METHODS OF STUDY
BACTERIOLOGICAL QUALITY OF GROUND WATER USED FOR HOUSEHOLD SUPPLY
This report describes the bacteriological results of a ground-water study conducted from 1993 to 1995 as part of the U.S. Geological Survey's National Water-Quality Assessment Program in the Lower Susquehanna River Basin study unit. Water samples collected from 146 household supply wells were analyzed for fecal-indicator organisms including total coliform, fecal coliform, Escherichia coli (E. coli), and fecal streptococcus concentrations. Supporting data used in the interpretations are selected water-quality constituents, well-construction information, and the environmental setting at the well site including land use, physiography, bedrock type. Water from nearly 70 percent of the wells sampled had total coliform present and thus was not suitable for drinking without treatment. Fecal coliforms were found in water from approximately 25 percent of the sampled wells. E. coli testing was not conducted in 1993. Approximately 30 percent of the 88 sampled wells had waters with E. coli. Fecal streptococcus bacteria was present in water from about 65 percent of the wells sampled. Bacteriological contamination was more likely to occur in water from wells in agricultural areas than in water from wells in forested areas. Water from wells sampled in the Ridge and Valley Physiographic Province was more likely to have bacteria than water from wells in the Piedmont Physiographic Province. Differences in bacterial concentrations among bedrock types are only statistically significant for E. coli. Bacterial concentrations are weakly related to well-age but not to other well characteristics such as the total well depth or the casing length. Relations exist between bacterial concentrations and selected water-quality constituents. Most wells from which water was sampled did not have sanitary seals and very few were grouted. This may have contributed to the number of detections of bacteria. It is uncertain whether the bacteria detected are the result of widespread aquifer contamination or site-specific factors.
The U.S. Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program is designed to determine the occurrence and distribution of water-quality characteristics in ground water and surface water (Gilliom and others, 1995). Studies began in 1991 in the Lower Susquehanna River Basin study unit, hereafter termed the study unit. The occurrence and distribution of bacteria in ground water are important water-quality issues in the study unit.
Ground water is an important source of household supply in the study unit. Private water-supply information from the U.S. Bureau of the Census (1990) for counties in the study unit shows a total of nearly 1,600,000 households, of which about 500,000 depend on ground water from private wells for their drinking water supply (table 1). Approximately 400,000 households are in Pennsylvania; the others are in Maryland. Because only parts of some counties are within the basin, these numbers overrepresent the number of households and private wells in the basin (table 1). To estimate the number of households and private wells, the number in each county was multiplied by the fraction of each county in the basin. Using this estimation, about 800,000 households and approximately 300,000 private wells are in the basin. Therefore, approximately 38 percent of the households in the study unit depend on ground water from private wells for water supply.
Table 1. Private water-supply information from the 1990 U.S. Bureau of the Census for counties in the Lower Susquehanna River Basin study unit. -------------------------------------------------------------------------------- County Number of Number of Percentage of Percentage of households households households county in in county in county the Lower with private with private Susque- wells wells hanna River Basin Adams 28,066 15,655 55 52 Baltimore (Md.) 268,638 23,845 8 2 Bedford 18,070 13,472 74 72 Berks 127,849 38,847 30 11 Blair 50,325 12,790 25 100 Carroll (Md.) 42,213 24,704 58 1 Cecil (Md.) 24,817 17,012 68 34 Centre 42,784 6,986 16 27 Chester 133,592 49,316 36 19 Columbia 23,436 11,292 48 2 Cumberland 73,506 19,587 26 100 Dauphin 95,123 21,655 22 100 Franklin 45,642 14,455 31 22 Fulton 5,127 4,444 86 34 Harford (Md.) 63,094 23,062 36 37 Huntingdon 15,541 10,118 65 100 Juniata 7,583 5,364 70 100 Lancaster 151,352 50,966 33 100 Lebanon 42,708 13,034 30 85 Mifflin 17,737 6,729 37 100 Northumberland 38,789 9,482 24 62 Perry 14,930 11,112 74 100 Schuylkill 60,690 14,685 24 41 Snyder 12,697 6,913 54 100 Somerset 29,592 11,228 37 3 Union 11,614 6,178 53 28 York 128,764 43,441 33 100 TOTALS 1,574,279 486,372 --------------------------------------------------------------------------------
This report describes and explains the bacteriological quality of raw water from private wells used for household water supplies in the Lower Susquehanna River Basin study unit. The results are based on samples collected by the NAWQA Program in 1993-95 from 146 wells in 17 counties in Pennsylvania and 2 counties in Maryland. Ground-water samples were analyzed for concentrations of total coliform, fecal coliform, Escherichia coli (E.coli), and fecal streptococcus.RETURN TO TOP
Bacterial, viral, and protozoan pathogens are among the most dangerous contaminants in drinking water. About 50 percent of the waterborne disease outbreaks in this country since the early 1900's were caused by contaminated ground water that was untreated or inadequately treated. Most outbreaks were caused by pathogenic (disease-causing) microorganisms (Yates and Yates, 1993).
