A Phase I Environmental Site Assessment (ESA) is a preliminary investigation conducted to identify potential or existing environmental contamination liabilities on a property. It involves reviewing historical records, inspecting the site, and interviewing relevant parties to determine if hazardous substances or petroleum products may be present. The assessment follows ASTM E1527 standards and is often required during real estate transactions to satisfy the U.S. EPA’s “All Appropriate Inquiries” rule under CERCLA, helping protect buyers and lenders from future environmental liability.