Effects of contamination age on phenanthrene desorption from aquifers

The length of contact time of contaminant with aquifer solids has a significant impact on the subsequent desorption process that normally occurs after the aquifer cleanup. In the present study, a diffusion model was built and validated with experimental results. Phenanthrene was brought in contact with sand and soil particles for different lengths of time. The distributions of solid-phase concentration within intraparticle pores were determined numerically and then used as the initial conditions for the subsequent desorption process. The purpose was to investigate the effect of contaminants' age on desorption time. Results revealed that a significant fraction of contaminants desorbs very slowly, even for freshly contaminated materials. For example, it has taken years for phenanthrene to release from freshly contaminated Jurassic limestone and Triassic limestone. The desorption time for aged contaminated material was found to be longer than for freshly contaminated material, at a more or less constant ratio with respect to the degree of aging.