Since 2009, the Environmental Protection Agency (EPA) has proposed, promulgated, and is developing a number of regulations affecting the operation of the nation's steam electric power plants. Given the central role of electric power in the nation's economy, concerns have been raised about the cost and potential impact of many of these regulations. Industry and environmental advocacy groups have been keenly interested in both the substance of these rules and schedules for their implementation. A particular issue has been whether the regulations, especially the cumulative impact of implementing multiple rules, will lead to retirement of a significant number of electric generating units, with negative effects on the reliability of the nation's power supply. All together, these rules have been characterized by critics as a regulatory "train wreck" that would impose excessive costs and lead to plant retirements that could threaten the adequacy of electricity capacity across the country. EPA and many other analysts maintain that this will not be the case. Much of the criticism addressed to EPA's actions has concerned Clean Air Act rules, but Clean Water Act (CWA) rules also have been part of the discussion, such as a 2014 rule to regulate cooling water intake structures at power plants and some industrial sources. The most recent major rule affecting power plants that EPA has promulgated concerns limits on discharges of wastewater, and it is the subject of this report. It is the last of a suite of Obama Administration utility sector rules that also includes greenhouse gas standards for utilities and a rule for disposal of coal combustion residuals from power plants. The CWA power plant rule is a complex regulation, involving limits on six pollutant wastestreams. Finalized in November 2015, it updates standards that were issued more than 30 years ago, which did not reflect today's power plant technology. The 1972 CWA established a comprehensive program to "restore and maintain the chemical, physical and biological integrity of the Nation's waters." To implement the act, EPA was directed to issue effluent limitation guidelines and standards, or technology-based regulations, for industrial dischargers. The effluent limitation guidelines (ELG) are to reflect pollutant reductions that can be achieved by categories or subcategories of industrial point sources using technologies that represent appropriate levels of control. Since 1972, EPA has promulgated effluent limitation guidelines for 57 industrial categories, including for the steam electric power industry. For point sources that introduce pollutants directly into U.S. waters (termed direct dischargers), limits on specific pollutants set in effluent guidelines are implemented through National Pollutant Discharge Elimination System (NPDES) permits that are issued by EPA or states. For sources that discharge to publicly owned treatment works, or POTWs (termed indirect dischargers), EPA promulgates pretreatment standards that apply to those sources and are enforced by POTWs, and state and federal authorities. The guidelines and standards apply to direct and indirect discharges of conventional pollutants; toxic pollutants, including toxic metals and toxic organic pollutants; and non-conventional pollutants, which are all other pollutants that are not categorized as conventional or toxic (e.g., ammonia-N, phosphorus, and total dissolved solids). The CWA established several different kinds of effluent limitations, four for new and existing direct dischargers and two for new and existing indirect dischargers. Effluent limitations are based on performance of specific technologies, but regulations do not require use of a specific control technology. In establishing effluent limitations, EPA considers the cost and/or economic achievability of the controls. The economic test differs based on the level of control specified in the ELG. Best Practicable Control Technology Currently Available (BPT)—BPT limitations generally are based on the average of the best existing performance of plants within the industry or subcategory. In specifying BPT, EPA considers the total cost of applying the control technology in relation to the effluent reduction benefits, as well as the age of the equipment and facilities, processes employed, and other factors. BPT limitations can cover conventional, toxic, and non-conventional pollutant discharges. Best Available Technology Economically Achievable (BAT)—BAT limitations generally represent the best existing performance in the industrial category or subcategory. BAT is the principal national means of controlling toxic and nonconventional pollutant discharges. Factors considered in assessing BAT include the cost of achieving BAT effluent reductions, processes employed, and other factors. The EPA Administrator has considerable discretion in assigning the weight accorded to these factors. BAT limitations may be based on effluent reductions attainable through changes in a facility's processes and operations. Best Conventional Pollutant Control Technology (BCT)—BCT is not an additional limitation, but it replaces BAT for the control of conventional pollutant discharges from existing industrial sources. The statute specifies factors to be assessed in determining BCT, including a two-part "cost reasonableness" test. New Source Performance Standards (NSPS)—NSPS are based on the