40 CFR §262.40

1. (a)A generator must keep a copy of each manifest signed in accordance with § 262.23(a) for three years or until he receives a signed copy from the designated facility which received the waste. This signed copy must be retained as a record for at least three years from the date the waste was accepted by the initial transporter.
2. (b)A generator must keep a copy of each Biennial Report and Exception Report for a period of at least three years from the due date of the report.
3. (c)See § 262.11(f) for recordkeeping requirements for documenting hazardous waste determinations.
4. (d)The periods or retention referred to in this section are extended automatically during the course of any unresolved enforcement action regarding the regulated activity or as requested by the Administrator.