Viral Contamination of Ground Water in Fractured Bedrock Aquifers in Baltimore and Harford Counties, Maryland

WRD PROJECT #: MD146
PROJECT CHIEF: Banks, William S.L.
BEGIN DATE: 20-September-1999
END DATE: 30-September-2001

Customers currently supporting the project:

Maryland Department of the Environment
U.S. Geological Survey

Problem

In response to the 1996 Amendments to the Safe Drinking Water Act, the U.S. Environmental Protection Agency (USEPA) is developing the Ground Water Rule to protect users of public ground-water supplies from viral contamination. Many ground-water suppliers do not currently practice any form of disinfection treatment, as monitoring of their water supply has not detected coliform microorganisms. Because of difficulties associated with monitoring directly for viral contamination, it has not been possible to routinely identify if viruses are present in water supplies. Therefore, studies are needed to characterize the true extent of viral pollution in ground water used for drinking throughout the United States.

More than 120 different types of potentially harmful enteric viruses are excreted in human feces, and are widely distributed in type and number in domestic sewage, agricultural wastes, and septic drainage systems (Gerba, 1988).

Illnesses in humans caused by these viruses range from severe (poliomyelitis, hepatitis, and gastroenteritis) to innocuous infections. Contamination of ground water and resulting outbreaks of illness from viruses often are caused by extremely low viral densities. As few as 1 hepatitis virus per 1,000 liters of drinking water can result in a lifetime mortality risk of 5 X 10-4 (Gerba, 1988). From 1971 to 1979, an estimated 57,974 persons in the United States were affected by outbreaks of waterborne pathogens (Craun, 1986). The consumption of contaminated ground water was responsible for about one-half of all reported outbreaks of waterborne diseases in the United States (Gerba, 1988). Up to 65 percent of the documented outbreaks of waterborne diseases in the United States could be attributed to viruses in drinking water (Keswick and Grebe, 1980).

Objectives

The objective of this study is to identify public supply wells using less than 10,000 gallons per day in selected parts of Baltimore and Harford Counties and determine the occurrence of viral contamination.

Approach

This is a cooperative project with the Maryland Department of the Environment (MDE) and the Baltimore office of the U.S. Geological Survey (USGS). Initially, all public water supplies in the Piedmont portion of the two counties permitted to provide less than 10,000 gallons per day (GPD) will be identified. From this population, a set of 100 wells will be sampled. Additionally, wells targeted to represent sites believed not to be susceptible to viral contamination will also be sampled for control and comparison. Samples will be collected and analyzed for viruses and other chemical constituents.

Task 1:

The Maryland Department of Environment will supply the USGS with a list of all known public water-supply wells in the Piedmont part of the study area that are permitted to withdraw 10,000 GPD or less. Each site will be evaluated to determine the well that supplies the permitted water. Sites where the well completion report is not available, sites where water individual taps are not available, or sites where there is doubt as to which well supplies water will not be selected.

This group of ground-water supply wells will represent the population from which sample sites will be selected.

Task 2:

The USGS will evaluate the susceptibility to viral contamination based on spatial variables such as soil type, land use, hydrology, previous bacteriological (coliform) contamination, age of well, casing depth and well depth for sites having permitted wells. One hundred wells deemed "likely to be at risk" will be sampled for viruses, nitrogen, dissolved organic carbon, phosphorus, and major ions and trace metals. Sample temperature, pH, alkalinity, and dissolved oxygen will be measured on site at the time of sampling. Sampling of major ions and nutrients will allow computation of an electro-chemical balance, chemical water type and the classification of aquifer lithology (Bolton, 1998). These forms of classification may provide insight on the vulnerability of a water system to viral pathogens based on geology and water type. Sampling for viruses will be conducted on each selected well using a laboratory-supplied pre-sterilized electropositive filter. A minimum of 300 gallons of ground water will be filtered at the wellhead. The filter will be removed from the housing, wrapped in foil, placed in ice, and shipped to the laboratory within 24 hours of collection. Following the collection of the filtered virus sample, field measurements will be made and a sample will be collected for analysis. To assure the quality of the data being collected, quality-control / quality-assurance (QA/QC) samples will be collected at a minimum number of sites to equal no less than 10 percent of the number of viral samples. The QA/QC samples will consist of, but may not be limited to, the collection of equipment, and shipping blanks, and replicates. Personnel from the Baltimore office of USGS will conduct sample collection and measurements of field parameters. The Wisconsin State Laboratory of Hygiene in Madison, Wisconsin will conduct viral analyses. Nutrient, major ion, trace metal, phosphorus, and dissolved organic carbon analyses will be conducted by the USGS National Water-Quality Laboratory (NWQL) in Denver, Colorado. All data will be verified by the USGS project manager and subsequently stored in a USGS data base.

Task 3:

The results of the sampling will be used to characterize the extent of viral contamination in small (10,000 GPD or less) water supplies in the Piedmont part of Baltimore and Harford Counties. MDE will be provided with all data files as requested. MDE will be provided with digital copies of well location, land use, soil type, and hydrogeologic setting associated with sample locations.

The results of the study will be published either as a USGS Water-Resources Investigations Report or in a refereed professional journal article.