Automated Impedance Tomography for Monitoring Permeable Reactive Barrier Health

76166B Although permeable reactive barriers (PRBs) are an important treatment option for groundwater remediation, no reliable methods are available to monitor or predict their long-term behavior. The large-scale implementation of reactive barriers will require a means of monitoring their long-term degradation. For example, gaps can occur in the placement of the reactive material, particularly when construction methods such as jetting or deep soil mixing are used. This project will develop a reliable method to verify placement and monitor the effectiveness of permeable reactive barriers. The approach will use arrays of inexpensive electrodes, coupled to autonomously operating hardware and software, to characterize the barrier and determine its effectiveness. In Phase I, column studies using ZVI and apatite PRB materials were performed. Numerical modeling showed that a monitoring configuration, consisting of boreholes spaced at 2 m intervals along the upstream face of the barrier, could be tuned to detect age-spots of 2x3 m in size. Existing instrumentation was modified to provide autonomous operation using solar power, and a reliable, low-overhead protocol for two-way communications was implemented. In Phase II, a full scale field validation for an existing, instrumented PRB will be performed. Web-based, automated geophysical monitoring systems will be enhanced, and software for imaging the temporal signature of an aging PRB will be developed. Commercial Applications and Other Benefits as described by the awardee: The automated monitoring system should find use in more than 100 permeable reactive barriers that will have been installed in North America by the time this project is completed.