Exploring the Hidden World of Layered Aquifers Along the Potomac River

[Loren Booda]

I have heard that the Potomac river has a subterranean twin. Is this common for such large volume, fresh water aquifers to exist virtually unnoticed? Can a stream above run perpendicular to another below?

 

[billiards]

What? I thought this was going to be about layered aquifers, but I don't see anything about layers here - wait - are you referring to the river as a separate layer?

Rivers can cut through an aquifer and there will invariably be some kind of interaction between the surface and ground waters; actually these relationships are very complex and I am not an expert so I will avoid the complexities. In simple terms the aquifer will either feed the river, or the river will feed the aquifer - this relationship will vary along the river (at the source you would imagine the aquifer to feed the river but at the sink you would expect the opposite) and this relationship will vary with time (you might expect a different relationship in the dry season than in the wet season).

Don't think of the ground water as flowing through some kind of underground river, it's a common misconception, only in very specific geology will this happen, like karstic geology where you can get cave systems developing and the water can flow through the caves. The groundwater flows through the pore spaces and fracture planes in the aquifer, the aquifer simply being a rock unit that yields water at economic rates, in other words just a layer of rock with water moving through it. It is quite possible, indeed it is quite likely, for the groundwater to be flowing perpendicular to the river, I've certainly come across case studies where this is what happens.

 

[Loren Booda]

billiards,

Now I know what an aquifer is fer, thanks to your introduction. Would you know what the deepest aquifer might be?

 

[billiards]

No, I don't really know. Having said that though, I do remember talk of the Colombia River Basalts as being not only a good example of an igneous aquifer, but also a place where some of the deepest living organisms have been found (that info might well be outdated/mistaken). So no conclusions to draw just yet, but perhaps worth following up?