To keep up with growing demand for potable water and a decreasing imported water supply, Southern California’s Irvine Ranch Water District (IRWD) adopted progressive water reuse and conservation standards and began ambitious capital improvement projects. The Michelson Water Reclamation Plant (MWRP) Phase 2 Expansion Project increased capacity of MWRP from approximately 18 million gallons per day (MGD) to 28 MGD. IRWD hired Tetra Tech to serve as a key partner in the design and construction engineering services for the project.

About 20 percent of IRWD’s current supply is recycled water, enough to provide landscape irrigation for 80 percent of the District’s business and community customers—including parks, school grounds, and golf courses—keeping IRWD’s water rates among the lowest in Orange County. The MWRP Phase 2 Expansion allowed IRWD to continue providing water to meet the community’s needs while decreasing IRWD’s dependence on imported potable water.

Tetra Tech was a key partner in the design and construction engineering services for the project. Improvements to the plant during Phase II included upgrades and additions to all portions of the plant. Upgrades included improvements to influent sewers, installation of a new headworks facility, addition of new sedimentation tanks, expansion of flow equalization tanks, a new aeration blower, construction of a membrane bioreactor, high-rate clarifiers, chlorine contact chamber improvements, ultraviolet disinfection facility, new water pumps, and an electrical system expansion. 

The team worked to replace the influent sewers that feed the plant from the north and south and joined them at a new junction structure that connected to the newly constructed headworks facility. The team designed this new facility to include three automatically cleaned screens and three vortex grit chambers. The headworks was constructed to handle average flow of 33 MGD and peak flow of 63 MGD.

In addition, four new primary sedimentation tanks were added to supplement the five existing tanks for a total capacity of 33 MGD, and the existing flow equalization tanks were expanded. A new primary effluent pump station was constructed to direct flow to the existing secondary treatment process and the newly constructed bioreactor. A new aeration blower also was added to the existing secondary treatment system to provide backup for the treatment process.

A 10 MGD membrane bioreactor, which is expandable to 15 MGD, was constructed to increase tertiary capacity. This cutting-edge process includes treatment basins similar to the typical secondary treatment process, but will replace the sedimentation tanks and dual-media filters with membrane filters. The result is high-quality water that can be disinfected without further treatment for reuse.
The high-quality water produced by the new membrane bioreactor is disinfected using ultraviolet light. The water flows by gravity in concrete channels past ultraviolet lights. The new ultraviolet disinfection facility will provide an initial capacity of 10 MGD day with the ability to expand to 15 MGD.
Disinfected water from the existing chlorine contact chamber and the new ultraviolet disinfection system will be blended and pumped for reuse at the existing recycled water pumping station. Two new 600-horsepower pumps will be added to the pumping station to supplement the four existing pumps, resulting in a station pumping capacity of 28 MGD.
The project site was located on difficult peat soil. Tetra Tech designed the structures and influent pipelines that were constructed on approximately 1,800 precast, pre-stressed concrete piles driven through the upper layers of incompetent soil and into suitable soils. The piles vary in length from 30 to 60 feet and provide vertical and lateral load resistance for the structures they support. An aggressive vibration monitoring program was established to prevent damage or disturbance of neighboring structures during the pile installation process. 
Tetra Tech designed the expansion of the electrical system, which involved a site lighting study and design, fiber optic system upgrade, added capacity for a 100 percent increase in demand load, and enhanced plant reliability by adding a 12 kilovolt (kV) service feed from Southern California Edison (SCE), a 12 kV SCE substation, 5 kV unit substations, and emergency generators. 
The Michelson Water Reclamation Plant provides tertiary treatment of wastewater resulting in excellent quality recycled water that is used for landscape and agricultural irrigation and industrial and commercial needs in Orange County. 
View a video about this project here.