Effluent Limitation Guidelines (ELGs) for Steam Electric Power Plants

Updated March 26, 2025

Effluent Limitation Guidelines (ELGs) for Steam Electric

Power Plants

Overview

The Clean Water Act (CWA) prohibits the discharge of

pollutants from any point source into “waters of the United

States” without a permit. Thus, industrial and other

facilities that discharge to waters of the United States must

obtain permits from the U.S. Environmental Protection

Agency (EPA) or delegated states that set limits on

pollutants in facilities’ effluents. To inform the limits set in

permits for industrial dischargers, EPA publishes Effluent

Limitation Guidelines (ELGs)—nationally applicable

regulations that establish technology-based standards for

categories of industrial dischargers. Since 1972, EPA has

promulgated ELGs for 59 industrial categories, including

the steam electric power industry—which covers power

plants that use nuclear or fossil fuels (e.g., coal, oil, and

natural gas) to generate steam used to produce electricity.

In 2015, EPA published revised ELGs for the steam electric

power industry (2015 Rule) to replace rules issued in 1982.

EPA determined that new ELGs were necessary to reflect

changes in the industry. For example, improvements in air

pollution control technologies since 1982, particularly at

coal-fired power plants, reduced air pollutant emissions but

transferred some of these pollutants to liquid wastestreams,

increasing pollutant discharges to surface waters. EPA

promulgated the 2015 Rule to address those water quality

impacts by establishing new or additional requirements for

several wastestreams from steam electric power plants.

Since that time, EPA has published additional regulations to

update the 2015 Rule to reflect developing treatment

technologies and new performance data, and to address

legal challenges. EPA published its most recent ELG

update for the steam electric power category in May 2024

(2024 Rule). The Biden Administration announced the rule

as one of a suite of final rules to reduce pollution from

fossil-fuel-fired power plants. On March 12, 2025, the

second Trump Administration announced its plans to

reconsider the 2024 Rule.

existing, and the category of pollutant discharged. ELGs are

based on the performance of specific control technologies,

but the regulations do not require a facility to use a specific

technology.

CWA Section 304(m) directs EPA to annually review

existing ELGs to determine whether revisions are needed.

During its 2005 review, EPA identified the steam electric

power industry ELGs for possible revision based in part on

data showing that the industry ranked high in discharges of

toxic and nonconventional pollutants. EPA initiated a study,

completed in 2009, which found that the 1982 regulations

did not adequately address the pollutants being discharged

and had not kept pace with changes in the industry. The

study focused primarily on coal ash handling operations and

flue gas desulfurization (FGD) systems (i.e., scrubbers)

used at coal-fired power plants to control air pollution.

While scrubbers reduce pollutant emissions into the air,

some create a significant liquid wastestream. The study

further noted that pollutants in wastewater at some coal

combustion plants have the potential to degrade water

quality when discharged to surface waters or leached into

groundwater.

In 2009, environmental groups sued EPA to compel the

agency to commit to a schedule for issuing revised ELGs

for this industry. Pursuant to a consent decree, EPA

promulgated a final rule in 2015. The 2015 rule included

the first federal limits on toxic metals and other pollutants

in wastewater discharges from steam electric power plants.

The rule included new or additional requirements for both

existing sources and new sources in several wastestreams.

These wastestreams (some of which are shown in Figure 1)

included the following:

• Flue gas desulfurization (FGD) wastewater: wastewater

generated from the wet FGD scrubber system (used to

prevent air emissions of sulfur dioxide) that contacts the

flue gas or the FGD solids

• Fly ash transport water: wastewater that is used to

Background and the 2015 Rule

ELGs set technology-based standards, including numeric

limits, for specific wastewater pollutants. For point sources

that introduce pollutants directly into U.S. waters—direct

dischargers—EPA or delegated states incorporate the limits

set in ELGs into National Pollutant Discharge Elimination

System (NPDES) permits. For sources that discharge to

publicly owned treatment works (POTWs)—indirect

dischargers—EPA promulgates pretreatment standards that

are enforced by POTWs and federal and state authorities.

The CWA requires industrial dischargers to achieve

specified levels of pollution control based on whether a

discharger is direct or indirect, whether a source is new or

convey fly ash from an ash collection or storage

equipment, or boiler, and has direct contact with the ash

• Bottom ash transport water (BATW): wastewater that is

used to convey bottom ash from an ash collection or

storage equipment, or boiler, and has direct contact with

the ash

• Flue gas mercury control (FGMC) wastewater:

wastewater generated from an air pollution control

system installed or operated for the purpose of removing

mercury from flue gas

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Effluent Limitation Guidelines (ELGs) for Steam Electric Power Plants

• Gasification wastewater: wastewater generated at an

integrated combined cycle plant from the gasifier or the

synthetic gas cleaning, combustion, and cooling

processes

• Combustion residual leachate (CRL): leachate from a

landfill or surface impoundment that contains

combustion residuals

Figure 1. Selected Wastestreams from Steam Electric

Power Plants

and included new data for EPA to consider. In response,

EPA agreed to reconsider the ELGs for two waste

streams—FGD wastewater and BATW—for existing

sources. EPA finalized a 2017 rule postponing compliance

deadlines for those wastestreams to allow the agency time

to revise the limits.

