Central Valley water-quality regulators released a final report Friday concluding oil field wastewater from central Kern County, when blended with other water sources, can safely be used to irrigate a variety of locally grown crops.
The report, based on five years' work and incomplete in some respects, found no evidence of risks to human health from watering tree nuts, citrus, berries, tubers and other ag products with the saline water that comes up from the ground along with oil and which contains small concentrations of toxic chemicals.
Although the findings may not be the final word on the matter, they strengthen confidence that farmers facing tighter water supplies because of the drought can safely irrigate with treated produced water that has been combined with groundwater or surface supplies.
It remains to be seen whether, or how soon, Friday's report by the Central Valley Regional Water Quality Control Board will lead to greater use of an irrigation source tapped locally for more than three decades and now irrigating about 95,000 acres of the valley's agricultural land.
Treating produced water can be expensive for reasons including transportation and filtration. But people familiar with the process have said costs are declining and that expectations are that the practice will be scaled up as the region's freshwater supplies diminish.
Oil industry representatives welcomed the findings, while an environmental organization noted important questions remain unanswered.
"This confirms what we’ve long known: Oil producers are a key part of providing much needed water to farmers during droughts," Rock Zierman, CEO of the California Independent Petroleum Association trade group, said by email. "When we shut down local oil production, we are also shutting down agriculture."
Added Christine Zimmerman, senior manager of regulatory affairs at industry group Western States Petroleum Association: "The findings provide clear evidence that food crops irrigated with beneficial reuse water are as safe and healthy as crops irrigated with other water sources. We support the findings of the panel and acknowledge the absolute need for consideration of all safe water sources.”
But the California director for Washington, D.C.-based Food & Water Watch, Alexandra Nagy, said the study did not put the matter entirely to rest.
"As its authors clearly state, the study largely passes over soil contamination from produced water, which can have substantial impacts on groundwater supply and thus on the health of the communities who depend on it," Nagy said by email. "Corporate greenwashing from industrial agriculture and fossil fuel interests have perpetuated a cycle that only benefits their bottom line, but threatens the health of our planet and our people.”
Authored by water board staff and the effort's science advisor, William Stringfellow, Friday's 37-page report notes researchers compared produced water-irrigated crops with a control group of crops watered with regular irrigation water.
Between 2017 and 2019 they tested for 399 chemicals associated with local produced water — including naturally occurring hydrocarbons, metals and radionuclides as well as additives like solvents and biocides — and were unable to identify any significant health and safety risks present in the crops irrigated with produced water that weren't present in the control group.
"While there are unanswered questions and data gaps, the information available does not indicate that there are concerns related to the presence of chemicals of interest at either background concentrations or elevated levels in blended produced water," the report states. "Also, while it has been demonstrated that some of the chemicals of interest have the potential for plant uptake, the available evidence does not indicate that this has or will occur at particularly higher rates than plants using conventional sources of irrigation water."
Among several unknowns identified in the report are the levels at which 19 percent of the chemicals of interest become toxic to humans. Other caveats range from a lack of analytical methods for monitoring certain chemicals to limited funding for a more thorough study.
The authors recommended changes to the wastewater discharge permits issued by the regional water board for produced-water irrigation. It said they should take into account not just the quality of the produced water but also the quantity, the type of crop irrigated and how the produced water was treated. They also advised the use of only low-hazard additives by oil producers whose wastewater goes to irrigation.
The report further advised evaluating risks associated with any new chemicals used by contributing oil producers, doing or supporting environmental studies of the effects of produced water on agriculture, the practice's effects on soils and a closer look at differences between produced water from different parts of the valley.
The study also found the Central Valley is the only region in the country using produced water for irrigation. Other countries have done so, including Mexico and Brazil, which used produced water with relatively high saline levels. But according to the study, nowhere else is the practice used for commercial ag production.
The report can be found online at https://www.waterboards.ca.gov/centralvalley/water_issues/oil_fields/food_safety/data/white_paper/foodsafety_whitepaper.pdf.