30 research outputs found
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Hydrological and geochemical investigations of selenium behavior at Kesterson Reservoir
This report describes research relevant to selenium specification, 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 1992 to September 1994. Much of the focus of these efforts was on the effects of two above-average rainfall years (1991/1992 and 1992/1993). These events marked a departure from the previous six years of drought conditions, under which oxidation of Se in the soil profile led to a marked increase in soluble Se. Evidence from the last two years show that much of the re-oxidized Se was once more reduced due to increased soil moisture content. Also, in areas of high hydraulic conductivity, major vertical displacement of selenium and other solutes due to rainfall infiltration was observed. Such observations underscore the dependence of the future of Se speciation and distribution on environmental conditions
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The Pond 2 selenium volatilization study: A synthesis of five years of experimental results, 1990--1995
Microbial volatilization is a potential remedial measure to decrease the selenium inventory in Kesterson Reservoir soils. Past studies in both the field and the laboratory suggest that a significant percentage of the selenium inventory may be removed in this fashion. The objectives of this study include the quantification of selenium losses and a test of a pilot-scale design which in the future may be used in other parts of the Reservoir
Micro-spectroscopic investigation of selenium-bearing minerals from the Western US Phosphate Resource Area
Mining activities in the US Western Phosphate Resource Area (WPRA) have released Se into the environment. Selenium has several different oxidation states and species, each having varying degrees of solubility, reactivity, and bioavailability. In this study we are investigating the speciation of Se in mine-waste rocks. Selenium speciation was determined using bulk and micro-x-ray absorption spectroscopy (XAS), as well as micro-x-ray fluorescence mapping. Rocks used for bulk-XAS were ground into fine powders. Shale used for micro-XAS was broken along depositional planes to expose unweathered surfaces. The near edge region of the XAS spectra (XANES) for the bulk rock samples revealed multiple oxidation states, with peaks indicative of Se(-II), Se(IV), and Se(+VI) species. Micro-XANES analysis of the shale indicated that three unique Se-bearing species were present. Using the XANES data together with ab initio fitting of the extended x-ray absorption fine structure region of the micro-XAS data (micro-EXAFS) the three Se-bearing species were identified as dzharkenite, a di-selenide carbon compound, and Se-substituted pyrite. Results from this research will allow for a better understanding of the biogeochemical cycling of Se in the WPRA
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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
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Monitoring and Data Analysis for the Vadose Zone Monitoring System (VZMS), McClellan AFB Quarterly Status Report (11/20/98-2/20/99)
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Monitoring and data analysis for the Vadose zone monitoring system (VZMS), McClellan AFB - Quarterly Status Report - 8/20/98 - 11/20/98
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Selenium fractionation and cycling in the intertidal zone of the Carquinez Strait. Annual report, October 1, 1995--December 31,1996
Selenium geochemistry in tidal wetlands is a topic of continuing study at Lawrence Berkeley National Laboratory. The program of studies described in this report was initiated in the fall of 1994 in response to concerns about elevated Se concentrations in waters, sediments, and biota in the Carquinez Strait. Processes by which selenium is introduced and potentially released from the sediment system have been the focus of research in 1996
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Selenium fractionation and cycling in the intertidal zone of the Carquinez Strait. Quarterly progress report, October 1995--December 1995
This quarterly report describes the research on selenium (Se) cycling in the marshes and mudflats of the Carquinez Strait between October 1, 1995 and December 31, 1995. Chapter 2 contains descriptions of field activities and laboratory work related to chemical characterization of sediments and soils. Eh and pH data are presented. Chapter 3 contains a summary of work in progress on the extraction of various Se species from sediment/soil samples, and efforts in measuring suspended sediment Se. Chapter 4 describes advances made in the analysis of parts-per-trillion level Se, using a lanthanum hydroxide co-precipitation method, and the determination of matrix effects. Chapter 5 is an update on stable Se isotope research and Se purification techniques. The reader is referred to the 1995 Annual Report for details on the project design, site selection, and methodology
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Monitoring and data analysis for the Vadose zone monitoring system (VZMS), McClellan AFB - Quarterly Status Report - 5/20/98-8/20/98
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Selenium fractionation and cycling in the intertidal zone of the Carquinez Strait. Draft annual report, October 1, 1994--September 30, 1995
Research aimed at gaining a better understanding of selenium cycling in marshes and mudflats of the Carquinez Strait is being performed by scientists from Lawrence Berkeley National Laboratory and collaborators from the University of California at Davis. This work was initiated in the Fall of 1994 and is scheduled to continue through the Fall of 1996. This report summarizes the results of the effort to date