D.C. Code § 34-1115
Every public utility shall carry a proper and adequate depreciation account. The Commission shall ascertain and determine what are the proper and adequate rates of depreciation of the several classes of property of each public utility. These rates shall be such as will provide the amounts required over and above the expense of maintenance to keep such property in a state of efficiency corresponding to the progress of the industry. Each public utility shall conform its depreciation accounts to such rates so ascertained and determined by the Commission. The Commission may make changes in such rates of depreciation from time to time as it may find to be necessary. The Commission shall also prescribe rules, regulations, and forms of accounts regarding such depreciation which the public utility is required to carry into effect. The Commission shall provide for such depreciation in fixing the rates, tolls, and charges to be paid by the public. All moneys in this fund may be expended in keeping the property of such public utility in repair and good and serviceable condition for the use to which it is devoted, or invested, and, if invested, the income from the investments shall also be carried in the depreciation fund. This fund and the proceeds thereof shall be used for no other purpose than as provided in this section, unless with the consent and by order of the Commission.
D.C. Code § 34-1115
Public Service Commission, creation, powers and duties, see § 34-802. .