California Water Regulators Still Haven’t Considered the Growing Body of Research on the Risks of Oil Field Wastewater


California is heading into its dry season after one of the driest winters on record, preceded by a brief reprieve from the worst drought in its history. No wonder water managers in the Central Valley’s parched farm belt are increasingly interested in a controversial practice: reusing oil field wastewater to grow crops. 

Last fall, the Central Valley Regional Water Quality Control Board assured critics that it had reviewed studies of the practice and found no elevated risks to human health or crop safety. The board focused primarily on one question—are crops grown with produced water safe to eat?—and considered as beyond the scope of its responsibility the wider range of potential harms associated with recycling the oil industry’s wastewater. 

The board acknowledged that it did not study how long-term use of oil companies’ “produced water” might affect crops and soil that are irrigated with it, or whether toxic chemicals in the wastewater could accumulate over time in the nuts, oranges and grapes that are sent around the world. Nor did the board consider the ecological risks of spreading oil field wastewater across the land in a county where at least 20 threatened or endangered species live within about a mile of an oil field, a proximity that has already resulted in millions of gallons of the oil and wastewater inundating their habitat.

But scientists in other parts of the country have investigated these questions, looking at both the consequences of intentional reuse of oil wastewater for irrigation and disposal and accidental spills of the wastewater on wildlife and the environment. And a growing body of research shows that even highly diluted produced water can harm soil, plants and aquatic life, and that oil drilling boosts groundwater concentrations of naturally occurring toxic elements like arsenic, and radioactive elements like radium, while also endangering sensitive ecosystems and protected wildlife, an Inside Climate News analysis has found.

Research over the past several years has shown that produced water can lower crop yields; suppress plant disease defenses; inhibit seed vigor and germination; impair soil health by reducing microbial diversity; and harm fish, amphibians and mollusks. Scientists have also documented accumulations of metals and other toxic compounds from produced water in plants, including the shoots and roots of grasses and the stems and grain of wheat. 

None of these studies have been done in Kern County. But scientists who have conducted, or reviewed, the findings said there’s enough evidence to proceed with caution in California. 

“There are a number of studies available now that can help guide what precautions we ought to take and what contaminants we might expect could be persistent or show up,” said Isabelle Cozzarelli, a research hydrologist with the U.S. Geological Survey who has studied the environmental impacts of oil and gas contaminants in several Eastern and Midwest states. “We know enough to know we better be careful.” 

Farmers have long struggled to sustain thirsty crops like almonds and pistachios in Kern County, where it rains less than 10 inches in a normal year. And with climate change, hopes of a “normal” year are disappearing faster than the Sierra Nevada snowpack needed to replenish the state’s water supplies.

But as it gets harder and harder to extract California’s tarry crude oil from aging wells, the massive stream of wastewater keeps increasing.

The ratio of wastewater generated to oil extracted has more than doubled over the last 20 years. And Chevron’s sale of produced water to Kern County’s Cawelo Water District increased from an average of 19,000 acre-feet—or about 6 billion gallons—in the mid-1990s to nearly 30,000 acre-feet, or nearly 10 billion gallons, in recent years, as regulators restricted groundwater pumping and surface water allocations evaporated with the drought.

The Central Valley Water Board, which oversees Cawelo and other water districts, approved two applications to expand the use of produced water for irrigation in 2019 and is currently reviewing another application.

More than 14 billion gallons of produced water from Chevron and a handful of other Kern County oil companies now saturate nearly 100,000 acres, about 11 percent of the county’s irrigated farmland.

Irrigation districts that supply the region’s multibillion dollar agricultural industry view produced water as a way to cope with its perpetual water woes. Public interest groups, in contrast, have pressured the state to stop growing food with produced water, citing concerns about potential risks to people, wildlife and the environment.

The Central Valley Water Board responded to the public concern by launching a Food Safety Project in 2015, and retained a firm it described as a “neutral third party” to study potential risks of the practice. In fact, the firm, GSI Environmental, had a long history of working for the oil industry, including Chevron, the largest provider of produced water for farmers.

The board’s review of GSI’s studies noted that chemicals in produced water used for irrigation had the potential to accumulate in crops and soil, said Clay Rodgers, who oversaw the Food Safety Project. Although the studies did not yield “significant differences” that could be attributed to produced water in the crops that were tested, he said, “There is an unknown potential that chemicals from produced water and other environmental sources may be accumulating in the soil.”

The water board is not proposing additional studies to close these data gaps, Rodgers said, “as funding is not available.”

