Page 1 | Page 2 | Page 3

The Limits of Endurance

A handful of relatively small ocean desalination plants exist in California, but the state's Coastal Commission is reviewing another 20 proposed projects on a case-by-case basis in an attempt to find a standard for acceptable impact. Most of the proposed operations have drawn fire from environmental groups for their potential to harm coastal ecosystems.

A Poseidon project in Carlsbad, Calif. has come the farthest in the permitting process and could set the bar for the other proposed projects, said Jenkins. In Carlsbad and Huntington Beach, Calif., Poseidon has proposed building desalination facilities on the grounds of existing power plants, using a fraction of the seawater used by the plants for cooling as source water for the reverse osmosis process, while the remainder is used to dilute the concentrated saltwater before it returns to the ocean. Each project would produce 50 million gallons of drinking water per day, enough to serve 300,000 people.

It takes about five parts of unaltered seawater to bring one part of hypersaline water to a concentration of 40 parts per thousand. In Carlsbad, Poseidon would build its plant on the grounds of the Encina Power Station, which uses as much as 800 million gallons of seawater a day. Presently, permits issued to the power station regulate consumption of that seawater. Poseidon must plan, however, for a future beyond Encina's possible decommissioning when the environmental responsibility for seawater consumption would be entirely on the desalination plant.

It has been Graham's role as an advisor to the Poseidon projects to determine what salinity fishes, marine invertebrates, and plants can tolerate. Jenkins has been tasked with determining how long the brine discharged from the desalination plant remains concentrated after it returns to the ocean, a process that requires him to model winds, currents, and other physical factors to determine how the hypersaline plume will disperse. His models have suggested that salinity levels in the brine plume would be within 10 percent of natural background salinity in less than 1,000 feet of the discharge channel when flowing at 250 million gallons per day.

The issue at the other end of the process is the loss of potential value of larval plankton. Jenkins studied possibilities for water intake, or entrainment, in a manner that spares a greater proportion of marine life. Two alternatives, one that employs natural seabed filtration and the use of large intake pipe networks known as seafloor galleries, were both found to be inappropriate for the Carlsbad site due to insufficient sediment cover over the bedrock along that section of the coast. The project's environmental impact report determined that continuing to use the power station's existing intake and discharge pipes would cause the least ecological damage.

At the same time that water-intake methods are being refined, Jenkins is also involved in assessing the suitability of compensatory measures that could be made at locations other than the Encina Power Station. The Coastal Commission's price for greenlighting Posiedon's Carlsbad project will likely include a condition that Poseidon restore at least 37 acres of wetland elsewhere in San Diego County. Jenkins is advising the company on where and how wetland restoration projects might be most effective.

Though the majority of the expertise Jenkins and Graham have brought to the table has been for the benefit of a client, Jenkins said a broader benefit has come in the development of more sophisticated coastal transport models that have application to pollution dispersion and beach erosion prediction in addition to desalination analysis. Jenkins added that as California moves into an era of desalination, the work done now could be parlayed into securing future grants to the institution to advise public agencies who are trying to prepare state residents for the impending water crisis.

Before California implements best practices in the delivery of desalinated water, however, Jenkins and Graham see two potential roadblocks. Even if environmental concerns are addressed to the Coastal Commission's satisfaction, will desalination companies bankrupt themselves to achieve compliance? Currently, desalinated water costs about $800 per acre foot to produce, according to Poseidon. That's half of what it cost 10 years ago but is still several hundred dollars more per acre foot than the cost of bringing water from traditional sources such as the Colorado River or the Sacramento Delta. Poseidon officials believe prices for water from other sources will only increase, but Jenkins fears that onerous regulations could still leave desalination economically uncompetitive, even as the state's need intensifies.

"Projects could be stillborn," he said.

Conversely, the two also fear that Gov. Arnold Schwarzenegger or one of his successors will feel pressured to pre-empt the Coastal Commission and order desalination projects before environmental impacts are understood. Graham sees "a significant danger" in that but also sees dwindling traditional water supplies and rising costs of the fuels needed to deliver water piled on top of a recession.

"Like most things in this world, they're all on collision courses," Graham said.

Page 1 | Page 2 | Page 3

Audio | Video | Subscribe
Download PDF

High | Med | Low

• 

• Published research: Ecological effects of desalination