Modelling PAH degradation in contaminated soils in Canada using a modified process-based model (DNDC)

Polycyclic aromatic hydrocarbons (PAHs) are persistent pollutants of concern. A process-based model of the PAH degradation can improve our understanding of ecological drivers and processes. In this paper, a processbased biogeochemistry model, DeNitrification-DeComposition (DNDC) is modified to simulate the dynamics of PAHs degradation in soils at abandoned oil and gas well sites. This new version of DNDC-Organic Pollutants, called DNDC-OP, coupled the rates of PAH degradation with dynamics of soil, vegetation and climate, such as soil moisture and temperature. The model was parameterized and validated against datasets of four soil PAHs: pyrene, fluorene, chrysene and anthracene, at three different abandoned oil and gas well site locations in Alberta, Canada. The sensitivity of the parameters was analyzed and tested. The simulated results were in good agreement with the measured data with a coefficient of determination (R²) of 70 to 97%, and the root mean square error (RMSE) of 4.5 to 9.1 at all three sites. We also evaluated the influence of environmental factors, such as soil temperature and moisture, on the degradation of PAHs. An increased degradation of all four PAHs occurred with increasing soil moisture content. An increase of soil temperature from 10 to 20°C and subsequently to 25°C resulted in a decreased appearance of all four PAHs from the three well sites. The result shows that this model can be used as a tool for evaluating PAH degradation for effective reclamation strategies.