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Environ Sci Technol

Title:		Determination of interstitial water chemistry and porosity in consolidated aquifer materials by diffusion equilibrium-exchange
Author(s):		Spence MJ; Thornton SF; Bottrell SH; Spence KH;
Address:		"Groundwater Protection and Restoration Group, Department of Civil and Structural Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom. m.spence@sheffield.ac.uk"
Journal Title:		Environ Sci Technol
Year:		2005
Volume:		39
Issue:		4
Page Number:		1158 - 1166
DOI:		10.1021/es049401v
ISSN/ISBN:		0013-936X (Print) 0013-936X (Linking)
Abstract:		"Diffusion equilibrium exchange (DEE) is presented as a novel, practical alternative to centrifugation for the recovery and chemical analysis of interstitial water in contaminated core samples from consolidated rocks and aquifers. The methodology is suitable for sampling organic and inorganic compounds, including redox sensitive species such as SO4(2-), NO3-, NO2-, Mn(II), Fe(II), and sulfide (HS-). DEE also permits analyte extraction from kilogram quantities of core, which avoids extended centrifugation or sample amalgamation and provides analyte masses appropriate for stable isotope analysis. The procedure involves simple and rapid on-site sectioning of representative core samples, which are preserved in the field by storage in airtight bottles filled with deoxygenated deionized water containing a conservative tracer (Br-). Equilibration times for individual solutes can be estimated in advance to reduce the need for time-series analysis; for an effective diffusion coefficient of 2.5 x 10(-10) m2 s(-1) (Br- in chalk rock) equilibration was >90% completed after 30 h, consistent with the predicted equilibration time. The DEE method presented minimizes sampling errors from temperature changes, oxidation of reduced chemical species, and loss of volatile compounds, which can occur with other interstitial water sampling techniques. It also gives superior resolution of in situ solute distributions and geochemical processes in consolidated sediments than centrifugation and can provide estimates of aquifer porosity in core samples. Laboratory experiments using chalk rock core and simulated extraction procedures confirm the superior performance of the DEE method over centrifugation for a range of solutes. The method has been used to generate detailed interstitial water profiles of electron acceptor and contaminant concentrations along the flow path of a petroleum hydrocarbon plume in the U.K. Upper Chalk aquifer as part of a natural attenuation assessment"
Keywords:		"*Environmental Monitoring Inorganic Chemicals/analysis Isotopes Organic Chemicals/analysis Oxidation-Reduction Porosity Risk Assessment Time Factors Water/analysis/*chemistry Water Movements Water Pollutants, Chemical/*analysis;"
Notes:		"MedlineSpence, Michael J Thornton, Steven F Bottrell, Simon H Spence, Keith H eng Comparative Study Research Support, Non-U.S. Gov't 2005/03/19 Environ Sci Technol. 2005 Feb 15; 39(4):1158-66. doi: 10.1021/es049401v"