RELATION BETWEEN

SELECTED WELL-CONSTRUCTION CHARACTERISTICS

AND OCCURRENCE OF BACTERIA

IN PRIVATE HOUSEHOLD-SUPPLY WELLS,

SOUTH-CENTRAL AND SOUTHEASTERN PENNSYLVANIA

by Tammy M. Zimmerman, Michele L. Zimmerman, and Bruce D. Lindsey

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4206

In cooperation with

THE PENNSYLVANIA DEPARTMENT OF ENVIRONMENTAL PROTECTION

BUREAU OF WATER SUPPLY AND WASTEWATER MANAGEMENT

New Cumberland, Pennsylvania

2001
ii

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information Copies of this report may be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

215 Limekiln Road Box 25286

New Cumberland, Pennsylvania 17070 Denver, Colorado 80225-0286
iii

CONTENTS

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Previous investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of study area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Well-construction practices in Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chester County . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Montgomery County . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

South Middleton Township. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Study methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Site selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Sample collection and analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Quality assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Statistical analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Relation between selected well-construction characteristics and occurrence of bacteria

in ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Sanitary and nonsanitary construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Bedrock type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Seasonal effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Other well-construction characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix: Selected well information and results of bacteria analyses for private

household-supply wells in south-central and southeastern Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . 20

ILLUSTRATIONS

1. Map showing location of study area in south-central and southeastern

Pennsylvania and bedrock types where ground water was sampled and

analyzed for total coliform and Escherichia coli bacteria . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Sketch showing cross-section of a ground-water well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3. Photographs showing loose-fitting and sanitary sealed well caps for 6-inch wells . . . . . . 7

4. Graph showing bacteria presence by well-construction characteristic and bedrock

type from wells sampled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5. Map showing sampling locations and detections of total coliform bacteria in wells

sampled. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6. Map showing sampling locations and detections of E. coli bacteria in wells sampled . . 13

7. Boxplots showing concentrations of total coliform bacteria in sanitary and

nonsanitary wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

8. Boxplots showing concentrations of total coliform bacteria in wells constructed

in areas underlain by carbonate and noncarbonate bedrock . . . . . . . . . . . . . . . . . . . . 14

9. Boxplots showing concentrations of total coliform bacteria in sanitary carbonate,

sanitary noncarbonate, nonsanitary carbonate, and nonsanitary noncarbonate

wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

10. Graph showing percentage of detections of total coliform and E. coli in bacteria

studies done in five National Water-Quality Assessment Program basins

compared to this study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
iv

TABLES

Page

1. U.S. Bureau of the Census information for the eight counties in the study area,

south-central and southeastern Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Percentages of total coliform and E. coli bacteria detected in ground water from wells

sampled by the Pennsylvania Department of Agriculture . . . . . . . . . . . . . . . . . . . . . . . 4

3. Selected characteristics of wells sampled and their locations . . . . . . . . . . . . . . . . . . . . . . . . 5

4. Comparison of U.S. Geological Survey environmental sample data to U.S. Geological

Survey replicate sample data and Pennsylvania Department of Environmental

Protection replicate sample data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5. Sample contingency table matrix for comparing the presence/absence of E. coli and

bedrock type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

CONVERSION FACTORS AND ABBREVIATIONS

Multiply By To obtain

Length

inch 25.4 millimeter

foot 0.3048 meter

Volume

gallon 3.785 liter

Temperature

degree Fahrenheit (°F) C = 5/9.× (°F − 32) degree Celsius (oC)
1

RELATION BETWEEN

SELECTED WELL-CONSTRUCTION CHARACTERISTICS

AND OCCURRENCE OF BACTERIA

IN PRIVATE HOUSEHOLD-SUPPLY WELLS,

SOUTH-CENTRAL AND SOUTHEASTERN PENNSYLVANIA

by Tammy M. Zimmerman, Michele L. Zimmerman, and Bruce D. Lindsey

ABSTRACT

Total coliform and Escherichia coli (E. coli)

bacteria were analyzed in ground water sampled

from 78 private household-supply wells as part of a

study by the U.S. Geological Survey in cooperation

with the Pennsylvania Department of Environmental Protection to evaluate the relation between wellconstruction characteristics and the occurrence of

bacteria in ground water. Sampling was done in

eight counties in south-central and southeastern

Pennsylvania from September 2000 to March 2001.

All samples were collected from wells in close proximity to agricultural land-use areas.

Total coliform bacteria were found in water

from 62 percent (48 of 78) of the wells, and bacteria

were just as likely to be found in sanitary wells

(grouted/loose-fitting well cap or grouted/sanitary

sealed well cap) as in nonsanitary wells (nongrouted/loose-fitting well cap). The areas underlain

by carbonate bedrock had the highest percentages

of total coliform detected (about 75 percent). Nearly

half of the samples collected in the areas underlain

by noncarbonate bedrock also were found to have

total coliform present. E. coli bacteria were found in

water from 10 percent of the wells. Seventeen percent of the samples that were positive for total

coliform also were positive for E. coli. The presence

of E. coli bacteria was more likely in water from

nonsanitary wells. Additionally, the presence of

E. coli bacteria was more likely in ground water

from wells underlain by carbonate bedrock. A further breakdown of the data into four groups on the

basis of sanitary construction and bedrock type

indicated the presence of E. coli was more likely in

water from nonsanitary wells in areas underlain by

carbonate bedrock.

Statistical analysis of other well-construction

characteristics that might relate to occurrence of

bacteria showed that the presence of total coliform

bacteria was related to the depth to water-bearing

zone in both sanitary and nonsanitary wells in

areas underlain by carbonate bedrock. Relations

also are present between the presence of total

coliform bacteria and casing length in nonsanitary

wells in areas underlain by noncarbonate bedrock.

Bacteria were found in wells both with and without

insects observed on the underside of the well cap.

Because of the small number of wells sampled that

had sanitary sealed caps, it is uncertain whether

installation of sanitary sealed well caps would

reduce the incidence of bacteria in ground water

from wells or if the presence of bacteria is because

of a combination of well-construction characteristics or aquifer-wide contamination of limited or

broad areal extent.
2

INTRODUCTION

A common belief is that untreated ground water

generally is safe for consumptive use. This belief is a

concern given that nationally, 24 million people rely on

private or individual water systems as their source of

drinking water supply (Barwick and others, 2000).

According to Yates and Yates (1993), the consumption

of contaminated ground water has been responsible for

about one-half of all reported outbreaks of waterborne

diseases in the United States since the early 1900’s.

Since 1971, the U.S. Environmental Protection Agency

(EPA) and the Center for Disease Control and Prevention jointly have maintained a surveillance system for

collecting and periodically reporting data that pertain

to waterborne-disease outbreaks (WBDO’s). The most

recent report was from WBDO’s in the United States in

1997 and 1998 (Barwick and others, 2000). A total of 13

states reported 17 outbreaks associated with drinking

water, causing approximately 2,083 individuals to

become ill. Fifteen of these outbreaks (88 percent) were

linked to ground-water sources. Four outbreaks

(24 percent) were in private or individual water systems with no form of water treatment. The etiologic

agents associated with the outbreaks from groundwater sources included Giardia, Cryptosporidium, and

the O157:H7 strain of Escherichia coli (E. coli). Because

the recognition, investigation, and reporting of

WBDO’s is voluntary on behalf of state, territorial, and

local health departments, the data probably are an

underestimate of the actual incidence of such outbreaks (Barwick and others, 2000).

Pennsylvania has a large rural population that

depends on ground water from private wells as a daily

source of drinking water and source of water for livestock. Private water-supply information from the

U.S Bureau of the Census (1992) shows about 1 million

Pennsylvania households rely on ground water from

private on-lot wells for daily water supply. Census statistics also show nearly 4 million households rely on

ground water from community or public water-supply

systems as their daily source of drinking water. Watersupply information for households with private wells

in counties associated with the study on which this

report is based is shown in table 1.

Even though Pennsylvania has a high dependency on ground water as a source of drinking water

supply, only public water-supply systems currently

(2001) require the routine monitoring and treatment of

their systems for microbiological contaminants. Protection and maintenance of private, household-supply

wells is not regulated and is the responsibility of the

homeowner (state water-quality regulations for publicsupply wells can be used as a guideline). In addition,

Pennsylvania currently has no statewide well-construction requirements, and in most parts of the state,

drilling and testing of private on-lot wells is done with

no regulatory oversight. However, the Pennsylvania

Department of Environmental Protection (PaDEP) recommends wells be sited uphill at least 100 feet from

potential sources of contamination such as septic leach

fields, roads, fuel tanks, and barnyards (Pennsylvania

Department of Environmental Protection, 2000). Typically, private on-lot wells are constructed as open holes

completed in bedrock with minimal surface casing, little or no annular grout seal, and a loose-fitting well

cap.

Bacteria commonly are detected in ground water

from private, on-lot wells used for household supply in

Pennsylvania (Sharpe and others, 1985; Bickford and

others, 1996). It is not known if the bacterial contamination of the water from these household-supply wells

is the result of well-construction characteristics that

can allow contaminants from the immediate vicinity to

enter the well or if bacterial contamination within the

aquifer is widespread. Coliform bacteria generally are

not disease-causing (pathogenic). However, the presence of coliform bacteria, a common indicator bacteria

used to test the sanitary quality of water supplies, indicates that pathogenic organisms may be present. The

U.S. Geological Survey (USGS), in cooperation with the

PaDEP, conducted a study to evaluate whether or not

the water from private household-supply wells constructed with annular grout have lower incidence of

bacterial contamination than wells completed without

this well-construction characteristic.

