant and dewatering wastewaters.
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    \96\ SE10376.
    \97\ This filing is available online at: www.mp-ccr.azurewebsites.net/Content/Facilities/Boswell/Closure_And_Post_Closure/BEC%20Pond%204%20Notice%20of%20Intent%20to%20Close.pdf.
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    While there may be technologies in use to treat these wastewaters,
EPA notes that the vast majority of SI decant and dewatering wastewater
is likely to have already been discharged pursuant to BPJ
determinations under existing permits rather than in any new permits
implementing any finalized ELG revisions. Rapid closure of many of
these surface impoundments is ongoing under the CCR rule. EPA notes
that the vast majority of surface impoundments had to cease receipt of
waste by April 11, 2021, and commence closure soon after. These surface
impoundments were either unlined and leaking, in violation of location
restrictions, or both. Thus, the vast majority of surface impoundments
have already begun the closure process, of which dewatering is one of
the first steps. Since closure must be completed within five years,
subject to limited extensions,\98\ most surface impoundments
potentially discharging SI decant and dewatering wastewater to comply
with the CCR rule will no longer

be discharging by 2026. As is the case for all promulgated effluent
limitations guidelines, the requirements for direct dischargers \99\ do
not become applicable to a given discharger until they are contained in
revised NPDES permits. NPDES permits are typically issued for the
maximum allowed five-year permit term. Most permits are not immediately
revised after EPA issues a new ELG rule. Moreover, it is not uncommon
for permits to be administratively continued beyond the five-year
permit term if a permittee submits a timely permit renewal application,
in which case the existing permit stays in effect until a new permit is
effective. EPA expects to issue the final rule in 2024. Thus, even if
these new ELG requirements were implemented into NPDES permits in a
timely manner, the vast majority of SI decant and dewatering wastewater
would have been discharged pursuant to BPJ determinations in existing
permits rather than pursuant to any regulations EPA might promulgate.
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    \98\ See 40 CFR 257.102(f).
    \99\ Indirect dischargers (those who discharge to POTWs) are
subject to pretreatment standards that are directly implemented and
enforceable. CWA section 307; 40 CFR part 403.
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    EPA proposes that a BPJ approach for permitting legacy wastewater
would result in reasonable further progress toward the CWA's goal of
eliminating the discharge of all pollutants because it would allow
permitting authorities to impose more stringent limitations (including
potentially zero-discharge limitations) based on technologies that
remove more pollutants than surface impoundments on a case-by-case
basis, depending on what is technologically available and economically
achievable for individual facilities.
    EPA solicits comment on the proposed approach of continuing the
current practice of case-by-case BPJ for determining BAT for legacy
wastewater. EPA also solicits comment on explicitly establishing BAT
equal to BPJ in the text of the regulations in a manner consistent with
CWA section 304(b)(2)(B), 33 U.S.C. 1314(b)(2)(B) and 40 CFR 125.3(d).
b. B. Less Stringent Technologies Than BPJ
    EPA is not proposing surface impoundments as the BAT basis for
control of legacy wastewater discharges because there are technologies
more stringent than surface impoundments that could be used at some
plants. Thus, to make reasonable further progress as required by the
CWA, EPA is proposing a case-by-case BAT approach rather than
defaulting to the BPT technology basis for the wastestreams implicated
here. This is in keeping with the Fifth Circuit's order vacating the
2015 legacy wastewater BAT limitations, which were set equal to
previously established BPT limitations based on surface impoundments,
in Southwestern Elec. Power Co. v. EPA, 920 F.3d at 1018.
