[Federal Register Volume 84, Number 226 (Friday, November 22, 2019)]
[Proposed Rules]
[Pages 64620-64677]
[FR Doc No: 2019-24686]

Vol. 84

Friday,

No. 226

November 22, 2019

Part II

 Environmental Protection Agency

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40 CFR Part 423

Effluent Limitations Guidelines and Standards for the Steam Electric
Power Generating Point Source Category; Proposed Rule

Federal Register / Vol. 84 , No. 226 / Friday, November 22, 2019 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 423

[EPA-HQ-OW-2009-0819; FRL-10002-04-OW]
RIN 2040-AF77

Effluent Limitations Guidelines and Standards for the Steam
Electric Power Generating Point Source Category

AGENCY: Environmental Protection Agency.

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (the EPA or the Agency) is
proposing a regulation to revise the technology-based effluent
limitations guidelines and standards (ELGs) for the steam electric
power generating point source category applicable to flue gas
desulfurization (FGD) wastewater and bottom ash (BA) transport water.
This proposal is estimated to save approximately $175 million dollars
annually in pre-tax compliance costs and $137 million dollars annually
in social costs as a result of less costly FGD wastewater technologies
that could be used with the proposed relaxation of the Steam Electric
Power Generating Effluent Guidelines 2015 rule (the 2015 rule) selenium
limitation; less costly BA transport water technologies made possible
by the proposed relaxation of the 2015 rule's zero discharge
limitations; a two-year extension of compliance timeframes for meeting
FGD wastewater limits, and additional proposed subcategories for both
FGD wastewater and BA transport water. EPA also believes that
participation in the voluntary incentive program would further reduce
the pollutants that these steam electric facilities discharge in FGD
wastewater by approximately 105 million pounds per year.

DATES:
    Comments. Comments on this proposed rule must be received on or
before January 21, 2020.
    Public Hearing. The EPA will conduct an online public hearing about
today's proposed rule on December 19, 2019. Following a brief
presentation by EPA personnel, the Agency will accept oral comments
that will be limited to three (3) minutes per commenter. The hearing
will be recorded and transcribed, and the EPA will consider all of the
oral comments provided, along with the written public comments
submitted via the docket for this rulemaking. To register for the
hearing, please visit the EPA's website at https://www.epa.gov/eg/steam-electric-power-generating-effluent-guidelines-2019-proposed-revisions.

ADDRESSES: Submit your comments on the proposed rule, identified by
Docket No. EPA-HQ-OW-2009-0819, by one of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/
(preferred method). Follow the online instructions for submitting
comments.
     Email<EMAIL_ADDRESS>Include Docket ID No. EPA-
HQ-OW-2009-0819 (specify the applicable docket number) in the subject
line of the message.
     Fax:<PHONE_NUMBER>. Attention Docket ID No. EPA-HQ-OW-
2009-0819 (specify the applicable docket number).
     Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OW-2009-0819, Office of Science and
Technology Docket, Mail Code 28221T, 1200 Pennsylvania Avenue NW,
Washington, DC 20460.
     Hand Delivery/Courier: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operations are 8:30 a.m.-4:30 p.m.,
Monday-Friday (except Federal Holidays).
    Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov/, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the ``Public Participation''
heading of the SUPPLEMENTARY INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: For technical information, contact
Richard Benware, Engineering and Analysis Division, Telephone: 202-566-
1369; Email<EMAIL_ADDRESS>For economic information, contact
James Covington, Engineering and Analysis Division, Telephone: 202-566-
1034; Email<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:
    Preamble Acronyms and Abbreviations. We use multiple acronyms and
terms in this preamble. While this list may not be exhaustive, to ease
the reading of this preamble and for reference purposes, the EPA
defines terms and acronyms used in Appendix A.
    Supporting Documentation. The rule proposed today is supported by a
number of documents including:
     Supplemental Technical Development Document for Proposed
Revisions to the Effluent Limitations Guidelines and Standards for the
Steam Electric Power Generating Point Source Category (Supplemental
TDD), Document No. EPA-821-R-19-009. This report summarizes the
technical and engineering analyses supporting the proposed rule. The
Supplemental TDD presents the EPA's updated analyses supporting the
proposed revisions to FGD wastewater and BA transport water. These
updates include additional data collection that has occurred since the
publication of the 2015 rule, updates to the industry (e.g.,
retirements, updates to FGD treatment and BA handling), cost
methodologies, pollutant removal estimates, corresponding nonwater
quality environmental impacts associated with updated FGD and BA
methodologies, and calculation of the proposed effluent limitations.
Except for the updates described in the Supplemental TDD, the Technical
Development Document for the Effluent Limitations Guidelines and
Standards for the Steam Electric Power Generating Point Source Category
(2015 TDD, Document No. EPA-821-R-15-007) is still applicable and
provides a more complete summary the EPA's data collection, description
of the industry, and underlying analyses supporting the 2015 rule.
     Supplemental Environmental Assessment for Proposed
Revisions to the Effluent Limitations Guidelines and Standards for the
Steam Electric Power Generating Point Source Category (Supplemental
EA), Document No. EPA-821-R-19-010. This report summarizes the
potential environmental and human health impacts that are estimated to
result from implementation of the proposed revisions to the 2015 rule.
     Benefit and Cost Analysis for Proposed Revisions to the
Effluent Limitations Guidelines and Standards for the Steam Electric
Power Generating Point Source Category (BCA Report), Document No. EPA-
821-R-19-011. This report summarizes estimated societal benefits and
costs that are estimated to result from implementation of the proposed
revisions to the 2015 rule.
     Regulatory Impact Analysis for Proposed Revisions to the
Effluent Limitations Guidelines and Standards for the Steam Electric
Power Generating Point Source Category (RIA), Document No. EPA-821-R-
19-012. This report presents a profile of the steam electric power
generating industry, a summary of estimated costs and impacts
associated with the proposed revisions to the 2015 rule, and an
assessment of

the potential impacts on employment and small businesses.
     Docket Index for the Proposed Revisions to the Steam
Electric ELGs. This document provides a list of the additional
memoranda, references, and other information relied upon by the EPA for
the proposed revisions to the ELGs.
    Organization of this Document. The information in this preamble is
organized as follows:

I. Executive Summary
II. Public Participation
III. General Information
    A. Does this action apply to me?
    B. What action is the Agency Taking?
    C. What is the Agency's authority for taking this action?
    D. What are the monetized incremental costs and benefits of this
action?
IV. Background
    A. Clean Water Act
    B. Relevant Effluent Guidelines
    1. Best Practicable Control Technology Currently Available (BPT)
    2. Best Available Technology Economically Achievable (BAT)
    3. Pretreatment Standards for Existing Sources (PSES)
    C. 2015 Rule
    D. Legal Challenges, Administrative Petitions, Section 705
Action, Postponement Rule, and Reconsideration of Certain
Limitations and Standards
    E. Other Ongoing Rules Impacting the Steam Electric Sector
    1. Clean Power Plan (CPP) and Affordable Clean Energy (ACE)
    2. Coal Combustion Residuals (CCR)
    F. Scope of This Proposed Rulemaking
V. Steam Electric Power Generating Industry Description
    A. General Description of Industry
    B. Current Market Conditions in the Electricity Generation
Sector
    C. Control and Treatment Technologies
    1. FGD Wastewater
    2. BA Transport Water
VI. Data Collection Since the 2015 Rule
    A. Information From the Electric Utility Industry
    1. Engineering Site Visits
    2. Data Requests, Responses, and Meetings
    3. Voluntary BA Transport Water Sampling
    4. Electric Power Research Institute (EPRI) Voluntary Submission
    5. Meetings With Trade Associations
    B. Information From the Drinking Water Utility Industry and
States
    C. Information From Technology Vendors and Engineering,
Procurement, and Construction (EPC) Firms
    D. Other Data Sources
VII. Proposed Regulation
    A. Description of the BAT/PSES Options
    1. FGD Wastewater
    2. BA Transport Water
    B. Rationale for the Proposed BAT
    1. FGD Wastewater
    2. BA Transport Water
    3. Rationale for Voluntary Incentives Program (VIP)
    C. Additional Proposed Subcategories
    1. Subcategory for Facilities With High FGD Flows
    2. Subcategory for Boilers With Low Utilization
    3. Subcategory for Boilers Retiring by 2028
    D. Availability Timing of New Requirements
    E. Regulatory Sub-Options To Address Bromides
    F. Economic Achievability
    G. Non-Water Quality Environmental Impacts
    H. Impacts on Residential Electricity Prices and Low-Income and
Minority Populations
    I. Additional Rationale for the Proposed PSES
VIII. Costs, Economic Achievability, and Other Economic Impacts
    A. Facility-Specific and Industry Total Costs
    B. Social Costs
    C. Economic Impacts
    1. Screening-Level Assessment
    a. Facility-Level Cost-to-Revenue Analysis
    b. Parent Entity-Level Cost-to-Revenue Analysis
    2. Electricity Market Impacts
    a. Impacts on Existing Steam Electric Facilities
    b. Impacts on Individual Facilities Incurring Costs
IX. Changes to Pollutant Loadings
    A. FGD Wastewater
    B. BA Transport Water
    C. Summary of Incremental Changes of Pollutant Loadings From
Proposed Regulatory Options
X. Non-Water Quality Environmental Impacts
    A. Energy Requirements
    B. Air Pollution
    C. Solid Waste Generation and Beneficial Use
    D. Changes in Water Use
XI. Environmental Assessment
    A. Introduction
    B. Updates to the Environmental Assessment Methodology
    C. Outputs From the Environmental Assessment
XII. Benefits Analysis
    A. Categories of Benefits Analyzed
    B. Quantification and Monetization of Benefits
    1. Changes in Human Health Benefits From Changes in Surface
Water Quality
    2. Changes in Surface Water Quality
    3. Effects on Threatened and Endangered Species
    4. Changes in Benefits From Marketing of Coal Combustion
Residuals
    5. Changes in Dredging Costs
    6. Changes in Air-Related Effects
    7. Benefits From Changes in Water Withdrawals
    C. Total Monetized Benefits
    D. Unmonetized Benefits
XIII. Development of Effluent Limitations and Standards
    A. FGD Wastewater
    1. Overview of the Limitations and Standards
    2. Criteria Used To Select Data
    3. Data Used To Calculate Limitations and Standards
    4. Long-Term Averages and Effluent Limitations and Standards for
FGD Wastewater
    B. BA Transport Water Limitations
    1. Maximum 10 Percent 30-Day Rolling Average Purge Rate
    2. Best Management Practices Plan
XIV. Regulatory Implementation
    A. Implementation of the Limitations and Standards
    1. Timing
    2. Implementation for the Low Utilization Subcategory
    a. Determining Boiler Net Generation
    b. Tiering Limitations
    3. Addressing Withdrawn or Delayed Retirement
    a. Involuntary Retirement Delays
    b. Voluntary Retirement Withdrawals and Delays
    B. Reporting and Recordkeeping Requirements
    C. Site-Specific Water Quality-Based Effluent Limitations
XV. Related Acts of Congress, Executive Orders, and Agency
Initiatives
    A. Executive Orders 12866 (Regulatory Planning and Review) and
13563 (Improving Regulation and Regulatory Review)
    B. Executive Order 13771 (Reducing Regulation and Controlling
Regulatory Costs)
    C. Paperwork Reduction Act
    D. Regulatory Flexibility Act
    E. Unfunded Mandates Reform Act
    F. Executive Order 13132: Federalism
    G. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    H. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    I. Executive Order 13211: Actions That Significantly Affect
Energy Supply, Distribution, or Use
    J. National Technology Transfer and Advancement Act
    K. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
    L. Congressional Review Act (CRA)
Appendix A to the Preamble: Definitions, Acronyms, and Abbreviations
Used in This Preamble

I. Executive Summary

A. Purpose of Rule

    Coal-fired facilities are impacted by several environmental
regulations. One of these regulations, the Steam Electric Power
Generating ELGs was promulgated in 2015 (80 FR 67838; November 3, 2015)
and applies to the subset of the electric power industry where
``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,
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.'' (40 CFR 423.10). The 2015 rule addressed
discharges from flue gas desulfurization (FGD) wastewater, fly ash
transport water, bottom ash transport water, flue gas mercury control
wastewater, gasification wastewater, combustion residual leachate, and
non-chemical metal cleaning wastes.
    In the few years since the steam electric ELGs were revised in
2015, steam electric facilities have installed more affordable
technologies which are capable of removing a similar amount of
pollution as those which existed in 2015. This proposal would revise
requirements for two of the waste streams addressed in the 2015 rule:
Bottom ash (BA) transport water and flue gas desulfurization (FGD)
wastewater--two of the facilities' largest sources of wastewater--while
reducing industry costs as compared to the costs of the 2015 rule's
controls. This proposal does not seek to revise the other waste streams
covered by the 2015 rule.

