Prepared in cooperation with the Allegheny County 

Sanitary Authority and Allegheny County Health Department

Occurrence and Trends in the Concentrations of FecalIndicator Bacteria and the Relation to Field Water-Quality 

Parameters in the Allegheny, Monongahela, and Ohio Rivers 

and Selected Tributaries, Allegheny County, Pennsylvania, 

2001–09

Scientific Investigations Report 2015–5136

U.S. Department of the Interior

U.S. Geological Survey

Occurrence and Trends in the Concentrations of Fecal-Indicator Bacteria and the 

Relation to Field Water-Quality Parameters 

in the Allegheny, Monongahela, and Ohio 

Rivers and Selected Tributaries, Allegheny 

County, Pennsylvania, 2001–09

By John W. Fulton, Edward H. Koerkle, Jamie L. McCoy, and Linda F. Zarr

Prepared in cooperation with the Allegheny County 

Sanitary Authority and Allegheny County Health Department

Scientific Investigations Report 2015–5136

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Fulton, J.W., Koerkle, E.H., McCoy, J.L., and Zarr, L.F., 2016, Occurrence and trends in the concentrations of fecalindicator bacteria and the relation to field water-quality parameters in the Allegheny, Monongahela, and Ohio Rivers 

and selected tributaries, Allegheny County, Pennsylvania, 2001–09: U.S. Geological Survey Scientific Investigations 

Report 2015–5136, 47 p., http://dx.doi.org/10.3133/sir20155136.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors thank Tim Prevost Allegheny County Sanitary Authority and John Schombert 

(3 Rivers Wet Weather) for collaborating on this project. Steve Corsi (U.S. Geological Survey 

[USGS]), Daniel Hippe (USGS), Robert Hainly (USGS, retired), Dale Simmons (USGS), and Charles 

Cravotta (USGS) provided constructive criticism, which improved the quality of the manuscript.

v

Contents

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

Introduction ....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Study Area..............................................................................................................................................2

Previous Investigations........................................................................................................................2

Networks.........................................................................................................................................................5

Main-Stem Rivers .................................................................................................................................5

Tributaries ..............................................................................................................................................5

Wet- and Dry-Weather Event Protocols ...........................................................................................5

Wet-Weather Sampling Event Criteria............................................................................................11

Type A .........................................................................................................................................11

Type B .........................................................................................................................................11

Dry-Weather Sampling Event Criteria .............................................................................................11

Methods.........................................................................................................................................................11

Streamflow Measurement, Water-Quality Sampling, and Laboratory Analyses.....................11

Statistical Analyses............................................................................................................................12

Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow .................13

Occurrence of Fecal-Indicator Bacteria ...............................................................................13

Allegheny River Basin......................................................................................................13

Monongahela River Basin...............................................................................................16

Ohio River Basin................................................................................................................16

Relations of Concentrations of Fecal-Indicator Bacteria to Other Water-Quality 

Parameters....................................................................................................................16

Main-Stem Sites ...............................................................................................................16

Tributary Sites....................................................................................................................19

Trend Analysis .....................................................................................................................................24

Summary and Conclusions.........................................................................................................................32

References Cited..........................................................................................................................................32
vi

Figures

1. Map showing study area and location of U.S. Army Corps of Engineers flow-control 

structures on the Allegheny, Monongahela, and Ohio Rivers, Allegheny County, 

Pennsylvania .................................................................................................................................3

2. Map showing location of U.S. Geological Survey streamgaging stations on the 

Allegheny, Monongahela, and Ohio Rivers, Allegheny County, Pennsylvania...................4

3. Map showing location of sampling sites and combined sewer overflow locations 

on the Allegheny River, Allegheny County, Pennsylvania......................................................6

4. Map showing location of sampling sites and combined sewer overflow locations 

on the Monongahela River, Allegheny County, Pennsylvania...............................................7

5. Map showing location of sampling sites and combined sewer overflow locations 

on the Ohio River, Allegheny County, Pennsylvania................................................................8

6. Map showing location of precipitation stations near the Allegheny, Monongahela, 

and Ohio Rivers, Allegheny County, Pennsylvania................................................................10

7. Graph showing streamflow statistics for U.S. Geological Survey streamgaging 

stations on the Allegheny, Monongahela, and Ohio Rivers, Allegheny County, 

Pennsylvania, during dry- and wet-weather events, October 1, 2001, to September 

30, 2009 .........................................................................................................................................15

8. Graph showing comparison of Escherichia coli concentrations in composite 

samples collected during wet- and dry-weather events at U.S. Geological Survey 

streamgaging station 03049652 on the Allegheny River near Pittsburgh, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................25

9. Graph showing comparison of fecal coliform concentrations in composite samples 

collected during wet- and dry-weather events at U.S. Geological Survey streamgaging station 03049652 on the Allegheny River near Pittsburgh, Allegheny County, 

Pennsylvania, 2001–09 ...............................................................................................................25

10. Graph showing comparison of Escherichia coli concentrations in composite 

samples collected during wet- and dry-weather events at U.S. Geological Survey 

streamgaging station 03049832 on the Allegheny River near Pittsburgh, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................26

11. Graph showing comparison of fecal coliform concentrations in composite samples 

collected during wet- and dry-weather events at U.S. Geological Survey streamgaging station 03049832 on the Allegheny River near Pittsburgh, Allegheny County, 

Pennsylvania, 2001–09 ...............................................................................................................26

12. Graph showing comparison of Escherichia coli concentrations in composite 

samples collected during wet- and dry-weather events at U.S. Geological Survey 

streamgaging station 03083903 on the Monongahela River near Pittsburgh, 

Allegheny County, Pennsylvania, 2001–09..............................................................................27

13. Graph showing comparison of fecal coliform concentrations in composite samples 

collected during wet- and dry-weather events at U.S. Geological Survey streamgaging station 03083903 on the Monongahela River near Pittsburgh, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................27
vii

14. Graph showing comparison of Escherichia coli concentrations in composite samples 

collected during wet- and dry-weather events at U.S. Geological Survey streamgaging station 03085150 on the Monongahela River near Pittsburgh, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................28

15. Graph showing comparison of fecal coliform concentrations in composite samples 

collected during wet- and dry-weather events at U.S. Geological Survey streamgaging station 03085150 on the Monongahela River near Pittsburgh, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................28

16. Graph showing comparison of Escherichia coli concentrations in composite 

samples collected during wet- and dry-weather events at U.S. Geological Survey 

streamgaging station 03085986 on the Ohio River near Pittsburgh, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................29

17. Graph showing comparison of fecal coliform concentrations in composite samples 

collected during wet- and dry-weather events at U.S. Geological Survey streamgaging station 03085986 on the Ohio River near Pittsburgh, Allegheny County, 

Pennsylvania, 2001–09 ...............................................................................................................29

Tables

1. Description of sampling and streamgage sites on the Allegheny, Monongahela, 

and Ohio Rivers and selected tributaries, Allegheny County, Pennsylvania, 

2001–09 .........................................................................................................................................34

2. Streamflow statistics in cubic feet per second at streamgaging stations on the 

Allegheny, Monongahela, and Ohio Rivers, Allegheny County, Pennsylvania, 

October 1, 1968, to September 30, 2004.....................................................................................9

3. U.S. Geological Survey streamgage statistics for the period of sampling October 1, 

2001, to September 30, 2009, in the Allegheny, Monongahela, and Ohio Rivers, 

Allegheny County, Pennsylvania..............................................................................................14

4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen 

concentration, specific conductivity, turbidity, and concentrations of fecal-indicator 

bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09....................39

5. Results of generalized Wilcoxon paired sample tests of sampling-location 

difference in concentrations of fecal-indicator bacteria and turbidity in dry- and 

wet-weather samples from five sampling locations on the Allegheny, Monongahela, 

and Ohio Rivers, Allegheny County, Pennsylvania, 2001–09................................................15

6. Results of Spearman’s rho correlations between concentrations of fecal-indicator 

bacteria and field water-quality characteristics, Allegheny River main-stem sites, 

Allegheny County, Pennsylvania, 2001–09..............................................................................17

7. Results of Spearman’s rho correlations between concentrations of fecal-indicator 

bacteria and field water-quality characteristics, Monongahela River main-stem 

sites, Allegheny County, Pennsylvania, 2001–09 ...................................................................18
viii

8. Results of Spearman’s rho correlations between concentrations of fecal-indicator 

bacteria and field water-quality characteristics, Ohio River main-stem sites (Ohio 

River at Sewickley, PA), Allegheny County, Pennsylvania, 2001–09 ..................................19

9. Results of Spearman’s rho correlations between concentrations of fecal-indicator 

bacteria and field water-quality characteristics, Monongahela River Basin, 

Allegheny County, Pennsylvania, 2001–09..............................................................................20

10. Results of Spearman’s rho correlations between concentrations of fecal-indicator 

bacteria and field water-quality characteristics, Ohio River Basin, Allegheny 

County, Pennsylvania, 2001–09.................................................................................................22

11. Results of Seasonal Kendall test for trends in bacteria at five sites on the Allegheny, 

Monongahela, and Ohio Rivers, Allegheny County, Pennsylvania, 2001–09 ....................30

12. Results of logistic regression test for trends in probability of exceeding recreational 

bacteria standards at five sites on the Allegheny, Monongahela, and Ohio Rivers, 

Allegheny County, Pennsylvania, 2001–09..............................................................................31
ix

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.59 square kilometer (km2)

Flow rate

cubic foot per second (ft3/s) 0.0283 cubic meter per second (m3/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 

(NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter 

(mg/L) or micrograms per liter (μg/L).

Occurrence and Trends in the Concentrations of FecalIndicator Bacteria and the Relation to Field WaterQuality Parameters in the Allegheny, Monongahela, and 

Ohio Rivers and Selected Tributaries, Allegheny County, 

Pennsylvania, 2001–09

By John W. Fulton, Edward H. Koerkle, Jamie L. McCoy, and Linda F. Zarr

Abstract

The U.S. Geological Survey (USGS), in cooperation

with the Allegheny County Health Department and Allegheny 

County Sanitary Authority, collected surface-water samples 

from the Allegheny, Monongahela, and Ohio Rivers and 

selected tributaries during the period 2001–09 to assess the 

occurrence and trends in the concentrations of fecal-indicator 

bacteria during both wet- and dry-weather conditions.

A total of 1,742 water samples were collected at 

52 main-stem and tributary sites. Quantifiable concentrations 

of Escherichia coli (E. coli) were reported in 1,667 samples, 

or 97.0 percent of 1,719 samples; concentrations in 

853 samples (49.6 percent) exceeded the U.S. Environmental 

Protection Agency (EPA) recreational water-quality criterion 

of 235 colonies per 100 milliliters (col/100 mL). Quantifiable concentrations of fecal coliform (FC) bacteria were 

reported in 1,693 samples, or 98.8 percent of 1,713 samples; 

concentrations in 780 samples (45.5 percent) exceeded the 

Commonwealth of Pennsylvania water contact criterion of 

400 col/100 mL. Quantifiable concentrations of enterococci 

bacteria were reported in 912 samples, or 87.5 percent of 

1,042 samples; concentrations in 483 samples (46.4 percent) 

exceeded the EPA recreational water-quality criterion of 

61 col/100 mL. The median percentage of samples in which 

bacteria concentrations exceeded recreational water-quality 

standards across all sites with five or more samples was 48 

for E. coli, 43 for FC, and 75 for enterococci. E. coli, FC, and 

enterococci concentrations at main-stem sites had significant 

positive correlations with streamflow under all weather conditions, with rho values ranging from 0.203 to 0.598. Seasonal 

Kendall and logistic regression were evaluated to determine 

whether statistically significant trends were present during 

the period 2001–09. In general, Seasonal Kendall tests for 

trends in E. coli and FC bacteria were inconclusive. Results of 

logistic regression showed no significant trends in dry-weather 

exceedance of the standards; however, significant decreases 

in the likelihood that wet-weather E. coli and FC bacteria 

concentrations will exceed EPA recreational standards were 

found at the USGS streamgaging station Allegheny River at 

9th Street Bridge. Nonparametric correlation analysis, including Spearman’s rho and the paired Prentice-Wilcoxon test, was 

used to screen for associations among fecal indicator bacteria 

concentrations and the field characteristics streamflow, water 

temperature, pH, specific conductance, dissolved-oxygen concentration, and turbidity.

Introduction 

The U.S. Geological Survey (USGS) collected surfacewater samples from October 2001 through September 2009 to 

assess the occurrence and trends in the concentrations of fecalindicator bacteria in the Allegheny, Monongahela, and Ohio 

Rivers (Three Rivers) near Pittsburgh, Pennsylvania (Pa.). 

Samples were collected at main-stem sites during both dry 

and wet weather from April through October during 2001–04 

and selected years thereafter and, in 2004, the program was 

changed to focus on wet-weather sampling and to include 

selected tributaries to the Three Rivers.

Exposure to pathogenic bacteria and viruses (pathogens) 

in surface water can have adverse health effects on humans 

by increasing the risk of gastrointestinal, respiratory, eye, ear, 

throat, and skin diseases. Because individual pathogens are 

difficult to detect and measure directly (Chapra, 1997, p. 504), 

monitoring programs commonly rely on the nonpathogenic 

indicator organisms, such as fecal coliform (FC) and fecal 

streptococcus bacteria, as surrogates; if they are present, it is 

assumed that additional, more harmful pathogens may coexist. 

Traditionally, FC was the most widely used fecal-indicator 

bacterium used for monitoring; however, its use is problematic 

because not all FC bacteria are fecal in origin. Enterococci and 

Escherichia coli (E. coli), in contrast, originate in the intestines of warm-blooded animals and their presence is evidence 
2 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

of fecal contamination. Both indicators can occur naturally 

in the environment (Hardina and Fujioka, 1991). Both can be 

sampled and quantified by using standard methods, and both 

are relatively abundant in human and animal waste. Because 

the die-off rates for enterococci and E. coli are lower than that 

of FC, they provide a better measure of the risk of gastrointestinal illness related to recreational contact with water (U.S. 

Environmental Protection Agency, 2001).

Purpose and Scope

This report (1) documents the 2001–09 streamflow and 

water-quality results for field parameters such as water temperature, pH, specific conductance, dissolved-oxygen concentration, and turbidity; (2) presents the results of trend analyses 

for fecal-indicator bacteria (E. coli and FC); (3) describes the 

influence of wet- and dry-weather events on fecal-indicator 

bacteria concentrations by comparing their spatial distribution 

at various receptor sites, such as marinas and water-supply 

intakes, and at sampling locations in the Three Rivers; and 

(4) presents results from nonparametric correlation analyses to screen for associations among fecal-indicator bacteria 

concentrations and the field characteristics streamflow, water 

temperature, pH, specific conductance, dissolved-oxygen concentration, and turbidity. A total of 1,742 water samples were 

collected at 52 main-stem and tributary sites on the Allegheny, 

Monongahela, and Ohio Rivers.

Study Area

The study area of approximately 730 square miles (mi2) 

includes the areal extent of Allegheny County, Pennsylvania 

(fig. 1) that consists of the Three Rivers and selected tributaries, which together constitute the river system entering and 

exiting the county. The Allegheny River reach begins at the 

C.W. Bill Young Lock and Dam (river mile 14.5) and extends 

downstream to Lock and Dam No. 2 (river mile 6.7) and to the 

Point at Pittsburgh, where the Allegheny and Monongahela 

Rivers join to form the Ohio River. Similarly, the Monongahela River reach begins at Locks and Dam No. 3 (river 

mile 23.8) and extends to the Lock and Dam at Braddock 

(river mile 11.2) and to the Point at Pittsburgh. The Ohio River 

reach extends from the Point at Pittsburgh (river mile 0.0) to 

the Emsworth Locks and Dam (river mile 6.2) on the main 

channel and the non-navigable back channel to the Dashields 

Locks and Dam (river mile 13.3).

Five tributaries (Deer Creek, Plum Creek, Squaw Run, 

Pine Creek, and Girtys Run) to the Allegheny River, five tributaries (Youghiogheny River, Thompson Run, Turtle Creek, 

Ninemile Run, and Streets Run) to the Monongahela River, 

and four tributaries (Sawmill Run, Chartiers Creek, Lowries 

Run, and Montour Run) to the Ohio River were incorporated 

in the sampling design. Tributary locations relative to the 

receiving water and approximate drainage-basin areas are 

summarized in table 1 (at end of report).

USGS streamgages were selected for monitoring water 

quality in the Allegheny County Sanitary Authority (ALCOSAN) service area (fig. 2) and to identify potential upstream 

contributions to the Three Rivers and its tributaries. Approximately 414 combined sewer overflows (CSOs) exist within 

Allegheny County (Committee on Water Quality Improvement 

for the Pittsburgh Region, 2005); however, the number and 

distribution of these structures vary from basin to basin. The 

Allegheny River serves as the principal water-supply source 

for the City of Pittsburgh and areas to the east and northeast. 

The Monongahela River services large areas south of Allegheny County. The Ohio River is the source of water for populations north of the river. In addition, several municipalities 

pump water from wells or galleries that are located adjacent to 

the Three Rivers.

Previous Investigations

Federal, State, local, and private agencies and other 

groups have monitored receiving waters in the Three Rivers 

since 1976. In general, concentrations of indicator bacteria 

are highest during the summer months after storm events. 

Previous investigations by Fulton and Buckwalter (2004) and 

Buckwalter and others (2006) are summarized briefly below.

