In order for a property owner to claim the “innocent landowners defense” under the CERCLA regulations they must first complete “due diligence” when investigating the environmental history of a piece of property. Persons who complete this due diligence must be properly certified and have adequate experience to do this type of investigation. These studies must also comply to the ASTM E 1527-00 standard for environmental site assessments as well as the new EPA rule of “All Appropriate Inquiry” standards made into law on January, 2002. Cutting corners when choosing your environmental professional could leave you unable to use the innocent landowners defense under CERCLA and financially responsible for any environmental contamination discovered on your property.