Come on in, the water's fine...for now
Public Works Director Dante Del Prete gave an update on Sebastopol's water system at Tuesday's council meeting
It’s always reassuring to learn how things work. Take Sebastopol’s water system, for example.
There have been rumblings of concern around town about Sebastopol’s water system recently—concerns about the age of the pipes and some of the wells and rumors of contamination. City Council candidate Key Nethery has made water—insuring the town doesn’t run out of water—one of the central issues in his campaign.
Del Prete’s presentation should calm some jittery nerves. Watch it here, starting at 38:42. We’ll do our best to summarize his talk, but it’s really worth a listen.
How water gets from the ground to your house
Sebastopol’s water system is based on wells drilled down into the Wilson Grove Aquifer, which is considered “low risk” by the Sustainable Groundwater Management Act.
“Low risk means it’s not showing signs of declining water levels,” Del Prete said after the meeting. “Even during drought, we don’t see a lot of modifications.” (He notes this is not a reason to not conserve water: “Water is a precious resource, and we have to treat it as such and take care of that resource,” he said.)
One hundred percent of Sebastopol’s water is well water.
The town is divided into two water zones: the lower elevation Zone 1 and the higher elevation Zone 2. The triangles in the image below are the town’s four wells, while storage tanks sit to the west on the hills.
“The water zones are designed to regulate pressure, and it’s based on gravity,” Del Prete said. “The elevation of the tanks determine the constant system pressure.”
Del Prete started out his presentation with a flow chart of how the water gets from the town’s four wells to either your home faucet or, when there’s overflow water, to one of the town’s three massive water storage tanks.
“The water wells pump directly into the distribution system,” Del Prete said. “When water production surpasses the demand usage, water then overflows into the reservoirs for storage.”
About the town’s four wells
Well 4
Well 4, which was installed in 1953, is located on Petaluma Avenue. It is drilled to a depth of 775 feet, with the well pump at 250 feet. The water goes through a sand separator, which removes fine grains of sand that are produced naturally from the aquifer, then it moves on through two carbon vessels that remove traces of a dry cleaning chemical (tetrachloroethylene). The backwash noted in the diagram is for maintenance of the carbon vessels.
Del Prete noted that “The current treatment [for tetrachloroethylene contamination] is granular activated carbon, which is coconut shells, and disinfection is with sodium hypochlorite.”
Well 4 produces 1,020 gallons per minute, and the average annual production is 157 million gallons.
This is Sebastopol’s most productive well—it provides half of Sebastopol’s water—and it’s also the town’s oldest.
“The infrastructure is very old, but the mechanical items of that have been swapped out, of course,” Del Prete told the council, noting that “There’s a schedule of routine maintenance and repair.”
Well 4 is scheduled to be replaced in the next five years. (More details on this at the end of the article.)
Well 7
Well 7, which is located on Village Way, was installed in 1996. It is drilled to a depth of 710 feet and the well pump is set at a depth of 440 feet. This well has some contamination from naturally occurring arsenic in the volcanic layer.
“It has a packer (or plug) that seals off water from a certain zone that is higher in arsenic so we’re pulling water that is better quality,” Del Prete said.
To treat the residual arsenic, which is Arsenic 3, the water goes through a ferric oxide vessel. The backwash vessel in the diagram is for maintenance of the ferric oxide vessel.
“We do a CO2 PH adjustment treatment that increases the efficiency of the granular ferric oxide media, helping to take out the rest of the arsenic,” Del Prete said, “Ferric oxide is basically rust.”
“The arsenic in Well 7 is Arsenic 3, which is different than the arsenic in Well 6, and they’re treated differently.” he said.
Well 7 produces 490 gallons per minute, and the average annual production is 86.5 million gallons annually.
Well 6
Well 6, which is located on South Gravenstein Highway, was installed in 1968. It is drilled to a depth of 1,015 feet, with a pump at 220 feet. Water from Well 6 shows contamination from naturally occurring Arsenic 5. To lower the amount of arsenic, it is blended with water from Zone 1, diluting the arsenic with a “dilution is the solution” approach.
“We are blending it to lower the arsenic to a safe level to meet the regulations,” Del Prete said.
Well 6 produces 26.6 million gallons a year.
Del Prete said that dilution was chosen as a cost-effective solution, but should the levels of arsenic rise, he said the city already has complete plans for a more extensive treatment system should that become necessary.
Well 8
Well 8 is the city’s newest well. Located on Jewell Avenue, it was installed in 2007. It is drilled to a depth of 580 feet, with the pump set at 400 feet. It has no contaminants, and the only treatment here is disinfection with sodium hypochlorite. Well 8 averages 445 gallons per minute and has an annual production of 44.5 million gallons a year.
About the town’s water storage system
Sebastopol has three welded-steel water storage tanks, one on Mackey Court and two on Pleasant Hill Road. The one on Mackey Court holds 1.5 million gallons, while the two on Pleasant Hill hold 3 million gallons each
“We have seven and a half million gallons of storage altogether,” Del Prete said, noting that, “We keep these tanks as full as possible at all times.”
Sebastopol uses a million gallons of water a day on average, which means, we have seven days’ worth of water in the storage tanks.
“There’s the storage reserve of seven-plus days of normal use,” Del Prete said. “If there was an emergency, we could put out conservation orders and extend that.”
Future significant distribution system upgrades
Del Prete then went on to list five upgrades the system needs in the near future.
“These are very expensive projects, and I wanted to get them on the radar,” he said, noting his upcoming retirement this fall.
Replacement of Aging Sections of Water System Infrastructure—Downtown corridor is approaching 65 years of service life.
Well 4 Replacement—Essential Water Treatment Facility Utilizing the oldest well site.
Pleasant Hill Reservoir Tank 1 Interior Relining—Tank Liner is due to be replaced with new material.
Well 6 Arsenic Treatment Facility—We have a design for a treatment facility should arsenic levels increase beyond current treatment.
Pleasant Hill Road Water System Connection Loop—Connection would provide a secondary connection for the current Lynch Road single pipe connection to Pleasant Hill Reservoirs.
Due to time constraints, Del Prete raced through these at the council meeting, but in a conversation after the meeting, he expanded on the process for the Well 4 replacement.
Del Prete said that the replacement of Well 4 is already in the city’s Capital Improvement Program (CIP), a five-year plan of capital projects.
“I think the design is scheduled for next year and the replacement is scheduled for the year after,” he said. “It’s a big project, so it has to have approval from the state. You can’t just drill a well. Design would take a full year, environmental approval and permits would probably take another year, and then bidding, bonding and construction…I’m thinking, another well probably won’t be on that site until four to five years from now.”
Ideally, Well 4 will still be producing water for the city while the replacement well is being built.
“One of the state requirements is that you have to be a certain distance away from the existing well drilling hole, so you have to be at least 50 feet away. But further is better so when you develop that well you’re not just pulling water from the old location.”
He felt there was room at the same location, Spooner Park, which also houses the solar array, to sink the new well.
The funding for that new well, which is estimated to cost $3,282,000, will be possible thanks to this summer’s water rate hike, which will allow the city to use those future rate payments as collateral to take out a loan to replace Well 4.
If you found this article interesting, but want more detail, we urge you to listen Dante Del Prete’s presentation to the city council, starting at 38:42. See the staff report and PowerPoint presentation here. Also check out the Consumer Confidence Report for 2023.
thank you so much for this informative article
Why did the Consumer Confidence Report for 2023 not include the samples from the problematic well 6?