Water sources that are free from disease-causing impurities and other harmful substances are said to be potable water sources. Potable water is water fit for human consumption. Public water supplies that have passed State potability standards must not have impurities in amounts above maximum contaminant concentrations that have been set by the State or the U.S. Environmental Protection Agency (USEPA). Each State has its own criteria defining the potability of water.
Bacterial potability of water is determined by testing for indicator organisms. Indicator organisms are bacteria whose presence in drinking water indicates that pathogens may be present (Gabler and others, 1988). Indicator organisms are easier to detect and test for than the pathogens themselves; therefore, analysis for the presence of indicator organisms is the method of choice in testing for potable water supplies. The indicator bacteria were the coliform bacteria group and the streptococcal bacteria group. The presence of E. coli in ground water indicates that the contamination of the water supply is fecal in origin. E. coli originates in the feces and intestines of warm-blooded animals (Bordner and others, 1978; American Public Health Association and others, 1992). Sources of fecal-indicator bacteria include septic system failure or improper septic system construction or design, feedlot or field runoff, manure application on fields, and application of municipal sludge. The presence of total coliform, fecal coliform, or fecal streptococcus could indicate that the contamination of the water supply is fecal in origin, but these bacteria types are also present in the soil and other environmental settings that do not come from the feces of warm-blooded animals.
A common misconception is that untreated ground water is generally safe for consumptive use and that most contaminants are removed as the water filters down through the soil. The soil does act as a natural filter for water percolating down through the ground, but this does not guarantee that ground-water supplies cannot become contaminated. Ground-water supplies are subject to bacterial contamination. Water from wells used for potable supply should be routinely tested to ensure that contamination has not occurred.RETURN TO TOP
Water samples were collected from wells in Pennsylvania and Maryland. With the exception of regulations in selected counties with health departments, no public health regulations exist for the permitting and inspection of private wells in most of Pennsylvania (Michael E. Moore, Pennsylvania Department of Conservation and Natural Resources, oral commun., 1995). In the study unit, wells in Chester County, Pa., and in Maryland are permitted and inspected by county health departments. The differences in the drilling of wells for private water supplies in the two states are described below. The significance of these differences on the bacteriological quality of the water samples collected could not be evaluated because only four samples were collected in Chester County, Pa. and six samples were collected in Maryland.
Pennsylvania currently has no statewide well-construction regulations. Well drillers are required by law (Act 610) to obtain certification through the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey (Commonwealth of Pennsylvania, 1976). The certifying state agency does not have the authority to regulate well-construction practices. In Chester County, Pa., the health department requires permit applications for installation of wells to be filed by a Chester County licensed well contractor. An approval to use water from the permitted well is issued only after submission of properly completed forms and reports. A report on water quality is required and must certify that the water meets numerous standards including a total coliform concentration of less than one colony per 100 mL (Ralph DeFazio, Chester County Health Department, oral commun., 1996). The requirements for Chester County are atypical and the vast majority of wells in the Lower Susquehanna River Basin of Pennsylvania are sited and drilled with no regulatory oversight.
Maryland has regulations for the construction of wells to be used as individual potable water supplies. Well drillers must be licensed by the Maryland State Board of Well Drillers and are required to submit well-permit applications that contain the proposed well-construction and location specifications to the Approving Authority. The Approving Authority is the Secretary of the Environment or a designee appointed by the Secretary of the Environment (Maryland Code (COMAR) 26.04.04.02.B). Wells must pass Maryland's definition of a "potable water source." Adherence to well-location standards (COMAR 26.04.04.05.B(2)), well-construction standards (COMAR 26.04.04.07), and well-abandonment standards is a prerequisite for approval of the well as a potable water source. Disinfection procedures must be followed upon completion of the well (COMAR 26.04.04.07.N(5)) and a certificate of potability must be obtained (COMAR 26.04.04.09). Wells are inspected for physical defects, and maximum contaminant concentrations have been set for bacteriological and chemical constituents (COMAR 26.04.01). The maximum contaminant concentration for total coliform is zero colonies per 100 mL (Woody Williams, Harford County Health Department, oral commun., 1995). In other words, total coliforms must not be detected in the water sample collected from the well for a certificate of potability to be issued.
Previous studies attempting to quantify the bacteriological quality of ground water have been conducted on private individual water supplies. Three studies of private well water supplies are summarized here: one in Pennsylvania; one in Ohio; and one national study.
A study was conducted by The Pennsylvania State University (Sharpe and others, 1985) in which ground water-quality data was collected from all regions of Pennsylvania from 1974 to 1983. The samples were collected from 268 private individual water systems, including about 200 wells, where water-quality problems were perceived to exist. Analyses were conducted for several water-quality constituents including total coliform bacteria. Approximately 40 percent of the private water-supply systems, both wells and springs, had bacterial contamination. Spring water supply sources were more frequently contaminated with bacteria than well water sources.
