PORTLAND - On the eve of the deadline to clean up all the underground gasoline tanks in Oregon, only about two-thirds of the owners had met state requirements needed to stay in business.

But the deadline affected only a handful of retail gasoline stations. Many of the remaining tanks are owned by government, farmers or businesses, and most are being decommissioned because upgrading is too costly.

"What's important to remember ... is most of those facilities are not gas stations," said Mike Kortenhof, state Department of Environmental Quality underground tank manager. "A large majority of them are choosing to close their tanks and get fuel elsewhere." By Monday, the DEQ had certified 1,756 of about 3,000 sites with underground tanks.

The Environmental Protection Agency set the tank closure deadline in 1988, prompted by concerns about groundwater contamination from leaking underground storage tanks.

The DEQ has been working for the past decade to enforce storage tank regulations to protect Oregon's drinking water, half of which comes from groundwater.

"A hole the size of a pin, if left unrepaired for a year, will release more than 400 gallons of gasoline into the environment," said Jacquiline Poston, leader of four EPA inspection crews.

Mike Sherlock, executive director of the Oregon Gasoline Dealers Association, said most retail gas station owners were preparing to replace their tanks anyway because they were at least 20 years old and made of steel.

The state had about 9,000 sites with underground fuel tanks in 1988, when regulators ordered the cleanup.