c. C. More Stringent Technologies and Solicitation of Comments on
Potentially Different Limitations for a Subset of Legacy Wastewater
    EPA is not proposing more stringent technologies, such as chemical
precipitation, biological treatment, membrane filtration, thermal
evaporation, and/or spray dryer evaporation as the BAT basis for
controlling discharges of legacy wastewater. EPA is not certain that
these systems can be used nationwide on the vast array of legacy
wastewaters that exist at steam electric plants without disrupting some
plants' already commenced (and contracted for) closure process, thereby
possibly jeopardizing the ability of those plants to meet their closure
deadlines under the CCR rule. However, EPA is soliciting comment on
limitations based on chemical precipitation, biological treatment,
membrane filtration, thermal evaporation, and/or spray dryer
evaporation or any other more stringent technologies that plants may be
using to dewater their surface impoundments. EPA is especially
interested in information related to the technological availability,
economic achievability, and non-water quality environmental impacts of
such technologies. Since these wastewaters are the same wastewaters as
those regulated elsewhere in Part 423, EPA solicits comment on whether
the Agency could transfer limitations, specifically any of the 2015 or
2020 limitations for FGD wastewater (including subcategories or VIP) or
the proposed zero-discharge limitations.
    Finally, EPA solicits comment on whether any presumptive standard
or other appropriate constraint should be placed on any BPJ analysis
should the Agency finalize a case-by-case BPJ approach. Even if EPA's
final rule adopts a BPJ standard for deriving BAT limitations for
legacy wastewater, recognizing that the wastewater contained in surface
impoundments can vary across sites in the country, EPA could expect
permitting authorities to thoroughly assess the technologies a plant
already uses (including for treatment of other wastewaters) to
determine whether the legacy wastewater could be directed to those
systems for treatment. This would presumably represent an acceptable
application of BPJ at the plant. For example, if a facility has
installed and already uses an SDE to treat its FGD wastewater, then it
would be reasonable for the permitting authority to find such
technology to be technologically available and economically achievable
to treat legacy wastewater that exists in a surface impoundment
designed to store legacy FGD wastewater.
    In contrast to most surface impoundments, EPA has identified 22
surface impoundments at 17 facilities that the record indicates are
composite lined and meet the location restrictions of the CCR rule. A
further discussion of these surface impoundments can be found in Legacy
Wastewater at CCR Surface Impoundments (SE10252). Since these surface
impoundments continue to operate, they would likely not begin closure
and dewatering until after the effective date of any final rule. Thus,
these surface impoundments do not present the same issue as the surface
impoundments which have commenced, or imminently will commence,
closure. A further discussion of these surface impoundments and the
corresponding costs and pollutant loadings associated with candidate
technologies for a potential BAT basis can be found in Legacy
Wastewater at CCR Surface Impoundments (SE10252). EPA solicits comment
on whether the Agency should establish a subcategory or different
limitations applicable to discharges of these wastewaters. EPA solicits
comment on what the subcategory could look like, including what cutoff
could be used to establish this subcategory, as well as whether the
subcategory should apply to surface impoundments that have not
triggered the cease receipt of waste and/or closure requirements of the
CCR rule, to surface impoundments that have not yet begun the
dewatering process, and to just the SI dewatering water where decanting
has already begun or completed. Finally, EPA is currently developing a
proposed CCR rule for legacy surface impoundments at inactive or
retired power plants. EPA solicits comment on the universe of potential
legacy surface impoundments under that rule that may become subject to
any limitations established under a final ELG.
5. Clarification on the Interpretation of 40 CFR 423.10 (Applicability)
With Respect to Inactive/Retired Power Plants and Solicitation of
Comments on Potential Clarifying Changes to Regulatory Text
    EPA is clarifying that part 423 applies to discharges of the
proposed SI decant

and dewatering wastewaters at inactive/retired power plants because the
discharge of these wastewaters ``result[s] from the operation of a
generating unit.'' \100\ Due to the potential expansion of the CCR rule
closure requirements to cover inactive surface impoundments at inactive
(i.e., retired) plants, these surface impoundments will likely need to
dewater and discharge legacy wastewater, specifically SI decant and
dewatering wastewaters. Thus, EPA wishes to clarify the applicability
of these proposed regulations at inactive/retired power plants.
