Levy Water Treatment Plant

"Meeting San Diego County's Growing Water Needs"

What is the best way to upgrade and expand a water treatment plant on a fast-track schedule — without interrupting the facility's operations?

MWH faced this challenge with the R.M. Levy Water Treatment Plant (WTP) Project in San Diego County, California. The US $46 million project for the Helix Water District received recognition from the San Diego/Imperial Counties (California) Chapter of the American Public Works Association. It was honored with the "Project of the Year Award" in the Environment category for projects over $10 million.

Two-Tier Project

The MWH project was comprised of two components:

• Upgrading and expanding the existing Levy WTP
• Designing and constructing new ozone disinfection and mid-plant pumping facilities

The major elements of the upgrade and expansion project included:

• Hydraulic improvements to the plant influent channel
• Improvements to flocculation/sedimentation basins
• Two new dual media filters
• Second filter washwater tank
• New chlorine contact basin
• New chlorine storage building
• Replacement of chemical storage facilities
• Secondary containment tanks for treatment chemicals
• Relocation of waste washwater sump
• New solids lagoon
• Upgrades to laboratory and operations building

The Levy WTP is the first municipal water treatment plant in the county with full-scale ozone disinfection facilities.

This allows the region to treat local water at all times during the year. Previously, taste or odor problems meant local water supplies couldn't always be used. Ozonation effectively removes these aesthetic problems and makes local water available more often.

That's important in San Diego. Only 19 percent of raw water supplied to the treatment plant is from local sources (Lake Jennings, El Capitan Reservoir and Lake Cuyamaca). Approximately 81 percent of the raw water supplied to the treatment plant is imported (State Project Water and Colorado River).

MWH designed the ozone disinfection facilities with a number of unique features, including:

• An in-plant pump station using four Archimedes screw pumps to provide simple and reliable control of flow rates through the ozonation system
• A balanced flap gate in the pump station influent channel that bypasses flow around the ozone plant in case of a power outage

A shortage of available space required MWH create a compact design for the ozone facilities. Experts built the ozone equipment, controls and tour areas on top of ozone basins. This required careful attention to the routing of piping between the generation building and the galleries below.

3-D Computer-Aided Design

Scheduling constraints put the ozone disinfection facility on a fast-track schedule. MWH employed a 3-D computer-aided approach to speed up the review time and allow the design phases to continue uninterrupted.

Using 3-D computer-aided design allowed engineers, plant operators and maintenance staff to visualize the proposed facilities. They could then identify beneficial changes to the design. MWH's approach substantially reduced design review time and changes.

The Levy WTP remained in service during construction. To accomplish this feat, MWH paid special attention to construction phasing and establishment of tie-in points. MWH scheduled critical tie-ins around routine plant maintenance shutdowns. This allowed the plant to stay in service until the new connections were made during a planned shutdown.

Imported Water Treated

MWH took into account the high percentage of imported water treated at the Levy WTP. The facility was designed to respond effectively to a range of water quality changes resulting from the multiple water sources. In addition to ozone control methods, the plant incorporates specific chemical treatment processes to accommodate variations in raw water quality.

Educational Benefits

The Helix Water District provides educational programs for approximately 6,500 students each year. MWH designed the new facilities to accommodate hands-on models, observation areas, special effects and assembly areas where educational videos are shown.

The educational components included pre- and post-tour modules that focus on the science and technology of the water treatment process and meet California's State Content Standards in science — as well as in math, history, geography and English.

Special tours also accommodate youth groups, nursing students at local colleges, water quality supervisors from other water districts, community groups and business leaders.