It turned out the returns were, indeed, radioactive, and the gas produced by the initial efforts was too 'hot' to market.
While a "rubble filled glass chimney" would be extensively fractured, in and of itself, and likely as producible as a clean breccia (little to no matrix material, just angular fragments) there is a question of how extensive the reservoir would be outside the blast zone, and how much producible reserve would be present, even if the product wasn't too radioactive to market.
IIRC, this was up on the Book Cliffs near Rifle, Colorado. I recall seeing a low level disposal site on the edge of the Colorado River near Rifle, fenced off with the usual warnings.
One thing about experiments, though, sometimes they tell you what won't work.
This was one of those, like so many of the attempts to use nuclear devices for civil engineering, and like the others, a fine example of what not to do.