Sec. 20. (a) This chapter does not affect an action or a claim, including a claim for contribution, that a person who implements or completes an approved voluntary remediation work plan has or may have against a third party.
(b) A person who implements or completes an approved voluntary remediation work plan under this chapter is not liable for claims for contribution concerning matters addressed in:
(1) the work plan; or
(2) a certificate of completion issued to the person under section 16 of this chapter.