B. Summary of Proposed Rule

    For existing sources that discharge directly to surface water, with
the exception of the subcategories discussed below, the proposed rule
would establish the following effluent limitations based on Best
Available Technology Economically Achievable (BAT):
     For flue gas desulfurization wastewater, there are two
sets of proposed BAT limitations. The first set of limitations is a
numeric effluent limitation on Total Suspended Solids (TSS) in the
discharge of FGD wastewater. The second set of BAT limitations
comprises numeric effluent limitations on mercury, arsenic, selenium,
and nitrate/nitrite as nitrogen in the discharge of FGD wastewater.
     For bottom ash transport water, there are two sets of
proposed BAT limitations. The first set of BAT limitations is a numeric
effluent limitation on TSS in the discharge of these wastewaters. The
second set of BAT limitations is a not-too-exceed 10 percent volumetric
purge limitation.
    The proposed rule includes separate requirements for the following
subcategories: High flow facilities, low utilization boilers, and
boilers retiring by 2028. The proposed rule does not seek to change the
existing subcategories for oil-fired boilers and small generating units
(50 MW or less) from the 2015 rule. For high flow facilities (FGD
wastewater flows over four million gallons per day after accounting for
that facility's ability to recycle the wastewater to the maximum limits
for the FGD system materials of construction) or low utilization
boilers (876,000 MWh per year or less), the proposed rule would
establish the second set of BAT limitations in the discharge of FGD
wastewater as numeric effluent limitations only on mercury and arsenic
(and not on selenium and nitrate/nitrite as nitrogen). For low
utilization boilers, the proposed rule would establish BAT limitations
for BA transport water for TSS, and would also include standards for
implementation of a best management practices (BMP) plan. For oil-fired
boilers, small boilers (50 MW or less), and boilers retiring by 2028,
the proposed rule would establish BAT limitations for TSS in FGD
wastewater and bottom ash transport water.
    The proposed rule would establish a voluntary incentives program
that provides the certainty of more time (until December 31, 2028) for
facilities to implement new standards and limitations, if they adopt
additional process changes and controls that achieve more stringent
limitations on mercury, arsenic, selenium, nitrate/nitrite, bromide,
and total dissolved solids in FGD wastewater. The optional program
offers environmental protections beyond those achieved by the proposed
BAT limitations, while providing facilities that opt into the program
more flexibility (such as additional time) than the current voluntary
incentives program.
    For indirect discharges (i.e., discharges to publicly owned
treatment works), the proposed rule establishes pretreatment standards
for existing sources that are the same as the BAT limitations, except
for TSS, where there is no pass through of pollutants at POTWs.
    Where BAT limitations in this rule are more stringent than
previously established BPT limitations, the EPA proposes that those
limitations do not apply until a date determined by the permitting
authority that is as soon as possible on or after November 1, 2020, but
that is no later than December 31, 2023 (for BA transport water) or
December 31, 2025 (for FGD wastewater).

C. Summary of Costs and Benefits

    The EPA has estimated costs and benefits of four different
regulatory options. The EPA estimates that its proposed option (i.e.,
Option 2) will save $136.3 million per year in social costs and result
in between $14.8 million and $68.5 million in benefits, using a three
percent discount, and will save $166.2 million per year in social costs
and between $28.4 million and $74.4 million in benefits, using a seven
percent discount. Table XV-1 summarizes the benefits and social costs
for the four regulatory options at a three percent discount rates. The
EPA's analysis reflects the Agency's understanding of the actions steam
electric facilities will take to meet the limitations and standards in
the final rule. The EPA based its analysis on a baseline that reflects
the expected impacts of announced retirements and fuel conversions,
impacts of relevant rules such as the Coal Combustion Residuals (CCR)
rule that the Agency promulgated in April 2015 and the Affordable Clean
Energy Rule (ACE) that the Agency promulgated in 2019, and the full
implementation of the 2015 rule. The EPA understands that these modeled
results have uncertainty and that the actual costs could be higher or
lower than estimated. The current estimate reflects the best data and
analysis available at this time. For additional information, see
Sections V and VIII.

II. Public Participation

    Submit your comments, identified by Docket ID No. EPA-HQ-OW-2009-
0819, at https://www.regulations.gov (our preferred method), or the
other methods identified in the ADDRESSES section. Once submitted,
comments cannot be edited or removed from the docket. The EPA may
publish any comment received to its public docket. Do not submit
electronically any information you consider to be Confidential Business
Information (CBI) or other information whose disclosure is restricted
by statute. Multimedia submissions (audio, video, etc.) must be
accompanied by a written comment. The written comment is considered the
official comment and should include discussion of all points you wish
to make. The EPA will generally not consider comments or comment
contents located outside of the primary submission (i.e., on the web,
cloud, or other file sharing system). For additional submission
methods, the full EPA public comment policy, information about CBI or
multimedia submissions, and general guidance on making effective
comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.

III. General Information

A. Does this action apply to me?

    Entities potentially regulated by any final rule following this
action include:

------------------------------------------------------------------------
                                                 North American Industry
        Category          Example of regulated    Classification System
                                 entity                (NAICS) code
------------------------------------------------------------------------
Industry...............  Electric Power                            22111
                          Generation
                          Facilities--Electric
                          Power Generation.
                         Electric Power                           221112
                          Generation
                          Facilities--Fossil
                          Fuel Electric Power
                          Generation.
------------------------------------------------------------------------

    This section is not intended to be exhaustive, but rather provides
a guide regarding entities likely to be regulated by any final rule
following this action. Other types of entities that do not meet the
above criteria could also be regulated. To determine whether your
facility is regulated by any final rule following this action, you
should carefully examine the applicability criteria listed in 40 CFR
423.10 and the definitions in 40 CFR 423.11 of the 2015 rule. If you
still have questions regarding the applicability of any final rule
following this action to a particular entity, consult the person listed
for technical information in the preceding FOR FURTHER INFORMATION
CONTACT section.

B. What action is the Agency taking?

    The agency is proposing to revise certain Best Available Technology
Economically Achievable (BAT) effluent limitations guidelines and
pretreatment standards for existing sources in the steam electric power
generating point source category that apply to FGD wastewater and BA
transport water.

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

    The EPA is proposing to promulgate this rule under the authority of
sections 301, 304, 306, 307, 308, 402, and 501 of the Clean Water Act
(CWA), 33 U.S.C. 1311, 1314, 1316, 1317, 1318, 1342, and 1361.

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

    This action is estimated to save $136.3 million per year in social
costs and result in between $14.8 million and $68.5 million in
benefits, using a 3 percent discount rate. Using a 7 percent discount
rate, the estimated savings are $166.2 million per year and benefits
are between $28.4 million and $74.4 million.

IV. Background

A. Clean Water Act

    Among its core provisions, the CWA prohibits the discharge of
pollutants from a point source to waters of the U.S., except as
authorized under the CWA. Under section 402 of the CWA, 33 U.S.C. 1342,
discharges may be authorized through a National Pollutant Discharge
Elimination System (NPDES) permit. The CWA establishes a dual approach
for these permits: (1) Technology-based controls that establish a floor
of performance for all dischargers, and (2) water quality-based
effluent limitations, where the technology-based effluent limitations
are insufficient to meet applicable water quality standards (WQS). As
the basis for the technology-based controls, the CWA authorizes the EPA
to establish national technology-based effluent limitations guidelines
and new source performance standards for discharges into waters of the
United States from categories of point sources (such as industrial,
commercial, and public sources).
    The CWA also authorizes the EPA to promulgate nationally applicable
pretreatment standards that control pollutant discharges from sources
that discharge wastewater indirectly to waters of the U.S., through
sewers flowing to POTWs, as outlined in sections 307(b) and (c) of the
CWA, 33 U.S.C. 1317(b) and (c). The EPA establishes national
pretreatment standards for those pollutants in wastewater from indirect
dischargers that pass through, interfere with, or are otherwise
incompatible with POTW operations. Pretreatment standards are designed
to ensure that wastewaters from direct and indirect industrial
dischargers are subject to similar levels of treatment. See CWA section
301(b), 33 U.S.C. 1311(b). In addition, POTWs are required to implement
local treatment limitations applicable to their industrial indirect
dischargers to satisfy any local requirements. See 40 CFR 403.5.
    Direct dischargers (those discharging to waters of the U.S. rather
than to a POTW) must comply with effluent limitations in NPDES permits.
Indirect dischargers, who discharge through POTWs, must comply with
pretreatment standards. Technology-based effluent limitations and
standards in NPDES permits are derived from effluent limitations
guidelines (CWA sections 301 and 304, 33 U.S.C. 1311 and 1314) and new
source performance standards (CWA section 306, 33 U.S.C. 1316)
promulgated by the EPA, or are based on best professional judgment
(BPJ) where EPA has not promulgated an applicable effluent limitation
guideline or new source performance standard (CWA section 402(a)(1)(B),
33 U.S.C. 1342(a)(1)(B)). Additional limitations are also required in
the permit where necessary to meet WQS. CWA section 301(b)(1)(C), 33
U.S.C. 1311(b)(1)(C). The ELGs are established by EPA regulation for
categories of industrial dischargers and are based on the degree of
control that can be achieved using various levels of pollution control
technology, as specified in the Act (e.g., BPT, BCT, BAT; see below).
    EPA promulgates national ELGs for industrial categories for three
classes of pollutants: (1) Conventional pollutants (total suspended
solids (TSS), oil and grease, biochemical oxygen demand (BOD5), fecal
coliform, and pH), as outlined in CWA section 304(a)(4), 33 U.S.C.
1314(a)(4), and 40 CFR 401.16; (2) toxic pollutants (e.g., toxic metals
such as arsenic, mercury, selenium, and chromium; toxic organic
pollutants such as benzene, benzo-a-pyrene, phenol, and naphthalene),
as outlined in CWA section 307(a), 33 U.S.C. 1317(a); 40 CFR 401.15 and
40 CFR part 423, appendix A; and (3) nonconventional pollutants, which
are those pollutants that are not categorized as conventional or toxic
(e.g., ammonia-N, phosphorus, and total dissolved solids (TDS)).

B. Relevant Effluent Guidelines

    The EPA establishes ELGs based on the performance of well-designed
and well-operated control and treatment technologies. The legislative
history also supports that the EPA need not consider water quality
impacts on individual water bodies as the guidelines are developed; see
Statement of Senator Muskie (principal author) (October 4, 1972),
reprinted in Legislative History of the Water Pollution Control Act
Amendments of 1972, at 170. (U.S. Senate, Committee on Public Works,
Serial No. 93-1, January 1973).
    There are four types of standards applicable to direct dischargers
and two types of standards applicable to indirect dischargers. The
three standards relevant to this rulemaking are described in detail
below.

