There are 2 different points here. One is who is responsible/liable ($$$ ) for the damage of which burden of proof plays a part. Second is envior. danger to water and clean up in which burden of proof is not applicable. From what you have said the CC must have decided that the spill is not a risk to surface or groundwater. Did they tell you that. If it were me I would sure like to know if it is still a danger to water. If you are concerned and any real $ are at risk you should talk to a natural resource lawyer. The normal way a matter like this is approached all the potentially responsible parties (PRP's) are notified and all are liable and they have to sort it out amongst themselves.