The District has a diverse water supply portfolio that allows for operational flexibility in the event of a drought, conditions at Lake Cachuma, or during an emergency. The ability to draw on multiple supply sources to meet customer demand, known as blending, is a critical tool for maintaining reliable water service to the Goleta Valley.
What is blending?
Blending operations involve supplying the distribution system with both surface water and groundwater. The District’s primary water supply consists of surface water from Lake Cachuma which is supplemented with imported water from the State Water Project. During blending operations, groundwater from nine District wells is pumped into the lowest elevation areas of the distribution system. Pumps at the District’s Patterson Pump Station are used to move groundwater to higher elevations of the the distribution system.
Why blend?
Blending provides operational flexibility, allowing the District to draw on multiple supply sources, respond to seasonal changes, and maintain consistent water delivery in case of supply interruptions from Lake Cachuma.
How does blending work?
Blending requires significant infrastructure including reservoirs, groundwater wells, pumps, motors, as well as valves and pipelines. Together, this equipment efficiently moves water throughout the system and maintains consistent pressure and fire flows. Switching between water supply sources reverses the flow of water in the distribution system, resulting in dissolved oxygen in groundwater escaping to create entrained air, or the loosening of mineral deposits that have accumulated over time in the distribution system pipes. To reduce the build-up of mineral deposits, the District periodically flushes water through the system.
What are the challenges of blending?
Blending is energy intensive and involves complex operation of the system. The District’s infrastructure was originally designed to deliver water from Lake Cachuma downhill using gravity to move water through the system. This gravity-fed design has required modification over time to be able to move groundwater to higher elevations. The location and number of groundwater wells, as well as pipeline sizing, also constrain blending operations. Many of the wells and pumping stations that were intended for use in emergencies have now been placed into permanent service, requiring a redesign of that infrastructure.
Maintaining adequate supplies and balancing the delivery of diverse water supply sources is more resource intensive and comes at a higher cost, but the flexibility and redundancy it provides is increasingly necessary to maximize service reliability. Over time, the District will further optimize system operations to help reduce the costs of blending.
