Pah Transport In The Unsaturated Zone At A Manufactured Gas Plant (mgp) Site
Abstract
The transport of polyaromatic hydrocarbons in the unsaturated zone at contaminated sites is governed by the interplay of different transport mechanisms: The most promi- nent are advective-dispersive and diffusive fluxes with water and non-aqueous phase liquids in the dissolved phase, and the carrier assisted transport with colloids and par- ticles. The driving gradients are gravity and, most important, the amount, the intensity and the spatio-temporal distribution of precipitation. In order to identify the govern- ing transport pathways as a function of the meteorological conditions, we studied the release and redistribution of PAHs at a former manufactured gas plant (MGP) site. We installed four field lysimeters to monitor the seepage water. Two lysimeters were located at the field site and two others - refilled with site material- were translocated and installed in a region with different meteorological conditions. After filtration, the seepage water was analysed for dissolved PAHs and the retentate, which resembles the particulate and colloidal fraction, was analysed for PAH, also. The PAH-pattern of the retentate was in high accordance to the soil PAH pattern. High molecular weigth PAH amount to 55 %, while low molecular weight PAH reach 45 %. In contrast, the amount of high molecular weight PAH in the filtrate amounts only to 40%. The con- centration of single PAH in the filtrate was found to be far below the water solubility. Thus, PAH dissolution is of minor importance for the release and transport, while particulate and colloid related PAH transport dominates the fate of PAH in the unsatu- rated zone. The meteorological characteristic of the original field site shows short and strong precipitation events during summer time which lead to surface runoff. Seepage and consequently PAH transport does not occur during this period. In contrast, higher total precicpitation and the different distribution pattern at the other site results in higher moisture contents over longer time and thus leads to PAH seepage throughout the year.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.1702H