GROUNDWATER CONTAMINATION BENEATH ANN ARBOR, MICHIGAN: APPLYING HYBRID GROUNDWATER MODELS TO MANAGE A COMPLEX GLACIAL AQUIFER SYSTEM

Glacial aquifer systems in the Midwestern Basin and Arches Region provide an abundant source of fresh water that is increasingly threatened by activities associated with industry, agriculture, urbanization, and growing populations. Sophisticated hydrogeologic models are needed to address complexity in the three-dimensional aquifer properties variability and contaminant plume morphology to effectively contain or remediate groundwater pollutants in these glacial aquifer systems. This presentation describes the use of hybrid models incorporating stochastic variability within a deterministic allostratigraphic framework to model spatial variability of physical hydrogeologic properties in a glacial aquifer system. The approach is illustrated with an example from the Pall Life Sciences (formerly Gelman Sciences) groundwater contamination site in Ann Arbor, Michigan.

At the Pall Life Sciences site, wastewater containing 1,4-dioxane was discharged into unlined seepage lagoons and spray irrigated across a 15 acre field from 1967 to 1985. Plumes of 1,4-dioxane-contaminated groundwater have migrated several kilometers from the site in different directions through 80m of underlying glacial drift. Because 1,4-dioxane is readily soluble in water and does not easily degrade or adsorb to soil particles, it provides a tracer-like record of solute transport. More than 130 monitoring wells and 20 extraction wells have been drilled to investigate and remediate 1,4-dioxane in the area. Today, remedial activities initiated more than 25 years ago continue along with efforts to characterize and model the aquifer system as the deepest known plume advances toward the Huron River through a groundwater Prohibition Zone established in 2005.