A study in northwestern Ohio (Breen and Dumouchelle, 1991) was conducted by the USGS, in cooperation with county and municipal agencies, from 1985 to 1988 to evaluate the hydrology and quality of ground water. Bacteriological tests of water from 141 wells completed in carbonate aquifers were conducted. Total coliforms were present in more than 50 percent of the collected samples, and fecal coliforms were present in approximately 20 percent. Nearly 40 percent of the collected samples tested positive for fecal streptococcus bacteria. Fecal streptococcus was present in approximately two thirds of the samples that had total coliform bacteria and approximately 70 percent of the samples that had fecal coliform bacteria.
Another study conducted on a broader scale and led by Cornell University (Francis and others, 1984) was a national assessment of the water quality of rural domestic water supplies in northeast, north central, south, and west regions of the United States from May 1978 through January 1979. Total coliform, fecal coliform, and fecal streptococcus bacteria types were among constituents tested. The results summarized here refer to testing conducted in intermediate (several households supplied by the same well) and individual water systems. About ninety percent of the households with individual systems and about 88 percent of the households with intermediate systems relied on wells. The remaining households relied on cisterns, springs, surface water, hauled, or purchased bottled water. More than 40 percent of the waters from intermediate or individual systems had total coliforms. Fecal coliforms were present in 20 percent of the intermediate or individual systems and fecal streptococcus was present in 19 percent of all rural water-supply systems in which testing was conducted. A breakdown of the percentage of fecal streptococcus present in intermediate or individual water systems was not given.RETURN TO TOP
The Lower Susquehanna River Basin study unit drains 9,200 mi2, extending from Sunbury, Pa. downstream to the Chesapeake Bay, Md., and includes the Northeast River drainage basin (fig.1). About 47 percent of the study unit is forested, and agricultural land use comprises another 47 percent of the area (Risser and Siwiec, in press). Water samples were collected in the following five study areas: (1) agricultural areas underlain by limestone and dolomite bedrock in the Piedmont Physiographic Province, (2) areas underlain by sandstone and shale in the Appalachian Mountain Section of the Ridge and Valley Physiographic Province, (3) areas underlain by igneous and metamorphic rocks (hereafter termed crystalline bedrock) in the Piedmont Physiographic Province, (4) agricultural areas underlain by limestone and dolomite bedrock in the Appalachian Mountain Section of the Ridge and Valley Physiographic Province, and (5) agricultural areas underlain by limestone and dolomite bedrock in the Great Valley Section of the Ridge and Valley Physiographic Province. The areas underlain by limestone and dolomite are referred to as carbonate subunits in this report. The areas, hereafter termed environmental subunits, are described in table 2 and are shown in figure 1.
Figure 1. Location of environmental subunits sampled and bedrock types, Lower Susquehanna River Basin study unit, Pennsylvania and Maryland.
Table 2. Environmental subunits and selected characteristics of wells representing subunits of the Lower Susquehanna River Basin study unit, Pennsylvania and Maryland ENVIRONMENTAL SUBUNIT ----------------------------------------------------------------- Characteristic Piedmont Piedmont Great Valley Appalachian Appalachian carbonate crystalline carbonate Mountain Mountain sandstone carbonate and shale -------------------------------------------------------------------------------- Bedrock limestone igneous and limestone sandstone limestone lithology and metamorphic and and and comprising dolomite dolomite shale dolomite aquifer Land use agricultural agricultural agricultural agricultural agricultural setting1 forested, and and forested suburban Topographic valley hilltop and valley valley and valley setting2 hillside hillside Percentage 5.91 14.26 3.95 14.92 7.56 of Lower Susquehanna River Basin Number of 29 30 28 29 30 wells sampled Number of 29 22 28 22 30 wells in agricultural areas Number of 0 8 0 7 0 wells in non- agricultural areas Depth of wells median:160 median:146 median:161 median:155 median:172 sampled, in maximum:200 maximum: 200 maximum: 290 maximum: 205 maximum: 243 feet Age of wells, median: 7 median: 10 median: 8 median: 8 median: 10 in years as maximum: 20 maximum: 20 maximum: 21 maximum: 21 maximum: 27 of 1995 ---------------------------------------------------------------------------------------------------------------------
The authors wish to express their thanks to all the homeowners
who kindly permitted the sampling of their private water wells. This manuscript
was prepared with the assistance of a report team that included Paul Stackelberg,
Donna Francy, Dennis Risser, Kevin Breen, Steven Siwiec, Kim Wetzel, Charles
Wood, James Gerhart and Russell Ludlow of the U. S. Geological Survey,
Stuart Reese of the Pennsylvania Department of Environmental Protection,
and Woody Williams of the Harford County Health Department in Maryland.
The authors thank the team for contributing their knowledge and expertise
throughout all stages of the report-writing process.
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