1. Best Practicable Control Technology Currently Available (BPT)
    Traditionally, the EPA establishes effluent limitations based on
BPT by reference to the average of the best performances of facilities
within the industry, grouped to reflect various ages, sizes, processes,
or other common characteristics. The EPA promulgates BPT effluent
limitations for conventional, toxic, and nonconventional pollutants. In
specifying BPT, the EPA looks at a number of factors. The EPA first
considers the cost of achieving effluent reductions in relation to the
effluent reduction benefits. The Agency also considers the age of
equipment and facilities, the processes employed, engineering aspects
of the control technologies, any required process changes, non-water
quality environmental impacts (including energy requirements), and such
other factors as the Administrator deems appropriate. See CWA section
304(b)(1)(B), 33 U.S.C. 1314(b)(1)(B). If, however, existing
performance is uniformly inadequate, the EPA may establish limitations
based on higher levels of control than those currently in place in an
industrial category, when based on an Agency determination that the
technology is available in another category or subcategory and can be
practically applied.
2. Best Available Technology Economically Achievable (BAT)
    BAT represents the second level of control for direct discharges of
toxic and nonconventional pollutants. As the statutory phrase intends,
the EPA considers the technological availability and the economic
achievability in determining what level of control represents BAT. CWA
section 301(b)(2)(A), 33 U.S.C. 1311(b)(2)(A). Other statutory factors
that the EPA must consider in assessing BAT are the cost of achieving
BAT effluent reductions, the age of equipment and facilities involved,
the process employed, potential process changes, non-water quality
environmental impacts (including energy requirements), and such other
factors as the Administrator deems appropriate. CWA section
304(b)(2)(B), 33 U.S.C. 1314(b)(2)(B); Texas Oil & Gas Ass'n v. EPA,
161 F.3d 923, 928 (5th Cir. 1998). The Agency retains considerable
discretion in assigning the weight to be accorded each of these
required consideration factors. Weyerhaeuser Co. v. Costle, 590 F.2d
1011, 1045 (D.C. Cir. 1978). Generally, the EPA determines economic
achievability based on the effect of the cost of compliance with BAT
limitations on overall industry and subcategory (if applicable)
financial conditions. BAT is intended to reflect the highest
performance in the industry, and it may reflect a higher level of
performance than is currently being achieved based on technology
transferred from a different subcategory or category, bench scale or
pilot studies, or foreign facilities. Am. Paper Inst. v. Train, 543
F.2d 328, 353 (D.C. Cir. 1976); Am. Frozen Food Inst. v. Train, 539
F.2d 107, 132 (D.C. Cir. 1976). BAT may be based upon process changes
or internal controls, even when these technologies are not common
industry practice. See Am. Frozen Food Inst., 539 F.2d at 132, 140;
Reynolds Metals Co. v. EPA, 760 F.2d 549, 562 (4th Cir. 1985); Cal. &
Hawaiian Sugar Co. v. EPA, 553 F.2d 280, 285-88 (2nd Cir. 1977).
    One way that EPA may take into account differences within an
industry when establishing BAT limitations is through
subcategorization. The Supreme Court has recognized that the
substantive test for subcategorizing an industry is the same as that
which applies to establishing fundamentally different factor
variances--i.e., whether the plants are different with respect to
relevant statutory factors. See Chem. Mfrs. Ass'n v. EPA, 870 F.2d 177,
214 n.134 (5th Cir. 1989) (citing Chem. Mfrs. Ass'n v. NRDC, 470 U.S.
116, 119-22, 129-34 (1985)). Courts have stated that there need only be
a rough basis for subcategorization. See Chem. Mfrs. Ass'n v. EPA, 870
F.2d at 215 n.137 (summarizing cases).
3. Pretreatment Standards for Existing Sources (PSES)
    Section 307(b) of the CWA, 33 U.S.C. 1317(b), authorizes the EPA to
promulgate pretreatment standards for discharges of pollutants to
POTWs. PSES are designed to prevent the discharge of pollutants that
pass through, interfere with, or are otherwise incompatible with the
operation of POTWs. Categorical pretreatment standards are technology-
based and are analogous to BPT and BAT effluent limitations guidelines,
and thus the Agency typically considers the same factors in
promulgating PSES as it considers in promulgating BPT and BAT.
Legislative history indicates that Congress intended for the
combination of pretreatment and treatment by the POTW to achieve the
level of treatment that would be required if the industrial source were
discharging to a water of the U.S. Conf. Rep. No. 95-830, at 87 (1977),
reprinted in U.S. Congress. Senate Committee on Public Works (1978), A
Legislative History of the CWA of 1977, Serial No. 95-14 at 271 (1978).
The General Pretreatment Regulations, which set forth the framework for
the implementation of categorical pretreatment standards, are found at
40 CFR 403. These regulations establish pretreatment standards that
apply to all non-domestic dischargers. See 52 FR 1586 (January 14,
1987).

C. 2015 Rule

    The EPA, on September 30, 2015, finalized a rule revising the
regulations for the Steam Electric Power Generating point source
category (40 CFR part 423) (hereinafter the ``2015 rule''). The rule
set the first federal limitations on the levels of toxic metals in
wastewater that can be discharged from steam electric facilities, based
on technology improvements in the steam electric power industry over
the preceding three decades. Prior to the 2015 rule, regulations for
the industry had been last updated in 1982.
    New technologies for generating electric power and the widespread
implementation of air pollution controls over the last 30 years have
altered existing wastewater streams or created new wastewater streams
at many steam electric facilities, particularly coal-fired facilities.
Discharges of these wastestreams include arsenic, lead, mercury,
selenium, chromium, and cadmium. Many of these toxic pollutants, once
in the environment, remain there for years, and continue to cause
impacts.
    The 2015 rule addressed effluent limitations and standards for
multiple wastestreams generated by new and existing steam electric
facilities: BA transport water, combustion residual leachate, FGD
wastewater, flue gas mercury control wastewater, fly ash (FA) transport
water, and gasification wastewater. The rule required most steam
electric facilities to comply with the effluent limitations ``as soon
as possible'' after November 1, 2018, and no later than December 31,
2023. Within that range, except for indirect dischargers, the
particular compliance date(s) for each facility would be determined by
the facility's National Pollutant Discharge Elimination System permit,
which is typically issued by a state environmental agency.
    On an annual basis, the 2015 rule was projected to reduce the
amount of metals defined in the Act as toxic pollutants, nutrients, and
other pollutants that steam electric facilities are allowed to
discharge by 1.4 billion pounds and reduce water withdrawal by 57
billion gallons. At the time, the EPA estimated annual compliance costs
for the final rule to be $480 million (in 2013

dollars) and estimated benefits associated with the rule to be $451 to
$566 million (in 2013 dollars).

D. Legal Challenges, Administrative Petitions, Section 705 Action,
Postponement Rule, and Reconsideration of Certain Limitations and
Standards

    Seven petitions for review of the 2015 rule were filed in various
circuit courts by the electric utility industry, environmental groups,
and drinking water utilities. These petitions were consolidated in the
U.S. Court of Appeals for the Fifth Circuit, Southwestern Electric
Power Co., et al. v. EPA.\1\ On March 24, 2017, the Utility Water Act
Group (UWAG) submitted to the EPA an administrative petition for
reconsideration of the 2015 rule. Also, on April 5, 2017, the Small
Business Administration (SBA) submitted an administrative petition for
reconsideration of the final rule.
---------------------------------------------------------------------------

    \1\ Case No. 15-60821.
---------------------------------------------------------------------------

    On April 25, 2017, the EPA responded to these petitions by
publishing a postponement of the 2015 rule compliance deadlines that
had not yet passed, under Section 705 of the Administrative Procedure
Act (APA). This Section 705 Action drew multiple legal challenges.\2\
The Administrator then signed a letter on August 11, 2017, announcing
his decision to conduct a rulemaking to potentially revise the new,
more stringent BAT effluent limitations and pretreatment standards for
existing sources in the 2015 rule that apply to FGD wastewater and BA
transport water. The Fifth Circuit subsequently granted EPA's request
to sever and hold in abeyance aspects of the litigation related to
those limitations and standards. With respect to the remaining claims
related to limitations applicable to legacy wastewater and leachate,
which are not at issue in this proposed rulemaking, the Fifth Circuit
issued a decision on April 12, 2019, vacating those limitations as
arbitrary and capricious under the Administrative Procedure Act and
unlawful under the CWA, respectively. The EPA plans to address this
vacatur in a subsequent action.
---------------------------------------------------------------------------

    \2\ See Clean Water Action. v. EPA, No. 17-0817 (D.D.C.), appeal
docketed, No. 18-5149 (D.C. Cir.); see also Clean Water Action. v.
EPA, No. 18-60619 (5th Cir.) (case dismissed for lack of
jurisdiction on October 18, 2018).
---------------------------------------------------------------------------

    In September 2017, the EPA finalized a rule, using notice-and-
comment procedures, postponing the earliest compliance dates for the
new, more stringent BAT effluent limitations and PSES for FGD
wastewater and BA transport water in the 2015 rule, from November 1,
2018 to November 1, 2020. The EPA also withdrew its prior action taken
pursuant to Section 705 of the APA. The rule received multiple legal
challenges, but EPA prevailed, and the courts did not sustain any of
them.\3\
---------------------------------------------------------------------------

    \3\ See Center for Biological Diversity v. EPA, No. 18-cv-00050
(D. Ariz. filed Jan. 20, 2018); see also Clean Water Action. v. EPA,
No. 18-60079 (5th Cir.). On October 29, 2018, the District of
Arizona case was dismissed upon EPA's motion to dismiss for lack of
jurisdiction, and on August 28, 2019, the Fifth Circuit denied the
petition for review of the postponement rule.
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E. Other Ongoing Rules Impacting the Steam Electric Sector

1. Clean Power Plan (CPP) and Affordable Clean Energy (ACE)
    The final 2015 CPP established carbon dioxide (CO2)
emission guidelines for fossil-fuel fired facilities based in part on
shifting generation at the fleet-wide level from one type of energy
source to another. On February 9, 2016, the U.S. Supreme Court stayed
implementation of the CPP pending judicial review. West Virginia v.
EPA, No. 15A773 (S.Ct. Feb. 9, 2016).
    On June 19, 2019, the EPA issued the ACE rule, an effort to provide
existing coal-fired electric utility generating units (EGUs) with
achievable and realistic standards for reducing greenhouse gas
emissions. This action was finalized in conjunction with two related,
but separate and distinct rulemakings: (1) The repeal of the CPP, and
(2) revised implementing regulations for ACE, ongoing emission
guidelines, and all future emission guidelines for existing sources
issued under the authority of Clean Air Act section 111(d). ACE
provides states with new emission guidelines that will inform the
state's development of standards of performance to reduce
CO2 emissions from existing coal-fired EGUs consistent with
the EPA's role as defined in the CAA.
    ACE establishes heat rate improvement (HRI), or efficiency
improvement, as the best system of emissions reduction (BSER) for
CO2 from coal-fired EGUs.\4\ By employing a broad range of
HRI technologies and techniques, EGUs can more efficiently generate
electricity with less carbon intensity.\5\ The BSER is the best
technology or other measure that has been adequately demonstrated to
improve emissions performance for a specific industry or process (a
``source category''). In determining the BSER, the EPA considers
technical feasibility, cost, non-air quality health and environmental
impacts, and energy requirements. The BSER must be applicable to, at,
and on the premises of an affected facility. ACE lists six HRI
``candidate technologies,'' as well as additional operating and
maintenance (O&M) practices.\6\ For each candidate technology, the EPA
has provided information regarding the degree of emission limitation
achievable through application of the BSER as ranges of expected
improvement and costs.
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    \4\ Heat rate is a measure of the amount of energy required to
generate a unit of electricity.
    \5\ An improvement to heat rate results in a reduction in the
emission rate of an EGU (in terms of CO2 emissions per
unit of electricity produced).
    \6\ These six technologies are: (1) Neural Network/Intelligent
Sootblowers, (2) Boiler Feed Pumps, (3) Air Heater and Duct Leakage
Control, (4) Variable Frequency Drives, (5) Blade Path Upgrade
(Steam Turbine), and (6) Redesign/Replace Economizer.
---------------------------------------------------------------------------

    The 2015 rule analyses incorporated compliance costs associated
with the 2015 CPP, resulting in, among other things, baseline
retirements associated with that rule in the Integrated Planning Model
(IPM). As noted in the ACE RIA, while the final repeal of the CPP has
been promulgated, the business-as-usual economic conditions achieved
the carbon reductions laid out in the final CPP. The EPA used the IPM
version 6 to analyze today's proposal to be consistent with the base
case analyses done for the ACE final rule. The Agency also performed a
sensitivity analysis on the proposed Option 2, following promulgation
of the ACE final rule, that estimates the impacts of the proposed
option relative to a baseline that includes the ACE rule. A similar
sensitivity analysis was not conducted for Option 4. The EPA intends to
perform IPM runs with the most up-to-date version of the model
available for the final rule. See additional discussion of IPM in
Section VIII of this preamble.
2. Coal Combustion Residuals (CCR)
    On April 17, 2015, the Agency published the Disposal of Coal
Combustion Residuals from Electric Utilities final rule. This rule
finalized national regulations to provide a comprehensive set of
requirements for the safe disposal of CCRs, commonly known as coal ash,
from coal-fired facilities. The final CCR rule was the culmination of
extensive study on the effects of coal ash on the environment and
public health. The rule established technical requirements for CCR
landfills and surface impoundments under subtitle D of the Resource
Conservation and Recovery Act (RCRA), the nation's primary law for
regulating solid waste.
    These regulations addressed coal ash disposal, including
regulations designed to prevent leaking of contaminants into ground
water, blowing of contaminants into the air as dust, and the
catastrophic failure of coal ash surface

impoundments. Additionally, the CCR rule set out recordkeeping and
reporting requirements as well as the requirement for each facility to
establish and post specific information to a publicly-accessible
website. This final CCR rule also supported the responsible recycling
of CCRs by distinguishing safe, beneficial use from disposal.
    As explained in the 2015 rule, the ELGs and CCR rules may affect
the same boiler or activity at a facility. That being the case, when
the EPA finalized both rules in 2015, the Agency coordinated them to
facilitate and minimize the complexity of implementing engineering,
financial, and permitting activities. The coordination of the two rules
continues to be a consideration in the development of today's proposal.
The EPA's analysis of this proposal incorporates the same approach used
in the 2015 rule to estimate how the CCR rule may affect surface
impoundments and the ash handling systems and FGD treatment systems
that send wastes to those impoundments. However, as a result of the
D.C. Circuit Court rulings in USWAG v. EPA, No. 15-1219 (D.C. Cir.
2018) and Waterkeeper Alliance Inc, et al. v. EPA, No. 18-1289 (D.C.
Cir. 2019), amendments to the CCR rule are being proposed which would
establish a deadline of August 2020 by which all unlined surface
impoundments \7\ must cease receiving waste, subject to certain
exceptions. This would not impact the ability of facilities to install
new, composite lined surface impoundments. This CCR proposal and
accompanying background documents are available at www.regulations.gov
Docket EPA-HQ-OLEM-2019-0172, and comments on that proposal should be
submitted to that docket.
---------------------------------------------------------------------------

