In an attempt to determine whether it is safe to use oilfield produced water for crop irrigation, a team of researchers from Duke and RTI International analyzed soil and water samples from the Cawelo Water District in California. Previous debates regarding the practice of using oilfield produced water (OPW) in irrigation have centered around concerns that OPW contains toxic metals or radioactivity accumulation in the soil. This new study, published in Science of the Total Environment, says otherwise.
"Those concerns assumed that the OPW generated by oil and gas wells in the Cawelo district contains similar mixtures of salts, metals, and naturally occurring radioactivity as OPW generated in oil fields in other regions. But our study shows that's not the case," said lead researcher Andrew Kondash, a research environmental scientist at RTI International, who conducted this study for his 2019 doctoral dissertation at Duke.
Kondash and the other researchers on the team specify that their findings are particular to the Cawelo district and should not be used to extrapolate to other regions for OPW practices. "You can't assume that the results in this study could be applied to OPW from other oilfields, where the salinity is typically much higher," he said. To get accurate readings on OPW from other regions would require a similar sample analysis of water and soil.
OPW is produced as a byproduct of oil and gas extraction at sites, many of which are located close to farm fields in Cawelo district. The practice of using OPW to irrigate crops comes as a consequence of the droughts that plague the region, yet there have been concerns that this proximity could impact water and soil quality, harm crop health or pose risks to human health.
But, according to the study’s findings, water quality is not affected by OPW in Cawelo. "We did not find any major water quality issues, nor metals and radioactivity accumulation in soil and crops, that might cause health concerns," said Avner Vengosh, professor of water quality and geochemistry at Duke's Nicholas School of the Environment.
"The OPW produced in Kern County is much more diluted and low-saline than common OPW from other parts of the country, so it can be used for irrigation if it is mixed with surface water," added Kondash.
The researchers say that while they did see slightly elevated levels of salts and boron in OPW compared to the local groundwater, the levels are still below the standards set by the state for safe drinking water and irrigation. Nevertheless, farmers should be alert, reports Eureka Alert, because salts and boron accumulate over time in the soil, so farmers must plant boron-tolerant crops and mix OPW with fresh water to avoid boron toxicity and salinity buildup.