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Congressman Josh Harder, second from right, visited the CCID/Del Puerto Water District pilot recharge project in 2019. 

NEWMAN - Two local water agencies are moving forward with plans to fully develop a groundwater banking project near Newman.

The groundwater recharge project has exceeded expectations in pilot studies, said Jarrett Martin, general manager of the Central California Irrigation District and Anthea Hansen, general manager of the Del Puerto Water District. They said plans are in the works to expand the 20-acre pilot project to an 80-acre recharge zone.

Martin said the two agencies have been awarded grants totaling $6.4 million to expand the recharge project to its full buildout, which is envisioned at 80 acres.

At its heart, the project is straightforward: The participating agencies, in years when water was available, can divert a portion of their surface water allocations from the Delta-Mendota Canal to the recharge project where it percolates into the aquifer for future extraction in years when water supplies are limited.

"I think it is a very basic model," Martin remarked. "When you keep things basic, they tend to work."

The water managers estimated that the project could provide 10,000 to 15,000 acre-feet of additional water each year which would be split between their agencies (Martin noted that technically the San Joaquin River Exchange Contractors are partnering with Del Puerto, but CCID is taking the lead on behalf of the contractors).

The amount of water is significant, particularly in the federal Del Puerto district. Del Puerto, with its junior water rights, is subject to deep cuts in annual surface water allocations and has resorted to aggregating water supplies from a variety of sources.

This year, for example, Del Puerto is expected to receive only 5 percent of its full contractual allocation, which equates to about two inches of water per acre. Hansen framed the potential benefit of the recharge against that allocation.

"If Del Puerto was short and we could extract 7,500 acre-feet, that is the equivalent of a 5 percent allocation," she explained. "It is only two inches per acre, but it is meaningful when you start adding it with the other projects."

Even though it enjoys senior water rights, CCID is not immune from reductions to its Central Valley Project allocation. This year, for example, has been declared by the Bureau of Reclamation to be "critical," meaning that the district will receive 75 percent of its full allocation.

Martin said groundwater recharge projects such as that west of Newman are one component of an overall water resources plan which has the target of establishing an additional 50,000 acre-feet of water supply for use in critical years.

Martin explained that the local project, which is in the area of Orestimba Creek, proved extremely effective in a one-acre pilot project and later the 20-acre project.

"The recharge on it was fantastic," Martin stated. He said the absorption rate was two and a half feet per acre over a 24-hour period - far exceeding the target goal of six inches a day.

While surface water will provide most of the recharge supply, Hansen and Martin said, the project could also be permitted to capture Orestimba Creek flows after heavy rain events.

A portion of the grant funding received by the agencies, Martin explained, is for a flood control component.

"This in an initial step in what folks have been talking about (regarding flood control on the creek)," he commented. "That doesn't prevent floods from ever occurring, but it is a step to capture flood flows that cause damage downstream and put them to beneficial use."

"That would capture that otherwise would be lost to the system, while preventing flooding and damaging downstream properties and infrastructure," Hansen said. That would involve diverting creek flow to an underground pipeline carrying the water to the recharge pond, she explained.

Martin said the partnership has an option to purchase the land needed to expand the project to 80 acres.

The terms of the grant funding require completion of the environmental studies no later than February 2022, and then allows two additional years to finish construction of the project.

Hansen and Martin said the project also has potential benefits to growers in the Eastin Water District, which is between the boundaries of their respective districts and has no surface water rights. Those landowners rely on private wells, they explained.

One premise of the project, they emphasized, is that they will leave behind more water in the aquifer than it introduces.

"We have had some initial discussions with Eastin folks to get them engaged in the project," Martin commented. "We will leave the aquifer better than we found it. There will be a leave-behind. If we put 10,000 acre-feet into the ground, the number we extract will be less than that."