Exactly a year after North Marin Water District's Tomales sewer system spilled more than a million gallons of partially treated sewage into Walker Creek, the district is coping with a large spill in Dillon Beach.

As much as 88,400 gallons of treated sewage leaked from a corroded pipeline at North Marin's treatment facility at Oceana Marin subdivision.

The leak was discovered on Oct. 8, and the pipeline was repaired the next day by district staff, said General Manager Chris DeGabriele. "The pipe had been on the ground for 16 years, and was weakened by corrosion and by cows traveling over it."

The pipeline, which carries waste from a storage pond near Ocean View Boulevard to a disposal field above, crosses part of a pasture within the Christopher Ranch.

About a mile below the hillside ranch lies the Estero de San Antonio, which was declared "problematic" by the Regional Water Quality Control Board in 1990 because of pollution and sedimentation. (As it happens, the regional board this week is scheduled to adopt a cleanup plan for the estero.)

"There's really no way the leak made it down to the estero," said North Marin operations manager Paul Smedshammer, who inspected the pipeline the day the leak was discovered.

"A small ravine lies about 250 feet away from the leak in the pipe, and we didn't observe any wastewater flowing down to the estero."

In a memo to North Marin's board of directors, Smedshammer reported, "The pipe material is military surplus, 8-inch diameter, thin walled and not coated nor lined in steel and was acquired by the district for emergency use [in 1981]. The pipeline was installed above ground to save installation costs."

"This clearly points out to us that we need to do some more maintenance, even if there's going to be a cost increase to customers," noted North Marin Director Dennis Rodoni.

"We were caught flat-footed at Oceana Marin," Manager DeGabriele acknowledged. "We knew the line needed to be replaced, but we hadn't planned to replace it until next year."

District directors and staff on Tuesday approved installation of a buried, 12-inch polyvinyl pipeline to replace the leaking steel line.

Although the new line will cost an estimated $50,000, DeGabriele said, "We don't want the leaking line to impact our customers. We're reorganizing our five-year budget plan to accomplish that."

So far, it's too early to tell if North Marin will be fined for the spill by the regional water board, said Tuck Vath, engineering geologist for the board's North Bay region. "The jury's still out on this. But it seems that [North Marin] has acted appropriately at each step."

In the wake of last year's sewage spill in Tomales, some residents of that town have advocated creating their own sewer district.

To make the Tomales system more attractive to independent operators bidding to take over running it, North Marin has offered the option of also bidding to simultaneously run the Oceana Marin system.

But most Oceana Marin customers remain faithful to North Marin despite of the accident, said Sullivan Cooper, president of the subdivision homeowners' association.

"We're happy with the water district," he said. "We don't want to be lumped together with Tomales."