[maple_leaf_eh]

One fellow told me how he recovered a scaley gas tank by throwing in a handful of sharp edged steel pieces and some chain links. Then he rolled and shook the tank until he was happy the crud had been broken free.

If your gelled fuel has an edge, what about attacking it with a pressure washer? Find the edge and it might come off it slabs. I think you are right about the toxicity. Try to keep the particles from washing into the surface creeks. The good people in Montreal will thank you for not polluting their water supply - much more.