Assessing the fate of polynuclear aromatic hydrocarbons from oily waste land spreading by modelling

Abstract

The organic wastes produced by petroleum refineries are often treated by spreading them on land sites, allowing hydrocarbons to degrade naturally. In such conditions, mathematical models representing the transport of organics in the soil are useful for predicting the quantities of hydrocarbons, like polynuclear aromatic hydrocarbons (PAHs), that could reach the water table in the short and long term. The pesticide root zone model (PRZM) simulates the fate of pesticides in the soil. Because of the analogy between the agricultural use of pesticides and the land spreading of petroleum residues containing hydrocarbons, and the similar physicochemical characteristics of these two types of potential organic contaminants, this model was applied to a land-spreading site in southern Quebec. The simulation results indicate that the studied PAHs may not migrate to depths of more than 40 cm. The predicted concentrations may be several hundred times lower when the degradation rate doubles. Natural variations in the local hydrodynamic conditions caused by soil texture do not greatly affect the concentrations of a relatively mobile PAH in soil or in water. In contrast to the texture, the soil organic matter content greatly influences the distribution of PAHs between the liquid and solid phases and, consequently, their migration through the soil. Key words: PAH, phenanthrene, pyrene, refinery, land treatment, mobility, degradation, simulation, PRZM.