In a case where an independent lab collects more than one sample from a batch (e.g., top/middle/lower samples), how many samples must be retained by the independent lab?

For EPA's purposes, an independent lab must collect a single representative sample for each batch of RFG, and it is this single sample that should be analyzed and retained for transfer to EPA if necessary. If more than one laboratory will be analyzing the properties of a batch, then the independent lab should collect two separate samples rather than splitting one sample after collection. Split samples are vulnerable to loss of light ends unless transfer is carefully performed according to the procedure outlined in Appendix E, section 8.1 and figure 1.1.

When collecting duplicate samples take care to assure consistency. For example, unless a storage tank is fully mixed, multiple running samples collected from that tank can vary according to retrieval rates, dwell at the bottom point, and consistency of the measurement of the bottom point. See the Sampling/Testing - Sampling Section, Question 1, for a discussion of the sampling methods that are appropriate for RFG.

In the case of additional samples collected by the independent lab, for example, to establish that a storage tank is fully mixed and is not stratified, there is no requirement that such samples must be retained. The independent lab should keep documents that reflect any sampling and testing that was performed to establish the effectiveness of tank mixing, however, in case questions arise about the quality of gasoline from a particular batch or to support the quality of the independent lab's work in the case of an EPA audit.(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)