Deep, Dark and Dangerous: Potential Harms of Groundwater Use

Illustration by Diane Kim

Cassie Pataky

Senior Staff Writer

Scientists at UC Santa Barbara (UCSB) have recently determined that heavy reliance on groundwater is increasing the risk of contamination in our drinking water. 

In an average year, groundwater makes up about 40 percent of California’s total water supply. During severe droughts, which have increased in intensity and frequency due to climate change, some regions of California get up to 60 percent of their water supply from groundwater wells. Because we rely so heavily on groundwater, it is important to understand the potential risks of relying on this source to such an extent.

So what exactly is groundwater? Just like digging a hole at the beach, when people drill deep enough into the ground, water begins to fill in. The water table is the level at which the ground becomes saturated with water. 

There are many other materials, however, that make up the ground and can affect the quality of groundwater. Some, like sandstone, are porous and precipitation is easily able to percolate (filter) through. Others, like clay or granite, are not as permeable, and water takes a long time to filter through. This means that the water table is not at the same level everywhere — it depends on the soil and rock that the ground consists of. As precipitation seeps deeper into the ground, a process that can take thousands of years, the contaminants from the surface are filtered out and broken down. Today, we use complex drills to dig deep wells into the ground, surpassing the layers of less permeable elements in order to find a consistent source of groundwater. This can disrupt the natural filtration process in the ground, increasing the risk of contamination in the water. 

Melissa Thaw, a postdoctoral fellow at UCSB, teamed up with Scott Jasechko, an associate professor at UCSB’s Bren School of Environmental Science, and postdoctoral UCSB student Merhawi GebreEgziabher GebreMichael in order to investigate the presence and risk of groundwater contamination. They also collaborated with Jobel Villafañe-Pagán, a researcher from the University of Puerto Rico and member of the Geosciences Education & Mentorship Support Program. 

Together, the team took data from 15,000 groundwater wells across the United States. They calculated roughly how old the well water was, unsurprisingly finding that older groundwater was found in wells that reached farther from the surface, and vice versa. Then, with the different ground permeability depths in mind, they calculated the likelihood that young groundwater would be found at the depths they analyzed. Based on statistical models, it was not likely that younger groundwater would be so deep due to natural processes. 

This indicates that pumping groundwater from deeper levels is contributing to this rapid percolation. Undisturbed, it takes thousands of years for groundwater to filter to the depths from which we draw it. Instead, as the old groundwater is pumped up to the surface, the young groundwater fills in to take its place. 

This means that the groundwater brought up from the wells has a higher concentration of contaminants than it would if the groundwater had the usual time to filter through the ground.

Within the Goleta water district, which serves UC Santa Barbara as well as Isla Vista, it was found that there are 18 contaminants exceeding the Environmental Working Group’s (EWG) health guidelines, with 35 total detected in the district’s groundwater. Many of these contaminants, including arsenic and chloroform, could lead to cancer. While none of the contaminants are above the current legal limit, these limits have not been updated in almost 20 years, according to the EWG. 

Alarmed by these statistics? A reverse osmosis filter reduces all but 3 of the detected contaminants, including all 18 of those found to be above the recommended health guidelines in our water district. An activated carbon filter, such as what is used in a Brita filtration system, filters seventeen of the detected contaminants, including the twelve currently above guideline levels. You can also contact local officials to inquire about the water quality where you live and hold them accountable for the issue, which will only become more pressing as we continue to pump groundwater to mitigate the effects of the changing climate.