Determination of nonvolatile organic carbon in aquifer solids after carbonate removal by sulfurous acid

The precise determination of total organic carbon (TOC) in aquifer materials is important in the estimation of retardation coefficients for organic compound transport. Commonly used methods for TOC determination after carbonate removal by acidification include: weight loss on ignition of solids at 550 degrees C, acid-dichromate oxidation, and combustion at 800-950 degrees C. Since carbonate carbon frequently is more abundant than organic carbon ail TOC methods depend on efficient and complete carbonate removal prior to the TOC quantification step. A method for the determination of TO C in aquifer solids involving carbonate removal by 0.73 M sulfurous acid and subsequent combustion at 800 degrees C was tested on solids from three aquifers and on mineral standards, The carbon quantification by combustion and infrared defection of CO2 was accurate at solid organic carbon contents between 30 and 10,000 mu gC/g. The acid treatment added small amounts of carbon to the sample, and siderite removal was incomplete, For samples without siderite or dolomite, the accuracy of TOC determinations was enhanced by grinding the solids, Measurement of very low TOC contents (50-100 mu gC/g) requires supplementary testing of grinding and acid treatment effects.