USGS Open-File Report 03-251: Chromium geochemistry of serpentinous sediment in the Willow core, Santa Clara County, CA

Chromium geochemistry of serpentinous sediment in the Willow core, Santa Clara County, CA

By Christopher J. Oze, Matthew J. LaForce, Carl M. Wentworth, Randall T. Hanson, Dennis K. Bird, and Robert G. Coleman

Abstract

A preliminary investigation of Cr geochemistry in serpentinous sediment completed for a multiple-aquifer ground-water monitoring well (Willow core of Santa Clara County, CA) determined sediment at depths >225 meters contains Cr concentrations ranging from 195 to 1155 mg/kg. Serpentinous sediment from this site is a potential source of non-anthropogenic Cr contamination. Chromium-bearing minerals such as Cr-spinel appear to be the main source of Cr in the sediment; however, Cr-bearing silicates and clay minerals are additional Cr sources. Aqueous Cr concentrations in the sediment are <4.6 mg/L; however, the valence of Cr was not identified in the solutions or in the sediment. Although there is no indication of Cr(VI) contamination derived from the serpentinous sediment, elevated Cr concentrations in the sediment, the observed ‘dissolution’ textures of the Cr-bearing minerals, the estimated redox environment, and water chemistry indicate the formation of Cr(VI) is potentially favorable.

First posted July 23, 2003

Report PDF (1.4 MB)

For additional information, contact:
Geology, Minerals, Energy, and Geophysics Science Center
U.S. Geological Survey
345 Middlefield Road, MS 901
Menlo Park, CA 94025-3591
http://geomaps.wr.usgs.gov/gmeg/

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Suggested citation:

Oze, Christopher J., LaForce, Matthew J., Wentworth, Carl M., Hanson, Randall T., Bird, Dennis K., Coleman, Robert G., 2003, Chromium geochemistry of serpentinous sediment in the Willow core, Santa Clara County, CA: U. S. Geological Survey Open-File Report 03-251, 24 pp., http://pubs.usgs.gov/of/2003/0251/.