Reports
Ground-water quality in the Piedmont region of Baltimore County, Maryland
1998, Bolton, D.W.
Report of Investigations 66
Key Results
A ground-water-quality study was conducted in the Piedmont portion of Baltimore County. Water samples from 112 wells and springs were analyzed for major ions, nutrients, trace elements, radon, pesticides, and volatile organic compounds (VOCs).
The key results of this study are:
- Ground water in the study area tends to be acidic, low in dissolved solids, and well oxygenated.
- Maximum Contaminant Levels (MCLs; health-related criteria established by the U.S. Environmental Protection Agency [US EPA]) were exceeded for nitrate and lead. About 5 percent of samples had nitrate concentrations greater than 10 milligrams per liter (mglL) as nitrogen; about 2 percent of samples had lead concentrations greater than 15 micrograms per liter (flglL). No other MCLs were exceeded for any inorganic constituent. Secondary Maximum Contaminant Levels (SMCLs; non-enforceable standards related to taste, odor, or other aesthetic qualities) were exceeded for pH (71 percent of samples had pH less than 6.5), iron (30 percent of samples contained greater than 300 flg/L), manganese (14 percent of samples contained greater than 50 flglL), color (about 5 percent of samples contained greater than 15 color units), total dissolved solids (TDS) (about 2 percent of samples contained greater than 500 mglL), and chloride (about 1 percent of samples contained greater than 250 mglL).
- Pesticides (including pesticide breakdown products) were detected in samples from 71 percent of the sites. Ninetyeight percent of the pesticide detections were less than 1 flglL, and most were less than 0.1 flglL. None of the pesticide detections exceeded any MCL. The most frequently detected pesticides were deethyl atrazine (DEA; a breakdown product of the herbicide atrazine), metolachlor, atrazine, carbofuran, and simazine. Volatile organic compounds (VOCs) were detected at 3 of 112 sites. Three compounds (methylene chloride, tetrachloroethylene, and 1,1,1- trichloroethane) were detected, two of which (methylene chloride and tetrachloroethylene) exceeded their respective MCLs.
- More than 95 percent of wells in the study area had detectable levels of nitrate. Analysis of nitrate with respect to land-use data, nitrogen isotopes, and pesticide detections indicates that nitrate concentrations in well water are associated with current and former agricultural activity (such as fertilizer application), and that septic-system emuent has had little overall impact on nitrate or other water-quality constituents.
- Chloride concentrations tended to be highest in wells located less than 200 ft from a paved road, indicating that chloride concentrations in ground water may be associated with road salt. However, only one well in the study had a chloride concentration higher than 250 mglL, the SMCL for chloride.
- Chloride, nitrate, and atrazine concentrations did not vary greatly in most of the wells that were sampled monthly between May 1995 and April 1996. There was little relationship between well-water chloride concentration and time of year, even in wells that had been affected by road salt. Atrazine concentrations tended to increase in late summer and early fall and decrease through January.
- There was little relationship between concentrations of water-quality constituents and well depth, casing depth, depth to water, well yield, or other well characteristics.
- Radon concentrations exceeded 4,000 picocuries per liter (pCilL) in samples from 29 percent of the sites. Radon concentrations tended to be higher in samples from schists and gneisses (median concentrations: 2,900 and 2,600 pCi/L, respectively), than in samples from marble and mafic rocks (median concentrations: 550 and 540 pCi/L, respectively).
- There was little local variation in well-water quality for wells sampled from the same residential development.
- There were statistically significant differences in concentrations of most major-ion constituents between the four rock types in the study area (schist, gneiss, marble, and mafic rocks).
