The emergency affects approximately 67 households in a Mountain View neighborhood north of Cuesta Park, where a city-hired contractor was conducting water replacement work on Friday, April 24.
City officials said the contamination occurred during a water main replacement project, when cement slurry seeped through a closed valve between an old pipe and a live pipe carrying water to homes. The city said in an FAQ that the new and old pipes “were not disconnected, but were separated by a closed valve.”
The city shut off water to impacted homes shortly after becoming aware of the problem. Water has since been restored only for toilet flushing, but not for drinking, cooking, bathing, brushing teeth, handwashing or washing dishes.
State regulators have also allowed residents to use tap water for irrigating lawns and watering ornamental, nonedible plants.
The affected area is a residential pocket with tree-lined streets and mostly mid-century single-family homes, according to real estate records.
The State Water Resources Control Board must approve before the city can restore drinking water service, Mountain View officials said. The city said it was preparing for the possibility that approval would not come before Sunday.
“The testing protocol for this incident is being developed in real time since the possibility of contamination from slurry is a unique situation that neither the City nor the State have encountered before,” the city said in its FAQ.
Earlier testing found bacteria in two of five water samples, prompting additional flushing and testing, officials said. The city said testing is also underway for inorganic compounds, including aluminum, lead and hexavalent chromium.
Mountain View has issued a stop-work order for the contractor and said it “will pursue all available remedies related to this incident.” The city added that its immediate priority is restoring safe drinking water.
The city is providing hotel accommodations through Sunday night, with checkout Monday, along with meal and incidental reimbursements of up to $92 per day per household member. Residents who arrange their own lodging may be reimbursed up to $192 plus tax per night, according to the city.
A neighborhood meeting for affected residents was scheduled for Friday. The city said residents needing assistance can call 650-903-6081 or email waterquality@mountainview.gov.