Irrigation of native rangeland using treated wastewater from in situ uranium processing

Although land disposal of municipal and industrial wastewater is a common p ractice, there is a potential for adverse environmental effects resulting f rom the application of some wastewaters. This study was conducted to assess the effects of rangeland irrigation using treated process waters from in s itu leaching (ISL) operations at the Highland Uranium Project in Wyoming. I rrigation water quality was evaluated based on guidelines developed by the U.S. Salinity Laboratory, and concentrations of Se, B, U, and Ra-226 were m onitored 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 obt ained from the literature. Although the water is moderately saline (EC appr oximate to 2.8 dS m(-1)), the site maintains adequate leaching to control s alt accumulation in the root zone. Selenium, B, U, and Ra-226 concentration s in grasses were within the natural ranges that have been documented in th e literature, and were also below phytotoxic levels. Boron concentrations i n both the irrigation waters and forage grasses were sufficiently low that they appear to pose no threat to livestock or waterfowl. Plant tissue Se co ncentrations were at or below the lowest reported tolerance level for lives tock during most years, and also below the threshold for Se toxicity in pro nghorn antelope. Therefore, sprinkler irrigation on rangeland appears to be a safe and practical wastewater disposal option at the Highland Uranium Pr oject, and may be a practical method of wastewater disposal for other ISL o perations as well.