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Modeling Fecal Coliform Bacteria
Dynamics in Onondaga Lake
CE5504 - Surface Water Quality Modeling
Case History
What are Coliform Bacteria ?
Coliform bacteria are considered to be indicator organisms, i.e. those used by public
health officials to indicate the potential presence of disease-causing organisms or
pathogens. It is logistically impractical and prohibitively expensive to test each
water sample for all of the pathogens potentially present.
The most commonly used indicator organisms are members of the coliform group,
named for Escherichia coli, a normal inhabitant of the digestive tract of humans and
other warm-blooded animals. Tests are made for total coliforms (an assay which
also detects some soil bacteria) and fecal coliforms (a group limited to the guts of
warm-blooded animals). Most strains of E. coli are not pathogenic, however, some
can cause gastroenteritis, and occasionally, death. Standards vary with water use:
contact recreation (200-1000), wastewater effluent (200) and drinking water (<1)
colony forming units or cfu.
What are Combined Sewer Overflows ?
Older cities have sewer systems which carry both sanitary wastewater and street
runoff or storm water to the wastewater treatment plant. Such systems are referred
to as combined sewers. Newer cities, and some renovated portions of older
municipalities, have separated sewers where the sanitary wastewater is transported to
the wastewater treatment plant and stormwater is discharged to receiving waters,
either with or without treatment.
Combined sewer overflows or CSOs are relief structures built into combined sewer
systems to prevent overloading at the treatment plant, surcharge flooding of streets
and the backup of raw sewage into homes. CSOs are designed with weirs which
automatically discharge a mixture of storm runoff and raw sewage to receiving
waters when water levels in the sewers reach a certain level.
How do CSOs impact water quality
and the management of Onondaga Lake ?
CSOs discharge untreated wastewater to receiving waters. As expected, this provides
a load of BOD, ammonia, and phosphorus which may stress these lakes and streams.
Perhaps of greatest importance is the discharge of fecal bacteria, with pathogens which
could potential endanger the human health, and sanitary detritus which is aesthetically
damaging. Concentrations of fecal coliform bacteria in streams receiving CSOs can
exceed 106 cells/100 mL and result in violation of the contact recreation standard over
much of Onondaga Lake.
Complete elimination of CSO discharges (sewer separation, capture and treatment,
treatment) is often beyond the financial resources of many municipalities. Further, the
extent and magnitude of the impact of a CSO event is difficult to predict due to the
interactions of loads, mass transport, and kinetics. Here, mathematical models are of
great benefit in guiding management efforts seeking to minimize CSO impacts.
Model Development
 Eij Aij 
dCi
Vi
 Wi   [Qij (C j  Ci )]   
  C j  Ci   Vi k Ci
dt
j
j 
 Lij 
Loads
Advection
Cell i
Diffusion
Cell j
Kinetics
Model Framework
A two-layer, 11-cell model
was developed with 8
surface and 3 bottom cells.
Cell dimensions were
selected to accommodate
spatial differences in fecal
coliform levels noted
through field monitoring.
Loading Sub-Model
Tributary loads were monitored
under dry weather conditions and
for two storms. Sampling was
conducted on an hourly basis
during storms, with the
frequency reduced to twice daily
as the hydrograph returned to
base flow conditions. Storms 1
and 2 had return frequencies of 1
and 7 years, respectively. Lake
stations were monitored 1-3
times per day over the course of
the storm event.
Mass Transport Sub-Model
Advective mass transport was
estimated as the cumulative
stream flow inputs for each cell.
Horizontal diffusive exchange
was calculated as a function of
epilimnion depth and wind
speed. Vertical diffusive
transport was calculated as a
function of the thermal profile
(vertical density gradient).
Kinetics Sub-Model
k  k d  ki  k s
The overall kinetic coefficient included terms for temperaturemediated loss in the dark (kd), losses as mediated by irradiance
(ki), and losses to sedimentation (ks).
Kinetics: Dark Death Rate
kd ,T  kd ,20 
(T  20)
Measurements of a temperature response made for this study
and those reported in the literature fail to make a strong case
that  differs from zero. An average dark death rate of 0.73
d-1, the intercept of the light response curve, was proposed
for use in the model.
Kinetics: Light Mediation
ki   I
I
I 0,avg
 ze
1  e
(   ze )

A strong linear correlation was noted between light intensity
and fecal coliform death rate. The slope of the light
response curve,  = 0.008, was used to calculate ki.
Kinetics: Sedimentation
Settling losses were determined by assessing the
association of fecal coliform bacteria with particles of
various size classes and then determining particle
settling velocities (mean = 1.38 m·d-1) using in situ
sediment traps.
v
ks 
z
Kinetics Submodel
k  k d  ki  k s
k  kd ,20 
(T  20)
 I 0,avg
v
(  z )

1 e



 ze
ze
e
The overall kinetic coefficient included terms for temperaturemediated loss in the dark (kd), losses as mediated by irradiance
(ki), and losses to sedimentation (ks).
Model Evaluation
Model Evaluation
Model Evaluation
Model Sensitivity and Application
Environmental Effects
• Wind
• Irradiance
• Thermocline Depth
Tributary Loads
• South tributaries
• North tributaries
Model Sensitivity and Application
Model Sensitivity and Application
Model Sensitivity and Application
Model Sensitivity and Application
Model Sensitivity and Application
CSO Remediation Plan
There are CSO discharges to three tributaries to Onondaga Lake: Onondaga Creek,
Harbor Brook, and Ley Creek. Onondaga Creek has the largest number of CSOs with
45 discharge points. Onondaga County is presently considering a plan which would
reduce CSO discharges by 56% (900 MGD  392 MGD) at a cost of $65-80 million.
The plan incorporates limited sewer separation (7% of the flow reduction), activation
of a dormant in-line storage system (43% of the flow reduction) and construction of
two ‘regional treatment facilties’ of RTFs (50% of the flow reduction). The RTFs are
composed of a wet well (~1 MG), swirl concentrators (~0.5 MG), and a disinfection
tank (2 MG). Swirl concentrators remove a fraction of the solids from the combined
wastewater before discharge to the receiving waters. Combined wastewater captured
through in-line storage and solids captured in swirl concentrators are routed to the
treatment plant as storm flows abate.
The Partnership for Onondaga Creek is contesting the County plan as an incomplete
and insufficient approach which violates the principles of environmental justice.
Modeling Fecal Coliform Bacteria
I. Field and Laboratory Determination of Loss Kinetics
by M.T. Auer and S.L. Niehaus
II. Model Development and Application
by R.P. Canale, M.T. Auer, E.M. Owens, T.M. Heidtke,
and S.W. Effler
Based on articles published in
Water Research, Volume 27,
Number 4, 1993.
Contributions No. 26 and 27 of
the Upstate Freshwater Institute.