Mountain View ‘Super Chlorinates’ Contaminated Pipes in Neighborhood Without Safe Drinking Water

More than a week and a half after a ruptured main left a Mountain View neighborhood without clean water, dozens of residents can now use or drink tap water after boiling it for a minute, while city pipes undergo “super chlorination” to kill remaining bacteria.

The city downgraded the threat from “do not use” to a “boil water” notice on Friday — welcome news for residents who can finally shower, do laundry and run dishwashers again. But recent testing continues to show trace amounts of coliform bacteria, or organisms that can indicate disease-causing pathogens in the water supply, in the water line serving homes on Drucilla Drive and Carla Court in the city’s Cuesta Park neighborhood.

The contamination began on April 24, when city contractor C2R Engineering accidentally pumped cement slurry into a live water main near Bonita Avenue and Cuesta Drive, affecting about 67 homes north of Cuesta Park. Crews immediately isolated the area, and the State Water Resources Control Board stepped in as the regulatory authority overseeing the cleanup.

To tackle the remaining bacteria, the city hired another contractor, West Valley Construction Co., to isolate and seal the pipe at both ends, and inject a high concentration of chlorine to decontaminate the pipe for 24 hours starting Monday morning, said Lenka Wright, the city’s chief communications officer. The chlorine is then flushed out and tested for bacteria twice, 12 hours apart. Results from those tests will be back on Tuesday.

“It’s a very unique, extraordinary situation,” Wright said. “This is not anything that the Water Board has apparently dealt with previously; cement slurry getting into a live water main. And that’s why we are trying this next approach to see if this will work.”

Wright said the city is sending water samples to multiple laboratories in an effort to turn results around more quickly.

Meanwhile, the city filed a stop-work order against C2R Engineering and a claim with the contractor’s insurer. Wright said the city is preserving all legal options, including the possibility of a lawsuit, while its review of the circumstances is ongoing.

Residents in the 23 households on Drucilla Drive and Carla Court will be temporarily connected to above-ground water lines from a nearby hydrant while super chlorination is underway. The boil water notice will remain in effect throughout that process.

For all other affected homes in the neighborhood, the boil water notice continues. Residents can shower, bathe, do laundry and run the dishwasher directly from the tap. Tap water used for drinking, cooking, making ice or brushing teeth must be boiled for at least one minute first.

At a neighborhood meeting held Friday night — attended by roughly 75 residents of the 67 affected households — residents pressed city officials on why the problem has taken so long to fix.

“They were relieved when they heard it was going to a boil water notice,” Wright said. “At the same time, there were concerns … But for the large majority, they were appreciative of the effort. And it was also an opportunity for us to say directly to them, look them right in the face and say: we are sorry that this happened to you.”

The city does not anticipate fully lifting the boil water restrictions before the weekend of May 9 and 10, though Wright cautioned that the timeline could shift depending on test results.

The city continues to offer free hotel stays through Monday, $92 per day per person in meal and incidental reimbursements with no receipts required, and shower access at the El Camino YMCA, Rengstorff Park Aquatics Center and Eagle Park Pool.

Wright also stressed that the rest of Mountain View’s water supply is safe and the boil water notice applies only to the neighborhood north of Cuesta Park: “Outside that area, the water is safe to drink in Mountain View.”