Digging deeper won’t help
Deep wells across US could drain water supply
Wells supply drinking water for about 120 million Americans and nourish farmlands from the Arizona desert to the High Plains. In areas where groundwater levels have fallen because of heavy pumping, people have often responded by drilling deeper wells.
But exactly how much that has been occurring on a nationwide scale wasn’t clear until water experts compiled nearly 12 million well-drilling records from state and local agencies across the country. In a newly published study, researchers found that Americans in many areas from coast to coast
are drilling deeper for groundwater.
The researchers said the widespread approach of drilling deeper wells is an “unsustainable stopgap” measure, putting some communities on a path toward exhausting their water supplies and coping with dry wells.
Researchers Debra Perrone and Scott Jasechko of the University of California-Santa Barbara spent four years piecing together and analyzing well records from 64 different state and local agencies. They used the data to create a nationwide map of wells, including their depths and uses.
Perrone said one of the goals of the study was to “make this invisible resource visible.” Through their analysis, the researchers saw the trend of well-deepening emerge in many areas.
“It stood out to me that this is not a phenomenon that we are just seeing in the arid West. People are drilling deeper across the continental United States,” said Perrone, an assistant professor in UC-Santa Barbara’s environmental studies program.
The study was published Monday in the journal Nature Sustainability. The authors didn’t examine causes behind the drilling of deeper wells but said factors can include declining water levels, improving pump technologies, different permit requirements for wells that tap deep aquifers and poor water quality in shallow aquifers.
They said continuing to drill deeper is likely unsustainable for various reasons. In some areas, drilling deeper may not yield sufficient water. Deep aquifers are often saltier and may require costly treatment to use the water. Pumping water from deeper underground requires more energy. And as the drilling costs increase with deeper wells, they may become too expensive for some people to afford.
“The average domestic well is tens of thousands of dollars in California. The average agricultural well is hundreds of thousands of dollars,” Perrone said. “And so, the question is, can people afford to drill a new deeper well?”
The researchers wrote in the study that in areas where water levels are declining, “rural private-well owners are likely to be at the greatest risk.”
Groundwater pumping also can draw away water that would otherwise flow in rivers and streams. In a separate study, scientists found that groundwater pumping has caused the flow in U.S. rivers to decline by as much as half over the past century.
Perrone said her findings point to the importance of managing aquifers for the future. While many aquifers are in decline, global warming is adding to strains on water supplies and is projected to bring more intense droughts.
“I think it’s going to be more and more important that we manage our groundwater resources over a long-term period so that it’s there, especially during these long periods of drought that are projected to happen,” Perrone said. “Climate change is likely going to make groundwater even more important. But it’s already really important.”
The researchers examined trends across the country and found well-deepening occurred in 59% of the areas they assessed between 2000-2015. When they narrowed their analysis to look at areas with significant trends, they found deeper wells were constructed in 72% of areas during that period.
“We expected to find that wells were being drilled deeper in California’s Central Valley, and our expectations were confirmed,” Jasechko said in an email. “I was surprised how widespread deeper well construction is in other parts of the USA that are not studied as often, such as Iowa, Missouri and Vermont.”
The study confirmed that drilling deeper wells is common in California’s food-producing Central Valley, and it has been for more than 50 years. Hundreds of homeowners with shallow wells saw their taps run dry in the Central Valley during California’s 2012-2017 drought, and household wells remain vulnerable to pumping by deeper agricultural wells.
The research also confirmed that drilling deeper wells is common in parts of the High Plains, such as southwest Kansas, where farms produce crops including corn, sorghum and wheat. But they also discovered that even as groundwater levels are declining, wells aren’t being drilled deeper in some areas on fringes of the southern High Plains.
If water levels decline further there, Jasechko said, more irrigation wells will dry up, affecting farms and crop production.
The researchers said their groundwater maps, when combined with other data, can be used to help identify shallow wells that are most at risk of running dry.
In Arizona, Perrone and Jasechko looked at areas with 10 or more wells and found a trend of drilling deeper in 72% of those areas from 2000-2015.
“The trend in Arizona is mostly deepening,” Perrone said.
They also assessed other regions where groundwater is being depleted, including the Mississippi Embayment aquifer system, the Northern Atlantic Coastal Plain aquifer system and the Floridan Aquifer.
In a previous study, Perrone and Jasechko analyzed records for about 2 million wells across 17 Western states from Texas to Oregon and estimated that one out of every 30 wells was dry between 2013 and 2015.
In preparing their new study, Perrone said they stitched together information from the 64 agencies they consulted to “create this comprehensive picture of groundwater infrastructure.” She said she’d like to see “some sort of nationwide standard for reporting well-construction so that we could really integrate all of this regional and local knowledge into a system that is assessable for researchers.”
“If we want to think about groundwater resources more holistically, then I think this would be one step in the right direction,” she said.
The researchers said their study is the first to map groundwater well locations, depths and purposes across the country. The only national well-construction paper they could find was a U.S. Geological Survey report from 1966, which examined regional trends in well-drilling.
Of the recorded wells they analyzed, 83% are for municipal or household use, while most of the remainder are used for agriculture.
Linda Estelí Méndez Barrientos, a doctoral researcher at the University of California, Davis, who studies groundwater in California, called the paper important and said it involved an “incredible amount of work.”
She said even after California’s passed its Sustainable Groundwater Management Act in 2014, parts of the Central Valley continue to be in a cycle of investing in deeper wells. And while local agencies have been formed to manage groundwater across the state, she said, the owners of household wells, who are most vulnerable, don’t have representation in most of those agencies and have little say in discussions about managing groundwater.
Newsha Ajami, director of urban water policy at Stanford University, praised the researchers’ work and said they created a map that is “one of a kind.”
She said her biggest concern is that by mining water from deeper and deeper, supplies of “fossil groundwater” that soaked underground long ago are being used up.
“It takes a very long time to get recharged,” Ajami said. Looking at the trends overall, she said, “it’s definitely not very sustainable.”
Reach reporter Ian James at ian.james@arizonarepublic.com or 602-444-8246. Follow him on Twitter: @ByIanJames. Environmental coverage on azcentral.com and in The Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and at OurGrandAZ on Facebook, Twitter and Instagram.