Modeling Application in Evaluating 1,4-Dioxane Remediation Alternatives for a Site with Unique Groundwater Flow Conditions

This paper presents a modeling application to evaluate the performance of remediation alternatives for a site with unique groundwater flow conditions. The site is underlain by interbedded silt, clay and sand, with a discontinuous, cohesive, low permeability clay unit identified at 60 ft below groundwater surface, which hydraulically divides the upper and lower units in a shallow aquifer. Groundwater flows to the west-northwest in the upper unit beneath the site, but in the opposite direction to the south-southeast in the lower unit. 1,4-dioxane is the main contaminant of concern (COC) for the site.

A groundwater flow and solute transport model was developed to evaluate the feasibility of remediation alternatives for 1,4-dioxane treatment. The remediation alternatives evaluated include monitored natural attenuation, groundwater pump and treat, and in situ chemical oxidation with persulfate. The specific objectives of the numerical modeling are to (1) accurately understand the groundwater flow conditions at the site, (2) delineate the COC migration pathway, and (3) estimate the anticipated clean-up times for different remediation alternatives.