Oil tank removed 25years and no record found

[Nishma Nana]

Need your advice: today my client was ready to sign contract to purchase a single family house and was told that there was a oil tank removed 25years ago.  There is  no record found as it was not needed to be reported to town hall at the time.  The list agent mentioned that the seller was present and had an insurance policy taken out incase there was a leak but did not use the policy as there was no spillage.

I plan to call enviro shield to find out how would they test for this type of situation - Has anyone experienced anything like this?  I am not sure what to do.  Please share your thoughts, thank you