40 CFR § 1036.735 - Recordkeeping.
(a) You must organize and maintain your records as described in this section. We may review your records at any time.
(b) Keep the records required by this section for at least eight years after the due date for the end-of-year report. You may not use emission credits for any engines if you do not keep all the records required under this section. You must therefore keep these records to continue to bank valid credits. Store these records in any format and on any media, as long as you can promptly send us organized, written records in English if we ask for them. You must keep these records readily available. We may review them at any time.
(c) Keep a copy of the reports we require in §§ 1036.725 and 1036.730.
(d) Keep records of the engine identification number (usually the serial number) for each engine you produce that generates or uses emission credits under the ABT program. You may identify these numbers as a range. If you change the FEL after the start of production, identify the date you started using each FCL and the range of engine identification numbers associated with each FCL. You must also identify the purchaser and destination for each engine you produce to the extent this information is available.
(e) We may require you to keep additional records or to send us relevant information not required by this section in accordance with the Clean Air Act.