This document discusses how new regulations in Illinois requiring the evaluation of indoor air vapor intrusion concerns have changed the scope and costs of environmental due diligence. Key points: 1) New IEPA regulations and updated standards now mandate investigating vapor intrusion from contaminated soil and groundwater. This has increased costs for Phase I and II assessments and obtaining no further remediation letters. 2) Evaluating vapor intrusion is now required to obtain an NFR letter from the IEPA, increasing the time and costs associated with the review and approval process. 3) Older NFR letters that do not address vapor intrusion may not provide full assurance about a property's environmental status, as they do not rule out