In Indiana they drill multiple test wells on every station lot. Most are marked with a lid that says Monitor well. Has a triangle on it. I have seen a few older ones that don't have the markings on them.
If contaminants are found in the water, they bring in a unit to clean it up. Gasoline contains numerous chemicals, and different chemicals require different process's to remove.
I am not sure about other states requirements.
The Federal EPA Guidelines for testing is once every three years. Here is a link to that info. It is a PDF file. http://www.epa.gov/swerust1/fedlaws/Inspection%20Final%20GL%204-24-07.pdf
Indiana's IDEM (Indiana Dept. of Environmental Management) has a huge website that even includes all the tanks in the state of Indiana that have been reported to leak. Their website:
http://www.in.gov/idem/programs/land/ust/index.html Indiana calls it the UST program (Underground Storage Tank).
In Georgia do a search for EPD GUST program for all their info. (Georgia Underground Storage Tank).
Here is a link to the Federal EPA's website on underground storage tanks. Look on the right for a map with links to your states info.
http://www.epa.gov/swerust1/ Other that that, I must admit I don't know a lot about that end. Just that I see this stuff everyday. The trailers come and go on some lots, and when they dig those trenches around a station to connect wells, I cannot get close to the tanks to unload and have to hook extra hoses together to get to the tanks.
Chuck
[This message has been edited by Gaspedler (edited 09-11-2007).]