In 2020, EPA published a final rule revising the limits for

existing facilities for those two wastestreams (the 2020

Rule). EPA concluded that more affordable technologies

capable of removing similar pollutant amounts had become

available since 2015, and changed the technology basis for

treatment of the two wastestreams. The 2020 Rule

established new subcategories and varying requirements for

high flow facilities, low utilization units, and units retiring

by 2028. Some of these changes reflected less stringent

standards for the new subcategories.

2024 Rule

Source: EPA, “Steam Electric Power Generating Effluent

Guidelines,” https://www.epa.gov/eg/steam-electric-powergenerating-effluent-guidelines.

Notes: ACI is activated carbon injection, ESP is electrostatic

precipitator, FGD is flue gas desulfurization, POTW is publicly owned

treatment works, and Hg is mercury.

Specifically, the 2015 Rule established effluent limits for

arsenic, mercury, selenium, and nitrogen for FGD

wastewater at existing sources, as well as more stringent

limits for these pollutants and a limit on total dissolved

solids for new sources. The 2015 Rule also set limits on

arsenic, mercury, selenium, and total dissolved solids in

gasification wastewater at existing and new facilities, with

more stringent limits at newer facilities. The rule also

required zero discharge of pollutants in fly ash transport

water, BATW, and FGMC wastewater for existing and new

sources. For CRL, the rule established limits for total

suspended solids (TSS) for existing facilities and for arsenic

and mercury at new facilities.

The 2015 Rule maintained requirements from the 1982

regulations (which were focused on settling out particulates

rather than treating dissolved pollutants) for TSS and oil

and grease. Additionally, EPA established limitations for

legacy wastewater equal to the 1982 limitations on TSS for

several wastestreams. EPA defined legacy wastewater to

mean FGD wastewater, fly ash transport water, bottom ash

transport water, FGMC wastewater, or gasification

wastewater generated prior to a date specified by the

permitting authority (to be set between November 2018 and

December 2023).

Revisions to the 2015 Rule

The 2015 Rule faced legal challenges and EPA received

two petitions for administrative reconsideration, which

raised “wide-ranging and sweeping objections to the rule”

In May 2024, EPA published a final rule to “strengthen” the

wastewater discharge standards that apply to coal-fired and

other steam-electric power plants. EPA explained that better

performing treatment technologies continued to develop

following the issuance of the 2020 Rule, and there was

more information about their performance. The 2024 Rule

established more stringent standards for three wastestreams

generated at existing facilities: FGD wastewater, BATW,

and CRL. These standards include a zero-limitation for

pollutants in FGD wastewater, BATW, and CRL. The 2024

Rule also established numeric discharge limitations for

mercury and arsenic for unmanaged CRL (i.e., certain

discharges through groundwater) and for discharges of

legacy wastewater from certain surface impoundments.

The 2024 Rule also eliminated less stringent requirements

for two subcategories of facilities (high flow facilities and

low utilization energy generating units) that were contained

in the 2020 Rule. The 2024 Rule also included certain

implementation flexibilities. For example, facilities that

permanently cease coal combustion by 2034 (whether

through closing or switching to fuels that generate fewer

pollutants) may continue to fall under the requirements in

the 2015 and 2020 rules, rather than the more stringent

2024 Rule requirements.

Reconsideration of the 2024 Rule

On March 12, 2025, EPA announced its plans to reconsider

the 2024 Rule, as part of the second Trump

Administration’s announcement of deregulatory actions to

“power the great American comeback.”

Stakeholder and Congressional Interest

Some stakeholder groups and Members of Congress

supported the 2024 Rule, pointing to EPA’s analysis that it

will reduce hundreds of millions of pounds of pollutants

from entering waterways each year. Others opposed the

rule, arguing that the new regulations are unachievable for

many facilities and will force their premature retirement.

The March 2025 announcement to reconsider the 2024 Rule

similarly prompted both congressional and stakeholder

support and opposition.

Laura Gatz, Specialist in Environmental Policy

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Effluent Limitation Guidelines (ELGs) for Steam Electric Power Plants

IF12705

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