D.C. Mun. Regs. tit. 20, r. 20-6006
A release detection method that uses manual tank gauging shall meet the requirements of this section.
An owner or operator may use manual tank gauging as the sole method of release detection only for a petroleum UST that is not a heating oil tank with a capacity of five hundred fifty (550) gallons or less.
Manual tank gauging shall be conducted weekly.
An owner or operator using manual tank gauging shall measure the liquid level in the tank at the beginning and end of a period of at least thirty-six (36) hours, during which no liquid is added to or removed from the tank. Each measurement shall be based on an average of two (2) consecutive stick readings. The measurements shall be recorded and maintained in accordance with § 5602.
The equipment used for manual tank gauging shall be capable of measuring the level of product over the full range of the height of the tank to the nearest one eighth (1/8) of an inch.
If the difference between the measurements at the beginning and end of a single weekly test exceeds ten (10) gallons, or if the average difference between the measurements at the beginning and end of four (4) consecutive weekly tests exceeds five (5) gallons, the owner or operator shall follow the requirements of Chapter 62 for a suspected release.
D.C. Mun. Regs. tit. 20, r. 20-6006