Table 1. U.S. Bureau of the Census (1990) information for

the eight counties in the study area, south-central and

southeastern Pennsylvania

County Number of

households

Number of

households

in county with

private wells

Percentage

of households

in county with

private wells

Chester 133,592 49,316 37

Cumberland 73,506 19,587 27

Dauphin 95,123 21,655 23

Lancaster 151,352 50,966 34

Lebanon 42,708 13,034 31

Montgomery 254,596 30,716 12

Perry 14,930 11,112 74

York 128,764 43,441 34

Total 894,571 239,827
3

Purpose and Scope

This report describes the relation between

selected well-construction characteristics in south-central and southeastern Pennsylvania and the occurrence

of bacteria in ground water. Private household-supply

wells in predominantly agricultural land-use settings

were the focus of the study; results are based on samples collected from September 2000 to March 2001.

Water samples were analyzed for concentrations of

total coliform and E. coli bacteria. The effect of rock

type in two geologic settings (areas underlain by carbonate rock and areas underlain by noncarbonate rock)

on the occurrence of bacteria in ground water from

sanitary and nonsanitary wells also is presented. A

sanitary well refers to a well constructed with grout

installed along the entire annulus of casing. A nonsanitary well refers to a well constructed with loose dirt or

fill around the annulus of casing.

Previous Investigations

Various studies were done on the occurrence of

bacteria in ground water from private, householdsupply wells. This section will describe studies conducted nationally, regionally, and locally (basin

specific) by the USGS and on a statewide scale by the

Pennsylvania Department of Agriculture (PDA).

USGS - NATIONAL MONITORING EFFORT

In 1997, the National Water-Quality Assessment

(NAWQA) Program selected four basins across the

Nation to participate in a microbiological monitoring

program for ground water: the Lake Erie-Lake Saint

Clair Basin (LERI), the Kanawha-New River Basin

(KANA), the Santee Basin and coastal drainage

(SANT), and the Upper Colorado Basin (UCOL)

(Francy and others, 2000). Ground-water samples were

collected and analyzed for microbiological constituents

from March to September 1997. Seventy-four of the 141

ground-water supply wells were private, householdsupply wells. Overall, total coliform bacteria were

found in 20 percent of 130 samples; E. coli bacteria were

found in less than 1 percent of the 130 samples.

USGS, TENNESSEE DISTRICT

 The USGS, Tennessee District, in cooperation

with the University of Tennessee Agricultural Extension Service and the Tennessee Farm Bureau,

conducted reconnaissance projects regionally in Tennessee in order to establish a better understanding of

the ground-water quality in selected areas of the state.

A total of 200 private, household-supply wells were

sampled in Bedford and Coffee Counties in the southcentral region of Tennessee in June and July 1991. Of

these, 38 percent had fecal coliform and 64 percent had

fecal streptococcus (Roman-Mas and others, 1991). In

August 1996, a follow-up study was conducted in Bedford County (Bennett, 1997). Of the 78 private,

household-supply wells sampled, 74 percent were positive for fecal coliform and 81 percent were positive for

fecal streptococcus.

Another study was done in western Tennessee in

the Beaver Creek watershed and other rural areas of

Fayette, Haywood, Shelby, and Tipton Counties. This

water-quality investigation in the Beaver Creek watershed was done in 1993 to gain an understanding of the

characteristics of the watershed. Of the 408 samples,

8 percent had fecal coliform and 30 percent were positive for fecal streptococcus (Williams, 1996).

PENNSYLVANIA DEPARTMENT OF AGRICULTURE

The PDA sampled ground water from wells

completed mainly in carbonate rocks in six counties in

Pennsylvania and from wells in rocks of Triassic age in

parts of seven counties in southeastern Pennsylvania

(John Pari, Pennsylvania Department of Agriculture,

written commun., 2001). The types of sites visited

include household-supply wells, farms, and commercial and public properties. Samples from the selected

wells were analyzed for a variety of ground-waterquality constituents including E. coli and total coliform

bacteria. The bacteriological data for the selected counties is summarized in table 2.

PENNSYLVANIA BASIN-SPECIFIC USGS PROJECTS

Microbiological data were collected as part of the

USGS NAWQA Program in two basins partly contained within Pennsylvania. Total coliform and E. coli

were analyzed as part of the Delaware River Basin

NAWQA. Total coliform, fecal coliform, E. coli, and

fecal streptococcus were analyzed as part of the Lower

Susquehanna River Basin NAWQA. Results of microbiological analyses in each of the basins are described

below.

USGS, Delaware River Basin NAWQA.—Thirty

private, household-supply and observation wells were

sampled as part of the NAWQA Program in the Delaware River Basin. Of these 30 wells, 24 are in 6 counties

in Pennsylvania (Berks, Carbon, Lehigh, Monroe,

Northampton, and Schuylkill). The other six wells are

in New Jersey (Sussex and Warren Counties). The wells

were sampled to assess the status of ground-water

quality in the clastic (mostly sandstone, siltstone, and

shale) bedrock of the Valley and Ridge Physiographic

Province. The bacteriological data (total coliform and

E. coli) from 1999 were not summarized because of the

unreliable performance of the bacteria media used.

EPA-approved media for drinking water was used in

2000, and of the 30 samples collected from domestic

and observation wells, total coliform was detected in

20 percent and E. coli was detected in 3 percent of the

samples (Durlin and Schaffstall, 2001).
4

USGS, Lower Susquehanna River Basin

NAWQA.—The Lower Susquehanna River Basin

(LSUS) NAWQA Program sampled 146 private household-supply wells from 1993 to 1995. Seventeen

counties in Pennsylvania and two counties in Maryland composed the study unit. Approximately

70 percent of the samples were positive for total

coliform, 65 percent for fecal streptococcus, and

25 percent for fecal coliform. Samples were not analyzed for E. coli during the first year of the project, but

E. coli was found in water from 30 percent of the

88 wells sampled in 1994 and 1995. Results of the study

showed the following: (1) bacteria were more likely in

ground water from wells in agricultural areas, (2) bacteria were more likely in ground water from wells in

the Valley and Ridge Physiographic Province, (3) E. coli

concentrations were higher in areas underlain by carbonate bedrock, and (4) weak relations are present

between bacteria concentrations and selected well

characteristics and selected water-quality constituents

(Bickford and others, 1996).

Results of the LSUS NAWQA Program raised

questions as to whether the contamination source is

site specific (relating to the well-construction methods)

or widespread (contamination of an entire aquifer) and

provided the impetus for this study. This study was

done to focus on well-construction characteristics in

Pennsylvania to determine if those differences make

wells any more or less susceptible to bacteriological

contamination in predominantly agricultural land-use

areas.

Description of Study Area

The study area spanned eight counties in southcentral and southeastern Pennsylvania: Chester, Cumberland, Dauphin, Montgomery, Lancaster, Lebanon,

Perry, and York (fig. 1). Sites were selected for sampling in two geologic settings: areas underlain by

limestone and dolomite bedrock (hereafter termed carbonate bedrock) and areas underlain by noncarbonate

bedrock. Areas underlain by carbonate bedrock were

targeted for sampling in Cumberland, Dauphin, Lebanon, and Perry Counties. Areas underlain by

noncarbonate bedrock were targeted for sampling in

Montgomery and York Counties. Areas underlain by

either carbonate or noncarbonate bedrock were targeted in Chester and Lancaster Counties. All water

samples were collected from wells adjacent to agricultural land-use areas. The areas sampled are described

in table 3.

Acknowledgments

The authors thank Stuart Reese of the PaDEP,

who provided assistance in developing the project and

providing input to USGS personnel as the project was

being implemented. The authors gratefully acknowledge the cooperation of the homeowners who allowed

access to their private wells for water sampling. The

authors also thank Michael Bradley and Douglas

Moyer of the USGS and Stuart Reese of the PaDEP for

their technical review of this manuscript. A special

thanks is extended to Ralph Defazio of the Chester

County Health Department, Rachel DeMarzio of the

Montgomery County Health Department, and Dave

Wetzel of Eichelberger’s Drilling Company for their

help in locating potential well sites for this study.

Table 2. Percentages of total coliform and E. coli bacteria detected in ground water from

wells sampled by the Pennsylvania Department of Agriculture

[John Pari, Pennsylvania Department of Agriculture, written commun., 2001]

Study

area

Total samples Samples from private households

Number

of samples

Number

of wells

Percentage

total coliform

Percentage

E. coli

Number

of samples

Percentage

total coliform

Percentage

E. coli

Blair County 120 118 84 48 56 86 36

Bedford County 73 73 70 37 11 73 27

Berks County 44 42 57 16 16 32 12

Lebanon County 26 26 50 12 10 40 0

Lehigh County 8 8 25 12 7 12 0

Northampton County 15 15 40 0 9 44 0

Triassic System 44 44 36 9 13 23 0
5

EXPLANATION

CARBONATE BEDROCK

NONCARBONATE BEDROCK

40o

42o

80o

76o

CHESTER

LANCASTER

DAUPHIN

LEBANON

YORK

MONTGOMERY

PERRY

CUMBERLAND

BEDROCK TYPE

0 50 MILES

0 50 KILOMETERS

COUNTIES IN THE STUDY AREA

Figure 1. Location of study area in south-central and southeastern Pennsylvania and bedrock types where ground water was

sampled and analyzed for total coliform and Escherichia coli bacteria.

