Permeable Reactive Barriers: Lessons Learned/New Directions

Lessons LearnedNew Directions was prepared by the ITRC Permeable Reactive Barriers Team to update previous guidance written by the team. The goal for this document was to compile the information and data on permeable reactive barriers PRBs that have been generated over the last 10 years of technology development and research, as well as to provide information on noniron-based reactive media that can be used in PRBs. This document also provides an update on a developing technology somewhat related to PRBs in which source zone contamination is treated with iron-based reactive media. A PRB is defined as an in situ permeable treatment zone designed to intercept and remediate a contaminant plume. Zero-valent iron is the most common media used in PRBs to treat a variety of chlorinated organics, metals, and radionuclides. Reactive media such as carbon sources compost, limestone, granular activated carbon, zeolites, and others had also been deployed in recent years to treat metals and some organic compounds. The proper design of a PRB is highly dependent on a complete and accurate site characterization. A conceptual site framework is discussed as a means to perform a detailed characterization for PRB deployment. Collection of hydrogeologic, geochemical, microbial, and geotechnical data along with the complete vertical and horizontal plume delineation are necessary to characterize a PRB site. The Triad concept is also introduced as a means to gather site data. The design of a PRB can be enhanced using probabilistic modeling to incorporate the variability of the input design parameters. Construction advancements include the use of biopolymer for trench stabilization or the use of vertical hydraulic fracturing for reactive media emplacement.