Spring 2022

To Be or Not to Be WOTUS: Tools for Making a Determination

By Kathleen A. Radloff, Ph.D., and Matthew J. Mayo, M.S., GISP, CPG, P.G.

A holistic scientific assessment factoring in national- and regional-scale information and field observations plays a critical role in WOTUS determinations.

Waterbodies that are classified as “Waters of the United States” (WOTUS) are subject to federal jurisdiction and, importantly, are regulated under the Clean Water Act (CWA). Determining whether a waterbody meets the “WOTUS” definition is a surprisingly complex question, and the answer depends on both the features of the waterbody as well as the frequently changing definition itself. The seemingly subtle recent variations in the WOTUS definition have far reaching influence on the development of properties, environmental clean ups, permitted discharges, and water rights disputes.

The definition of WOTUS was stable for almost 30 years until a series of court challenges, including several Supreme Court cases, led United States Environmental Protection Agency (US EPA) in 2015 to expand the definition and include additional waterbodies under federal jurisdiction. More challenges ensued and a narrower definition was adopted in 2020. In December 2021, US EPA proposed a revision that is more similar to the “pre-2015” definition, with updates based on the various court rulings. In addition, a recent legal decision (County of Maui v. Hawaii Wildlife Fund in 2020) further provides regulatory authority under the CWA over non-point discharges into jurisdictional waters, thereby potentially extending CWA authority to qualifying groundwater discharges. Over the course of 2022, US EPA and the United States Army Corps of Engineers will be hosting regional roundtables as they work to finalize the WOTUS definition.

The seemingly subtle recent variations in the WOTUS definition have far reaching influence on the development of properties, environmental clean ups, permitted discharges, and water rights disputes.”

Larger waterbodies – such as navigable rivers and streams – clearly fall into WOTUS; however, as the rule has been revised, gray areas have emerged for adjacent wetlands, irregularly flowing creeks, groundwater discharges, and constructed ditches. A strong, scientifically based argument about the jurisdictional status of a waterbody requires a holistic weight-of-evidence approach that draws upon regional and national datasets as well as site specific studies and field observations of the waterbody. This approach needs to capture how the waterbody changes over time and consider both historical and seasonal changes.

To illustrate some of the analyses that contribute to the weight-of-evidence, we can consider the case of a waterbody that flows into a jurisdictional waterbody on an ephemeral basis in a typical year, which would have not been designated a jurisdictional water under the 2020 definition. However, the proposed 2021 revision expands the “pre-2015” definition to include more ephemeral waters that have a significant effect on the integrity of a downstream jurisdictional water (proposed to be based on a biological, chemical or physical characteristic, while the “pre-2015” definition used an “and”). Therefore, a first step in assessing an ephemeral waterbody is to trace upgradient from a known jurisdictional water to the waterbody in question. If the connections are present on at least a seasonal basis, or in a manner that contributes to the jurisdictional waterbody’s integrity, then it is likely that the waterbody is indeed jurisdictional.

National datasets provide broad assessments of an area of interest and can help determine how a specific site and waterbody fit into the larger geographic context. Resources such as wetland inventories from United States Fish and Wildlife Service, soil surveys from United States Department of Agriculture, and the National Hydrography Dataset from United States Geological Survey can document large-scale patterns of runoff, drainage, and water flow through an area. This information can then be coupled with more refined regional datasets, such as tributaries identified by regional water management boards. These desktop analyses can identify jurisdictional waterbodies in and adjacent to the area of interest, and they can be used to evaluate how water is expected to move based on surface topography, soil type, and other features.

These observations then need to be further evaluated through site-specific assessments before a WOTUS determination can be made. For areas with significant land management activities, it is essential to review how important land features, including constructed drainage features, have evolved over time. Historical aerial imagery provides an overview of changes over time and can be used to create a timeline of both man-made and naturally occurring site changes. For constructed waterways, aerial imagery is essential for determining whether the waterway was constructed within or relocated a tributary.

Waterbodies to Evaluate Under the WOTUS Rule

Diagram of Various Types of Waterbodies Evaluated Under WOTUS Rule

Click to Enlarge Figure.

The site-specific assessment may also require field observations to validate water flow directions and connections, or a formal wetland survey. Field observations are representative of the season when they are conducted and multiple field visits may be required to capture seasonal and annual variations. If ephemeral waters are re-integrated to meet the WOTUS definition, then multi-season field observations will be essential going forward. One way to approximate changes over shorter time periods (months to years) is to utilize US EPA’s Antecedent Precipitation Tool (APT) to determine if observations are “typical” for a location – that is, falling within the range of a normal water year. Potential inconsistencies between the national-scale information, regional-scale information, and observations made in the field require careful evaluation.

The definition of WOTUS is anticipated to be in flux for at least the rest of 2022. However, it is clear that a robust technical analysis, as described above, will be relevant to the jurisdictional status of a waterbody regardless of the “final” definition.

Contact Info

The authors can be reached at mmayo@gradientcorp.com and kradloff@gradientcorp.com.