Property owners in the coastal California city of Malibu preferred a local wastewater treatment solution to a regional approach. The choice is proving to be beneficial.

Under government orders to phase out of septic systems, the oceanfront community of 13,000 chose to construct its own collections system and deliver wastewater to a state-of-the-art treatment and recycling plant. The alternative would have been to hook up to the neighboring Los Angeles County sewer system.

“Even though residents get their drinking water from the LA Water, I think they felt the extension of sewer lines from Los Angeles would lead to unwanted development and would ruin the small-town character of the community,” Rob DuBoux, P.E., Public Works director.

The Civic Center Water Treatment Facility, so-called because it serves the area around the Civic Center, is rated at 200,000 gpd. It began operating last October, staffed by the private firm Integrated Performance Consultants. “The company provides a Grade 5 lead operator and two Grade 3 operators during normal business hours,” DuBoux says. “During off hours, they are able to monitor plant operations remotely.”

The plant was named 2018 Project of the Year by the American Public Works Association Southern California Chapter and 2018 Plant of the Year by the WateReuse Association.

Phased approach

The plant and its companion collections system represent phase one of a long-term plan to rid the area of septic systems and operate a community-based water treatment and recycling facility. The plant, designed by Woodard & Curran, serves 57 properties in the Civic Center area, mainly commercial establishments with a few residential properties mixed in.

In phase two, a larger area of the community, consisting of houses and condominiums, will be added to the collections system by 2024. Phase three, which would expand the system to the rest of the community, depends on water-quality testing in phases one and two. The phased approach was laid out in a memorandum of understanding between the city and the state’s regional water control board.

DuBoux praises a collaborative approach that helped both the utility and property owners understand the problem and the solution. “We had a number of stakeholder meetings with property owners,” he says. “We kept them informed and dealt with questions they had about project unknowns. I think it eased their minds.”

The process also helped the staff get to know the property owners and hear their concerns. In the end, residents were happy the city would process their wastewater and they wouldn’t have to worry about septic systems. “We were a bit surprised they were so receptive to that,” DuBoux says.

Treat and recycle

The new plant is equipped with the latest technologies, enabling it to produce effluent that meets California Title 22 standards for reuse as irrigation or secondary source water. The flow enters through in-channel coarse screens (Veolia Water Technologies) and then passes through a vortex grit chambers and rotary-drum fine screens (WesTech Engineering).

An equalization basin regulates the amount of wastewater sent through the system. Biological treatment occurs in a membrane bioreactor containing submersible pumps (Flygt - a Xylem Brand) and fine-bubble diffusers (Environmental Dynamics International). The water is disinfected in a TrojanUVFit UV system. Solids are thickened and trucked to the Joint Water Pollution Control Plant in Carson; the material is ultimately composted, land-applied or landfilled.

With neighbors close by, the plant has odor-control biofilters, which include a mulch bed and ventilating fans. Foul air is drawn from the influent pump station, screening and grit areas, equalization basin, biological reactors and membranes, and the solids handling processes.

Extensive recycling

About 70 million gallons of treated water per year is available to contributing customers for irrigation or use in dual plumbing systems. Customers can receive the recycled water free of charge up to the amount of wastewater they discharge. Recycled water meters (Badger Meter) are installed at each property to measure usage. Excess effluent can be discharged to three deep injection wells, which reach a buried ancient riverbed.

Because it receives potable water directly from Los Angeles County, Malibu had to devise a different system for billing sewer customers. Flow and concentration estimates have been worked out and agreed upon for each customer, and billing goes on the property tax bill for each parcel.

Based on the allowable development for each property, the city can also develop estimates for the flow and concentration of wastewater for each customer. “Wastewater and recycled water rates have been established via a Proposition 218 process and estimated operation and maintenance expenses,” DuBoux says. “After the first year, these rates will be reevaluated based upon actual expenses.”

Lessons learned

DuBoux says the city has already learned lessons that will prove valuable as the project heads into phases two and three: “We have a number of drains around the plant. They collect and return the stormwater to the influent pump station for treatment.”

While the system prohibits any untreated water from leaving the site, the drains also collect rainwater. In heavy storms, rainwater can double the flow of water through the plant. “We’re looking at different ways to address that,” DuBoux says. One solution might be underground detention tanks to regulate flows to the influent pump station.

While it has begun the process of eliminating septic systems and provided sustainable local wastewater treatment, the plant has also enhanced the city, DuBoux says: “The project has transformed the Civic Center area from one dotted with wastewater treatment and disposal systems to a centralized community facility with a robust level of treatment and a recycled water system.”

Even more important, the Civic Center facility promises to save a substantial amount of freshwater that otherwise would have been used to water lawns. “Our treated wastewater will be available to irrigate some of our most popular parks and public spaces, as well as customer sites,” DuBoux says.

“The facility represents a meaningful and responsible way to produce recycled water that will help ease the impacts of future drought cycles. Malibu has always been a step ahead in adopting environmentally focused programs.”

Tight pipes

At just 6.5 miles, the sewers and recycled-water lines serving the Civic Center Water Treatment Facility in California may not be the longest system in the industry, but they are surely the tightest.

The system was designed to be leak-proof because of its location along the shore of the Pacific Ocean, says Rob DuBoux, P.E., Malibu Public Works director. “We have to prevent ocean water intrusion into the system, because our treatment facility is not designed to handle that kind of water. Everything has to be watertight.”

Malibu used high-density polyethylene pipe welded at the joints. Some sections were installed using opencut construction. In other cases, especially where the groundwater table was high, the contractors used tunneling; both sewer and recycle lines were enclosed in 36- to 48-inch steel casings.

The city made sure manholes were tightly sealed as well. “Contractors were able to successfully dewater the excavations,” DuBoux says. “We didn’t have a lot of tunnel failures.”

Two lift stations power the lines. They were built to size but contain enough extra space to add equipment, which will be needed for the next phases of the project.