News Feature | June 22, 2018

Overpumping Groundwater Linked To Arsenic Threat

Sara Jerome

By Sara Jerome,
@sarmje

san joaquin valley landscape reg new

A new study found that groundwater overpumping can result in potentially dangerous water quality problems.

The study, published in June in the journal Nature Communications, linked overpumping to the overconcentration of arsenic in aquifers. The study focused on the San Joaquin Valley in California, a region with many poor, farmworker towns where clean drinking water is often inaccessible.

“The bad news is that groundwater is the main source of drinking water for about 1 million people in the study area. Many of them reside in small, low-income communities with limited resources for treating contaminated water sources. And others may be even worse off, including thousands of people that rely on essentially unregulated private wells there,” News Deeply reported.

The findings “heighten concern about water quality as California’s agricultural belt faces a lingering water shortage even while much of the state has recovered from the recent drought,” The San Francisco Chronicle reported.

Compared to surface water use, groundwater use comes with some water quality challenges, the researchers state. Naturally-occurring contaminants in aquifer sediments can affect water quality. With this in mind, the researchers studied the connection between overpumping and high concentrations of contaminants.

“Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping,” the researchers wrote.

Ryan Smith, coauthor of the study and a doctoral student in geophysics at Stanford University, spoke to News Deeply about the significance of the findings.

“There is a huge societal impact behind this study, because not only is overpumping depleting our groundwater, it’s also contaminating it,” he said. “A lot of the groundwater pumping is being done by the agricultural industry, but the people that are being most strongly affected by it are those who are living in this area and need groundwater for their drinking water.”

Smith explained the process whereby arsenic enters drinking water sources.

“When people pump a lot of groundwater it drops the pressure in the aquifers a lot and when the pressure is really low that pulls the water out of the clays, when normally it wouldn’t come out of the clays,” he said. “You’re overstressing the groundwater system and that causes water to be drawn out of the clays and the water in the clays tend to have higher arsenic concentrations so you’re essentially bringing arsenic out of the clays into the groundwater system in the aquifer.”

Groundwater overpumping in California has drawn scientific and media attention in recent years in part due to findings that the Central Valley is actually sinking due to this practice.

Image credit: "san joaquin valley," Doug Letterman © 2009, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/