I think you have to dig quite deep ('scuse the pun) to find more about this project, although I have seen photos of the various outfalls both then & now.
The construction company were from Germany, but don't have any further information on that score. Ironically, the need for more water to feed the heavy industry on Teeside (the original purpose of this amazing feat of engineering) lessened as time went on - which now leaves the aqueduct more or less redundant. Perhaps someone will start doing underground guided bike tours from Keilder reservoir to Eggleston - should be a smooth ride as the tunnel is concrete lined all the way.
I think there was a clear policy not to complicate things by going after any minerals, hence no mining activity. But nowadays, who knows?
David