Desalination Could Produce 25 Percent of South OC Water

Humming along quietly at one end of the Doheny Beach parking lot in Dana Point is the beginning of the potential desalination project that could provide 25 percent of south Orange County's drinking water -- water that's now almost entirely and expensively imported from the north.

The apparatus, a pilot project by the Orange County Municipal Water District, draws water from a well that slants out under the surf, plunging into the saltwater aquifer about 250 feet deep. Above ground, the system sits in a trailer about the size of one you'd see on a semi truck.

Water engineers such as MWDOC's Richard Bell, who runs the pilot project, are using this first well to monitor the quality of the water that comes through, make sure the equipment is up-to-snuff and discover the dynamics of the aquifer.

"Every project is site-specific," Bell said at a Friday open house at the pilot plant. "You look at what you got."

So far, it appears the district has struck paydirt with the Dana Point spot.

The system purifies saltwater by reverse osmosis, meaning pumps force the water through a membrane that doesn't allow the salt molecules to pass.

But salt isn't the only impurity in the water; there is also magnesium and iron and a host of other naturally occurring trace chemicals that have to be removed.

Bell said one of the advantages of tapping into the aquifer, rather than pulling in water through a surface intake, is that the 250 feet of sand and gravel act as a natural pre-filtration system. Also, as seawater percolates down into the water table, microbes appear to use up all the oxygen in the water. This is great, Bell said, because it prevents the iron from turning into rust, which is much harder to remove and can ruin filters.

Furthermore, the wastewater -- which takes the form of brine that's about twice as salty as regular seawater -- can be combined with the nearby treated sewage water stream.

MWDOC engineers explained that this is a great environmental benefit; runoff that's too high in salt sinks to the bottom of the ocean, while fresh water -- which is essentially what the treated sewage is -- floats on top. Both of these facts of physics create unnatural conditions along the coast.

When the two-wastewater streams are blended, however, the water is about as salty as the ocean itself and combines seamlessly with the seawater.

Also, Bell said, the whole project will cost about $150 million. It's not cheap, but the district would have to spend another $160 million on a pipe intake and pre-filtration system to build a system that drew water at or near the ocean surface. Tapping into the aquifer allows the system to skip all that, Bell said.

Technicians and engineers are still monitoring the plant, and there are still some unknowns, Bell said. For instance, the pilot system is mostly drawing water now that percolated into the aquifer 7,500 years ago (scientists working for the district figured that out through testing radio isotopes in the water). This raises the question of whether the present-day ocean water that seeps in to replenish the aquifer after the full plant is up and running will be as high quality.

There's no way of knowing for sure, Bell said, but about 15 percent of the water the pilot plant is purifying now is contemporary ocean water, and it appears to be of the same quality as the old stuff.

The full plant will be on the east side of Pacific Coast Highway on land the MWDOC owns, and the tentative date for completion is 2018. But that depends on how the districts served want to proceed, Bell said.

Moulton Niguel Water District, San Clemente, the Laguna Beach County Water District and the South Coast Water District are partnering to fund the pilot project and the eventual nine-well desalination plant.

The city of San Juan Capistrano, which operates a upstream from Dana Point, was originally part of the desalination plant study, but decided to forego participation when .

If the plant gets up and running, it would be a second major source of water to pipe throughout south Orange County.