3.5: FotE- LUST

Focus on the Environment (FotE)

Leaking Underground Storage Tanks (LUST)

Underground storage tanks (USTs) are used to store fuel at gas stations, industrial sites, airports, and anywhere that large volumes of fuel are used. They do not last forever, and eventually they start to leak their contents into the ground. This is a particular problem at older gas stations — although it may also become a future problem at newer gas stations. You may have noticed gas stations that have been closed and then surrounded by chain-link fence (Figure \(\PageIndex{2}\)). In virtually all such cases the closure has been triggered by the discovery of leaking USTs and the requirement to cease operations and remediate the site.

Figure \(\PageIndex{1}\) A depiction of the fate of different components of a petroleum spill from an underground storage tank. © Steven Earle. CC BY 4.0.

Petroleum fuels are complex mixtures of hydrocarbon compounds and the properties of their components—such as density, viscosity, solubility in water, and volatility—tend to vary widely. As a result, a petroleum spill is like several spills for the price of one. The petroleum liquid slowly settles through the unsaturated zone and then tends to float on the surface of the groundwater (Figure \(\PageIndex{2}\)). The more readily soluble components of the spill dissolve in the groundwater and are dispersed along with the normal groundwater flow, and the more volatile components of the spill rise toward the surface, potentially contaminating buildings.

Find a leaking UST in your community

There is likely a leaking UST at a former gas station near you. Look for an empty property that is surrounded by a chain-link fence with “No Trespassing” signs. You might see evidence of monitoring wells (like those shown in Figure \(\PageIndex{2}\), and there could be some petroleum barrels around that are being used to store contaminated water. Once you’ve identified one of these, you’ll probably start seeing them everywhere!

Throughout the 2000s California has worked hard to clean these up , but many sites still remain. If you live in California, check out this website to see if there are any active LUST cleanup sites near you.

Figure \(\PageIndex{2}\) A closed and fenced gas station site in Nanaimo, B.C. The white pipes in the background are wells for monitoring groundwater contamination on the site. © Steven Earle. CC BY 4.0.

Volatile Organic Compounds (VOCs)

The chemical compounds present in fuels contain mostly carbon and hydrogen and are generally known as "Organic Compounds", which will be covered in Chapter 7. The organic compounds that evaporate easily are known as "Volatile Organic Compounds" or "VOCs". These are a major cause of Air Pollution or Smog, which will be discussed in Chapter 5.5.

Oxygenates (Including MTBE)

In the late 1970s compounds containing carbon, hydrogen, AND Oxygen began to be added to gasoline. These helped replace the lead that had previously been added to gasoline and helped the gasoline burn cleaner, producing less air pollution. Unfortunately, these compounds also helped the fuel that had leaked into the soil move faster toward contaminating groundwater. This accelerated the problem of leaking fuel tanks.

Figure \(\PageIndex{3}\) Methyl tert-butylether molecule. Marvin JS, 2025, ChemAxon ([www.chemaxon.com])

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