City's water supply is subject of study

<p>Clean water may be in short supply in Petaluma for quite some time if the aging pipeline that supplies water to the city ruptures in a major earthquake. A Sonoma County Water Agency study planned for this year will determine what can be done to protect the water supply for Petaluma in the event of such a catastrophe.</p><p>The Petaluma Aqueduct carries over 90 percent of the water used by the City of Petaluma, over 8 million gallons a day. The underground structure is 50 years old, has exceeded its predicted lifespan, and could rupture during an earthquake.</p><p>“The inherent risk for stream crossings is liquefaction,” said Kent Gylfe, Principal Engineer with the water agency, which provides water to much of Sonoma County and parts of northern Marin County. Liquefaction occurs when loose soils are subjected to pressure, such as a seismic event, that causes the soils to temporarily act like liquid. The severe damage in the Marina District of San Francisco in the 1989 Loma Prieta quake was due to liquefaction. Soils near water can be loose and sandy and especially prone to liquefaction.</p><p>How important is this issue locally? The local water system has survived plenty of seismic events, after all. “We have had earthquakes,” said Pam Tuft, Special Projects Manager for the Petaluma Department of Water Resources and Conservation. Tuft points out that Petaluma has had municipal water systems for a very long time. “The community (infrastructure) is incredibly old, we have pipes that are over a century old and they're still functioning.”</p><p>Steve Simmons agrees. The Utility Manager for the Department of Water Resources was here during the Loma Prieta earthquake and said that “we haven't had any issues at all” during that and other seismic events.</p><p>Like most Sonoma County cities, Petaluma drew its own water from municipal wells for decades. According to the Department of Water Resources website, the original water source for the community was the headwaters of Adobe Creek. In 1960, Petaluma leaders signed an agreement to receive water from the water agency and the Petaluma Aqueduct was completed in December 1961, 50 years ago last month. As a contractor of the water agency, Petaluma agrees to purchase water at guaranteed rates and the water agency handles a two-county distribution system.</p><p>The water agency owns and maintains a series of underground pipes that run from water collectors at Wohler Bridge near Forestville to northern Marin County. Significant funding for large maintenance and upgrade projects often comes from the Federal Emergency Management Agency, which requires the water agency to prepare a Local Hazard Mitigation Study every five years. The latest revision of that study is under way and will be published in January 2013.</p><p>According to Ann DuBay, Public Information Officer for the water agency, the updated plan will include the results from a study to be conducted this year on the Petaluma Aqueduct. “Our infrastructure is very sound,” said DuBay. “We will be doing testing of the aqueduct this year and we're hopeful that it's in good shape.” DuBay noted that a recent project in Santa Rosa allowed the water agency to closely inspect a pipe the same age of the Petaluma system and that engineers were pleased with the condition of the pipe.</p><p>While the Petaluma Aqueduct itself warrants monitoring and study, Petaluma is just part of an 85-mile system of water transmission lines. Being at the south end of the system means that any breakdown affects everyone downstream. Simmons recalled times over the years when the water agency had to shut down its system. By implementing conservation measures and using water held in storage, Petaluma was able to manage the temporary loss of its primary supply. “The county (water agency) has two or three days supply in storage, we have a couple of days ourselves, and we have the wells.” Simmons said.</p><p>Petaluma does have its own source of municipal water. Typically, it only comprises 2 percent of the city's water use, but in recent drought years, local wells were run more often and made up 10 percent of the city's average water use.</p><p>Petaluma City Councilmember Mike Healy would like to use more local groundwater for municipal use, and said as much recently during a discussion about water rate increases, but was overridden by concerns about drawing down the local aquifer. Healy said, “It's cheaper than relying on the water agency and it reduces velocities (of water) in the aqueduct,” </p><p>DuBay said that water conservation in Petaluma and elsewhere has made a big impact on the water agency's direction. With a reduced need for water the agency can focus on reliability of the system instead of growth. “People in Petaluma have changed their water use habits and there's less pressure in the aqueduct. It gives us an opportunity to make improvements.”</p><p>(Contact Ray Holley at argus@arguscourier.com)</p>