Last week, we started with the bottom line of the Administration’s new Waters of the US Rule – describing the waters that are now always jurisdictional by definition and those probably always jurisdictional in practice. Today, we start to leave clarity behind and examine the waters that may be jurisdictional. Or may not be. For you “waters of the US” cognoscenti, you know what that means – we’re discussing how the Administration has finalized the “significant nexus” test.

In a later post, we’ll address the policy implications of the Administration enshrining the “significant nexus” into law. But for now, we start by recalling that, under the significant nexus test, EPA and the Corps consider to be jurisdictional any water which – alone or in aggregation with other similarly situated waters in the region – has a significant nexus with a traditionally navigable water downstream. The proposed rule, though, left open a big question: the scope of the “aggregation” component of the test – just what are the “similarly situated” waters in the “region?” On Friday, we looked at the first half of the answer – the administration will aggregate five broad classes of waters (Prairie Potholes, Californian Vernal Pools and more).

The second half of the answer is that the Agencies will aggregate – throughout the watershed draining to the nearest “traditionally navigable water” (more on that in another post) – all “similarly situated” waters located within

• 4,000 feet of the high tide line or ordinary high water mark of any other jurisdictional water (including dry tributaries)

• the 100-year floodplain of a traditionally navigable or interstate water or territorial sea

This is obviously a broad area, geographically much larger than the five general classes of waters covered by the first half of the significant nexus rule. Unfortunately, it’s not possible to determine the extent of the waters covered by this part of the rule. That’s because, while the rule defines “similarly situated” waters, that definition provides little clarity – “waters are similarly situated when they function alike and are sufficiently close to function together in affecting downstream waters.”

How broad the Agencies will interpret this definition is open to question. While certain classes of wetlands function in slightly different ways, most function alike from the lay perspective – they provide habitat, flood storage, and are nutrient and chemical sinks for example. So, in theory, all wetlands may “function alike.” And as for their proximity – whether they are “sufficiently close to function together” – the Administration has already shown via the first half of the significant nexus test (containing the five general classes of waters) that it is capable of viewing all wetlands in a watershed as sufficiently close together.

So there is a definite possibility that the administration may view all waters within 4,000 feet of any tributary to be jurisdictional. That’s more than ¾ of a mile from the numerous small, dry tributaries that only flow when it rains or snow melts now considered jurisdictional under the rule. And that’s just the first bullet point above; the FEMA floodplain of an actually-wet waterbody can be much larger (for example, the current floodplain map for Fargo, ND, shows the FEMA 100-year floodplain extending four miles into downtown). Unfortunately, without additional agency guidance, either generally or on a case-by-case basis, there’s no way to know for sure if only some, or all of the waters in these broad regions will be considered jurisdictional.

And that’s not the only uncertainty remaining after the issuance of the final rule. Tomorrow, we’ll look at more.