CSO Facility Performance
The CSO retention/treatment basins are designed to capture the first
flush flows and to then route flows to a second flow-through compartment
after the first compartment is full. This prevents the discharge of
any pollutant loads that may be captured with the first flush, which
has been found to have higher concentrations of pollutants. The basins
are dewatered after a storm water event when capacity is available
in the receiving interceptor for conveyance to the Detroit wastewater
treatment plant. The facilities all included influent or effluent screens,
skimming baffles, storage and settling basins that can capture small
events or work in a flow-through mode for large events. All facilities
are designed to meet NPDES effluent limits for fecal coliform of 400
cts / 100 ml and an effluent goal for total residual chlorine (TRC)
of 1 mg/L. A basin only discharges treated effluent to the Rouge River
during large rainfall events when the basin is full and the interceptor
sewer is unable to accept any more water for conveyance to the treatment
plant. Note that the treated overflows occur when the assimilative
capacity of the river is the greatest due to the higher river flows.
The CSO basins are dewatered when the interceptor sewer is able to
accept the flows. Most of the CSO basins use tipping buckets to remove
settled debris after an event. The basins have to be good neighbors
to surrounding land uses, which include nature centers, a golf course,
and recreational facilities.
CSO Basin Evaluations
As discussed in Overview Description of
the CSO Control Program, a detailed evaluation study of the nine
of the completed CSO control basins has been undertaken. The information
below is extracted from the "Overview Description".
The purpose of the evaluation study, utilizing approximately two years
of sampling at each basin, was to examine the performance of the facilities
and the water quality impacts of their discharges. The results of the
evaluation study, coupled with efforts to control storm water and other
pollution sources in the watershed, is providing the basis for the
Phase II and Phase III CSO control program on the remaining CSO sources
in the watershed. The information gained from the evaluation of design
storms and control technologies is useful nationwide for determining
cost effective CSO controls to meet water quality standards.
There are four key questions being asked by MDEQ of the evaluation
of the CSO control basins: (1) Is the discharge from a CSO control
facility clean enough to meet water quality standards? (2) What in-stream
impacts should be measured? (3) How can the in-stream impacts of CSOs
be evaluated when there are other sources of wet weather in the watershed?
(4) When is there enough data to make decisions?
The MDEQ has established a process
for assessing compliance with the NPDES permits and the phased
CSO control requirements in order to answer the above questions. The
process fully involved the Rouge Project and the CSO communities. The
MDEQ established three CSO Retention/Treatment Basin (RTB) Committees
to analyze discharge data from groups of RTBs. The RTB Committee reviews
discharge data in relation to the Phase II
Criteria for Success in CSO Treatment established by MDEQ with
input from the Rouge Project and the CSO Communities. The Rouge Stream
Data Committee evaluates receiving stream data for impacts from the
individual RTBs. The Committee then determines whether the receiving
water downstream from each individual RTB is achieving the Phase II
criteria for success and, if not, to what extent the RTB discharge
is contributing to the water quality problem. Finally, the CSO Workgroup
compiles the information on success of the individual RTBs in meeting
the Phase II and Phase III criteria for success and proposes what level
of treatment should be considered adequate. The Workgroup is composed
of MDEQ staff and representatives of the RTB communities.
In February 2001, the Rouge Stream Data Committee issued its Interim
Report in which they analyzed the data collected to assess the
effectiveness of the CSO demonstration basins and whether the receiving
water downstream from each basin is achieving Phase III criteria
for success and, if not, to what extent are the basins contributing
to the remaining water quality problems. The MDEQ Phase III criteria
for success state that achievement of state water quality standards
(WQS) at times of discharge will be measured by the following criteria:
- the dissolved oxygen (DO) standard;
- the physical characteristics standard;
- the total residual chlorine (TRC) standard; and
- the health of the biological community (as a surrogate for toxic
materials and other pollutants).
Additional details of the in-stream evaluation process can be found
in the paper titled "Evaluation
of In-Stream Impacts of CSO Control Facilities." For other reports on the CSO control program, please
see Products and Data,
Combined Sewer Overflows.
It is very important to note that MDEQ has concluded that nine of
the CSO retention treatment facilities are currently meeting the Phase
II criteria of the elimination of raw sewage and the protection of
public health. A June 9, 2000 Letter
of Approval for Phase II Review focused on the following retention
treatment basins: Acacia Park CSO Retention Treatment Basin, Birmingham
CSO Retention Treatment Basin, and Bloomfield Village CSO Retention
Treatment Basin. The August 7, 2000
Letter of Approval for Phase II Review ocused on the following
retention treatment basins: Inkster CSO Retention Treatment Basin,
Dearborn Heights CSO Retention Treatment Basin, Redford Township
CSO Retention Treatment Basin. A February 14, 2002 Letter of
Approval for Phase II Review focused on the following retention
treatment basins for the City of Detroit: Hubbell-Southfield CSO
Retention Treatment Basin, Puritan-Fenkell CSO Retention Treatment
Basin, and Seven Mile CSO Retention Treatment Basin. In addition,
the three Oakland County CSO basins (Acacia Park, Birmingham, and
Bloomfield) are achieving the Phase III goal of meeting water quality
standards at times of discharge, except for meeting the yet-to-be-evaluated
total residual chlorine standard.
This Phase III certification is expected on the other six basins very
soon. The tenth CSO basin, River Rouge, became operational in March
2002. Its performance will be evaluated over the next two years.
Evaluation of the Performance of the CSO Basins: What the Rouge Project
As stated earlier, each of the retention/treatment basins is sized
for different design storms and several employ innovative technology.
