THOUSAND OAKS — The troubled Hill Canyon Wastewater Treatment Plant, which is beginning a $27-million upgrade, spilled about 1.7 million gallons of treated sewage into Conejo Creek last week and from there into the ocean, officials reported Thursday.
Officials had not pinpointed the cause of the problem by Thursday evening, and only became aware of the March 31 spill on Wednesday, they said.
"Obviously, there's a great deal of concern about this, given all the issues at Hill Canyon," said Mayor Dennis Gillette of the plant, which has had a series of high-profile spills during the past decade. "We're focusing on the upgrade, and trying to answer the question: Was the response immediate?"
The time lag occurred because plant employees were looking at conflicting information that took several days to decipher, according to Chuck Rogers, waste water superintendent.
"In retrospect it should have been reported earlier," Rogers said. "The people at the time at the facility took a look at the data and apparently did not feel this was a permit violation. I concluded after taking a look at the data that it should be brought to official attention."
Rogers said he reported the spill to the city, the Environmental Health Division and the California Regional Water Quality Control Board on Wednesday.
The spill occurred between 2:45 and 6:15 p.m. March 31 and discharged downstream into Conejo Creek, Arroyo Santa Rosa, Calleguas Creek and ultimately into Point Mugu Lagoon and into the ocean, officials said.
The 1.7 million gallons of treated sewage would have been completely clear, and would not be visible amid the 11 million gallons of reclaimed water that flows through the plant and into the creek.
"The good news is that it wasn't raw sewage," said Mike Byrne, the supervising environmental health specialist at the Ventura County Environmental Health Division.
"But there will certainly still be an elevated level of bacteria that can cause illness," Byrne said.
Byrne said enough time has passed so that the spill can no longer be considered a health risk. City officials said it's possible some of the spill may have been disinfected with chlorine, which is toxic, but officials said they are not certain yet of its concentration level or its impact.
Environmental health officials have notified the state Food and Drug Administration because the waterways are used for irrigation, Byrne said.
Thousand Oaks received a $2.3-million fine from the Regional Water Quality Control Board for the city's role in allowing an aging pipe to rupture and dump 86 million gallons of raw sewage into the Arroyo Conejo in February 1998. The huge spill forced the temporary closure of 31 miles of coastline.
In July of the same year, the state water board determined 14,400 gallons of raw sewage were being improperly discharged daily from the plant.