Project Description

The Twin Oaks Valley Water Treatment Plant is the largest submerged membrane water treatment plant in the world and the first treatment plant built by the San Diego County Water Authority. Construction was completed under budget and on schedule, in April 2008.

Located next to the Water Authority’s aqueduct in a semirural area north of the city of San Marcos, the high-capacity treatment plant produces up to 100 million gallons of treated water per day -- enough to supply up to 220,000 typical four-person households each year.

Project Fact Sheet

Submerged Membrane Fact Sheet

Why Was the Water Treatment Plant Needed?

The Water Authority identified the need for a new water treatment plant in San Diego County in 2004 to:

• Increase the treated water supply for the county.
• Avoid supply shortfalls during warm-weather months when water use was highest.
• Reduce the San Diego region’s reliance on treated water from outside the county.

Location Map

Printable version

Treatment Plant Benefits

The Twin Oaks Valley Water Treatment Plant is a project with many benefits beyond the high-quality water it produces. Its strategic location, creative design, and use of membrane technology make it an efficient, money-saving facility.

• High Volume – Each day 100-million gallons of water can treated at the facility.
• Scarcely a Drop Wasted – Nearly all water entering the plant leaves as high-quality drinking water.
• Energy and Money Savings – The plant’s location next to the Water Authority’s existing pipelines made pumping and new pipeline construction unnecessary.
• High Quality – The facility not only meets current regulations, but is prepared to meet more rigorous water quality regulations anticipated in the future.
• Emergency Water Availability – The plant can supply treated water to the region’s emergency water system if catastrophe strikes (no water boiling required).
  

About Water Treatment

Water from rivers and reservoirs can contain a variety of organisms and inorganic material that must be removed at a water treatment plant before the water is safe for drinking and other uses. Treatment plants vary in the specific processes they use, but they generally follow the same basic steps.

Larger particles such as sand, vegetation and other materials must be screened out first, then smaller particles are removed in a separate process. To eliminate organisms that can cause disease or unpleasant odors and taste in water, disinfecting chemicals are added. In many treatment plants, water passes through an additional filtering medium such as sand, gravel, carbon or anthracite, to remove any remaining tiny particles. The last step is to apply an additional, long-lasting disinfectant that will keep water safe and healthy for the days or weeks it may travel through pipelines to reach homes and businesses.

The Water Authority selected the submerged membrane method for treating water at the plant. This method of separating water molecules from contaminants is safe and highly effective in producing high-quality treated water. 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.

What is Submerged Membrane Water Treatment?

Water treated at the Twin Oaks Valley Water Treatment Plant is drawn through very fine pores in membrane fibers. The pores are just large enough for water to pass through, but small enough to leave behind contaminants and particles, such as dirt, dust, bacteria, cryptosporidium, giardia, and others. The contaminants that do pass through are eliminated in a disinfection process. In addition, as part of the treatment process, fluoride is added to the treated water.

Please refer to the Submerged Membrane Fact Sheet for more information.

Connected to Emergency Water Delivery

In the event of a prolonged drought or earthquake, the delivery of imported water from Northern California and the Colorado River could be interrupted. The Twin Oaks Valley Water Treatment Plant’s strategic location enables the Water Authority to provide an emergency supply of treated water, eliminating the need for consumers to boil water. Integrating the treatment plant with the Emergency Storage Project will keep high-quality drinking water flowing in the event of an earthquake or other interruption in imported water deliveries. Click here to learn more about the Water Authority’s Emergency Storage Project.

One Contract, Many Benefits

Creating a new facility like the Twin Oaks Valley Water Treatment plant requires many phases of work: design, permitting, obtaining materials and equipment, construction, and operation. Rather than having multiple contracts for these efforts, the Water Authority combined them and awarded a single contract to one company, CH2M HILL Constructors Inc. CH2M HILL designed, built, and operates (DBO) the facility. The DBO approach accelerated the project by combining three contracts into one and improved coordination between the design and construction teams and the operators of the completed plant. For 15 years, the Water Authority will share the operational responsibilities of the Twin Oaks Valley plant with its DBO contractor. The Water Authority retains ownership of the facility and has the ultimate responsibility for the safe and efficient operation of the plant. Key DBO benefits include:

Saving Time – By overlapping design and construction efforts and eliminating multiple redesigns and contract bidding, the DBO approach enabled the project to be completed approximately one year ahead of time.

Saving Money – The resulting time savings translates into lower costs and earlier operation of the facility. Further, guaranteed construction costs were known much earlier using the DBO contract method.

Publications

Project Fact Sheet

Submerged Membrane Fact Sheet

Twin Oaks Valley View Newsletter:

• Fall 2008
• Spring 2008
• Summer 2007
• Fall 2006
• Fall 2005
• Winter 2005

Community Outreach

We’re Committed to Our Neighbors

The Water Authority values community input and strives to provide clear, open communication early in the planning process on its construction projects. This commitment to the Twin Oaks Valley community prompted the formation of the Twin Oaks Valley Working Group. Working group members included Twin Oaks Valley residents, a business owner, and representatives from the Twin Oaks Valley Sponsor Group and the Twin Oaks Valley Property Owners’ Association.

The working group identified 50 suggestions to improve traffic, noise, lighting, chemical safety, landscaping, and visual impacts. Thirty-five of the working group’s ideas were incorporated into the design, construction and operation of the water treatment plant. These contributions to the design process helped the Water Authority build a better facility. Throughout the facility’s operation, the Water Authority will work hard to minimize impacts and be a good neighbor.

Working Group - Summary Report (November 2004)

Letters and postcards to community:

• Postcard Update - January 11, 2008
• Grading work Postcard April 2007
• 24-hour Work Notification Letter – November 14, 2006
• Construction Update Meeting Invitation – June 24, 2006
• Construction Postcard - January 18, 2006
• Construction Notification Letter – December 13, 2005
• EIR Approval Meeting Postcard – August 23, 2005
• First Working Group Meeting Postcard - March 23, 2005
• Geotechnical Work Postcard – February 4, 2005
• Sept. 1, 2004 Letter
• July 14, 2004 Letter
• Project Open House Postcard - June 30, 2004
• June 16, 2004
• April 9, 2004

Meeting summaries:

• Oct. 12, 2004
• Sept. 28, 2004
• Sept. 14, 2004

• Oct. 17, 2007
• Nov. 15, 2006
• Nov. 17, 2004
• July 21, 2004