Clean Water Act jurisdiction for Little Sycamore Wash, Arizona: Hydrologic connectivity and changing federal regulatory interpretation in the arid western U.S.

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Infrequent streamflow in arid landscapes presents challenges for determining Clean Water Act (CWA) jurisdiction. Because of such uncertainty, Freeport McMoRan (Freeport) – the second-largest copper producer worldwide – requested an assessment of possible federal jurisdiction for Little Sycamore Wash, a headwater tributary, in Arizona. CWA jurisdiction depends on the definition of “Waters of the United States” (WOTUS), which has been widely interpreted and continuously litigated nationwide. Mining activities impacting the wash would be federally regulated only if it is a WOTUS (referred to here as jurisdictional water) or there is evidence of hydrologic connectivity to a jurisdictional water.

Over the past 40 years, courts and agency interpretation and guidance have shaped the definition of WOTUS, making the scope of jurisdiction broader and narrower as practice changed. Currently there are three definitions of jurisdictional waters that are relevant: 1) pre-2015 practice, shaped primarily by guidances issued by EPA and USACE following Supreme Court cases in the 2000s, 2) the 2015 Obama administration Clean Water Rule (2015 CWR), which broadened the scope of jurisdiction in some cases and aimed to clarify questions of jurisdiction, and 3) the 2019 Trump administration proposed rule (2019 proposed rule), which takes a narrower view of jurisdiction. Due to a complex legal landscape, some parts of the U.S. are subject to pre-2015 practice and some are subject to the 2015 CWR. The 2019 proposed rule is being developed into a final rule as of April 2019, and therefore will also become relevant. Because of these complexities, the jurisdictional status of Little Sycamore Wash depends on which definition is in place.

Furthermore, the way jurisdictional waters are defined in arid landscapes can be problematic, as regulation and practice were generally developed based on humid landscape characteristics and associated assumptions. Physical indicators of channel form, such as Ordinary High Water Mark (OHWM), are not necessarily representative of the same flow regimes in humid and arid landscapes. Because of these difficulties, we use physical flow connectivity to determine possible jurisdiction.

A standard, simplified flow routing model (HEC-HMS) is used to quantify the probability of continuous hydrologic connectivity along the arid stream river network to the closest Traditionally Navigable Water (Santa Maria River to outlet at Alamo Lake by proxy). Modeling results indicate that there is a low level of hydrologic connectivity via stream flow during storm events. When three of the major headwater sub-basins of the Santa Maria experience simultaneous 10-year frequency storms, the river does not discharge to its outlet under realistic field conditions. Based on these results, we estimate that it is unlikely that there is continuous hydrologic connectivity more than once a decade to downstream jurisdictional waters. Based on this lack of connectivity, the wash is unlikely to be considered jurisdictional under past, present, or anticipated future definitions of WOTUS.

The study area is unlikely to be deemed jurisdictional by any version of the rule analyzed or proposed. In order to be jurisdictional Little Sycamore Wash would have to meet these qualifications:

  1. Pre-2015 practice: Ephemeral streams are jurisdictional depending on a significant nexus test, which consists of case-by-case determination of whether flow function significantly affects chemical, physical, and biological integrity of the TNW (this is current Arizona practice as of April 2019).

  2. 2015 CWR: If flow of the wash contributes flow directly or indirectly to a TNW and the wash is indicated by physical markers of bed, bank, and OHWM.

  3. 2019 proposed rule: If the wash is flowing during the wet time of year or flowing continuously during a typical year.

Arizona is in the process of developing a state program to assume administration of the 404 program. They are in the middle of a stakeholder engagement process. They formed technical working groups on a variety of topics, including Jurisdictional Determinations and the Permits Process. The working groups have written white papers focusing on their technical area with an analysis of the current state, ideal future state, and gaps between the two. Arizona state law requires that the program, if assumed by the state, be no more stringent than the federal program; federal law requires regulation to be no less stringent in states than in the federal government. This would leave Arizona’s 404 program exactly the same as federal environmental regulation, and the only aspect that may change for the regulated community is the party to which applications are submitted. Therefore, regardless of whether and how specifically Arizona decides to assume the program, the jurisdictional status of Little Sycamore Wash is unlikely to change.

Although it is not likely that Little Sycamore Wash is a jurisdictional water, Freeport would benefit by investing in additional monitoring gauges to obtain a more accurate depiction of physical hydrologic connectivity in the Santa Maria watershed. This would allow Freeport to make the strongest possible case for whether the wash should be considered jurisdictional and avoid regulatory uncertainty. Freeport should also monitor the Arizona 404 assumption process to stay abreast of any developments that may impact their operations in this uncertain regulatory and political climate.





Landes, Laura, Christopher Meyer, Laurie Muzzy and Sara Yeh (2019). Clean Water Act jurisdiction for Little Sycamore Wash, Arizona: Hydrologic connectivity and changing federal regulatory interpretation in the arid western U.S. Master's project, Duke University. Retrieved from

Dukes student scholarship is made available to the public using a Creative Commons Attribution / Non-commercial / No derivative (CC-BY-NC-ND) license.