23 C.F.R. § 635.123

(a) The State DOT shall have procedures in effect which will provide adequate assurance that the quantities of completed work are determined accurately and on a uniform basis throughout the State. All such determinations and all related source documents upon which payment is based shall be made a matter of record.

(b) Initial source documents pertaining to the determination of pay quantities are among those records and documents which must be retained pursuant to 2 CFR 200.333.