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March 28, 2001: Water Online


Small water districts have similar short- and long-term engineering needs as do their larger counterparts. But because they only service at most a few thousand customers, their operating budgets are much smaller and therefore they not only have to watch the dollars carefully, but also usually retain an outside engineering firm to serve as District Engineer.

Such is the case with the Purissima Hills Water District. Established in 1955, the District serves 2,100 commercial and residential customers in Los Altos Hills, CA, an affluent Silicon Valley city located about 35 miles south of San Francisco. The District has eight employees and an operating annual budget of $2.5 million.

According to Patrick Walters, the District's general manager, Berryman & Henigar has served as District Engineer since 1991 and has provided project management, design and construction management services to help with the District's master Capital Improvement Plan (CIP), and has served as a resource to the general manager and board members. Key projects have included:

  • Distribution system improvements
  • Pump station design and improvements
  • Seismic modifications
  • System hydraulic model development and distribution system analysis
  • Tank painting and safety modifications

"Our CIP budget is about $1.7 million for this fiscal year," Walters said. "Because we're a small water district, it's not cost-effective for us to maintain an in-house engineer. By having an outside firm serve as our District Engineer, we're able to ramp up and down depending upon how many projects we have going."

One of the tasks the District has outsourced is the Neary Tank Inlet/Outlet Modifications project. The Neary Tank is a three million gallon storage facility that will be susceptible to nitrification due to low turnover in the stored water, when the San Francisco Water Department, which sells water to the District, converts to chloramine in 2003. Chlorine is currently used to disinfect the water supply.

The solution for the District called for modifying the single inlet/outlet by installing HPDE pipe along the diameter of the tank with separate inlets/outlets at opposite sides of the tank. The new inlet and outlets are equipped with flexible fabric-type check valves installed at different angles that improve the water mixing. In addition, District crews installed the piping, which saved approximately $50,000 compared to going through the bid process.

Another major project involved the design of 6,200-linear feet of 12-inch pipe and 700-linear feet of 8-inch pipe, which were needed to replace undersized and deteriorating mains installed in 1955. This project, completed in December 2000, will improve fire protection in the area, because it provides a high pressure, large diameter main, interconnected to the system at several locations. This allows water to be fed simultaneously from several directions, improving fire flows and reliability.

"We also used a software program, WaterCAD, which models the distribution system that showed us best/worse case scenarios once the pipe was installed," Walters said. "This was very helpful as it demonstrated what the new hydraulics would do in the system and showed how the water would flow."

Additional CIP projects the District will be implementing include drilling a well and building a retaining wall at the Neary tank site.

"We need a well for emergency purposes in case we are cut off from the San Francisco's Hetch Hetchy system, our sole water source," Walters said. "The District Engineer will determine where the well should be drilled and help us in selecting a well driller."

Retaining wall construction is slated to begin this spring and will be about 12-feet high. The retaining wall will prevent erosion of the access road along the east side of the Neary tank.

"Our CIP program is paramount in order to effectively reduce system maintenance and provide the most reliable and highest quality water service to our customers," Walters said. "Having a qualified District Engineer to manage many of these tasks helps us be more productive which results in a cost savings for the customer."

Return to: 2001 Feature Stories