https://crsreports.congress.gov
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.
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
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
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
