For decades, farmers in California’s Kern County have turned to wastewater from oil production to help irrigate their crops during extended dry spells.

The wastewater provides an alternative to groundwater, which has become increasingly scarce as farmers have pumped more than they could replenish.

But the use of the recycled water, a byproduct of oil and natural gas extraction that is mixed with surface water for irrigation, has stirred controversy. Because the water, known as oilfield produced water or oilfield brine, contains chemicals like salt, boron, arsenic and radioactive elements, scientists and environmentalists worry that it poses a risk to human health.

California water officials have argued that the water from the east side of the county is safe to use because of its low salinity levels. Other experts have said further testing of the water is needed and contend that the state should impose tighter restrictions on its use. 

A study released earlier this year has added to the debate. Conducted by a team of California and North Carolina researchers, the study found that the concentrations of boron, salt, radionuclides and other chemicals in samples of water and soil in Kern County’s Cawelo Water District met safety standards for irrigation water.  

The findings should reduce fears about the impact of the contaminants in Cawelo’s water on soil quality and human health, according to Dr. Avner Vengosh, a professor of earth and ocean sciences at Duke University and a co-author of the research.  

“That’s kind of giving reassurance that this practice, as long as they keep the salinity low and mix it with enough [surface] water, is safe from having a negative effect on the soil or the crops,” he said. 

But in the study, published in the journal Science of the Total Environment, also called for further testing of the chemicals in the water, testing in other locations and investigation of the long-term effects on human health of consuming crops irrigated by oilfield wastewater. 

Even if chemicals in the oilfield water did not pose a health risk, the researchers noted, salt and boron might accumulate in the soil to levels higher than traditional groundwater, imperiling crops in the long-term. 

As a result, farmers would have to replace or grow more boron-tolerant crops, such as grapes, peanuts and carrots, and keep mixing the produced water with fresh water to prevent this build-up.

A Dry State and Even Drier County

Water shortages are all too familiar in California. For the farmers in the state, making sure there is water for their crops is one of the highest costs of producing a majority of the nation’s food supply. In Kern County, water scarcity is a defining characteristic of the region. 

Climate change is making things worse, lengthening dry periods. California only last year came out of an eight-year drought, then returned to drought conditions in February.

Faced with water shortages and a 2014 law that puts limits on groundwater use, farmers have increasingly turned to oilfield wastewater. The water irrigates 95,000 acres of cropland in California’s southern San Joaquin Valley, according to the California Regional Water Quality Control Board. 

David Ansolabehere, general manager of the Cawelo Water District, which has used diluted oilfield water for more than 25 years, said the water has helped farmers maintain crop yield during dry years. The recycled water makes up 25 to 30 percent of the district’s yearly irrigation water and irrigates 34,000 acres of the surrounding farms, according to Ansolabehere. 

“Without this water, thousands of acres of high value crops could be fallowed,” Ansolabehere said. 

Oilfield wastewater is also abundant in Kern County, which produces 70 percent of the state’s oil. 

Every barrel of oil generates around 15 barrels of produced water, according to the Cawelo Water District. As of 2015, Chevron, one of Kern County’s main oil suppliers, recycled 21 million gallons of water each day and sold it to farmers who used it on 10 percent of Kern County’s farmland, according to the Los Angeles Times. 

Groundwater, a Dwindling Resource

One reason farmers have turned to oilfield produced water is that without it, water shortages could force them to significantly reduce their acreage. 

Tom Frantz, an almond farmer in Shafter, does not use oilfield-produced water for his 40-acre almond farm. But bigger farms have a higher crop yield and require more water, an amount that’s unavailable most years. 

“We’ve over-planted too many acres for the amount of water we have, that’s why we start using more questionable water supplies,” Frantz said.

Historically, farmers have relied on groundwater during droughts, but too much pumping has led to water scarcity in the long-term. In some agricultural regions of the state, the groundwater overdraft—the extent to which more water is pumped than is replenished—is between one to two million acre-feet annually. 

Laura Feinstein, a senior researcher at the Pacific Institute and one of the study’s authors, said that rising temperatures contribute to groundwater overdraft because they reduce the amount of surface water available, which leads to more groundwater pumping. In 2014, the state created the Sustainable Groundwater Management Act (SGMA) to manage groundwater resources and halt groundwater overdraft by the 2040s. SGMA, which allows for more federal control over groundwater use, requires that local groundwater agencies develop sustainability plans that set limits on how much water can be pumped. 