    \7\ Due to the Court vacatur of 40 CFR part 257.71(a)(1)(i)
(provision for clay-lined surface impoundments) clay-lined surface
impoundments are currently also considered unlined.
---------------------------------------------------------------------------

    In order to account for the CCR rule proposed amendments in this
proposed rule, the EPA conducted a sensitivity analysis to determine
how the closure of unlined surfaced impoundments would impact the
compliance cost and pollutant loading estimates for today's proposal.
After conducting this sensitivity analysis, the EPA found that the
capital and operation and maintenance compliance cost estimates
decrease by 50 to 60 percent and the total industry pollutant loadings
decrease by five percent (see DCN SE07233).
    The EPA solicits comment on the overlap between these two rules,
including whether the Agency's cost benefit and regulatory impact
analyses appropriately capture the overlap of the two rules, and ways
that the Agency could harmonize the timelines for regulatory
requirements. The Agency also solicits comment on the extent to which
facilities have chosen to construct new composite lined surface
impoundments for the treatment of bottom ash transport water or FGD
wastewater. Comments on the intersection of the two rules should be
submitted to both dockets.

F. Scope of This Proposed Rulemaking

    This proposal, if finalized, would revise the new, more stringent
BAT effluent limitations guidelines and pretreatment standards for
existing sources in the 2015 rule that apply to FGD wastewater and BA
transport water. It does not propose otherwise to amend (nor is the EPA
requesting comment on) the effluent limitations guidelines and
standards for other wastes discharged by the steam electric power
generating point source category. The EPA plans to address the Court's
remand in Southwestern Elec. Power Co. v. EPA with respect to the
limitations for leachate and legacy wastewater in a subsequent action.

V. Steam Electric Power Generating Industry Description

A. General Description of Industry

    The EPA provided a general description of the steam electric power
generating industry in the 2013 proposed rule and the 2015 rule, and
has continued to collect information and update that profile. The
previous descriptions reflected the known information about the
universe of steam electric facilities and incorporated applicable final
environmental regulations at that time. For this proposal, as described
in the Supplemental TDD Section 3, the EPA has revised its description
of the steam electric power generating industry (and its supporting
analyses) to incorporate major changes such as additional retirements,
fuel conversions, ash handling conversions, wastewater treatment
updates, and updated information on capacity utilization.\8\ The
analyses supporting this proposal use an updated baseline that
incorporates these changes in the industry. The analyses then compare
the effect of today's proposed rules for FGD wastewater and bottom ash
transport water to the effect of the 2015 rule's limitations for FGD
wastewater and BA transport water on the industry as it exists today.
---------------------------------------------------------------------------

    \8\ The data presented in the general description continues to
rely on some 2009 conditions, as the industry survey remains the
EPA's best available source of information for characterizing
operations across the industry.
---------------------------------------------------------------------------

B. Current Market Conditions in the Electricity Generation Sector

    Market conditions in the electricity generation sector have changed
significantly and rapidly in the past decade. These changes include
availability of abundant and inexpensive natural gas, emergence of
alternative fuel technologies, and continued aging of coal-fired
facilities. These changes have resulted in coal-fired unit and facility
retirements and switching of fuels. The lower cost of natural gas and
technological advances in solar and wind power have had a depressive
effect on both coal-fired and nuclear-powered generation. (This
proposal, if finalized, would have no effect on the nuclear-powered
sector, except as it might affect relative prices through its impacts
on coal-fired generation.) In the coal-fired sector, the market forces
are manifest as scaling back coal-fired power generation (including
unit and facility closures) at an accelerated rate. The rate of coal
capacity retirement is affected by regulation affecting coal-fired
electricity generation as there have been regulations adopted,
particularly in the last decade (e.g., CCR, CPP and 2015 Steam Electric
ELG), that are cited by some power companies when they announce unit or
facility closures, fuel switching, or other operational changes. Among
some utilities, there is also a general trend of supplementing or
replacing traditional generation with alternative sources. As these
changes happen in the industry, the electric power infrastructure
adjusts and generally trends toward the optimal infrastructure and
operations that deliver the country's power demand, with negative
effects for some communities and positive effects for others. The
negative distributional effects can be particularly difficult for
communities affected by company decisions to scale back or retire a
facility. Also see Section 2.3 of the RIA.

C. Control and Treatment Technologies

    In general, control and treatment technologies for some
wastestreams have continued to advance since the 2015 rule. Often,
these advancements provide facilities with additional ways of meeting
effluent limitations, in some instances at a lower cost. For this
proposal, the EPA incorporated updated information and evaluated
several technologies available to control and treat FGD wastewater and
BA transport water produced by the steam electric

power generating industry. See Section VIII of this preamble for
details on updated cost information.
1. FGD Wastewater
    FGD scrubber systems, either dry or wet, are used to remove sulfur
dioxide from flue gas so that sulfur dioxide is not emitted into the
air. Dry FGD systems generally do not discharge wastewater, as the
water they use is evaporated during operation; wet FGD systems do
produce a wastewater stream.
    As part of this proposed rule, the EPA is including two additional
FGD wastewater treatment technologies among the suite of regulatory
options that were not evaluated as main regulatory options in the 2015
rule: Low Hydraulic Residence Time Biological Reduction (LRTR) and
membrane filtration, which are further described below.
     LRTR System. A biological treatment system that targets
removal of selenium and nitrate/nitrite using fixed-film bioreactors in
smaller, more compact reaction vessels than those used in the
biological treatment system evaluated in the 2015 rule (referred to in
this proposal as HRTR--high residence time biological reduction). The
LRTR system is designed to operate with a shorter residence time (on
the order of 1 to 4 hours, as compared to a residence time of 10-16
hours for HRTR), while still achieving significant removal of selenium
and nitrate/nitrite. The LRTR technology option considered as part of
this proposed rule includes chemical precipitation as a pretreatment
stage prior to the bioreactor and ultrafiltration as a polishing step
following the bioreactor.
     Membrane Filtration. A membrane filtration system designed
specifically for high TDS and TSS wastestreams. These systems are
designed to eliminate fouling and scaling associated with industrial
wastewater. These systems typically combine pretreatment for potential
scaling agents such as calcium, magnesium, and sulfates, and one or
more types of membrane technology (e.g., nanofiltration, or reverse
osmosis) to remove a broad array of particulate and dissolved
pollutants from FGD wastewater. The membrane filtration units may also
employ advanced techniques, such as vibration or creation of vortexes
to mitigate fouling or scaling of the membrane surfaces.
    Steam electric facilities discharging FGD wastewater currently
employ a variety of wastewater treatment technologies and operating/
management practices to reduce the pollutants associated with FGD
wastewater discharges. As part of the 2015 rule, the EPA identified the
following types of treatment and handling practices for FGD wastewater:
     Chemical precipitation systems that use tanks to treat FGD
wastewater. Chemicals are added to help remove suspended solids and
dissolved solids, particularly metals. The precipitated solids are then
removed from solution by coagulation/flocculation, followed by
clarification and/or filtration. The 2015 rule focused on a specific
design that employs hydroxide precipitation, sulfide precipitation
(organosulfide), and iron coprecipitation to remove suspended solids
and to convert soluble metal ions to insoluble metal hydroxides or
sulfides.
     Biological treatment systems that use microorganisms to
treat FGD wastewater. The EPA identified three types of biological
treatment systems used to treat FGD wastewater: (1) Anoxic/anaerobic
fixed-film bioreactors, which target removals of nitrogen compounds and
selenium, as well as other metals; (2) anoxic/anaerobic suspended
growth systems, which target removals of selenium and other metals; and
(3) aerobic/anaerobic sequencing batch reactors, which target removals
of organics and nutrients. The 2015 rule focused on a specific design
of anoxic/anaerobic fixed-film bioreactors that employs a relatively
long residence time for the microbial processes. The bioreactor design
used as the basis for the 2015 rule, with typical hydraulic residence
time on the order of approximately 10 to 16 hours, is referred to in
this rulemaking as high residence time reduction (HRTR). The BAT
technology basis for the 2015 rule also included chemical precipitation
as a pretreatment stage prior to the bioreactor and a sand filter as a
polishing step following the bioreactor (i.e., CP+HRTR).
     Thermal evaporation systems that use a falling-film
evaporator (or brine concentrator), following a softening pretreatment
step, to produce a concentrated wastewater stream and a distillate
stream to reduce the volume of wastewater by 80 to 90 percent and also
reduce the discharge of pollutants. The concentrated wastewater is
usually further processed in a crystallizer that produces a solid
residue for landfill disposal and additional distillate that can be
reused within the facility or discharged. These systems are designed to
remove the broad spectrum of pollutants present in FGD wastewater to
very low effluent concentrations.
     Constructed wetland systems using natural biological
processes involving wetland vegetation, soils, and microbial activity
to reduce the concentrations of metals, nutrients, and TSS in
wastewater. High temperature, chemical oxygen demand (COD), nitrates,
sulfates, boron, and chlorides in the wastewater can adversely affect
constructed wetlands' performance. To avoid this, facilities typically
find it necessary to dilute the FGD wastewater with service water
before it enters the wetland.
     Some facilities operate their wet FGD systems using
approaches that eliminate the discharge of FGD wastewater. These
facilities use a variety of operating and management practices to
achieve this.

--Complete recycle. Facilities that operate in this manner do not
produce a saleable solid product from the FGD system (e.g., wallboard-
grade gypsum). Because the facilities are not selling the FGD gypsum,
they are able to allow the landfilled material to contain elevated
levels of chlorides, and as a result do not need a separate wastewater
purge stream.
--Evaporation impoundments. Some facilities in warm, dry climates have
been able to use surface impoundments as holding basins from which the
FGD wastewater evaporates. The evaporation rate from the impoundments
at these facilities is greater than or equal to the flow rate of the
FGD wastewater and amount of precipitation entering the impoundments;
therefore, there is no discharge to surface water.
--Fly ash (FA) conditioning. Many facilities that operate dry FA
handling systems will add water to the FA to suppress dust or improve
handling and/or compaction characteristics in an on-site landfill. The
EPA is not aware of any plants using FGD wastewater to condition ash
that will be marketed.
--Combination of wet and dry FGD systems. The dry FGD process involves
atomizing and injecting wet lime slurry, which ranges from
approximately 18 to 25 percent solids, into a spray dryer. The water in
the slurry evaporates from the heat of the flue gas within the system,
leaving a dry residue that is removed from the flue gas by a fabric
filter (i.e., a baghouse) or electrostatic precipitator (ESP).
--Underground injection. These systems dispose of wastes by injecting
them into an underground well as an alternative to discharging
wastewater to surface waters.