Table 3. Selected characteristics of wells sampled and their locations, south-central and southeastern Pennsylvania

[Med, median; Max, maximum; Twp, township; Co., county; Dept., department; NAWQA, National Water-Quality Assessment Program]

Well type Rock type County Data source

Number

of wells

sampled

Well age,

in years

as of 2000

Depth of

wells

sampled,

in feet

Casing

length,

in feet

Depth to

first waterbearing zone,

in feet

Sanitary1 Carbonate Cumberland S. Middleton Twp. or well

driller’s records

13

19 Med: 4

Max: 16

Med: 180

Max: 260

Med: 80

Max: 84

Med: 110

Max: 210 Perry Well driller’s records 1

Chester Chester Co. Health Dept. 4

Dauphin Well driller’s records 1

Noncarbonate Chester Chester Co. Health Dept.

or NAWQA

8

20 Med: 2

Max: 13

Med: 175

Max: 250

Med: 40

Max: 75

Med: 90

Max: 140 Montgomery Montgomery Co. Health

Dept.

11

York NAWQA 1

Nonsanitary2 Carbonate Cumberland NAWQA, S. Middleton

Twp., or well driller’s

records

15

20 Med: 12

Max: 23

Med: 176

Max: 250

Med: 41

Max: 89

Med: 108

Dauphin NAWQA 1 Max: 220

Lancaster NAWQA 3

Lebanon NAWQA 1

Noncarbonate Chester Well driller’s records or

NAWQA

6

19 Med: 20

Max: 30

Med: 150

Max: 240

Med: 40

Max: 87

Med: 62

Max: 178 Lancaster NAWQA 3

Montgomery Well driller’s records 6

York NAWQA 4

Total wells 78 78

1 A “sanitary” well refers to a well installed with grout the entire annulus of the casing.

2 A “nonsanitary” well refers to a well installed with loose dirt or fill around the annulus of the casing.
6

WELL-CONSTRUCTION PRACTICES

IN PENNSYLVANIA

Water-well construction for private household

supply is not regulated in most parts of Pennsylvania.

Typically, private on-lot wells are constructed as open

holes completed in bedrock with minimal surface casing, little or no annular grout seal, and a loose-fitting

well cap. The PaDEP has established guidelines for

water-well construction in a Fact Sheet, “Guidelines for

installing private water wells in bedrock” (Pennsylvania Department of Environmental Protection, 2000).

According to these guidelines, “State law does require

drillers to have a yield rig permit and a water-well

drillers license” but “When a new well is drilled, no

state requirements for construction materials, yield, or

quality apply.” The guidelines offer recommendations

for the construction of a well designed to protect the

water source by including such features as a “verminproof” cap and casing grout (fig. 2). They also offer criteria to consider when choosing a well site,

information about common “undesirable” water-quality constituents homeowners should consider having

the ground water from their private wells tested for

periodically, and preventative measures that homeowners can take to ensure that they do not contaminate

their own water supply. Because the relatively new

(2000) PaDEP guidelines are not rules or regulations, it

is not known to what extent they presently are being

followed or have been followed in the past.

A few counties in Pennsylvania have established

countywide well-construction regulations and some

townships have instituted well-construction ordinances within their municipalities. For the purposes of

this report, well-construction regulations in two counties with Health Departments in southeastern

Pennsylvania, Chester and Montgomery Counties, will

be discussed. Both counties were targeted for sampling

because they currently have well-construction regulations in place and, therefore, a database of wells with

known well-construction practices. Well-construction

regulations as part of a township ordinance within

South Middleton Township, Cumberland County, also

will be discussed. This was another area selected for

sampling because of regulated well-construction practices currently in effect. Regardless of whether or not a

well is constructed in a county or municipality in Pennsylvania with well-construction regulations, waterwell drillers are required to submit a copy of the welldrillers’ record to the Pennsylvania Department of

Conservation and Natural Resources (DCNR) for each

well they construct. In all cases, it is the responsibility

of homeowners to ensure the potability of their private

water supply with routine testing.

Chester County

Chester County Health Department’s (CCHD)

well-construction regulations have been in effect since

March 21, 1983 (Chester County Health Department,

1993). A main objective in enacting these regulations is

to establish minimum, countywide standards for

water-well construction, monitoring wells, individual,

noncommunity and community water supplies, and

geothermal boreholes. All well contractors and pumpinstallation contractors must obtain a license to conduct business in Chester County, and in order to obtain

a license, they need to pass an examination given by

the CCHD. License renewal is required annually. In

addition, contractors must obtain a permit before each

new well is drilled, before a well is repaired or modified, and prior to installation of any pumping

equipment.

The CCHD regulations specify requirements that

must be met in order to maintain minimum standards

for quality of water-supply wells (Chester County

Health Department, 1993). The CCHD requires that the

source of supply shall be from a water-bearing zone at

least 25 feet below land surface. The well must be constructed at a minimum distance from potential sources

of pollution that include, but are not limited to, septic

tanks, sewer lines, bio-solids disposal areas, barnyards,

and manure pits. The watertight casing must extend to

a depth of at least 20 feet, with an additional 5 feet of

casing extending into bedrock or similarly competent

strata. The annular space must be filled completely

with an approved grouting material such as neat

cement grout, concrete grout, sand cement grout, or

bentonite grout. The well casing must extend a minimum of 12 inches above finished land surface. Upon

completion of installation, the well must be pumped

until the discharged water runs clear. To disinfect the

well, pump, piping, and fixtures, they must be filled

with a solution of water containing at least 100 parts

per million of free chlorine. A portion of the solution

shall be recirculated to the well to insure proper agitation. The well may not be used for a period of 24 hours.

All required information must be submitted on the

appropriate form to the CCHD within 30 days of completion of well drilling.

The CCHD recently revised its well-construction

regulations, and it is now mandatory (as of March 9,

2001) that all wells drilled in Chester County be completed with a sanitary sealed well cap (Chester County

Health Department, 1993). The revised regulations also

state that a sanitary sealed well cap must replace the

present well cap when the well or pump warrant

repair. A typical loose-fitting well cap and a common

type of sanitary sealed well cap are shown in figure 3.
7

PUMP

DRIVE SHOE

CASING

GROUT SEAL

PITLESS ADAPTER

VERMIN-PROOF,

VENTED WELL CAP

BEDROCK BEDROCK

BACK FLOW PREVENTION

WATER TABLE

NOT TO SCALE

Figure 2. Cross-section of a ground-water well. (Used with permission from “Guidelines

for Installing Private Water Wells in Bedrock,” Pennsylvania Department of Environmental

Protection, 2000. For more information, go to: http://www.dep.state.pa.us and enter

“Private Wells” in the Direct Link box.)

LOOSE-FITTING CAP SANITARY SEALED CAP

Figure 3. Loose-fitting and sanitary sealed well caps for 6-inch wells.
8

Montgomery County

Montgomery County Health Department’s

(MCHD) well-construction regulations have been in

effect since February 1, 1997 (Montgomery County

Health Department, 1997). By law, in Montgomery

County, permits to construct a well must be obtained

prior to installation or modification of any individual

water-supply well. Water-well drillers must have a

DCNR license to construct wells for individual water

supply.

Chapter 17, Individual Water Supply System

Regulations, of the Montgomery County Public Health

Code (Montgomery County Health Department, 1997)

aims to establish the standards for location, construction, modification, and abandonment of individual

water-supply wells to protect public health and welfare. Section 17-7 of the regulations refers to the

minimum isolation distances from possible pollution

sources. According to the construction specifications

set forth by the MCHD, the casing must extend a minimum of 30 feet below land surface or 5 feet into

bedrock or competent strata (whichever is deeper).

Also, the casing must be grouted in place. The annular

space between the well casing and the earth formation

must be completely filled with an approved grout

material such as neat cement grout, sand cement grout,

or bentonite or sealing clay. This filling is done in order

to prevent the entrance of pollution from surface runoff

or polluted aquifers (Montgomery County Health

Department, 1997). The casing must be steel, unless

written permission from the MCHD has been granted

for the use of alternate casing types. The casing shall

extend a minimum of 12 inches above the finished land

surface, or a proper height that would be necessary to

prevent surface contamination, whichever is greater.

After completion of well construction and pump installation, the well shall be pumped until the discharged

water is clear. The well, pump, piping, and other fixtures then must be filled with a concentration of at least

50 parts per million of free chlorine in order to disinfect. The solution shall be properly agitated by

recirculating a portion of it directly to the well; the well

should not be used for 24 hours. The grout information

and other required data must be submitted to MCHD

by the DCNR-licensed water-well driller within

30 days of completion of the well drilling process.

South Middleton Township

The South Middleton Township Well Ordinance

No. 98-22 has been in effect since October 20, 1998

(Board of Supervisors of South Middleton Township,

1998). The ordinance intends to protect the quality of

domestic water supply and maintain the minimum isolation distance between water supplies and sources of

possible contamination such as agricultural fields

(50 feet) and sewage disposal systems (100 feet from a

sewage drain field or absorption system and 50 feet

from a septic tank, distribution tank, and (or) pump

box). A sewage permit must be obtained before a

water-supply well permit can be issued. Water-supply

well permits must be obtained from the Codes Enforcement Officer prior to the installation of a well or major

repair to a present well. The water-well driller must be

licensed by the Commonwealth of Pennsylvania and

provide a copy of required information to South Middleton Township upon completion of the well

construction.

