What you do not know can, and probably will, cost you money
You have discovered that certain operations conducted (either by others or by yourself and others) on property you own have resulted in a release of hazardous substances requiring clean up. The other potentially responsible parties (PRPs) will require extensive investigation to confirm their involvement and the response to the release (in this case, remediation) will be extensive, expensive and take several years. The decisions you make next are critical. It is essential to gather the right information to ensure sound fiscal and operational decisions.