State investigators are still looking for the cause of a Mount Veeder winery treatment pond breach that sent perhaps 850,000 gallons of wastewater spilling toward Redwood Creek.
Initial reports put the July 31 spill from The Hess Collection Winery at 1.9 million gallons. But Keith Lichten of the San Francisco Bay Regional Water Quality Control Board said Tuesday that the treatment pond, though it can hold about 1.9 million gallons, was about half-full.
By comparison, an Olympic-sized swimming pool holds 660,000 gallons.
A Napa County notice described the wastewater as “domestic sewage and winery process wastewater.” It apparently wasn’t raw sewage, but had seen a degree of treatment.
The wastewater had been through septic tanks to remove solids, then an aeration pond. It was in a final pond that holds water that is later sprayed onto a hillside with scrub oak, Lichten said.
“That said, we never want to see a pond fail,” Lichten said. “If it does fail, we don’t want to see (wastewater) going to a creek.”
Wastewater apparently escaped through a hole in the berm, Lichten said. He hadn’t seen the berm himself and said Hess is having an engineering firm investigate. The ponds had operated for 30 years without this type of problem.
Matt Wood, vice president of operations for The Hess Collection, said in written statement that the structural breakdown at the pond likely resulted from “natural causes.” That could range from a gopher hole to latent effects from the 2014 South Napa earthquake.
Hess discovered the problem the morning of July 31, Wood wrote. The winery notified the county and Regional Water Quality Control Board and is working with third-party engineers to repair the pond.
“The Hess Collection is committed to the preservation and enhancement of the environment and our community and we will remain transparent in our findings and actions along the way,” he wrote.
Redwood Creek flows from near Mount Veeder through the southwest city of Napa, joining Napa Creek on the way to the Napa River.
County Planning, Building and Environmental Services Director David Morrison said Tuesday that the spill apparently didn’t reach the city. County officials found the creek dry near city limits.
The state Department of Fish and Wildlife could not be reached on Tuesday. Morrison said said the agency had indicated there are no impacts to fish.
The San Francisco Bay Regional Water Quality Control Board, not the county, oversees wastewater systems the size of the one at Hess, Morrison said.
Lichten said the pond operators inspect the ponds monthly. These recent monthly reports didn’t indicate a possible spill cause.
Napa County sent a notice dated Aug. 4 to residents living in the Mount Veeder area warning them to avoid contact with the creek. It advised using soap to wash humans or pets touching creek water.
Lichten said his agency will work with Hess and Napa County and other parties to find out what happened and to make any needed changes. It will later decide whether to take enforcement action, which could range from a corrective letter to a fine.
Other Napa County wineries have treatment ponds. Lichten said breaks leading to spills are far from common.
“I’ve been working at the Water Board for 22 years,” Lichten said. “I can’t remember when it happened before. It is an unusual occurrence.”