AWWA INF52165

The Vallecitos Water District (District) located in northern San Diego County, California, operates a highly efficient water infrastructure system consisting of pumping, storage, transmission, and disinfection facilities. VWD is a rapidly growing district providing water service to over 15,000 customers. Currently, the District is experiencing rapid growth which necessitates the expansion of the District's infrastructure. The need for a reservoir was driven by two conditions: a State of California, Department of Health Services directive to cover or abandon an existing open Twin Oaks Reservoir; and the need to provide additional operational and emergency storage to meet rapidly growing demands. The District is also entirely dependent on imported potable water. The additional storage would help enable the District to provide water service in the event of a disruption in the water supply due to disaster or scheduled maintenance shutdowns. The District prepared a Master Plan in 1991 that recommended a 52 million gallon (mg) water storage facility at the Twin Oaks Reservoir site. The 66mg Twin Oaks reservoir consists of twin 33mg circular pre-stressed tanks. Construction of the first tank was completed in September 1999. The second tank is planned in 5 to 7 seven years or when water demands require it. The construction of the first tank is believed to be the largest structure of its kind within the United States. Due to the size of the reservoir, special considerations were taken into account during the planning, design, and construction of the facility.