Putting Your Well Field on a Low Salt Diet

In the late 1970s researchers started to notice an increase in chloride and sodium levels in a few aquifers in the Upper Midwest and Northeast.  Since then, this trend has spread and intensified to the point where many wells in northern states have chloride levels over 100 ppm and rising.  Trend lines for many wells suggest that this will be a significant problem for many decades.

Road salt is the major culprit.  Depending on the aquifer, about 25% to 65% of the road salt applied ends up in groundwater.  Recent efforts have reduced salt application rates to some degree, but public expectations of snow free roads has resulted in total salt loading continuing to increase.  Decades of past heavy salt use will result in rising chloride and sodium levels for decades in many aquifers.

The keys to managing this problem are monitoring, prevention, and mitigation.  We present case histories from New Hampshire, New York, and Wisconsin where chloride impacts in shallow wells were tracked to road salt application, the lateral and vertical extent of contamination were defined by monitoring wells or geophysical methods, future salt levels were predicted, and mitigation methods have been proposed and implemented.

We present a salt budget that was calculated for a capture zone of a well field in Central Wisconsin that has a history of elevated sodium and chloride levels.  We compared the salt loading in the capture zones to recharge and residence time of the groundwater as a simple way to estimate future salt levels.  In this example the aquifer had short residence times and sodium and chloride levels were approaching steady state.  Several simple steps such as diverting snow melt from parking lots away from infiltration basins were successful in reducing sodium and chloride levels at specific wells.