U.S. Geological Survey

Bacteriological Quality of Groundwater Used for Household Supply, Lower Susquehanna River Basin, Pennsylvania and Maryland


Table of Contents








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       
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                                                                                                                            

Purpose and Scope

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.

to the top RETURN TO TOP

Bacteria and Potability of Ground Water

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.

to the top RETURN TO TOP

Regulations for Private Wells in Pennsylvania and Maryland

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) Wells must pass Maryland's definition of a "potable water source." Adherence to well-location standards (COMAR, well-construction standards (COMAR, 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 and a certificate of potability must be obtained (COMAR 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 Investigations

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.

to the top RETURN TO TOP

Description of the Study Area

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.

map of areaFigure 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

Land use     agricultural agricultural  agricultural  agricultural agricultural    
setting1                  forested, and               and forested                               
Topographic     valley    hilltop and   valley        valley and    valley          
setting2                   hillside                    hillside                                   

Percentage      5.91      14.26         3.95          14.92         7.56            
of Lower                                                                                                             
River Basin                                                                                                        

Number of        29       30            28            29            30              

Number of        29       22            28            22            30              
wells in 

Number of         0       8              0            7             0               
wells in non-                                                                                                          
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    
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                                                                                                                   
From GIRAS land use data of mid 1970's (Mitchell and others, 1977.)
Risser and Siwiec, in press


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.

to the top RETURN TO TOP


Copies of this report may be purchased from:

U.S. Geological Survey
Branch of Information Services
Box 25286
Denver, Colorado 80225-0286

For additional information about USGS programs and
activities in Pennsylvania, please visit our web site at:

Return to the Water Resources of Pennsylvania Home Page Go Home
or go directly to:

[ Water Data ][ Map/GIS Data ] [ Publications ][ General Information ]
[ Project Highlights ] [ Site Index ][Search ]

[ Dept. of the Interior ] [ USGS ] [ USGS Water Resources ]
[ USGS Biological Resources ] [ USGS Mapping ] [ USGS Geology]


The URL for this page is http://pa.water.usgs.gov/reports/wrir_96-4212/report.html

Answers to many common questions can be found on our
Frequently Asked Questions (FAQ) page. Please direct content comments
or questions to the PA District Information Specialist or contact:

District Chief
U.S. Geological Survey
840 Market Street
Lemoyne, PA 17043-1584
Phone: (717) 730-6912
FAX: (717) 730-6997
Email: dc_pa@usgs.gov
Please direct web related comments to GS-W-PA_Webmaster@usgs.gov