    The EPA also collected new information on other FGD wastewater
treatment technologies, including spray

dryer evaporators, direct contact thermal evaporators, zero valent iron
treatment, forward osmosis, absorption or adsorption media, ion
exchange, electrocoagulation, and electrodialysis reversal. These
treatment technologies have been evaluated at fullscale or pilotscale,
or are being developed to treat FGD wastewater. See Section 4.1 of the
Supplemental TDD for more information on these technologies.
2. BA Transport Water
    BA consists of heavier ash particles that are not entrained in the
flue gas and fall to the bottom of the furnace. In most furnaces, the
hot BA is quenched in a water-filled hopper.\9\ Many facilities use
water to transport (sluice) the BA from the hopper to an impoundment
system or a dewatering bin system. In both the impoundment and
dewatering bin systems, the BA transport water is usually discharged to
surface water as overflow from the system, after the BA has settled to
the bottom. In addition to wet sluicing to an impoundment or dewatering
bin system, the industry also uses the following BA handling systems
that generate BA transport water:
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    \9\ Consistent with the 2015 rule, boiler slag is considered BA.
---------------------------------------------------------------------------

     Remote Mechanical Drag System. These systems use the same
processes as wet-sluicing impoundment or dewatering bin systems to
transport bottom ash to a remote mechanical drag system. A drag chain
conveyor dewaters the bottom ash by pulling it out of the water bath on
an incline. The system can either be operated as a closed-loop
(evaluated during the 2015 rule) or a high recycle rate system. For
this proposed rule, under the high recycle rate option, facilities
would be permitted to purge a portion of the wastewater from the system
to maintain a high recycle rate, as described in Section VII of this
preamble.\10\
---------------------------------------------------------------------------

    \10\ In some cases, additional treatment may be necessary to
maintain a closed-loop system. This additional treatment could
include polymer addition to enhance removal of suspended solids, or
membrane filtration of a slip stream to remove dissolved solids.
---------------------------------------------------------------------------

     Dense Slurry System. These systems use a dry vacuum or
pressure system to convey the bottom ash to a silo (as described below
for the ``Dry Vacuum or Pressure System''), but instead of using trucks
to transport the bottom ash to a landfill, the facility mixes the
bottom ash with water (a lower percentage of water compared to a wet-
sluicing system) and pumps the mixture to the landfill.
    As part of the 2015 rule and this reconsideration, the EPA
identified the following BA handling systems that do not generate
bottom ash transport water.
     Mechanical Drag System. These systems are located directly
underneath the boiler. The bottom ash is collected in a water quench
bath. A drag chain conveyor dewaters the bottom ash by pulling it out
of the water bath on an incline.
     Dry Mechanical Conveyor. These systems are located
directly underneath the boiler. The system uses ambient air to cool the
bottom ash in the boiler and then transports the ash out of the boiler
on a conveyor. No water is used in this process.
     Dry Vacuum or Pressure System. These systems transport
bottom ash from the boiler to a dry hopper without using any water. Air
is percolated through the ash to cool it and combust unburned carbon.
Cooled ash then drops to a crusher and is conveyed via vacuum or
pressure to an intermediate storage destination.
     Vibratory Belt System. These systems deposit bottom ash
into a vibratory conveyor trough, where the ash is air-cooled and
ultimately moved through the conveyor deck to an intermediate storage
destination without using any water.
     Submerged Grind Conveyor. These systems are located
directly underneath the boiler and are designed to reuse slag tanks,
ash gates, clinker grinders, and transfer enclosures from the existing
wet sluicing systems. The system collects bottom ash from the discharge
of each clinker grinder. A series of submerged drag chain conveyors
transport and dewater the bottom ash.
    See Section 4.2 of the Supplemental TDD for more information on
these technologies.

VI. Data Collection Since the 2015 Rule

A. Information From the Electric Utility Industry

1. Engineering Site Visits
    During October and November 2017, the EPA conducted seven site
visits to facilities in five states. The EPA selected facilities to
visit using information gathered in support of the 2015 rule,
information from industry outreach, and publicly available facility-
specific information. The EPA visited four facilities that were
previously visited in support of the 2015 rule because they had
recently conducted, or were currently conducting, FGD wastewater
treatment pilot studies. The EPA also revisited facilities that had
implemented new FGD wastewater treatment technologies or BA handling
systems (after the 2015 rule) to learn more about implementation
timing, start-up and operation, and implementation costs.
    The specific objectives of these site visits were to gather general
information about each facility's operations; their pollution
prevention and wastewater treatment system operations; their ongoing
pilot or laboratory scale studies for FGD wastewater treatment; and BA
handling system conversions.
2. Data Requests, Responses, and Meetings
    Under the authority of Section 308 of the Clean Water Act (CWA) (33
U.S.C. 1318), in January 2018, the EPA requested the following
information from nine steam electric power companies that own coal-
fired facilities generating FGD wastewater:
     FGD wastewater characterization data associated with
testing and implementation of treatment technologies, in 2013 or later.
     Information on halogen usage to reduce flue gas emissions,
as well as halogen concentration data in FGD wastewater.
     Projected installations of FGD wastewater treatment
technologies.
     Cost information for projected or installed FGD wastewater
treatment systems, from bids received in 2013 or later.
    After receiving each company's response, the EPA met with these
companies to discuss the FGD-related data submitted, other FGD and BA
data outside the scope of the request that the company believed to be
relevant, and suggestions each company had for potential changes to the
2015 rule with respect to FGD wastewater and BA transport water. The
EPA used this information to learn more about the performance of
treatment systems, inform the development of FGD wastewater
limitations, learn more about facility-specific halogen usage (such as
bromide), and obtain information useful for updating cost estimates of
installing candidate treatment technologies. As needed, the EPA
conducted follow-up meetings and conference calls with industry
representatives to discuss and clarify these data.
3. Voluntary BA Transport Water Sampling
    In December 2017, the EPA invited seven steam electric facilities
to participate in a voluntary BA transport water sampling program
designed to obtain data to supplement the wastewater characterization
data set for BA transport water included in the record for the 2015
rule. The EPA asked facilities to provide analytical data for

ash pond effluent and untreated BA transport water (i.e., ash pond
influent). The EPA selected the facilities based on their responses to
its 2010 Questionnaire for the Steam Electric Power Generating Effluent
Guidelines (see Section 3.2 of the 2015 TDD). Two facilities chose to
participate in the voluntary BA sampling program. These data were
incorporated into the analytical data set used to estimate pollutant
removals for BA transport water.
4. Electric Power Research Institute (EPRI) Voluntary Submission
    EPRI conducts studies--funded by the steam electric power
generating industry--to evaluate and demonstrate technologies that can
potentially remove pollutants from wastestreams or eliminate
wastestreams using zero discharge technologies. Following the 2015
rule, the EPA reviewed 35 reports published between 2011 and 2018 that
EPRI voluntarily provided regarding characteristics of FGD wastewater
and BA transport water, FGD wastewater treatment pilot studies, BA
handling practices, halogen addition rates, and the effect of halogen
additives on FGD wastewater. The EPA used information presented in
these reports to inform the development of numeric effluent limitations
for FGD wastewater and to update methods for estimating the costs and
pollutant removals associated with candidate treatment technologies.
5. Meetings With Trade Associations
    In May and June of 2018, the EPA met with the Edison Electric
Institute (EEI), the National Rural Electric Cooperatives Association
(NRECA), and the American Public Power Association (APPA). These trade
associations represent investor-owned utilities, electric cooperatives,
and community-owned utilities, respectively. The EPA also met with the
Utility Water Act Group (UWAG), an association comprising the trade
associations above as well as individual electric utilities. The EPA
met with each of these trade associations separately and together to
discuss the technologies and the analyses presented in the 2015 rule
and to hear suggestions for potential changes to the 2015 rule. The EPA
also used information from these meetings to update industry profile
data (i.e., accounting for retirements, fuel conversions, and updated
treatment technology installations).

B. Information From the Drinking Water Utility Industry and States

    The EPA obtained additional information from the drinking water
utility sector and states on the effects of bromide discharges from
steam electric facilities on drinking water treatment processes. First,
the EPA received letters from, and met with, the American Water Works
Association (AWWA), the Association of Metropolitan Water Agencies
(AMWA), the National Association of Water Companies (NAWC), the
Association of Clean Water Administrators (ACWA), and the Association
of State Drinking Water Administrators (ASDWA). Second, the EPA visited
two drinking water treatment facilities in North Carolina that have
modified their treatment processes to address an increase in
disinfection byproduct levels due to bromide discharges from an
upstream steam electric power facility. Finally, the EPA obtained data
on surface water bromide concentrations and data from drinking water
monitoring from the two drinking water treatment facilities. The EPA
also obtained existing state data from other drinking water treatment
facilities from the states of North Carolina and Virginia.

C. Information From Technology Vendors and Engineering, Procurement,
and Construction (EPC) Firms

    The EPA gathered data on availability and effectiveness from
technology vendors and EPC firms through presentations, conferences,
meetings, and email and phone contacts regarding FGD wastewater and BA
handling technologies used in the industry. The data collected informed
the development of the technology costs and pollutant removal estimates
for FGD wastewater and BA transport water. The EPC firms also suggested
potential changes to the 2015 rule.

D. Other Data Sources

    The EPA gathered information on steam electric generating
facilities from the Department of Energy's (DOE's) Energy Information
Administration (EIA) Forms EIA-860 (Annual Electric Generator Report)
and EIA-923 (Power Plant Operations Report). The EPA used the 2015
through 2017 data to update the industry profile prepared for the 2015
rule, including commissioning dates, energy sources, capacity, net
generation, operating statuses, planned retirement dates, ownership,
and pollution controls of the boilers.
    The EPA conducted literature and internet searches to gather
information on FGD wastewater treatment technologies, including
information on pilot studies, applications in the steam electric power
generating industry, and implementation costs and timelines. The EPA
also used the internet searches to identify or confirm reports of
planned facility and boiler retirements, and reports of planned unit
conversions to dry or closed-loop recycle ash handling systems. The EPA
used this information to inform the industry profile and identify
process modifications occurring in the industry.
    The EPA received information from several environmental groups and
other stakeholders following the 2015 rule. In general, these groups
voiced concerns about extending the period that facilities could
continue to discharge FGD wastewater and BA transport water pollutants
subject to BPT limitations, as well as steam electric bromide
discharges, their interaction with drinking water treatment facilities,
and the associated human health effects. They also noted the improved
availability of technological controls for reducing or eliminating
pollutant discharges from FGD and BA handling systems. Finally, they
provided examples where they believed that states had not properly
considered the ``as soon as possible date'' for the new, more stringent
BAT requirements in the 2015 rule when issuing permits.

VII. Proposed Regulation

A. Description of the BAT/PSES Options

    The proposal evaluates four regulatory options and identifies one
proposed option, as shown in Table VII-1. All options include similar
technology bases for BA transport water, except that Option 2 allows
surface impoundments and a BMP plan for low utilization boilers. In
general, each successive option from Option 1 to 4 would achieve a
greater reduction in FGD wastewater pollutant discharges. Each
subcategorization is described further in Section VII.C below. In
addition to some specific requests for comment included throughout this
proposal, the EPA solicits comment on all aspects of this proposal,
including the information, data and assumptions EPA relied upon to
develop the proposed regulatory options, as well as the proposed BAT,
effluent limitations, and alternate approaches included in this
proposal.

                                                          Table VII-1--Main Regulatory Options
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Technology basis for the BAT/PSES  regulatory options
            Wastestream                    Subcategory      --------------------------------------------------------------------------------------------
                                                                        1                      2                      3                      4
--------------------------------------------------------------------------------------------------------------------------------------------------------
FGD Wastewater.....................  N/A...................  Chemical precipitation  Chemical               Chemical               Membrane filtration.
                                                                                precipitation + low    precipitation + low
                                                                                hydraulic residence    hydraulic residence
                                                                                time biological        time biological
                                                                                treatment.             treatment.
                                     High FGD flow           NS....................  Chemical               Chemical               Chemical
                                      facilities.                                     precipitation.         precipitation.         precipitation.
                                     Low utilization         NS....................  Chemical               NS...................  NS.
                                      boilers.                                        precipitation.
                                     Boilers retiring by     Surface impoundments..  Surface impoundments.  Surface impoundments.  Surface impoundments.
                                      2028.
--------------------------------------------------------------------------------------------------------------------------------------------------------
FGD Wastewater Voluntary Incentives Program (Direct          Membrane filtration...  Membrane filtration..  Membrane filtration..  N/A.
 Dischargers Only).
--------------------------------------------------------------------------------------------------------------------------------------------------------
BA Transport Water.................  N/A...................  Dry handling or High    Dry handling or High   Dry handling or High   Dry handling or High
                                                              recycle rate systems.   recycle rate systems.  recycle rate systems.  recycle rate
                                                                                systems.
                                     Low utilization         NS....................  Surface impoundments   NS...................  NS.
                                      boilers.                                        +BMP plan.
                                     Boilers retiring by     Surface impoundments..  Surface impoundments.  Surface impoundments.  Surface impoundments.
                                      2028.
--------------------------------------------------------------------------------------------------------------------------------------------------------
NS = Not Subcategorized.
Note: The table above does not present existing subcategories included in the 2015 rule as the EPA is not proposing any changes to the existing
  subcategorization of oil-fired units or units with a nameplate capacity of 50 MW or less.

