Three-year, $15 million Sonoma sewer line upgrade to begin this summer
Work is to begin this summer on the next phase of replacing an old and failing sewer main that runs through Sonoma Valley, periodically leaking wastewater during heavy winter storms.
Crews are going to be tackling three pipeline segments totaling 1.8 miles over the next three years, beginning with a section likely to be the most disruptive, given its intersection with a key transportation corridor in northwest Sonoma. The first stretch of pipeline to be upgraded starts on Sixth Street West but quickly aligns with West Napa Street/Highway 12 and then turns north toward Maxwell Farms Regional Park.
The Sonoma Valley County Sanitation District, which manages the area’s wastewater treatment system, has laid plans for the roughly $15 million project to proceed as smoothly as possible, officials said.
The impacts on traffic and daily life are a trade-off to upgrade and enlarge a roughly 60-year-old sewer main. The work is meant to stop the accidental discharge of untreated wastewater that has occurred over several decades when abundant rainfall hits the area.
“We’re going to do some pretty heavy outreach as it gets closer, just so people know,” said Mike Thompson, assistant general manager with Sonoma Water, which operates the system through the sanitation district. “It looks simple but it’s extremely complicated, and we’ll be happy when it’s done.”
Spills come primarily during heavy storms that allow rain runoff and groundwater to seep into cracks in deteriorating sewer laterals and collection lines — a situation known as inflow and infiltration — overwhelming the system with so much volume that wastewater can leak out or overflow, usually through manhole covers.
The discharge is highly diluted, agency spokesman Barry Dugan said. But it contains untreated sewage, and it floods onto the street and into storm drains, often working its way into local creeks, potentially risking wildlife and water quality, and putting the district in violation of the California Environmental Quality Act.
Heavy rains last month led to eight such overflows on two occasions, Jan. 6 and 16, involving a combined 498,843 gallons of wastewater.
Separately, a faulty valve on the Sonoma Valley system failed to close Jan. 12 and released more than 2 million gallons of wastewater into a slough before being discovered and stopped.
Nearly 170 known spills from the Sonoma Valley system totaling more than 2.5 million gallons have been reported to the San Francisco Bay Regional Water Quality Control Board since 2007, most as a result of such accidental discharges, though Sonoma Water staffers say the frequency has diminished as repairs have been made in recent years.
They also note that aging collection systems and related overflow problems are widespread in California and elsewhere, a point validated by reports and enforcement by state regulators in other areas.
Private property owners in the Sonoma Valley system, which serves more than 17,000 accounts, also are partly to blame. They’re responsible for maintenance and replacement of the sewer laterals that connect their homes and businesses to the public sewer main. The city, believing that many are likely in need of repair, given their age, has made allowances for video inspections and rebates for repair and replacement.
As far back as 2010, San Francisco Bay water quality regulators said the Sonoma Valley district was not moving fast enough to replace and enlarge capacity in the public sewer main.