The independent sampling and testing provisions require the independent lab to collect a separate sample from each batch of RFG. "Batch of reformulated gasoline" is defined at § 80.2(gg) as "a quantity of reformulated gasoline which is homogeneous with regard to those properties which are specified for reformulated gasoline certification."
As a result, when an independent lab identifies a sample it collects as being representative of the gasoline contained in a batch of RFG, that lab is independently representing that the gasoline being sampled is homogeneous with regard to the RFG properties - that the tank is fully mixed and is not stratified.
EPA expects the independent lab to use its best professional judgment in determining the procedures that are necessary in order to classify the gasoline in a storage tank as being fully mixed. For example, if the independent lab's normal practice is to analyze the gravity of top/middle/lower samples to determine tank mixing, EPA believes the independent lab should follow that practice with regard to the RFG independent sampling and testing requirements.(7/1/94)
This question and answer was posted at Consolidated List of Reformulated Gasoline and Anti-Dumping Questions and Answers: July 1, 1994 through November 10, 1997 (PDF)(333 pp, 18.17 MB, EPA420-R-03-009, July 2003, About PDF)