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Mike Eng
Senior Project Manager/
Natural Resources Specialist


Waters of the United States
Definition Rule Finalized

Controversial “Significant Nexus”
Language Clarified
The U.S. Environmental Protection Agency (EPA) and U.S. Army Corps of Engineers recently finalized the Clean Water Rule in 40 CFR 230.3, clarifying the protection of navigable waters and their tributaries. The new Rule more clearly defines the controversial “significant nexus” language from the 2006 U.S. Supreme Court decision, Rapanos v. United States, that applies to geographically isolated waterbodies. The main effect of this new Rule is that the lengthy, site-specific analysis previously needed to determine jurisdiction of these semi-isolated waterbodies should be reduced dramatically, because evaluation criteria are specified. Given the outpouring of comments during the drafting process, EPA shaped the final Rule to safeguard natural waterways and not constructed water conveyance features. The Rule should expedite delineation decisions and give more practical flexibility to regulators when considering built waterways, including agricultural ditches and municipal water systems. Some highlights of the rule include:
  • Tributaries to traditionally navigable waters (TNW): The Rule defines tributaries for the first time as those water features that have a defined bed, banks, ordinary high water mark (OHWM), and downstream flow. This excludes wetlands and open waters without beds, banks, and high water marks; those may still be evaluated on a case-by-case basis.
  • Adjacent waters/wetlands: Defines the distance of waters adjacent to jurisdictional waters by describing “neighboring” waters that are considered “adjacent” and, therefore, jurisdictional water features. They include features located: within 100 feet of the OHWM of a jurisdictional water; in whole or part in the 100-year floodplain (“floodplain waters”) and within 1,500 feet of the OHWM of a jurisdictional water; and in whole or part within 1,500 feet of the high tide line of a TNW or territorial sea, including within 1,500 feet of the OHWM of one of the Great Lakes.
  • Isolated waters or “other” waters: Describes when distinct types of waters have a significant nexus: prairie potholes, Carolina and Delmarva bays, pocosins, Texas coastal prairie wetlands, and specific to us in California, western vernal pools. This includes waters with a significant nexus to waters of the U.S. within the 100-year floodplain of a TNW, interstate water, or the territorial sea, as well as waters with a significant nexus within 4,000 feet of jurisdictional waters.
  • Exclusions: Expands the exclusion for ditches, constructed components of Municipal Separate Storm Sewer Systems (MS4s), and water delivery/reuse and erosional features, and retains exclusions for waste treatment systems and prior converted cropland.
The new Rule is based on the previous report, Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence, input from hundreds of stakeholder meetings across the country, and over one million public comments. The Rule is important for the critically needed, ongoing protection of America’s streams, wetlands, and downstream waterbodies.

If you have questions, please feel free to contact Ascent Senior Project Manager and Natural Resources Specialist, Mike Eng, at 916.627.6413

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