A pilot project involving two local ag water agencies will explore the feasibility of storing water supplies in underground aquifers.

The project, a joint effort of the Central California Irrigation District and Del Puerto Water District, involves construction of a shallow, 20-acre basin into which the agencies will pump water to recharge the aquifer.

The concept is straightforward: Develop a basin which can be used to percolate water supplies into the aquifer, which in turn can be pumped out and used when needed at a later date.

The pilot project follows an earlier test involving a one-acre basin that was promising enough to move ahead with an expanded endeavor, explained Chris White, CCID general manager.

“We are serious about testing the concept (of underground storage) to make sure that this is something we could build on,” White explained. “This will test the feasibility of the site for a groundwater project. This simple task will either prove the project out or not.”

He said CCID has been studying potential groundwater storage sites as part of its resources plan. The site of the pilot project, which is south of the Orestimba Creek and east of the Delta-Mendota Canal, has good water quality and a good aquifer.

“It all looked favorable toward a groundwater storage program,” he stated.

Additional water storage is always welcome, said Anthea Hansen, general manager of the Del Puerto district.

“The benefit we see right now is an opportunity to store water in wet years for use during dry years. That is always something we are looking to do,” said Hansen. “This is a supplement to our ability to store water in (San Luis) reservoir. It is another place we can store water.

After a prolonged drought, Hansen noted, Del Puerto saw a situation arise this this year where the district had access to water supplies - but with San Luis at capacity had nowhere to put that water.

“Multiple projects like that could give the district more management tools in terms of its ability to protect water supplies from one year to the next. It is hard to watch water supplies that you could potentially benefit from in the future be lost to the fact that you have no place to store it,” she added.

Hansen said the environmental review on the pilot project has been completed. It has been approved by the CCID board, she said, and the Del Puerto board will be asked to sign off on the environmental document as well this month.

White said final designs are being drawn up for the basin, and he anticipates construction beginning this fall. He described the basin as being one to two feet in depth and located on privately-owned land.

Studies have indicated that the basin could percolate 10 acre-feet of water a day into the aquifer, he told Mattos Newspapers.

The basin is well situated for a recharge project, White said.

“It is sited such that we could get water out of the (Delta-Mendota) canal to put into the ground for recharge, and at some point in the future we could route flows from Orestimba Creek into the pond as well,” he explained. “We are hopeful that we have a site that can use some natural run-off in the pond.”

If a groundwater recharge project proves feasible, a number of steps would follow.

One, the water managers said, would involve coming up with an agreement with surrounding landowners for use of the water.

“We are committed, with Del Puerto, to work with landowners in the area to make sure that we can come up with a program that is agreeable to the neighbors and beneficial to everybody,” White stated. “Usually there is an accounting within a groundwater banking program. You put water in the ground and agree to leave behind a percentage of that flow for the benefit of those around you, and you have a right to pick up a percentage in the future,” he explained.

Hansen said the pilot project carries a price tag of $1.2 million. Grant funding will cover nearly half the project cost, with the two agencies splitting the remainder.