The regulations for the Pennsylvania Board of Probation and Parole (PBPP) are found in volume 37 of the PA Code which contains regulations for the Commonwealth. PBPP's regs are found in Chapter 61 commencing with §61.1. That being said, the Board will schedule a hearing for you if your PO forwards notice of an alleged violation. You will have an opportunity to present evidence contradicting any evidence offered that you violated the terms of your supervision. I would recommend that you seek the assistance of an experienced criminal defense attorney, and one with experience in dealing with PBPP. If your work exposes you to the controlled substance you've indicated and there is no other known/suspected sources, you should by all means attempt to defend against any allegations of violation. Your testimony before the Board IS evidence but not likely to be persuasive without some independent support. A skilled attorney can help you come up with convincing support if your theory holds water. Good luck.