(a) When the plaintiff in any such action has made a prima facie showing that the conduct of the defendant, acting alone, or in combination with others, has, or is reasonably likely unreasonably to pollute, impair or destroy the public trust in the air, water or other natural resources of the state, the defendant may rebut the prima facie showing by the submission of evidence to the contrary. The defendant may also prove, by way of an affirmative defense, that, considering all relevant surrounding circumstances and factors, there is no feasible and prudent alternative to the defendant’s conduct and that such conduct is consistent with the reasonable requirements of the public health, safety and welfare. Except as to the aforesaid affirmative defense, nothing in this section shall be construed to affect the principles of burden of proof and weight of the evidence generally applicable in civil actions.

(b) The court before which such action is brought may appoint a master or referee, who shall be a disinterested person and technically qualified, to take testimony and make a report to the court in the action. The costs of such appointment may be apportioned to the parties if the interests of justice require.