Summary

Description

Soda ash is a pulverized mineral, commonly referred to as trona, and harvested from underground deposits in southwestern Wyoming. Four companies own 5 mining operations in the vicinity of Green River, Wyoming, and produce 90 percent of the soda ash in the United States, which accounts for more than 30 percent of the world supply. Trona refining produces tailings water that is either discharged into open evaporation ponds or recycled back into the mining operation and used to facilitate trona ore extraction. As water evaporates from the ponds, chemical residues become concentrated. At cooler temperatures generally 40F sodium decahydrate precipitates out of the water and crystallizes on solid objects in the ponds or on the water surface. Migratory birds landing on the evaporation ponds and being exposed to the water are affected by the sodium decahydrate and other chemical precipitates. Water samples collected from multiple evaporation ponds had similar physical and chemical composition with the exception of phytoplankton species present. Representative total dissolved solids TDS ranged from approximately 40,000 ppm parts per million to greater than 300,000 ppm depending on the pond and time of year. Eared grebe mean serum sodium, chloride, bicarbonate, aspartate aminotransferase, creatine kinase, and uric acid were elevated immediately after capture compared to serum biochemical parameters from eared grebes collected from a reference site in British Columbia, Canada. Histopathologic evidence consistent with drowning was observed in all grebes, but it is not known whether this was a direct mortality factor or a late terminal event.