Road Salt

Saline melt water from road salt applications that has percolated into a fine sandy soil in winter is rinsed out of the soil by infiltrating rainwater in the following warmer seasons. This sequence of saturated and unsaturated flow processes associated with saline water transport in a fine sandy soil was studied by simulation and exploratory laboratory experiments. Experiments in soil columns of 300-μm sand revealed that two rinses of pure water, each of one pore volume, were sufficient to reduce the salt concentration by 99% of its original value in the soil column. Simulated time variations of salt concentration in the effluent from the column agreed with experimental results. Based on simulated and experimental results, a sandy soil must become saturated to experience pore water flow in order to efficiently rinse saline snowmelt water. Depending on the saturated hydraulic conductivity and the soil depth, days, weeks, or months of freshwater infiltration in summer are needed to rinse saline melt water from an unsaturated sandy soil after road salt applications in winter. This explains findings of significant salt concentrations in surface and shallow groundwater during summer months, long after road salt application and infiltration has ceased.

Executive Summary:

Wolfville Harbour is a part of the Minas Basin, which is known to be a highly productive ecosystem. One would often visit Waterfront Park at the Wolfville Harbour and wonder what the sources were of the effluent being discharged into the Harbour. Questions rose as to what the effects were on populations such as Spartina alterniflora and Corophium volutator, which provide ecosystem services that benefit animals and humans. After doing some research, one would learn that the effluent is discharged into the Harbour untreated and unmonitored. This was alarming since stormwater effluents are derived from rainfall and snowmelt – essentially surface runoff, which can contain a myriad of pollutants, including debris and chemicals that can be detrimental to ecosystems.

A major component of stormwater effluent is road salt. As a result of this, in addition to available instrumentation for data collection, one focused this study on the effects of salinity. Spartina alterniflora and Corophium volutator can both tolerate wide ranges of salinity, however there are limits. Despite these limits, it was determined through research and review of literature that the volume of input of stormwater effluent in the Harbour is negligible in terms of its salinity. This is because the Harbour naturally experiences wide variations in salinity due to freshwater input from rivers and strong tidal influences from the Bay of Fundy that efficiently mix the water. However, it is recommended that further research be conducted to study effects of climate change on tidal influence, as well as concentrations of chemicals in stormwater effluent and their potential impact on the ecology in the Wolfville Harbour.

Michigan, like many other states, uses chemical deicers on roadways during the winter. Through meltoff and rainfall events, this road salt is washed off the roads, dissolved into runoff and drained into the surrounding watershed. In particular, the addition of chloride to surface and groundwater can affect local vegetation and biota. The purpose of the seminar project (Lynn) was to monitor water quality in a pond-well-stream system at the nearby Allendale Middle School and observe how the conductivity levels and chloride concentrations change during major meltoff and rainfall events. The small pond receives surface water runoff directly via pipe from an adjacent parking lot and road. This pond is near and upgradient from a small stream. A well was installed midpoint to intercept subsurface flow between the pond and the stream. Water samples were collected from each source every other day between mid February and early April of 2015 (daily during the meltoff event), and were then filtered and tested in the lab for conductivity and chloride. Water levels were recorded from stream and pond gauges and the well. When sampling started there was over a foot of snow and the pond surface was frozen.
Over the monitoring period, chloride concentrations ranged from 48  155 mg/l in the pond, 68  142 mg/l in the well and 22  87 mg/l in the stream. Higher chloride values were associated with elevated conductivity readings. The first major snow meltoff event occurred March 7-14, and was followed weeks later by several rainfall events. The chloride concentrations in the stream and well peaked during early snow meltoff but then decreased significantly as snow meltoff continued. Peak chloride concentrations in the pond were measured under ice cover and before meltoff. Our explanation is that the initial small amount of runoff from snow meltoff was heavily impacted by road salt and had a high concentration of chloride but that this chloride was later diluted by additional snow melt. This initial snowmelt peak was not observed in the pond, perhaps because melting ice cover enhanced the dilutional effect. Although chloride concentrations did not exceed the secondary drinking water standard of 250 mg/l, they do highlight the need for early meltoff monitoring and that dilution may mask the input of chloride to water bodies.

As much as 40% of salt use in some areas is from private users. Salt is not only used on public roads, but on parking lots and internal roads of commercial and industrial establishments, schools, churches and other nonprofit institutions, apartment complexes and other residences, and by individual home and small business owners. Education about ways to improve efficiency among private contractors can go a long way toward reducing salt loadings to the environment. Highway superintendents should share educational materials and training and maintain open lines of communication with private salt users. Remember that the end result is cleaner surface water and groundwater, so it's for the public good. There's the added benefit of direct cost savings in using less salt. Some insurance companies may reduce liability rates if workers are trained in efficiently maintaining ice-free travelling surfaces. Municipalities can offer a certification program for sidewalk and parking lot contractors. Minnesota is the first state to offer this, but it should extend to other states. Public awareness campaign Every year at the onset of winter drivers should be informed about snow ordinances and safe driving habits in written communications or workshops.