Tank Locating is now a very common service due to somewhat recent regulations which require a tank to be properly closed if not in use before a real estate transaction can be finalized.  In the late 20th centry (late 80's & early 90's) local authorities didn't require this, nor did they require a permit or inspection to be completed if in fact a tank was closed.  So with the lack of readily available documentation at the local town hall, Tank Locating or Tank Searching Services come much in need this day and age.