Hydrological and geochemical investigations of selenium behavior at Kesterson Reservoir. Progress report, October 1, 1994--September 30, 1996

This report describes research relevant to selenium (Se) speciation, fractionation, physical redistribution, reduction and oxidation, and spatial distribution as related to Kesterson Reservoir. The work was carried out by scientists and engineers from the Earth Sciences Division of the Lawrence Berkeley Laboratory over a two year period from October 1994 to September 1996. Much of the focus of this research was on long-term, Reservoir-wide changes in Se concentrations and distribution; estimation and prediction of the physical extent ephemeral pools; and the quantification and prediction of Se levels in ephemeral pools waters and underlying sediments. Chapter 2 contains descriptions of field monitoring of soil processes. In Section 2.1, elevated Se concentrations observed in groundwater in the northern part of Pond 9 are investigated. The past removal of the original surface soil in the northern Pond 9 area resulted in the enhancement of Se transport into the shallow groundwater in this area. Removal of the most organic-rich surface soil horizon left the remaining profile with a lower capacity to generate and sustain reducing conditions needed to immobilize Se. Furthermore, removal of the lower permeability surface soil left the remaining profile more hydraulically conductive since sands are encountered at fairly shallow depths. These conditions result in Se remaining oxidized down to the 2.00 m depth throughout the year