Guidance document re-emphasizes the importance of timely issuance of notices letters and the exchange of information between EPA and potentially responsible parties (PRPs). OSWER Directive No. 9834.10-1a. Issued 10/19/1987. Appendix C of this guidance - Model Notice Letters - was re-issued 2/7/1989, but then superseded on 7/26/1996 (also superseded).You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.