USGS scientists are studying the prospects of reusing industrial waste like produced waters, particularly in drought-prone regions, said Madalyn Blondes, a research geologist with the agency. “If we can do it safely, then we should look into those options.”

She added, “But it’s important to look at what potential impacts are and actually analyze where there might be certain unintended effects.”

“It’s not just a matter of saying everything’s fine, let’s do it,” Blondes said.

Drone footage of a “surface expression,” or spill, in Chevron’s Cymric Oil Field. When oil companies inject high-pressure steam into wells to extract oil, crude and water can erupt through fissures in the ground and reach the surface. California didn’t ban these inland spills until April 2019. Credit: Tom Frantz

Unintended Consequences

For decades, San Joaquin Valley farmers enjoyed unfettered access to the state’s aquifers, severely depleting groundwater supplies to cope with droughts.

Former state Sen. Fran Pavley (D-Agoura Hills) put an end to unregulated pumping in 2014, when she helped pass California’s Sustainable Groundwater Management Act, or SGMA.

But now, Kern water districts are promoting the wastewater of an industry that has contaminated the state’s dwindling groundwater reserves as a resource that instead conserves them.

For Pavley, who also authored the first law requiring oil companies to report how much water they use and what chemicals they add to fracked wells, this approach perverts the intent of the law.

California’s water is in critically short supply, said Pavley, now the environmental policy director for the University of Southern California’s Schwarzenegger Institute. “We need to make sure we’re not contaminating the water we have and affecting the health and safety of people and the agricultural crops people digest.”

Water districts typically blend produced water with ground and surface water before sending it to farmers for irrigation. Kern County is one of the few regions in the country where produced water has low enough saline levels that even lightly blended water doesn’t kill crops outright. That’s partly because seasonal runoff from melting Sierra snowpack recharges the groundwater and dilutes toxic salts.

But climate models suggest that salinity in Kern County produced waters is likely to rise as the planet warms. That’s because county aquifers will see less seasonal influx of freshwater from the mountains as rising global temperatures evaporate more water and keep Sierra snowpack levels low.

Rodgers said the harmful effects on plants and soils that studies outside of California have linked to oil field wastewater are primarily related to salinity, which is not an issue in Kern.

However, recent studies have shown that salt compounds are not the only contaminants that affect plant and soil health.

In 2019, researchers reported the first evidence that produced water can impair plant defenses against pathogens in the peer-reviewed journal Environmental Science & Technology Letters.

The researchers suspected that it wasn’t salinity that was primarily responsible for weakening the immune responses of wheat plants, but possibly boron and petroleum hydrocarbons. Both contaminants are common in Kern County’s produced water.

And though California still has lower salinity than other groundwater basins USGS scientists have studied, said Blondes, “that doesn’t mean it can’t have high concentrations of other compounds.”

Even when compounds are present at low levels, she added, if you have enough compounds from a similar class, they could combine to prove harmful.

And it’s naturally occurring toxic elements like cancer-causing radium and arsenic left behind in groundwater and surface water by oil extraction that are most concerning to Blondes. “Everyone talks about the risks of fracking fluids,” she said. “But there are lots of naturally occurring chemicals that aren’t additives that have all kinds of environmental and health impacts.”

The Kern River once supported diverse species and vegetation along its banks before thousands of pump jacks claimed its floodplains. Credit: Liza Gross
The Kern River once supported diverse species and vegetation along its banks before thousands of pump jacks claimed its floodplains. Credit: Liza Gross

Drowning in Oil Waste

The oil-drilling techniques that generate produced water for irrigation pose serious risks to wildlife and the environment.

To coax Kern’s heavy crude to the surface, oil companies inject high-pressure steam and water into wells. This technique uses so much pressure that, in the county’s highly developed oil fields, it can accidentally force oil and wastewater to burst out through fissures in the earth, causing above-ground spills called “surface expressions.”

Surface expressions weren’t explicitly banned in California until April 2019.

About a month after the state regulated these inland spills, oil and wastewater escaped from wells at Chevron’s Cymric Oil Field, some 140 miles north of Los Angeles. More than 1.3 million gallons of hot oil and water, including 400,000 gallons of crude, gushed up from the earth over four months, turning a dry streambed into a river of oily wastewater.

Wildlife officials found four birds covered in oil but could not save them. Chevron, meanwhile, stood to make nearly $400,000 from selling oil recovered from the spill, state records show.

