Are you concerned about contaminating the groundwater?
I can assure you that landfill leachate contains much worse than a bit of Euthanyl. Modern landfills are designed to contain and control contaminants. To make things clear, there is very little chance that Euthanyl will contaminate groundwater supplies if animals are deposited in a landfill.
Dr. Twidale is correct that burying stock on farms in a simple trench may lead to groundwater contamination, and I would never advocate that the SPCA bury its disposed animals in such a way, but burying in the back forty is not equivalent to disposal in a proper landfill.
Joann U. Bessler
Hydrogeologist
M.Sc. Environmental Sciences