A ZVI Permeable Reactive Barrier (PRB) showed reduced flow after only 2 years of operation with the flow being deflected around the PRB. 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. These observations fit the theory that the front face was biofouled and would require ongoing antibiofouling measures no matter what restoration method was chosen.
A study was designed with an academic laboratory to evaluate antifouling agent; moderate concentrations of ethanol work well. Groundwater is pumped over the plugged face and occasionally dosed with ethanol which also serves as an electron donor for a biobarrier installed down gradient to treat any CVOCs exiting the PRB. A 2nd biobarrier treats low pH groundwater going around the end of the PRB.