The National Ground Water Assn. (NGWA) announced that ...
The Los Vaqueros project, the first major water project to be built in northern California in over a decade, was recently completed in a valley 45 miles east of San Francisco. The result of a collaborative planning process in which environmental issues were put on equal footing with technical and financial considerations, Los Vaqueros will provide better water quality and reliability for over 400,000 customers of the Contra Costa Water District (CCWD).
Los Vaqueros taps high-quality water from a new intake at the Old River in the Sacramento-San Joaquin Delta for blending with water from an existing source when the salinity levels rise during dry periods. A new 100,000-acre-foot off-stream reservoir stores a 3-month water supply for emergencies (a significant increase over the former 3-day supply) and gives spawning fish a 30-day respite from pumping each spring. The $450-million project is composed of a 192-foot earth-filled dam nine miles south of Brentwood, a pumping plant on Old River, a transfer facility, 15 miles of large-diameter AWWA C300 reinforced concrete cylinder pipeline, and five miles of MLMC steel pipeline.
A century ago, los vaqueros (the cowboys) grazed cattle in the valley that now holds the reservoir. At the inception of CCWD some 40 years later, the area remained primarily agricultural, and salinity was not the concern it is today for the district's residential and municipal customers. The problem was that the district's primary intake, the existing Rock Slough intake in Oakley, is close enough to San Francisco Bay to be adversely affected by salt water intrusion during dry periods. Desalinization was not a feasible alternative. Not only does it use a great deal of energy, but it also creates a mineral-laden byproduct requiring disposal.
The Los Vaqueros project, in creating a new intake six miles farther from the bay and a reservoir, gives CCWD the flexibility to divert higher-quality water directly to the Contra Costa Canal, the main artery to customers. The district also can store this good-quality water in the newly built Los Vaqueros reservoir. Whenever salinity increases in the water at the Rock Slough intake, CCWD now can blend it with the stored water, maintaining consistent quality all year.
CCWD identified 126 ways to achieve its dual objectives of consistent water quality and reliability. The district's goal was to select the least environmentally damaging practicable alternative. Following a rigorous feasibility analysis, the alternatives were narrowed to five. Some alternatives failed to achieve both quality and reliability; others, such as desalinization, were not economically feasible; still others, such as a dam and reservoir upstream of the current project, would have resulted in greater impacts on animals and plants. Los Vaqueros emerged as the CCWD's preferred alternative.
One of the major challenges was a continually shifting regulatory environment. The Sacramento-San Joaquin Delta Estuary was undergoing constant change. A major water source for southern California's agricultural area, the delta had been seriously affected by increasing demand over the years. Each change in environmental requirements for projects affecting the delta called for analyses of project operations.
CCWD met these challenges through a dedicated use of resources. The district's staff includes experts in water issues and computer modeling. This modeling is a tool being relied on heavily in planning California's water future. More than 200 studies were conducted to describe alternatives for operation of the Los Vaqueros Project during long-term hydrologic cycles.
Ultimately, CCWD had to show that the Los Vaqueros project would have a net environmental benefit to the delta. The ability to store water in the off-stream reservoir means that neither the Rock Slough nor Old River intakes must operate continuously, as Rock Slough had in the past. This enables CCWD to shut down both intakes for 30 days each spring, when Chinook salmon and Delta smelt are spawning. In fact, this is the key environmental benefit of the Los Vaqueros Project, and an important example of the results of this collaborative approach.
The district also has an active public communication program in place. During this project, the program included sharing information and progress reports about Los Vaqueros through community newsletters, fact sheets, a web site, and a telephone hotline. In 1988, CCWD received voter authorization to sell municipal bonds to finance the project.
During the planning process, it was known that the area near the proposed dam and reservoir was likely to contain human remains and artifacts of prehistoric people. Beginning in 1994, tests were conducted at nine sites in the area. Archeological excavations revealed burial sites that were more than 2,000 years old, as well as numerous artifacts believed to be up to 8,000 years old. CCWD worked very closely with representatives of the local Native American community and experts from Sonoma State University to develop and carry out plans for cataloging and conserving archeological discoveries and reburying human remains.
The contractor, ARB Inc. of Brentwood, California, selected the pipe based on CCWD's performance specifications. Reinforced concrete cylinder pipe (AWWA C300) was selected because of the ease of installation that resulted in reduced cost compared with steel, given the poor supporting strength of the soils at the site.
Under these conditions, use of steel pipe would have required the contractor to substantially increase the volume of the excavation to provide the necessary compaction for support of the pipe. The design pressure for the pipeline ranged from 50 to 175 psi, and earth cover from 8 to 40 feet. A six-inch layer of pea gravel and geotextile fabric was used as pipe bedding.
Ameron International furnished the reinforced concrete cylinder pipeline from its Tracy, California, plant. That plant is certified by the American Concrete Pressure Pipe Association, under its third-party, audited, compliance audit and certification program to produce concrete pressure pipe according to AWWA standards.
Geological conditions posed other challenges as well. Soft peat at the Old River intake site required the facility's perimeter to be stabilized with 1,500 stone columns sunk 40 feet into the ground as well as 152 composite concrete and steel piles supporting the intake structure.
However, the most significant engineering challenge of the project arose when geotechnical studies showed that the rock on the left dam abutment had several fissures that were up to a foot in width. Working closely with the California Department of Safety of Dams and a team of technical consultants, the contractor excavated this unstable rock and installed a concrete overlay that solved the problem.
Construction of the Los Vaqueros Project began in 1994. By the end of 1997, most of the system's components were in place (the new 13-mile road around the 18,500-acre watershed; the dam and spillway; the new intake and transfer facilities; and the pipeline) and testing was underway. Early 1998 saw the first surge of water from the Old River intake into the reservoir. It is expected to fill to 100,000 acre feet. Even before that, customers began to benefit from the better quality water diverted to the Contra Costa Canal.
Now and in the future, Los Vaqueros will provide consistent water quality and reliability for the people throughout the Contra Costa Water District.