Methods of Determining Retardation Coefficients of Organic Compounds in Aquifers

Sorption is an important mechanism that affects the mobility of organic compounds in the subsurface environment. Sorbed compounds move slower than that of groundwater, causing retardation in their movement. Accurate determination of retardation coefficients (R) of organic compounds in aquifers is critical for understanding their movement, fate, and remediation. Several methods, including predictive tools, laboratory experiments, and field experiments have been utilized for determining sorption-related retardation. The objective of this paper was to review and compare between the different methods used for the determination of R of organic compounds, with emphasis on predictiveand laboratory-based approaches. Predictive tools are based on the use of quantitative structure-activity relationships (QSARs). Laboratory methods utilize different types of reactors including batch, stirred-flow, circulationthrough-column, or miscible displacement through packed columns. In addition, data from the column method have been analyzed in various ways to determine R. Discrepancies between results from different methods or from different analysis approaches have been reported. This create uncertainty about the suitability of some of these methods or the used analysis approaches. This paper highlights the possible causes for the observed discrepancy and establishes the limitations and appropriateness of the used methods and analysis approaches.