2009 E3 Design Honor

Twin Oaks Valley Water Treatment Plant DBO Project

San Marcos, California
ENTRANT: CH2M Hill
ENGINEER IN CHARGE: Daniel P. Wetstein, P.E., BCEE

CH2M HILL aerial site view June 2007. The Twin Oaks Valley Water Treatment Plant is located on 11 acres of a 45 acre site.	CH2M HILL site overview June 2007. Twin Oaks Valley plant one year into the construction process and less than one year from completion.	CH2M HILL building frame June 2007. Workers install the frame work of a building.
CH2M HILL installing building June 2007. A pre-fabricated building is installed. Using pre-fabrication when possible reduced costs for the San Diego County Water Authority.	CH2M HILL water pipes and worker. The pipes delivering water throughout the Twin Oaks Valley Water Treatment Plant are large in diameter.	CH2M HILL clearwell tanks during construction. Each large clearwell tank holds 7.5 million gallons of water.

Entrant Profile

The Twin Oaks Valley Water Treatment Plant is one of the largest treatment plants in the world to use submerged membrane technology to produce high-quality drinking water. The plant - San Diego County Water Authority's first treatment plant to build and own - was constructed under a design-build-operate contract by CH2M HILL. The high capacity plant provides enough water to serve approximately 220,000 households per year.

San Diego County Water Authority decided on the design-build-operate approach to reduce the overall cost of construction and allow for a rapid construction schedule. CH2M HILL was selected in October 2005, and the 100-million-gallon-per-day plant was operational in April 2008 - a period of only 30 months - providing the Water Authority's customers with a new source of water in time for the high-demand summer season.

The strategic location, creative design and state-of-the-art submerged membrane technology combine to make it environmentally-friendly and cost-effective. The $157 million facility also incorporates ozonation for disinfection and taste and odor control, biological activated carbon contactors, and on-site hypochlorite generation to eliminate chlorine transport. Additionally, the facility was designed and built with access to the region's emergency water delivery system so that treated water can continue to be sent to customers in the event of an emergency, without the need to issue boil water notices.

Key CH2M HILL personnel:

Daniel Wetstein, PE, BCEE
Richard Pyle, PE
Dennis Nelson, PE
Sue Frey, PE
Steve Payne
Curt Basnett, PE
Randy Denton, PE
Jack White

Project Description

Introduction

Project Description

San Diego County Water Authority realized the need for an additional water treatment facility in the region because a single treatment plant, owned and operated by another water district, provided most of the region's treated water; and had been operating at or near capacity for several years. The Water Authority decided on the design-build-operate approach to reduce the overall cost of construction and allow for a rapid construction schedule. CH2M HILL was selected in October 2005, and the 100-million-gallon-per-day plant was operational in April 2008 - a period of only 30 months after contract execution - providing the Water Authority's customers with a new source of water in time for the high-demand summer season. Final construction would continue past the start-up date.

Integrated Approach

Submerged membrane technology. The Twin Oaks Valley plant offers many benefits in addition to the high-quality water it provides. Its strategic location, a 40-acre site already owned by the Water Authority, creative design and state-of-the-art submerged membrane technology combine to make it environmentally-friendly and cost-effective. The state-of-the-art facility also incorporates ozonation for primary disinfection and taste and odor control, biological activated carbon contactors, and on-site hypochlorite generation to eliminate chlorine transport. Gravity moves water from/to the Water Authority's aqueduct system, eliminating the need for pumping. The submerged membrane technology is less expensive than conventional processes, uses fewer chemicals and produces minimal byproducts. Also, the design has a smaller footprint and required less concrete during construction than a similarly sized conventional process plant.

Environmental sensitivity. To reduce the facility's footprint, CH2M HILL established the plant on 11 acres, avoiding sensitive environmental areas that comprised part of the Water Authority's site. Additionally, arrangements were made with an adjacent construction site to utilize excess material for the facility. This eliminated more than 10,000 truck trips through the narrow valley in which the site is located.

Quality

Concurrent design, procurement, construction. The 30-month design, permitting and construction process required a complete team effort. The design process, including more than 800 drawings, was completed in six months, and seven early packages were provided to assist site work, pipe and equipment procurement, and foundations construction.

Community outreach. CH2M HILL and the Water Authority worked extensively with local neighborhoods to minimize disruptions. CH2M HILL met stringent noise requirements during construction and full-scale operations.

Met owner's time schedule. The facility began delivering water to the region as scheduled within 30 months of contract execution. The facility is designed and prepared to meet rigorous water quality standards for both now and in the future.

Originality and innovation

State-of-the-art. Twin Oaks Valley WTP is one of the largest facilities in the world to utilize state-of-the-art submerged membrane technology. The technology reduces chemical usage and creates fewer byproducts.

Zero discharge. The facility is a zero liquid discharge installation; 99.9 percent of the water that enters the plant leaves as treated product. It is highly automated and operates with a substantially smaller staff than comparable conventional plants.

Seismic faults. Since Twin Oaks Valley is located near active seismic faults, the project was designed to a specific seismic spectrum. Hydraulic structures are predominantly concrete so the reinforcing steel quantities were substantially greater than for conventional concrete construction. All electrical and HVAC supports were custom-designed for the building frame limitations and seismic resistance. Additionally, the plant is connected to emergency back-up water delivery systems which will allow it to continue to provide treated water in case of emergencies - eliminating the need for customers to boil water.

Complexity

Location. Twin Oaks Valley WTP is located in a narrow valley with varied terrain, environmental concerns and active seismic faults. The design and construction, from the reduced size of the facility to its actual location on the Water Authority's acreage, dealt with these concerns, as did the composition of the buildings. Connecting the plant to back-up water systems allows customers to avoid boil water notices in emergency situations.

Delivery schedule. The 30-month delivery schedule required teamwork and coordination from CH2M HILL and the Water Authority to not only design and build the facility, but get permits from several different agencies.

Social or economic advancement

Safe working environment. Employees worked more than 925,000 man-hours with only one lost-time injury; this safety performance is far superior to industry standard expectations.

Reduction of treated water shortages. The high quality water that Twin Oaks Valley provides reduces concerns of water shortages in this quickly growing area by providing an additional supply of treated water, relieving reliance on a single plant that served the majority of the region and was operating at or near its capacity. The plant will provide consumers with water for many decades.

Treated water through emergency back-up system. Additionally, the facility was designed and built with access to the region's emergency water delivery system so that treated water can continue to be sent to customers in the event of an emergency, without the need to issue boil water notices.

Community involvement. Finally, the Water Authority and CH2M HILL worked with the community to integrate the facility into the neighborhood and minimize disruptions. Meetings were held to discuss appearance of buildings and structures, color schemes, and landscaping. The facility is one that residents can be proud of and depend on for years to come.

CH2M HILL worker inspects pipes. The combined DBO approach allowed CH2M HILL to start construction and procurement of pipes before final designs were completed.	CH2M HILL construction 2008. Protected environmental areas are near the work site and the design and construction teams took care to avoid them.	CH2M HILL scope of pipes. The worker on the ground and those on the walkway above give perspective on the size of the pipes that crisscross the water plant.
CH2M HILL facility testing. Every step of the way testing was done to ensure high-quality water would be delivered as soon as the plant became fully operational.	CH2M HILL submerged membrane technology. The 100-million-gallon-per-day water plant uses submerged membrane technology and is one of the largest facilities in the world to do so.	CH2M HILL think safety. Think safety is CH2M HILL's motto, each and every day. Twin Oaks Valley Water Treatment Plant was built with workers putting in more than 925,000 hours and only one lost time injury; well below industry standards.