MODELING OF ROAD SALT CONTAMINATION AND TRANSPORT IN GROUNDWATER: CASE STUDY IN SE MASSACHUSETTS

We report on a study and numerical simulation model of road salt impact on water quality in a typical aquifer in southeastern Massachusetts. The study area is a public water well field in the Town of Norwell presently instrumented with 3 multi-parameter sensors at different aquifer depths and one sensor located in a nearby stream. The well field is within a glacial outwash area with simple subsurface geology and lies a short distance from major road salt sources including MA Rt. 3, a mall, and lies downstream from a road salt storage shed. The study includes an expanded water quality monitoring in the field, measurements and chemical analyses of water samples at Boston College, and a numerical simulation/modeling of ground water with the objective to delineate sources and transport modes of dissolved road salt within the underlying aquifer. Bench top experiments done earlier at Boston College have shown that due to the higher densities of the brine runoffs in winter months, the contaminated water inevitably forces a free convective transport within the subsurface in addition to an advective flow. The observed patterns provide the initial input into a variable density simulation computer program (USGS SEAWAT finite difference model) designed to better delineate and constrain road salt pathways within the subsurface by constructing multiple 2D numerical simulations of chloride concentrations and flow paths around the highway toward the public wells.