Contamination of groundwater by outdoor highway deicing agent storage

Abstract

This research quantifies the impact of outdoor highway deicing agent storage on groundwater quality. Data and theory realize the objective at a well characterized salt/premix storage facility on a glacial drumlin comprised of clayey sand till. Tritium and tritiogenic helium were observed in 17 monitoring wells in 2003, while chloride concentrations were measured in 43 monitoring wells from 1998 through 2004. The 3He/ 3H ratios confirm an analytical model of drumlin hydraulics (Ostendorf, D.W., DeGroot, D.J., Shelburne, W.M., and Mitchell, T.J., 2004. Hydraulic head in a clayey sand till over multiple timescales. Can. Geotech. J. 41, 89-105.), and support advective travel time estimates from the monitoring well screens back to the water table. An advective balance of recharge, precipitation, and surface runoff routes the water table Cl − concentrations inwards to the outdoor storage pile maintained at the site from the 1960s to the mid 1980s. Concentrations as high as 320 meq Cl −/L were observed in groundwater, although the deicing agent contamination had not yet reached the bottom of the drumlin in the study area. The travel time simulations yield a 200 meq Cl −/L water table isopleth in 1985 under the prior outdoor storage pile. The recharge concentration model matches the radial decrease of Cl − water table concentrations from the pile, and implies that 4400 kg of Cl − leached into the groundwater in 1985. This is about 0.3% of the deicing agent Cl − stored at the site each year. These results suggest that outdoor storage of highway deicing agents significantly impacted groundwater quality near the pile. The groundwater quality began to recover after source removal however: the leached Cl − flux dropped to 2,300 kg in 1992, more than 5 years after elimination of the outdoor storage pile.