D.C. Mun. Regs. tit. 20, r. 20-2702
Sounds emanating from pre-existing sources shall, to the extent indicated, be exempt from the specific noise limitations contained in § 2701 of this chapter; Provided, that the exemption shall not preclude enforcement under any other section of Chapters 27 and 28 of this subtitle.
Pre-existing sources shall be exempt for one hundred and twenty (120) days after May 15, 1978.
Any owner or person in control of a pre-existing source that exceeds the maximum permissible sound levels as prescribed in § 2701 of this chapter shall, within one hundred and twenty (120) days after May 15, 1978, file with the Mayor a written plan for the Mayor's approval for the reduction of those sound levels to the maximum permissible levels.
Each plan submitted pursuant to § 2702.3 shall include a time schedule for the accomplishment of the reduction of noise levels, and shall provide for periodic increments of progress. The Mayor shall treat the plan as a request for a variance as provided in § 2706 of this chapter.
D.C. Mun. Regs. tit. 20, r. 20-2702