Construction on a massive three-line water main project is under way and on schedule, with the first line set to be operating by August, and work on the second line scheduled to begin this week.
Last month crews began constructing three new water mains under Highway 29 in north Napa in an effort to replace broken lines and improve water transmission between the eastern and western parts of the city, said city engineer Megan Thomas. Crews will remain at various sites along Salvador Avenue, Sierra Avenue and F Street possibly through the remainder of 2013 as they drill underground and lay 24- and 16-inch pipes under the highway, and connect them with the transmission systems on either side.
Most of the work currently under way is at Salvador, scheduled to happen first so it would not cause traffic issues for Salvador Elementary School.
“Our timeline was designed to do the area that is in most need,” Thomas said.
Unlike older, more traditional methods for installing pipelines, the Livermore contractor Mountain Cascade Inc. is installing the lines via horizontal directional drilling, which reduces the need for trenching. Rather than digging wide trenches, setting the pipe and then burying it, a drill is used to bore a long corridor under Highway 29 so a pipe can be threaded through.
Per Caltrans regulations, each pipe will be installed in a casing to prevent damage to the highway in the event of a break.
“If a pipeline breaks, it will bubble up at the ends, which is city property,” Thomas said.
A 24-inch, polyvinyl chloride (PVC) pipe will be installed at Salvador to house a 16-inch water main. The same size pipes will be installed at Sierra. A 16-inch casing will be installed at F Street and surround a 12-inch line. Smaller 6- and 8-inch lines in the area of each job site will also be replaced, but that work will largely be done through trenching, so it may be more noticeable to onlookers.
The pipelines have an expected life span of more than 80 years, Thomas said.
The work will move from Salvador to Sierra, then on to F Street. Some nighttime street closures have already been required and may be needed in the future.
Recently residents in the area have experienced colored water out of the tap, but Joy Eldredge, general manager of the city’s water division, said that’s not because of the pipeline work. The discolored water, which disappears when the tap is left to run usually for a few seconds, is due to the heavy volume of water use in the area.
The high summer demand is forcing water through a 36-inch water main at a higher pressure than normal, which causes mineral buildups to break free, discoloring the water. The city has issued several notices recently about this happening, and Eldredge said she hopes the city is past this most recent issue.
The city is posting regular updates about the project on its website, CityOfNapa.org.
Thomas said work on all three lines could be wrapped up by the end of the calendar year, but it could last into February depending on any unexpected conditions or weather delays.