Under the diesel sulfur program, there is no one time or physical location that a distributor must utilize for sampling. The party must use its knowledge of the distribution system, and information regarding each receipt of product (e.g., whether the shipment may include fuel that is very close to an interface with higher sulfur product) to determine when and where to sample.
However, as a general matter, we believe that a terminal should take samples during and/or after receipt of new product into the tank so that if there is a problem, it can be discovered and remedied before the product is distributed further downstream. If there is reason to believe that piping or a tank may contain high sulfur product then that may affect both sampling strategy and actions to prevent a potential violation.
This is but one example of many possible situations. In regards to terminals not testing for sulfur content at the rack, if a terminal does not conduct a sampling and testing program, it will likely be difficult to be able to establish a defense to presumptive liability.
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)