The following standards apply to well construction in South Middleton Township (Board of

Supervisors of South Middleton Township, 1998). The

casing must be a minimum of 20 feet below the finished grade and extend 10 feet into bedrock or other

competent strata. The annular space shall be filled

completely with cement grout or an equivalent sealing

material from the bottom of the casing to within 5 feet

of the land surface. A tremie pipe and a grout pump

are used for external grouting, and the casing shall be

sealed against entrance from potentially contaminated

water-bearing formations. The top of the casing must

extend a minimum of 24 inches above land surface,

and surface drainage must be diverted away from the

well. A well cover must overlap the outside of the well

casing at least 2 inches. The source of the water supply

shall be from a water-bearing formation of at least

100 feet below land surface, unless a formation yields a

discharge of 6 gallons per minute at a lesser depth.

STUDY METHODS

Water samples were collected from private,

household-supply wells for bacteriological analysis

from September 2000 to March 2001. Ground water

from each of 78 wells was sampled one time for this

study. Wells chosen generally were less than 250 feet

deep and generally less than 25 years old. The project

was designed to analyze for presence of bacteria in

water from wells of “sanitary” construction and water

from wells of “nonsanitary” construction. A “sanitary”

well was defined as a well that had been installed with

a sanitary sealed well cap and with grout along the

entire annulus of the casing. A “nonsanitary” well was

defined as a well constructed with loose dirt or fill

around the annulus of the casing and a loose-fitting

well cap. It was obvious a few months into the study

that wells within the study area installed with a sanitary sealed cap were rare. Consequently, the definition

of a “sanitary” well was modified to mean wells constructed with grout installed along the entire annulus

of the casing.
9

Site Selection

Sites were selected for this study on the basis of a

field inventory of candidate wells conducted to verify

well locations with respect to bedrock type and to document the land-use and well characteristics that could

be the source of bacteria or promote its movement into

the well. Approximately one-third of the well sites

selected previously were sampled as part of the USGS

LSUS NAWQA Program. Only wells on sites adjacent

to agricultural land-use areas were targeted for bacteriological sampling in this study. Once a good candidate

well was found, permission to sample the well was

obtained. An attempt was made to pair wells with sanitary and nonsanitary construction with similar rock

type and site-specific and regional land-use

characteristics.

An equal number of wells with sanitary and

nonsanitary construction were selected for sampling

for total coliform and E. coli in each of two geologic

settings: areas underlain by carbonate rocks and areas

underlain by noncarbonate rocks. The well-selection

matrix shown in table 3 includes information on the

location of the 78 wells selected for inclusion in this

study, as well as the data sources used to locate the

wells and selected characteristics of those wells.

Wells were selected for this study using a variety

of resources. Wells with sanitary construction in areas

underlain by noncarbonate bedrock were found by

searching well records in the CCHD and MCHD and

by obtaining permission to sample a well in York

County previously sampled as part of the LSUS

NAWQA Program. In Montgomery County, well regulations were enacted in 1997; thus, wells of recent

construction could be found with sanitary and conventional (nonsanitary) construction. Sanitary wells in

Montgomery County, located by searching MCHD

records, were paired with nonsanitary wells (located

by well driller’s records) constructed in areas underlain by noncarbonate bedrock in areas of similar

agricultural land use. In Chester County, regulations

have been in place for nearly 20 years; thus, recently

constructed wells all have sanitary construction. Sanitary wells in Chester County in areas underlain by

noncarbonate bedrock were paired with wells of nonsanitary construction in areas of similar agricultural

land use and rock type in neighboring Lancaster and

York Counties. The nonsanitary wells selected for sampling in Lancaster and York Counties in areas

underlain by noncarbonate bedrock previously were

sampled as part of the LSUS NAWQA Program. It was

extremely difficult to locate wells of sanitary construction in areas underlain by carbonate bedrock. For this

reason, a single township was heavily targeted, South

Middleton Township, because a well-construction

ordinance currently is in place within the township

(enacted 1998). Other wells with sanitary construction

in areas underlain by carbonate bedrock were found in

Chester County by searching CCHD files and in Perry

and Dauphin Counties by searching well driller’s

records. Nonsanitary wells drilled in areas underlain

by carbonate bedrock were found in (1) Cumberland

County by searching well driller’s records and by

obtaining permission to sample wells previously sampled as part of the LSUS NAWQA Program, and (2) in

Dauphin, Lancaster, and Lebanon Counties by obtaining permission to sample wells previously sampled as

part of the LSUS NAWQA Program.

Sample Collection and Analysis

Water samples were collected for analysis of two

indicator bacteria (total coliform and E. coli). Total

coliform bacteria was chosen because it is used as an

EPA drinking-water standard for public supplies (there

are no national standards for household-supply wells),

even though its presence may be of nonfecal origin

such as that found naturally in soils, plants, and other

media. E. coli bacteria was chosen because it is a species of the coliform group exclusively of fecal origin.

Therefore, E. coli bacteria serves as a more direct indicator of fecal contamination and the possible presence

of enteric pathogens (U.S. Environmental Protection

Agency, 2000). Indicator bacteria were chosen because

they are not usually pathogenic; however, their presence in drinking water indicates the possible presence

of pathogens.

The USGS used the standard plate count membrane-filter method for enumeration of total coliform

on m-Endo media and E. coli bacteria on NA-MUG

media. In this procedure, the sample aliquot was

passed through a membrane filter with a pore size of

0.45 micrometer. After the aliquot was passed through

the membrane filter, the filter was aseptically placed on

a sterile 50 millimeter petri dish containing m-Endo

medium. The petri dish with the membrane filter then

was placed in an incubator at 35°C for 22 to 24 hours. If

total coliform bacteria were present in the sample, individual cells on the membrane filter multiply after the

proper incubation time. Each colony counted represents the single bacteria cell from which it originated.

The membrane filters having colonies that exhibit a

golden-green metallic sheen are positive for total

coliform bacteria (Britton and Greeson, 1989). If total

coliform bacteria were present, the membrane filter

was aseptically transferred to a 50 millimeter petri dish

containing NA-MUG medium and incubated for a

period of 4 hours at 35°C. Colonies that produce a

bright blue fluorescent perimeter around a darker colony under ultraviolet light are positive for E. coli. The

result is reported as number of colonies per 100 mL

(milliliter) of sample (U.S. Environmental Protection
10

Agency, 1991). Both m-Endo and NA- MUG mediums

are approved by the EPA for analysis of drinking and

source waters (U.S. Environmental Protection Agency,

1991). Total coliform bacteria media and sterile buffered water were obtained from the USGS WaterQuality Supply Unit in Ocala, Fla. E. coli bacteria

media was a Difco Brand obtained from Fisher Scientific. Media from both entities was quality assured

prior to shipment.

The Colilert method (Clesceri and others, 1998),

performed by the PaDEP on sequential replicate samples collected for quality control, uses multiple dilution

tubes in order to determine the most probable number

of total coliform and E. coli in water samples. A serial

dilution is performed on an aliquot of sample, and the

appropriate volume is placed in tubes containing nutrient broth and indicator chemicals. The result, number

of total coliform or E. coli colonies per 100 mL, is a statistical estimate of the mean density of bacteria in a

water sample. The MPN is derived from a table that is

based on the number of sample tubes testing positive

(Clesceri and others, 1998).

Samples were collected one time only at each site

from an outside faucet that bypassed any water-treatment systems such as a chlorination system, water

softener, ultra-violet light, charcoal filter, and others.

The types of samples collected included routine sample aliquots at each site and additional split and

sequential replicate sample aliquots at 21 of the 78 sites

for quality-control purposes. The goal was to obtain an

ideal colony count (20-80 colonies per 100 mL) for total

coliform and E. coli bacteria where possible. Combinations of 200 mL, 100 mL, or 10 mL aliquots were

filtered for each ground-water sample in an attempt to

obtain bacteria detections. The decision to filter aliquots was made on the basis of previous experience

testing for bacteria in ground water and that bacteria

detections generally are rare in small sample volumes

of ground water, especially in the ideal colony count

range. All samples were collected in 1-liter glass bottles

that had been autoclaved prior to use. Water samples

were collected after purging a minimum of one well

volume of water and obtaining stable measurements

for pH, specific conductance, dissolved oxygen, and

temperature. Water samples were immediately processed at the site using membrane filtration techniques

(Myers and Sylvester, 1997). Sample processing and

analyses for bacteria were done by USGS personnel in

the Pennsylvania District Office with the exception of 9

sequential replicates that were done at approximately

10 percent of the sites and sent to PaDEP personnel for

processing within 24 hours at the PaDEP Laboratory in

Harrisburg, Pa.

Quality Assurance

For quality control, split replicate and (or)

sequential replicate aliquots (combinations of 200 mL,

100 mL, or 10 mL aliquots) were collected at 21 of the

78 sites and resulted in an additional 28 samples

(table 4). Split replicates are samples collected in the

same bottle and divided into subsamples for identical

analyses. They are collected to assess reproducibility in

sample-processing results. Sequential replicates are

collected consecutively (instead of simultaneously) in

two or more bottles and are used to assess variability

among samples resulting from sample collection

(Wilde and others, 1999).

