Evaluation of lead concentrations in well water from the Piedmont area of Harford County, Maryland
2013, Burgy, K., Resline, J., and Smith, P.
Report of Investigations 81
A water-quality study was conducted of domestic wells located in the Piedmont terrane of Harford County to evaluate the reported occurrence of elevated lead concentrations in drinking water. Samples were collected from 80 wells and were analyzed for lead, pH, specific conductance, nitrate, and chloride. Three different water samples were collected and analyzed for lead at each site: a pre-distribution (“purge”) sample, and two postdistribution samples (a first-draw sample and a 30-second-flush sample). The key results of this study are:
- Six first-draw samples exceeded the U.S. Environmental Protection Agency Action Level for lead in drinking water (0.015 milligrams per liter), while none of the 30-second-flush samples did so. The range of reported concentrations for first-draw lead samples was less than 0.005 milligrams per liter (the laboratory reporting level) to 0.039 milligrams per liter. The range for 30-second-flush samples was less than 0.005 milligrams per liter to 0.013 milligrams per liter.
- All pre-distribution system (purge) well-water samples tested below the U.S. Environmental Protection Agency Action Level of 0.015 milligrams per liter for lead. Only one sample (0.006 milligrams per liter) tested above the laboratory reporting limit of 0.005 milligrams per liter.
- No geologic sources of lead in drinking water were identified in this study or correlated with lead results. All but one lead detection appear to be the result of distribution-system contributions.
- pH values ranged from 4.7 to 8.3, with a median value of 6.1. The ground water is predominantly acidic, with 90 percent of pH values less than 7.0.
- Specific conductance, which can be used as a proxy for total dissolved solids, was highly variable, ranging from 22 to 1,706 microsiemens per centimeter at 25 degrees Celsius.
- Nitrate concentrations ranged from less than 0.2 to 18.25 milligrams per liter as nitrogen, with a median concentration of 3.94 milligrams per liter. Four samples exceeded 10 milligrams per liter, the U.S. Environmental Protection Agency Maximum Contaminant Level (standard related to health effects).
- Chloride concentrations ranged from less than 10 to 552 milligrams per liter. The U.S. Environmental Protection Agency Secondary Maximum Contaminant Level (a non-enforceable standard related to taste, odor, or other aesthetic considerations) for chloride in drinking water is 250 milligrams per liter; only one sample exceeded this standard.
- Plumbing materials, including faucets, valves, sink pipes, and well tanks, were evaluated with respect to lead detections. Lead was present in water samples passing through a variety of materials, although only five of 75 samples included fixtures adhering to the new, reduced lead content plumbing codes set forth in Maryland’s 2012 Code of Regulations.
- Lead detections did not show an association with any particular part of the distribution system.
- All lead detections greater than 0.015 milligrams per liter were from samples where the pH was less than 6.2. All lead detections were from samples where the pH was less than 6.3.
- The age of the single-family homes sampled in this study, which relates to acceptable lead content in plumbing fixtures, did not appear to be associated with first-draw lead results, as compared to other factors such as pH and stagnation time of the distribution system supplying the sample.
- The U.S. Environmental Protection Agency recommendations for reduction of lead in drinking water, including using only the cold-water line as a source for cooking and drinking water, and flushing the system by allowing water to run for a few minutes before use, are supported by the findings of this study.