Hydrogeologic modeling of a 1,4-dioxane plume in a glacial aquifer system; Washtenaw County, Michigan

Alternative hydrogeologic interpretations were incorporated into numerical groundwater models to test the viability of three conceptualized system architectures and three hypothesized source locations for a 1,4 dioxane plume in a heterogeneous glacial aquifer system. Steady state and transient flow simulations of the alternative models were evaluated using observed hydraulic flow field characteristics for natural conditions and the perturbed response after local remedial pumping activity began. Advective transport particle tracking was utilized to assess the consistency of the hypothesized source locations with observed contaminant migration pathways inferred from the mapped location of the plume. Evaluation of the combinations of hydrogeologic conceptualizations and 1,4 dioxane source locations indicate that the most complex distribution of hydrostratigraphic units produces the best model performance for flow and transport from the most probable source location. Application of the alternative modeling approach to this 1,4 dioxane plume has reduced the uncertainty associated with the heterogeneous distribution of aquifer and aquitard units and their properties that influence the migration pathways and environmental fate of the contaminant.