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    \100\ 40 CFR 423.10 Applicability. The provisions of this part
apply to discharges resulting from the operation of a generating
unit by an establishment whose generation of electricity is the
predominant source of revenue or principal reason for operation, and
whose generation of electricity results primarily from a process
utilizing fossil-type fuel (coal, oil, or gas), fuel derived from
fossil fuel (e.g., petroleum coke, synthesis gas), or nuclear fuel
in conjunction with a thermal cycle employing the steam water system
as the thermodynamic medium. This part applies to discharges
associated with both the combustion turbine and steam turbine
portions of a combined cycle generating unit.
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    On August 21, 2018, the U.S. Court of Appeals for the District of
Columbia issued a decision in Utility Solid Waste Activities Group, et
al. v. EPA, which vacated and remanded the CCR rule provision that
exempted inactive impoundments at inactive facilities from the CCR rule
requirements. As a first step to respond to the Court's order, EPA
sought comments and data on inactive surface impoundments at inactive
facilities in an advanced notice of proposed rulemaking (ANPRM) to help
develop future regulations for these CCR units (85 FR 65015, October
14, 2020). This ANPRM also discussed the related research conducted to
date, described EPA's preliminary analysis of that research, and sought
additional data and public input on issues that may inform a future
proposed rule.
    As a result of the ANPRM, EPA's understanding of the potential
universe of legacy surface impoundments has grown. Specifically,
comments by Earthjustice et al. identified an estimated 170 surface
impoundments and 47 landfills at 72 retired power plants in Potential
CCR Legacy Units (2021).101 EPA is currently evaluating this
information, as well as comments submitted by states, local
governments, environmental groups, tribes, and industry, as part of
Hazardous and Solid Waste Management System: Disposal of Coal
Combustion Residuals From Electric Utilities; Legacy Surface
Impoundments (RIN: 2050-AH14).\102\ EPA notes that many of these 72
facilities were still operating for some or all of the period during
which EPA performed its detailed study for the steam electric power
generating industry, 2013 proposal, and 2015 final rule. The record
includes no information that these wastewaters have changed during
closure such that there is any difference between the types of wastes
and wastewaters in these units as compared to units at active power
plants.
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    \101\ Available online at: www.regulations.gov/comment/EPA-HQ-OLEM-2020-0107-0073.
    \102\ EPA is currently evaluating potential legacy surface
impoundments and intends to include a more refined estimate in its
upcoming proposal.
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    EPA wishes to clarify the applicability of 40 CFR part 423 to
inactive/retired plants because some may question whether the existing
effluent guidelines apply to discharges from surface impoundments at
inactive/retired plants. Because the existing requirements under the
ELGs for legacy wastewater were based on the pollutant removals
achieved by surface impoundments (i.e., gravity settling), whether the
rule applied or not did not make a practical difference in terms of the
technology-based limitations for this wastewater. Should EPA finalize
limitations for SI decant and dewatering wastewater at inactive/retired
plants that are more stringent than those based on the treatment
achieved by surface impoundments, it is important that permittees with
the estimated 170 legacy surface impoundments at inactive/retired power
plants understand EPA's interpretation of the rule's applicability.
    EPA notes that the current applicability text in Sec.  423.10
conditions applicability on whether a discharge is ``resulting from the
operation of a generating unit.'' Generally, when a plant ceases
electricity production and retires, it either turns off, removes, or
demolishes wastewater equipment such as intakes, cooling towers, pumps,
and other equipment related to power generation. Thus, EPA expects that
most wastewaters would no longer be generated and, therefore, no longer
discharged. In contrast, some wastewaters, such as stormwater, will
clearly continue to be generated and discharged after retirement, but
cannot be said to result from the operation of an EGU. Between these
two groupings of wastewaters lay wastewaters that, but for the
operation of the generating unit, would not have been generated and
discharged. Specifically, the proposed SI decant and dewatering
wastewaters (legacy wastewaters) can be generated years in advance and
retained in surface impoundments, either at the surface of the unit or
in its pore water.
