Recent decades have seen increased national attention to the presence of “emerging
contaminants” or “contaminants of emerging concern” (CECs) in surface water and groundwater.
Although there is no federal statutory or regulatory definition of CECs, generally, the term refers
to unregulated substances detected in the environment that may present a risk to human health,
aquatic life, or the environment and for which the scientific understanding of potential risks is
evolving. CECs can include many different types of manufactured chemicals and substances—
such as those in pharmaceuticals, industrial chemicals, agricultural products, and microplastics—as well as naturally occurring substances, such as algal toxins. Data on CECs that would help determine their risk to humans and aquatic life or other aspects of the environment are often limited. Increased monitoring and detections of one particular group of chemicals, per- and polyfluoroalkyl substances (PFAS), has recently heightened public and congressional interest in these CECs and has also prompted a broader discussion about how CECs are identified, detected, and regulated and whether additional actions should be taken to protect human health and the environment. While several statutes provide authorities to the U.S. Environmental Protection Agency (EPA) and states to address CECs, this report examines authorities available under the Clean Water Act (CWA)—which Congress established to restore and protect the quality of the nation’s surface waters.
EPA has several CWA authorities it may use to address CECs, although it faces some challenges in doing so. Under the CWA, a primary mechanism to control contaminants in surface waters is through permits. The statute prohibits the discharge of pollutants from any point source (i.e., a discrete conveyance) to waters of the United States without a permit. The CWA authorizes EPA and states to limit or prohibit discharges of pollutants in the National Pollutant Discharge Elimination System (NPDES) permits they issue. These permits incorporate technology-based and water-quality-based requirements.
The CWA authorizes EPA and states to address CECs through technology-based effluent limitations using national Effluent Limitation Guidelines and Standards (ELGs) or by setting technology-based effluent limits in NPDES permits on a case-by- case basis. The CWA requires EPA to publish ELGs, which are the required minimum standards for industrial wastewater discharges. The CWA also requires EPA to annually review all existing ELGs and to publish a biennial plan that includes a schedule for review and revision of promulgated ELGs, identifies categories of sources discharging toxic or nonconventional pollutants that do not have ELGs, and establishes a schedule for promulgating ELGs for any newly identified categories. In cases where EPA has not established an ELG for a particular industrial category or type of facility, or where pollutants or processes were not considered when an ELG was developed, the permitting authority (EPA or states) may still impose technology-based effluent limits on a case-by-case basis. Although EPA and states have these authorities available to address CECs, there are some challenges to doing so, including a lack of data available to support new ELGs or updates to existing ELGs. Agency officials stated that it is difficult for the agency to keep pace with the growth of new chemicals in commerce.
The CWA also authorizes EPA and states to address CECs through water-quality-based requirements. States are required to adopt water quality standards for waters of the United States and review them at least once every three years. The CWArequires EPA to publish, and “from time to time thereafter revise” water quality criteria that reflect the latest scientificknowledge. States use EPA’s criteria as guidance in developing their water quality standards. The CWA directs states to adopt criteria to protect their water bodies’ designated uses and to also adopt criteria for all pollutants on the Toxic Pollutant List, for which EPA has published criteria. Once a state adopts water quality criteria for a contaminant as part of its water quality standards, several CWA tools are available to the state for achieving them. The primary tool is to establish water- quality-based effluent limitations in NPDES permits. Although EPA and states have authority to address CECs through water-quality-based requirements, they often lack data needed to support development of criteria or water-quality-based effluent limitations.
The CWA also authorizes EPA to designate contaminants as toxic pollutants or as hazardous substances, which may trigger other actions under the CWA and the Comprehensive Environmental Response, Compensation, and Liability Act.
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