D.C. Code § 8-634.05

If the Mayor selects a response action pursuant to § 8-634.01 that results in any hazardous substances remaining at the site, the Mayor shall review the response action no less often than each 5 years after the initiation of the response action to assure that human health and the environment are being protected by the response action being implemented. If, after the review, it is the judgment of the Mayor that action is appropriate at the site in accordance with § 8-634.01, the Mayor shall take or require the action.