Reclaimed Waste Water Will Keep Side of I-15 Green

Aiming to save money and help San Diego County reduce its reliance on imported water, state transportation officials on Friday began using treated sewage to irrigate shrubbery along a five-mile stretch of Interstate 15.

During a ceremony at the city’s experimental sewage-treatment plant in Mission Valley, officials flipped a switch and sent the first drops of reclaimed waste water on their way to the 100-acre border of trees and ground cover lining the freeway between Clairemont Mesa Boulevard and Aero Drive.

Protection Against Drought

Under an agreement between the city and the state California Department of Transportation, 80,000 gallons a day of treated sewage will initially be used to nourish the greenery along Interstate 15, which consists largely of hardy, drought-resistant trees and plants. Eventually, as many as 150,000 gallons will be dispensed along the freeway as new pipelines expand the area that can be serviced.

“Ultimately, we’re interested in converting as much of our landscaping as possible along the freeways to reclaimed water,” Caltrans spokesman Jim Larson said. “It’s just a smart move. This is an arid region, and the more potable water we free up for domestic use, the better shape we’ll be in.”

Moreover, the use of sewage will protect freeway vegetation in the event of a drought. In the late 1970s, a water shortage forced state officials to cut irrigation and damaged some plantings.

“We’ve got millions and millions of dollars invested out there,” Larson said. “This is a guarantee that we’ll be able to protect it if we get hit by a drought. Our supply won’t be shut off.”

The cost of using the sewage--which undergoes advanced “secondary” treatment through a system known as aquaculture and also is chlorinated--is about one-sixth what Caltrans has been paying to water the plants with imported water, Larson said.

The Interstate 15 project represents the first use of reclaimed water on the state’s highway network in San Diego County. Later this year, a four-mile stretch of Interstate 5 from Camp Pendleton south to Carlsbad will be irrigated with about 220,000 gallons of sewage effluent daily under a contract with the Fallbrook Sanitary District. Sections of Interstate 8 also may be doused with effluent in the near future.

Freeways aren’t the only beneficiaries of treated sewage. Fallbrook’s reclaimed water is used by the City of Oceanside for golf course irrigation and other projects. And Los Angeles County reinjects its most highly treated sewage into groundwater supplies that are ultimately tapped for residential use.

Assemblyman Larry Stirling (R-San Diego), an avid proponent of reclamation, presided over Friday’s ceremony and proclaimed the initiation of the freeway-watering project as “key to educating the public about the need to reuse water.”

“This is an excellent way to familiarize people with reclamation through a legally and socially acceptable use,” Stirling said.

He added that having a distribution system in place would be useful in the event of a drought, when a water shortage might prompt officials to tap the waste water source to irrigate parks or for other purposes.

To dramatize his faith in reclamation, Stirling mixed up “sewage” cocktails--complete with maraschino cherries--from the effluent after it completed a final treatment stage at the city’s aquaculture plant.

“I figure if I live through the week, maybe people will realize that reclaimed water could be used for everything, even in the home,” said Stirling, who persuaded Caltrans officials and City Councilwoman Judy McCarty to try the water too.

Sponsored Legislation

It was legislation by Stirling that in part stimulated the freeway irrigation project. A law on the books for about two years requires that any county that imports more than 50% of its water may not use potable water for highway landscaping, the assemblyman said. San Diego imports 90% of its supply.

Under the agreement between the agencies, a total of 900 acre-feet of water will be provided to Caltrans for freeway irrigation. That amount is forecast to last for 10 years, but may run out sooner depending on the extent of the use.

The waste water used in the project comes from the city’s controversial aquaculture plant, located near the stadium. Aquaculture was pioneered by San Diego in the 1970s and uses shallow beds of water hyacinths to help treat sewage. Theoretically, the plants add oxygen to the water, an essential step in secondary treatment, and provide a home for microorganisms that feed on solids in sewage.

Billed as a low-tech, cheap way to treat waste water, aquaculture has fallen short of its goals--largely because the ponds would stink and attract mosquitoes if workers did not use air injectors to pump oxygen into them. Until Friday, the entire sewage load at the plant--about 300,000 gallons a day--was pumped back into the sewage system and ultimately ended up in the ocean.