CAN LOW-SALINE OILFIELD WATER BE USED FOR IRRIGATION IN CALIFORNIA?

After several years of drought and reductions in natural water availability, farmers throughout California have been in dire need of additional irrigation water. One way they are supplementing local groundwater is through reuse and irrigation with oilfield produced water (OPW). While OPW throughout the United States is typically characterized by high salinity, naturally occurring radioactive materials (NORM) and heavy metal concentrations, OPW from some fields from the eastern section of Kern County in California has low salinity. For the past 25 years, OPW has been blended with surface water and used for irrigation in the Cawelo water district in Kern County. In this study, we characterize the chemistry of OPW and the Cawelo canal water used for irrigation. We examined the inorganic chemistry, metal concentrations, and NORM in both water and soil samples to evaluate (1) the quality of OPW and irrigation water; and (2) the possible accumulation of salts, metals, and NORM in soil irrigated by OPW. We also examined a site where unblended OPW has been used for irrigation. While we observed geochemical differences between regional groundwater and blended OPW, we found that with the exception of relatively high arsenic and to a lesser extent boron in the blended OPW, all parameters (Cl, Al, Ce, Cd, Cu, F, Pb, and Ba) fall below EPA maximum contaminate levels and regional water quality guidelines. In addition to water quality, we examined water leachates from soil in Kern County, finding higher Cl, SO₄, Ca, Na, B, and As in soil irrigated with blended OPW relative to sites irrigated by local low-saline groundwater. However, we did not find systematic differences in NORM concentrations in soil irrigated by OPW relative to groundwater. We conclude that blended OPW provided by the Cawelo water district is of comparable quality to the local low-saline groundwater in the region and does not pose risks to human health. The relatively high boron in OPW results however boron accumulation in the soil that can pose long-term risks to plant health. The salinity of OPW seems to be the key for assessing the suitability and the long-term risks of using OPW for irrigation in California.