40 CFR §35.572

In addition to the definitions in § 35.502, the following definitions apply to the Clean Air Act's section 105 grant program: Nonrecurrent expenditures are those expenditures which are shown by the recipient to be of a nonrepetitive, unusual, or singular nature such as would not reasonably be expected to recur in the foreseeable future. Costs categorized as nonrecurrent must be approved in the grant agreement or an amendment thereto. Recurrent expenditures are those expenses associated with the activities of a continuing environmental program. All expenditures are considered recurrent unless justified by the applicant as nonrecurrent and approved as such in the grant award or an amendment thereto.