A study by researchers from Stanford University found that subsidence is not the only consequence of overpumping of groundwater – deadly water quality problems could also result.
| WRITTEN BYTara Lohan |
IN CALIFORNIA’S AGRICULTURAL heartland, the San Joaquin Valley, excessive pumping of groundwater has resulted in subsidence, damaging crucial infrastructure, including roads, bridges and water conveyance. A study last year from NASA’s Jet Propulsion Laboratory in Pasadena, California, found overpumping of groundwater since the 1920s had caused parts of the San Joaquin Valley to sink as much as 28ft.
But groundwater overpumping may have another serious side effect, according to a study published June 5 in the journal Nature Communications. Researchers found that recent groundwater pumping caused an increase in the concentrations of arsenic in the aquifer. Arsenic has been linked to many kinds of cancer and can also cause stomach pain, paralysis and blindness. The scientists focused on the Tulare Basin, which stretches across the San Joaquin Valley from Fresno to just south of Bakersfield and is home to about 4 million people and a large agricultural economy.
“There is a huge societal impact behind this study, because not only is overpumping depleting our groundwater, it’s also contaminating it,” said Ryan Smith, coauthor of the study and a doctoral student in geophysics at Stanford University. “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.”
The link between overpumping and arsenic concentrations in California is tied to the region’s geology. The Tulare Basin already has naturally occurring arsenic that originated in the rocks of the Sierra Nevada and coastal ranges and were deposited over millions of years in the valley by rivers. Some of this arsenic has ended up in groundwater, contaminating drinking water, and some of it is trapped in clay layers underground.
Under regular groundwater pumping conditions, the arsenic in the clay remains suspended, but when too much water is pumped, it becomes mobile, increasing the arsenic in the aquifer.
“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,” explained Smith. “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.”
At the same time, when the water is pulled out, the clay compacts and causes subsidence of the land surface.
California Department of Water Resources senior engineer Glenn Moeller visits the site of a water well being installed in Porterville, Calif. (Florence Low/California Department of Water Resources)
“So therefore when you see subsidence, you have arsenic in the water,” said Rosemary Knight, study coauthor and a professor of geophysics at Stanford. “The link to both being through the clays.”
The study focused only on the Tulare Basin and the potential for the same mechanism to be active in other areas would depend on both existing arsenic sources and clay layers, said Smith.
A similar correlation has only ever been reported once before. A 2013 study by Stanford researchers found that excessive pumping of groundwater had increased arsenic in aquifers in southern Vietnam.
Modeling in the Tulare Basin study was done with an algorithm that used public well data on arsenic levels, and to measure subsidence the researchers tapped Interferometric Synthetic Aperture Radar (InSAR) data, which has been deployed for years to understand changes in groundwater levels. InSAR uses information from satellites that measure tiny changes in the elevation of the Earth’s surface.
“I think what’s most exciting [about this study] is this new way of using the remote sensing InSAR data,” said Knight. “We’ve always thought of subsidence in terms of water quantity issues, and this is the first study that is clearly showing that we can be using this remote sensing data as what I call an early warning system for water quality issues.”
The study concluded that, “Land subsidence due to overpumping increases the probability that groundwater is contaminated beyond the [World Health Organization] drinking water standard by a factor of two to three for the San Joaquin Valley.” The World Health Organization standard is 10 micrograms/liter (or 10 parts per billion), which is the same as California’s health standard.
The good news is that an increase in arsenic concentrations in groundwater doesn’t have to be permanent. “We need to stop pumping as much groundwater and we need to avoid overstressing the aquifer system,” said Smith. “Our study also indicates that if we can reduce pumping than the arsenic levels can return to safer levels within about 10–20 years or so.”
The bad news, however, 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.
“The areas that are most at risk here are people who are using private domestic wells because they are not checking them for groundwater quality regularly and there is not a lot they can do if the arsenic levels exceed the safe standards and there are a number of those communities in this study area in the Tulare Basin,” said Smith.
Also of concern may also be crops irrigated with the water, he added.
Implementation of California’s 2014 Sustainable Groundwater Management Act (SGMA) aims to curb overpumping, especially in the San Joaquin Valley, but new agencies governing groundwater have two decades before sustainability goals need to be achieved.
SGMA, however, provides an important framework for Californians to think about how to achieve the sustainable management of groundwater, said Knight. “I’m a real advocate of data-supported science and policy,” she said. “This is could be used as a guide to be thinking about how much pumping is reasonable, how much pumping is sustainable. I’m hopeful that these kinds of data can promote more sustainable groundwater management.”
