Hydraulic causes for time-dependent variability of PAH-contamination in a gravel aquifer

摘要

At a former industrial site for impregnation of wood for tracks, the groundwater of the Quaternary gravel aquifer is highly contaminated with polycyclic aromatic hydrocarbons (PAHs) which have shown very rapid fluctuations during the investigation periods. A comparison of two concentration time lines along the same streamline shows two different components, a parallel, area-wide component and a local, time-varying component of the concentration behaviour. These components also have a strong relationship between the different percentage occurrences of the PAHs at the measuring points. As one cause for the time-dependent variability, a correlation between a relatively rapid change of the groundwater level and the PAH-concentration has been observed. In addition, extreme rainfall events strongly influence the variation of the PAH-concentrations and lead to maximum concentration-peaks in the groundwater. These processes produce impulse-like inputs of the PAHs into the groundwater. A 1D-analytical model of the time dependent PAH-concentration variability indicates that impulse PAH-mobilisations from contamination sources at different locations are the dominant mobilisation processes at the investigation site.