On January 26, 2006, EPA issued new protective guidance for cleaning up perchlorate contamination recommending a preliminary clean-up goal for perchlorate of 24.5 parts per billion in water. EPA's guidance is derived from the agency's reference dose for perchlorate which is based on the 2005 recommendations and conclusions of the nation's foremost science advisory committee (National Academy of Sciences). This assessment guidance for perchlorate offers clear guidance to site managers to help ensure national consistency in evaluating perchlorate in light of widely varying state guidance. This decision was based on the best available science and will be updated as new information becomes available.