D.C. Code § 44-608

If a nonprofit entity is a party to a conversion approved pursuant to § 44-603, the District shall make an assessment, to recover part of the charitable assets, equal to 10% of the amount of the real property tax the healthcare entity would have paid during the past 5 years had it not been exempt from federal income taxation under sections 501(c) or (e) of the Internal Revenue Code. Such amount shall be paid in three equal installments.