As those of you who have read our prior blog posts know, one of the primary changes between the proposed and final rules redefining the scope of jurisdictional waters under the Clean Water Act is the more objective measurements contained in the final rule. The proposed rule defined adjacent (and therefore jurisdictional) waters as those within certain scientific boundaries – floodplains and riparian areas, for example, which were defined based on their ecological and hydrological relation to traditionally-navigable and other similar waters. The final rule eliminated the need for this scientific analysis, stating instead that adjacency would be based on distances – waters are automatically jurisdictional a minimum of 100 feet away and up to 1,500 feet away if measured from a high tide line or Great Lake or contained in a 100-year floodplain. Similarly, the significant nexus test applies to features up to 4,000 feet from such waters. This increased clarity makes it easier for the regulated community and regulators to identify jurisdictional and non-jurisdictional waters.

Today, EPA and the Corps removed a bit of this clarity.

In advance of tomorrow’s effective date of the rule, the agencies held a webinar and released a set of Qs and As expounding a bit on their interpretation of the rule. Much of the information they presented was expected or could have been discerned from a close reading of the preamble, but one Q and A stood out to me –

Q: Is distance thresholds measured as straight-line distances or do they account for vertical changes?

Distance thresholds should be measured perpendicular to the ordinary high water mark or high tide line, whichever is applicable, in straight-line distance extending landward. Such distance measurements do not account for vertical changes

This is significant if you’re measuring distances in a hilly or mountainous area, since in these regions there can be a fair amount of difference between perpendicular measurements and on-the ground distances. Placing a tape measure on the ground and walking off 4,000 feet can result in a much different ending point than looking at a map and using a scale to identify where 4,000 ends. This is because a map is two dimensional and the earth isn’t.

Thus, 4,000 feet on the ground in a mountainous area will cover much less than 4,000 perpendicular feet. EPA and the Corps confirmed that they will be using perpendicular measurements, not ground distances in applying the rule’s various distance threshold. So make sure that tomorrow you start using a map, not a tape measure, to identify the jurisdictional boundaries under the rule.