May 27, 1997
by Stephen McClurg
Did you notice gas stations all over neighborhoods in Mobile were shut down during the last two years for a few weeks and had their gas tanks dug up and replaced? Gas stations had to do that to meet the December 1998 deadline established by the Environmental Protection Agency (EPA) to protect groundwater.
UST is not an important part of many people's vernacular, in fact many people may be unaware that they use one every time they fill their automobile with gasoline. There are approximately 153 UST (underground storage tank) sites in Mobile, including petrochemical tanks and emergency generators such as those found in hospitals and shopping centers. USTs are tanks (including their piping) that have at least ten percent of their volume underground. They have been used for petroleum and certain hazardous chemicals for decades, but only recently were the potential dangers to groundwater and soil or possible explosions and fires from USTs recognized (with about 7,000 leaks found in Alabama alone).
Inevitably, some leakage will occur around a tank, whether from corrosion of the tank itself or from human error in overfilling and spilling, but the potential dangers have been kept under control through EPA regulations. The EPA reports that there are several million USTs in the United States and that tens of thousands of them are leaking or have leaked at some time. Major points of the regulations tackle these issues. All tanks installed after December 1988 must meet requirements for installation, spill and overfill prevention, corrosion protection, and leak detection, while older tanks must have corrosion protection and spill/overfill prevention in order to pass the December 1998 deadline for upgrades of all tanks. The reason local gas stations are being shut down and having their tanks dug up is to meet these upgrade standards.
Most older tank systems are made of bare steel that corrodes underground, whereas newer tanks are either made of a noncorrodible material such as fiberglass or are steel tanks lined with noncorrodible materials. According to EPA studies, piping is the main cause of leaks, and it must meet the same standards as tanks. To prevent spills from delivery hoses, tanks should have catchment basins and some sort of overfill alarm or float valve. Groundwater contamination has been considered the most serious threat that USTs pose to the environment. Fuel hydrocarbon plume lengths (contaminants) in detection limits (fifty parts per billion) did not extend beyond 200 feet in 90 percent of cases studies by the EPA. This means that if detected late these contaminants may not cause as many problems as originally thought and that it will be easier to contain. Many tank owners are changing to above-ground tanks so that leaks can be detected faster and clean-ups can be implemented sooner, but fire marshals haven't been too excited about this idea. Luckily, the control measures have helped avoid any major disasters.
The Mobile area is lucky in that it doesn't rely on groundwater, and many of the most dangerous problems associated with USTs are virtually zero for the area. It is a good idea to make sure that children do not play around sites or in soil that has been removed from a contaminated site. If you do use well water it is a good idea to have your water tested, and if you are buying land make sure that you know what has been there before because you could inherit the problems from an old UST. Even though the contamination from UST is generally easy to contain from any one site, prevention needs to be implemented to its fullest extent because of the overall large number of these systems used. We are all connected, and even a small amount of prevention from harm helps.
The author wishes to acknowledge Dr. Doug Haywick of the University of South Alabama, Bill Brenner of South Earth Sciences, and Steve O'Hearn at Thompson Engineering for their assistance in preparing this article.