Irrigation of Native Rangeland Using Treated Wastewater from In Situ Uranium Processing

Abstract

AbstractAlthough land disposal of municipal and industrial wastewater is a common practice, there is a potential for adverse environmental effects resulting from the application of some wastewaters. This study was conducted to assess the effects of rangeland irrigation using treated process waters from in situ leaching (ISL) operations at the Highland Uranium Project in Wyoming. Irrigation water quality was evaluated based on guidelines developed by the U.S. Salinity Laboratory, and concentrations of Se, B, U, and 226Ra were monitored in soil and vegetation for 6 yr. The effects of Se and B to forage grasses and wildlife were evaluated based on known toxicity thresholds obtained from the literature. Although the water is moderately saline (EC = 2.8 dS m−1), the site maintains adequate leaching to control salt accumulation in the root zone. Selenium, B, U, and 226Ra concentrations in grasses were within the natural ranges that have been documented in the literature, and were also below phytotoxic levels. Boron concentrations in both the irrigation waters and forage grasses were sufficiently low that they appear to pose no threat to livestock or waterfowl. Plant tissue Se concentrations were at or below the lowest reported tolerance level for livestock during most years, and also below the threshold for Se toxicity in pronghorn antelope. Therefore, sprinkler irrigation on rangeland appears to be a safe and practical wastewater disposal option at the Highland Uranium Project, and may be a practical method of wastewater disposal for other ISL operations as well.