Desalination of Aquifers Offers Drought-weary California New Hope

A new report by the Pacific Institute that explores the cost of potential water sources in California is spurring hopes that the desalination of brackish water could quickly become a vital tap in the state.

“There are places in California where there may be groundwater available, but it may not be fresh,” said Heather Cooley, director of the water program at the Oakland-based think tank. “Those are places where it’s possible to use brackish desalination at a much lower cost and with fewer social and environmental impacts than ocean desalination.”

The new analysis comes just months before the U.S. Geological Survey is expected to issue a groundbreaking report that will map out aquifers throughout the country that contain brackish groundwater.

Perhaps the greatest appeal of brackish water desalination is that the salt concentration ranges from 1,000 to 10,000 milligrams per liter, making brackish water about 3.5 times less salty than seawater and roughly twice as cheap to desalt. The Pacific Institute report estimates brackish water desalination costs $950 to $1,300 per acre-foot, compared with $2,100 to $2,500 per acre-foot for seawater desalination.

“The more saline the water, the more intensive the treatment and the more energy required, which makes the cost higher,” Cooley noted.

Desalination of brackish water is also far less controversial because, unlike ocean desalination, it doesn’t kill marine life. “It’s never been a big deal because there aren’t many environmental issues related to it,” said Newsha Ajami, director of urban water policy at Stanford University’s Water in the West. “Ocean desalination is much more complex, especially because it has to be designed in a way so it doesn’t impact marine life either during the extraction of water or in the dumping of leftover salts,” called brine.

Brackish water naturally exists underground across the U.S. “In most parts of the country, including Northern California, if you drill deep enough you’re going to encounter water,” said David O’Leary, a USGS hydrologist. “And if you drill deeper, you’ll encounter brackish water.”

In some parts of the U.S., brackish water is old seawater that used to cover the land in ancient geologic time, O’Leary explained. Water also becomes brackish when rain flushes concentrated salts from the soil into the ground. In coastal areas, groundwater often becomes brackish when seawater mixes with fresh groundwater. Referred to as “saltwater intrusion,” the process happens naturally to some extent, but becomes more of a problem when coastal areas pump too much water from aquifers, causing seawater to replace the fresh groundwater. Removing salts from this mix becomes a valuable way to produce water.

Desalination is hardly a new concept — sailors and islanders survived for a long time by removing salt from seawater using chemical methods, Ajami noted. The technology we now use works by forcing a huge amount of water through microscopic membranes at extremely high pressures. The difference in the cost of brackish desalination and ocean water desalination comes from the amount of energy used in forcing the water through the membranes.

Read more on: The Mercury News