Reactive Transport Modeling: A New Paradigm in Design of In Situ Treatment Systems

Application of three-dimensional, numerical, reactive transport modeling is emerging, we believe, as a new paradigm in the design process of in situ treatment systems. Its rapid emergence as a design tool is reminiscent of the paradigm that began to appear in the early 1980s when use of numerical groundwater flow modeling started to become standard practice in the design of groundwater extraction systems (despite the now apparent limitations in software and hardware at the time). In the last few years, reactive transport modeling has been applied with great success to evaluation and design of in situ chemical oxidation (ISCO), in situ chemical reduction (ISCR), and both aerobic and anaerobic in situ bioremediation (ISB) systems. Experience has shown that it can help optimize the performance of in situ treatment (IST) remedies, reduce the risk of outright failure, and save overall costs. A reactive transport model is built upon the foundation of a three-dimensional groundwater flow model and includes the ability to model the chemical interactions between injected substrates or chemicals and the contaminants of concern; between the injected chemicals and the aquifer skeleton; and other subsidiary reactions. As with any numerical model, best results are obtained when the model is calibrated to laboratory and field data. Several case studies will be briefly described where three-dimensional, reactive transport models were instrumental in the evaluation and design of full-scale ISCR, ISCO, and ISB systems.