Test Uncovers Seawater in Major Aquifer

For the first time, scientists have found strong signs of seawater intrusion in aquifers deep below the surface of the Oxnard Plain, indicating sharp new limits on the life of the county’s long-term water supply.

If tests due back next month confirm suspicions of seawater in the deep recesses of the Fox Canyon Aquifer, pumping restrictions and other conservation measures could be imposed on about 500 wells on the Oxnard Plain, the county’s richest agricultural area. About 400 of the wells belong to growers.

“If the Fox Canyon Aquifer gets intruded with seawater, it’s another step in the demise of agriculture,” said Jim Naumann, a major citrus and vegetable grower on the Oxnard Plain. Shutting down wells would devastate the county’s biggest industry, he said.

“It would be the end of farming,” he said. “It’s as simple as that.”

In addition, if the intrusion were to worsen over time, more drastic measures would be in store, ranging from mandatory household conservation to the extreme of a prohibition on new construction, according to contingency plans developed by the county’s Public Works Agency.

However, officials and the scientist who performed the tests caution that results are still preliminary.

“We want to be sure of the facts before we sound an alarm,” said County Supervisor John Flynn, who represents the Oxnard area and is considered a leader on regional water issues. “But the signals are pretty strong that we’ve got a problem.”

The problem emerged after discovery of saltwater in a test well 720 to 760 feet deep at Point Mugu. Tests of another well at Port Hueneme revealed no saltwater. The results were revealed to the county’s Groundwater Management Agency at a meeting Monday.

U.S. Geological Survey hydrologist Peter Martin told the board of the need for more data, not only in the form of laboratory analyses of test results but also in results from a planned third well, which was drilled Tuesday at Harbor Boulevard and Fifth Street in Oxnard. He stressed the need for a fourth well near Ormond Beach and a long-term study on ground-water management in the Oxnard Plain.

The United Water Conservation District offered to fund the drilling of the fourth well and may decide to cover half the cost of a $1.4-million study that Martin proposes. The United board was to decide the matter this week.

Since the early 1920s, seawater unfit for drinking or irrigation has crept into shallow underground reservoirs. That intrusion occurs when more water is pumped from the aquifers each year than is replaced by rainfall.

The United Water Conservation District exists primarily to replenish those supplies, and its $20- million Freeman Diversion Project is being built to recharge the aquifers.

Until now, it has been believed that the deep aquifers, the Fox Canyon in particular, were safe. The Fox Canyon aquifer would provide the county with at least a 100-year supply of fresh water, it was believed.

The aquifer, which was formed about 500,000 years ago, extends several miles offshore beyond Point Mugu and Ormond Beach. It is buried beneath the ocean floor by layers of clay and debris.

It was believed that any seawater would have to seep through at least two other aquifers to get to Fox Canyon. But Martin’s findings suggest that the aquifer is more directly exposed to seawater.

Laboratory analyses will tell scientists whether the saltwater they found has been there since the formation of the aquifer about 500,000 years ago or whether it moved in more recently from the sea, Martin said. If it is a salty pocket that is stagnant, it still represents contamination but not necessarily a grave, ongoing seawater intrusion problem, Martin said.

Some at Monday’s meeting questioned whether Martin had really tapped Fox Canyon or another aquifer. But Greg Middleton, a hydrologist for the United Water Conservation District, said Martin’s study was the most thorough ever done on the water systems underlying the Oxnard Plain.

Regardless of which aquifer is affected, the discovery of saltwater could have a profound effect on growers such as Naumann.

“What it points out to me is how desperately we need alternative sources of water in the county, and how badly we need more information,” said Rex Laird, executive director of the Ventura County Farm Bureau. “It points out that people need to be concerned about water.”