(a) Apportionment of costs for the elimination of the release or threatened release of solid waste among the persons responsible for solid waste under Section 361.271 shall be made according to:
(1) the relationship between the parties' actions in storing, processing, and disposing of solid waste and the remedy required to eliminate the release or threatened release;
(2) the volume of solid waste each party is responsible for at the solid waste facility or site to the extent that the costs of the remedy are based on the volume of solid waste present;
(3) consideration of toxicity or other waste characteristics if those characteristics affect the cost to eliminate the release or threatened release; and
(4) a party's cooperation with state agencies, its cooperation or noncooperation with the pending efforts to eliminate the release or threatened release, or a party's actions concerning storing, processing, or disposing of solid waste, as well as the degree of care that the party exercised.
(b) In apportioning costs under Subsection (a), the court shall credit against a responsible party's share of the costs of eliminating a release or threatened release of solid waste the party's expenditures related to the cleanup at issue if the commission or the executive director approves the cleanup. If the expenditures were made before the property was proposed to be listed on the state registry and the commission or the executive director approves the cleanup, the court shall also reduce in an equitable and just manner the party's proportionate share of the costs.
(c) The apportionment of costs only adjusts the rights of parties identified by Section 361.271 and does not affect a person's liability to the state.