best available demonstrated control technology (BADCT) and represent the most stringent control attainable through the application of technology. New plants have the opportunity to install the best and most efficient production processes and wastewater treatment technologies. EPA is directed to take into consideration the cost of achieving the effluent reduction and any non-water quality environmental impacts and energy requirements. Pretreatment Standards for Existing Sources (PSES)—PSES are designed to control the discharge of pollutants that pass through, interfere with, or are otherwise incompatible with the operation of a POTW. PSES standards are analogous to BAT for direct dischargers. Pretreatment Standards for New Sources (PSNS)—Like PSES, PSNS are designed to control the discharge of pollutants that pass through, interfere with, or are otherwise incompatible with the operation of a POTW. EPA considers the same factors in promulgating PSNS that it does in promulgating NSPS. The requirements of the statute embody the concept that, over time, industrial sources will achieve greater pollutant removal by employing progressively more stringent technologies. Thus, the 1972 law required sources to achieve effluent limitations based on BPT by July 1, 1977, and effluent limitations based on BAT by July 1, 1983 (in 1987 Congress modified the BAT compliance date to March 31, 1989). New sources are expected to comply with applicable effluent limitations when they commence operation. Requirements of ELGs apply to direct discharges through incorporation into NPDES permits issued by EPA or authorized states under CWA Section 402 and to indirect discharges through local pretreatment programs under CWA Section 307. EPA initially promulgated effluent limitation guidelines for the steam electric industry in 1974 and issued revised standards in 1982. The 1982 rules apply to about 1,100 nuclear- and fossil-fueled steam electric power plants nationwide, 495 of which are coal-fired. Under CWA Section 301(d), EPA has a duty to review existing effluent limitation guidelines at least every five years and, if appropriate, revise them. EPA had been studying the ELG for the steam electric power generating category since the mid-1990s and on several occasions indicated that a preliminary study of discharges from this category was necessary. During the 2005 review of the existing effluent guidelines for all categories, EPA identified the rules governing the steam electric power point source category for possible revision, based in part on data showing that the industry ranked high in discharges of toxic and nonconventional pollutants. Power plant discharges account for about 30% of all toxic pollutants discharged into U.S. surface waters by all industrial categories that are regulated under the CWA. Broadly speaking, two factors have altered existing wastestreams or created new wastestreams at many power plants since promulgation of the 1982 power plant ELG. The first is the development of new technologies for generating electric power, such as coal gasification. The second, a result of federal and state requirements, is the widespread implementation of air pollution controls to reduce emissions of hazardous air pollutants and acid gases (e.g., flue gas desulfurization [FGD], selective catalytic reduction [SCR], and flue gas mercury controls [FGMC]). In particular, the use of wet FGD systems (the kind that generate liquid discharges) to control sulfur dioxide air emissions has increased significantly since 1982. Consequently, each year the pollutant discharges from this industry are increasing in volume, with additional chemical constituents. They account for 50%-60% of all toxic pollutants discharged into surface waters by all industrial categories currently regulated under the CWA, according to EPA. The main pollutants of concern for these discharges include metals (mercury, arsenic, selenium), nitrogen, and total dissolved solids (TDS). EPA initiated a study, completed in 2009, which found that the 1982 regulations did not adequately address the pollutants being discharged and have not kept pace with changes that have occurred in the electric power industry over the last three-plus decades, specifically the increase of FGD systems, or scrubbers, at coal-fired power plants to control air pollution. According to EPA, as of 2008, 30% of coal-fired power plants were using FGD systems to control sulfur dioxide emissions from the flue gas generated in the plants' boilers and prevent buildup of certain corrosive constituents such as chlorides, and by 2025, nearly 80% of coal-fired generating capacity is expected to employ FGD systems. While scrubbers dramatically reduce emissions of harmful pollutants into the air, some create a significant liquid waste stream (especially wet scrubbers). In addition, discharges from coal combustion residual (CCR) surface impoundments at steam electric power plants have a potential to degrade water quality. EPA believes that many current CWA permits for power plants do not fully address potential water quality impacts of these discharges through appropriate pollutant limits and monitoring and reporting requirements. In addition, EPA identified several wastestreams that are relatively new to the industry (e.g., carbon capture wastewater) and others for which there is little characterization data (e.g., gasification wastewater).