DETERMINATION OF NONVOLATILE ORGANIC-CARBON IN AQUIFER SOLIDS AFTER CARBONATE REMOVAL BY SULFUROUS ACID

The precise determination of total organic carbon (TOC) in aquifer mat erials is important in the estimation of retardation coefficients for organic compound transport. Commonly used methods for TOC determinatio n after carbonate removal by acidification include: weight loss on ign ition of solids at 550 degrees C, acid-dichromate oxidation, and combu stion at 800-950 degrees C. Since carbonate carbon frequently is more abundant than organic carbon ail TOC methods depend on efficient and c omplete carbonate removal prior to the TOC quantification step. A meth od for the determination of TO C in aquifer solids involving carbonate removal by 0.73 M sulfurous acid and subsequent combustion at 800 deg rees C was tested on solids from three aquifers and on mineral standar ds, The carbon quantification by combustion and infrared defection of CO2 was accurate at solid organic carbon contents between 30 and 10,00 0 mu gC/g. The acid treatment added small amounts of carbon to the sam ple, and siderite removal was incomplete, For samples without siderite or dolomite, the accuracy of TOC determinations was enhanced by grind ing the solids, Measurement of very low TOC contents (50-100 mu gC/g) requires supplementary testing of grinding and acid treatment effects.