EXPLORATORY LABORATORY EXPERIMENTS ON THE PERCOLATION OF ROAD SALT THROUGH SOIL COLUMNS

Road salt (typically NaCl) is commonly used in cold climates during winter months to remove ice from roads to ensure safe driving. In the United States, the quantity applied to the roads annually has reached 20 million tons. Because of its high solubility, sodium chloride is easily transported in water through the environment and potentially to sensitive water bodies. Some studies have found high concentrations of salt in surface waters during summer months, when they are expected to be negligible.

To study the interaction of salt with soil, clear plastic columns were filled with sand of differing grain sizes. Salt (NaCl) was mixed with water at a concentration of 33 g/L, and passed through the columns to saturate the media with salt. Two rinses of pure water, each 1-2 pore volumes, were enough to remove 99% of the original salt concentration in the columns. The amount of salt remaining in columns was measured and shown to be minimal.

From the results of this study, salt is expected to move quickly through uniform granular material down to 300 microns with very little, if any, retention. This means that areas with sandy soils could be expected to transport salt from surface water into shallow, and potentially deep, groundwater quickly and easily. This is a significant concern for shallow and deep aquifers in these areas and could result in costly drinking water treatment by reverse osmosis. However, the percolation of salt through sediment smaller than 300 microns, or sediment with significant organic matter content, still needs to be investigated in future experiments.