Monitoring surface water chemistry near magnesium chloride dust suppressant treated roads in Colorado.

Magnesium chloride (MgCl 2 )-based dust suppression products are commonly used throughout western United States on nonpaved roads for dust suppression and road stabilization by federal, state, and county transportation agencies. The environmental implications of annually applying these products throughout spring and summer months on adjacent stream chemistry are not known. Sixteen streams were monit o red biweekly for 1 to 2 yr in two Colorado counties for a suite of water quality variables up and downstream of nonpaved roads treated with MgCl 2 -based dust suppression products. Eight of 16 streams had significantly higher downstream than upstream concentrations of chloride or magnesium over the entire monitoring period (p ≤ 0.05). Mean downstream chloride concentrations ranged from 0.17 to 36.2 mg/L and magnesium concentrations ranged from 1.06 to 12.8 mg/L. Several other ions and compounds, including those commonly found in dust suppression products such as sodium, calcium, and sulfate, were also significantly higher downstream at some sites. Downstream electrical conductivity (EC), chloride and magnesium concentrations were positively correlated with road surface area draining water toward the stream and yearly amount of MgCl 2 applied (R 2 = 0.75, 0.51 and 0.49, respectively), indicating that road managers can limit the amount of product entering roadside streams by assessing drainage characteristics and application rates in best management practices. Although MgCl 2 -based dust suppressants did move into some roadside streams, the concentrations detected were below those reported to adversely affect fresh water aquatic organisms, but the ultimate fate of these ions in Colorado waterbodies are not known.