World’s Largest Submerged Membrane Water Treatment Plant Operating at
Twin Oaks Valley Near San Marcos

Short Title
World’s Largest Submerged Membrane Water Treatment Plant Operating at
Twin Oaks Valley Near San Marcos
Water Authority holds ribbon-cutting to dedicate new facility
May 05, 2008

The reliability of the region’s treated water supply will be greatly enhanced by world’s largest submerged-membrane water treatment plant is now in operation just north of San Marcos.

“The state-of-the-art Twin Oaks Valley Water Treatment Plant reduces the region’s reliance on treated water from outside the county,” said Fern Steiner, Water Authority Board Chair, at a dedication ceremony today at the facility. “It will give our residents and businesses much greater protection from treated water shortfalls during future warm-weather months and provide more local control of the county’s treated water supply.”

The plant, which has a capacity of 100 million gallons per day of treated water (enough for 220,000 families annually), began delivering water into the Water Authority’s distribution system April 7. Prior to the completion of this facility, nearly half of San Diego County’s drinking water came from the Metropolitan Water District of Southern California’s Skinner Filtration Plant in Riverside County.

The Water Authority selected the submerged-membrane treatment process because it is efficient, environmentally friendly and produces high-quality drinking water. The plant treats virtually all the untreated water entering the plant, eliminating almost all wastewater. Submerged membrane treatment uses fewer chemicals than conventional treatment, so fewer supplies need to be trucked in, there are fewer byproducts from treatment and there is less waste disposal required. The membrane treatment, in conjunction with the other processes at the plant, has such a high degree of contaminant removal that the plant will be able to meet increasingly rigorous state and federal water quality regulations.

In the membrane treatment process, untreated water is drawn through very fine pores in membrane fibers. The pores are just large enough for water molecules to pass through, but small enough to leave behind contaminants and particles, such as dirt, dust, bacteria, cryptosporidium, giardia, and others. By 2010, these systems are expected to produce more than a billion gallons of high-quality drinking water per day.

The Water Authority selected the Twin Oaks Valley site because it allows treated water to be delivered by gravity to the existing aqueduct system. This eliminates the need for energy-intensive pump stations or new pipelines. In addition, the plant enables the Water Authority to deliver treated water through its emergency water delivery system rather than untreated water, eliminating the need to issue boil-water notices. Integrating the treatment plant with the emergency system will keep treated water flowing in the event of an earthquake or other interruption in imported water deliveries.

The Twin Oaks Valley plant must adhere to rigorous health standards and will be monitored by state and federal drinking water regulatory agencies. The plant also meets safety requirements for the chemicals used in water treatment.

For the next 15 years, the Water Authority will share the operational responsibilities of the Twin Oaks Valley plant with Operations Management Inc, an affiliate of the internationally recognized water infrastructure firm CH2M HILL Constructors, Inc. The Water Authority owns the facility and has the ultimate responsibility for the plant’s safe and efficient operation.
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