David A. Battigelli | Geology Reports

USGS2002

Occurrence and distribution of microbiological contamination and enteric viruses in shallow ground water in Baltimore and Harford counties, Maryland

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, ortho-phosphate, calcium, magnesium, sodium, potas-sium, 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 poly-merase chain-reaction analysis. Twenty-nine per-cent of the samples (26 of 90) had bacterial con-tamination. 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 sam-ples (3 of 87) had oxidized nitrogen concentra-tions 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 cor-relation with the concentration of sulfate and sample pH as measured at the U.S. Geological Survey National Water-Quality Laboratory in Denver, Colorado.

Water-Resources Investigations Report↗

USGS2001

Occurrence and distribution of enteric viruses in shallow ground water and factors affecting well vulnerability to microbiological contamination in Worcester and Wicomico counties, Maryland

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 water-table aquifer in the Coastal Plain in Worcester and Wicomico Counties, Maryland.Two hundred seventy-eight well sites were evaluated with regard to simulated ground-water flow paths, land use, natural soils groups, and well characteristics, such as well depth and well age. Flow and transport simulations of the water-table aquifer indicated that wells screened less than about 50 feet below land surface (shallow wells) were most vulnerable to surface contamination, which in some cases could originate from as far as 2,000 feet upgradient of the well. Animal-feeding and agricultural-storage operations were considered among the most likely sources for viral contamination; therefore, sites close to these activities were considered most vulnerable. Soil groups were evaluated with regard to depth to water and moisture-holding capacity. Wells with shallow depths to water or in very sandy soils were considered more vulnerable to contamination than deep wells (greater than 50 feet) and those completed in finer-grained soils. Older wells and wells where coliform bacteria had been detected in the past were classified as highly vulnerable. On the basis of this evaluation, 27 sites considered to be susceptible were sampled.Samples were collected by pumping up to 400 gallons of untreated well water through an electropositive 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 nonculturable viruses; grab samples were analyzed for somatic and male-specific coliphages, Bacteroides fragilis, Clostridium perfringens, enterococci, Escherichia coli, total coliforms, total oxidized nitrogen, dissolved organic carbon, organic nitrogen, total phosphate, orthophosphate, acid-neutralizing capacity, pH, specific conductance, temperature, and dissolved oxygen.Eleven percent of the samples analyzed (3 of 27) tested positive for either culturable viruses or the presence of viral ribonucleic acid. Approximately 15 percent of the samples (4 of 27) tested positive for one or more bacterial contaminants.

Water-Resources Investigations Report↗