During my time at BEAK (1993-1998), I closely followed what our subsidiary, EnviroMetal Technologies Inc (ETI) was doing with zero-valent iron (ZVI). Chloroethenes are degraded at different rates by ZVI; for example PCE is degraded much faster than DCE. Iron barrier design (thickness) is based on ground water velocity and influent concentrations. An early pilot test at a PCE site with high ground water flow had very thick (4’) ZVI gates which contained several piezometers within. Toward the end of the pilot test, very high levels of cis-DCE were observed in the most up gradient piezometer within the gate and cis-DCE was not completely degraded by the time it left the wall. The site had moderate levels of sulfate (> 100 mg/l).
Sulfate-reducing bacteria (SRBs) had established themselves in the up gradient portion of the PRB, using sulfate and the hydrogen generated by the ZVI. As observed at many sites, PCE was being reductively dechlorinated to cis-DCE by SRBs. I recommended that in all future designs in high sulfate ground water, PCE and TCE be treated as if they were cis-DCE for the purpose of sizing wall thickness.