Dr. Graham Fogg, a professor emeritus of hydrology at University of California Davis, said excessive groundwater pumping has caused a compaction in clay layers and subsidence of land surface, damaging roads, pipelines and canals. He said in at least one case, land subsidence damage reduced the carrying capacity of a major canal by about 40 percent. 

But for some farmers in Kern County, the amount they are allowed to pump under the Act is not enough to water their farms, making the land unprofitable. A study by University of California, Berkeley researchers estimates that current groundwater regulations will cause California to lose one-fifth of the cultivated farmland in the San-Joaquin Valley, 85,000 jobs and $7 billion per year in farm revenue. 

That makes oil water all the more valuable because it’s constantly available. 

“Water should never be wasted—recycling of municipal and industrial water is a central tenet of California statewide water policy,” Ansolabehere said. 

Rodgers said recycled produced water could potentially be a longer-term solution to dry periods, as long as there is oilfield production. “We do everything we need to do to confirm that there aren’t any issues with recycling of this water and recycling is something the state of California supports,” he said. “We are interested in making sure that what we’re doing with water is appropriate.” 

An Argument Over Health Risks

Although some farmers in the Cawelo district have been using oilfield produced water for more than three decades, not everyone is happy about it. Environmental activists have argued that although the regional water control board has approved the use of the water, it’s still uncertain whether the water poses health risks.

Bill Allayaud, the California Director for Government Affairs at the Environmental Working Group, said in an email that experts need to test other organic and industrial chemicals that may be present in oil production, and not just boron, salt and arsenic.

“We waited years for this report and the main conclusion was “‘we need more study,’” he said.

Until state officials are certain the oilfield water is safe, activists argue that it shouldn’t be used for irrigation. Water agencies did not have access to information on hazardous chemicals used in oil production until the state legislature passed a bill in 2017, Rodgers said. 

The bill provides additional authority to the State Water Board and regional water boards to obtain information from oil suppliers or other entities on chemicals in the wastewater. The bill also requires that the water board disclose this information to the public on their website.

“Oil industry waste fluid contains a wide array of chemicals, both known and unknown, and we do not understand the full extent of harm it will inflict on our crops and on our health,” said Hollin Kreztmann, senior attorney for the Center of Biological Diversity.

He said residents have long been concerned about whether the oil wastewater posed risks to their crops.

Andrew Grinberg, special projects manager with Clean Water Action, said that the testing methods and toxicity information for some chemicals that could be present in produced water are not available.

“So we’re unclear on what the impacts are on human health and the environment,” he said. 

Regulators and Industry Dispute Health Risks

For their part, California water and oil officials like Ansolabehere say the wastewater is already properly regulated.

Salt accumulation, Ansolabehere said, does not pose a risk because regulations from the regional water control board prevent salinity from exceeding normal levels. Produced water is blended with surface or groundwater to lower the salt content to a level crops can tolerate. “Salt build-up has been and will continue to be a concern for all farmers, whether using recycled produced water or any traditional water source,” he said. 

He said the study confirmed years of research by the  regional board that indicated the practice of using wastewater was safe in that area of Kern County, he said. 

Since then, the Cawelo Water District and the Regional Water Control Board, with the assistance of a Food Expert Safety Panel, have tested more than over 160 compounds that could be in the water, he said.

Clay Rodgers, assistant executive officer for the California Regional Water Quality Control Board, Central Valley, said that so far, the regional control board has not found any evidence that indicates the recycled produced water is unsafe to use for irrigation. 

“But that doesn’t mean the board isn’t still looking and everything is resolved,” Rodgers said. “If we get any evidence that the water is unsafe, we’ll take steps to stop it.” 

A spokeswoman from Chevron, one of the county’s main oil producers, said that the Duke University study conclusions are consistent with findings from studies initiated by the regional board.

“Protecting people and the environment is one of Chevron’s core values,” she said. “We remain committed to cooperating with regulators and partnering with organizations like the Cawelo Water District on innovative solutions to California’s water challenges,” she said in an email.

Frantz, however, said farmers shouldn’t be dependent upon oil suppliers because excess salts in their water will eventually adulterate the soil. He said while farmers can profit from it now, it will create problems for future generations. 

“It’s short-term thinking for profit instead of looking many generations down the road to see what’s best for society as a whole,” he said.

With the threat climate change poses to the southern San Joaquin Valley region, Frantz said, farmers are likely to face a lot of uncertainty and struggle in the years ahead.

“It’s very hard to quantify an ever-present looming disaster,” he said.

An earlier version of this article incorrectly identified the director for government affairs at Environmental Working Group (EWG). He is Bill Allayaud, not Ben Allayaud.