TIVERTON — The hazards created by large numbers of aging underground fuel tanks in town will be explored next Wednesday, Jan.18., in a workshop organized by the Tiverton Conservation Commission.

“It is clearly a very serious matter that has been overlooked,” said commission member Richard Guimond.

Fellow commission member Tom Molinski, who assembled the presentation, reports that there are 207 known unmonitored private underground storage tanks in town (per fire department records) holding (worst case scenario) 177,890 gallons of fuel oil, most of which is used for heating. While the state Department of Environmental Management monitors large tanks, such as those at service stations, typical smaller home and farm tanks are not monitored.

Most of these are in areas with drinking water wells nearby and within sensitive watershed areas, and “many of these tanks are 30 years old or even older.”

A rupture, even a small one, could have “an enormous impact on resident wells, or even drinking water suppliers like Nonquit and Stafford Ponds.”

The extent of cleanup required when fuel is spilled into the ground became evident when a delivery man mistakenly pumped 366 gallons of heating oil into a dental office’s fill pipe back in October. That pipe had long since been disconnected and the tank removed causing that oil to flood into be basement and soil beneath.

Cleanup crews have had to dig out the basement floor to a depth of 12 feet and the business can’t reopen until June.

Most leaks are less evident and sudden, Mr. Molinski says in his presentation.

Storage tanks usually fail from corrosion on the interior of the tank — water in home heating oil can combine with sulphur and become acidic and corrosive.

Even slow leaks can send oil migrating through Tiverton’s glacial soil and through bedrock fractures with the ability to ruin wells at some distance.

The workshop will be held at 7 p.m. in the Tiverton Library