ABSTRACT
Contamination at Kesterson Reservoir led to the assessment of a naturally occurring, potentially toxic, trace element, selenium (Se), from source geologic formations in the surrounding California Coast Ranges. Selenium has been mobilized and concentrated by weathering and evaporation in the process of soil formation and alluvial fan deposition in the arid and semiarid climate of the west-central San Joaquin Valley. This deposition has created a soil salinization problem, and impeding alluvial clay layers have led to waterlogged soils as lands have been reclaimed by flooding to remove the salt and then have been continued to be irrigated. Through current practices of agricultural wastewater management in the valley, subsurface drains are used to collect the saline, shallow groundwater threatening the crop root zone. This wastewater is essentially a soil leachate that was transferred to and stored in wetland areas. This in turn led to extended ecological community exposure to toxic levels of Se and consequent bird deaths and deformities [1].
