TRACE-ELEMENT (SE, AS, MO, B) CONTAMINATION OF EVAPORITES IN HYPERSALINE AGRICULTURAL EVAPORATION PONDS

Disposal of saline drainage waters containing elevated concentrations of the trace elements Se, As, B, and Mo poses a severe environmental h azard in the western part of the San Joaquin Valley of California. Thi s study investigated the partitioning of these trace elements into eva porite minerals formed in agricultural evaporation ponds to determine trace element behavior during the evaporite formation stage and to pro vide information for development of management strategies to minimize environmental hazards. The trace elements were largely excluded from t he evaporite minerals (similar to 100 times depleted relative to the s olution phase), resulting in comparatively low trace element concentra tions in these minerals. The affinity of trace element partitioning to the solid phase follows: Se approximate to B approximate to As approx imate to Mo. No differences in trace element partitioning were evident between summer and winter seasons, the type of evaporite formed, or w hether the evaporites were collected wet or dry. Since trace elements accumulate in the solution phase, highly evapoconcentrated waters may exceed threshold levels for hazardous waste classification. Isolating these trace element-rich solutions during the latter stages of evapoco ncentration into specialized treatment and handling facilities may pro vide an effective management strategy that minimizes both exposure to waterfowl and the amount of hazardous solid waste generated.