Ohio Rev. Code § 3746.06: Contamination level below background level of hazardous substance or petroleum - ground water standards.

(A) If applicable standards otherwise established in this chapter and rules adopted under it establish a contamination level for a hazardous substance or petroleum that is below the background level of the hazardous substance or petroleum, the voluntary action conducted at a property is required to achieve only the background level of the hazardous substance or petroleum, notwithstanding the contamination level established in the applicable standard.

(B) If the ground water underlying a property complies with standards for residential use established in or pursuant to rules adopted under division (B)(1) or (2) of section 3746.04 of the Revised Code, the remedy or remedial activities undertaken in connection with a voluntary action to address sources of potential ground water contamination at or upon the property shall ensure the continued compliance of the ground water underlying the proeprty with those standards for residential use.