A written report prepared by an independent, certified environmental professional detailing the findings of a Phase I environmental site assessment (Phase I ESA) for real property. The Phase I ESA identifies potential or existing environmental contamination on or beneath the surface of the land and in the improvements located on the land. A Phase I assessment is typically ordered as part of the environmental due diligence conducted by:

The principal (but not only) purpose of a Phase I ESA is to conduct all appropriate inquiries into the prior ownership and uses of real property. Performing all appropriate inquiries is one element of certain protections against liability under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).

A Phase I ESA generally consists of a records review and a noninvasive, visual examination of the land and the improvements to identify releases or threatened releases at the property of:

Although it is not required as part of all appropriate inquiries, a Phase I ESA may also include an analysis of additional environmental risks, including:

A Phase I ESA does not include the collection and analysis of physical samples, such as soil and water samples. This is included in a Phase II Environmental Site Assessment Report, which is performed if contamination is suspected.

The Environmental Protection Agency (EPA) has issued regulations specifying the standards and requirements for all appropriate inquiries, consistent with good commercial and customary standards and practices, into the previous ownership and uses of the property (42 U.S.C. § 9601(35)(B) and 40 C.F.R. § 312.20). Effective February 13, 2023, a Phase I ESA performed according to ASTM E1527-21 meets the EPA's standards for all appropriate inquiries.

For more information, see Practice Note, ASTM E1527-21 Standards for Phase I Environmental Site Assessments.