Replicate samples at 15 of the 21 sites where

quality-control samples were collected were split replicate sample aliquots done by the USGS. Sequential

replicate sample aliquots were collected and analyzed

by the USGS at an additional four sites. Bacteria concentrations in the routine samples and the replicate

samples generally were similar (table 4). There were a

few exceptions but differences typically were at the

detection limit. For example, data for the routine sample would indicate that there was one total coliform

and (or) E. coli colony per 100 mL, whereas the replicate sample would not have any bacteria detections or

opposite. Because this occurs is not surprising. As was

stated previously, bacteria detections—especially bacteria colonies in the ideal range—generally are rare in

small sample volumes of ground water. This resulted

once for total coliform and 5 times for E. coli when

comparing USGS environmental data and USGS split

and sequential replicate data at those 19 sites. Because

these differences were at or very near the detection

limit indicates the reproducibility of results by the

USGS is good. It also indicates the USGS sample-collection methodology is consistent.

The PaDEP analyzed sequential replicate samples from 9 of the 21 sites where quality-control

samples were collected. These replicates were processed to assess reproducibility of results between

laboratories. Total coliform bacteria were found at one

site and E. coli bacteria at two sites by the USGS but not

by the PaDEP at those same sites. Similarly, the PaDEP

found total coliform bacteria at a site that the USGS did

not. These differences could most likely be explained

by the difference in methodologies between the two

agencies as discussed above. The PaDEP data indicate

the most probable number using the Colilert method;

the USGS data indicates an actual colony count using

the membrane-filter method. These quality-control

analyses were done to confirm the presence/absence of

bacteria with another laboratory.
11

Blank samples of sterile water also were collected for quality control and were filtered prior to the

environmental sample at each site. Blanks were 100 mL

of sterile buffered water (sterile phosphate buffer solution with peptone) that were processed with the

sterilized equipment. The blank samples were analyzed to determine the effectiveness of the sterilization

procedures. All the blank samples of sterile water that

were analyzed were free of bacteria detections with the

exception of one sample. The blank at one site had one

total coliform colony that formed on the 100 mL plate.

The associated USGS routine sample data (10 colonies

per 100 mL) was not excluded as a result of this

because a PaDEP sequential replicate sample (collected

in another bottle) also was analyzed for this site that

produced a similar result (16 colonies per 100 mL).

Statistical Analysis

Nonparametric statistical analyses were conducted to determine relations between bacteria

concentrations and discrete variables (also known as

categorical variables) such as bedrock type, whether or

not the well was grouted, and combinations of both

variables. Statistical tests were chosen on the basis of

the amount of censored data for each bacteria type.

Censored data are data that include concentrations that

are essentially “nondetects”—detected at levels below

(less than) a set detection limit. The detection limit

used for both total coliform and E. coli bacteria was

1 colony per 100 mL. Therefore, anything less than

1 (zero) colony per 100 mL constitutes a “nondetect” of

bacteria. An alpha value of 0.05 was used for all statistical analyses. If statistical analyses indicate an alpha

value of 0.05 or less, there is a 95-percent chance an

association is present mathematically among the variables being compared.

Kruskal-Wallis tests were used when less than

50 percent of the data were censored. The Kruskal-Wallis test was computed by ranking a continuous variable

(in this case the bacteria concentrations) and then testing for differences in the medians of the ranks among

Table 4. Comparison of U.S. Geological Survey environmental sample data to U.S. Geological Survey

replicate sample data and Pennsylvania Department of Environmental Protection replicate sample data

[USGS, U.S. Geological Survey; PaDEP, Pennsylvania Department of Environmental Protection; mL, milliliters;

<, less than; TNTC, too numerous to count; --, bacteria was not analyzed at this sample volume; split replicate

results are shown in light gray and sequential replicate results are shown in dark gray]

Site identifier

USGS environmental

sample USGS replicates PaDEP replicates

Total coliform

100 mL

E. coli

100 mL

Total coliform

100 mL

E. coli

100 mL

Total coliform

100 mL

E. coli

100 mL

394606076002001 <1 -- <1 -- <1 <1

400945077104201 1 1 1 <1 1 <1

400854077112701 23 1 21 <1 53 <1

400805077074101 3 <1 2 <1 <1 <1

400854077161801 3 <1 4 1 16 1

400711076113801 5 <1 4 <1 <1 <1

400827077083101 <1 -- <1 -- 1 <1

401735075293001 10 <1 -- -- 16 <1

400229076020301 <1 -- -- -- <1 <1

401125077195801 11 <1 3 <1 -- --

400515077205501 1 <1 <1 -- -- --

400746077262201 2 1 2 <1 -- --

401750076274601 TNTC TNTC TNTC TNTC -- --

401445076440801 39 4 44 3 -- --

400824077085501 1 <1 1 <1 -- --

395204076262101 <1 -- <1 -- -- --

400834077134401 <1 -- <1 -- -- --

401744075312801 <1 -- <1 -- -- --

401316077023001 3 1 3 1 -- --

401046077094601 6 <1 4 1 -- --

401254076114701 1 <1 2 <1 -- --
12

categorical variables. This test was used on the total

coliform data set because 38 percent of the data were

censored.

Contingency tables were used when greater than

50 percent of the data were censored. This method of

statistical analysis measures the association between

two nominal (no ordering such as high, medium, low)

categorical variables (Helsel and Hirsch, 1992). The

bacteria concentration data were converted to a

present/absent variable and analyzed to determine if

this variable was independent of another variable or

variables (bedrock type, grout/no grout). This test was

used on the E. coli data set because 90 percent of the

data were censored. Two conditions are necessary for

the test to be valid: All the cells must have an

expected number of observations greater than one, and

at least 80 percent of the cells must have an expected

number of observations greater than five (Helsel and

Hirsch, 1992, p. 381). An example of a 2 × 2 contingency table matrix set up to show whether or not the

presence of E. coli bacteria is related to bedrock type is

given in table 5.

Spearman’s rank correlation was used to analyze

two or more continuous variables to determine

whether or not there was a linear association between

the two variables. This method may be used when both

variables are censored (Helsel and Hirsch, 1992, p. 374)

and is done by first ranking each variable separately

and then calculating the Spearman’s rank correlation

coefficient for the ranks (Ott, 1993). Ranking of the data

ensures the full extent of the monotonic relation (y

increases, or decreases, with x) is analyzed. As stated

above, an alpha of 0.05 was used in the analyses. If the

probability from Spearman's correlation test is less

than alpha, there is a 95-percent chance an association

is present mathematically between the variables.

Spearman’s rho was used to determine the strength of

this association among total coliform or E. coli bacteria

and other continuous variables (values are on a continuous scale) such as well depth, casing length, well age,

and depth to the first water-bearing zone.

RELATION BETWEEN SELECTED

WELL-CONSTRUCTION CHARACTERISTICS

AND OCCURRENCE OF BACTERIA IN

GROUND WATER

Waters from about 48 of the 78 wells sampled

(62 percent) for this study contained total coliform bacteria. E. coli bacteria were detected in waters from 8 of

the same 78 wells (10 percent). Seventeen percent of the

samples that were positive for total coliform also were

positive for E. coli. In contrast, neither total coliform

nor E. coli bacteria were found in waters from 30 of 78

wells sampled (38 percent). All samples were collected

from wells adjacent to agricultural land-use areas. The

bacteriological data from this study is presented in

appendix A.

Percentages of total coliform and E. coli bacteria

found in sanitary and nonsanitary wells and in wells

completed in carbonate and noncarbonate rocks are

shown in figure 4. Total coliform bacteria were just as

likely to be found in sanitary wells (nearly 60 percent)

as in nonsanitary wells (nearly 65 percent). The areas

underlain by carbonate bedrock had the highest percentages of total coliform detected (about 75 percent)

but nearly half of the samples collected in the areas

underlain by noncarbonate bedrock were found to

have total coliform present as well. E. coli bacteria were

found in 15 percent of the nonsanitary wells compared

to 5 percent of the sanitary wells and only were found

in areas underlain by carbonate bedrock.

The locations of the wells sampled and the distribution of the presence of total coliform and E. coli

bacteria in the waters of those wells (both sanitary and

nonsanitary) are shown in figures 5 and 6, respectively.

Total coliform detections were uniformly distributed

throughout the study area. Conversely, E. coli detections were concentrated in the areas underlain by

carbonate bedrock predominantly in the nonsanitary

wells (fig. 6). These distribution patterns are consistent

with the LSUS NAWQA Program findings (Bickford

and others, 1996).

Statistical tests for this study were conducted to

determine if the presence of bacteria was related to categorical variables such as bedrock type, whether or not

a well was grouted, and combinations of the two variables at a 95-percent confidence interval. These tests

were done in an effort to assess aquifer vulnerability to

bacterial contamination by determining the bacteriological quality of water from wells constructed in

varying bedrock types (carbonate and noncarbonate)

and the effect, if any, that different well-construction

characteristics have on the quality of the drinking

water supply.