The Ohio River Valley Water Sanitation Commission 

(ORSANCO) has been monitoring bacteria in the Ohio River 

since 1992. From May through October each year, three 

surface-water grab samples are collected near the left water’s 

edge (LWE facing downstream), near the right water’s edge 

(RWE facing downstream), and at mid-stream locations at 

river mile 1.4 and 4.3 (distance measured in miles downstream 

from the confluence of the Allegheny and Monongahela Rivers 

in Pittsburgh) at a frequency of five per month. Electronic data 

can be accessed from the Ohio River Valley Water Sanitation 

Web site, http://www.orsanco.org/bacteria (Ohio River Valley 

Water Sanitation Commission, 2010).

From 1976 through 1989, the USGS partnered with 

the U.S. Environmental Protection Agency (EPA) to operate a surveillance network at the Allegheny River at New 

Kensington, Pa., and the Monongahela River at Braddock, 

Pa. Samples were collected at these sites from 1989 through 

1994 as part of another USGS program, the National Stream 

Quality Accounting Network (NASQAN). These same stations were operated in 1995 as part of the USGS National 

Water-Quality Assessment (NAWQA) Program. During each 

program, surface-water samples were collected mid-stream at 

a frequency of either one per month or quarterly and analyzed 

for concentrations of FC and fecal streptococci. The USGS 

participated in two supplemental programs in the Three Rivers 

area near Pittsburgh, Pa., that included sampling and analysis for indicator bacteria. Fulton and Buckwalter (2004) and 

Buckwalter and others (2006) discuss their findings associated 

with E. coli, enterococci, FC, and various field parameters in 

main-stem river and tributary samples collected during July–

September 2005. All water-quality data can be accessed from 
Introduction 3

80°15' 80° 79°45'

40°30'

40°15'

The point

PENNSYLVANIA

0 5 10 MILES

0 5 10 KILOMETERS

County and Pittsburgh boundary from U.S. Geological Survey digital 

data, 1983, 1:100,000, Municipality and lock and dam locations from 

U.S. Geological Survey Digital Raster Graphic, 2005, 1:24,000

Allegheny River

(Pool 4)

Allegheny River

(C.W. Bill Young Pool)

Allegheny River

(Pool 2)

Allegheny River

(Emmsworth Pool)

Monongahela River

(Emmsworth Pool)

Monongahela River

(Braddock Pool)

Youghiogheny River

(Braddock Pool)

Ohio River

(Emmsworth Pool)

Ohio River

(Dashields Pool)

Bridgeville

Bethel Park

Sewickley

Elizabeth

Braddock

Natrona Heights Wexford

EXPLANATION

City of Pittsburgh

Allegheny County study-area boundary

River

U.S. Army Corps of Engineers 

lock and dam

Municipality

Location of study area

ALLEGHENY COUNTY

Figure 1. Study area and location of U.S. Army Corps of Engineers flow-control structures on the Allegheny, Monongahela, and Ohio 

Rivers, Allegheny County, Pennsylvania.
4 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

80°15' 80° 79°45'

40°30'

40°15'

03085100

03049658

03049807

03085049

03085947

03049819

03049646

03084698

03084800

03085213

03085956

03085500

03083500

03086000

03075070

ALLEGHENY COUNTY 03049500

03084698

03083500

PENNSYLVANIA

0 5 10 MILES

0 5 10 KILOMETERS

Shaded Relief Base: World Shaded Relief (ESRI, 2009) Hydrology: U.S. Geological Survey, 

National Hydrography Dataset, 1:24,000 County Boundary: U.S. Geological Survey, 

1:100,000 Pennsylvania State Plane South projection, North American Datum 1983 EXPLANATION

City of Pittsburgh

Allegheny County study-area boundary

River or selected tributary

Allegheny County Sanitary Authority 

sewer service area boundary

 U.S. Geological Survey streamgage 

 and station number

Main-stem gage and number

Tributary gage and number Location of study area

Ohio River

Montour Run

Lowries Run

Girtys Run

Pine Creek

Deer Creek

Plum Creek

Allegheny River

Thompson Run

Ninemile Run

Turtle Creek

Youghiogheny River

Chartiers Creek

Streets Run

Sawmill Run

Monongahela River

Figure 2. Location of U.S. Geological Survey streamgaging stations on the Allegheny, Monongahela, and Ohio Rivers, Allegheny 

County, Pennsylvania.
Networks 5

the USGS National Water Information System (NWIS) Web 

site at http://nwis.waterdata.usgs.gov/pa/nwis/qwdata.

Bacteria monitoring has been implemented by a variety 

of local groups, including water companies; the Allegheny 

County Health Department (ACHD); and the 3 Rivers 2nd 

Nature project at the Frank-Ratchye STUDIO for Creative 

Inquiry (3R2N), part of the College of Fine Arts at Carnegie 

Mellon University in Pittsburgh. Pa. The bacteria data collected by the water companies and the ACHD are unpublished. 

3R2N-issued annual reports summarizing water-quality data 

for the Three Rivers and selected tributary sites that focus 

on various navigation pools within the region, where recreational boating is common in the summer. Sampling sites 

are selected on the basis of public access and inflow points 

discharging to the Three Rivers. Water-quality constituents 

and other parameters measured as part of this program include 

total coliform, E. coli, enterococci, pH, temperature, specific 

conductance, and dissolved-oxygen concentration. Knauer 

and Collins (2002) summarized findings that include results 

of fecal-indicator bacteria sampling during the summer of 

2001 for sites on the Monongahela River from river mile 11.5 

to 35.0 and on selected tributary streams to the Monongahela 

River.

A comprehensive report on water resources, water quality, and causes of water-quality impairment in southwestern 

Pennsylvania that included data from several sources such as 

water-treatment plants, the ACHD, the USGS, the U.S. Army 

Corps of Engineers, universities, and independent studies was 

published in 2005 (Committee on Water Quality Improvement for the Pittsburgh Region, 2005). The report documented 

concentrations of E. coli, enterococci, and FC as well as the 

waterborne, pathogenic protozoans Giardia and Cryptosporidium in the Three Rivers and selected tributaries. Other studies 

have documented the presence of fecal-indicator bacteria in 

rivers, streams, and wastewaters also found to be contaminated 

with Giardia and Cryptosporidium. Giardia was found in water 

samples collected from the Allegheny and Youghiogheny Rivers during 1994–97 (States and others, 1997). The relevance of 

the documented presence of pathogens in surface waters in the 

Three Rivers area is that recreational contact with these waters 

carries the risk of contracting illnesses, and the occurrence of 

nonpathogenic fecal-indicator bacteria (E. coli, enterococci, 

and FC) may indicate when that risk is present.

Networks

To evaluate the occurrence of and trends in concentrations of fecal-indicator bacteria, a network of rain gages and 

streamgages was established to characterize water quality and 

quantity during dry- and wet-weather events of varying magnitudes and spatial distribution of rainfall in both the main-stem 

river and tributary systems.

Main-Stem Rivers

The study-area boundaries were selected to evaluate 

water quality within the ALCOSAN service area and to identify potential upstream contributions of fecal-indicator bacteria 

to both the Three Rivers and their tributaries. Sampling was 

not done synoptically; rather, an individual basin (for example, 

the Allegheny River Basin) and its associated tributaries were 

targeted during a particular sampling event. River transects, 

continuous-record tributary sites, and candidate receptor sites 

(sensitive areas including surface-water intakes and areas of 

intensive river recreational use) are illustrated in figures 3 

through 5 for the Allegheny, Monongahela, and Ohio Rivers, 

respectively. Periodic adjustments to river-transect sampling 

locations were necessary as a result of river traffic and lock 

and dam renovations.

Streamflow was monitored for prescribed flow conditions 

at four stations (Allegheny River at Natrona, Pa., Monongahela River at Elizabeth, Pa., Monongahela River at Braddock, 

Pa., and Ohio River at Sewickley, Pa.) during the recreational 

season (table 2). Water samples were collected from 10 additional sites on the Allegheny River, 9 additional sites on the 

Monongahela River, and 10 additional sites on the Ohio River. 

The Allegheny River at Oakmont was sampled because it is 

near the boundary of the ALCOSAN service area, the Monongahela River at McKeesport was sampled because its location coincides with the upstream boundary of the ALCOSAN 

service area, and the Ohio River at Sewickley was sampled 

as a representative site near the downstream boundary of the 

ALCOSAN service area.

Tributaries

Water samples also were collected from five tributaries 

to the Allegheny River, five tributaries to the Monongahela 

River, and four tributaries to the Ohio River to quantify loads 

entering the Three Rivers. In general, two sites were selected 

on each of the tributaries—an upstream site near the boundary 

of the ALCOSAN service area, and a downstream site at the 

location of an existing streamgaging station—except Turtle 

Creek at East Pittsburgh, Pa..

Wet- and Dry-Weather Event Protocols

Variations in streamflow and the spatial distribution 

of rainfall posed considerable challenges to scheduling the 

collection of water samples at sites throughout the study 

area. Precipitation data from the 3 Rivers Wet Weather 

(3RWW) raingage network (fig. 6) and radar-rainfall on a 

1-square-kilometer (km2) (0.37-mi2) grid was used to evaluate antecedent dry-weather conditions and the magnitude of 

wet weather for a given watershed. In addition, streamflow 

data from the USGS streamgaging network were monitored to 
6 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

9 8

7 6

5 4 3

2

1

80°15' 80° 79°45'

40°30'

40°15'

Ohio River

Allegheny 

River

Youghiogheny 

River

Monongahela 

River

City of 

Pittsburgh

35

9 8

7 6

5

4

3

2 1

32

37

36

34

33

City of 

Pittsburgh

Girtys Run

Pine Creek

Squaw Run

Deer Creek

Plum Creek

161*

5*

9*

Sewer outfall locations from Timothy Prevost, Allegheny

County Sanitary Authority, written commun., 2002

EXPLANATION

Sampling-site name and map number

01 - Allegheny River below Falling Springs Run at Oakmont, PA

02 - Allegheny River at Hulton Bridge at Oakmont, PA

03 - Allegheny River above Quigley Creek at Blawnox, PA

04 - Allegheny River above Shades Run at Aspinwall, PA

05 - Allegheny River below Shades Run at Aspinwall, PA

06 - Allegheny River at Sharpsburg, PA

07 - Allegheny River above Girtys Run at Millvale, PA

08 - Allegheny River above 31st Street Bridge at Pittsburgh, PA

09 - Allegheny River below 31st Street Bridge at Pittsburgh, PA

32 - Allegheny River at 9th Street Bridge at Pittsburgh, PA

33 - Deer Creek at Route 910 near Cheswick, PA

34 - Plum Creek at Milltown, PA

35 - Plum Creek at Verona, PA

36 - Squaw Run at Old Freeport Road near Blawnox, PA

37 - Pine Creek at Etna, PA

0 5 10 MILES

0 5 10 KILOMETERS

0 2 4 MILES

0 2 4 KILOMETERS

Allegheny County study-area boundary

River or selected tributary

Sewer outfall

Monitoring location

Direction of flow

Number of sewer outfalls upstream

ALLEGHENY COUNTY

9*

Shaded Relief Base: World Shaded Relief (ESRI, 2009) Hydrology: 

U.S. Geological Survey, National Hydrography Dataset, 1:24,000

County Boundary: U.S. Geological Survey, 1:100,000 Pennsylvania 

State Plane South projection, North American Datum of 1983

Figure 3. Location of sampling sites and combined sewer overflow locations on the Allegheny River, Allegheny County, Pennsylvania.
Networks 7

20

19

18

17 16

15 14

13

11 12

10

38

80°15' 80° 79°45'

40°30'

40°15'

Ohio River

Allegheny 

River

Youghiogheny 

River

Monongahela 

River

City of 

Pittsburgh

20

19

18

17

16

15

14

13

12

11

10

43

42

41

40

39

City of 

Pittsburgh

94* 127*

Sewer outfall locations from Timothy Prevost, Allegheny

County Sanitary Authority, written commun., 2002

Sampling-site name and map number

10 - Monongahela River at Dravosburg, PA

11 - Youghiogheny River at McKeesport, PA

12 - Monongahela River at McKeesport, PA

13 - Monongahela River above Turtle Creek at Duquesne, PA

14 - Monongahela River above Rankin Bridge at Rankin, PA

15 - Monongahela River above Ninemile Run at Homestead, PA

16 - Monongahela River below Streets Run near Baldwin, PA

17 - Monongahela River at South Pittsburgh, PA

18 - Monongahela River at Greenfield at Pittsburgh, PA

19 - Monongahela River at Brady Street Bridge at Pittsburgh, PA

20 - Monongahela River at Pittsburgh, PA

38 - Turtle Creek at Trafford, PA

39 - Thompson Run at Gascola, PA

40 - Thompson Run at Turtle Creek, PA

41 - Turtle Creek at East Pittsburgh, PA

42 - Ninemile Run at Mouth near Swissvale, PA

43 - Streets Run 1000 ft upstream of Mouth at Hays, PA

0 5 10 MILES

0 5 10 KILOMETERS

0 2 4 MILES

0 2 4 KILOMETERS

Thompson Run

Becks Run

Ninemile Run

Turtle Creek

Streets Run

EXPLANATION

Allegheny County study-area boundary

River or selected tributary

Sewer outfall

Monitoring location

Direction of flow

Number of sewer outfalls upstream

Shaded Relief Base: World Shaded Relief (ESRI, 2009) Hydrology: 

U.S. Geological Survey, National Hydrography Dataset, 1:24,000

County Boundary: U.S. Geological Survey, 1:100,000 Pennsylvania 

State Plane South projection, North American Datum of 1983

ALLEGHENY COUNTY

94*

Figure 4. Location of sampling sites and combined sewer overflow locations on the Monongahela River, Allegheny County, 

Pennsylvania.
8 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

31

30

29

28 27

26

25

24

23 22

21

45 44

80°15' 80° 79°45'

40°30'

40°15'

Shaded Relief Base: World Shaded Relief (ESRI, 2009) Hydrology: 

U.S. Geological Survey, National Hydrography Dataset, 1:24,000

County Boundary: U.S. Geological Survey, 1:100,000 Pennsylvania 

State Plane South projection, North American Datum of 1983

Ohio River

Allegheny 

River

Youghiogheny 

River

Monongahela 

River

City of 

Pittsburgh

31

30

29

28

27

26

25

24

23

22

21

48

46

47

City of 

Pittsburgh

Sampling-site name and map number

21 - Allegheny River at 9th Street Bridge at Pittsburgh, PA

22 - Monongahela River at Pittsburgh, PA

23 - Ohio River at Point State Park at Pittsburgh, PA

24 - Ohio River above Brunot Island at Pittsburgh, PA

25 - Ohio River below Jacks Run near Pittsburgh, PA

26 - Ohio River above Neville Island at Avalon, PA

27 - Ohio River below Lowries Run at Emsworth, PA

28 - Ohio River above Toms Run at Emsworth, PA

29 - Ohio River below Emsworth back channel at Emsworth, PA

30 - Ohio River below Neville Island at Coraopolis, PA

31 - Ohio River at Sewickley Bridge at Sewickley, PA

44 - Sawmill Run at Castle Shannon, PA

45 - Chartiers Creek near Bridgeville, PA

46 - Chartiers Creek at Crafton, PA

47 - Lowries Run 1000 ft above Mouth at Ben Avon, PA

48 - Montour Run at Coraopolis, PA

Sewer outfall locations from Timothy Prevost, Allegheny

County Sanitary Authority, written commun., 2002

0 5 10 MILES

0 5 10 KILOMETERS

0 2 4 MILES

0 2 4 KILOMETERS

Lowries Run

Montour Run

Robinson Run

Chartiers Creek

Sawmill Run

EXPLANATION

Allegheny County study-area boundary

River or selected tributary

Sewer outfall

Monitoring location

Direction of flow

ALLEGHENY COUNTY

Figure 5. Location of sampling sites and combined sewer overflow locations on the Ohio River, Allegheny County, Pennsylvania.
Networks 9

Table 2. Streamflow statistics in cubic feet per second at streamgaging stations on the Allegheny, Monongahela, and Ohio Rivers, 

Allegheny County, Pennsylvania, October 1, 1968, to September 30, 2004.

[USGS, U.S. Geological Survey; 7Q10, annual 7-day, 10-year low-flow event; Recreational, May 1 to September 30; Non-recreational, October 1 to 

April 30]

USGS 

station 

number

USGS station name Season 7Q10 Median 

flow

Bankfull 

flow1

03049500 Allegheny River at Natrona, PA Recreational 2,660 7,750 75,400

03049500 Allegheny River at Natrona, PA Non-recreational 3,140 21,420 75,400

03075070 Monongahela River at Elizabeth, PA Recreational 688 2,870 61,160

03075070 Monongahela River at Elizabeth, PA Non-recreational 854 8,640 61,160

03085000 Monongahela River at Braddock, PA Recreational 1,660 4,550 74,650

03085000 Monongahela River at Braddock, PA Non-recreational 1,820 11,760 74,650

03086000 Ohio River at Sewickley, PA Recreational 4,600 12,690 128,500

03086000 Ohio River at Sewickley, PA Non-recreational 5,380 36,460 128,500

1

Bankfull flow refers to the 0.80 exceedance probability annual peak flow (1.25-year recurrence interval).
10 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

80°15' 80° 79°45'

40°30'

40°15'

PENNSYLVANIA

0 5 10 MILES

0 5 10 KILOMETERS

County and Pittsburgh boundary from U.S. Geological Survey digital 

data, 1983, 1:100,000, Municipality and lock and dam locations from 

U.S. Geological Survey Digital Raster Graphic, 2005, 1:24,000

Bridgeville

Bethel Park

Sewickley

Elizabeth

Braddock

Natrona Heights

Wexford

EXPLANATION

City of Pittsburgh

Allegheny County study-area boundary

River

Allegheny County Sanitary Authority sewer 

service area

3 Rivers Wet Weather rain gage network

Municipality Location of study area

ALLEGHENY COUNTY

Figure 6. Location of precipitation stations near the Allegheny, Monongahela, and Ohio Rivers, Allegheny County, Pennsylvania.
Methods 11

target flow conditions in the receiving waters for a given storm 

event. The criteria used to designate wet- and dry-weather 

events are described below.

