A large ZVI Permeable Reactive Barrier (PRB) showed reduced flow after only 5 years of operation with a large portion of the flow being deflected around the PRB. An initial investigation showed that removing a few inches of material from the up gradient face via a boring resulted in immediate flow increase, however, the flow slowed again within a year. Both of these observations fit the theory that the front face was biofouled and restoring flow would require ongoing antibiofouling measures no matter what method was chosen. Sulfate reducers are prime suspects.
A study was designed with an academic laboratory to evaluate antifouling agents that can be used in ground water. Preliminary results have shown that oxidants (bleach, chlorine dioxide) are destroyed by the ZVI before they can effectively kill microbes deep in the iron. Moderate concentrations of ethanol which can also serve as electron donor are currently being evaluated.