It isn't really minimal since the water cycle on earth is all connected.
Water in the ocean evaporates. It's carries inland by Hadley cells that deposit the moisture inland. It gets dumped on the highest points which all run back the ocean and creating all our aquifers along the way. Those aquifers feed our great lakes and wells.
But you're suggesting we bury toxic material that remains toxic for hundreds or thousands of years somewhere remote that would just be high up in that water cycle. In places where private companies would be out of the eyes of watchdog groups