    The interpretation above is consistent with EPA's long-time view on
the applicability of part 423 to inactive/retired plants and consistent
with implementation by state permitting authorities. For example, in
2016, South Carolina DHEC reissued a permit to the South Carolina
Electricity & Gas Company's Canadys Station Site (SC0002020) which
stated, ``Because electricity is not being generated, 40 CFR part 423--
Steam Electric Power Generating Point-Source Category will only apply
to the discharge of legacy wastewaters.'' \103\
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    \103\ DHEC (Department of Health and Environmental Control).
2016. FACT SHEET AND PERMIT RATIONALE: South Carolina Electric & Gas
Company, Canadys Station Site. NPDES Permit No. SC0002020. May 16.
---------------------------------------------------------------------------

    In summary, EPA interprets the rule to apply to legacy wastewater
at inactive/retired steam electric power plants. EPA solicits comment
on whether Sec.  423.10 should be amended to further support such a
clarification with respect to legacy wastewater or whether the existing
regulatory text already sufficiently supports this interpretation. In
particular, the current applicability provision means that discharges
of legacy wastewater that occur after the unit has ceased generating
still ``result from'' the operation of the generating unit because but
for the operation of the generating unit, there would be no subsequent
discharge.
    EPA solicits comment on whether there are other wastewaters that
may continue to be discharged after the retirement of a facility and
the generation of electricity is the ``but for'' cause of the
discharge. EPA solicits comment on whether the Agency should clarify
its interpretation for any such wastewaters or modify the text of
section 423.10 to further clarify applicability to these wastewaters.
For example, EPA solicits comment on whether CRL generated after
retirement should continue to remain subject to 40 CFR part 423.
Finally, EPA solicits comment on whether there are wastewaters at
retired power plants that the Agency should clarify are explicitly
excluded from the applicability of 40 CFR part 423.

C. Proposed Changes to Subcategories

    In the 2015 rule, EPA established subcategories for small EGUs
(less than or equal to 50 MW nameplate capacity) and oil-fired EGUs. In
the 2020 rule, EPA established additional subcategories for high FGD
flow facilities, LUEGUs, and EGUs permanently ceasing coal combustion

by 2028. For these subcategorized units, EPA established differentiated
limitations with different technology bases from the remaining steam
electric point source category. EPA has authority in a national
rulemaking to establish different limitations for different plants
after considering the statutory factors listed in section 304(b). See
Texas Oil & Gas Ass'n v. EPA, 161 F.3d 923, 938 (5th Cir. 1998)
(stating that the CWA does not ``exclude a rule allowing less than
perfect uniformity within a category or subcategory.'').
    EPA is not proposing to eliminate the 2015 rule subcategorization
of small EGUs or oil-fired EGUs. Furthermore, while the Agency is
soliciting comment on the permanent cessation of coal combustion
subcategory, it is also not proposing to eliminate this 2020 rule
subcategorization. However, EPA is proposing to remove both the high
FGD flow and low utilization 2020 rule subcategories. EPA is also
proposing a new subcategory for early adopters which permanently cease
coal combustion by December 31, 2032. These subcategories are discussed
below.
1. Plants With High FGD Flows
    EPA is proposing to eliminate the high FGD flow subcategory. EPA
proposes that, after evaluating the factors specified in CWA section
304(b)(2)(B), the subcategory is no longer warranted. In the 2020 rule,
EPA evaluated one facility, TVA Cumberland, when it established the
high FGD flow subcategory. At the time, this facility was found to have
the highest costs due to its high FGD flows. Several commenters on the
2019 proposal claimed that this subcategory of one facility was
inconsistent with the CWA, and further contested that the costs
estimated for TVA were overestimated and not disparate.\104\ EPA
acknowledges that its cost estimates were higher than TVA's own
estimates for installing biological treatment, and thus costs may not
be as disparate as indicated in the 2020 rule. Nevertheless, EPA need
not reach a determination on these costs as TVA has since issued a
Federal Register notice for plans to retire the facility, which are
further detailed in a draft Environmental Impact Statement (EIS) (86 FR
25933. May 11, 2021). This draft EIS solicits comment on three
alternatives, all of which include retirement but with different
electricity replacement scenarios.
