Aquifer facies distributions have a strong impact on groundwater flow
and contaminant transport, but are often difficult to characterize in
hydrologic settings. The City of Hays, Kansas, is fortunate in having
abundant subsurface lithologic and transport data for their Quaternary
alluvial drinking water aquifer, allowing direct investigation of the
three-dimensional (3-D) effects of facies distribution and
connectivity. The aquifer is comprised of intercalated
high-permeability sand-channel facies (Qal) and low-permeability silt
overbank facies (Qt). Geologic and hydrologic modeling in 3-D
indicates that high aquifer contamination susceptibility areas are
found where well-connected Qal becomes unconfined. Comparison of the
hydrogeologic model with existing contaminant plumes indicates strong
transport control by interconnected zones of thick Qal. Detailed knowledge
of Qal connectivity at depth, and of the geometry of the intersection
of the water table and Qal-Qt facies boundary, is required to adequately
understand past and future contaminant transport beneath Hays. An
Internet-based 3-D
interactive model of this site is included to allow independent
exploration of these concepts.
