WASHINGTON — There’s a good chance your diesel underground storage tank (UST) is significantly corroded, and even leaking.

That’s the conclusion from a recent study by the Environmental Protection Agency (EPA), which found rampant moderate to severe corrosion in an examination of diesel USTs.

In early 2015, the EPA inspected 42 operating diesel USTs at 40 locations in the United States. Two dozen of the USTs had fiberglass tanks, while the other 18 had steel. The team used in-tank video cameras and photos to document conditions and collected samples of fuel, vapor and aqueous phase (or water bottom), if it was present. UST owners also filled out a detailed questionnaire on storage history, operation and maintenance practices.

After analyzing the samples, reviewing the videos and considering the UST history, the EPA researchers came to an alarming conclusion: Eighty-three percent of the USTs showed moderate to severe metal corrosion. Moreover, less than one-quarter of the UST owners reported that they were aware of the corrosion.

The EPA team found corrosion on all metal UST system components, from submersible turbine pump shafts and automatic-tank-gauge probe shafts to risers and overfill equipment. Corrosion was often severe in the USTs’ upper vapor space, an area of the tank that, before 2007, was not known to be susceptible. Investigators could not pinpoint a specific cause for the corrosion, but they suspect a microbiological source.

The high degree of corrosion in the USTs heightens the possibility of leaking and groundwater contamination.

While the EPA cannot project how many diesel USTs in the entire United States are impacted by corrosion based on this sample, it is warning owners about the risk and urging they inspect their USTs’ condition. By acting early, they could not only prevent leaking but also avoid higher repair costs. For guidance on minimizing corrosion, visit the EPA’s UST website, www.epa.gov/ust.