MGS geologists presented talks at the 28th Annual Maryland Groundwater Symposium, September 26, 2019

Road Salt Contamination in Groundwater and Surface Water in the Maryland Piedmont

Tiffany VanDerwerker

ABSTRACT

Road salt has been applied to roads during winter storm events since the 1940’s. As a result, chloride concentrations in Maryland streams and groundwater have increased over time. In the Maryland Piedmont, unconfined aquifers are the primary water source for people on private water wells, and these aquifers are very susceptible to surface-based contamination. Water with elevated chloride concentrations can damage plumbing fixtures, appliances, and pipes. Chloride is unreactive and therefore it does not degrade in the environment and is likely transported through groundwater by advection. Chloride is difficult to remove from water, often requiring reverse osmosis. This process is expensive and requires large amounts of water.

Chloride transport between surface water and groundwater in Maryland has not been adequately evaluated. To investigate this relationship, the Maryland Geological Survey (MGS) performed a review of the literature for road salt impacts to both groundwater and surface water. Because chloride and conductivity have a strong linear relationship, conductivity can be used as a proxy for chloride concentrations as conductivity measurements are easy to record in the field. A monitoring well in Montgomery County near a major freeway (MD Route 200) has been monitored continuously for conductivity since December 2018. These data should provide better insight into the rate of movement of chloride from road salt within the groundwater-flow system.

As part of a multi-year study (conducted by MGS) to evaluate road salt contamination in groundwater, chloride data were compiled from the following sources: U.S. Geological Survey National Water Information System, National Uranium Research Evaluation, County databases, and public water supply (transient/non-transient wells). These data were mapped in ArcGIS to evaluate spatial distribution of available data and changes in chloride concentrations over time.

An Overview of Groundwater in Maryland

Johanna Gemperline

ABSTRACT

More than one-quarter of Marylanders depend on groundwater as their primary water source. Yet to many people, groundwater is somewhat mysterious, largely because we cannot observe it directly. This talk will introduce the fundamental concepts of groundwater, with emphasis on groundwater settings that exist in Maryland. Topics for discussion will include the hydrologic cycle, porosity, permeability, recharge, water table versus confined aquifers, and cones of depression. Methods of investigation including water-level measurement, geophysical well logs, pump tests, and groundwater flow models also will be covered. In addition, challenges to our groundwater quality and availability, including drought, drawdown, and saltwater intrusion will be discussed.

The occurrence of groundwater in Maryland is largely dependent on the subsurface geology in which it is found. The aquifers consisting of unconsolidated sediments of the Coastal Plain, for example, will store and transmit groundwater very differently from the fractured crystalline bedrock of the Piedmont. As a result, aquifers in the varied regions of the State will respond differently to drought and excessive pumping, and will be susceptible to contamination in different ways.