Reports
Ground-water quality in the Piedmont region of Baltimore County, Maryland: Comparison of data collected in 2000-01 to data collected in 1994-96
2002, Bolton, D.W.
Supplemental Report S2 / Report of Investigations 66
Key Results
Forty-six wells and three springs in the Piedmont region of Baltimore County that had been sampled in 1994-96 were resampled in 2000-01 to document what changes, if any, had occurred in the ground-water quality. Samples were analyzed for major ions and nutrients, iron, manganese, lead, five volatile organic compounds, 47 pesticides, radon, gross alpha-particle activity and gross beta-particle activity. Data analysis has resulted in these key results:
- Ground-water quality in the study area continues to be of generally good quality. There were no statistically significant differences in major-ion concentrations (calcium, magnesium, sodium, potassium, alkalinity, sulfate, chloride, nitrate) between the 1994-96 samples and the 2000-01 samples. Chloride and nitrate concentrations tended to change more than other constituents. One sample exceeded the U.S. Environmental Protection Agency's (EPA) primary drinking-water standard for nitrate, and two samples exceeded the standard for lead; these concentrations were similar to samples collected In 1994-96. No other primary drinking-water standards were exceeded.
- The number and type of pesticides detected, as well as the pesticide detection frequency and ranges of concentrations, changed very little between 1994-96 and 2000-01. About two-thirds of the samples had at least one pesticide detection. Approximately 95 percent of the detections were less than one microgram per liter (ug/L) or parts per billion (ppb), and more than half of the detections were less than 0.1 ppb. Eight different pesticides or pesticide breakdown products were detected (alachlor, atrazine, carbofuran, deethyl atrazine, dieldrin, metolachlor, simazine, and terbacil). None of the detections exceeded any of the U.S. EPA's drinking-water standards.
- Methyl tert-butyl ether (MTBE), a gasoline additive widely used in Maryland, was detected in about 14 percent of the samples. MTBE concentrations increased between 1994-96 and 2000-01 at three sites. None of the MTBE detections exceeded the U.S. EPA's Drinking Water Advisory level of 20 to 40 ug/L. The wells with MTBE detections were located away from commercially developed areas, although most were located near residential fuel storage areas. This indicates that MTBE has the potential to be present in ground water throughout the study area, regardless of land use around a site. The appearance of MTBE in wells within the past five years indicates the need for continued monitoring. None of the other volatile organic compounds analyzed for (benzene, toluene, ethylbenzene, and xylene) were detected.
- The overall health risk due to consumpfion of radium and other alpha-particle and beta-particle emitting radionuclides appears to be low. Gross alpha-particle activity, which is used as a screening test for radium and uranium, indicated that only one of the 49 samples exceeded the U.S. EPA's drinking-water standard. This was confirmed by follow-up testing for radium in 10 percent of samples.
- Well water was less likely than spring water to test positive for total coliform bacteria and E.Coli. Four of the 46 well-water samples tested positive for total coliform bacteria; none tested positive for E.Coli. Two of the four wells had visible defects at the wellhead. By comparison, all three spring-water samples tested positive for total coliform bacteria; one, located in a cow pasture, tested positive for E.Coli. The low detection rate of coliform bacteria in well water, which are widely used as indicators of contamination from septic and sewage effluent, likely reflects the effectiveness of county and state regulations governing the construction and siting of wells and septic systems.
