Understanding hydrocarbon fate and transport in peat soils using column experiments

Increasing hydrocarbon resource developments in and around peatlands impose risks of petroleum hydrocarbon spills on these important wetland landscapes. Despite the potential severity of consequences, there is a big gap of knowledge on parameter values controlling liquid hydrocarbons’ redistributions in peat soil after a spill. Complete excavation of contaminated peat soil is a common practice in contaminated sites, but destroys wetland function, and contributes nothing to the understanding of the problem. To partially fill this knowledge gap and to examine potential remediation strategies that are less destructive, we examined the fate, transport, and degradation of petroleum hydrocarbon non-aqueous phase liquids (NAPLs) in peat soils using a series of column tests on intact peat monoliths. Three-phase flow experiments with numerical simulations provided values of multiphase flow parameters that control NAPL redistribution in a variety of peat soils. We observed that water table fluctuations reduced residual NAPL saturation from 8.1-11.3% to 7.7-9.5%; increased headspace concentrations of n-C₈ and n-C₁₂ an average 163.7% and 13.4%, due to volatilization. Results also illustrated that water table dynamics promoted growth (from 10⁴ CFU/gram to 10⁶ CFU/gram peat) of specialized microbial communities in NAPL polluted peat columns. These results suggest that water table fluctuation can be a suitable tool for physical and microbial NAPL removal in peat soils, and for the first time provide evidence for it. We also observed a high ratio of Proteobacteria to Acidobacteria in the NAPL contaminated zone, which can be linked to the restoration success for a NAPL polluted peatland. The results could help environmental scientists in forecasting the behavior of spilled non-aqueous phase liquids (NAPLs) in peatland.