County Considering Building Salt Barrier for Water Supply

By Warren Lutz, The Record, Stockton, Calif.

Apr. 1–STOCKTON – Officials are considering whether to build a special barrier to keep salt from infiltrating the county’s only local water supply.

Salt causes a huge problem in the underground aquifer, the level of which has been steadily dropping for decades. The lower the water, the saltier it gets.

“We’re taking out more from the basin that what’s naturally being put in there,” said Brandon Nakagawa, a San Joaquin County water resources engineer. “We need to stop that, or else the basin won’t be able to support the people that live here or the agricultural economy.”

Officials say it will be even tougher to provide clean water for the growing region. San Joaquin County’s population is expected to double in the next 30 years, according to state projections.

While the county is surrounded by rivers and the Delta, local agencies obtained very few rights to such water supplies over the years, leading to a dependence on groundwater. Each year, the aquifer drops by as much as 200,000 acre-feet, enough water for up to 400,000 families a year. Recent tests at some wells found salt at levels that were eight times the standard for drinking water.

A barrier could cost millions. But officials aren’t sure of the true cost, because they’re still studying the extent of the problem.

They may need to make a decision before the end of the year, however. That’s when local water officials need to submit a regional water strategy in order to qualify for state funds. Members of the Northeastern San Joaquin County Groundwater Banking Authority are meeting monthly to discuss the plan.

Nakagawa called the barrier idea “exploratory” right now, but it is one officials are taking seriously.

“We’re starting to discuss what a salt barrier looks like and what it looks like in other areas,” he said.

Salt barriers take different forms but essentially do the same thing: prevent salty water from moving where water officials don’t want it to go.

Most barriers work by injecting water into the ground, creating a water “dam” that prevents sea water from seeping into inland groundwater basins. Barriers in Los Angeles and Orange counties work this way.

Another approach is to simply remove salty water. Alameda County, for example, pumps salty, brackish water out of basins along the San Francisco Bay shoreline, then desalinates it, producing 5 million gallons of water daily.

The process keeps salt water from intruding farther into the county’s larger groundwater basin further inland, said Paul Piraino, general manager of the Alameda County Water District.

“It’s technically not a barrier, but it’s kind of keeping us ahead of the game,” Piraino said.

The state is partly responsible for preventing salty water from reaching the Delta, where most of the county’s underground salt problem originates. The 1,000-square mile Delta provides drinking water for two-thirds of the state.

The state operates salinity “gates” on Montezuma Slough in the Suisun Marsh that keep much of the Bay’s salty water out of the Delta while holding in fresh water from the Sacramento River. The three automated gates rise when tides are high.

Temporary rock barriers throughout the Delta also help retain enough water in the region to dilute salt levels.

John Izbicki, a U.S. Geological Survey hydrologist who is researching the county’s groundwater problem, said salinity barriers are often designed and managed differently because every region is different.

He said the county still has time to decide.

“Groundwater tends to move slow,” Izbicki said. “That works in your favor.”

Nakagawa said a local salt barrier would work in conjunction with other efforts, such as groundwater recharge, which involves putting water underground to build up groundwater levels. “There’s not a single solution,” he said.

Contact reporter Warren Lutz at (209) 546-8295 or wlutz@recordnet.com

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Copyright (c) 2006, The Record, Stockton, Calif.

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