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| Publications— Scientific Investigations Reports |
In cooperation with the Allegheny County Sanitary Authority and the Allegheny County Health Department
U.S. Geological Survey Scientific Investigations Report 2006-5216
By Theodore F. Buckwalter, Tammy M. Zimmerman, and John W. Fulton
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Concentrations of fecal-indicator bacteria were determined in 1,027 water-quality samples collected from July 2001
through August 2005 during dry- (72-hour dry antecedent period) and wet-weather (48-hour dry antecedent period and at
least 0.3 inch of rain in a 24-hour period) conditions in the Allegheny, Monongahela, and Ohio Rivers (locally referred to
as the Three Rivers) and selected tributaries in Allegheny County. Samples were collected at five sampling sites on the
Three Rivers and at eight sites on four tributaries to the Three Rivers having combined sewer overflows.
Water samples were analyzed for three fecal-indicator organisms fecal coliform, Escherichia coli (E. coli), and enterococci
bacteria. Left-bank and right-bank surface-water samples were collected in addition to a cross-section composite sample at
each site.
Concentrations of fecal coliform, E. coli, and enterococci were detected in 98.6, 98.5, and 87.7 percent of all samples,
respectively. The maximum fecal-indicator bacteria concentrations were collected from Sawmill Run, a tributary to the Ohio
River; Sawmill Run at Duquesne Heights had concentrations of fecal coliform, E. coli, and enterococci of 410,000, 510,000,
and 180,000 col/100 mL, respectively, following a large storm.
The samples collected in the Three Rivers and selected tributaries frequently exceeded established recreational standards
and criteria for bacteria. Concentrations of fecal coliform exceeded the Pennsylvania water-quality standard
(200 col/100 mL) in approximately 63 percent of the samples. Sample concentrations of E. coli and enterococci exceeded the
U.S. Environmental Protection Agency (USEPA) water-quality criteria (235 and 61 col/100 mL, respectively) in about 53 and
47 percent, respectively, of the samples.
Fecal-indicator bacteria were most strongly correlated with streamflow, specific conductance, and turbidity. These
correlations most frequently were observed in samples collected from tributary sites. Fecal-indicator bacteria concentrations
and turbidity were correlated to the location of sample collection in the cross section. Most differences were between bank
and composite samples; differences between right-bank and left-bank samples were rarely observed. The Allegheny
River sites had more significant correlations than the Monongahela or Ohio River sites.
Comparisons were made between fecal-indicator bacteria in composite samples collected during dry-weather, wet-weather day-one, wet-weather day-two (tributary sites only), and wet-weather day-three (Three Rivers sites only) events in the Three Rivers and selected tributary sites. The lowest median bacteria concentrations generally were observed in the dry-weather composite samples. All median bacteria concentrations in dry-weather composite samples in the five Three Rivers sites were below water-quality standards and criteria; bacteria concentrations in the upstream tributary sites rarely met all standards or criteria. Only Turtle Creek, Thompson Run, and Chartiers Creek had at least one median bacteria concentration below water-quality standards or criteria. Median bacteria concentrations in the composite samples generally were higher the day after a wet-weather event compared to dry-weather composite samples and other wet-weather composite samples collected. In the five Three Rivers sites, median bacteria concentrations 3 days after a wet-weather event in composite samples tended to fall below the water-quality standards and criteria; in the eight tributary sites, median bacteria concentrations in the dry-weather and wet-weather composite samples generally were above the water-quality standards or criteria. Composite samples collected at the upstream sites on the Three Rivers and selected tributaries generally had lower median bacteria concentrations than composite samples collected at the downstream sites during dry- and wet-weather events. Higher concentrations downstream may be because of the large number of sewer outfalls in the reach between the upstream and downstream sites.
Abstract
Introduction
Purpose and Scope
Description of Study Area
Previous Investigations
Study Design
Site Selection
Sampling Protocol
Streamflow Measurements
Water-Quality Sampling and Laboratory-Analysis Methods
Statistical Methods
Quality Control
Occurrence and Distribution of Fecal-Indicator Bacteria
Field Characteristics and Bacteria Concentrations and Distributions
Weather Effects
Allegheny River Subbasins
Monongahela River Subbasins
Ohio River Subbasins
Summary and Conclusions
References Cited
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
View the full report in PDF 3.8 MB
For more information about USGS activities in Pennsylvania contact:
Director
USGS Pennsylvania Water Science Center
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.
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