The pipe will connect the San Carlos Pump Station to the Silicon Valley Clean Water treatment facility on Radio Road near the tip of the Redwood Shores peninsula, transporting waste over a distance of nearly 3 miles. The community is part of incorporated Redwood City.
Project officials are reviewing possible routes under major roadways, through the Steinberger Slough levee and in the central lagoon.
“The majority [of the pipe] is through a highly populated residential area and it’s extremely challenging because you’re dealing with people’s day-to-day lives going through a neighborhood,” said Dan Child, manager of Silicon Valley Clean Water.
Running the new pipe under Redwood Shores Parkway, a main traffic artery, is expected to have minimal environmental impact but would cause extended traffic disruption and interfere with utilities already buried under the pavement, Child said. The roughly $60 million option would take three to four years to complete.
A faster and cheaper alternative involving levees would avoid street excavation, but construction would abut waterfront properties and potentially disturb the area’s fragile ecosystem, he noted.
“We have a lot of people that are concerned about each one of the options,” Child said. “[Our goal is] to provide the best service and least disruption to the community during construction and the best solution to the problem.”
The existing concrete pipe, which is located in a muddy area of the Bay and is punctuated by joints every 12 feet, has become vulnerable to stress and breakage, officials said. It has suffered 64 leaks since its construction in 1969 and the rate of new leaks has increased in recent years.
During peak flow times after storms, the pipe sustains up to 2½ times the pressure it was designed to withstand, and at 45 years old, it has already outlasted most estimates for its life expectancy, officials explained.
“I immediately thought of the Loma Prieta earthquake which was 30 miles away,” said U.S. Geological Survey geologist and Redwood Shores resident Harry Cook, after hearing about the aging pipe. “There is a seismic risk all by itself in this.”
“The levee probably is densely packed, but it’s very narrow and there’s Bay mud on one side and Bay mud on the other side. It would shake a lot more than down the street, which is over a broad swath of engineered fill,” Cook added.
The replacement pipe will have the same 63-inch exterior diameter, but will be made of fusion-welded, high-density polyethylene, a stronger, more durable and joint-free configuration.
“We’re not expanding capacity for treatment as much as reliability of the system,” Child said.
Silicon Valley Clean Water’s entire infrastructure serves more than 200,000 people in Redwood City, Belmont, San Carlos, Menlo Park and Portola Valley. Average flow through the system in dry weather is 13 million gallons of water per day.