Wet-Weather Sampling Event Criteria

The two types of wet-weather event criteria are:

Type A

• No precipitation (rainfall) greater than 0.1 inches (in.) 

in the local watershed for 48 hours followed by a 

minimum of approximately 0.3 in. of rainfall (spatially 

averaged) over a 24-hour period along the Allegheny, 

Monongahela, or Ohio River. (Attempts were made 

to capture a range of precipitation greater than 0.3 in. 

over a 24-hour event period.)

• CSO source streams such as outfalls and tributaries 

discharging into the Allegheny, Monongahela, or Ohio 

River are generally active.

• CSO source streams discharging into tributary streams 

are generally active. 

When applicable, additional samples were collected from 

main-stem rivers on days 1, 3, and 5 following the precipitation event to evaluate bacteria die-off; because of the short 

duration of the discharge hydrograph and variations in CSO 

loading, no attempts were made to assess die-off in tributaries 

following a precipitation event. 

Type B

Receiving-water sampling and monitoring data also were 

collected during extended wet-weather events. The criteria 

are consistent with guidance for initiating monitoring of 

wet-weather events as described in the EPA Combined Sewer 

Overflows Guidance for Monitoring and Modeling (U.S. Environmental Protection Agency, 1999). 

The criteria that were used to define an extended wetweather sampling event (Type B) are similar to those for a 

wet-weather type A sampling event, with the exception that 

the 0.3 in. of rainfall may occur over a 72-hour period instead 

of only a 24-hour period. The specific criteria were—

• No precipitation greater than 0.1 in. in the local 

watershed for 48 hours followed by a minimum of 

approximately 0.3 in. of rainfall (spatially averaged) 

over a 24- to 72-hour period along the corridor of the 

Allegheny, Monongahela, or Ohio River. (Attempts 

were made to capture a range of precipitation greater 

than 0.3 in. over a 24- to 72-hour event period)

• Sources discharging into the Allegheny, Monongahela, 

or Ohio River are generally active during one or more 

of the periods of precipitation.

• Sources discharging into tributary streams are generally active during one or more of the periods of 

precipitation.

When applicable, additional samples were collected from 

main-stem rivers on days 1, 3, and 5 following the precipitation event to evaluate bacteria die-off.

Dry-Weather Sampling Event Criteria

The criteria used to define suitable dry-weather sampling 

events on the Three Rivers and tributaries follow those of 

ORSANCO (Ohio River Valley Water Sanitation Commission, 

2006):

• ALCOSAN wet well, a control structure regulating 

flows at the wastewater-treatment plant, is operating 

under normal conditions.

• No precipitation greater than 0.1 in. in the local watershed 72 hours before a sampling event (determined 

from data obtained from the 3RWW rain-gage network 

at www.3riverswetweather.org).

Dry-weather conditions had to prevail throughout the 

sampling event. If rain began after some dry-weather samples 

had been collected, the field program manager determined 

whether the samples that had already been collected would be 

discarded or analyzed.

Methods

Streamflow was measured and water-quality samples 

were collected in accordance with USGS methods or an 

equivalent. Discharge measurements were made with a current 

meter or acoustic Doppler current profiler (ADCP) described 

by Turnipseed and Sauer (2010); Rantz and others (1982); 

Craig (1983); and Carter and Davidian (1968) and the USGS 

Office of Surface Water Hydroacoustics Web page, available at 

http://il.water.usgs.gov/adcp/ (U.S. Geological Survey, 2014). 

Water-quality samples were collected in accordance with the 

USGS National Field Manual for the Collection of WaterQuality Data (U.S. Geological Survey, 1997 to present). Statistical analyses described in detail below were used to compare 

data and test for trends. 

Streamflow Measurement, Water-Quality 

Sampling, and Laboratory Analyses

Streamflows at the time of water-quality sampling were 

estimated from continuous-record streamgages or on the basis 

of ACDP streamflow measurements in accordance with the 

methods described by Oberg and others (2005). Streamflow 

and corresponding stage were measured at low, medium, and 

high stages to facilitate streamflow estimation at any given 
12 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

stage. With the exception of Turtle Creek at East Pittsburgh 

(for which flow was estimated by adding streamflow at 

Thompson Run at Turtle Creek and streamflow at Turtle Creek 

at Wilmerding, then applying a correction factor for the small, 

ungaged portion of Turtle Creek between Wilmerding and East 

Pittsburgh), streamflow was measured at streamgaging stations (table 1) or was estimated where water-quality samples 

were collected. Stage-discharge relations were developed at 

streamgaging stations on selected tributaries and the Ohio 

River at Sewickley by using standardized techniques described 

in Rantz (1982).

Depending on the site (main-stem river, tributary, receptor) and conditions at the time of sampling, either equal-discharge-increment (EDI), equal-width-increment (EWI), single 

vertical (SV), or grab sampling was used to collect water-quality samples. The degree of mixing was an important consideration in establishing sampling locations. Under conditions 

of poor mixing, point discharges such as a tributary in which 

bacteria concentrations are elevated may be strongly deflected 

by the receiving water and “hug” the side of the receivingwater channel. The velocity distribution from bank to bank 

was reviewed to establish appropriate EDI sample centroids 

that were composited to produce the EDI sample characteristic 

of the transect. During each event, three samples were collected at the main-stem sites: one characteristic of the channel 

cross-section (EDI or EWI sample), and one grab sample near 

each bank at each section (approximately 20 feet from shore 

at a depth of 18 in.). EDI samples provide an advantage over 

conventional grab samples in that they represent an integrated, 

discharge-weighted sample. As a result, the concentration can 

be used in conjunction with the flow rate measured at the section to determine the load at the time of sampling. At tributary 

sites, one depth-integrated EWI sample was collected; at 

receptor sites, one depth-integrated SV sample was collected 

immediately upstream from the selected receptor.

When possible, hydrographs were reviewed for each 

site, and samples were collected to coincide with a point on 

the rising limb, at peak flow, and on the falling limb of the 

hydrograph. Main-stem river flows are regulated and generally respond slowly to wet-weather events, except in instances 

when they are influenced by power generation. As a result 

of regulation, main-stem sites were sampled the day following a wet-weather event. Urban streams, in contrast, respond 

quickly to runoff events. In 2007, the water-quality sampling 

design was modified in an attempt to capture these variations 

in stage by sampling the day of the storm.

Water samples were collected using methodologies consistent with those referenced in the USGS National Field Manual for the Collection of Water-Quality Data (U.S. Geological 

Survey, 1997 to present) or an equivalent. Water temperature, 

pH, specific conductance, dissolved-oxygen concentration, and 

turbidity were measured in the field using a YSI 6920 multiparameter water-quality sonde.

During sampling, aseptic techniques, sterile containers, 

and equipment were maintained. Water samples to be analyzed 

for fecal-indicator bacteria were packed in ice and transported 

within the 6-hour hold time for analysis as required by the 

USGS (U.S. Geological Survey, 1997 to present) and the EPA 

(U.S. Environmental Protection Agency, 1999). Concentrations of fecal-indicator bacteria were determined at Microbac 

Laboratories, Warrendale, Pa., by using membrane-filtration 

techniques for approved methods to determine bacteriological enumeration. Concentrations of FC bacteria were determined by using procedures described in Standard Methods 

for the Examination of Water and Wastewater (American 

Public Health Association and others, 1998, p. 9–63 to 9–65). 

Concentrations of enterococci bacteria were determined by 

using standard methods described in American Public Health 

Association and others (1998, p. 9–76 to 9–78). The method 

used for E. coli bacteria (Method 1103.1 using mTEC Agar) 

was that of the EPA (U.S. Environmental Protection Agency, 

2000, p. 24–35).

Statistical Analyses

Nonparametric correlation analysis was used to screen 

for significant associations among indicator bacteria concentrations and the field characteristics of streamflow, water 

temperature, pH, specific conductance, dissolved-oxygen 

concentration, and turbidity. Significant associations were used 

to identify those water-quality characteristics that could be 

useful as potential explanatory variables in additional statistical analyses. Although other parameters may provide valuable 

information, we chose to review fecal-indicator bacteria and 

field parameters. The reasons for this approach are many; 

however, we wanted to conduct a retrospective study based on 

data from the initial 2001 CSO project, which did not include 

many of the supplemental parameters available after 2006 

(Buckwalter and others, 2006). Spearman’s rho, a measure of 

monotonic association computed on the ranks of data (Helsel, 

2005), was used for the analysis. Because rho cannot be computed directly for data with multiple censoring limits, the presence of multiple-censored bacteria data required recoding of 

values less than the highest detection limit to censored values 

at the highest detection limit (less than [<] 10 col/100 mL). 

Because the large sample approximation used to compute 

p-values does not fit the Spearman test statistic for small 

sample sizes (Helsel and Hirsch, 1992), only sites with 25 or 

more data values underwent correlation analysis. Significance 

of correlations was evaluated at the 95-percent confidence 

level (alpha = 0.05).

The paired Prentice Wilcoxon (PPW) test was applied 

to determine whether differences were present among data 

obtained from left-bank, right-bank, and composite samples at 

a given river location. The presence or absence of significant 

differences among the three sample types provided information about the representativeness of each type with regard to 

the mean water quality in the cross section and about possible 

elevated bacteria concentrations downstream from tributary 

and outfall locations. The PPW test is a nonparametric pairedsample test suitable for use with data with multiple censoring 
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 13

limits (Helsel, 2005). E. coli and FC counts from six Three 

Rivers and eight tributary sites were grouped by dry- and wetweather conditions and tested for differences across sampling 

locations. Enterococci were not included as no additional 

enterococci concentration data had been collected since Buckwalter and others (2006) reported on sampling-location differences. A minimum dataset size of 12 samples was enforced to 

minimize p-value errors resulting from large-sample approximation. Censoring levels for E. coli and FC were less than 

< 5 and < 10 col/100 mL. The significance level was set at 

95 percent (alpha = 0.05).

The Seasonal Kendall trend test was used to estimate 

changes in E. coli and FC concentrations during the 2001–09 

study period. Two versions of the Seasonal Kendall trend test 

are available in the program ESTREND (Schertz and others, 

1991). One version accommodates multiple-censored data 

but does not accommodate flow adjustment of the data. This 

version was preferred because of the presence of multiple 

censoring levels in the data, but it imposes more constraints 

on the size and distribution of the dataset than the second version. These constraints resulted in all sites being identified as 

having insufficient data. The second version of the test permits 

flow adjustment but has conditions that limit censoring to one 

level and to about 5 percent of the data. Flow adjustment is 

desirable if bacteria concentrations have an identifiable relation to the magnitude of streamflow and if the streamflows 

concurrent with sample collection have tended to increase or 

decrease over the study period. A log-log linear model was 

selected to flow-adjust E. coli and FC concentrations. The 

model consists of a linear regression applied to the relation 

between the logarithms of E. coli and FC concentrations and 

the logarithm of streamflow. Residuals from the model are 

tested for trends over time. The residuals were tested for trend 

only if the flow-adjustment model was statistically significant. 

A single season, the May through October recreational period, 

was defined. Trend significance was evaluated at the 95-percent confidence level.

Logistic regression was used to determine whether 

the probability of bacteria concentrations in water samples 

exceeding the recreational standards changed over the sampling period. The standards were 235 col/100 mL for E. coli

and 400 col/100 mL for FC. For this study, logistic regression 

was used to model the probability of exceeding recreational 

standards as a function of the effects of explanatory variables 

(Helsel, 2005). Multiple-censored data are permissible. Time, 

streamflow, and turbidity were the modeled explanatory 

variables. The hypothesis that the probability of exceeding 

recreational bacteria standards has changed over time is supported if time is determined to be a significant explanatory 

variable. Streamflow and turbidity were included on the basis 

of the results of correlation analysis. They were shown to have 

the strongest and most consistent associations with bacteria 

concentrations over the study period. Restrictions on the size 

of the dataset used for logistic regression limited analysis 

to the five Three Rivers main-stem sites where composite, 

right-bank, and left-bank samples could be included in the test 

dataset to ensure a sufficient number of samples. The generally 

no-significant-difference outcomes of the PPW test for locational differences were considered sufficient justification to 

include right- and left-bank samples with composite samples 

in the test dataset without introducing bias in the analysis. 

Trends in enterococci concentrations were not determined as a 

result of insufficient data.

Occurrence and Trends in 

Concentrations of Fecal-Indicator 

Bacteria in Streamflow

The range in daily streamflow at the main-stem stations 

during 2001–09 is shown in figure 7. Summary statistics for 

streamflow at each of the continuous-record stations are given 

in table 3.

Occurrence of Fecal-Indicator Bacteria

From July 2001 to October 2009, 1,742 water samples 

were collected at 52 sites in the Three Rivers and selected 

tributaries for this study. Analytical results for bacteria 

concentrations and associated field characteristics for those 

samples are summarized in table 4 (at end of report). Quantifiable concentrations of E.coli bacteria were detected in 1,667 

(97.0 percent) of 1,719 samples, and the EPA recreational 

water-quality criterion of 235 col/100 mL was exceeded in 

853 samples (49.6 percent). FC bacteria concentrations were 

quantified in 1,693 (98.8 percent) of 1,713 samples, and the 

Commonwealth of Pennsylvania water contact criterion of 

400 col/100 mL was exceeded in 780 samples (45.5 percent). 

Enterococci bacteria concentrations were quantifiable in 912 

(87.5 percent) of 1,042 samples, and the EPA recreational 

water-quality criterion of 61 col/100 mL was exceeded in 

483 samples (46.4 percent). The median percentage of samples 

in which recreational water-quality standards were exceeded 

across all sites from which five or more samples were analyzed was 48 for E. coli, 43 for FC, and 75 for enterococci.

Allegheny River Basin

Significant differences in composite, left-bank, and rightbank samples from the Allegheny River reported by Buckwalter and others (2006) continued to be observed with the addition of the 2006–09 data and the increase in the confidence 

level from 90 to 95 percent (table 5). E. coli and FC bacteria 

concentrations were higher in wet-weather samples collected 

on the left and right banks than in composite samples at the 

Oakmont site. Median wet-weather E. coli concentrations for 

left-bank, right-bank, and composite samples were 57, 135, 

and 22 col/100 mL, respectively; however, FC concentrations 

in samples collected on the left bank and composite samples 

were not significantly different. Median wet-weather FC 
14 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 3. U.S. Geological Survey streamgage statistics for the period of sampling October 1, 2001, to September 30, 2009, in the 

Allegheny, Monongahela, and Ohio Rivers, Allegheny County, Pennsylvania.

[USGS, U.S. Geological Survey; min, minimum; max, maximum; shaded stations are wire-weight gages; ft3/s, cubic feet per second]

USGS station name

USGS 

station 

number

Period of 

sampling

Instantaneous min 

discharge

(ft3/s)

Instantaneous max 

discharge

(ft3/s)

Mean 

discharge

(ft3/s)

Median 

discharge

(ft3/s)

Allegheny River Basin

Allegheny River at Natrona, PA 03049500 Oct 2001–Sep 2009 1,490 184,970 20,700 15,760

Deer Creek near Dorseyville, PA 03049646 June 2006–Nov 2009 0 1,347 36 18

Plum Creek at Milltown, PA 03049658 Jun 2006–Oct 2009 0.04 807 23 14

Squaw Run at Old Freeport Road near Blawnox, PA 03049676 Oct 2007–Sep 2009 0.1 725 9 4.2

Girtys Run above Grant Avenue at Millvale, PA 03049819 Jun 2006–Sep 2009 0.59 975 14 5.2

Pine Creek at Grant Avenue at Etna, PA 03049807 Jun 2006–Sep 2009 1.9 2,226 84 48

Monongahela River Basin

Monongahela River at Elizabeth, PA 03075070 Oct 2001–Sep 2009 180 121,080 9,755 6,025

Youghiogheny River at Sutersville, PA 03083500 Oct 2001–Sep 2009 485 46,370 3,381 2,120

Thompson Run at Turtle Creek, PA 03084800 May 2004–Sep 2009 1 5,283 22 16

Turtle Creek at Wilmerding, PA 03084698 Aug 2004–Sep 2009 13 10,051 191 109

Monongahela River at Braddock, PA 03085000 Oct 2001–Sep 2009 887 142,193 14,288 9,373

Ohio River Basin

Ninemile near Swissvale, PA 03085049 Jun 2006–Sep 2009 0.11 1,274 3.3 1.7

Sawmill Run at Duquesne Heights nr Pittsburgh, PA 03085213 Apr 2004–Sep 2009 1.2 6,535 19 8

Chartiers Creek at Carnegie, PA 03085500 Oct 2001–Sep 2009 37 27,400 324 200

Lowries Run at Camp Horne near Emsworth, PA 03085947 Jun 2006–Sep 2009 0.5 4,902 16 7.7

Montour Run at Scott Station near Imperial, PA 03085956 Oct 2001–Sep 2009 1.8 8,284 34 16

Ohio River at Sewickley, PA 03086000 Oct 2001–Sep 2009 1,582 313,931 35,870 26,078

Sawmill Run at Castle Shannon, PA 03085160 Mar 2004–Nov 2009 0.11 143 7.5 0.55

Chartiers Creek near Bridgeville, PA 03085290 Mar 2004–Nov 2009 24 11,200 685 114

Thompson Run at Gascola, PA 03084750 Mar 2004–Nov 2009 0.83 162 19 7.3

Streets Run at Hays, PA 03085100 June 2006–Nov 2009 1.04 11 4.2 2.6

Turtle Creek at Trafford, PA 03084400 Mar 2004–Nov 2009 6.3 1,120 123 51
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 15

0

20,000

40,000

60,000

80,000

10,000

Allegheny River Monongahela 

River

Ohio River

Discharge, in cubic feet per second

Outlier

Discharge

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

Figure 7. Streamflow statistics for U.S. Geological Survey streamgaging stations on the Allegheny, Monongahela, and Ohio Rivers, 

Allegheny County, Pennsylvania, during dry- and wet-weather events, October 1, 2001, to September 30, 2009.

