TREATMENT FOR SELENIUM REMOVAL FROM WELLS FORMATION DISCHARGES IN PHOSPHATE MINING AREA OF SOUTHEAST IDAHO

The Smoky Canyon Mine, operated by the JR Simplot Company of Boise, Idaho, is situated along an anticline near the eastern edge of a large thrust plate. Regional groundwater discharges from discrete springs at the edge of this plate. These spring discharges comprise the majority of the surface water flowing in streams which cross the anticline. Selenium concentrations have been monitored at these springs over the past 10 years. Since selenium was first detected, extensive source controls have been implemented at the mine. As part of this process, evaluation of treatment technologies is being performed. Defining and intercepting contaminated groundwater within the aquifer underlying the mine is not feasible due to the karst environment. Additionally, concentrations of selenium in the discrete springs vary widely, although the springs are separated by only a few meters, thus suggesting highly variable groundwater flow paths.

Simplot has reviewed all pertinent selenium water treatment technologies and is further evaluating three technologies via pilot studies at the springs: (1) zero-valent iron, (2) biological selenium reduction, and (3) low-pressure reverse osmosis. This review also considers the combination of technologies. The low-pressure reverse osmosis technology could be used to concentrate the selenium from the spring water and then feed the concentrate to a biological selenium reduction treatment system. The treated water from both systems could then be recombined and discharged to the stream.