California fined Chevron more than $2.7 million for numerous violations, noting that the spills caused “significant threat of harm to human health and the environment.” ​​

Crews had barely cleaned up the spill, one of the largest in California history, when hundreds of thousands of gallons of oily water oozed through the ground in another section of the same oil field. More than 5 million gallons of gooey wastewater from these eruptions have reached the surface at an adjacent site since May 13, according to state records.

These types of practices endanger people and wildlife, said Hollin Kretzmann, senior attorney with the Center for Biological Diversity’s Climate Law Institute, “but the company hasn’t paid a dime of that $2.7 million fine.”

Chevron representatives said they’ve been working with regulators to resolve the issue.

Sean Comey, senior communications advisor with Chevron’s San Joaquin Valley division, said in an email that Chevron had submitted reports of soil studies and remediation activities to the Central Valley Water Board. “The parties are making progress and continue to engage in good-faith efforts to reach a resolution,” he said.

CalGEM, the agency that regulates oil and gas, did not respond to repeated requests for comment about how the state planned to resolve Chevron’s case.

In 2020, Aera Energy, jointly owned by ExxonMobil and Shell, applied for a U.S. Fish and Wildlife Service permit under the Endangered Species Act that exempts companies from prosecution if their operations harm or kill protected species. Aera’s application for an “incidental take” permit seeks protection if current or expanded oil operations over the next 35 years harm any of five protected species: the San Joaquin kit fox, blunt-nosed leopard lizard, San Joaquin antelope squirrel and giant kangaroo rat.

The Center for Biological Diversity has filed comments with USFWS opposing Aera’s application, which is still under review, arguing that climate change is already increasing species extinction risk by disrupting ecosystems. “Any expanded oil operations are inherently incompatible to species protection,” the group said.

“Kern County is smack dab in the middle of a really biodiverse San Joaquin Valley,” said Kretzmann. Aera’s application “is essentially an admission that, ‘Yeah, our oil and gas operations are going to affect these species.’”

Aera did not respond to multiple requests for comment.

Intensive oil development has denuded the Kern County valleys where lakes, wetlands, grasslands and saltbush scrublands once dominated the landscape.

An ecological risk assessment is warranted, said Andrew Gordus, a California Department of Fish and Wildlife toxicologist who served on the water board’s expert panel. “But someone has to come up with the funding to do such a study.”

The water board study of wastewater irrigation, said Gordus, who retired last year, had a much narrower focus: “Is the edible part of the plant safe to eat?”

At least 20 threatened or endangered species live within about a mile of a Kern County oil field, where pump jacks suck up oil around the clock. Yet relatively few peer-reviewed studies have investigated the ecological impacts of these oil operations, let alone how intentionally spreading produced water across fields affects native flora and fauna.

Many imperiled species have met their demise in oil waste. Over the years, scientists have found endangered blunt-nosed leopard lizards, San Joaquin kit foxes and giant kangaroo rats, one of the foxes’ primary prey, drowned in oil spills and oil wastewater. All three species are found only in California.

San Joaquin Kit fox
San Joaquin Kit foxes are among the species that have been found dead in oil waste. Credit: Greg Schechter/flickr

So far, no independent studies have revealed how native plants and wildlife are coping with millions of gallons of hot water and oil inundating their habitat.

More Questions than Answers

Scientists still know very little about all the ecological and health consequences of growing crops with produced water, but have gleaned clues from investigating spills like the one at the Cymric oil field. Cozzarelli of the USGS studies has long studied spills and disposal of produced water to understand the potential risks of intentional reuse.

In a 2016 study of a West Virginia produced water disposal facility, Cozzarelli’s team found concentrations of radioactive elements and other toxics in a nearby stream. The toxic chemicals reduced microbial diversity, signaling effects on the freshwater ecosystem, they reported in Environmental Science & Technology. A related study showed that water from the stream disrupted several hormones in lab tests, raising concerns about health risks for wildlife and, because the stream flows into a river used for drinking water, people.

But the disposal facility cut off the team’s access halfway through the study, Cozzarelli said, “once we started to find out that there were some negative environmental effects.”

USGS scientists have had better luck at a county-owned site near Bemidji, Minnesota, where a high-pressure pipeline burst open in 1979, spilling close to 450,000 gallons of crude. They’ve had decades of uninterrupted access because the site is on public land. They have also studied spills of produced water on federal land.

Many studies have shown that the hydrocarbons in crude that release greenhouse gases when burned harm aquatic ecosystems. And studies of produced water spills show that chloride and other naturally occurring elements have proved particularly harmful to soil, plants and freshwater species like fish and mussels, Cozzarelli said. 

