D.C. Mun. Regs. tit. 20, r. 20-6003
Each owner or operator of a petroleum UST system shall provide release detection for tanks in accordance with the provisions of this section.
The owner or operator of a petroleum UST system shall conduct release detection in accordance with the requirements for the release detection method set forth in §§ 6005 through 6012 of this chapter.
At least once every thirty (30) days, each petroleum UST shall be monitored for a release using one of the methods listed in §§ 6008 through 6012, except as provided in § 6003.4.
An owner or operator of a heating oil tank with a capacity of one thousand one hundred (1,100) gallons or more may use one of the following methods of release detection as the sole method of release detection:
The owner or operator of a petroleum UST that is not a heating oil tank, with a capacity of five hundred fifty (550) gallons or less, may use manual tank gauging in accordance with § 6006 as the sole method of release detection.
The owner or operator of a petroleum UST, other than a heating oil tank or petroleum UST with a capacity of five hundred fifty (550) gallons or less, installed or replaced after February 8, 2007, shall check for evidence of a release at least once every thirty (30) days using interstitial monitoring.
The owner or operator shall test the secondary containment system every three (3) years to ensure that the interstitial area is liquid-tight or use continuous monitoring methods.
D.C. Mun. Regs. tit. 20, r. 20-6003