Prediction of Longevities of ZVI and Pervious Concrete Reactive Barriers Using the Transport Simulation Model

Abstract

This investigation involved a column study and model simulation to evaluate longevity of zero-valent ion (ZVI) and pervious concrete (PERVC) reactive barriers for treatment of acid mine drainage (AMD). Each of the reactive media were evaluated for sorption capacity and hydraulic performance under the dynamic flow conditions of a column setup. The test data obtained were applied to the one-dimensional advective-dispersion transport equation to predict geochemical changes in concentration of contaminants flowing through a reactive barrier, as a function of time and distance. PERVC was found to be more effective in contaminant removal from AMD than ZVI. PERVC raised the pH of AMD from 2.99 to an average value of 11, compared with a maximum pH of 9 attained by ZVI treatment. While both media achieved complete removal of the main contaminants comprising Al, Fe, and Zn, the PERVC containing 3% fly ash (3FA-PERVC) had greater retardation factors and higher overall removal efficiency than ZVI. The hydrodynamic dispersion coefficient for 3FA-PERVC was .4 to 4×1−4 m2/s compared with .2 to 5×1−6 m2/s for ZVI. A barrier wall of 1.5 m thickness was estimated to provide indicative treatment life spans of 5 and 1 years for ZVI and 3FA-PERVC reactive media, respectively. Based on these results, the longevity of 3FA-PERVC reactive barriers can be about twice that of ZVI barriers.