• The present owner or operator of the contaminated facility.
• Any person who owned or operated the facility at the time at which hazardous substances were disposed at the site.
• Any person who arranges for the disposal, treatment, or transport of hazardous substances owned by or possessed by such person.
• Any person who accepts hazardous substances for transfer to a disposal or treatment site selected by such person.

• An act of God (e.g., hurricane, tornado)
• An act of war.
• An act or omission of a third party other than an employee or agent and other than a person whose act occurs in connection with a contractual relationship. A defendant cannot rely on this "third party" defense unless the defendant (i) exercised due care with respect to the hazardous substance and (ii) took precautions to prevent the foreseeable actions or omissions or the third party. Due to the narrow scope of this defense, its principal effect is to provide a defense to an owner or operator who is the victim of a "midnight dumper".

To establish that the defendant had no reason to know…the defendant must have undertaken, at the time of acquisition, all appropriate inquiry into the previous ownership AND uses of the property consistent with good commercial or customary practice in an effort to minimize liability.

According to CERCLA all appropriate inquiry into the previous ownership must be undertaken to comply with the innocent landowner defense. As a party to a commercial real estate transaction it is imperative that the environmental due diligence adheres to both Statute 9601(35)(B) and ASTM Phase I ESA. The American Society for Testing and Materials (ASTM), which is a private not-for profit standards-writing organization, has developed a standard (Designation E 1527-00) for conducting a Phase I Environmental Site Assessment (ESA). The Phase I ESA standards were written to establish good site assessment practices that satisfy the due diligence responsibilities of participants in commercial real estate transactions.

This practice is intended to permit a user to satisfy one of the requirements to qualify for the innocent landowner defense to CERCLA liability: that is, the practices that constitute "all appropriate inquiry into the previous ownership AND uses of the property consistent with good commercial or customary practice" as defined in 42 U.S.C.§9601(35)(B).

According to the ASTM (ASTM Designation E 1527-00, ¶ 7.3.4), standard historical sources include aerial photographs, fire insurance maps, property tax files, recorded land title records, minute topographical maps, street directories, building department records, and zoning and land use records.

Historical chains of title can reveal previous owners and historical uses of a property, but according to the ASTM it cannot be the sole historical source consulted. Though the ASTM standard prescribes many historical sources for determining previous uses of the property, directories, photographs, and maps do not provide the required information to identify a list of previous owners.

This exclusion by the ASTM has led to confusion by professionals in the environmental, financial, and real estate communities, incorrectly believing that historical title records can be eliminated as long as other historical sources of information have been utilized in the report. As a result of consultants’ recommendations of sources that do not include a chain of title, potentially responsible parties and details of particular ownership are not identified. Yet to satisfy due diligence and one of the qualifying requirements to the innocent landowner defense, both previous ownership and uses of the property must be identified as per both 42 U.S.C §9601(35)(B) and ASTM Phase I ESA standards (above).