Evaluation of Two Strategies to Enhance the Long-Term Hydraulic Performance of Permeable Reactive Barriers

摘要

Groundwater flow and geochemical reactive transport models were used to assess the effectiveness of two strategies that are used to enhance the long-term hydraulic behavior of continuous-wall permeable reactive barriers (PRBs) employing granular zero valent iron (ZVI). The flow model accounted for geological heterogeneity and the reactive transport model included a geochemical algorithm for simulating iron corrosion and mineral precipitation reactions that have been observed in ZVI PRBs. The two strategies that were evaluated are (i) adding pea gravel equalization zones up gradient and down gradient of the reactive zone and (ii) placement of an up gradient sacrificial pre-treatment zone containing a mixture of pea gravel and ZVI. Results of simulations show that installation of pea gravel equalization zones results in a more uniform distribution of residence times within the PRB, slightly greater average porosity reductions, and smaller maximum porosity reductions. Sacrificial pre-treatment zones elevate the groundwater pH and consume many of the mineral forming ions that form secondary minerals, reducing mineral precipitation in the reactive zone. However, mineral fouling by Fe(OH)_2 still occurs within the PRB in response to iron corrosion reactions.