U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5009
By John W. Fulton and Theodore F. Buckwalter
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This report presents the results of a study by the Allegheny County Health Department (ACHD) and the U.S. Geological Survey (USGS) to determine the concentrations of fecal-indicator bacteria in the Allegheny, Monongahela, and Ohio Rivers (Three Rivers) in Allegheny County, Pittsburgh, Pa. Water-quality samples and river-discharge measurements were collected from July to September 2001 during dry- (72-hour dry antecedent period), mixed-, and wet-weather (48-hour dry antecedent period and at least 0.3 inch of rain in a 6-hour period) conditions at five sampling sites on the Three Rivers in Allegheny County. Water samples were collected weekly to establish baseline conditions and during successive days after three wet-weather events.
Water samples were analyzed for fecal-indicator organisms including fecal-coliform (FC) bacteria, Escherichia coli (E. coli), and enterococci bacteria. Water samples were collected by the USGS and analyzed by the ACHD Laboratory. At each site, left-bank and right-bank surface-water samples were collected in addition to a composite sample (discharge-weighted sample representative of the channel cross section as a whole) at each site. Fecal-indicator bacteria reported in bank and composite samples were used to evaluate the distribution and mixing of bacteria-source streams in receiving waters such as the Three Rivers.
Single-event concentrations of enterococci, E. coli, and FC during dry-weather events were greater than State and Federal water-quality standards (WQS) in 11, 28, and 28 percent of the samples, respectively; during mixed-weather events, concentrations of fecal-indicator bacteria were greater than WQS in 28, 37, and 43 percent of the samples, respectively; and during wet-weather events, concentrations of fecal-indicator bacteria were greater than WQS in 56, 71, and 81 percent of samples, respectively.
Single-event, wet-weather concentrations exceeded those during dry-weather events for all sites except the Allegheny River at Oakmont. For this site, dilution during wet-weather events or the lack of source streams upgradient of the site may have caused this anomaly. Additionally, single-event concentrations of E. coli and FC frequently exceeded the WQS reported during wet-weather events.
It is difficult to establish a short-term trend in fecal-indicator bacteria concentrations as a function of time after a wet-weather event due to factors including the spatial variability of sources contributing fecal material, dry-weather discharges, resuspension of bottom sediments, and flow augmentation from reservoirs. Relative to E. coli and enterococci, FC concentrations appeared to decrease with time, which may be attributed to the greater die-off rate for FC bacteria.
Fecal-indicator bacteria concentrations at a site are dependent on the spatial distribution of point sources upstream of the station, the time-of-travel, rate of decay, and the degree of mixing and resuspension. Therefore, it is difficult to evaluate whether the left, right, and composite concentrations reported at a particular site are significantly different. To evaluate the significance of the fecal-indicator bacteria concentrations and turbidity reported in grab and composite samples during dry-, mixed-, and wet-weather events, data sets were evaluated using Wilcoxon rank sum tests. Tests were conducted using the fecal-indicator bacteria colonies and turbidity reported for each station for a given weather event. For example, fecal coliform counts reported in the left-bank sample were compared against the right-bank and composite samples, respectively, for the Ohio River at Sewickley site during dry-, mixed-, and wet-weather events.
The statistical analyses suggest that, depending on the sampling site, the fecal-bacteria concentrations measured at selected locations vary spatially within a channel (left bank compared to right, right bank compared to composite). The most significant differences occurred between fecal-indicator bacteria in the left bank compared to composite and right bank compared to composite samples (p-values = 0.003 to 0.1), suggesting that during some wet- and dry-weather events, the mixing of source streams and the receiving water is incomplete. Turbidity (p-values = 0.003 to 0.1) and enterococci (p-values = 0.007 to 0.02) most frequently demonstrated a correlation between sample locations (left bank versus composite). Correlations between left-bank and right-bank samples were rare.
Abstract
Introduction
Purpose and Scope
Description of Study Area
Water-Quality Criteria
Previous Work
Ohio River Valley Water Sanitation Commission
U.S. Geological Survey
Local Efforts
Related Studies
Sources of Bacteria
Point Sources
Nonpoint Sources
Fate and Transport
Study Design
Site Selection
Sampling Protocol
Sampling Protocol Evaluation
Streamflow Measurements
Water-Quality Sampling Methods
Quality Assurance
Occurrence and Distribution of Fecal-Indicator Bacteria
Bacteria Concentrations and Distributions
Weather Effects
Monongahela River Subbasins
Allegheny River Subbasins
Ohio River Subbasins
Comparison to Water-Quality Standards
Load Estimates
Summary and Conclusions
References Cited
Appendixes
Figures
1. Map showing study area and location of sampling sites on the Allegheny, Monongahela, and Ohio Rivers region near Pittsburgh, Pennsylvania
2. Graph showing cumulative percentage of discharge and stream cross section in an example of an equal discharge incremental sample
3. River cross-section and stream-velocity profile generated from acoustic Doppler current profiler, Monongahela River at Braddock, Pennsylvania (03085000), August 28, 2001
4. Hydrograph from the streamflow-gaging station on the Ohio River at Sewickley, near Pittsburgh, Pa., on August 4-7, 2001, prior to the August 8 wet-weather event
5-7. Boxplots showing fecal-indicator bacteria colonies in composite samples collected on the Allegheny, Monongahela, and Ohio Rivers near Pittsburgh, Pa., during:
5. Dry weather, 2001
6. Mixed weather, 2001
7. Wet weather, 2001
8-11. Maps showing:
8. Concentrations of fecal-indicator bacteria during dry weather on August 7, 2001, from five sites on the Allegheny, Monongahela, and Ohio Rivers near Pittsburgh, Pennsylvania
9. Concentrations of fecal-indicator bacteria after wet weather on August 8, 2001, from five sites on the Allegheny, Monongahela, and Ohio Rivers near Pittsburgh, Pennsylvania
10. Land cover of five subbasins within the Allegheny, Monongahela, and Ohio Rivers region, Allegheny County, Pennsylvania
11. Distribution of combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs) near Pittsburgh, Pennsylvania
Tables
1. Description of sampling sites on the Allegheny, Monongahela, and Ohio Rivers near Pittsburgh, Pennsylvania
2. Comparison of bacteria concentrations in discrete and composite samples collected from the Ohio River at Sewickley, Pennsylvania
3. Concentrations of field replicate samples for fecal-indicator bacteria, Allegheny and Monongahela Rivers, July-September 2001
4. Summary of concentrations of fecal-indicator bacteria that are above or below water-quality criteria for dry-, mixed-, and wet-weather events, July-September 2001, Allegheny County, Pennsylvania
5. Summary statistics for streamflow, temperature, and concentrations of fecal-indicator bacteria for the five sampling sites within the Three Rivers region, Pa., July-September 2001
6. Concentrations of fecal-indicator bacteria in composite samples collected during wet-weather events, Allegheny, Monongahela, and Ohio Rivers near Pittsburgh, Pennsylvania, August-September 2001
7. Statistically significant relations for fecal-indicator bacteria for dry-, mixed-, and wet-weather samples July-September 2001, Allegheny County, Pa.
8. Estimated daily loads of fecal-indicator bacteria within the Allegheny, Monongahela, and Ohio Rivers near Pittsburgh, Pennsylvania, July-September 2001
Appendix
1. Summary of streamflow and water-quality samples
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 (7.2 MB)
For more information about USGS activities in Pennsylvania contact:
District Chief
U.S. Geological Survey
Water Resources Discipline
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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