Water securityGroundwater recharge project helps California’s sustainability efforts
The depletion of California’s aquifers by over-pumping of groundwater has led to growing interest in “managed aquifer recharge,” which replenishes depleted aquifers using available surface waters, such as high flows in rivers, runoff from winter storms, or recycled waste water. At the same time, there is growing concern about contamination of groundwater supplies with nitrate from fertilizers, septic tanks, and other sources. Study shows how collecting storm-water runoff to replenish depleted groundwater supplies can be coupled with a simple strategy to reduce nitrate contaminants.
The depletion of California’s aquifers by over-pumping of groundwater has led to growing interest in “managed aquifer recharge,” which replenishes depleted aquifers using available surface waters, such as high flows in rivers, runoff from winter storms, or recycled waste water. At the same time, there is growing concern about contamination of groundwater supplies with nitrate from fertilizers, septic tanks, and other sources.
Researchers at UC Santa Cruz are addressing both issues with an ongoing program in the Pajaro Valley, where they have been implementing and studying groundwater recharge projects and evaluating methods to improve water quality as it infiltrates into the ground.
“As we ramp up groundwater recharge efforts, it’s important to avoid contributing to problems with water quality. If we’re putting good quality water into the ground, it will dilute any contaminants that are already in the groundwater,” said Andrew Fisher, professor of Earth and planetary sciences at UC Santa Cruz.
In a study accepted for publication in Water Research, Fisher’s team showed that simply adding a layer of woodchips where water infiltrates into the ground can remove nitrate from the water by stimulating microbial activity in the underlying soil. Sarah Beganskas, who led the study as part of her Ph.D. thesis research, said the wood chips provide a source of carbon needed by denitrifying bacteria in the soil.
“We were able to see an increase in the removal of nitrate from the water and, at the same time, increased abundance of the microbes that carry out this process,” she said. “Wood chips increased nitrate removal even at fast infiltration rates, which is important because recharge sites with high infiltration rates are often preferred.”
Just as important is that wood chips are relatively inexpensive. “It has to be a cost-effective technology to be practical,” Fisher said.
Sustainable groundwater management
UCSC says that Fisher’s groundwater research program is yielding valuable results just as California has begun a serious push for sustainable groundwater management throughout the state. Under the Sustainable Groundwater Management Act (SGMA) passed in 2014, new agencies are being established throughout the state to manage groundwater resources.
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