Numerous studies have been conducted on the Ft. Wainwright Army Post, in Fairbanks, Alaska that have documented extensive petroleum-related contamination in both soils and groundwater (E & E, 1993). Within Operable Unit 3 (OU3), located at the northwestern corner of the post, significant masses of permafrost have also been detected during well installations and other studies. Permafrost has made predicting the hydrology and contaminant transport extremely difficult; and complicated remediation design for the site.
Due to these complications, the Army Corp of Engineers (ACOE) and Cold Regions Research Engineering Laboratory (CRREL) contracted the University of Alaska (UAF) to identify potential contaminant migration pathways and the effect of permafrost has on the subsurface hydrology. SUTRA, Saturated- Unsaturated TRAnsport, a 2-D finite-element simulation model was applied to the OU3 area in order to identify potential transport pathways and determine the effect permafrost has on the subsurface hydrology. SUTRA was first used to analyze data from a tracer study performed within OU3 in order to get estimates for dispersion coefficients and hydraulic conductivities. Then, the entire Tank Farm and TFS source area within OU3 was modeled using benzene as the contaminant. The results of these separate applications were synthesized to develop a conceptual model of the OU3 area that was used to explore the effects of permafrost on the contaminant transport pathways in the area.
The model results showed permafrost to act as a significant retarding force in contaminant transport to the point of stalling movement completely in some cases. Discontinuous masses of permafrost redirected the groundwater and created steeper gradients, thus, changing the local hydrology completely. Sensitivity analyses indicated concentrations were most affected by the source strength and the permafrost configuration. These results may be influenced by the two-dimensional nature of SUTRA, but indicate a strong influence by the permafrost on the hydrology and transport pathways
Ann Farris AGRA Earth & Environmental P. O. Box 81727 Fairbanks, AK 99708 Tel: (907) 452-1884 email: ftamf@aurora.alaska.edu