Table 5. Results of generalized Wilcoxon paired sample tests of sampling-location difference in concentrations of fecal-indicator 

bacteria and turbidity in dry- and wet-weather samples from five sampling locations on the Allegheny, Monongahela, and Ohio Rivers, 

Allegheny County, Pennsylvania, 2001–09.

[n, number of samples; LB, left stream bank looking downstream; RB, right stream bank looking downstream; Comp, composite; 

>, greater than; ns, not significant at the 95-percent confidence level (p-value < 0.05)]

Number of samples 

and comparison 

tested

Allegheny River Monongahela River Ohio River

Oakmont 9th Street Bridge McKeesport Pittsburgh Sewickley Bridge

Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet

Eschericia coli

n 21 30 24 36 13 12 25 36 21 31

LB-Comp ns 0.0075 ns ns 0.0423 ns ns ns ns ns

RB-Comp ns 0.0001 ns ns ns ns ns ns 0.0052 ns

LB-RB ns 0.0101 ns ns ns ns ns ns ns ns

Fecal coliform

n 21 30 23 36 13 12 24 35 21 31

LB-Comp ns ns ns ns ns ns ns ns ns ns

RB-Comp ns 0.0073 ns ns ns ns ns ns 0.0052 ns

LB-RB ns ns ns ns ns ns ns ns ns ns

Turbidity

n 18 28 22 33 12 12 23 31 18 29

LB-Comp ns ns ns 0.0012 ns ns ns 0.0337 ns ns

RB-Comp ns ns ns 0.0025 ns ns ns ns ns ns

LB-RB ns ns ns ns ns ns ns ns ns ns
16 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

concentrations in right-bank and composite samples were 188 

and 82 col/100 mL, respectively. Turbidity was significantly 

higher in composite wet-weather samples from the 9th Street 

Bridge sampling location than in left- or right-bank samples. 

Median differences were small (< 2 Nephelometric Turbidity Units [NTUs]) and indicate that median turbidity was 

20 percent lower in left- and right-bank samples than in the 

composite samples from the 9th Street Bridge location, where 

the median turbidity was lowest (7.2 NTUs) among all mainstem locations. Increasing the number of years of data used in 

the analysis increased the confidence levels associated with the 

significant differences, indicating that the conditions responsible for the locational differences, as discussed in Buckwalter 

and others (2006), persist.

Monongahela River Basin

Differences among bacteria concentrations in composite, left-bank, and right-bank samples from the Monongahela 

River changed little from those reported by Buckwalter and 

others (2006). Of the two significant differences found in this 

study (table 5), the higher turbidity values in wet-weather 

composite samples from Pittsburgh had been reported previously. A new finding was lower E. coli concentrations in 

dry-weather left-bank samples than in composite samples from 

the McKeesport station. Median concentrations in left-bank 

samples were about 60 percent of those in composite samples. 

Buckwalter and others (2006) discuss possible mechanisms for 

the differences.

Ohio River Basin

Several changes were observed in composite, left-bank, 

and right-bank sample differences for Ohio River sites compared to those found by Buckwalter and others (2006). They 

reported a significant difference between left- and right-bank 

dry-weather FC concentrations for the Ohio River at Sewickley site. Re-analysis at the 95-percent confidence level with 

additional data showed an insignificant difference between 

left- and right-bank FC concentrations (table 5); however, 

median left-bank FC concentrations remain about twice the 

right-bank counts. Also, differences between dry-weather 

right-bank and composite sample concentrations of E. coli and 

FC became significant with the addition of 2006–09 data.

Relations of Concentrations of Fecal-Indicator 

Bacteria to Other Water-Quality Parameters

The relations between FC concentrations and other 

water-quality parameters at main-stem and tributary sites are 

presented below.

Main-Stem Sites

Significant correlations between concentrations of fecalindicator bacteria and various field water-quality characteristics were found at all Three Rivers main-stem sites (tables 6, 

7, and 8) and nine tributary sites (tables 9 and 10). The strongest and most consistent correlations at the five Three Rivers 

sites were those between streamflow and dry-weather bacteria 

concentrations.

E. coli, FC, and enterococci concentrations at all Three 

Rivers sites showed significant positive correlations with 

streamflow (rho = 0.248–0.758). Wet-weather correlations 

were somewhat weaker (rho = 0.141–0.624) and were not significant at two sites. The constantly changing contributions of 

bacteria from a multitude of sources during wet weather likely 

result in a more variable relation to streamflow than during dry 

weather, yielding the lower correlation coefficients.

Turbidity also exhibited a significant positive correlation 

with bacteria concentration. With two exceptions, turbidity 

was significantly correlated with fecal-indicator bacteria concentrations during both dry- and wet-weather conditions. At 

the Monongahela River sites, the correlation between turbidity 

and bacteria concentration showed weather dependency but, 

unexpectedly, this dependency was not consistent given the 

proximity of the sites. Samples from the McKeesport station 

showed significant dry-weather correlations and poor wetweather correlations. The reverse was true for samples from 

Pittsburgh.

All significant correlations of pH and specific conductance with bacteria concentrations were negative. Buckwalter and others (2006) attribute the negative association with 

specific conductance to an inverse relation between streamflow and specific conductance. This relation results from the 

dilution of dissolved solids in base flow by increasing amounts 

of runoff from rainfall with low specific conductance.

Water temperature and dissolved-oxygen concentrations 

show a range of positive and negative correlations with respect 

to bacteria, depending on streamflow condition. For example, 

water temperature typically showed a weak negative correlation (-0.341 maximum) with bacteria concentration but weak 

positive correlations were found for the three bacteria types in 

wet-weather samples from the Allegheny River at 9th Street 

Bridge station and for enterococci in samples from the Ohio 

River at Sewickley station. No significant positive correlations were found by Buckwalter and others (2006); however, 

positive coefficients were reported in this study. Other than 

significance levels, little change in the pattern of water-temperature correlations was noted. Dissolved-oxygen concentration showed significant correlations only under wet-weather 

conditions. The correlations were negative, with rho less than 

0.464, except at the Ohio River at Sewickley station, where 
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 17

Table 6. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Allegheny River main-stem sites, Allegheny County, Pennsylvania, 2001–09.

[n, number of samples; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence level)]

03049652 Allegheny River at Oakmont, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.432 0.365 0.269 0.418 0.387 0.260 0.459 0.415 0.348

p-value <.0001 <.0001 0.0008 0.0007 0.0017 0.0392 <.0001 <.0001 0.0008

n 153 153 153 63 63 63 90 90 90

Water temperature -0.298 -0.257 -0.029 -0.325 -0.300 0.074 -0.219 -0.144 -0.009

p-value 0.0007 0.0037 0.7451 0.0120 0.0210 0.5764 0.0751 0.2437 0.9414

n 126 126 126 59 59 59 67 67 67

pH 0.001 -0.066 -0.161 0.207 0.222 -0.042 -0.128 -0.272 -0.272

p-value 0.9897 0.4160 0.0474 0.0925 0.0708 0.7376 0.2445 0.0118 0.0119

n 152 152 152 67 67 67 85 85 85

Specific conductance -0.290 -0.164 -0.138 -0.266 -0.070 -0.111 -0.325 -0.293 -0.249

p-value 0.0003 0.0421 0.0872 0.0297 0.5761 0.3729 0.0021 0.0058 0.0203

n 154 154 154 67 67 67 87 87 87

Dissolved oxygen -0.116 -0.030 0.092 -0.208 -0.018 0.076 -0.157 -0.226 0.003

p-value 0.2284 0.7578 0.3399 0.1308 0.8976 0.5847 0.2487 0.0944 0.9814

n 110 110 110 54 54 54 56 56 56

Turbidity 0.545 0.328 0.296 0.598 0.521 0.373 0.543 0.279 0.331

p-value <.0001 <.0001 0.0003 <.0001 <.0001 0.0042 <.0001 0.0088 0.0018

n 144 144 144 57 57 57 87 87 87

03049832 Allegheny River at 9th Street Bridge at Pittsburgh, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.262 0.203 0.309 0.482 0.404 0.487 0.133 0.073 0.207

p-value 0.0003 0.0055 <.0001 <.0001 0.0003 <.0001 0.1674 0.4480 0.0303

n 185 185 185 75 75 75 110 110 110

Water temperature -0.099 0.040 0.143 -0.432 -0.133 -0.120 0.189 0.226 0.298

p-value 0.1738 0.5833 0.0504 <.0001 0.2385 0.2893 0.0493 0.0181 0.0016

n 189 189 189 80 80 80 109 109 109

pH -0.190 -0.153 -0.239 -0.180 -0.045 -0.211 -0.187 -0.214 -0.259

p-value 0.0097 0.0378 0.0011 0.1142 0.6988 0.0631 0.0547 0.0276 0.0074

n 184 184 184 78 78 78 106 106 106

Specific conductance -0.140 0.050 -0.225 -0.273 0.060 -0.254 -0.138 -0.040 -0.263

p-value 0.0540 0.4897 0.0018 0.0138 0.5955 0.0223 0.1514 0.6775 0.0058

n 190 190 190 81 81 81 109 109 109

Dissolved oxygen -0.232 -0.251 -0.359 0.015 0.009 -0.220 -0.456 -0.436 -0.464

p-value 0.0028 0.0012 <.0001 0.8973 0.9382 0.0630 <.0001 <.0001 <.0001

n 163 163 163 72 72 72 91 91 91

Turbidity 0.349 0.242 0.131 0.477 0.209 0.322 0.266 0.248 0.019

p-value <.0001 0.0011 0.0833 <.0001 0.0744 0.0051 0.0066 0.0114 0.8462

n 177 177 177 74 74 74 103 103 103
18 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 7. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Monongahela River main-stem sites, Allegheny County, Pennsylvania, 2001–09.

[n, number of samples; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence level)]

03083903 Monongahela River at McKeesport, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.557 0.485 0.472 0.757 0.681 0.758 0.141 0.158 0.168

p-value <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 0.4105 0.3583 0.3271

n 66 66 66 30 30 30 36 36 36

Water temperature -0.513 -0.406 -0.341 -0.547 -0.426 -0.279 0.085 0.122 -0.110

p-value <.0001 0.0002 0.0022 0.0002 0.0049 0.0731 0.6215 0.4776 0.5243

n 78 78 78 42 42 42 36 36 36

pH -0.541 -0.449 -0.400 -0.578 -0.582 -0.559 -0.059 0.060 -0.044

p-value <.0001 <.0001 0.0002 <.0001 <.0001 <.0001 0.7335 0.7268 0.7972

n 81 81 81 45 45 45 36 36 36

Specific conductance -0.597 -0.496 -0.543 -0.712 -0.658 -0.570 -0.135 -0.014 -0.322

p-value <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 0.4328 0.9343 0.0552

n 81 81 81 45 45 45 36 36 36

Dissolved oxygen -0.069 -0.108 -0.200 -0.089 -0.165 -0.273 -0.297 -0.234 -0.359

p-value 0.5382 0.3364 0.0735 0.5618 0.2786 0.0692 0.0786 0.1698 0.0315

n 81 81 81 45 45 45 36 36 36

Turbidity 0.587 0.502 0.306 0.696 0.586 0.533 0.091 0.095 -0.132

p-value <.0001 <.0001 0.0062 <.0001 <.0001 0.0002 0.5984 0.5800 0.4429

n 79 79 79 43 43 43 36 36 36

03085150 Monongahela River at Pittsburgh, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.301 0.283 0.338 0.317 0.248 0.423 0.260 0.214 0.251

p-value <.0001 <.0001 <.0001 0.0057 0.0319 0.0002 0.0061 0.0245 0.0083

n 185 185 185 75 75 75 110 110 110

Water temperature -0.291 -0.140 -0.016 -0.401 -0.263 -0.062 -0.200 -0.017 -0.001

p-value <.0001 0.0568 0.8253 0.0002 0.0186 0.5875 0.0388 0.8632 0.9928

n 187 187 187 80 80 80 107 107 107

pH -0.320 -0.354 -0.232 -0.155 -0.182 -0.028 -0.385 -0.405 -0.301

p-value <.0001 <.0001 0.0014 0.1660 0.1031 0.8036 <.0001 <.0001 0.0018

n 186 186 186 81 81 81 105 105 105

Specific conductance -0.271 -0.254 -0.395 -0.082 -0.022 -0.178 -0.376 -0.366 -0.471

p-value 0.0002 0.0004 <.0001 0.4655 0.8438 0.1115 <.0001 <.0001 <.0001

n 189 189 189 81 81 81 108 108 108

Dissolved oxygen 0.072 0.005 -0.218 0.209 0.083 -0.164 -0.157 -0.183 -0.318

p-value 0.3617 0.9502 0.0054 0.0736 0.4832 0.1636 0.1462 0.0900 0.0027

n 161 161 161 74 74 74 87 87 87

Turbidity 0.353 0.246 0.232 0.180 0.085 0.068 0.521 0.407 0.379

p-value <.0001 0.0009 0.0018 0.1198 0.4673 0.5573 <.0001 <.0001 <.0001

n 178 178 178 76 76 76 102 102 102
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 19

Table 8. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Ohio River main-stem sites (Ohio River at Sewickley, PA), Allegheny County, Pennsylvania, 2001–09.

[n, number of samples; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence level)]

03085986 Ohio River at Sewickley Bridge at Sewickley, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.598 0.470 0.431 0.698 0.622 0.439 0.624 0.455 0.458

p-value <.0001 <.0001 <.0001 <.0001 <.0001 0.0003 <.0001 <.0001 <.0001

n 156 156 156 63 63 63 93 93 93

Water temperature -0.199 -0.001 0.267 -0.184 0.005 0.138 -0.341 -0.077 0.346

p-value 0.0207 0.9943 0.0018 0.1485 0.9709 0.2795 0.0034 0.5230 0.0029

n 135 135 135 63 63 63 72 72 72

pH 0.129 0.119 0.056 0.203 0.202 0.161 0.143 0.130 0.043

p-value 0.1038 0.1331 0.4802 0.0998 0.1018 0.1933 0.1703 0.2152 0.6828

n 160 160 160 67 67 67 93 93 93

Specific conductance -0.373 -0.280 -0.339 -0.553 -0.524 -0.287 -0.360 -0.242 -0.423

p-value <.0001 0.0003 <.0001 <.0001 <.0001 0.0185 0.0004 0.0193 <.0001

n 160 160 160 67 67 67 93 93 93

Dissolved oxygen 0.344 0.214 0.002 0.192 -0.072 -0.153 0.397 0.339 0.052

p-value 0.0004 0.0297 0.9855 0.1767 0.6162 0.2826 0.0036 0.0139 0.7144

n 103 103 103 51 51 51 52 52 52

Turbidity 0.600 0.589 0.537 0.669 0.770 0.592 0.589 0.526 0.530

p-value <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001

n 149 149 149 59 59 59 90 90 90

positive correlations for E. coli and FC were found. Buckwalter and others (2006) reported only negative correlations for 

water temperature but positive and negative correlations for 

dissolved-oxygen concentration, consistent with the current 

analysis. The significant positive and negative correlations for 

water temperature and dissolved-oxygen concentration were 

unexpected, and the reasons for this variability have not been 

established.

Tributary Sites

Correlations between bacteria concentrations and field 

water-quality characteristics at the tributary sites varied widely 

(tables 9 and 10). Tributaries in order of weakest to strongest 

correlations were Thompson Run, Turtle Creek, Sawmill Run, 

and Chartiers Creek. Because several of the tributary correlation datasets contain less than 25 values, these correlations 

should be interpreted with caution. At the two Thompson Run 

sites, few significant correlations and no favored weather pattern were found, except for turbidity in wet-weather samples 

from the Thompson Run at Turtle Creek station. The two 

Turtle Creek sites were similar to the Thompson Run sites in 

number and distribution of significant correlations.

