This Explanation of Significant Differences (ESD) applies to the remedial actions performed under the Final Record of Decision for Test Area North, Operable Unit 1-1 0, Idaho National Engineering and Environmental Laboratory (DOE-ID 1999) as amended by the Explanation of Significant Differences for the Record of Decision for the Test Area North Operable Unit 1-10 (DOE-ID 2003), the Record of Decision Amendment for the V-Tanks (TSF-09 and TSF-18) and Explanation of Significant Differences for the PM-2A Tanks (TSF-26) and TSF-06, Area IO, at Test Area North, Operable Unit 1-1 0 (DOE-ID 2004a), and the Explanation of Significant Differences for the Record of Decision for the Test Area North Operable Unit 1-10 (DOE-ID 2005). The U.S. Department of Energy (DOE) Idaho Operations Office; U.S. Environmental Protection Agency (EPA), Region 10; and the Idaho Department of Health and Welfare-now identified as the Idaho Department of Environmental Quality (DEQ)-signed the Record of Decision (ROD) in December 1999, the 2003 ESD in April 2003, the ROD Amendment/ESD in February 2004, and the 2005 ESD in January 2005. The EPA and DEQ support the need for this ESD.