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9th September 2021
EDITORS NOTE: Do not think the same things are not happening here!!

Drought threatens access to clean water in California farming communities, study finds


Researchers have suspected for years that drought conditions worsen groundwater quality, but a study published this week provides strong evidence proving the long-held assumption.

While previous studies have focused on the risk of wells being overdrawn and run dry during drought, the study from the United States Geological Survey and the California State Water Resources Control Board is the first to directly link drought to deteriorating water quality on a regional scale.

The study looked at 30 years of data from California’s Central Valley.

“This has been a real big missing link in understanding how drought and groundwater use during drought actually affects the quality of the resource,” said Zeno Levy, a research geologist for USGS and lead author on the paper released Wednesday.

Based on their analysis, researchers found higher levels of nitrate at public drinking water wells in the Central Valley in areas where groundwater levels dropped rapidly during drought.

But why is this the case?

Aquifers are pumped more frequently during times of water scarcity from drought. As a result, shallow groundwater — often contaminated by agricultural runoff in areas such as the Central Valley — is pushed down into the deepest parts of aquifers, the areas commonly tapped for public drinking-water supply, Levy said.

As drought conditions get worse, groundwater pumping increases and water quality becomes further contaminated — threatening the supply for communities who rely on aquifers for agriculture and drinking water.

“This speaks to increased vulnerability of public drinking water supply when pumping increases during droughts,” Levy said.

The study’s findings are troubling for California, a state currently ravaged by drought. Nearly 40% of California’s water is pumped from aquifers and about 85% of residents are reliant on groundwater for a portion of their water supply.

California officials said the report will help with groundwater quality monitoring by the state.

“Having access to safe and sustainable water supply is critical to the state’s residents and also to the economy,” said John Borkovich, a water quality section manager at the state water board.


In the Central Valley, it’s not a surprise that the study found high concentrations of nitrate, a contaminant found in fertilizer, in the shallow groundwater. Due to decades of fertilizer use and livestock runoff, the San Joaquin Valley has some of the highest rates of nitrate contamination in the United States.

Researchers have linked nitrates to birth defects and various forms of cancer and high levels of the toxin can cause “blue baby syndrome,” a disorder where oxygen levels drop in newborns’ blood.

By focusing their study on the Central Valley, the researchers looked for large-scale patterns of groundwater usage and quality in public-supply wells. In the past, most efforts were focused on individual well management, said Kim Taylor, the program officer for the California Water Science Center.

“People are starting to think about how you manage a basin as a whole thing,” Taylor said.

The findings are useful for making assessments on groundwater quality on a regional scale, even though water quality is not pinpointed well by well in the study, Borkovich said.

Water purveyors, who must keep nitrate levels below the maximum contamination level for nitrate to serve the water to the public, may also find the study useful. To mitigate high nitrate concentrations, purveyors will need to either treat the water (which Levy said is costly and difficult to do for nitrate), or dilute the water with lower levels of nitrate.

While it’s challenging to generalize the study’s specific findings beyond the Central Valley, the researchers would expect to see similar high concentrations of nitrate in drought years among areas with similar geology, pumping habits and long-term inputs of nitrate into the water supply, Taylor said.

Despite these limitations, by defining the linkage between groundwater quality and drought, researchers can be more predictive for the future, Levy said.

“This is the first step for future work,” Levy said.