Significant correlations for the Sawmill Run sites were 

limited to samples collected under wet-weather conditions, 

with one exception. Water temperature, specific conductance, 

dissolved-oxygen concentration, and turbidity correlations 

for wet-weather samples were significant, with rho ranging 

from 0.347 to 0.687 for Sawmill Run. Significant correlations 

at upstream and downstream sites were similar in magnitude, with the exception of the correlations of E. coli and FC 

concentrations to streamflow. Correlations of E. coli and FC 

concentrations to streamflow for samples from the Sawmill 

Run at Duquesne Heights station were the strongest correlations observed in the study. These findings are consistent with 

those of Buckwalter and others (2006) for the 2001–05 time 

period. In addition, median FC bacteria concentrations at the 

Duquesne Heights station were the highest measured during 

the study. High bacteria concentrations together with the high 

rho values indicate that water with a high bacteria content 

contributes a greater percentage of the streamflow volume at 

Duquesne Heights than at other sites. As noted for some of the 

main-stem site correlations, the correlations of wet-weather 

enterococci concentrations in wet-weather samples with water 

temperature, specific conductance, and dissolved-oxygen 

concentration reversed direction from positive to negative 
20 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 9. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Monongahela River Basin, Allegheny County, Pennsylvania, 2001–09.—Continued

[n, number of samples; nd, no data; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence 

level)]

03084400 Turtle Creek at Trafford, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.283 0.213 0.109 0.101 0.021 -0.450 0.117 -0.030 -0.027

p-value 0.1451 0.277 0.5794 0.7963 0.9572 0.2241 0.6342 0.9034 0.9141

n 28 28 28 9 9 9 19 19 19

Water temperature -0.015 0.090 -0.107 -0.357 -0.151 0.383 0.233 0.385 -0.035

p-value 0.9378 0.6406 0.5821 0.3454 0.6977 0.3089 0.3239 0.094 0.884

n 29 29 29 9 9 9 20 20 20

pH -0.159 -0.158 -0.193 -0.468 -0.468 0.081 0.054 0.059 -0.046

p-value 0.4026 0.4042 0.3061 0.1725 0.1725 0.8233 0.8196 0.8048 0.8482

n 30 30 30 10 10 10 20 20 20

Specific conductance -0.402 -0.369 -0.232 0.012 0.243 -0.038 -0.442 -0.381 -0.244

p-value 0.0278 0.0446 0.2177 0.9734 0.4984 0.918 0.0513 0.0977 0.3

n 30 30 30 10 10 10 20 20 20

Dissolved oxygen -0.554 -0.599 -0.179 -0.803 -0.720 -0.237 -0.409 -0.495 -0.159

p-value 0.0018 0.0006 0.3517 0.0091 0.0288 0.5387 0.073 0.0266 0.5026

n 29 29 29 9 9 9 20 20 20

Turbidity 0.409 0.336 0.494 -0.604 -0.588 0.100 0.521 0.407 0.534

p-value 0.0247 0.0693 0.0056 0.0646 0.0735 0.7827 0.0185 0.0749 0.0154

n 30 30 30 10 10 10 20 20 20

03084750 Thompson Run at Gascola, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.128 0.100 0.191 -0.383 -0.407 -0.504 0.185 0.140 0.227

p-value 0.5153 0.6142 0.3305 0.349 0.3167 0.2029 0.4344 0.5557 0.3354

n 28 28 28 8 8 8 20 20 20

Water temperature 0.219 0.253 -0.047 0.448 0.460 -0.110 0.235 0.294 0.018

p-value 0.2533 0.1859 0.8097 0.2268 0.2132 0.7781 0.3178 0.2076 0.9395

n 29 29 29 9 9 9 20 20 20

pH 0.201 0.133 -0.123 -0.071 -0.068 -0.799 0.225 0.175 0.102

p-value 0.295 0.4916 0.5253 0.8569 0.8612 0.0099 0.3392 0.4604 0.67

n 29 29 29 9 9 9 20 20 20

Specific conductance -0.790 -0.698 -0.224 -0.661 -0.656 0.247 -0.780 -0.721 -0.354

p-value <.0001 <.0001 0.2345 0.0375 0.0392 0.4911 <.0001 0.0003 0.1256

n 30 30 30 10 10 10 20 20 20

Dissolved oxygen -0.354 -0.322 0.097 -0.463 -0.305 -0.100 -0.296 -0.331 0.129

p-value 0.0592 0.089 0.6151 0.209 0.4246 0.7988 0.2046 0.1544 0.589

n 29 29 29 9 9 9 20 20 20

Turbidity 0.175 0.118 0.212 -0.113 -0.215 -0.135 0.193 0.149 0.258

p-value 0.346 0.5264 0.2519 0.7553 0.5513 0.7103 0.4024 0.5183 0.259

n 31 31 31 10 10 10 21 21 21
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 21

Table 9. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Monongahela River Basin, Allegheny County, Pennsylvania, 2001–09.—Continued

[n, number of samples; nd, no data; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence 

level)]

03084800 Thompson Run at Turtle Creek, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.296 0.105 -0.078 -0.212 -0.298 -0.914 0.335 0.205 0.135

p-value 0.1196 0.5887 0.6888 0.5563 0.4032 0.0002 0.1608 0.3992 0.5802

n 29 29 29 10 10 10 19 19 19

Water temperature -0.083 -0.073 -0.163 0.092 0.159 -0.151 -0.038 -0.064 -0.091

p-value 0.6689 0.7064 0.3969 0.8138 0.6828 0.6977 0.875 0.7889 0.7013

n 29 29 29 9 9 9 20 20 20

pH -0.007 0.065 -0.066 -0.177 -0.239 -0.438 0.124 0.245 0.165

p-value 0.9701 0.7345 0.7302 0.625 0.5069 0.2052 0.6035 0.2969 0.4867

n 30 30 30 10 10 10 20 20 20

Specific conductance -0.479 -0.332 -0.248 -0.212 -0.049 -0.448 -0.532 -0.372 -0.232

p-value 0.0074 0.0731 0.1872 0.5563 0.8939 0.1943 0.0157 0.106 0.3239

n 30 30 30 10 10 10 20 20 20

Dissolved oxygen 0.028 -0.021 -0.001 -0.353 -0.445 -0.684 0.156 0.109 0.144

p-value 0.8869 0.912 0.9954 0.3515 0.2296 0.0424 0.5115 0.6488 0.5438

n 29 29 29 9 9 9 20 20 20

Turbidity 0.414 0.345 0.308 0.017 -0.433 -0.374 0.436 0.469 0.445

p-value 0.0228 0.0615 0.0975 0.9659 0.2446 0.3215 0.0484 0.032 0.0433

n 30 30 30 9 9 9 21 21 21

03084808 Turtle Creek at East Pittsburgh, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.439 0.300 0.412 -0.632 0.000 -0.600 0.484 0.383 0.400

p-value 0.0409 0.1752 0.0565 0.3675 1 0.4 0.0418 0.1168 0.1004

n 22 22 22 4 4 4 18 18 18

Water temperature -0.354 -0.429 -0.555 0.396 -0.718 -0.613 -0.299 -0.255 -0.387

p-value 0.0702 0.0257 0.0027 0.3786 0.0691 0.1436 0.1999 0.2779 0.0916

n 27 27 27 7 7 7 20 20 20

pH -0.060 -0.131 -0.311 0.000 -0.355 -0.695 -0.063 -0.109 -0.230

p-value 0.7613 0.5063 0.107 1 0.3876 0.0559 0.7908 0.6486 0.3298

n 28 28 28 8 8 8 20 20 20

Specific conductance -0.492 -0.390 -0.434 0.323 0.778 0.286 -0.451 -0.349 -0.344

p-value 0.0079 0.0401 0.0209 0.4346 0.0229 0.4927 0.0458 0.1314 0.1379

n 28 28 28 8 8 8 20 20 20

Dissolved oxygen -0.125 -0.187 -0.107 -0.036 -0.432 -0.714 0.032 -0.055 -0.010

p-value 0.5423 0.3592 0.6025 0.9394 0.3325 0.0713 0.8979 0.8221 0.9687

n 26 26 26 7 7 7 19 19 19

Turbidity 0.594 0.713 0.647 -0.151 0.693 0.719 0.579 0.530 0.607

p-value 0.0007 <.0001 0.0002 0.7219 0.0568 0.0446 0.0059 0.0135 0.0035

n 29 29 29 8 8 8 21 21 21
22 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 10. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Ohio River Basin, Allegheny County, Pennsylvania, 2001–09.—Continued

[n, number of samples; nd, no data; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence 

level)]

03085160 Sawmill Run at Castle Shannon, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.562 0.401 0.413 0.367 0.293 0.096 0.286 0.137 0.271

p-value 0.0005 0.0187 0.0153 0.3317 0.4444 0.8064 0.1651 0.5137 0.1893

n 34 34 34 9 9 9 25 25 25

Water temperature -0.086 -0.025 0.170 -0.123 -0.053 0.218 0.328 0.452 0.466

p-value 0.5991 0.8803 0.2954 0.7043 0.871 0.4971 0.0879 0.0158 0.0124

n 40 40 40 12 12 12 28 28 28

pH -0.634 -0.404 -0.336 -0.368 -0.288 -0.146 -0.456 -0.101 -0.176

p-value <.0001 0.0107 0.0363 0.2657 0.3904 0.6686 0.0147 0.6084 0.3699

n 39 39 39 11 11 11 28 28 28

Specific conductance -0.140 -0.286 -0.227 0.049 0.144 0.121 -0.490 -0.762 -0.546

p-value 0.3964 0.0772 0.1644 0.8799 0.6561 0.7079 0.0094 <.0001 0.0032

n 39 39 39 12 12 12 27 27 27

Dissolved oxygen -0.239 -0.240 -0.277 -0.518 -0.442 -0.043 -0.455 -0.479 -0.475

p-value 0.1374 0.1353 0.0833 0.0842 0.1501 0.895 0.015 0.0099 0.0107

n 40 40 40 12 12 12 28 28 28

Turbidity 0.603 0.591 0.398 0.342 0.306 0.124 0.587 0.587 0.356

p-value <.0001 0.0001 0.0148 0.3037 0.3602 0.7161 0.0016 0.0016 0.0742

n 37 37 37 11 11 11 26 26 26

03085213 Sawmill Run at Duquesne Heights near Pittsburgh, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.808 0.821 0.069 0.240 0.331 0.037 0.814 0.818 0.066

p-value <.0001 <.0001 0.6141 0.4777 0.32 0.9145 <.0001 <.0001 0.6663

n 56 56 56 11 11 11 45 45 45

Water temperature 0.270 0.326 -0.451 0.400 0.423 0.074 0.347 0.429 -0.489

p-value 0.0426 0.0133 0.0004 0.1976 0.1703 0.819 0.0197 0.0033 0.0007

n 57 57 57 12 12 12 45 45 45

pH -0.272 -0.204 -0.049 0.116 0.270 0.604 -0.138 -0.107 -0.143

p-value 0.0409 0.1274 0.7193 0.7189 0.3964 0.0374 0.3674 0.486 0.3471

n 57 57 57 12 12 12 45 45 45

Specific conductance -0.463 -0.526 0.391 -0.322 -0.500 -0.077 -0.382 -0.465 0.491

p-value 0.0003 <.0001 0.0029 0.307 0.0978 0.8109 0.0106 0.0015 0.0007

n 56 56 56 12 12 12 44 44 44

Dissolved oxygen -0.365 -0.383 0.493 -0.203 -0.373 0.190 -0.351 -0.392 0.553

p-value 0.0053 0.0033 <.0001 0.5266 0.2321 0.5539 0.0181 0.0078 <.0001

n 57 57 57 12 12 12 45 45 45

Turbidity 0.743 0.716 -0.154 -0.078 -0.189 -0.037 0.684 0.687 -0.230

p-value <.0001 <.0001 0.2664 0.8205 0.5788 0.9151 <.0001 <.0001 0.1378

n 54 54 54 11 11 11 43 43 43
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 23

Table 10. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Ohio River Basin, Allegheny County, Pennsylvania, 2001–09.—Continued

[n, number of samples; nd, no data; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence 

level)]

03085290 Chartiers Creek near Bridgeville, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.788 0.833 0.739 -0.116 0.211 0.267 0.771 0.803 0.711

p-value <.0001 <.0001 <.0001 0.7206 0.5106 0.4016 <.0001 <.0001 <.0001

n 44 44 44 12 12 12 32 32 32

Water temperature -0.068 -0.119 0.024 0.804 0.613 0.314 0.216 0.148 0.303

p-value 0.6646 0.4463 0.8809 0.0016 0.0342 0.3206 0.2424 0.4254 0.0979

n 43 43 43 12 12 12 31 31 31

pH -0.575 -0.542 -0.434 0.470 0.246 0.201 -0.679 -0.601 -0.469

p-value <.0001 0.0001 0.0032 0.1234 0.4417 0.5301 <.0001 0.0003 0.0067

n 44 44 44 12 12 12 32 32 32

Specific conductance -0.760 -0.829 -0.732 0.550 0.239 0.050 -0.731 -0.802 -0.697

p-value <.0001 <.0001 <.0001 0.064 0.4544 0.8778 <.0001 <.0001 <.0001

n 43 43 43 12 12 12 31 31 31

Dissolved oxygen -0.092 -0.038 -0.188 -0.413 -0.265 -0.446 -0.192 -0.135 -0.275

p-value 0.5506 0.8077 0.2222 0.1821 0.406 0.1457 0.2921 0.4607 0.1277

n 44 44 44 12 12 12 32 32 32

Turbidity 0.845 0.808 0.723 0.556 0.224 0.046 0.787 0.792 0.758

p-value <.0001 <.0001 <.0001 0.0758 0.5084 0.8935 <.0001 <.0001 <.0001

n 40 40 40 11 11 11 29 29 29

03085500 Chartiers Creek at Carnegie, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow 0.650 0.605 0.694 -0.385 -0.405 0.185 0.612 0.596 0.562

p-value <.0001 <.0001 <.0001 0.0358 0.0264 0.3274 <.0001 <.0001 <.0001

n 109 109 109 30 30 30 79 79 79

Water temperature -0.093 -0.066 0.104 0.379 0.125 0.339 0.010 0.051 0.267

p-value 0.3391 0.4989 0.2862 0.0391 0.5106 0.0671 0.9293 0.6579 0.0181

n 108 108 108 30 30 30 78 78 78

pH -0.075 -0.046 -0.194 0.389 0.484 0.218 -0.158 -0.157 -0.204

p-value 0.4376 0.6353 0.0443 0.0334 0.0068 0.2477 0.1661 0.1686 0.0728

n 108 108 108 30 30 30 78 78 78

Specific conductance -0.666 -0.679 -0.666 -0.001 -0.203 0.242 -0.673 -0.656 -0.659

p-value <.0001 <.0001 <.0001 0.9972 0.2823 0.1967 <.0001 <.0001 <.0001

n 108 108 108 30 30 30 78 78 78

Dissolved oxygen -0.062 -0.102 -0.219 -0.230 -0.171 -0.611 -0.294 -0.326 -0.410

p-value 0.5378 0.3066 0.0269 0.2206 0.3669 0.0003 0.0123 0.0052 0.0003

n 102 102 102 30 30 30 72 72 72

Turbidity 0.561 0.592 0.727 -0.596 -0.522 0.087 0.583 0.627 0.691

p-value <.0001 <.0001 <.0001 0.0071 0.022 0.7246 <.0001 <.0001 <.0001

n 90 90 90 19 19 19 71 71 71
24 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 10. Results of Spearman’s rho correlations between concentrations of fecal-indicator bacteria and field water-quality 

characteristics, Ohio River Basin, Allegheny County, Pennsylvania, 2001–09.—Continued

[n, number of samples; nd, no data; p-value, probability; <, less than; bold type indicates p-values of 0.05 or less (significance at the 95-percent confidence 

level)]

03085550 Chartiers Creek at Crafton, PA

All conditions Dry weather Wet weather

Eschericia 

coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci Eschericia coli

Fecal 

coliform Enterococci

Streamflow -0.035 -0.523 nd -0.500 0.500 nd -0.009 -0.519 nd

p-value 0.9132 0.081 nd 0.6667 0.6667 nd 0.9827 0.152 nd

n 12 12 12 3 3 3 9 9 9

Water temperature 0.251 0.055 0.559 -0.311 -0.587 0.238 0.230 -0.032 0.606

p-value 0.1893 0.7785 0.0016 0.416 0.0969 0.5376 0.3303 0.8932 0.0046

n 29 29 29 9 9 9 20 20 20

pH 0.015 0.129 0.001 -0.741 0.094 -0.430 -0.201 -0.299 -0.096

p-value 0.9395 0.5059 0.9947 0.0225 0.8106 0.2475 0.3958 0.2006 0.6876

n 29 29 29 9 9 9 20 20 20

Specific conductance -0.590 -0.639 -0.391 -0.311 -0.587 0.238 -0.616 -0.377 -0.655

p-value 0.0008 0.0002 0.0359 0.416 0.0969 0.5376 0.0038 0.1011 0.0017

n 29 29 29 9 9 9 20 20 20

Dissolved oxygen -0.309 -0.116 -0.635 0.356 0.390 -0.061 -0.675 -0.423 -0.801

p-value 0.1025 0.5478 0.0002 0.3471 0.2996 0.8769 0.0011 0.063 <.0001

n 29 29 29 9 9 9 20 20 20

Turbidity 0.607 0.854 0.386 0.857 0.536 0.090 0.517 0.851 0.261

p-value 0.0006 <.0001 0.0423 0.0137 0.2152 0.8477 0.0165 <.0001 0.2523

n 28 28 28 7 7 7 21 21 21

between the upstream Castle Shannon site and the downstream 

Duquesne Heights site on Sawmill Run. Although significant, 

these correlations cannot be explained with existing data 

because of the sign reversal.

Bacteria concentrations at the Chartiers Creek sites also 

showed significant correlations with most of the field characteristics under wet-weather conditions. Significant correlations in dry-weather samples were limited to two each for the 

Bridgeville and Crafton sites and eight for the Chartiers Creek 

at Carnegie station. Change in the sign of the correlation was 

evident for several of the dry-weather sample correlations. 

