A standard for an investigation into the prior ownership and uses of real property to assess the likelihood of the presence of hazardous substances on the real property. Parties often perform all appropriate inquiries by commissioning a Phase I Environmental Site Assessment (Phase I ESA).

Performing all appropriate inquiries is one element of specific liability protections that are available under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) to:

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.