Yes, its swimming with ocherous water.
The inflow to the culvert can only be located by prodding, the outflow is over to the left looking up from the road in a sort of gulley amongst the trees.
Moving on from this, there are a lot of unanswered questions about this mine, and indeed Hafan. Both have only a brief mention in O T Jones.
The Henfwlch Adit cuts what he calls the "Hafan Shaft", this is the one on the underlie where you crawl through the boulders underground.
So how deep was it sunk? Did the two mines connect?
David Bick says not but the water in the inner reaches of Henfwlch definately drains by the Hafan Deep Adit.
I used to agree with David but now I wonder.
My avatar is a poor likeness.