Sources of elevated chloride concentrations in groundwater and surface water in northern Garrett County, Maryland
Background
Chloride is a common groundwater contaminant. While chloride itself is not a threat to human health, associated constituents such as sodium can have adverse health effects. Additionally, at high chloride concentrations (above 250 milligrams per liter [mg/L]) water may develop a salty taste. Chloride may also facilitate corrosion and cause damage to household appliances, plumbing fixtures and pipes.
Groundwater from numerous wells in Garrett County, Maryland show elevated concentrations of chloride (greater than 100 mg/L). The source of the elevated chloride is often attributed to road-salting operations. However, elevated chloride in some well water does not appear to be related to surface sources as indicated by chloride/bromide ratios (VanDerwerker et al., 2019). These wells, along roads not typically treated with road salt, are located within the area of the Accident Dome, an anticlinal structure of historically intensive gas extraction now utilized for gas storage. Recent geologic mapping in northern Garrett County indicates that the faults that provide the trapping mechanism for natural gas fields on the flanks of the Accident dome may extend to the land surface (Brezinski, 2019; Brezinski and Conkwright, 2013), which raises the question of whether the faults provide a conduit for subsurface brines to enter the shallow groundwater flow system.
The objective of this study is to investigate spatial and temporal variations in chloride in groundwater in the vicinity of the Accident dome near the Town of Accident in order to develop an objective method for differentiating between deep brine and surface-derived sources (road salt, water-softener effluent, fertilizer, swimming pool treatment, etc.). Additionally, the study will attempt to identify distances from geologic structures and depths that should be avoided when installing new wells.
References:
Brezinski, D.K., 2019, Geologic Map of the Accident and McHenry Quadrangles, Garrett County, Maryland: Maryland Geological Survey, Quadrangle Geologic Map, scale 1:24,000 (version ACCID_McHEN2019.1.0)
Brezinski, D.K. and Conkwright, R.D., 2013, Geologic map of Garrett, Allegany and Western Washington Counties in Maryland: Maryland Geological Survey, 1 sheet, scale 1:100,000
VanDerwerker, T.J., Bolton, D.W., and Gemperline, J. M., 2019, Wellwater Quality in the Appalachian Plateau Physiographic Province of Maryland, Maryland Geological Survey Report of Investigations No. 85, 75 p.