The U.S. Environmental Protection Agency recently issued a technical guidance document that may be the most significant change in cleanup assessments and cleanup costs in years. EPA believes that there is far greater risk to human health caused by vapors from contaminated soils and groundwater accumulating in buildings than was previously thought. The guidance outlines a detailed and possibly costly screening procedure for evaluating this vapor intrusion pathway at contaminated sites, including RCRA Corrective Action, CERCLA, and Brownfields development sites. However, EPA has not made it clear when it is appropriate to implement this new guidance, which leaves contaminated property owners unsure if regulators will want to revisit previous remediation decisions to evaluate possible indoor air concerns. It is important that the regulated community demand clarification from EPA concerning the conditions of its use.