Diversion Projects Protecting Water, Study Finds

SANTA PAULA — Diversion projects, including the massive Freeman Dam, are protecting the county’s most precious underground water supply from the twin threats of seawater intrusion and excess pumping.

That is the key finding of a U. S. Geological Survey study of the Fox Canyon Aquifer beneath the Oxnard Plain. The study was released at a Wednesday meeting of the United Water Conservation District.

Three local water districts--United, Fox Canyon Groundwater Management Agency and Calleguas Municipal Water District--joined the Geological Survey in paying for the more than $4 million. The three agencies will meet jointly today for a more detailed accounting of the study, which was started in 1990.

“It seems that we’re almost at a point where we can declare victory over overdraft,” said Fredrick J. Gientke, general manager of United, which monitors pumping and replenishes underground water supplies for much of the county. “Now we just have to do something about seawater intrusion.”

Fox Canyon, the county’s largest underground water basin, supplies freshwater to 200,000 county residents from Oxnard to Ventura and Camarillo. It has been overdrawn for the last 50 years by growers and cities that pump out more each year than rainwater can replenish. That has allowed seawater to gradually seep into the aquifer’s upper and lower levels.

Using mathematical models, the Geological Survey looked at existing water management projects and possible future projects to show the conditions of ground-water basins 20 years from now.

The survey took into account the diversion of the Freeman Dam on the Santa Clara River, opened in 1991, which funnels about 30,000 acre-feet of water a year into the aquifer. An acre-foot is enough water to supply two families for about a year.

The findings--as presented by Kenneth H. Turner, a United ground-water manager, were dramatic:

* The upper level of the aquifer--which sits 100 to 400 feet below the ground--will have a surplus of 13,000 acre-feet of water in 2017. That surplus means that the tide of seawater intrusion is being reversed in the upper level.

* The lower level, 500 to 1,200 feet below ground level, will continue to be overtapped, showing a deficit of 1,900 acre-feet in two decades. As a result, seawater will continue to seep into the lower level.

* The Las Posas basin of the aquifer will continue to be a trouble spot, with overdraft conditions in both the upper and lower aquifers.

The Las Posas situation will have to be addressed in the future, said Donald Kendall, general manager of Calleguas, which stores up to 300,000 acre-feet of treated state project water in the basin.

“The only way it’s going to get solved is the three agencies working together,” he said.

To address overdraft and seawater pollution, the three districts are considering several strategies: shifting pumping from the lower to upper aquifer levels, diverting more water from the Santa Clara River to reduce pumping, and extending pipelines through the south Oxnard Plain.

While the costs of those projects are not yet known, members of United’s board of directors do not expect them to be prohibitive.

“The recommendations are very doable and very inexpensive,” board member Dan Pinkerton said. “Competitively, Ventura County is going to be the envy of Southern California for water.”