During the period from May 1 through September 15, inclusive, the Bureau and the Department shall, until such time as the United States Environmental Protection Agency approves the use of ASTM Test Method D-5190-92, determine the vapor pressure of gasoline in accordance with the test methods described in 40 CFR Part 80, Appendix E, which is incorporated by reference. Following approval by the United States Environmental Protection Agency, ASTM Test Method D-5190-92 shall be used. Regulated parties are free to use other accepted test methods for quality assurance programs. However, these programs do not exempt regulated parties from enforcement action. Regulated parties are encouraged to develop a correlation program with the Bureau and the Department to reduce the probability of inconsistent test results.