The small dataset sizes likely contributed to this inconsistency. 

Unlike those for samples from Sawmill Run, values of rho

for samples from Chartiers Creek generally decreased from 

the upstream to the downstream sites, although the small 

dataset size for Chartiers Creek at Crafton, Pa. (USGS station 

03085550) should be noted. 

The results of correlation analysis show few reasonably 

strong and consistent associations between bacteria concentrations and field characteristics. Most of the correlations have 

low coefficients, have an inconsistent positive or negative 

sign, or lack sufficient data to support a reliable statistical 

evaluation of the relations. The strongest and most consistent 

correlations were those for the relations of bacteria concentrations to streamflow and turbidity for samples from the 

main-stem Three Rivers sites, and those for the relations of 

bacteria concentrations to turbidity and specific conductance 

for samples from the tributary sites. The field characteristics 

with the strongest correlations were used as covariates in trend 

analysis.

Trend Analysis

No consistent trends in bacteria concentrations at mainstem sites are apparent over the 2001–09 period (figs. 8–17), 

with the possible exception of decreases in E. coli and FC 

concentrations in samples from the Monongahela River at 

Pittsburgh station after 2007. Because the number of samples 

collected during this period was small, however, the statistical 

significance of the decreases is questionable. Seasonal Kendall 

and logistic regression trend tests were applied to determine 

whether trends exist.

Seasonal Kendall tests for trends in E. coli and FC 

bacteria over the study period were generally inconclusive. 
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 25

10,000

1,000

100

10

1

Log10 Eschericia coli concentration, 

in colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03049652 Allegheny River at Oakmont

EPA recreational 

water-quality criterion

Detection limit

Year

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

Figure 8. Comparison of Escherichia coli concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03049652 on the Allegheny River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; EPA, U.S. Environmental Protection Agency)

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

Outlier

10,000

1,000

100

10

1

Log10 fecal coliform concentration, 

in colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03049652 Allegheny River at Oakmont

Year

PaDEP water contact criterion

Figure 9. Comparison of fecal coliform concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03049652 on the Allegheny River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; PaDEP, Pennsylvania Department of Environmental Protection)
26 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

100,000

10,000

1,000

100

1

Log10 Eschericia coli concentration, 

in colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03049832 Allegheny River at 9th Street Bridge

Year

10

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

EPA recreational 

water-quality 

criterion

Figure 10. Comparison of Escherichia coli concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03049832 on the Allegheny River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; EPA, U.S. Environmental Protection Agency)

100,000

10,000

1,000

100

1

Log10 fecal coliform concentration, 

in colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03049832 Allegheny River at 9th Street Bridge

Year

10

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

PaDEP water 

contact criterion

Figure 11. Comparison of fecal coliform concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03049832 on the Allegheny River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; PaDEP, Pennsylvania Department of Environmental Protection)
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 27

10,000

1,000

100

10

1

Log10 Eschericia coli concentration, 

in colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03083903 Monongahela River at McKeesport

Year

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

EPA recreational 

water-quality criterion

Detection limit

Figure 12. Comparison of Escherichia coli concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03083903 on the Monongahela River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; EPA, U.S. Environmental Protection Agency)

10,000

1,000

100

10

1

Log10 fecal coliform concentration, in 

colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03083903 Monongahela River at McKeesport

Year

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

PaDEP water contact criterion

Figure 13. Comparison of fecal coliform concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03083903 on the Monongahela River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; PaDEP, Pennsylvania Department of Environmental Protection)
28 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

100,000

10,000

1,000

100

1

Log10 Eschericia coli concentration, in 

colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03085150 Monongahela River at Pittsburgh

Year

10

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

EPA recreational 

water-quality 

criterion

Detection limit

Figure 14. Comparison of Escherichia coli concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03085150 on the Monongahela River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; EPA, U.S. Environmental Protection Agency)

100,000

10,000

1,000

100

1

Log10 fecal coliform concentration, in 

colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03085150 Monongahela River at Pittsburgh

Year

10

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

PaDEP water 

contact criterion

Figure 15. Comparison of fecal coliform concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03085150 on the Monongahela River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; PaDEP, Pennsylvania Department of Environmental Protection)
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 29

100,000

10,000

1,000

100

1

Log10 Eschericia coli concentration, in 

colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03085986 Ohio River at Sewickley

Year

10

EPA recreational 

water-quality criterion

Detection limit

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

Figure 16. Comparison of Escherichia coli concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03085986 on the Ohio River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; EPA, U.S. Environmental Protection Agency)

100,000

10,000

1,000

100

1

Log10 fecal coliform concentration, in 

colonies per 100 milliliters

2001 2002 2003 2004 2005 2006 2007 2008 2009

03085986 Ohio River at Sewickley

Year

10

Outlier

Fecal-indicator bacteria 

concentration

EXPLANATION

Interquartile

 range

90th percentile

75th percentile

50th percentile

 (median)

25th percentile

10th percentile

PaDEP water 

contact criterion

Figure 17. Comparison of fecal coliform concentrations in composite samples collected during wet- and dry-weather events at U.S. 

Geological Survey streamgaging station 03085986 on the Ohio River near Pittsburgh, Allegheny County, Pennsylvania, 2001–09. 

(Wet-weather events shown in red; dry-weather events shown in blue; PaDEP, Pennsylvania Department of Environmental Protection)
30 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Considering the large number of potential sources contributing 

bacteria to the Three Rivers under varying conditions, significant trends in the data for samples from the main-stem sites 

were not expected.

No significant trends were detected in E. coli or FC concentrations in samples collected under dry-weather conditions 

from the Allegheny River at Oakmont and at 9th Street Bridge, 

and from the Monongahela River at Pittsburgh (table 11). 

Trends in samples collected from the Monongahela River at 

McKeesport and the Ohio River at Sewickley Bridge stations 

could not be tested as a result of poor temporal distribution of 

the dry-weather data.

Table 11. Results of Seasonal Kendall test for trends in bacteria at five sites on the Allegheny, Monongahela, and Ohio Rivers, 

Allegheny County, Pennsylvania, 2001–09.

[USGS, U.S. Geological Survey; n, number of samples; na, not applicable; ns, not significant at the 95-percent confidence level (p-value < 0.05)]

USGS station 

number USGS station name

Eschericia coli Fecal coliform

n p-value Trend n p-value Trend

Dry weather without flow adjustment

03049652 Allegheny River at Hulton Bridge at Oakmont, PA 42 0.462 ns 41 0.312 ns

03049832 Allegheny River at 9th St. Bridge at Pittsburgh, PA 64 1.000 ns 64 1.000 ns

03083903 Monongahela River at McKeesport, PA 27 na na 27 na na

03085150 Monongahela River at Pittsburgh, PA 69 0.707 ns 67 0.707 ns

03085986 Ohio River at Sewickley bridge at Sewickley, PA 50 0.181 ns 51 0.133 ns

Dry weather with flow adjustment

03049652 Allegheny River at Hulton Bridge at Oakmont, PA 42 0.806 ns 41 0.221 ns

03049832 Allegheny River at 9th St. Bridge at Pittsburgh, PA 64 1.000 ns 64 0.764 ns

03083903 Monongahela River at McKeesport, PA 27 na na 27 na na

03085150 Monongahela River at Pittsburgh, PA 69 0.707 ns 67 0.452 ns

03085986 Ohio River at Sewickley bridge at Sewickley, PA 50 na na 51 0.133 ns

Wet weather without flow adjustment

03049652 Allegheny River at Hulton Bridge at Oakmont, PA 37 0.221 ns 37 0.086 ns

03049832 Allegheny River at 9th St. Bridge at Pittsburgh, PA 54 0.035 down 54 0.024 down

03083903 Monongahela River at McKeesport, PA na na na na na na

03085150 Monongahela River at Pittsburgh, PA 52 0.230 ns 52 0.072 ns

03085986 Ohio River at Sewickley bridge at Sewickley, PA na na na na na na

Wet weather with flow adjustment

03049652 Allegheny River at Hulton Bridge at Oakmont, PA 37 0.221 ns 37 0.806 ns

03049832 Allegheny River at 9th St. Bridge at Pittsburgh, PA 54 0.035 down 54 0.024 ns

03083903 Monongahela River at McKeesport, PA na na na na na na

03085150 Monongahela River at Pittsburgh, PA 52 0.230 ns 52 0.072 ns

03085986 Ohio River at Sewickley bridge at Sewickley, PA na na na na na na

A significant trend in bacteria concentrations in samples 

collected under wet-weather conditions was observed at one 

site—significant decreasing trends in wet-weather E. coli and 

FC concentrations in samples from the Allegheny River at 9th 

Street Bridge station (table 11). The trend rates reported for 

the 9th Street Bridge location were fairly strong at -43 and 

-66 percent per year for E. coli and FC, respectively.

The trends in bacteria reported for the 9th Street Bridge 

location may reflect short-term variability rather than a 

sustained decrease in bacteria concentration. Median bacteria 

concentrations in wet-weather samples show a pronounced 

and consistent decline from 2002 through 2006; it is on the 
Occurrence and Trends in Concentrations of Fecal-Indicator Bacteria in Streamflow 31

strength of this decline that a significant trend was reported. 

The addition of data for 2007 and 2008 did not alter this 

result because the difference in concentration from 2006 to 

2007 was minimal and data for 2008 were lacking. In 2009, 

however, median concentrations of E. coli and FC were two 

orders of magnitude greater than those in 2007 and were the 

highest reported for the location during the entire study period 

(figs. 10 and 11). Although these increases did not alter the 

outcome of the Seasonal Kendall trend test, additional data on 

the natural variability in bacteria concentrations and factors 

that influence bacteria—specifically, a comparison of rainfall variables and their influence on bacteria concentrations 

(Walker, 1993)—would be needed to determine whether the 

2009 concentrations are outliers or are indicative of a return 

to E.coli and FC concentrations in the ranges reported prior to 

the 2002–06 decline.

Significant trends in the probability of fecal-indicator 

bacteria concentrations exceeding recreational standards 

were limited to one site and one weather condition. Logistic 

regression trend tests were performed on E. coli and FC data 

collected from the five main-stem Three Rivers sites. No 

trends in dry-weather exceedance of the standards were found 

for the Allegheny River at 9th Street Bridge or the Monongahela River at Pittsburgh station (table 12). Dry-weather trends 

could not be evaluated at the three remaining sites because 

of an insufficient number of data points with concentrations 

that exceeded the recreational standards. Significant decreases 

in the likelihood that E. coli and FC bacteria concentrations 

will exceed recreational standards under wet-weather conditions were found at the Allegheny River at 9th Street Bridge 

station. The probability of detecting E. coli at concentrations 

greater than 235 col/100 mL and FC at concentrations greater 

Table 12. Results of logistic regression test for trends in probability of exceeding recreational bacteria standards at five sites on the 

Allegheny, Monongahela, and Ohio Rivers, Allegheny County, Pennsylvania, 2001–09.

[USGS, U.S. Geological Survey; mL, milliliters; n, number of samples; na, not applicable; ns, not significant at the 95-percent confidence level (p-value 

< 0.05)]

USGS station 

number USGS station name

Eschericia coli greater than 235 

colonies per 100 mL1

Fecal coliform greater than 400 

colonies per 100 mL2

n p-value Trend n p-value Trend

Dry weather

03049652 Allegheny River at Hulton Bridge at Oakmont, PA 42 na na 41 na na

03049832 Allegheny River at 9th St. Bridge at Pittsburgh, PA 64 0.073 ns 64 0.081 ns

03083903 Monongahela River at McKeesport, PA 27 na na 27 na na

03085150 Monongahela River at Pittsburgh, PA 69 0.225 ns 67 0.078 ns

03085986 Ohio River at Sewickley bridge at Sewickley, PA 50 na na 51 na na

Wet weather

03049652 Allegheny River at Hulton Bridge at Oakmont, PA 37 0.099 ns 37 0.257 ns

03049832 Allegheny River at 9th St. Bridge at Pittsburgh, PA 54 0.026 -0.085 54 0.001 -0.193

03083903 Monongahela River at McKeesport, PA na na na na na na

03085150 Monongahela River at Pittsburgh, PA na na na na na na

03085986 Ohio River at Sewickley bridge at Sewickley, PA 39 0.195 ns 37 0.846 ns

1 Eschericia coli: U.S. Environmental Protection Agency recreational water-quality criterion (U.S. Environmental Protection Agency, 1986).

2

 Fecal coliform: Pennsylvania Department of Environmental Protection water contact criterion (Commonwealth of Pennsylvania, 2015).
32 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

than 400 col/100 mL decreased 8 and 19 percent, respectively 

(table 12). These results support the Seasonal Kendall trend 

test results; however, the caveats regarding the validity of 

the Seasonal Kendall results apply to the logistic regression 

results as well. Although streamflow and turbidity were used 

as covariates, neither was a significant explanatory variable.

Summary and Conclusions

The U.S. Geological Survey and its partners collected 

surface-water samples from the Three Rivers and its tributaries in Allegheny County, Pennsylvania, during the period 

2001–09 to assess the occurrence and trends in concentrations 

of fecal-indicator bacteria during dry- and wet-weather conditions. To quantify the effects of these organisms on receiving 

waters, a network of rain and streamgages was established to 

target sampling efforts to weather events of varying magnitudes and distributions.

Nonparametric correlation analyses, including Spearman’s rho and the paired Prentice Wilcoxon test, were used to 

screen for associations among indicator-bacteria concentrations and field characteristics streamflow, water temperature, 

pH, specific conductance, dissolved-oxygen concentration, and 

turbidity. The Seasonal Kendall trend test and logistic regression were used to quantify discernable trends in the data.

The data evaluated were the results of analyses of 

1,742 water samples collected at 52 main-stem and tributary 

sites. Quantifiable concentrations of Escherichia coli (E.coli)

bacteria were detected in 97.0 percent of 1,719 samples; 

concentrations in 49.6 percent exceeded the U.S. Environmental Protection Agency (EPA) recreational water-quality 

criterion of 235 colonies per 100 milliliters (col/100 mL). 

Fecal-coliform (FC) bacteria were detected in 98.8 percent 

of 1,713 samples; concentrations in 45.5 percent exceeded 

the Commonwealth of Pennsylvania water contact criterion 

of 400 col/100 mL. Enterococci bacteria were detected in 

87.5 percent of 1,042 samples; concentrations in 46.4 percent exceeded the EPA recreational water-quality criterion of 

61 col/100 mL. The median percentage of samples in which 

bacteria concentrations exceeded recreational water-quality 

standards across all sites with five or more samples was 48 

for E. coli, 43 for FC, and 75 for enterococci. E. coli, FC, and 

enterococci concentrations at all Three Rivers sites had significant positive correlations with streamflow under all weather 

conditions, with correlation coefficients ranging from 0.203 to 

0.598. Two trend tests (Seasonal Kendall and logistic regression) were evaluated to determine whether statistically significant trends were present. In general, results of the Seasonal 

Kendall test for trends in E. coli and FC bacteria were inconclusive. Given the number and distribution of source streams 

that contribute bacteria to the receiving water, this conclusion 

was expected. No significant dry-weather trends in concentrations of E. coli and FC were detected at either the Allegheny 

River at Oakmont, Allegheny River at 9th Street Bridge, or 

Monongahela River at Pittsburgh station.

On the basis of logistic regression, no significant trends 

in dry-weather exceedance of the standards were reported; 

however, significant decreases in the likelihood that wetweather E. coli and FC bacteria concentrations will exceed 

recreational standards were found at the Allegheny River at 

9th Street Bridge site. The probability of detecting E. coli

concentrations greater than 235 col/100 mL and FC concentrations greater than 400 col/100 mL decreased 8 percent and 

19 percent, respectively, during the period examined. As a 

result of the variability of weather, sampling patterns, and 

sampling frequency, the cause of this downward trend could 

not be determined. These trends may be associated with shortterm weather effects or sampling patterns rather than with a 

corrective engineering measures designed to reduce loads of 

bacteria to the Allegheny River upstream from the 9th Street 

Bridge in Allegheny County, Pennsylvania.

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Association, and Water Environment Federation, 1998, 

Standard methods for the examination of water and wastewater (20th ed.): Washington, D.C., American Public Health 

Association, 1,100 p. 

Buckwalter, T.F., Zimmerman, T.M., and Fulton, J.W., 2006, 

Fecal-indicator bacteria in the Allegheny, Monongahela, 

and Ohio Rivers and selected tributaries, Allegheny County, 

Pennsylvania, 2001–05: U.S. Geological Survey Scientific 

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Carter, R.W., and Davidian, Jacob, 1968, General procedure 

for gaging streams, U.S. Geological Survey Techniques of 

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Chapra, S.C., 1997, Surface water-quality modeling: New 

York, McGraw-Hill Publisher, Inc., 844 p.

Committee on Water Quality Improvement for the Pittsburgh 

Region, 2005, Regional cooperation for water quality 

improvement in southwestern Pennsylvania: Washington, 

D.C., National Research Council of the National Academies, The National Academies Press, 282 p.

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criteria: The Pennsylvania Code, chapter 93, section 93.7: 

accessed November 16, 2015, at http://www.pacode.com/

secure/data/025/chapter93/s93.7.html. 

Craig, J.D., 1983, Installation and service manual for U.S. 

