Field application of biogeochemical reductive dechlorination by permeable reactive barrier

Biogeochemical reductive dechlorination (BiRD) uses biotically generated iron sulphide minerals to abiotically reduce chlorinated aliphatic hydrocarbons (CAH). BiRD was applied by permeable reactive barrier (PRB) at Dover Air Force Base, the first time this approach was tested in the field. Iron sulphide minerals were generated in trenches filled with iron rich sand (iron), mulch (organic), mineral gypsum (sulphate), and limestone (pH control). For comparison purposes, trenches were also filled with sand, mulch, and limestone to create conditions favourable to biostimulation. Compared to biostimulation, BiRD showed little evidence of methanogenesis, indicating that the reductive capacity of the applied organic was converted to mineral iron sulphide rather than methane. CAH treatment in the biostimulation PRB appeared to be incomplete after 150 days, apparently stalling at DCE. In comparison, for the BiRD treatment area, CAH treatment appeared to be rapid and reduced PCE, TCE and DCE levels within the 150 day time period.