I've been told by tank removal companies that if there is a high water table or a lot of ground water in the area and the tank was not properly decommissioned your chance of having a leak could be high.  

Our biggest issue right now is severe drought and the BOR unilaterally deciding not to release water to our irrigation district this year so groundwater rechard did not happen and the water table has lowered dramatically.

Hi Eron,Well you could test it out by laying a big plastic sheet over the area and seeing if it works.But if the water is coming from a general raising of ground water that won't stop it.Good Luck!

Also ask about ground water mitigation.

@Dennis M. you do know the poison leeches into the ground water which someone might end up drinking right.

EPA has completed removal of hexavalent chromium from thirteen basements and installed systems to prevent further infiltration of contaminated groundwater.

I know in Florida landfill space is limited due to high ground water which makes disposal costs expensive.

Do you have adequate projection on your eaves - 2’Do you have proper drainage 3/4 crush works best or create a ditch away from the property to collect ground water etc Cracked foundation you could try aqua plug depending on the cracks etc

If you do apartments in basement --check for plumbing problems or costs --for kitchen bathrooms etc --and seepage ( if ground water high) or flooding etc -- If you like so much --pay $1000 and get an Option for six to 12 months --tie up property and then do creative thinking and marketing --even find a partner-- If zonend for 24 untis MF --it may be easy to get zonned for a 40 room hotel - independent or weekly rentals --with kitchen --more profitable --if there is lot or tourists --good night life downtown -- etcOR basement can also have a retail --Salon / or restaurant --or health spa-- --think about long term --tenants-- Good luck..

You are getting ground water vapors at the dirt portion.