Rodgers of the water board said concerns about harmful effects to aquatic life are not relevant because Kern’s produced water isn’t discharged into streams.

Yet not much is known about how contaminants in oil and gas wastewater move from fields into streams and other surface waters, said Cozzarelli. Monitoring runoff from irrigated fields is particularly important for substances that don’t easily break down and have toxic effects, she said.

The same elements found to harm aquatic species taint Kern County’s produced water, as do the hydrocarbons in petroleum. Crude oil can both contain arsenic and trigger its release when hydrocarbons in crude degrade and change groundwater chemistry, Cozzarelli reported in a peer-reviewed study in 2015.

Chronic exposure to arsenic can cause numerous ailments, including liver disease and several types of cancer. Arsenic levels in the tainted groundwater in Bemidji were 23 times higher than drinking water standards, Cozzarelli and her team found. Once hydrocarbons get into groundwater, they trigger reactions with compounds in sediments to release more arsenic.

Both the upper Midwest and Kern County have high arsenic levels in groundwater, Cozzarelli said, “just from natural organic material that’s degrading.”

Oil extraction accelerates that process “by dumping in a whole bunch more” rapidly biodegradable hydrocarbons, she said. The petroleum releases not only more arsenic into groundwater but also trace metals like cadmium, copper and zinc.

USGS studies of both intentional reuse and spills reveal that even low levels of toxic compounds in water and soil can build up and move across the landscape—and why studying soil irrigated with produced water is so important. 

Bonnie McDevitt, a postdoctoral researcher with the USGS, spent years studying a site in Wyoming where produced water is discharged into streams and used for irrigation and livestock drinking water. The produced water had low salinity, like Kern County’s.

She focused on the radioactive element radium. Although radium at the discharge site fell below levels allowed by federal rules, she reported in a 2019 peer-reviewed study, it accumulated at much higher levels in sediments downstream.

McDevitt also saw “significant uptake” in wetland plants, particularly cattails. She said she didn’t do any studies on irrigated crops and is unsure if any have been done. “But small discharges of radium can still accumulate,” she said.

The Central Valley Water Board concluded that radioactive elements in produced water were unlikely to pose a risk, based on a review of its consulting firm’s studies. “Although GSI did not evaluate the potential for radionuclides to accumulate in the water distribution system, GSI did conclude that radionuclides do not appear to be a health risk in irrigated crops,” the board said in response to a public comment.

McDevitt said she would approach that conclusion with caution, especially in an arid region where evaporation is likely. Concentrations that appear safe at one point in a water system could prove hazardous miles downstream, she said, “where you have almost 100 percent evaporation.”

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That’s exactly what happens during drought, when salts and other harmful compounds are likely to accumulate, said Cozzarelli. “Even if the concentration in the applied water didn’t seem concerningly high, it could accumulate to levels that affect soil health.”

Oil wastewater is “loaded with things we need to be concerned about,” she said, pointing to the carcinogens benzene and arsenic. And once these toxic substances get into groundwater, they can persist for years.

Contaminated sediments act like a leaky storage locker, releasing their toxic cache as water levels change.

When Cozzarelli studied a spill in North Dakota’s Blacktail Creek, she found that contaminated water infiltrated riverbanks during high flow, then escaped during low flow. The study demonstrated that there can be long-term storage of both contaminated sediment and contaminated water in pores in the soil, she said.

Flooding can also move toxic compounds across the landscape.

There was a lot of radium on the floodplain of Blacktail Creek, Cozzarelli said, because a heavy flood carried sediment there from the river channel.

If toxic compounds are building up in the soil of fields irrigated with produced water in Kern County, floods could well wash them away. California is stuck in another multiyear drought, but climate models predict that extreme precipitation is likely to follow exceptionally dry years. And when it does, Kern County faces “relatively high” risk of flooding, according to FEMA.

With “thousands of things in these produced waters,” Cozzarelli said, scientists have started to focus on evaluating how the water itself rather than individual chemicals affect organisms and ecosystems.

But that work has just begun.

“We do more studies, we answer a few questions, and then it brings up so many more questions,” Cozzarelli said.

For Pavley, known for her pioneering climate legislation, questions about the environmental and health risks of produced water distract from the real goal: weaning ourselves from oil and gas.

“You wouldn’t have oil field wastewater,” she said, “if you didn’t have oil fields.”



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