Table 5. Sample contingency table matrix for comparing the

presence/absence of E. coli and bedrock type

Number of sites with E. coli

present in areas underlain by

carbonate bedrock

Number of sites with E. coli

present in areas underlain by

noncarbonate bedrock

Number of sites with E. coli

absent in areas underlain by

carbonate bedrock

Number of sites with E. coli

absent in areas underlain by

noncarbonate bedrock
13

SANITARY NONSANITARY

WELL TYPE

0

70

10

20

30

40

50

60

PERCENTAGE OF WATER SAMPLES WITH BACTERIA PRESENT

CARBONATE NONCARBONATE

BEDROCK TYPE

TOTAL COLIFORM

ESCHERICHIA COLI ESCHERICHIA COLI

80

TOTAL COLIFORM

Figure 4. Bacteria

presence by wellconstruction characteristic and bedrock type

from wells sampled,

south-central and

southeastern

Pennsylvania.

CHESTER

LANCASTER

DAUPHIN

LEBANON

YORK

MONTGOMERY

PERRY

CUMBERLAND

EXPLANATION

SANITARY WELL, NO TOTAL COLIFORM DETECTED

NONCARBONATE BEDROCK

CARBONATE BEDROCK

SANITARY WELL, TOTAL COLIFORM DETECTED

NONSANITARY WELL, NO TOTAL COLIFORM DETECTED

NONSANITARY WELL, TOTAL COLIFORM DETECTED

0 10 20 30 MILES

0 10 20 30 KILOMETERS

39°45'

75°00'

78°00'

40°45'

Figure 5. Sampling locations and

detections of total coliform bacteria

in wells sampled, south-central and

southeastern Pennsylvania.

CHESTER

LANCASTER

DAUPHIN

LEBANON

YORK

MONTGOMERY

PERRY

CUMBERLAND

EXPLANATION

0 10 20 30 MILES

0 10 20 30 KILOMETERS

39°45'

75°00'

78°00'

40°45'

SANITARY WELL, NO DETECTED E. COLI

SANITARY WELL, DETECTED E. COLI

NONSANITARY WELL, NO DETECTED E. COLI

NONSANITARY WELL, DETECTED E. COLI

NONCARBONATE BEDROCK

CARBONATE BEDROCK

Figure 6. Sampling locations and

detections of E. coli bacteria in wells

sampled, south-central and

southeastern Pennsylvania.
14

Sanitary and Nonsanitary

Construction

Bacteria concentrations

were compared among wells

constructed using different

well-construction characteristics. Concentrations in wells

with grout (sanitary) installed

along the entire annulus of the

casing and without grout

(nonsanitary) were compared.

The range in concentrations

and median concentrations of

total coliform in both types of

wells were similar (fig. 7). The

results of this comparison for

total coliform do not indicate a

statistically significant difference. Boxplots are not shown

for E. coli because of the small

number of detections. E. coli

was more likely in water from

nonsanitary wells than in

water from sanitary wells.

Seventy-five percent of the

E. coli bacteria detected was

observed in water from wells

of nonsanitary construction.

Bedrock Type

Comparisons also were

made between the presence of

bacteria and wells constructed in areas underlain by

carbonate and noncarbonate

bedrock. The range in concentrations and median

concentrations for total

coliform bacteria from wells

are similar between bedrock

types (fig. 8). Therefore, this

relation is not statistically significant for total coliform. As

stated earlier, boxplots are not

shown for E. coli because of

the small number of detections, but all of the E. coli

detections (100 percent) were

observed in ground water

from wells underlain by carbonate bedrock. This

observation indicates high

aquifer vulnerability to E. coli

bacteria contamination in carbonate bedrock.

WELL CONSTRUCTION SANITARY NONSANITARY

90

0

10

20

30

40

50

60

70

80

CONCENTRATION OF TOTAL COLIFORM BACTERIA, IN COLONIES

PER 100 MILLILITERS

25th percentile

Median

75th percentile

90th percentile

10th percentile

BEDROCK TYPE CARBONATE NONCARBONATE

0

90

10

20

30

40

50

60

70

80

CONCENTRATION OF TOTAL COLIFORM BACTERIA, IN COLONIES

PER 100 MILLILITERS

25th percentile

Median

75th percentile

90th percentile

10th percentile

Figure 7. Concentrations of total coliform bacteria in sanitary and nonsanitary

wells, south-central and southeastern Pennsylvania.

Figure 8. Concentrations of total coliform bacteria in wells constructed in

areas underlain by carbonate and noncarbonate bedrock, south-central and

southeastern Pennsylvania.
15

Bacteria concentrations also were compared to

the combined effects of well-construction practices and

bedrock type—sanitary wells in carbonate bedrock,

sanitary wells in noncarbonate bedrock, nonsanitary

wells in carbonate bedrock, and nonsanitary wells in

noncarbonate bedrock. The results of these comparisons for total coliform do not indicate statistically

significant differences among the four groups (fig. 9).

Again, because of the small number of E. coli bacteria

detections, boxplots are not shown. E. coli bacteria,

however, were detected more frequently in water from

nonsanitary wells in areas underlain by carbonate

bedrock.

Seasonal Effects

Comparisons were made between bacteria data

from waters of 26 wells sampled for this study that also

were sampled as part of the LSUS NAWQA Program to

determine if bacteria presence had any seasonal variation. Bacteria concentrations in 17 of the 26 wells were

found to be lower for this study than when sampled

for the NAWQA Program (1993–95). Further breakdown of the data from those 17 wells indicates that

both the total coliform and E. coli concentrations were

lower for this study than for the LSUS NAWQA Program. Data from 11 of the 17 wells indicates lower total

coliform concentrations for this study (7 of them are

now free of total coliform) than for the LSUS NAWQA

Program, but E. coli concentrations remained relatively

unchanged. The fact that such a high percentage of the

sites analyzed had lower concentrations for this study

than for the LSUS NAWQA Program can most likely be

explained by the seasons in which sampling took place.

The LSUS NAWQA Program samples were collected

from June to August in the summers of 1993–95 during

the growing season when manure is applied to fields.

Samples were collected for this study in the fall of 2000

and the winter of 2001 after the growing season was

over and manure application to fields was not occuring. Higher total coliform concentrations were detected

in water from 7 of the 26 wells for this study than when

they were sampled as part of the LSUS NAWQA Program. On closer inspection, however, five of those

samples had total coliform concentrations that were

close to the detection limit of less than 1 colony per

100 mL. E. coli concentrations for all seven of these

wells remained unchanged. Two sites sampled for both

studies had samples that were now grossly contaminated with total coliform; one of the two also was

contaminated with E. coli. The site that was grossly

contaminated with total coliform and E. coli for this

study is a nonsanitary well in an area underlain by carbonate bedrock that did not have detections of either

bacteria type during the LSUS NAWQA Program. Possible explanations for the high number of bacteria now

present in this well could include physical defects now

present in the well such as leakage around the pitless

adapter and a cracked or corroded casing (fig. 2).

Because the top of the casing is not sealed and the

annulus around the outside of the casing for this well is

not grouted, the bacteria could be a direct result of surface contamination. A failing septic system is another

potential contamination source.

Comparisons also were made between bacteria

data collected for a national NAWQA Program (Francy

and others, 2000), the LSUS NAWQA Program (Bickford and others, 1996), and this study. Differences in

percentages of bacteria are shown in figure 10. The

SANITARY

NONCARBONATE

NONSANITARY

CARBONATE

90

0

10

20

30

40

50

60

70

80

SANITARY

CARBONATE

NONSANITARY

NONCARBONATE

25th PERCENTILE

MEDIAN

75th PERCENTILE

90th PERCENTILE

10th PERCENTILE

CONCENTRATION OF TOTAL COLIFORM BACTERIA, IN COLONIES

PER 100 MILLILITERS

WELL CONSTRUCTION AND BEDROCK TYPE

Figure 9. Concentrations of total

coliform bacteria in sanitary

carbonate, sanitary noncarbonate,

nonsanitary carbonate, and

nonsanitary noncarbonate wells,

south-central and southeastern

Pennsylvania.
16

LSUS NAWQA Program took place predominantly in

Pennsylvania as did this study focusing on well construction. Both Pennsylvania studies were analyzing

exclusively water from private, household-supply

wells. The national NAWQA Program focused on a

combination of present private, household-supply,

community, and noncommunity wells. Percentages of

total coliform bacteria detected in the LSUS NAWQA

and this study (69 and 62 percent, respectively) were

well above the percentages found in the national study

(LERI, KANA, SANT, and UCOL NAWQA studies).

E. coli bacteria detections were observed mainly in

Pennsylvania and were not present in the national

NAWQA study. The KANA Basin was the only basin

where E. coli was observed in the national study. The

reason bacteria detections were so much higher in

Pennsylvania compared to the other areas sampled

could not be quantified. Differences in soils, geologic

features, and well-construction characteristics could be

the reason (or part of the reasons) for these detections.

Other Well-Construction Characteristics

Statistical tests also were conducted to determine

if there was a relation between the concentrations of

bacteria and selected well-construction characteristics

such as well depth, casing length, well age, and depth

to the first water-bearing zone. Spearman’s correlations

were used to analyze the data, and relations exist if

probabilities were less than 0.05. Strong relations are

indicated by high Spearman’s rho values and weak

relations are indicated by low Spearman’s rho values.