Geological Survey manometers, U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 8, 

chap. A2, 1983, 57 p.
References Cited 33

Fulton, J.W., and Buckwalter, T.F., 2004, Fecal-indicator 

bacteria in the Allegheny, Monongahela, and Ohio Rivers, near Pittsburgh, Pennsylvania, July–September 2001: 

U.S. Geological Survey Scientific Investigations Report 

2004–5009, 39 p.

Hardina, C.M., and Fujioka, R.S., 1991, Soil: The environmental source of Escherichia coli and enterococci in 

Hawaii’s streams: Environmental Toxicology and Water 

Quality, v. 6, p. 185–195, doi:10.1002/tox.2530060208.

Helsel, D.R., 2005, Nondetects and data analysis: New Jersey, 

John Wiley and Sons, Inc., 250 p.

Helsel, D.R., and Hirsch, R.M., 1992, Studies in environmental science 49—Statistical methods in water resources: New 

York, Elsevier, 522 p.

Knauer, K., and Collins, T., 2002, 3 Rivers 2nd Nature Aquatic 

Report, Monongahela River Valley, Phase 2, 2001—Water 

quality: Pittsburgh, Pennsylvania, Carnegie Mellon University, STUDIO for Creative Inquiry, 36 p.

Oberg, K.A., Morlock, S.E., and Caldwell, W.S., 2005, 

Quality-assurance plan for discharge measurements using 

acoustic Doppler current profilers: U.S. Geological Survey 

Scientific Investigations Report 2005–5183, 44 p. (available 

online at http://pubs.usgs.gov/sir/2005/5183/).

Ohio River Valley Water Sanitation Commission, 2006, Combined sewer overflow studies: accessed June 26, 2006, at 

http://www.orsanco.org/.

Ohio River Valley Water Sanitation Commission, 2010, Combined sewer overflow studies: accessed March 10, 2010, at 

http://www.orsanco.org/.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow—volume 1, Measurement of stage and discharge: U.S. Geological Survey Water-Supply Paper 2175, 

284 p.

Schertz, T.L., Alexander, R.B., and Ohe, D.J., 1991, The computer program Estimate Trend (ESTREND)—A system for 

the detection of trends in water-quality data: U.S. Geological Survey Water-Resources Investigations Report 91–4040, 

60 p.

States, S., Stadterman, K., Ammon, L., Vogel, P., Baldizar, J., 

Wright, D., Conley, L., and Sykora, J., 1997, Protozoa in 

river water—Sources, occurrence, and treatment: Journal 

of the American Water Works Association, v. 89, no. 9, 

p. 74–83.

Turnipseed, D.P., and Sauer, V.B., 2010, Discharge measurements at gaging stations: U.S. Geological Survey Techniques and Methods, book 3, chap. A8, 87 p., http://pubs.

usgs.gov/tm/tm3-a8/.

U.S. Environmental Protection Agency, 1986, Ambient waterquality criteria for bacteria—1986: Washington, D.C., U.S. 

Environmental Protection Agency, Office of Water, 

EPA-440/5-84-002, 18 p.

U.S. Environmental Protection Agency, 1999, Combined 

sewer overflows—Guidance for monitoring and modeling: 

U.S. Environmental Protection Agency, Office of Water, 

EPA 832-B-99-002, variously paged.

U.S. Environmental Protection Agency, 2000, National water 

quality inventory—1998 report; http://water.epa.gov/

lawsregs/guidance/cwa/305b/98report_index.cfm.

U.S. Environmental Protection Agency, 2001, Protocol for 

developing pathogen TMDLs: Washington, D.C., U.S. 

Environmental Protection Agency, Office of Water (4503F), 

EPA-841-R-002, 132 p.

U.S. Geological Survey, 1997 to present, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, 

book 9, chaps. A1–A9, v. 2, variously paged.

U.S. Geological Survey, 2014, Office of Surface Water—

Hydroacoustics: accessed June 2, 2014, at http://il.water.

usgs.gov/adcp/.

Walker, J.F., 1993, Techniques for detecting effects of bestmanagement practices on stream-water chemistry in 

selected watersheds in Texas, Minnesota, and Illinois: U.S. 

Geological Survey Open-File Report 93–130, 16 p.
34 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 1. Description of sampling and streamgage sites on the Allegheny, Monongahela, and Ohio Rivers and selected tributaries, 

Allegheny County, Pennsylvania, 2001–09.—Continued

[USGS, U.S. Geological Survey; ALCOSAN, Allegheny County Sanitary Authority; **, shown in figure 2; --, not determined; NA, not applicable as site is for 

computing stream discharge only; QW, water quality; RM, river mile]

USGS 

station 

name

Purpose

USGS 

station 

number

Map 

identifier

for figures 

3–5

Sample

obtained

from:

River 

mile1

 (miles)

Drainage 

area 

(square 

miles)

Allegheny River and tributaries

Allegheny River at Natrona, PA

Continuous-record streamgage 

used to estimate discharge 

into the Allegheny River 

Basin

03049500 ** NA 24.3 11,410.0

Allegheny River bl Falling 

Springs Run at Oakmont, PA QW receptor 03049643 1 boat 13.3 11,548.0

Allegheny River at Hulton 

Bridge at Oakmont, PA

Main-stem upstream QW transect near ALCOSAN service 

area boundary

03049652 2 bridge, boat 12.7 11,577.0

Allegheny River ab Quigley 

Creek at Blawnox, PA

Main-stem intermediate QW 

transect

03049668 3 boat 10.4 11,625.0

Allegheny River ab Shades Run 

at Aspinwall, PA

Main-stem intermediate QW 

transect

03049677 4 boat 8.1 11,640.0

Allegheny River bl Shades Run 

at Aspinwall, PA QW receptor 03049678 5 boat 8.0 11,641.0

Allegheny River at Sharpsburg, 

PA

Main-stem intermediate QW 

transect

03049690 6 boat 6.0 11,652.0

Allegheny River above Girtys 

Run at Millvale, PA

Main-stem intermediate QW 

transect

03049812 7 boat 3.8 11,733.0

Allegheny River ab 31st St 

Bridge at Pittsburgh, PA QW receptor 03049825 8 boat 2.5 11,736.0

Allegheny River bl 31st St 

Bridge at Pittsburgh, PA

Main-stem intermediate QW 

transect

03049828 9 boat 2.0 11,739.0

Allegheny River at 9th St. Bridge 

at Pittsburgh, PA

Main-stem downstream QW 

transect

03049832 32 boat 0.7 11,710.0

Allegheny River and tributaries

Deer Creek near Dorseyville, PA

Continuous-record tributary 

streamgage upstream from the 

ALCOSAN service area

03049646 ** NA -- 27.0

Deer Creek at Route 910 near 

Cheswick, PA

Tributary QW transect upstream 

from the ALCOSAN service 

area

03049649 33 wading -- 49.1

Plum Creek at Milltown, PA

Continuous-record tributary 

streamgage upstream from the 

ALCOSAN service area

03049658 34 NA -- 17.4
Table 1 35

Table 1. Description of sampling and streamgage sites on the Allegheny, Monongahela, and Ohio Rivers and selected tributaries, 

Allegheny County, Pennsylvania, 2001–09.—Continued

[USGS, U.S. Geological Survey; ALCOSAN, Allegheny County Sanitary Authority; **, shown in figure 2; --, not determined; NA, not applicable as site is for 

computing stream discharge only; QW, water quality; RM, river mile]

USGS 

station 

name

Purpose

USGS 

station 

number

Map 

identifier

for figures 

3–5

Sample

obtained

from:

River 

mile1

 (miles)

Drainage 

area 

(square 

miles)

Plum Creek at Verona, PA

Tributary QW transect upstream 

from the ALCOSAN service 

area

03049660 35 wading -- 20.3

Squaw Run at Old Freeport Road 

near Blawnox, PA

Continuous-record tributary 

streamgage and QW transect 03049676 36 wading -- 8.07

Pine Creek at Grant Avenue at 

Etna, PA

Continuous-record tributary 

streamgage

03049807 ** NA -- 57.3

Pine Creek at Etna, PA

Tributary QW transect upstream 

from the ALCOSAN service 

area

03049810 37 wading -- 66.8

Girtys Run above Grant Avenue 

at Millvale, PA

Continuous-record tributary 

streamgage and QW transect 03049819 ** wading -- 13.4

Monongahela River and tributaries

Monongahela River at Elizabeth, 

PA

Continuous-record streamgage 

used to estimate discharge 

into the Monongahela River 

Basin

03075070 ** NA 24.0 5,340.0

Monongahela River at Dravosburg, PA

Main-stem upstream QW transect near ALCOSAN service 

area boundary

03076900 10 boat 16.0 5,433.0

Youghiogheny River at Sutersville, PAContinuous-record tributary 

streamgage

03083500 ** NA -- 1,715.0

Youghiogheny River at McKeesport, PA QW tributary transect 03083900 11 boat 0.5 1,732.0

Monongahela River at McKeesport, PAMain-stem intermediate QW 

transect

03083903 12 boat 14.7 7,200.0

Monongahela River ab Turtle Cr 

at Duquesne, PA

Main-stem intermediate QW 

transect

03083910 13 boat 12.0 7,208.0

Monongahela River ab Rankin 

Bridge at Rankin, PA

Main-stem intermediate QW 

transect

03085008 14 boat 10.0 7,364.0

Monongahela River ab Ninemile 

Run at Homestead, PA

Main-stem intermediate QW 

transect

03085030 15 boat 8.0 7,369.0

Monongahela River bl Streets 

Run near Baldwin, PA

Main-stem intermediate QW 

transect

03085116 16 boat 5.5 7,389.0

Monongahela River at South 

Pittsburgh, PA QW receptor 03085120 17 boat 4.5 7,360.0
36 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 1. Description of sampling and streamgage sites on the Allegheny, Monongahela, and Ohio Rivers and selected tributaries, 

Allegheny County, Pennsylvania, 2001–09.—Continued

[USGS, U.S. Geological Survey; ALCOSAN, Allegheny County Sanitary Authority; **, shown in figure 2; --, not determined; NA, not applicable as site is for 

computing stream discharge only; QW, water quality; RM, river mile]

USGS 

station 

name

Purpose

USGS 

station 

number

Map 

identifier

for figures 

3–5

Sample

obtained

from:

River 

mile1

 (miles)

Drainage 

area 

(square 

miles)

Monongahela River at Greenfield 

at Pittsburgh, PA

Main-stem intermediate QW 

transect

03085134 18 boat 3.5 7,394

Monongahela River and tributaries

Monongahela River at Brady 

Bridge at Pittsburgh, PA QW receptor 03085140 19 boat 2.2 7,400.0

Monongahela River at Pittsburgh, 

PA

Main-stem downstream QW 

transect

03085150 20 boat 0.8 7,367.0

Turtle Creek at Trafford, PA Tributary streamgage and QW 

transect

03084400 38 wading, bridge -- 55.5

Thompson Run at Gascola, PA Tributary streamgage and QW 

transect

03084750 39 wading, bridge -- 5.77

Thompson Run at Turtle Creek, 

PA

Continuous-record tributary 

streamgage and QW transect 03084800 40 wading, bridge -- 18.0

Turtle Creek at Wilmerding, PA Continuous-record tributary 

streamgage

03084698 ** wading, bridge -- 123.0

Turtle Creek at East Pittsburgh, 

PA QW tributary transect 03084808 41 bridge -- 147.0

Ninemile Run near Swissvale, PA Continuous-record tributary 

streamgage

03085049 ** NA -- 5.31

Ninemile Run at Mouth near 

Swissvale, PA QW tributary transect 03085050 42 wading 0.1 6.09

Streets Run at Hays, PA Continuous-record tributary 

streamgage

03085100 ** NA -- 8.21

Streets Run 1000 ft upstream of 

Mouth at Hays, PA QW tributary transect 03085113 43 wading 0.2 10.0

Ohio River and tributaries

Allegheny River at 9th Street 

Bridge at Pittsburgh, PA

Main-stem upstream QW 

transect

03049832 21 boat 0.7 11,710.0

Monongahela River at Pittsburgh, 

PA

Main-stem upstream QW 

transect

03085150 22 boat 0.8 7,367.0
Table 1 37

Table 1. Description of sampling and streamgage sites on the Allegheny, Monongahela, and Ohio Rivers and selected tributaries, 

Allegheny County, Pennsylvania, 2001–09.—Continued

[USGS, U.S. Geological Survey; ALCOSAN, Allegheny County Sanitary Authority; **, shown in figure 2; --, not determined; NA, not applicable as site is for 

computing stream discharge only; QW, water quality; RM, river mile]

USGS 

station 

name

Purpose

USGS 

station 

number

Map 

identifier

for figures 

3–5

Sample

obtained

from:

River 

mile1

 (miles)

Drainage 

area 

(square 

miles)

Ohio River at Point State Park at 

Pittsburgh, PA QW receptor 03085154 23 boat 0.0 19,145.0

Sawmill Run at Castle Shannon, 

PA

Tributary streamgage and QW 

transect

03085160 44 wading, bridge 8.2 1.04

Sawmill Run at Duquesne 

Heights nr Pittsburgh, PA

Continuous-record tributary 

streamgage and QW transect 03085213 ** wading, bridge 0.9 18.1

Chartiers Creek near Bridgeville, 

PA

Tributary streamgage and QW 

transect

03085290 45 wading, bridge 16.1 160.0

Chartiers Creek at Crafton, PA Tributary streamgage and QW 

transect

03085550 46 wading, bridge 4.2 270.0

Chartiers Creek at Carnegie, PA Continuous-record tributary 

streamgage and QW transect 03085500 ** wading, bridge 8.9 257.0

Ohio River above Brunot Island 

at Pittsburgh, Pa

Main-stem intermediate QW 

transect

03085215 24 boat 1.5 19,166.0

Ohio River below Jacks Run near 

Pittsburgh, PA

Main-stem intermediate QW 

transect

03085670 25 boat 4.0 19,452.0

Ohio River above Neville Island 

at Avalon, PA QW receptor 03085700 26 boat 4.8 19,400.0

Ohio River below Lowries Run 

at Emsworth, PA

Main-stem intermediate QW 

transect

030859502 27 boat 6.7 19,478.0

Ohio River above Toms Run at 

Emsworth, PA

Main-stem intermediate QW 

transect

030859504 28 boat 6.9 19,480.0

Ohio River and tributaries

Ohio River below Emsworth 

Back Channel Dam at Emsworth, PAQW receptor 030859512 29 boat 7.9 19,479.0

Lowries Run at Camp Horne near 

Emsworth, PA

Continuous-record tributary 

streamgage

03085947 ** NA 1.5 15.4

Lowries Run 1000 ft above 

Mouth at Ben Avon, PA QW tributary transect 030859501 47 wading, bridge 0.7 16.9

Montour Run at Scott Station 

near Imperial, PA

Continuous-record tributary 

streamgage downstream from 

ALCOSAN service area

03085956 ** NA -- 25.4
38 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09

Table 1. Description of sampling and streamgage sites on the Allegheny, Monongahela, and Ohio Rivers and selected tributaries, 

Allegheny County, Pennsylvania, 2001–09.—Continued

[USGS, U.S. Geological Survey; ALCOSAN, Allegheny County Sanitary Authority; **, shown in figure 2; --, not determined; NA, not applicable as site is for 

computing stream discharge only; QW, water quality; RM, river mile]

USGS 

station 

name

Purpose

USGS 

station 

number

Map 

identifier

for figures 

3–5

Sample

obtained

from:

River 

mile1

 (miles)

Drainage 

area 

(square 

miles)

Montour Run at Coraopolis, PA

QW tributary transect downstream of ALCOSAN service 

area

03085960 48 wading, bridge 6.7 36.2

Ohio River below Neville Island 

at Coraopolis, PA

Main-stem intermediate QW 

transect

03085966 30 boat 10.0 19,532.0

Ohio River at Sewickley bridge 

at Sewickley, PA

Main-stem downstream QW 

transect

03085986 31 boat, bridge 11.8 19,538.0

Ohio River at Sewickley, PA

Continuous-record streamgage 

used to estimate discharge out 

of the basin

03086000 ** NA 13.3 19,500.0

1

River miles are measured from the site to the mouth of the Allegheny River, the mouth of the Monongahela River, or, for the Ohio River and tributaries, 

the confluence of the Allegheny and Monongahela Rivers. River miles are not given for some main-stem and tributary sampling sites that do not coincide with 

long-term streamgaging stations or sites not within the study-area boundaries.
Table 4 39

Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued[USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled]

