Made For TV Sci Fi Late 70’s into the 80’s Leaking Poison

This was definitely a made for TV type of movie, almost certainly run by either ABC, CBS or NBC. The movie involves a leaking concrete tank. The stuff leaking from the tank is dark or black, and I recall it oozing along the ground and possibly finding a water source. It is not the movie with a meteor and not Impluse (1984). I seem to recall the storage tank was on higher ground, so the leakage was slowly running down grade. If I remember correctly, the storage tank was a secret, nobody knew about it.