Transcript bacteria sources and data analyses 2012 EWRI

Sources of Bacteria and their
Variability in Urban Watersheds
Robert Pitt
Cudworth Professor Urban Water Systems
Department of Civil, Construction, and Environmental
Engineering
The University of Alabama
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Observed Bacteria Data in the National Stormwater
Quality Database, version 3 (average and COV)
Land Use (number of
observations)
Fecal Coliform
(CFU/100 mL)
Overall (2,154)
47,700 (5.0)
Residential (505)
55,900 (5.7)
Commercial (270)
26,100 (3.0)
Industrial (317)
47,300 (6.1)
Freeways (67)
8,600 (2.7)
Open Space (7)
7,300 (1.2)
Very large variabilities and widely ranging numbers of samples2
Experimental Design - Number of
Samples Needed
The number of samples
needed to characterize
stormwater conditions for a
specific site is dependent on
the COV and allowable error.
For fecal coliforms, the COV
values are very large (1.2 to
6.1 in the NSQD). A typical
goal of 25% allowable errors
would require hundreds of
samples, unless a better
understanding/explanation
of the variability was
possible.
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Burton and Pitt 2002
Fecal Coliform Bacteria by Land Use Categories
1e+8
1e+7
FC (mpn/100 mL)
1e+6
As noted before, the differences between land uses may be somewhat
NSQD
3 others, but limited data). Even
helpful (freeways and open
spaceVersion
lower than
though
large overall
ranges in each land use, most data are within two
25th to
75th percentiles
of most FC monitoring locations
orders of magnitude (the 25 to 75 percentile ranges from the high
are between
1,000
20,000 MPN/100
Statistically,
hundreds
to the low
tensand
of thousands
of CFU/100 mL;
mL, and
most
transportation
lowest
residential areas highest, but
observations
well above
anyand
criteria).
wide range seen
1e+5
1e+4
1e+3
1e+2
1e+1
1e+0
1e-1
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Commercial, Freeways, Industrial, Institutional, Open Space, and Residential
Residential Fecal Coliforms vs. Rain Depth
Not much of a trend here….
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Monitoring of 0.4 ha Parking Lot and Surrounding
Landscaped Area, Tuscaloosa, AL
Definite “first flush”
of turbidity at small
source area
Bacteria generally
increased during
rain
Bacteria also increasing
during this rain event
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Strong
seasonal
influences on
bacteria
levels,
especially
when
comparing
snowmelt with
stormwater
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Tuscaloosa, AL, “Library” File Data (flow
components affect combined water quality)
Mean/COV
E. Coli
(CFU/100 mL)
Enterococci
(CFU/100 mL)
Tap water
0
(0)
0
(0)
Spring water
2.4
(0.8)
1.0
(1.6)
Car wash
water
1480
(0.07)
1213
(1.4)
Industrial
wastewater
409
(2.7)
477
(2.3)
Potential baseflow components during warm weather
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Roof runoff E. coli levels greatly affected by overstory trees that
provide habitat for urban wildlife (squirrels and birds)
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Fate of bacteria after discharge investigated in
receiving waters during several studies:
Die-off curves for E. coli and Enterococci during in-situ microcosm tests
1.00E+05
1.00E+04
Cells/ml
k = 0.18 day-1
E. Coli
Enterococci
Background EC
Background Ent.
1.00E+03
1.00E+02
k = 0.09 day-1
1.00E+01
1.00E+00
0
2
4
6
8
10
Time (days)
12
14
16
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Easton, et al. 1999
In-situ microcosm tests of die-off curves for
Giardia lamblia in urban receiving waters
14000
Intact
Degraded
12000
Total
Cysts/L
10000
8000
6000
4000
2000
k = 0.11 day-1
0
0
1
3
7
Time (days)
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Easton, et al. 1999
Fate of Bacteria
after Discharge:
Interstitial Water
Bacteria Levels
using Peepers
Peeper being pushed
partway into sediments
Delrin peepers with 7 mL
cavities every 1 cm; 75micrometer screening and
2 hr equilibrium time
Bacteria levels increase
near sediment interface
and are elevated in
interstitial water.
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Ellis, et al. 1998
Full Factorial Experiment to Investigate Bacteria
Survival on Pavement and Urban Soils: Moisture,
temperature, and light vs. time
Wilson 2011
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E. coli survival on concrete for different
environmental conditions
Warm, wet, and dark
moderate die-off rate
Other conditions have initial rapid die-off rate, then
moderate re-growth, then moderate dieoff
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Enterococci survival on concrete for different
environmental conditions
Warm, wet, and dark steady-state population
Other conditions have initial rapid die-off
rate, then moderate re-growth
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Conclusions
• Stormwater bacterial levels are high and variable, requiring many
storm samples to confidently quantify.
• Some differences by land use (as expected, most open space
areas have lower bacteria levels than developed areas).
• Seasonal variations very important (especially comparing
stormwater with snowmelt)
• Many factors affect stormwater bacteria levels: contamination by
industrial or sewage and urban wildlife (and their habitats).
• Upon discharge, rapid die-off then reach equilibrium conditions.
• Sedimentation with increased populations near sediment/water
interface and elevated interstitial water bacteria levels.
• Survival on concrete is similar, with potential several growth and
die-off stages. Warm, dark, and moist conditions result in their
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greatest survival.
R. Pitt
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