Developing protocols for geochemical baseline studies: An example from the Coles Hill uranium deposit, Virginia, USA

• Published in: Applied geochemistry Vol. 43; pp. 88 - 100
• Main Authors: Levitan, Denise M., Schreiber, Madeline E., Seal, Robert R., Bodnar, Robert J., Aylor, Joseph G.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-04-2014; Elsevier
• Subjects: Deposits; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochemistry; Pollution, environment geology; Sediments; Statistical methods; Streams; Surface water; Temporal logic; Trace elements; Uranium; United States; Virginia; USA, Virginia; detection limit; streams; sampling; climate variability; concentration; protection; baseline; North America; surface water; trace elements; regression; standard samples; ecosystems; hills; discharge; stream sediments; spatial variations; drinking water; uranium; statistical analysis; statistics
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2014.02.007

•We outline protocols for baseline geochemical surveys of stream sediments and water.•Regression on order statistics was used to handle non-detect data.•U concentrations in stream water near this unmined ore were below regulatory standards.•Concentrations of major and trace elements were correlated with stream discharge.•Methods can be applied to other extraction activities, including hydraulic fracturing.
In this study, we determined baseline geochemical conditions in stream sediments and surface waters surrounding an undeveloped uranium deposit. Emphasis was placed on study design, including site selection to encompass geological variability and temporal sampling to encompass hydrological and climatic variability, in addition to statistical methods for baseline data analysis. The concentrations of most elements in stream sediments were above analytical detection limits, making them amenable to standard statistical analysis. In contrast, some trace elements in surface water had concentrations that were below the respective detection limits, making statistical analysis more challenging. We describe and compare statistical methods appropriate for concentrations that are below detection limits (non-detect data) and conclude that regression on order statistics provided the most rigorous analysis of our results, particularly for trace elements. Elevated concentrations of U and deposit-associated elements (e.g. Ba, Pb, and V) were observed in stream sediments and surface waters downstream of the deposit, but concentrations were below regulatory guidelines for the protection of aquatic ecosystems and for drinking water. Analysis of temporal trends indicated that concentrations of major and trace elements were most strongly related to stream discharge. These findings highlight the need for sampling protocols that will identify and evaluate the temporal and spatial variations in a thorough baseline study.