1. FGD Wastewater
    Under Option 1, the EPA would establish BAT limitations and PSES
for mercury and arsenic based on chemical precipitation. For Options 2
and 3, the EPA would establish BAT limitations and PSES for mercury,
arsenic, selenium, and nitrate/nitrate based on chemical precipitation
followed by LRTR and ultrafiltration. Option 2 subcategorizes boilers
producing less than 876,000 MWh per year \11\ and for those boilers
would require mercury and arsenic limitations and pretreatment
standards based on chemical precipitation.\12\ Finally, for Option 4,
the EPA would establish BAT limitations and PSES for mercury, arsenic,
selenium, nitrate-nitrite, bromide, and TDS based on membrane
filtration. Options 2, 3, and 4 would subcategorize facilities with
high FGD flows, and for this subcategory would establish limitations
and standards for mercury and arsenic based on chemical precipitation.
Under all four options, boilers retiring by December 31, 2028, would be
subcategorized, and for this subcategory BAT limitations would be set
equal to BPT limitations for TSS based on the use of surface
impoundments. Finally, the EPA would establish voluntary incentives
program limitations for mercury, arsenic, selenium, nitrate-nitrite,
bromide, and TDS based on membranes.
---------------------------------------------------------------------------

    \11\ The equivalent of a 100 MW boiler operating at 100%
capacity or a 400 MW boiler operating at 25% capacity.
    \12\ As explained above, EPA is not proposing to revise BAT
limitations or PSES for oil-fired boilers and/or small boilers (50
MW or smaller).
---------------------------------------------------------------------------

2. BA Transport Water
    Under all options described above, the EPA proposes to control
discharge of pollutants from BA transport water by establishing daily
BAT limitations and PSES on the volume of BA transport water that can
be discharged based on high recycle rate systems. A high recycle rate
system is a recirculating wet ash handling system operated such that it
periodically discharges (purges) a small portion of the process
wastewater from the system. Under all options, boilers retiring by
December 31, 2028, would be subcategorized, and for this subcategory,
BAT limitations would be set equal to BPT limitations for TSS, based on
gravity settling in surface impoundments. Under Option 2, for boilers
producing less than 876,000 MWh per year, BAT effluent limitations for
BA transport water would be set equal to the BPT effluent limitations
based on gravity settling in surface impoundments to remove TSS.\13\
Such facilities would also be required to develop and implement a BMP
plan to minimize the discharge of pollutants from BA transport water.
Because POTWs are designed to treat conventional pollutants such as
TSS, TSS is not considered to pass through and EPA would establish PSES
based on the inclusion of a BMP plan only. For additional information
on pass through analysis, see Section VII(C) of the 2015 rule preamble.
Finally, the EPA proposes a slight modification of the definition of BA
transport water to exclude water remaining in a tank-based high recycle
rate system at the end of the useful life of the facility.\14\ The EPA
proposes not to characterize a technology basis for BAT/PSES applicable
to such wastewater at this time.\15\
---------------------------------------------------------------------------

    \13\ Although TSS is a conventional pollutant, as it did in the
2015 rule, whenever EPA would be regulating TSS in any final rule
following this proposal, it would be regulating it as an indicator
pollutant for the particulate form of toxic metals.
    \14\ Under this modified definition, the water at the end of the
useful life of the facility would be at most the volume of a full
system. Since the high recycle rate system being selected as BAT
allows for a 10 percent purge of the system volume each day, this
would be the equivalent of 10 days discharge, a marginal, one-time
increase in pollution.
    \15\ As illustrated above, there is a wide range of technologies
currently in use for pollutant discharges associated with BA
transport water, and new approaches continue to emerge. For the
exclusion proposed today, permitting authorities would establish BAT
limitations for such discharges on a site-specific, best
professional judgement (BPJ) basis. 33 U.S.C. 1342 (a)(1)(B); 40 CFR
124.3. Pretreatment program control authorities would need to
develop local limitations to address the introduction of pollutants
from this wastewater to POTWs that cause pass through or
interference, as specified in 40 CFR 403.5(c)(2).
---------------------------------------------------------------------------

B. Rationale for the Proposed BAT

    In light of the criteria and factors specified in CWA sections
304(b)(2)(B) and 301(b)(2)(A) (see Section IV of this preamble), the
EPA proposes to

establish BAT effluent limitations based on the technologies described
in Option 2.
1. FGD Wastewater
    This proposal identifies treatment using chemical precipitation
followed by a low hydraulic residence time biological treatment
including ultrafiltration as the BAT technology basis for control of
pollutants discharged in FGD wastewater because after considering the
factors specified in CWA section 304(b)(2)(B), the EPA proposes to find
that this technology is available and economically achievable. More
specifically, the technology basis for BAT would include the same
chemical precipitation system described in the 2015 rule. Thus, it
would employ equalization, hydroxide and sulfide (organosulfide)
precipitation, iron coprecipitation, and removal of suspended and
precipitated solids. This chemical precipitation system would be
followed by a low hydraulic residence time, anoxic/anaerobic biological
treatment system designed to remove heavy metals, selenium, and
nitrate-nitrite.\16\ The LRTR bioreactor stage would be followed by an
ultrafilter to remove suspended solids exiting the bioreactor,
including colloidal particles.
---------------------------------------------------------------------------

    \16\ Similar to the 2015 rule and consistent with discussions
with engineering firms and facility staff, EPA assumed that in order
to meet the limitations and standards, facilities would take steps
to optimize wastewater flows as part of their operating practices
(by reducing the FGD purge rate or recycling a portion of their FGD
wastewater back to the FGD system), where the FGD system metallurgy
can accommodate an increase in chlorides. See Section 5 of the
Supplemental TDD.
---------------------------------------------------------------------------

    Both chemical precipitation and biological treatment are well-
demonstrated technologies that are available to steam electric
facilities for use in treating FGD wastewater. In addition to the 39
facilities mentioned as using chemical precipitation in the 2015 rule
preamble, facilities have installed, or begun installation of such
systems, because they have taken steps to cease using surface
impoundments to treat their FGD wastewater. In addition, chemical
precipitation has been used at thousands of industrial facilities
nationwide for the last several decades as described in the 2015 rule
record. Ultrafilters downstream of the biological treatment stage are
designed for the removal of suspended solids exiting the bioreactor,
such as any reduced, insoluble selenium, mercury, and other
particulates. Ultrafiltration uses a membrane with pore size small
enough to remove these smaller suspended particulates after the
biological treatment stage, but still much larger than the pore size of
the membrane technology (i.e., nanofiltration or reverse osmosis) that
is the basis for option 4 and the VIP which is designed to remove
dissolved metals and inorganics (e.g., nutrients, bromides, etc.).
Unlike the nanofiltration and reverse osmosis technologies,
ultrafilters do not generate a brine that would require encapsulation
with fly ash or other disposal techniques. The types and amount of
solids removed by the ultrafilter in the CP+LRTR treatment system are
identical to the solids removed by the sand filter in the CP+HRTR
treatment technology and do not result in the same non-water quality
environmental impacts that are associated with the brine generated by
the membrane technology of Option 4 and proposed for the VIP program.
    After accounting for the changes in the industry described in
Section V of this preamble, fifteen steam electric facilities with wet
scrubbers have technologies in place able to meet the proposed BAT
effluent limitations for FGD wastewater.\17\ Of these fifteen
facilities, nine are currently operating anoxic/anaerobic biological
treatment designed to substantially reduce nitrogen compounds and
selenium in their FGD wastewater. These biological treatment systems
are a mix of low and high hydraulic residence time.\18\ The EPA
identified a tenth facility that previously operated an anoxic/
anaerobic biological treatment system; however, more recently installed
a thermal system for the treatment of FGD wastewater. Another five
steam electric facilities are also operating thermal treatment systems
for FGD wastewater.
---------------------------------------------------------------------------

    \17\ These fifteen facilities represent 11 percent of steam
electric facilities with wet scrubbers. The EPA notes that a further
40 percent of all steam electric facilities with wet scrubbers use
FGD wastewater management approaches that eliminate the discharge of
FGD wastewater altogether. But, although these technologies (which
are described above in Section V.C.1) may be available for some
facilities, none of them are available nationwide, and thus do not
form the basis for the proposed BAT. For example, evaporation ponds
are only available in certain climates. Similarly, complete recycle
FGD systems are only available at facilities with appropriate FGD
metallurgy. Facility conditions and availability of these
technologies have not materially changed since the 2015 rule, and
the EPA thus reaffirms that these technologies are not individually
available nationwide and are not a basis for the proposed BAT.
    \18\ In addition to these nine facilities, some facilities
employ other types of biological treatment. Some of these systems
are sequencing batch reactors (SBR), which treat nitrogen, and that
technology can be operated to remove selenium. The SBR systems
currently operating at power facilities, however, would likely not
be able to meet the limitations discussed in today's proposal
without reconfiguration.
---------------------------------------------------------------------------

    In the 2015 rule, the EPA rejected three availability arguments
made against biological treatment generally. The EPA is not proposing
to change these findings based on record information received since the
2015 rule but solicits comment on whether, and to what extent, these
findings should be retained for the final rule. First, the EPA rejected
the argument that maintaining a biological system over the long run was
infeasible. Of the ten full-scale systems discussed above, four
facilities have used the biological technology to treat FGD wastewater
for more than a decade under varying operating conditions, climate
conditions, and coal sources. Many pilot tests of the biological
technology have been conducted at various facilities, and data from
these tests demonstrate that even in the face of major upsets within
the chemical precipitation stage of treatment, the biological stage
continues to reduce selenium and nitrogen.
    In the 2015 rule, the EPA also rejected the argument that selenium
removal efficacy was subject to the type of coal burned (specifically
subbituminous coal) and coal-switching. Facilities have continued to
operate biological treatment systems while switching coals and, in
those cases, have maintained a consistent level of selenium removal.
Furthermore, at least three pilot and two full-scale systems have now
been successfully run or installed to treat FGD wastewater at
facilities burning sub-bituminous coals or blends of bituminous and
sub-bituminous coals, encompassing both HRTR and LRTR technologies.
    Finally, in the 2015 rule the EPA rejected arguments that cycling
of facilities up and down in production, and even out of service for
various periods of time, would affect the ability of facilities to meet
the effluent limitations. Industry provided data for two facilities
showing that they successfully operated biological systems while
cycling operations and undergoing shutdowns in the years since the 2015
rule.
    While the rationale above applies to both HRTR and LRTR
technologies, the EPA proposes to establish BAT based on the LRTR
technologies. LRTR reductions are comparable to HRTR reductions,\19\
are less costly, and require significantly less process or facility
footprint modifications than the HRTR option. As explained in Section
XIII of this preamble, the long-term averages forming the basis of the
selenium limitations for LRTR and HRTR are similar, and the higher
selenium

limitations for the LRTR systems are largely driven by increased short-
term variability around that average, rather than a meaningful
difference in long-term pollutant removals.\20\
---------------------------------------------------------------------------

    \19\ For example, while the effluent from LRTR is more variable
than HRTR, both technologies achieve long-term average effluent
concentrations for selenium lower than 20 mg/L.
    \20\ Courts have recognized that while Section 301 of the CWA is
intended to help achieve the national goal of eliminating the
discharge of all pollutants, at some point the technology-based
approach has its limitations. See Am. Petroleum Inst. v. EPA, 787
F.2d 965, 972 (5th Cir. 1986) (``EPA would disserve its mandate were
it to tilt at windmills by imposing BAT limitations which removed de
minimis amounts of polluting agents from our nation's waters [. .
.]'').
---------------------------------------------------------------------------

    LRTR is less costly than HRTR. Compared to the baseline of the 2015
rule, LRTR is estimated to save approximately $72 million per year in
after-tax costs to industry.
    LRTR requires fewer process changes than HRTR. Compared to HRTR,
LRTR installations are less complex and require fewer modifications to
a facility's footprint. The HRTR systems selected in the 2015 rule were
large, concrete tanks which, along with their associated piping and
pumping and control equipment, would be fabricated on site. By
contrast, new LRTR systems have smaller footprints, and in many cases
come prefabricated as modular components, including the ultrafilter
polishing stage, requiring little more than a concrete foundation,
electricity supply, and piping connections.
    The EPA is not proposing to establish BAT limitations or PSES based
on chemical precipitation alone (Option 1). As the EPA noted during the
development of the 2015 rule, chemical precipitation is effective at
removing mercury, arsenic, and certain other heavy metals. While basing
BAT limitations and PSES on this technology alone could save industry
$103 million per year in after-tax costs relative to the 2015 rule,
this technology alone does not remove nitrogen, nor does it remove the
majority of selenium. Furthermore, the data in the EPA's record
demonstrate that both LRTR and HRTR remove approximately 90 percent of
the mercury remaining in the effluent from chemical precipitation
treatment.\21\ Because the combination of chemical precipitation with
LRTR provides substantial further reductions in the discharge of
pollutants, the EPA proposes chemical precipitation followed by LRTR
for BAT.
---------------------------------------------------------------------------

