40 CFR §312.31

1. (a)Persons to whom this part is applicable per § 312.1(b) and environmental professionals conducting an inquiry of a property on behalf of such persons must take into account the information collected under § 312.23 through 312.30 in considering the degree of obviousness of the presence of releases or threatened releases at the subject property.
2. (b)Persons to whom this part is applicable per § 312.1(b) and environmental professionals conducting an inquiry of a property on behalf of such persons must take into account the information collected under § 312.23 through 312.30 in considering the ability to detect contamination by appropriate investigation. The inquiry of the environmental professional should include an opinion regarding additional appropriate investigation, if any.