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    \104\ EPA notes that these commenters were also petitioners in
the consolidated Appalachian Voices case discussed in Section IV of
this preamble above.
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    EPA bases this proposal principally on TVA's primary decision to
permanently cease coal combustion at the Cumberland plant. Because all
the alternatives TVA is considering (including its preferred
alternative) would result in the plant's retirement, EPA proposes to
eliminate the 2020 rule high FGD flow subcategory as unnecessary. EPA
solicits comment on the 2020 basis of disparate costs used to
subcategorize this facility in the first place. Since this subcategory
consists of only mercury and arsenic limitations based on chemical
precipitation, EPA also solicits comment on whether, should TVA step
back from its retirement plans, elimination of the subcategory would
still be warranted.
2. Low Utilization EGUs (LUEGUs)
    EPA proposes to eliminate the low utilization subcategory after
evaluating the factors specified in CWA section 304(b)(2)(B) and based
on EPA's proposed finding that the subcategory is no longer warranted.
EPA proposes that the low utilization subcategory is no longer
warranted given that only one plant has expressed an interest in
availing itself of the BAT limitations in the subcategory, and the
concerns EPA originally sought to address by creating the subcategory
are not present for that plant. EPA established the subcategory for
LUEGUs in the 2020 rule based on cost (disparate capital costs), non-
water quality environmental impacts (including energy requirements),
and other factors the Administrator deemed appropriate (i.e.,
harmonization with CAA and RCRA regulations that apply to electric
utilities). Any facility seeking subcategorization of one or more EGUs
as an LUEGU was required to submit a NOPP to the permitting authority
by October 13, 2021. While EPA did not perform a comprehensive search
for NOPPs, EPA's large collection of NOPPs across several states
(described above in Section VI.B of this preamble) only included one
submission for participation in the LUEGU subcategory from a direct
discharger. This submission was for EGUs at the GSP Merrimack Station
in Bow, New Hampshire. This plant is discussed below.
    Merrimack Station has two EGUs (MK1 and MK2). Although these units
were once baseload generating units, over approximately the last 10
years, these units have transitioned to only operating intermittently
when needed, primarily during winter and (even less frequently) summer
months when natural gas supplies are constrained. As provided in
Merrimack Station's 2021 NOPP, MK1 has a nameplate capacity of 113.6 MW
and in 2019 and 2020 had capacity utilization factors (CUFs) of 6.6
percent and 3.6 percent, respectively. MK2 has a nameplate capacity of
345.6 MW and had 2019 and 2020 CUFs of 7.8 percent and three percent,
respectively.
    Following Merrimack Station's request for permit modification to
incorporate the 2020 steam electric ELGs for both its BA transport
water and FGD wastewater, the facility submitted a timely NOPP. In its
NOPP, the facility requested coverage under the low utilization
subcategory for both wastestreams, as well as the ability to transition
to the 2020 rule subcategory for permanent cessation of coal combustion
by 2028 or the 2020 rule VIP for its FGD wastewater, pursuant to 40 CFR
423.13(o). EPA acknowledges the facility's request to participate in
the low utilization subcategory but to have the flexibility to
potentially shift to operate under another subcategory or the VIP, as
allowed by the 2020 rule.
    However, EPA does not think the subcategory is warranted for this
plant because the facility has already installed an advanced FGD
wastewater treatment system capable of meeting the limitations in this
proposed rule, and thus is not expected to incur any capital costs, let
alone disparate costs, to meet the proposed FGD wastewater limitations.
