U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 01-4216
The U.S. Geological Survey, in cooperation with the Maryland Department of the Environment and the Wisconsin State Laboratory of Hygiene, conducted a study to characterize the occurrence and distribution of viral contamination in small (withdrawing less than 10,000 gallons per day) public water-supply wells screened in the shallow aquifer in the Piedmont Physiographic Province in Baltimore and Harford Counties, Maryland. Two hundred sixty-three small public water-supply wells were in operation in these counties during the spring of 2000. Ninety-one of these sites were selected for sampling using a methodology that distributed the samples evenly over the population and the spatial extent of the study area. Each site, and its potential susceptibility to microbiological contamination, was evaluated with regard to hole depth, casing interval, and open interval. Each site was evaluated using characteristics such as on-site geology and on-site land use.
Samples were collected by pumping between 200 and 400 gallons of untreated well water through an electropositive cartridge filter. Water concentrates were subjected to cell-culture assay for the detection of culturable viruses and reverse-transcription polymerase chain reaction/gene probe assays to detect viral ribonucleic acid; grab samples were analyzed for somatic and male-specific coliphages, Bacteroides fragilis, Clostridium perfringens, enterococci, Escherichia coli, total coliforms, total oxidized nitrogen, nitrite, organic nitrogen, total phosphate, orthophosphate, calcium, magnesium, sodium, potassium, chloride, sulfate, iron, acid-neutralizing capacity, pH, specific conductance, temperature, and dissolved oxygen.
One sample tested positive for the presence of the ribonucleic acid of rotavirus through polymerase chain-reaction analysis. Twenty-nine percent of the samples (26 of 90) had bacterial contamination. About 7 percent of the samples (6 of 90) were contaminated with either male-specific coliphage, somatic coliphage, or bacteriophages of Bacteroides fragilis. About 3 percent of the samples (3 of 87) had oxidized nitrogen concentrations that exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level of 10.0 milligrams per liter. A statistical analysis showed that no significant relation exists between the presence of bacteria or coliphage and all variables, except the mean temperature of the water sample as measured in the field. Additionally, the concentration of total coliform bacteria had a statistically significant, moderately strong correlation with the concentration of sulfate and sample pH as measured at the U.S. Geological Survey National Water-Quality Laboratory in Denver, Colorado.
Purpose and scope
Location and description of study area
Study design and methods
Quality assurance and quality control
Occurrence and distribution of viral contamination
Summary and conclusions
Appendix: Microbiological and water-quality data for 91 public water-supply wells in Baltimore and Harford Counties, Maryland, April through November 2000
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For more information about USGS activities in Maryland, Delaware and the District of Columbia contact:
MD-DE-DC Water Science Center
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Baltimore, MD 21237
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or access the USGS Water Resources of Maryland, Delaware, and District of Columbia home page at: http://md.water.usgs.gov/.
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