1. Indicators of Fecal Contaminants in Publicly Accessible
Frederick County Streams
Sara Eckard, Andrea Kozlosky, Drew Ferrier, and Claire Hudson
Hood College Center for Coastal and Watershed Studies, Frederick , MD
see9@hood.edu | dferrier@hood.edu
Results
Methods
• Six sites across Frederick County were sampled
• Wet samplings took place within 24 hours of a
significant rain period, which was defined as 0.5 inches
of rain or greater
• Dry samplings were preceded by at least 72 hours
without rainfall
• Sampling and bacterial plating was done following EPA
Method 1600 (US EPA, 2009)
• Bacteria counts were converted into colony forming
units per 100 mL
Acknowledgements
I would like to thank Ashley McAvoy, Alana Carveth, Andrea Kozlosky, Ron
Albaugh, Drew Ferrier, and Claire Hudson for helping with the collection of
samples and guidance in the filtration procedure. I would also like to
acknowledge the Chesapeake Bay Foundation for providing funding for the
sampling and materials.
Introduction
Enterococcus bacteria are indicators of fecal
contamination. Like E. coli, another commonly used
bacterial indicator, Enterococcus is not an inherently
dangerous bacterium. However, its presence is used as an
indicator of potentially other pathogenic bacteria. E. coli
levels are closely monitored in recreational waterways
such as public bathing beaches, but are rarely monitored
in public accessible waters like shallow streams. This has
serious implications, as citizens still wade and explore
these public waters, despite them not being official
bathing areas. The EPA standard for a 30-day geometric
mean of Enterococcus is 30 cfu/100 mL for public bathing
waters.
In partnership with the Chesapeake Bay Foundation, six
sites in Frederick County were monitored for Enterococcus
from June to August of 2015 (Figure 1).
Conclusion
All sites were well above the EPA recommended mean of
30 cfu/100 mL in both wet and dry sampling. In five out of
six sites, Enterococcus levels were higher in wet samplings
than in dry samplings (Figure 2). The remaining site,
Maryvale Tributary, a tributary leading to Carroll Creek in
Baker Park, experienced higher levels of Enterococcus
during a dry period, specifically close to 72 hours following
a wet event. After 72 hours, the level would again
decrease and return to similar levels following a rain
event.
This unusual trend may be indicative of a sewage leak or
other contamination source that becomes diluted
following a rain, hence the lower levels of bacteria during
the wet sampling months. The spike could also indicate a
stronger run off source further upstream that travelled
downstream to the sampling point over a course of 72
hours. Additional sampling in an upstream portion of the
same tributary (labeled Maryvale Upstream) showed the
peak Enterococcus levels occurred roughly 48 hours after
a rain event, possibly indicating the movement of
significantly enterococcus rich run off moving down the
tributary from an upstream source (Figure 3).
Figure 3. Graphical representation of enterococcus cfu/100 mL versus time since last precipitation.
0
5000
10000
15000
20000
25000
30000
0 20 40 60 80 100 120 140 160
CFU/100mL
Hours since last precipitation
Maryvale
Tributary
Maryvale
Upstream
Sampling
Figure 2. Comparison of the geometric means of wet and dry sampling in the six sample sites. Error bars are +/- 1 standard errors.
0.00
2000.00
4000.00
6000.00
8000.00
10000.00
12000.00
Rock Creek Owen's Creek Glade Run Culler Lake Maryvale
Tributary
Carroll Creek
CFU/100mL
Wet
Dry
U.S. Environmental Protection Agency (U.S. EPA). 2009. Method 1600: Enterococci in Water by Membrane Filtration Using
membrane-Enterococci Indoxyl-β-D-Glucoside Agar (mEI). Office of Water, U.S. Environmental Protection Agency, Washington, DC.
EPA-821-R-09-016
Citation
Figure 1. Maps showing Frederick County sampling sites contracted by CBF labelled in blue. Additional sampling site labeled in gray.