Few significant correlations were observed with

the Spearman’s correlation test. The correlations that

were found were for total coliform bacteria. Looking at

the entire data set, there was a positive relation

between concentrations of total coliform bacteria in

water from the nonsanitary wells and the depth to the

first water-bearing zone. This positive relation means

that as the depth to the water-bearing zone increased,

the total coliform concentrations increased. Further

analyses were done by independently analyzing each

of the four groups on the basis of sanitary construction

and bedrock type. This breakdown of the data showed

concentrations of total coliform had a negative correlation to water-bearing zone in the sanitary wells in areas

underlain by noncarbonate bedrock. In other words,

total coliform concentrations decreased with increasing

depth to water-bearing zone. In addition, concentrations of total coliform had a positive correlation to

water-bearing zone in the sanitary wells in areas

underlain by carbonate bedrock. So for those wells,

total coliform concentrations increased with increasing

depth to water-bearing zone. A negative correlation is

what would be expected with bacteria concentrations

decreasing in deeper water-bearing zones because of

the filtering of the water and the bacteria die-off rate

with longer traveltimes. However, because flow in carbonate bedrock is controlled by conduit flow, water

produced from deeper water-bearing zones has not

necessarily undergone more filtration, nor does it have

a longer residence time. Therefore, bacterial concentrations would not necessarily decrease with depth to

water-bearing zone, and in this data set, bacterial concentrations actually increase with depth to waterbearing zone.

The Spearman’s correlation test also showed

concentrations of total coliform bacteria had a negative

correlation to casing length in water from nonsanitary

wells in areas underlain by noncarbonate bedrock.

Again, this negative correlation is what would be

expected with bacteria concentrations decreasing in

deeper water-bearing zones because of the filtering of

the water and the bacteria die-off rate with longer

traveltimes.

Because the number of wells with sanitary seals

found during this study was minimal, it was not possible to compare the occurrence of bacteria among wells

with and without this well-construction feature. However, detailed information on the condition of

individual wells was recorded during field visits and

this information was used as a surrogate of the effects

of unsealed well caps on bacteria detections. Upon

removing the well cap to make water-level measurements, observations on the presence of insects were

recorded by sampling crews. This information was

somewhat subjective; however, the presence of insects

0

10

20

30

40

50

60

70

80

BACTERIA STUDY

TOTAL COLIFORM

E. COLI

LERI

KANA

SANT

UCOL

LSUS

THIS STUDY

PERCENTAGE OF GROUND-WATER

SAMPLES WITH BACTERIA PRESENT

Figure 10. Percentage of detections of total coliform and

E. coli in bacteria studies done in five National Water-Quality

Assessment Program basins (Francy and others, 2000;

Bickford and others, 1996) compared to this study.

[LERI, Lake Erie–Lake St. Clair Basin; KANA, Kanawha–New

River Basin; SANT, Santee Basin and coastal drainage;

UCOL, Upper Colorado Basin; LSUS, Lower Susquehanna

River Basin]
17

was obvious. Of the 78 wells sampled, 38 wells had

evidence of insects inside the well cap, on the wiring,

plumbing, or inside the casing. Bacteria were present

in wells with evidence of insects inside the well

slightly more than in wells without evidence of insects.

Statistical tests (contingency tables) comparing the

presence of bacteria to presence of insects showed no

statistically significant differences. When the data were

broken down into smaller subsets on the basis of bedrock type, grout, or combinations of both, no

additional significant relations were observed.

Although the presence of bacteria was not significantly

related to the presence of insects, this result does not

indicate that a sanitary seal is not important. Only six

of the wells actually were sealed. The reason for lack of

correlation among wells with and without insects may

be because the presence of insects is not a good surrogate for a sanitary seal (insects may have been present

but not observed). Also, a combination of grout, bedrock type, and lack of a sealed well cap may all be

characteristics affecting bacterial contamination. The

evidence that insects (earwigs) can be the source of

bacteria has been demonstrated (Wisconsin Department of Natural Resources, 1993); therefore, sanitary

seals continue to be an issue to consider in well

construction.

SUMMARY AND CONCLUSIONS

This study, completed by the USGS, in cooperation with the PaDEP, provides an assessment of the

bacteriological quality of untreated ground water from

private, household-supply wells in south-central and

southeastern Pennsylvania. Water samples were collected from 78 wells in 8 counties (Chester,

Cumberland, Dauphin, Lancaster, Lebanon, Montgomery, Perry, and York) from an equal number of sanitary

(grouted) and nonsanitary (nongrouted) wells. Sampling took place from September 2000 to March 2001.

All samples were collected from wells adjacent to agricultural land-use areas.

Waters from 48 of 78 wells (62 percent) sampled

for this study were found to contain total coliform bacteria. E. coli bacteria were found in 8 of 78 wells

(10 percent). Seventeen percent of the samples that

were positive for total coliform also were positive for

E. coli.

Statistical tests were conducted to determine if

the presence of bacteria was related to whether or not

grout was installed. Total coliform bacteria were just as

likely to be detected in sanitary (grouted) wells as in

nonsanitary (nongrouted) wells. However, water from

nonsanitary wells was more susceptible to E. coli bacteria contamination. E. coli bacteria were detected in

water from eight household-supply wells sampled; all

but two of those wells were nonsanitary wells.

Statistical tests also were conducted to determine

if the presence of bacteria was related to bedrock type.

The areas underlain by carbonate bedrock had higher

percentages of total coliform detected than areas

underlain by noncarbonate bedrock but this relation is

not statistically significant for total coliform. However,

all of the E. coli detections were observed in ground

water from wells underlain by carbonate bedrock, indicating carbonate aquifers are more vulnerable to E. coli

bacteria contamination than noncarbonate aquifers.

Statistical tests were done after dividing the data

into four groups on the basis of sanitary construction

and bedrock type. Comparisons for total coliform do

not indicate statistically significant differences among

the four groups. On the other hand, 75 percent of the

E. coli bacteria detected was from water from nonsanitary wells in areas underlain by carbonate bedrock (six

of eight wells).

Statistical analyses also were done to determine

if the presence of bacteria was related to well-construction characteristics such as well depth, casing length,

well age, and depth to the first water-bearing zone. Statistically significant relations are present between the

presence of total coliform bacteria and the depth to

water-bearing zone in both sanitary and nonsanitary

wells in areas underlain by carbonate bedrock. Statistically significant relations also are present between the

presence of total coliform bacteria and casing length in

nonsanitary wells in areas underlain by noncarbonate

bedrock.

Bacteria were found in water samples from wells

both with and without insects observed on the underside of the well cap. The data set of wells with sanitary

sealed well caps was too small to conduct statistical

analyses for this study; therefore, it is uncertain

whether installation of sanitary sealed well caps would

reduce the incidence of bacteria in ground water from

wells.

This study showed a high number of detections

of total coliform throughout the study area indicative

of the ubiquitous nature of total coliform in the environment (enteric, plant derived, soil derived, and

others). Potential pathways for total coliform to enter a

well include localized entry from a poorly protected

wellhead (no sanitary sealed cap) by pests, particularly

earwigs, known to contribute coliform bacteria contamination to ground water. In this scenario, the

occurrence of bacteria could be reduced by installing a

sanitary sealed well cap. However, because total

coliform was detected in a similar number of wells on
18

the basis of sanitary and nonsanitary construction and

bedrock type, a combination of characteristics could all

be contributing to the bacterial contamination. Aquifer-wide contamination may be likely.

E. coli bacteria is a subset of total coliform bacteria and is not ubiquitous in the environment. Because

of this result, fewer detections were observed for E. coli

than total coliform. Ground water from nonsanitary

wells installed in areas underlain by noncarbonate bedrock were most vulnerable to E. coli contamination.

One possible explanation for the exclusive occurrence

of E. coli in carbonate aquifers is explained in the following scenario. If the depth to bedrock is shallow in a

carbonate system, the capacity of the soil overburden

to filter out contaminants would be greatly reduced

and the bacteria would have a direct pathway to enter

ground water in the well through the porous carbonate

bedrock material. Because 75 percent of the E. coli

detected was in nonsanitary wells, having a well constructed with grout installed along the entire annulus

of casing greatly reduces the chance that water from

that well will be contaminated with E. coli bacteria.

One potential pathway for the E. coli bacteria to enter

water from a nongrouted well would be if the source of

contamination is on site—possibly the result of a faulty

septic system—and there is a compromised (cracked)

casing that could allow a direct path for the bacteria to

enter into the well. It also could indicate other localized

sources from nearby agricultural operations.

