Twin Cities WRS Seminar

Monitoring, Enhancement, and Prediction of Subsurface Pollutant Transformation by Fe-bearing Minerals


Matt Berens
Graduate Student, Dept. of Civil, Environmental, and Geo-Engineering

November 1, 2019


Iron-bearing minerals represent an important reductant for many groundwater pollutants. Despite an abundance of these minerals in the subsurface, pollutant transformation is often limited by competition for (bio)available Fe(II) and complex hydrogeologic pathways restricting pollutant transport to reactive mineral surfaces. In situ chemical reduction (ISCR) is an effective approach to circumvent many of these issues. Perturbations introduced to the subsurface by ISCR, however, often present a challenge in quantifying pollutant concentrations and thus the extent of transformation. In this study, compound specific isotope analysis (CSIA) was used to characterize C and N isotope fractionation associated with the reduction of 2,4-dinitroanisole (DNAN) by a suite of iron-bearing minerals and under various matrix conditions including systems representing ISCR. These data were used to generate models of DNAN transformation based on measurements of δ 15 N and make quantitative estimates of DNAN removal. Not only was isotope fractionation unaffected in each set of conditions, but the models were used to accurately predict the extent of DNAN transformation from δ 15 N measurements. These observations illustrate the utility of CSIA as a robust method to evaluate the success of in situ remediation techniques. These results are applicable to other nitroaromatic compounds in the subsurface and are important given the continuing need for assessment of the success of in situ remediation techniques.