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Three Ways to Protect Your Interests as a Groundwater User in California
As California works to implement its Sustainable Groundwater Management Act, water rights attorney Sean Hood explains why it’s important to engage actively in the process.
| WRITTEN BYSean Hood | PUBLISHED ON | READ TIMEApprox. 3 minutes |
CALIFORNIA’S SUSTAINABLE GROUNDWATER Management Act (SGMA) requires each local Groundwater Sustainability Agency to develop and implement a Groundwater Sustainability Plan for its basin and the first plans for critically overdrafted basins are due to be completed by January 31, 2020. Each plan must be designed to achieve safe yield within 20 years.
This new regime of groundwater management is a monumental change in California water law. Overlying land owners have long enjoyed the right to extract groundwater for beneficial use on their land, and the agricultural, municipal, mining and industrial sectors rely heavily on groundwater resources to meet their water needs. It is difficult to fathom the collective investment that California businesses have made in reliance on the right to make beneficial use of groundwater.
In response to SGMA’s passage, public and private stakeholders have scurried to identify new water sources to augment existing supplies. However, the Department of Water Resources’ recently issued Water Available for Replenishment report seems to confirm longstanding conventional wisdom: There is no water supply panacea for solving California’s groundwater management crisis.
California is not the first Western state to grapple with groundwater overdraft, and there are lessons to be learned from previous experiences. In Arizona, the interest groups that were effectively represented in the negotiations resulting in the new groundwater regulations fared much better than the groups that waited for the process to unfold. Some water users enjoyed widespread protection of existing groundwater uses, while others were cut off from valuable supplies that would have supported significant economic growth.
Accordingly, the next 18 months are critical for stakeholders in California. Each Groundwater Sustainability Agency is evaluating an assortment of potential measures to reduce groundwater uses in its basin, including “regulating, limiting, or suspending extractions from individual groundwater wells.” That’s right – the Groundwater Sustainability Agency in your basin has the statutory authority to turn off your pumps.
SGMA provides little in the way of substantive protections for groundwater users. However, procedurally, SGMA requires each Groundwater Sustainability Agency to consider the interests of all groundwater users in the basin, and diligent stakeholders who make certain that their interests are considered are likely to find themselves in a much better place on January 31, 2020 than those who sit on the sidelines and wait for the dust to settle.
Proactive engagement in the process is the name of the game. Here are three things to make sure to do:
- Every concerned stakeholder should request to be added to the Groundwater Sustainability Agency’s notification list. This gets you invited to the party.
- You must show up to the party – repeatedly and consistently. Getting on the mailing list does you little good unless you actively engage in the plan preparation process. This includes participating in meetings, and providing thoughtful, substantive input on proposals and drafts.
Participation in this way serves multiple important purposes. First, it is critical that your Groundwater Sustainability Agency representatives get to know you. You want them to have a sense for your water uses and the businesses they support. They need to understand what is at stake for you and your business.
You also want your Groundwater Sustainability Agency to understand clearly that you are in this for the long haul, and that you will do whatever is reasonably necessary to protect your water uses and your business. In this regard, it is wise to assemble an interdisciplinary team capable of addressing the various legal, scientific and business issues that influence a plan’s contents. As we’ve experienced in Arizona, choosing the right expertise is critical. For instance, teaming with an experienced water litigator will enable you to navigate the complicated water law issues, while also harmonizing your plan development activities with litigation strategy.
- Document your interests as a water user. Each stakeholder should create a comprehensive written record reflecting the information that the Groundwater Sustainability Agency is required to consider, and do it in a way that is likely to have a positive influence on plan development.
This written record also supports a legal challenge if your concerns are not adequately considered. This is important, because the measures that will be required to achieve sustainable yield are likely to involve unacceptable levels of future economic risk for many stakeholders, and it therefore seems inevitable that many Groundwater Sustainability Plans will be litigated. A stakeholder who helped to create the written record of the plan development process will be in a much better position, whether that stakeholder ultimately seeks to defeat the Groundwater Sustainability Plan, or defend the plan against others who may fare worse under its measures.
While neither curtailment nor litigation can be avoided across the board, some stakeholders will avoid adverse outcomes through successful participation in the plan development process. The opportunities to protect your water use are much greater today than they will be in 18 months. Now is the time to actively engage in the process.
The views expressed in this article belong to the author and do not necessarily reflect the editorial policy of Water Deeply.
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