A $35 million contract to expand Napa’s Jamieson Canyon water treatment plant was awarded by the City Council Tuesday.

The contract went to C. Overaa & Co. of Santa Rosa, the lowest of four bidders. Overaa bid $6 million less than the next lowest bidder, Western Water.

Plant capacity will be expanded from 12 million gallons a day to 20 million gallons. Treatments to improve water quality will be added.

Expansion will take three years, allowing the city to draw more water from the State Water Project, said Joy Eldredge, a city engineer.

The city is setting aside $3.5 million for cost overruns. Construction management and design is costing another $5.2 million. The total project is costing $43.8 million, paid for by water bonds.

The cost of these bonds has been figured into today’s water rates, officials said./Register