Wellwater Quality in the Appalachian Plateau Physiographic Province of Maryland
2019, VanDerwerker, T.J., Bolton, D.W., and Gemperline, J.M.
Report of Investigations 85
Wellwater quality data from the Appalachian Plateau Physiographic Province of Maryland (Garrett County and western Allegany County) were compiled from local, state, and federal agencies. Concentrations of major ions, nutrients, trace elements, radioactivity, and indicators (pH, total dissolved solids, specific conductance, dissolved oxygen) were evaluated from 2,314 wells with respect to drinking water standards, geologic units, land use, topographic position, and other factors.
- Wellwater samples in the study area tended to have a near-neutral pH (median: 7.1), and were moderately hard (median: 70 mg/L as CaCO3), reduced (dissolved oxygen <1 mg/L), and low in dissolved solids (median: 132 mg/L).
- Twenty-two percent of wells exceeded the Drinking Water Advisory for sodium of 20 mg/L (for individuals on a 500 mg/day restricted sodium diet).
- Manganese exceeded the 0.3 mg/L Lifetime Health Advisory in 15 percent of wells.
- Arsenic concentrations exceeded the Maximum Contaminant Level (MCL) of 0.010 mg/L in approximately 7 percent of wells sampled. Approximately 22 percent of samples collected in the Hampshire Formation exceeded the MCL.
- Fifty-seven percent of wells exceeded the Secondary Maximum Contaminant Level (SMCL) – established for taste, odor, or other aesthetic considerations – for iron (0.3 mg/L); the highest percentage of iron exceedances was observed in the Allegheny Formation (88 percent of wells); the lowest was in the Hampshire Formation (37 percent).
- Fifty-four percent of wells exceeded the manganese SMCL of 0.05 mg/L. The highest percentage of manganese exceedances were observed in the Allegheny Formation (96 percent of wells) and the lowest was in the Hampshire Formation (52 percent).
- Chloride concentrations exceeded the SMCL of 250 mg/L in about 2 percent of wells. Most of the high chloride concentrations are associated with road salt and possibly other surface-based anthropogenic chloride sources. A small subset of wells having chloride concentrations greater than 50 mg/L had a different chemical composition than other high-chloride wells in the study area, and more closely resembles the impact of shallow brackish water rather than road salt.
- Gross alpha-particle activity (an indicator of radioactivity in water) was low (only one in 61 wells tested exceeded the MCL of 15 pCi/L). The median radon concentration was 230 pCi/L.
- There were no clear differences in wellwater quality between wells in different land use categories, or between wells in different topographic settings. There were also no clear relations between wellwater quality and well depth, casing depth, or age of wells.
- Dissolved solids, hardness, pH, iron, and manganese tended to be higher and dissolved oxygen and nitrate tend to be lower in Appalachian Plateau wellwater compared to wellwater in the crystalline-rock regions in Baltimore, Cecil, and Howard Counties.