There shall be exempt from the levy of the taxing unit that is the party to an agreement entered into under ORS § 311.860 for each tax year indicated in the agreement, the percentage amount of real market value, allocable to or within the taxing unit, of the facility specified in the agreement for that tax year. The assessor shall modify the amount of the exemption or terminate the exemption at such time as the assessor determines that the monetary value of the exemption has equaled the amount of moneys paid by the facility under the agreement plus interest. [1975 c.563 § 4; 1991 c.459 § 263]