    \21\ Recall that the FGD mercury and arsenic limitations in the
2015 rule were based on chemical precipitation data alone because
the facilities operating biological systems were not using all of
the chemical precipitation additives in the technology basis.
---------------------------------------------------------------------------

    The EPA is not proposing to establish BAT limitations based on
membrane filtration (Option 4). Based on the EPA's record, the EPA
could not conclude that membrane filtration is technologically
available nationwide at this time, as the term is used in the CWA, but
may become ``available'' on a nationwide basis by 2028 (this is
reflected in the date of compliance for the VIP program under Options 2
and 3). Furthermore, membrane filtration entails non-water-quality
environmental impacts (associated with management of the brine) that
the EPA proposes to find unacceptable.
    At the time of the 2015 rule, the EPA had no record of information
about membrane filtration technologies being used to treat FGD
wastewater. Since that time, the EPA collected information on several
types of membrane filtration technologies. Microfiltration and
ultrafiltration membranes are used primarily for removing suspended
solids, including colloids. Nanofiltration, reverse osmosis, forward
osmosis, and electrodialysis reversal (EDR) membranes are used to
remove a broad range of dissolved pollutants. Each of these membrane
filtration technologies generate both a treated effluent and a residual
requiring further treatment or disposal. Microfiltration and
ultrafiltration generate a solid waste residual which is disposed.
Similarly, nanofiltration, reverse osmosis, forward osmosis, and EDR
all produce a concentrated brine residual which must be disposed.
    The EPA's current record includes information on seven pilot
studies of FGD wastewater treatment at domestic facilities using four
different membrane filtration technologies.\22\ All of these
technologies first employed some form of suspended solids removal such
as microfiltration or chemical precipitation. This pretreated FGD
wastewater was then fed into either nanofiltration or reverse osmosis
membrane filtration systems.\23\ For several of the pilot studies, the
resultant brines were mixed with FA and/or lime to test the potential
for encapsulation of the concentrated brine wastestream.\24\
---------------------------------------------------------------------------

    \22\ Two of these pilot studies were completed in 2014, but
information about these tests was not provided to EPA prior to the
2015 rule.
    \23\ The EPA has also learned of an eighth pilot on an EDR
system, but no data have yet been provided (https://www.filtsep.com/water-and-wastewater/news/saltworks-completes-fgd-pilot-in-us/).
    \24\ The record includes additional encapsulation studies and
data not explicitly linked to these seven pilots.
---------------------------------------------------------------------------

    The EPA is not aware of any domestic facilities which have to date
installed nanofiltration or reverse osmosis membrane filtration systems
to remove dissolved pollutants in FGD wastewater, although EPA is aware
of three facilities in China which have installed such membrane
filtration systems.\25\ The record contains limited information about
these facilities. Two of the facilities employ pretreatment and a
combination of reverse osmosis and forward osmosis. The EPA does not
have detailed information about the specific configurations or the
long-term performance of these two systems, nor is the EPA aware of how
the resultant brine is being disposed.\26\ Furthermore, the company
that sold these two systems has since ceased commercial operations.\27\
The third facility operating in China employs pretreatment followed by
nanofiltration and reverse osmosis. At this facility, the brine is
crystallized and the resulting salt is sold for industrial uses. The
EPA does not have information on the long-term performance of this
system.
---------------------------------------------------------------------------

    \25\ Ultrafiltration has been installed as part of FGD
wastewater treatment systems in the U.S.; however, these membranes
are intended to remove suspended solids, not dissolved pollutants.
    \26\ This is in contrast to biological treatment systems for
which EPA has long-term performance data. Although LRTR and HRTR
systems differ in their configuration (e.g., residence time), the
underlying performance has been well demonstrated on this
wastewater.
    \27\ The following story summarizes the forward osmosis company
Oasys ceasing commercial operations: https://www.bluetechresearch.com/news-blog/comment-oasys-hits-funding-drought/.
---------------------------------------------------------------------------

    While the EPA does have some information about the use of membrane
filtration on FGD wastewater from pilot studies, uncertainty remains
regarding operation of the suite of membrane filtration technologies
evaluated by the EPA as the basis for Option 4. With respect to data
from the pilot studies, these studies focused on membrane technologies
that would remove dissolved pollutants. For the technologies designed
to remove dissolved pollutants, several studies either did not include
a second stage of membrane filtration (i.e., a reverse osmosis
polishing stage which electric utilities and vendors indicated would
need to be part of any potential future membrane filtration system they
would install and operate with a discharge) or provided only summaries
of effluent data because of nondisclosure agreements between EPRI,
treatment technology vendors, and/or the plant operators. In both
cases, this prevented the EPA from fully analyzing the pollutant
removal efficacy and effluent variability associated with the treatment
systems used in those studies. The pilot tests that omitted the second
stage of membrane filtration do not provide sufficient insight into the
performance capabilities of the membrane technology because the initial
membrane filtration step (e.g., a nanofilter unit) does not by

itself remove the broad range of pollutants as effectively as would be
achieved by the two-stage configuration. The pilot tests for which the
EPA has only summary-level data provide summary statistics, such as the
observed range of pollutant concentrations, average influent and
effluent pollutant concentrations, and duration of the testing periods.
However, the EPA lacks the individual daily sample results that are
needed to fully evaluate treatment system operation and calculate
effluent limitations. Complete data sets were only available from three
pilot facilities using a single vendor's reverse osmosis
technology.\28\
---------------------------------------------------------------------------

    \28\ These three data sets served as the basis of the proposed
revisions to the VIP limitations, described further in Section XIII
of this preamble. These limited data sets do not provide sufficient
information to evaluate the performance of nanofiltration and
reverse osmosis membrane filtration technology as the primary
treatment for dissolved pollutants FGD wastewater. The EPA
anticipates that additional pilots, tests and data collection could
result in these technologies becoming available by the VIP
compliance date of 2028. By contrast and for the reasons explained
in section VII.2.B., the EPA proposes to conclude that
ultrafiltration technology is available for use in the polishing
stage for systems using LRTR biological systems as the primary
treatment technology for FGD wastewater.
---------------------------------------------------------------------------

    In addition, while the EPA does have information about membrane
filtration application to FGD wastewater from bids and engineering
documents, those sources express concerns about operating a technology
on this wastewater that would be the first of its kind in the U.S. With
respect to information from bids for full-scale installations and
related documents, the EPA obtained copies of bids that represented a
single vendor's reverse osmosis-based technology and that incorporated
performance guarantees. Such guarantees, which are standard within the
steam electric power generating industry, act to transfer the costs of
specific performance issues from the purchaser of the equipment to the
vendor. While the willingness of this vendor to take on these risks
might suggest confidence in the long-term performance of its
technology, third-party EPC firms with no vested interest in the
technology are hesitant to recommend that a client be the first site in
the U.S. to adopt membrane filtration for the treatment of FGD
wastewater because of uncertainty related to system performance and the
ability to operate successfully without frequent, if not excessive,
chemical cleaning. This further supports EPA's proposal to find, at
this time, that membrane filtration is not, technologically available
or an appropriate basis for mandatory requirements for the entire
industry. The EPA solicits comment on this availability finding, and
whether membrane filtration may become nationally available sooner or
later than 2028.
    The EPA also rejects membranes as the technology basis for BAT for
all existing facilities because it could discourage more valuable forms
of beneficial reuse of FA (such as replacing Portland cement in
concrete) potentially causing more FA to be incorporated in wastes
being disposed.\29\ While there are several alternative ways to treat
or dispose of the brine generated by membrane filtration, the method
most likely to be employed (based on bids, engineering documents, and
discussions with electric utilities) is encapsulation with FA and lime
for disposal of the resulting solid in a landfill.\30\
---------------------------------------------------------------------------

    \29\ While the EPA considers FA use for waste solidification and
stabilization as beneficial use, the CCR waste being solidified or
stabilized must still be disposed of in accordance with 40 CFR 257.
    \30\ Bids also indicate that this would be the least-cost brine
management alternative.
---------------------------------------------------------------------------

    Landfilling an encapsulated material raises challenges. For
instance, comingling might result in a leachate blowout. The King
County Landfill in Virginia experienced a leachate blow out when
compact CCR materials with a low infiltration rate were layered with
normal municipal solid waste having a higher infiltration rate.
Similarly, in the case of encapsulated brine paste, the paste would set
and thereafter achieve a very low infiltration rate. When comingled
with CCRs having a higher infiltration rate, this would lead to layers
with disparate infiltration rates akin to those experienced in the King
County scenario. Thus, segregation of low infiltration rate
encapsulated brine in a landfill cell separate from other, higher
infiltration wastes could be necessary to prevent this layering, and a
potential leachate blowout. Such dedicated landfill cells do not exist
today, and would require time to permit and construct.
    Moreover, instead of disposing of their FA, facilities can sell it
for beneficial use. As stated in the 2015 CCR rule:

    The beneficial use of CCR is a primary alternative to current
disposal methods. And as EPA has repeatedly concluded, it is a
method that, when performed correctly, can offer significant
environmental benefits, including greenhouse gas (GHG) reduction,
energy conservation, reduction in land disposal (along with the
corresponding avoidance of potential CCR disposal impacts), and
reduction in the need to mine and process virgin materials and the
associated environmental impacts.\31\
---------------------------------------------------------------------------

    \31\ 80 FR 21329 (April 17, 2015).

    According to 2016 EIA data, the median percent of FA sold for
beneficial use by the facilities with wet FGD systems is approximately
fifty percent, with a range of zero to one hundred percent. The fact
that encapsulation with FA and lime is the most likely, and least cost,
brine management method that facilities could employ nationally,
combined with the high percent of FA currently being beneficially used,
indicates that selection of membrane filtration as BAT could discourage
environmentally preferable beneficial uses of FA, such as replacement
of Portland cement in concrete.\32\ Specifically, the Agency estimated
in U.S. EPA (2011) that each ton of fly ash used as a substitute for
Portland cement would avoid 5,400 megajoules of nonrenewable energy
use, 690 liters of water use, 1,000,000 grams (g) of CO2
emissions, 840 g of methane emissions, 1,400 g of CO emissions, 2,700 g
of NOX emissions, 2,500 g of SOX emissions, 2,400
g of PM, 0.08 g of Hg, 490 g of TSS discharge, 23 g of BOD discharge,
and 46 g of COD discharge.\33\ After considering these cross-program
environmental impacts, the EPA proposes to find that discouraging this
beneficial use of FA would result in unacceptable non-water-quality
environmental impacts.
---------------------------------------------------------------------------

    \32\ Although the EPA evaluated FA and lime encapsulation as the
least-cost nationally available brine disposal alternative, other
alternatives may have higher costs and non-water quality
environmental impacts. For example, if a facility chose to
crystallize the resulting brine to continue selling its FA, this
thermal crystallization process could have a higher cost and
parasitic energy load.
    \33\ U.S. EPA (Environmental Protection Agency). 2011. Waste and
Materials--Flow Benchmark Sector Report: Beneficial Use of Secondary
Materials--Coal Combustion Products. Office of Solid Waste and
Emergency Response. Washington, DC 20460. April.
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    Finally, while the EPA views the foregoing reasoning as sufficient
to find that membrane filtration is not BAT for all existing sources,
the EPA notes that membrane filtration is projected to cost industry
more than the proposed BAT option for FGD wastewater, i.e., chemical
precipitation plus LRTR. Added to these costs are the costs to
facilities of disposing of the resulting brine. Some facilities that
otherwise sell their FA may choose to use their FA to encapsulate the
brine, thereby foregoing revenue from FA sales. Other facilities that
choose to continue to sell their FA must dispose of the brine using
another disposal alternative, such as crystallization, at an additional
cost. Costs are a separate statutory factor that the EPA considers in
selecting BAT (see, for example, BP Exploration & Oil, Inc. v. EPA, 66
F.3d 784, 796 (6th Cir. 1996).

