An amendment to add language for apportionment of damages among liable parties, that the court may consider, among other factors, a) the amount of the hazardous substance, b) the degree of toxicity, c) the degree of involvement by the parties in the generation transportation, treatment, storage, or disposal of the substance, and d) the degree of cooperation by the parties with Federal, State, or local officials to prevent any harm to the public health or the environment.