How does this look in practice? You need the water to transfer the heat, so in response to a disaster that has already poisoned the water table you need to extract the water, put it somewhere, and backfill with concrete, all while you've already poisoned miles of water table and fighting from spreading further and damning all workers involved? For what gain?
How exactly will it poison the water table? A mile is in bedrock much deeper than the water table and any radioactive material will stay at the bottom because it is heavy.