Water customers in Santa Rosa and Sonoma should avoid projects such as watering the lawn or filling swimming pools on Wednesday and Thursday as the Sonoma County Water Agency works on a key water line under Sonoma Avenue, known as the Santa Rosa Aqueduct.

The agency will shut down the 36-inch pipeline for about 27 hours starting on July 31 to finish a major upgrade that will make the line less vulnerable to earthquakes.

The agency installed about 2,000 feet of new pipe earlier this year in the section of the water line that crosses the Rodgers Creek Fault. That is the point most vulnerable to earthquake damage anywhere in the system, Project Manager Steve Koldis said.

The work this week involves installing new valves at each end of the new pipe, which is more flexible and less likely to break in an earthquake.

Customers will not lose water service during the shutdown, Koldis said, since there is water in reserve in tanks at Spring Lake. Conserving water over those two days, however, will help maintain the water level in the tanks while the main is shut down.

Glen Wright, deputy director of water and engineering resources for the City of Santa Rosa, said there should be plenty of water in agency tanks and city-owned reservoirs to meet the needs for two days of the 18,000 affected water meters in Santa Rosa, in addition to customers in the Valley of the Moon system, but conservation is still a wise precaution.

"We should be fine, but the problem could come if the contractor has an issue and the shutdown lasts longer" than expected, Wright said. "We don't want to take that chance."

Motorists on Sonoma Avenue will experience delays between Farmers Lane and Brookwood Avenue on Aug. 1 as a result of the work, the agency warned Monday.

This is the last major phase of the $3.4 million project, Koldis said, but there is some remaining surface work in the area, including replacing the pavement removed to install the pipe. That work should be finished by the end of August.

There are three more earthquake-related projects still in the works, but none should be as disruptive to the public as replacing the main under Sonoma Avenue. One project will be to install 20 new isolation valves at various parts of the system to make it easier to shut down pipes in the case of major earthquake damage.

The other two projects will be to strengthen the pipelines that cross the Russian River and Mark West Creek. Those pipes are buried in relatively shallow soil that could shift in the case of an earthquake, damaging the pipes. The agency will bury those pipes more deeply to surround them with more stable soil.

Each of the remaining projects will cost as much as $4 million. About three-quarters of that will be paid by a grant from the Federal Emergency Management Agency, which put up $1.3 million for the Santa Rosa Aqueduct upgrade.

You can reach Staff Writer Sean Scully at 521-5313 or sean.scully@pressdemocrat.com.