(a) Disposal units must be closed to achieve the long-term stability of the disposal unit and to minimize, the need for ongoing active maintenance of the disposal unit following closure so that only surveillance, monitoring, or minor custodial care are required.

(b) The permittee must obtain a modification to the permit in accordance with section 383-3.12 of this Part before commencing disposal unit closure. Disposal unit closure must be performed in accordance with the modification to the permit and the closure plan approved by the department in accordance with Subpart 383-3 and, if applicable, Subpart 383-4 of this Part.

(c) Unless otherwise authorized by the department, the permittee must complete closure of each disposal unit within one year after the final volume of waste is emplaced in the disposal unit.

(d) The measures to be undertaken for disposal unit closure must be compatible with the provisions for site closure and stabilization and the facility's design goals for recovery or retrieval of waste, if applicable.

(e) All design and construction activities necessary for disposal unit closure must comply with the applicable requirements of Subpart 383-7 of this Part.

(f) The permittee must install inadvertent intruder barriers, if required by sections 382.33(a) and 382.34 of this Title, as part of disposal unit closure.

(g) The closure of any disposal unit which contains mixed waste must also comply with the requirements of Part 373 of this Title.

(h) Closure of belowground disposal units must include installation of the multilayer earthen cover required by section 383-7.6 of this Part and the markers required by section 383-11.3 of this Part.

(i) Disposal unit closure in an underground mined repository must include provisions for disposal unit monitoring as required by section 383-10.5 of this Part.

(j) Within 180 days of completion of closure activities for any disposal unit, the permittee must submit to the department documentation, including as-built drawings, that disposal unit closure has been performed in conformance with the closure plan. The certification must be signed by the permittee and signed and stamped by a licensed professional engineer. After reviewing the certification and inspecting the closed disposal unit, the department may direct the permittee to correct any errors or deficiencies found.