San Marcos reservoir set to serve

The Vallecitos Water District (VWD) in San Marcos, Calif., has completed construction of a project that will ensure the district’s ability to supply water well into the future. The Twin Oaks Reservoir – a concrete, circular tank wrapped in pre-stressing strand – was built last year and is, according to VWD, the largest reservoir of its kind in the world. Holding 33 million gallons of water, the facility is scheduled to go on line this month.

VWD is an independent special district serving approximately 62,000 customers within a 45-square-mile area in north San Diego County. In 1991, district officials called for the construction of two tanks as part of a master plan to expand the area’s water storage capacity and to replace an 8.9-million-gallon open reservoir. (California requires that water stored in open reservoirs be treated more extensively than water held in closed facilities.)

The project got under way in 1995, when VWD bought 29 acres of rural land in the northern portion of the district. Also that year, Pasadena, Calif.-based ASL Consulting Engineers prepared a pre-design report recommending that VWD construct two buried, 33-million-gallon, circular reservoirs. The district decided to move forward with one tank and review the need for a second tank at a later date.

Anaheim, Calif.-based C.W. Poss began mass grading in September 1997, and the general contractor – Gateway Pacific Contractors, Sacramento, Calif. – broke ground on the Twin Oaks Reservoir in April 1998. Measuring 392 feet in diameter, the tank contains roughly 200 miles of pre-stressing strand installed on the exterior by DYK, El Cajon, Calif. Additionally, Speiss Construction, Santa Monica, Calif., installed approximately 4 miles of 36- and 42-inch pipeline to connect the tank to the rest of the district’s distribution system.

Water from the Twin Oaks Reservoir will be able to reach nearly 95 percent of the district. It also will provide additional security during unexpected interruptions of water service and annual maintenance shutdowns.

The $25 million project – including land acquisition, grading, tank construction and pipeline installation – was financed primarily with water revenue certificates of participation. The certificates were issued in March 1998 and are scheduled to be fully repaid by July 2030. The district plans to repay the certificates using money from the capital improvement projects reserve and customer “replacement” fees, which are collected on water bills and allocated for fixing or replacing aging facilities.

With the completion of the first phase of the Twin Oaks Reservoir site, VWD has nearly doubled its overall storage capacity. “With the population and construction currently booming in our service area and projected growth in the years to come, Twin Oaks Reservoir will provide a long-awaited, crucial component of the district’s storage and distribution system,” says Dennis Lamb, director of engineering and operations for VWD. The district expects to review the need for the second reservoir in about five years.