Here, while these costs do not make the membrane filtration option
economically unachievable, the additional costs associated with
membrane filtration provide additional support for the EPA's proposal
that membrane filtration is not BAT for all existing sources.
    Although the EPA is proposing to reject membranes as the national
technology basis for BAT, the EPA proposes to establish a VIP based on
membrane technology, as discussed later in this section. The EPA
solicits comment on this conclusion. Furthermore, the EPA solicits
comment on whether there are early adopters who have already contracted
for, purchased, or installed biological technology for compliance with
the 2015 rule, and whether these facilities should be included as a
subcategory not subject to the final BAT of Option 4, if finalized. The
EPA solicits comment on whether such a subcategory could be based on
the age of the new pollution control equipment that had not yet lived
out its useful life, the disparate costs of purchasing two sets of
equipment, or other statutory factors.
    As described further below, the EPA is also not proposing to
establish BAT limitations based on other technologies also evaluated in
the 2015 rule.
    First, except for the end of life boiler and low-utilization
subcategories discussed below, the EPA is not proposing to establish
BAT limitations based on surface impoundments. Surface impoundments are
not as effective at controlling pollutants like dissolved metals and
nutrients as available and achievable technologies like CP and LRTR.
EPA drew a similar conclusion in the 2015 rule, and nothing in the
record developed by the Agency since the 2015 rule would change this
determination.
    Second, the EPA is not proposing to establish BAT limitations based
on thermal technologies, such as chemical precipitation (including
softening) followed by a falling film evaporator, on the basis of high
costs to industry. In the 2015 rule, the EPA rejected this technology
as a basis for BAT limitations due to high costs to industry. Since the
2015 rule, the EPA has collected additional information on full-scale
installations and pilots of thermal technologies to treat FGD
wastewater. The EPA's record includes information about approximately
10 pilot studies conducted in the U.S., providing performance data for
five different thermal technologies. In addition, full scale
installations are operating at six facilities,\34\ and a seventh
purchased thermal equipment, but elected not to install it.\35\ While
new thermal technologies have been pilot tested and used at full-scale
since the 2015 rule, and related cost information demonstrates that
thermal technologies are less costly than estimated for the 2015 rule,
the thermal costs evaluated in the EPA's memorandum FGD Thermal
Evaporation Cost Methodology (DCN SE07098) are still three to five
times higher than any other option presented in Table VIII-1. As
authorized by section 304(b) of the CWA, which allows the EPA to
consider costs, the Agency is not proposing that thermal technologies
are BAT due to the unacceptable costs to industry. Given the high costs
associated with the technology, and the fact that the steam electric
power generating industry continues to face costs associated with
several other rules, in addition to this rule, the EPA is not proposing
to establish BAT limitations for FGD wastewater based on evaporation
for all steam electric facilities. The EPA solicits comment on this
finding, as well as the accuracy of the revised costs estimates.
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    \34\ One of these facilities successfully ran three different
thermal systems to treat its wastewater, transitioning from a
falling film evaporator to a direct-contact evaporator that mixes
hot gases in a high turbulence evaporation chamber, and finally to a
spray dryer evaporator.
    \35\ This facility purchased a falling film evaporator for the
purpose of meeting water quality-based effluent limitations for
boron, but then elected to instead pay approximately $1 million per
year to send its wastewater to a local POTW.
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    Furthermore, since membrane filtration technologies included in
Option 4 appear to achieve similar pollutant removals for lower costs
than thermal, the EPA is proposing to revise the basis for the VIP
limitations adopted in the 2015 rule to membrane filtration, instead of
thermal technologies, as discussed later in this section.\36\ The EPA
solicits comment on the extent to which membrane filtration
technologies could be used in lieu of, or in combination with, thermal
technologies.
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    \36\ The EPA notes that thermal technologies could continue to
be used to meet the voluntary incentives program limitations based
on membrane filtration.
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    Finally, the EPA is not proposing to decline to establish BAT and
leave BAT effluent limitations for FGD wastewater to be established by
the permitting authority using BPJ. The EPA explained in the 2015 rule
why BPJ determinations would not be appropriate for FGD wastewater,
particularly given the availability of several other technologies, and
nothing in EPA's record would alter its previous conclusion.
2. BA Transport Water
    This proposal identifies treatment using high recycle rate systems
as the BAT technology basis for control of pollutants discharged in BA
transport water because, after evaluating the factors specified in CWA
section 304(b)(2)(B), the EPA proposes to find that this technology is
available and economically achievable. In the 2015 rule, the EPA
selected dry BA handling or closed-loop wet ash handling systems as the
technology basis for the ``zero discharge'' BAT requirements for BA
transport water. The EPA established zero pollutant discharge
limitations based on these technologies and included a limited
allowance for pollutant discharges associated with certain maintenance
activities.\37\
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    \37\ See 40 CFR part 423.11(p).
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    At the time of the 2015 rule, the EPA estimated that more than 50
percent of facilities already employed dry handling systems or wet
sluicing systems designed to operate closed-loop, or had announced
plans to switch to such systems in the near future. Based on new
information collected since the 2015 rule, that value is now over 75
percent, nearly evenly split between dry and wet systems. However,
since the 2015 rule, the EPA's understanding of the types of available
dry systems, and the ability of wet systems to achieve complete recycle
has changed, as discussed below.
    There have been advances in dry BA handling systems since the 2015
rule.\38\ For example, in addition to under-boiler mechanical drag
chain systems (described in the 2015 rule), pneumatic systems and
submerged grinder conveyors are now available and in use at some
facilities. Such systems often can be installed at facilities that are
constrained from retrofitting a mechanical drag system due to
insufficient vertical space under the boiler.
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    \38\ The term ``dry handling'' is used to refer to ash handling
systems that do not use water as the transport medium for conveying
ash away from the boiler. Such systems include pneumatic and
mechanical processes (some mechanical processes use water to cool
the BA or create a water seal between the boiler and ash hoppers,
but the water does not act as the transport medium).
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    With respect to wet BA handling systems, in their petitions for
reconsideration and in recent meetings with the EPA, utilities and
trade associations informed the EPA that many existing remote wet
systems are, in reality, ``partially closed'' rather than closed-loop,
as indicated by the EPA in

the 2015 rule. Utilities and trade associations informed the EPA that
these systems operate partially closed, rather than closed, due to
small discharges associated with additional maintenance and repair
activities not accounted for in the 2015 maintenance allowances,\39\
water imbalances within the system such as those associated with
stormwater,\40\ and water chemistry imbalances including acidity and
corrosiveness, scaling, and fines build-up. While some facilities have
controlled or eliminated these challenges with relatively
straightforward steps (See DCNs SE08179 and SE06963), others require
more extensive process changes and associated increased costs or find
them difficult to resolve (See DCNs SE08188, SE08180, and SE06920).
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    \39\ The 2015 rule maintenance discharges were characterized as
not a significant portion of the system volume, compared to, for
example, potential discharges resulting from maintenance of the
remote MDS tank or the conveyor itself. Such maintenance could
require draining the entire system, which would not be permissible
under the 2015 rule maintenance discharge allowance.
    \40\ The 2015 rule provided no exemption or allowance for
discharges due to precipitation events. While systems are often
engineered with extra capacity to handle rainfall/runoff from a
certain size precipitation event, these events may occur back-to-
back, or facilities may receive events with higher rates of
accumulation beyond what the facility was designed to handle.
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    The EPA agrees that the new information indicates that some
facilities with wet ash removal systems generally operate as zero
discharge systems, but in many cases must operate as high recycle rate
systems. While some facilities currently handle the challenges
discussed above by discharging some portion of their BA transport water
(as the zero discharge limitations in the 2015 rule are not yet
applicable), the record demonstrates that facilities can likely
eliminate such discharges with additional process changes and
expenditures. Just as the EPA estimated costs of chemical additions in
the 2015 rule to manage scaling, companies could add additional
treatment chemicals (caustic) to manage acidity or other chemicals to
control alkalinity, make use of reverse osmosis filters to treat a slip
stream of the recycled water to remove dissolved solids, add polymer to
enhance settling and removal of fine particulates (``fines''), and
build storage tanks to hold water during infrequent maintenance or
precipitation events. Industry-wide, the EPA estimates the costs of
fully closing the loop to be $43 million per year in after-tax costs,
above and beyond the costs of the systems themselves.\41\ These
additional costs and process changes were not accounted for in the 2015
rule; however, as discussed in Section 5.3 of the Supplemental TDD, in
estimating the baseline costs of the BA limitations in the 2015 rule,
the EPA now accounts for these costs. The EPA solicits comment on
whether these assumptions and costs are appropriate and requests
commenters identify and include available data or information to
support their recommended approach.
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    \41\ Utilities and EPC firms have discussed the availability of
new dry systems, such as the submerged grinder conveyor or pressure
systems, which at some facilities would have costs similar to
recirculating wet systems that would require a purge. Because the
EPA did not have cost information to determine the subset of
facilities for which new dry systems might be least costly, some
portion of the costs estimated for this proposal may be based on
selecting recirculating wet systems at facilities which could
ultimately go dry. Thus, the EPA may overestimate costs or
underestimate pollutant removals at the subset of facilities where
such a dry system would be selected.
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    The EPA also recognizes the need for facilities to consider the
standards of multiple environmental regulations simultaneously. As
discussed in Section IV above, the EPA is separately proposing changes
to the CCR rule that, if finalized, would allow facilities to cease
receiving waste in unlined surface impoundments by August 2020.\42\ The
challenges of operating a truly closed-loop system discussed above are
compounded when considered in conjunction with the requirements of the
CCR rule. Facilities often send various CCR and non-CCR wastestreams,
such as coal mill rejects, economizer ash, etc., with BA transport
water into their surface impoundments. According to reports provided to
the EPA and conversations with electric utilities, several facilities
have already begun the transition away from impoundments, and also use
the BA treatment system for some of their non-CCR wastewaters.\43\ This
reportedly can lead to or exacerbate problems with scaling, corrosion,
or plugging of equipment that complicate achievement of a closed-loop
system and require additional process changes and expense to address.
All of which problems could be avoided by purging the system from time
to time, as necessary. While those facilities that have not yet
installed a BA transport water technology (less than 25 percent) could
potentially employ a dry system, and those facilities with existing wet
systems could potentially segregate their BA transport water from their
non-CCR wastewaters, short compliance timeframes under the CCR rule may
limit the availability of such options.
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    \42\ As discussed in Section IV of this preamble, further
information about this proposal is available at http://www.regulations.gov, Docket EPA-HQ-OLEM-2019-0172.
    \43\ In some cases, the treatment system predated even the
proposed CCR rule.
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    In light of the foregoing process changes (and associated
engineering challenges) that facilities would need to make to implement
a true zero discharge BA transport water limitation in combination with
the CCR rule, and to give facilities flexibilities that will facilitate
orderly compliance with the fast-approaching CCR rule deadlines, the
EPA proposes to base the BA transport water BAT limitations on the use
of dry handling or high recycle rate systems rather than dry handling
or closed-loop systems, the technologies on which the zero discharge
BAT limitation adopted in the 2015 rule were based. The EPA's proposal
is based on its discretion to give particular weight to the CWA Section
304(b) statutory factor of ``process changes.'' Process changes to
existing high recycle rate systems that do not currently operate as
closed loop, or that will be installed in the near-future, to comply
with this rule in conjunction with the CCR rule as discussed above
could be more challenging without a further discharge allowance, and in
some cases could also result in the prolonged use of unlined surface
impoundments.
    The EPA considers that the factors discussed above are sufficient
to support the Agency's decision not to select closed-loop systems as
BAT for BA transport water. The EPA also notes that cost is a statutory
factor that it must consider when establishing BAT, and that closed-
loop systems cost more than high recycle rate systems for treatment of
BA transport water. While the EPA does not find this higher cost to be
economically unachievable, the higher cost of closed loop systems is an
additional reason for the EPA to not select closed loop systems as BAT
for treating BA transport water.
    Under the proposed option, the EPA would allow facilities with a
wet transport system, on an ``as needed'' basis, to discharge up to 10
percent of the system volume per day on a 30-day rolling average to
account for the challenges identified above, including infrequent large
precipitation and maintenance events. The EPA proposes that the term
``30-day rolling average'' means the series of averages using the
measured values of the preceding 30 days for each average in the
series. This does not mean that the EPA expects all facilities to
discharge up to 10 percent on a regular basis, rather this option is
designed to provide flexibility if and when needed to address site-
specific challenges of operating the recirculating

ash system (for more on implementation, see Section XIV of this
preamble).\44\ The EPA also solicits comment on a facility-specific
recycle rate alternative to the 10 percent 30-day rolling average
option. Under such an alternative, each facility operating a high
recycle rate system would take proactive measures (e.g., acid or
caustic addition for pH control, chemical addition to control
alkalinity, polymer addition to remove fines) to maintain system water
chemistry within control limitations established by the facility in a
BMP plan similar to that proposed for low utilization units in Section
VII.C.2 below. Under this approach, when reasonable active measures are
insufficient to maintain system water chemistry or water balance within
acceptable limitations, or to facilitate maintenance and repairs of the
BA system, the facility would be authorized to purge a portion of the
system volume. The purge volume would be determined based on plant-
specific information and would be minimized to the extent feasible and
limited to a maximum of 10 percent of the total system volume. The EPA
solicits comment on whether these two options provide sufficient notice
and regulatory certainty for facilities to understand potential
obligations under the proposed rule and associated costs. The EPA
solicits comment on an alternate approach that establishes a standard