Moreover, the facility operates in a capacity futures market that helps
offset the financial challenges potentially faced by a facility that
operates at a reduced capacity. Because the cost/financial concerns EPA
discussed in the 2020 rule are not present for this facility, EPA also
proposes to find that there are no grid reliability concerns with
eliminating this subcategory.
    After an initial startup period,\105\ Merrimack Station has
operated since 2012 with zero discharges of its FGD wastewater. To
operate with zero discharge, the plant has both a primary and secondary
wastewater treatment system. The primary system consists of
equalization tanks, reaction tanks, a softener, gravity filters, an
enhanced mercury and arsenic removal system, and a holding tank. The
secondary wastewater treatment system, referred to by the facility as
the vapor compression evaporation system, generally consists of a brine
concentrator, two crystallizers, and a belt filter press. Although the
plant has operated with

zero discharge, in its most recent permit application, the plant at one
point requested authorization to discharge FGD wastewater, but later
withdrew the request. While technically the anti-backsliding provisions
of 40 CFR 122.44(l) do not apply to Merrimack's FGD wastewater (since
it has never had a limitation in its permit), the current permit does
not allow FGD wastewater discharges and thus the permit would
effectively become less stringent through the application of the low
utilization subcategory, which would allow such discharges. Where a
technology has already been in use at a facility for a decade and has
been shown to be available and economically achievable for that
facility, with acceptable non-water quality environmental impacts,
relaxing a permit so use of that technology can be discontinued is
inconsistent with the statute's BAT provisions intended to make
reasonable further progress toward eliminating discharges into U.S.
waters.\106\
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    \105\ The wet scrubbers became operational on September 28,
2011. For approximately two years, while the treatment system was
being adjusted and optimized, wastewater was periodically hauled
off-site to local POTWs for disposal.
    \106\ This plant is arguably one of the best performing plants
in the industry with respect to its FGD wastewater, further
supporting that subcategorization is not appropriate.
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    Furthermore, Merrimack Station receives a production-independent
revenue stream in the form of payments from the Independent System
Operator (ISO) New England region's capacity futures markets. These
competitive markets were designed to ensure sufficient capacity and
reliability for the New England grid as described by ISO New England:

    The Forward Capacity Market (FCM) ensures that the New England
power system will have sufficient resources to meet the future
demand for electricity. Forward Capacity Auctions (FCAs) are held
annually, three years in advance of the operating period. Resources
compete in the auctions to obtain a commitment to supply capacity in
exchange for a market-priced capacity payment. These payments help
support the development of new resources. Capacity payments also
help retain existing resources. For example, they incentivize
investment in technology or practices that help ensure strong
performance. They also serve as a stable revenue stream for
resources that help meet peak demand but don't run often the rest of
the year.\107\
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    \107\ See www.iso-ne.com/markets-operations/markets/forward-capacity-market/.

    In 2019, an independent estimate suggested that, between 2018 and
2023, Merrimack Station would receive approximately $189 million in
these capacity market payments.\108\ Thus, the plant is in a different
financial situation than the other plants discussed in the 2020 rule
record, which EPA was concerned would be forced to prematurely retire
due to costs associated with the rule and reduced utilization and
which, as a result, would potentially impact grid reliability.
Furthermore, the fact that several of the plants that EPA estimated
would participate in the low utilization subcategory in the 2020 rule
record have since retired despite the flexibility of the subcategory
and without causing grid reliability problems suggests that EPA may
have overestimated both the financial viability of these plants and the
threat of reliability issues. Since Merrimack Station also requested
the ability to transfer to limitations for the permanent cessation of
coal combustion subcategory for its discharges of both FGD wastewater
and BA transport water, it is also possible that regardless of any
flexibilities EPA affords, the plant is headed toward retirement. EPA
notes that the ISO New England's last two Forward Capacity Auctions
show a downward trend of reduced capacity commitments for Merrimack
Station.