Further study is needed to provide evidence that

a well constructed with sanitary features is less likely

to contain bacteria. A study designed to revisit wells

with bacteria contamination, add a sanitary sealed well

cap, sterilize the ground water in the well by chlorination, and resample the water at a later date would help

to determine the level of water-source protection

afforded by sanitary construction.
19

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Water-Resources Investigations Report 96-4212,

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selected sites in the Beaver Creek Watershed, West

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——— 20 ———

Appendix. Selected well information and results of bacteria analyses for private household-supply wells in south-central and southeaste[mL, milliliter; <, less than; --, no data; TNTC, too numerous to count]

Site Identifier Local well number Date Time County Geology Sanitary or nonsanitary Well depth (feet) Well age (years) Casing length (feet) Depth to first water-bearing zone (feet) 

400846077112501 CU 930 9/27/00 1000 Cumberland Carbonate Sanitary 260 1 80 121 

401616076362501 DA 830 10/04/00 1345 Dauphin Carbonate Sanitary 180 5 84 95 401901075254801 MG 1811 10/10/00 1105 Montgomery Noncarbonate Nonsanitary 140 16 40 90 

401344075311801 MG 1802 10/10/00 1330 Montgomery Noncarbonate Sanitary 147 2 59 -- 

401037077072901 CU 933 10/11/00 930 Cumberland Carbonate Sanitary 220 1 83 208 

394550076100001 LN 2053 10/12/00 1030 Lancaster Noncarbonate Nonsanitary 63 22 43 47 402337077173801 PE 475 10/16/00 1300 Perry Carbonate Sanitary 140 7 81 98 400806077073801 CU 932 10/17/00 1535 Cumberland Carbonate Sanitary 240 10 200 210 401248077064701 CU 935 10/17/00 1200 Cumberland Carbonate Sanitary 200 8 -- 148 400624075443701 CH5992 10/17/00 1330 Chester Noncarbonate Sanitary 157 5 40 50 

401624075344901 MG 1803 10/18/00 1400 Montgomery Noncarbonate Sanitary 200 11 100 110 400759075421301 CH 5990 10/23/00 1700 Chester Noncarbonate Sanitary 180 2 59 70 402227075350001 MG 1816 10/23/00 1200 Montgomery Noncarbonate Sanitary 250 2 75 135 401801075313201 MG 1806 10/23/00 900 Montgomery Noncarbonate Sanitary 121 13 44 48 400342075515201 CH 5989 10/24/00 1030 Chester Noncarbonate Sanitary 180 2 100 120 

394721076390101 YO 1206 10/25/00 1230 York Noncarbonate Nonsanitary 140 16 40 -- 394343076361301 YO 1207 10/25/00 1600 York Noncarbonate Nonsanitary 200 17 42 42 

395003076110001 LN 2052 10/26/00 900 Lancaster Noncarbonate Nonsanitary 180 11 60 80 401127077050601 CU 934 10/26/00 1400 Cumberland Carbonate Sanitary 160 6 57 60 400658075511601 CH 5410 10/30/00 900 Chester Noncarbonate Nonsanitary 150 19 51 55 

400348075552601 CH 5988 10/30/00 1500 Chester Noncarbonate Sanitary 120 2 61 75 400858075490101 CH 5986 10/30/00 1130 Chester Noncarbonate Sanitary 120 2 -- 90 402054075342301 MG 1818 10/31/00 1245 Montgomery Noncarbonate Nonsanitary 200 20 25 65 400839075490901 CH 1350 10/31/00 1600 Chester Noncarbonate Nonsanitary 66 30 42 58 401422075292301 MG 1805 10/31/00 1045 Montgomery Noncarbonate Sanitary 247 1 40 -- 

401153075261001 MG 1804 11/2/00 1015 Montgomery Noncarbonate Sanitary 180 2 32 60 401151075260101 MG 1808 11/2/00 1230 Montgomery Noncarbonate Nonsanitary 176 21 40 60 

400135075542101 CH 4988 11/6/00 900 Chester Noncarbonate Nonsanitary 190 23 -- 70 400034075525001 CH 5987 11/8/00 1530 Chester Noncarbonate Sanitary 100 2 37 45 400135075300001 MG 1807 11/7/00 1200 Montgomery Noncarbonate Nonsanitary 140 18 42.5 90 
——— 21 ———

401734075333101 MG 1817 11/7/00 1000 Montgomery Noncarbonate Sanitary 123 11 64.5 70 400400075560901 CH 1272 11/14/00 900 Chester Noncarbonate Nonsanitary 183 30 30 38 

401101077072301 CU 936 11/14/00 1150 Cumberland Carbonate Nonsanitary 250 9 60 -- 

394759075560301 CH 4933 11/14/00 1200 Chester Noncarbonate Nonsanitary 157 25 87 28 401829075354501 MG 1813 11/15/00 1530 Montgomery Noncarbonate Sanitary 180 4 60 140 

402145075263201 MG 1809 11/15/00 1200 Montgomery Noncarbonate Nonsanitary 240 12 40 178 401815075382001 MG 1810 11/15/00 1000 Montgomery Noncarbonate Nonsanitary 147 9 80.4 119 401727075360801 MG 1812 11/16/00 800 Montgomery Noncarbonate Sanitary 123 2 49.2 -- 400230076410201 YO 1202 11/20/00 1100 York Noncarbonate Nonsanitary 140 26 26 65 394816076463001 YO 1199 11/20/00 1400 York Noncarbonate Nonsanitary 175 23 20.5 71 

401125077195801 CU 911 11/21/00 1200 Cumberland Carbonate Nonsanitary 176 20 108 108 

400942077041201 CU 919 11/21/00 900 Cumberland Carbonate Nonsanitary 165 14 102 102 

401011077061401 CU 923 11/21/00 1000 Cumberland Carbonate Nonsanitary 225 12 80 220 401155077001901 CU 942 11/21/00 730 Cumberland Carbonate Sanitary 150 9 -- 131 

395752076045001 LN2050 11/27/00 930 Lancaster Noncarbonate Nonsanitary 130 22 20 20 

394426075533501 CH4931 11/27/00 1230 Chester Noncarbonate Sanitary 132 9 59 70 400515077205501 CU 914 11/29/00 1130 Cumberland Carbonate Nonsanitary 147 16 145 139 400853077230101 CU 912 11/29/00 1000 Cumberland Carbonate Nonsanitary 162 10 120 109 400754077195201 CU 913 11/29/00 1500 Cumberland Carbonate Nonsanitary 162 11 60 60 

401136077152701 CU 918 11/30/00 1100 Cumberland Carbonate Nonsanitary 203 8 179 198 

400746077262201 CU 910 11/30/00 900 Cumberland Carbonate Nonsanitary 198 9 126 126 400835077171701 CU 916 11/30/00 1330 Cumberland Carbonate Nonsanitary 123 21 89 115 400824077085501 CU 944 12/4/00 1300 Cumberland Carbonate Sanitary 100 1 80 90 401445076440801 DA 841 12/4/00 1200 Dauphin Carbonate Nonsanitary 180 23 40 105 401750076274601 LB 1164 12/4/00 1000 Lebanon Carbonate Nonsanitary 150 13 73 85 

395204076262101 YO 1209 12/4/00 1700 York Noncarbonate Sanitary 175 8 52 115 400834077134401 CU 917 12/5/00 1100 Cumberland Carbonate Nonsanitary 200 12 60 60 400103075561801 CH 5991 12/6/00 1400 Chester Noncarbonate Sanitary 180 3 126 140 401744075312801 MG 1815 12/6/00 1100 Montgomery Noncarbonate Sanitary 160 2 63 130 401735075293001 MG 1814 12/6/00 1000 Montgomery Noncarbonate Sanitary 240 11 240 120 

Appendix. Selected well information and results of bacteria analyses for private household-supply wells in south-central and southeaster[mL, milliliter; <, less than; --, no data; TNTC, too numerous to count]

Site Identifier Local well number Date Time County Geology Sanitary or nonsanitary Well depth (feet) Well age (years) Casing length (feet) Depth to first water-bearing zone (feet) 
——— 22 ———

394606076002001 CH 4932 12/19/00 1200 Chester Noncarbonate Nonsanitary 143 20 52 52 401316077023001 CU 946 12/20/00 1000 Cumberland Carbonate Sanitary -- -- -- -- 

400854077112701 CU 941 12/20/00 1600 Cumberland Carbonate Sanitary 125 2 80 -- 

400945077104201 CU 943 12/20/00 1400 Cumberland Carbonate Nonsanitary 200 6 20 -- 

401111077073001 CU 939 12/21/00 1000 Cumberland Carbonate Nonsanitary 150 -- -- -- 

400805077074101 CU 940 12/21/00 1200 Cumberland Carbonate Sanitary 200 1 80 -- 400854077161801 CU 937 12/26/00 900 Cumberland Carbonate Nonsanitary 200 2 100 -- 401046077094601 CU 938 12/26/00 1430 Cumberland Carbonate Nonsanitary -- -- -- -- 

401254076114701 LN 2017 1/28/01 900 Lancaster Noncarbonate Nonsanitary 160 9 42 105 

400229076020301 LN 2027 1/29/01 1300 Lancaster Carbonate Nonsanitary 175 15 102 102 

400711076113801 LN 2019 1/29/01 1130 Lancaster Carbonate Nonsanitary 200 12 20 176 

400827077083101 CU 948 1/31/01 900 Cumberland Carbonate Sanitary 200 5 57.5 -- 400238075341301 CH 6398 2/13/01 1030 Chester Carbonate Sanitary -- 1 -- -- 400327075324901 CH 6397 2/13/01 1200 Chester Carbonate Sanitary -- 6 -- -- 405732075541001 CH 5364 2/15/01 1600 Chester Carbonate Sanitary 160 3 -- -- 

395747075531301 CH 6179 2/20/01 1000 Chester Carbonate Sanitary -- 16 -- -- 400953077105101 CU 945 3/27/01 1000 Cumberland Carbonate Sanitary 180 1 -- -- 401030077105801 CU 947 3/29/01 910 Cumberland Carbonate Sanitary 260 1 100 100 

Appendix. Selected well information and results of bacteria analyses for private household-supply wells in south-central and southeaster[mL, milliliter; <, less than; --, no data; TNTC, too numerous to count]

Site Identifier Local well number Date Time County Geology Sanitary or nonsanitary Well depth (feet) Well age (years) Casing length (feet) Depth to first water-bearing zone (feet)