Mobilization of major and trace constituents of highway runoff in groundwater potentially caused by deicing-chemical migration is indicated by analyses of groundwater samples collected at test sites adjacent to Route 25 in southeastern Massachusetts during February and August 1991 and March, August, and November 1993. Analyses indicate that concentrations of major and trace chemical constituents of highway runoff in groundwater are substantially higher downgradient than upgradient from the highway. Highway runoff containing road salt and calcium-magnesium acetate seems to have the greatest effect on groundwater quality at one test site where highway runoff discharges locally to the land surface. This site has an open-drainage system typical of many highways. Analyses from these five sampling rounds are indicative but not conclusive because additional spatial and temporal data are needed. However, this information, when combined with 4 years ofmonthly groundwater-level measurements and water-quality analysis ofgroundwater and highway-runoff samples, show that potential mobilization processes include winter recharge, effects related to ion exchange, and acidification and mineral weathering caused by deicing-chemical migration. These processes are hypothesized because 75 percent of annual recharge occurred during the winter months, sodium was exchanged for calcium in infiltrating water, and pH decreased significantly in downgradient groundwater. None of the measured concentrations of the major and trace constituents in groundwater exceed national primary drinking-water standards. However, secondary standards were exceeded for chloride and manganese, and recommendations for surface-water criteria were exceeded for chloride, cadmium, and copper.

The quality of water in the unsaturated zone (1) and ofgroundwater (2, 3) is affected by major ions in deicing chemicals applied to roads and highways. Assessment of the environmental effects of highway runoff requires investigations to determine whether other major and trace constituents are mobilized during deicing chemical migration through the unsaturated zone and in groundwater. To protect groundwater quality, the Massachusetts Highway Department (MHD) has taken steps to reduce salt contamination while maintaining highway safety (4). The US Geological Survey (USGS), in cooperation with MHD, is currently investigating therelative effectiveness of four highway drainage designs in preventing contamination of groundwater by road salt (5) along Route 25 in southeastern Massachusetts (Figure 1).