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    \108\ See www.concordmonitor.com/merrimack-station-bow-nh-28840181.
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    With respect to BA transport water, Merrimack Station does not have
a dry handling or high recycle rate system. The plant has an unlined
boiler slag pond that is also used to accept other wastestreams from
around the plant. The utility represented to EPA Region 1 permitting
staff that this surface impoundment was not subject to the CCR rule.
EPA plans to further evaluate this issue, but for purposes of
estimating costs for this rule, EPA is currently relying on the
facility's representation and has included costs of BA conversion in
its analysis. Working with EPA Region 1 permitting staff, Merrimack
Station previously represented that it could achieve zero discharge
through construction of a new remote MDS system by 2022.\109\
Furthermore, this system was estimated to cost $14.9 million at
most.\110\ Given the timing of this proposal, Merrimack Station's
representations about what date it could achieve zero discharge and
cost of the relevant BA system are no longer accurate. EPA now
conservatively estimates the raw capital costs of a closed-loop system
to be over $26 million. Of this, approximately $22 million would be for
the installation of a remote MDS and associated equipment, while
approximately $4 million would be capital costs to achieve complete
recycle. As discussed in Section VII.B.2 of this preamble, the over $4
million in capital costs to close the loop may be unnecessary or
overstated, and EPA has incorporated these cost estimates into its
consideration of cost and economic achievability for BA transport water
BAT limitations.
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    \109\ See January 30 email from Linda Landis, available online
at: www3.epa.gov/region1/npdes/merrimackstation/pdfs/ar/AR-1513.pdf.
After EPA announced its reconsideration of the 2015 steam electric
rule in 2017, the facility announced it would halt any efforts
toward achieving zero discharge of its BA transport water pending
revision of the rule. See April 20 letter from Linda Landis,
available at: www3.epa.gov/region1/npdes/merrimackstation/pdfs/ar/AR-1362.pdf. Ultimately, EPA issued a renewed NPDES permit for
Merrimack Station in 2020 with a zero discharge BA transport water
limitation to be achieved by December 31, 2023.
    \110\ See www3.epa.gov/region1/npdes/merrimackstation/pdfs/final/merrimack-final-rtc-ch-5.pdf.
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    After considering the record discussed above, EPA proposes to
remove the 2020 rule low utilization subcategory. The record now
indicates that there has been only one facility seeking to avail itself
of low utilization discharge limitations for FGD wastewater, and that
single facility already has zero discharge treatment equipment in
place. Thus, it is not appropriate to continue the subcategory for this
wastewater, as there are no disparate capital costs, no unacceptable
non-water quality environmental impacts (including potential grid
reliability impacts), and no need to allow this facility to otherwise
discontinue use of its very efficient pollution treatment equipment to
``harmonize'' with other regulations. EPA solicits comment on whether
any additional facilities with FGD wastewater have submitted NOPPs for
the low utilization subcategory of which the Agency is not aware.
    Finally, EPA does not think that Merrimack Station's costs (e.g.,
in installing and operating a technology to meet the proposed BA
transport water limitations), even if higher, warrant a special
subcategory, given that this facility receives a production-independent
revenue stream in the form of payments from New England's capacity
futures markets. EPA is continuing to examine whether the plant's
unlined slag settling pond is ``a natural topographic depression, man-
made excavation, or diked area, which is designed to hold an
accumulation of CCR and liquids, and the unit treats, stores, or
disposes of CCR.'' \111\ Should the slag settling pond meet this
definition, the unlined status of this pond would mean the facility is
obligated under the CCR rule to cease receipt of waste in the surface
impoundment and construct an alternative BA handling system,
eliminating any potentially disparate

capital costs associated with meeting potentially more stringent BA
transport water limitations. Even if the pond is not subject to the CCR
rule, EPA questions whether there would be disparate costs for treating