That is, if your loan officer was good enough to detect it.

Do you set up a computer at the property and connect the cameras to it and record everything when motion is detected so that you can review things later? 

Have got the leak detection team on it.

Hire a private detective to find the heirs.

I don't think there is any detectable effect now.News of it at http://www.paloaltoonline.com/news_features/storm98/paw_print.html

I have read that this is still a hazard and soil-testing should be done because the owner does not have documentation showing the tank was properly decommissioned and no leaks were detected (soil tested and cleared of spillage).

One or a few of these could help alert you next time this is an issue. https://www.biggerpockets.com/forums/52/topics/412542-water-leak-detection-devices?

It monitors water flow and can detect leaks based on changes in water pressure (and theoretically shut off the water before a leak causes much damage). 

Amit-  I sent you a private message with the contact details for John at the Home Detectives.

I didn't hear anything, so I thought they served her outside the building, because they call themselves detectives.