The branded refiner would be liable for any violation that occurs at the branded facility. To establish a branded refiner defense, the branded refiner must, among other things, establish that it had an appropriate quality assurance sampling and testing program. See questions 12.18 and 4.35 for liability and defense provisions for retailers and distributors.
Question and Answer was originally posted at Questions and Answers on the Clean Diesel Fuel Rules (PDF)(135 pp, 888 K, EPA420-B-06-010, July 2006, About PDF)