USGS 

station 

number

Streamflow, in cubic feet per second Water temperature, in degrees Celsius pH, in standard units

n

Maximum Median Minimum n Maxi- mum Median Mini- mum n Maxi- mum Median Mini- mum

03049652 154 26,300 4,930 3,080 126 33.0 24.1 14.5 152 8.7 7.3 6.303049832 185 69,890 5,220 2,530 189 30.0 23.6 11.2 184 8.6 7.6 4.603083903 66 74,000 6,381 1,707 78 29.6 24.1 15.3 81 8.0 7.4 7.103085150 185 70,160 5,270 1,390 187 30.0 24.3 14.6 186 8.7 7.6 4.603085986 156 81,500 11,550 4,070 135 32.0 22.5 11.3 160 8.3 7.2 6.503084400 28 960 34.25 9.33 29 23.5 18.5 3.5 30 8.8 7.8 7.103084750 28 120 4.19 1.97 29 20.0 16.5 5.0 29 8.1 7.7 5.103084800 29 665 16.2 7.87 29 22.0 17.0 4.5 30 8.7 7.8 6.903084808 22 8,710 164.5 57.8 27 27.5 18.5 4.0 28 8.4 7.8 6.603085160 34 43.7 0.73 0.1 40 25.5 16.1 5.6 39 8.3 7.8 7.103085213 56 1530 14.55 4.03 57 27.0 19.3 4.5 57 8.2 7.8 6.803085290 44 13,500 133 36.6 43 22.8 17.0 3.9 44 8.2 7.7 6.603085500 109 11,600 289 54 108 23.1 15.1 4.0 108 8.6 7.5 5.803085550 12 326 111 54 29 27.5 19.5 5.1 29 8.5 7.8 7.003049643 2 7,630 7,034 6,437 5 23.7 23.5 22.0 5 8.0 7.5 7.303049649 8 385 5.3 0.47 8 19.4 16.9 6.3 8 8.3 8.0 7.303049660 8 85 8.8 2.8 8 21.0 18.9 6.9 8 8.2 8.1 7.203049668 18 13,500 5,448 4,410 18 24.3 23.8 22.2 18 8.2 7.7 7.1
40 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09 Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued [USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled] USGS station number Streamflow, in cubic feet per second Water temperature, in degrees Celsius pH, in standard units

n

Maximum Median Minimum n Maxi- mum Median Mini- mum n Maxi- mum Median Mini- mum

03049674 nd nd nd nd 3 24.1 22.4 10.3 3 7.6 7.1 6.703049676 4 49 12.7 4.7 5 18.8 17.7 6.3 5 8.2 8.0 7.303049677 18 13,900 5,758 4,410 18 24.3 24.0 21.7 18 8.3 7.7 7.203049678 2 7,660 7,320 6,980 6 24.3 23.8 21.8 6 8.3 7.8 7.303049690 21 14,100 4,710 3,800 21 24.5 23.4 21.6 21 8.2 7.8 7.203049810 7 504 62 7.2 8 20.3 18.6 6.8 8 8.1 7.8 7.003049812 21 13,800 4,830 2,878 21 24.3 23.3 21.4 21 8.1 7.7 7.203049819 8 62 4 2 8 19.6 17.6 7.5 8 8.0 7.9 6.603049825 3 8,580 5,825 4,883 7 24.2 23.3 21.6 7 8.0 7.9 7.103049828 21 13,800 4,936 2,878 21 24.2 23.4 21.4 21 8.0 7.7 7.103076900 21 73,900 3,408 777 21 27.4 25.0 18.4 21 7.7 7.6 6.803083900 21 8,610 1,054 791 21 25.1 23.3 17.1 21 8.9 7.7 7.103083910 21 74,000 4,576 2,532 21 26.9 24.5 18.3 21 8.1 7.7 7.103084698 1 84 nd 84 1 24.6 24.6 24.6 1 9.1 9.1 9.103085008 21 76,464 7,000 1,925 21 26.9 24.3 18.7 21 8.1 7.7 7.003085030 21 75,000 7,087 2,107 21 27.1 24.1 18.8 21 7.9 7.7 7.003085050 5 12 6 2 5 22.5 21.1 17.8 5 8.8 8.5 7.803085113 7 9 5 3 7 21.7 19.2 16.3 7 8.1 7.6 6.5
Table 4 41

Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued[USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled]

USGS 

station 

number

Streamflow, in cubic feet per second Water temperature, in degrees Celsius pH, in standard units

n

Maximum Median Minimum n Maxi- mum Median Mini- mum n Maxi- mum Median Mini- mum

03085116 21 77,481 7,087 1,472 21 26.8 24.1 18.7 21 7.9 7.6 6.903085120 3 9,311 2,057 1,712 6 26.7 24.0 18.8 6 7.8 7.6 6.803085134 21 69,398 7,087 1,550 21 26.8 24.1 18.6 21 7.7 7.6 6.703085140 4 11,571 5,224 1,504 7 26.7 24.1 18.8 7 7.7 7.5 7.103085154 1 10,496 10,496 10,496 7 24.7 21.1 14.8 6 8.2 7.6 7.603085215 21 84,000 8,529 5,050 21 33.0 20.6 11.2 21 8.3 7.6 7.403085670 18 81,640 8,315 5,050 18 25.6 21.0 11.3 18 8.2 7.6 7.503085700 1 11,201 11,201 11,201 7 23.8 20.7 12.0 7 8.2 7.6 7.5030859501 7 10 6 2 8 24.9 18.0 5.6 8 8.7 8.4 7.1030859502 18 20,216 5,906 3,840 18 23.5 20.6 17.9 18 8.1 7.5 7.3030859504 2 20,216 15,709 11,201 7 23.5 20.4 12.2 7 8.1 7.5 6.6030859512 15 6,980 1,686 1,300 18 23.5 20.3 18.1 18 8.0 7.6 7.4030859515 1 11,201 11,201 11,201 3 22.6 19.6 11.5 3 7.6 7.3 6.803085960 8 24,290 40 3 8 24.3 17.2 5.9 8 8.2 8.0 7.203085966 18 77,860 8,390 5,280 21 23.5 20.1 12.3 21 8.0 7.5 7.303085000 85 9,090 4,210 532 84 29.0 26.5 19.5 85 8.6 7.6 6.9
42 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09 Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued [USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled] USGS station number Dissolved-oxygen concentration, in milligrams per liter Specific conductivity, in μS/cm Turbidity, in NTU

n

Maximum Median Minimum n Maxi- mum Median Mini- mum n Maxi- mum Median Mini- mum

03049652 110 12.5 9.0 6.0 154 483 350 171 144 95 7 1 03049832 163 14.0 8.5 1.2 190 505 348 132 177 120 6 0 03083903 81 12.0 7.8 0.6 81 569 314 168 79 220 10 1 03085150 161 11.9 8.0 0.4 189 618 386 178 178 180 10 2 03085986 103 11.2 8.3 6.5 160 510 375 229 149 60 11 2 03084400 29 14.7 10.7 8.0 30 918 784 250 30 340 12 0 03084750 29 13.8 9.7 8.2 30 1,857 1,390 550 31 1,130 6 0 03084800 29 14.0 9.7 8.6 30 2,044 1,535 580 30 900 8 2 03084808 26 14.2 10.0 6.0 28 1,479 1,043 294 29 2,000 47 8 03085160 40 13.8 9.1 5.6 39 4,300 1,270 154 37 75 2 0 03085213 57 14.0 8.9 6.2 56 2,509 1,186 195 54 600 20 0 03085290 44 13.3 8.6 6.1 43 1,470 902 115 40 340 25 1 03085500 102 16.9 9.7 6.0 108 1,677 1,130 251 90 1,850 65 11 03085550 29 15.9 8.2 6.0 29 1,877 1,340 614 28 200 42 0 03049643 5 9.2 8.8 7.9 5 442 380 302 4 14 4 4 03049649 8 10.7 10.0 8.4 8 1,566 1,249 435 8 810 13 0 03049660 8 11.0 9.5 8.2 8 3,332 1,677 472 7 490 10 1 03049668 18 9.3 8.7 7.9 18 483 412 314 15 41 6 2 
Table 4 43

Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued[USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled]

USGS 

station 

number

Dissolved-oxygen concentration,

in milligrams per liter Specific conductivity, in μS/cm Turbidity, in NTU

n

Maximum Median Minimum n Maxi- mum Median Mini- mum n Maxi- mum Median Mini- mum

03049674 3 11.7 8.8 8.3 3 340 318 314 2 24 12 0 03049676 5 11.3 9.6 8.8 5 935 797 687 4 46 24 3 03049677 18 9.7 8.6 8.1 18 464 406 314 15 24 5 4 03049678 6 11.4 8.9 8.1 6 466 405 313 5 21 5 3 03049690 21 9.6 9.2 8.3 21 480 385 304 18 56 5 1 03049810 8 11.2 9.0 8.4 8 1,130 883 603 7 260 18 2 03049812 21 9.6 9.1 8.0 21 483 400 305 15 77 7 0 03049819 8 11.0 9.1 8.7 8 1,455 1,207 559 7 120 8 1 03049825 7 9.6 9.0 8.0 7 476 405 304 6 44 6 0 03049828 21 9.4 9.0 7.8 21 468 409 309 18 31 7 1 03076900 21 9.0 8.1 7.6 21 554 421 232 21 210 13 1 03083900 21 10.4 8.5 7.5 21 538 354 213 21 32 15 2 03083910 21 9.2 8.2 7.6 21 775 399 204 21 280 12 1 03084698 1 15.9 15.9 15.9 1 1,012 1,012 1,012 1 41 41 41 03085008 21 9.6 8.1 7.8 21 547 424 292 21 510 21 4 03085030 21 9.6 8.2 7.8 21 554 416 46 21 970 16 2 03085050 5 9.2 8.2 7.9 5 1,542 1,173 580 4 77 10 0 03085113 7 9.0 8.2 8.0 7 1,338 1,178 825 6 570 1 0 
44 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09 Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued [USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled] USGS station number Dissolved-oxygen concentration, in milligrams per liter Specific conductivity, in μS/cm Turbidity, in NTU

n

Maximum Median Minimum n Maxi- mum Median Mini- mum n Maxi- mum Median Mini- mum

03085116 21 9.5 8.3 7.9 21 554 405 18 21 220 15 3 03085120 6 9.4 8.3 7.1 6 558 420 208 6 500 11 4 03085134 21 9.2 8.4 8.0 21 570 404 276 21 1,000 15 4 03085140 7 9.2 8.1 7.5 7 579 405 284 7 170 19 6 03085154 5 10.2 9.6 7.6 7 542 423 309 5 26 5 1 03085215 19 11.1 8.7 6.6 21 450 428 164 15 76 6 2 03085670 18 11.7 9.8 7.7 18 483 456 170 15 77 6 0 03085700 7 10.8 8.5 7.2 7 478 450 206 4 51 5 1 030859501 8 15.4 12.0 2.1 8 1,208 981 559 5 270 24 5 030859502 18 10.1 9.3 7.1 18 495 460 238 9 9 5 3 030859504 7 10.9 9.4 6.7 7 498 458 263 4 31 4 3 030859512 18 11.3 9.4 7.8 18 495 457 263 9 7 5 1 030859515 3 12.4 9.4 9.2 3 448 445 434 1 15 15 15 03085960 8 13.2 9.9 9.0 8 1,900 1,018 675 7 34 0 0 03085966 21 11.4 9.3 8.3 21 524 456 274 15 120 12 2 03085000 66 9.9 7.6 6.2 85 789 404 235 85 60 10 2 
Table 4 45

Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued[USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled]

USGS 

station 

number

Eschericia coli, in colonies per 100 milliliters Fecal coliform, in colonies per 100 milliliters Enterococci, in colonies per 100 milliliters

n

Maximum Median Minimum Percent exceed- ing WQS n Maxi- mum Median Mini- mum Percent exceed- ing WQS n Maxi- mum Median Mini- mum Percent exceed- ing WQS

03049652 159 1,400 60 3 14 158 5,750 95 <5 11 141 690 15 <5 21 03049832 189 24,000 150 <5 42 187 22,000 255 5 43 149 995 30 <5 30 03083903 81 1,600 110 <5 23 81 1,800 125 <5 12 60 320 15 <5 17 03085150 191 39,000 250 <5 52 187 50,000 370 <5 48 149 3,400 30 <5 35 03085986 161 18,000 130 <5 39 158 31,000 170 <5 30 141 2,000 25 <5 26 03084400 29 13,000 580 10 72 31 15,000 510 40 61 24 11,000 305 <10 75 03084750 30 30,000 115 <10 33 31 34,000 120 <10 23 24 9,600 50 <10 42 03084800 30 49,000 1,200 60 83 32 43,000 1,250 50 75 25 9,100 340 <10 88 03084808 28 42,000 4,700 790 100 30 77,000 5,350 720 100 25 17,000 730 60 96 03085160 39 28,000 1,500 10 95 40 110,000 1,600 200 90 33 21,000 640 <10 94 03085213 59 510,000 8,000 70 97 60 410,000 11,500 220 93 37 180,000 2,200 70 100 03085290 43 28,000 1,200 40 65 44 32,000 1,500 20 66 34 23,000 1,200 10 91 03085500 108 150,000 2,000 <10 84 109 110,000 2,300 <10 83 97 40,000 1,200 40 94 03085550 29 39,000 580 110 72 30 47,000 1,400 200 83 18 3,900 1,470 200 100 03049643 5 330 110 30 20 5 510 110 10 20 -- -- -- -- --03049649 8 20,000 310 80 50 8 20,000 398 70 50 -- -- -- -- --03049660 8 16,000 390 30 63 8 16,000 350 50 50 -- -- -- -- --03049668 18 1,200 110 <10 28 18 1,100 90 30 17 -- -- -- -- --
46 Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09 Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued [USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled] USGS station number Eschericia coli, in colonies per 100 milliliters Fecal coliform, in colonies per 100 milliliters Enterococci, in colonies per 100 milliliters

n

Maximum Median Minimum Percent exceed- ing WQS

n

Maximum Median Mini- mum Percent exceed- ing WQS

n

Maximum Median Mini- mum Percent exceed- ing WQS

03049674 3 34,000 890 20 67 3 49,000 870 10 67 -- -- -- -- --03049676 5 4,700 340 80 60 5 4,700 250 60 20 -- -- -- -- --03049677 18 1,100 115 10 33 18 1,000 190 <10 39 -- -- -- -- --03049678 6 680 95 10 33 6 610 160 40 33 -- -- -- -- --03049690 21 19,000 140 30 43 21 27,000 310 50 43 -- -- -- -- --03049810 8 14,000 870 <10 88 8 18,000 1,055 20 75 -- -- -- -- --03049812 21 13,000 140 20 43 21 10,000 280 50 43 -- -- -- -- --03049819 8 29,000 9,350 20 88 8 36,000 9,950 30 88 -- -- -- -- --03049825 7 6,900 130 10 43 7 11,000 260 110 43 -- -- -- -- --03049828 21 12,000 120 <10 43 21 14,000 240 60 43 -- -- -- -- --03076900 21 630 130 <10 24 21 810 210 <10 19 -- -- -- -- --03083900 21 3,200 90 <10 43 21 5,000 150 20 38 -- -- -- -- --03083910 21 970 220 <10 48 21 1,300 410 80 52 -- -- -- -- --03084698 1 110 110 110 0 1 150 150 150 0 -- -- -- -- --03085008 21 1,200 230 30 48 21 4,200 300 60 38 -- -- -- -- --03085030 21 820 220 <10 48 21 810 260 30 38 -- -- -- -- --03085050 5 33,000 280 80 60 5 31,000 370 120 40 -- -- -- -- --03085113 7 200,000 520 90 71 7 200,000 430 100 57 -- -- -- -- --
Table 4 47

Table 4. Summary statistics for streamflow, water temperature, pH, dissolved-oxygen concentration, specific conductivity, turbidity, and concentrations of fecal-indicator bacteria for 52 sampling sites in Allegheny County, Pennsylvania, 2001–09.—Continued[USGS, U.S. Geological Survey; n, number of samples; nd, no data; μS/cm, microsiemens per centimeter at 25 degrees Celsius; WQS, water-quality standard; NTU, Nephelometric Turbidity Units; <, less than; --, not sampled]

USGS 

station 

number

Eschericia coli, in colonies per 100 milliliters Fecal coliform, in colonies per 100 milliliters Enterococci, in colonies per 100 milliliters

n

Maximum Median Minimum Percent exceed- ing WQS n Maxi- mum Median Mini- mum Percent exceed- ing WQS n Maxi- mum Median Mini- mum Percent exceed- ing WQS

03085116 21 6,700 300 20 52 21 6,500 280 10 48 -- -- -- -- --03085120 6 980 230 30 50 6 640 120 40 33 -- -- -- -- --03085134 21 1,400 300 <10 52 21 2,100 390 10 43 -- -- -- -- --03085140 7 520 200 100 43 7 930 260 80 29 -- -- -- -- --03085154 6 2,900 72 20 33 7 3,600 155 50 29 -- -- -- -- --03085215 21 27,000 100 <10 43 17 4,400 240 10 41 -- -- -- -- --03085670 18 3,500 220 <10 50 16 5,000 200 <10 38 -- -- -- -- --03085700 6 1,300 22 <10 17 7 9,000 130 20 29 -- -- -- -- --030859501 7 200,000 4,300 570 100 8 200,000 5,750 390 88 -- -- -- -- --030859502 18 1,100 66 <10 28 16 7,600 148 20 31 -- -- -- -- --030859504 6 1,300 156 <10 33 6 1,400 188 20 33 -- -- -- -- --030859512 15 980 160 20 27 15 1,100 220 20 20 -- -- -- -- --030859515 3 930 80 10 33 3 1,100 80 30 33 -- -- -- -- --03085960 7 1,800 80 <10 29 8 5,500 395 19 50 -- -- -- -- --03085966 21 26,000 190 10 38 17 5,000 110 <10 24 -- -- -- -- --03085000 85 12,000 320 <5 58 85 23,000 360 25 47 85 1,300 25 <5 33
Publishing support provided by the 

U.S. Geological Survey Science Publishing Network, 

West Trenton Publishing Service Center 

For more information concerning the research in this report, contact:

Director, Pennsylvania Water Science Center

U.S. Geological Survey

215 Limekiln Road

New Cumberland, PA 17070

http://pa.water.usgs.gov/
Fulton and others— Concentrations of Fecal-Indicator Bacteria in the Allegheny, Monongahela, and Ohio Rivers and Selected Tributaries, PA, 2001–09—Scientific Investigations Report 2015–5136

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155136