40 CFR §63.6660

1. (a)Your records must be in a form suitable and readily available for expeditious review according to § 63.10(b)(1).
2. (b)As specified in § 63.10(b)(1), you must keep each record for 5 years following the date of each occurrence, measurement, maintenance, corrective action, report, or record.
3. (c)You must keep each record readily accessible in hard copy or electronic form for at least 5 years after the date of each occurrence, measurement, maintenance, corrective action, report, or record, according to § 63.10(b)(1).