Martin,
Although SSp2 lists ASTM Phase I and Phase II ESA in the requirements, CIRs have generally given allowances for alternatives as long as they meet the intent of the credit. For instance, a CIR issued on 07/10/2006 ruled, in part: “The geotechnical assessment as performed essentially meets the objectives of a Phase II Environmental Site Assessment…”. Given the fact that California’s environmental regulations are some of the most stringent in the nation, I could not foresee LEED mounting any challenge to this. LEED respects California standards as witnessed by their deferring to California’s testing procedures for VOCs on School projects. The website linked below refers to a 2009 DTSC proposed analysis at a school site under consideration. As described in the article, I would suspect that LEED would readily accept this.
http://www.ci.hercules.ca.us/index.aspx?page=23&recordid=173