Water quality regulators are threatening to fine Sonoma County $10,000 per day if it doesn't figure out a way to eliminate runoff from the composting operations at the county's central landfill site west of Cotati.

The 25-acre compost facility run by the Sonoma County Waste Management Agency has been under orders since last year to prevent runoff from reaching nearby creeks.

In a March 18 letter, the North Coast Water Quality Control Board officials said they were "concerned by the lack of progress" in resolving the problem before next winter's rainy season.

Regulators ordered the facility to cease all discharges of wastewater from composting operations by Oct. 1 or face fines of up to $10,000 per day and $10 per gallon over 1,000 gallons.

The waste agency has had a license to operate the composting facility at the county-owned landfill for the past 20 years. But it is the county that is ultimately responsible for ensuring all operations at the landfill comply with environmental regulations.

"We're taking this letter extremely seriously," said Susan Klassen, the county's transportation and public works director.

The waste agency, the county and its landfill operator, Republic Services, have been in discussions about how to comply with the wastewater restriction on compost, which was added to the landfill's new permit for the first time in March last year, Klassen said.

The water board considers runoff from compost to be different and potentially more harmful to aquatic environments than the storm water allowed to run off the landfill site, said David Leland, assistant executive officer for the water board.

When rain hits the long rows of compost it soaks into the piles and picks up nutrients and organic matter which, after mixing with landfill storm water, during heavy rains can be carried into nearby Stemple Creek, he said. That drains into San Antonio Estero and empties in the Pacific north of Dillon Beach.

Klassen said the inclusion of additional restrictions on the runoff was a surprise, but Leland said they shouldn't have been.

"We have been talking about this for at least 10 years," Leland said.

The waste agency submitted a plan to deal with the problem in May of 2013, but the board has rejected some of its ideas, including treatment of the runoff prior to discharge. Another plan to capture runoff in massive portable tanks has been abandoned as well.

Instead the waste agency is trying to better manage the runoff by spraying some of the water onto the roads and onto the compost piles themselves, which have to remain at about 60 percent moisture for optimal composting, explained Henry Mikus, executive director of the waste management agency. They are also draining some of storage ponds and disposing of the runoff at the Llano Road treatment plant, Mikus said.

But those efforts have failed to satisfy regulators or silence critics.

Roger Larsen, who lives in the Happy Acres subdivision east of the landfill, filmed runoff from the site following a large February storm. He presented the video to the waste agency, water quality regulators and posted it to YouTube.

He did so because he was fed up with what he described as inaction on the issue and excuses from public officials. Compost is a natural material, but he called the runoff from it "stinky, black and disgusting." Allowing it to mix with storm water only makes the problem worse, he said.

"It's pollution. It doesn't belong in Stemple Creek and they've been doing it for 15 years," Larsen said.

The composting operation ought to be moved from the landfill property to a new location, Larsen said.

But Klassen said the short-term focus is on finding a way to bring the existing operation into compliance. There are some options, but they are "not necessarily inexpensive nor are they ideal," she said.

These include the construction of additional holding ponds, scaling back the composting operations, or possibly covering the piles to keep rainwater off them, she said.

"I do think that at some level a pond construction will be taking place this summer," she said.

(You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. On Twitter @citybeater.)