The CSO basins also incorporate a variety of additional features or
variations in compartment sizing and flow sequencing in an effort to
improve their effectiveness. As stated earlier, a two-year period was
established in the NPDES permits to evaluate the performance of the
CSO control basins implemented under Phase I of the program. Evaluation
findings would then establish the level of control needed for the remaining
CSOs in the watershed. Such controls would be implemented in Phase
II of the program. Phase I and Phase II controls were to achieve the
elimination of raw sewage and the protection of public health. Phase
III of the control program would require the installation of additional
controls, if needed, in order to meet water quality standards in the
Rouge River. Working with the local communities, the MDEQ established
rigorous "Criteria for Success in CSO Treatment" to
evaluate whether the CSO basins met the goals established for each
phase of the program. The process by
which these Criteria were established and the specific details of the
criteria are explained in documents contained on the Rouge Project
web site and therefore will not be discussed here.
A detailed evaluation of the approximately two years of sampling at
each of the CSO retention treatment basin for which data were available
(nine basins) was undertaken to examine the performance of the facilities
and the water quality impacts of their discharges. Details of the protocols
used and the full results of all studies are available on the Rouge
River web site. (See "Technical Papers and Professional Presentations
on CSO Control Program"). The results
of the evaluation study, coupled with efforts to control storm water
and other pollution sources in the watershed, are providing the basis
for the Phase II and Phase III CSO control program on the remaining
CSO sources in the watershed. The information gained from the evaluation
of design storms and control technologies is also being used to demonstrate
cost effective CSO controls. This information is needed for nationwide
use in implementing the national CSO Control Policy embodied in the
Clean Water Act.
In order to make the wealth of data gathered during the two-year evaluation
program at each retention/treatment basin more available, the Rouge
Project summarized the more important findings in a report titled: "CSO
Basins: Getting the Most Performance for Your Pollution Control Dollar" (hereinafter
referred to as "CSO
Basins: Getting the..."). That report presents an excellent
summary of the insights and lessons learned from the design, construction,
and operation of the Rouge Project Phase I CSO facilities. The reader
is urged to review that full report for the detailed information. Some
of the information contained in that report is summarized below. In
addition, there is a wealth of additional and more detailed information
on the performance of the CSO treatment facilities on the Rouge Project
web site at the aforementioned "Technical
Papers and Professional Presentations."
While developing the summation of the data from the CSO basin evaluations,
four major evaluation questions emerged relative to the Rouge Project
CSO control program. Those questions were:
- How can compliance with NPDES Permits and Water Quality Standards
- What treatment and hydraulic processes are most effective?
- What is needed for operational effectiveness?
- What is the proper size for CSO basins to comply with regulatory
The answers to these questions are provided in the above referenced report (CSO
Basins: Getting the...) What follows is a summary of that report including
the answers, the insights and lessons learned.
Evaluation Question 1: How Can Compliance With NPDES permits and
Water Quality Standards Be Measured?
Methodology for Evaluating CSO Basins
Following the implementation of the Rouge CSO control program, the
permittees and MDEQ realized that additional guidance was necessary
to define terminology such as "elimination of raw sewage".
As was discussed earlier, the methodology for evaluating the success
of the basins in meeting permit requirements was developed by the MDEQ
as part of its work with the Rouge Project. MDEQ developed criteria
for evaluating the success of the basins in meeting permit requirements
through close consultation with the owners of the facilities and representatives
of the Rouge Project. Two work groups were established, one to evaluate
individual basin performance and one to evaluate the in-stream impacts
for dissolved oxygen, physical characteristics, total residual chlorine,
and biological impacts. For each of these evaluations, the work groups
established a set of measurements and analytical methods to perform
the evaluation. This collaboration resulted in a document entitled: "Criteria
for Success in CSO Treatment".
The goals and processes for evaluation of these goals established
as part of MDEQ's document are summarized in Table 3. Further description
of the importance of the collaborative, consensus building process
for the entire Rouge River restoration effort that included all stake
holder interests and focused on well-defined technical issues are described
in a paper titled: "Can a Watershed Be Managed? Leading the Efforts
of Public Agencies and Local Communities in the Rouge River Watershed".
Methodology for Evaluating Rouge Phase I CSO Retention Treatment
*Great Lakes and Environmental Assessment Section (GLEAS) Procedure 51
||General Process to Evaluate Goal
- Ability to compare data from all basins
| Estimate actual detention times at design storms
for each facility to be able to compare basins on a common basis.
- Protect public health and eliminate raw sewage (Goal for
Phase I and Phase II Controls)
- Evaluate protection of public health based on disinfection
of effluent and determining if the effluent fecal coliform
limit of 400 cts/100 ml is met while minimizing total residual
- Evaluate elimination of raw sewage based on the ability of
the basins to remove sanitary trash and identifiable sanitary
solids. This evaluation to include:
- visual observations
- determining removal efficiency of materials greater
- determining if any readily identifiable sanitary trash
is found in a 4-millimeter mesh effluent net or basket.
- Achieve state water quality standards in the receiving stream
at times of discharge (Goal for Phase III Controls)
Success of this goal are measured by the following criteria:
- The dissolved oxygen (DO) standard - measure DO to show
that the basin does not contribute to DO of less than 5 mg/L.
- The physical characteristics standard - measure TSS, turbidity,
oil and grease, and deposition areas to show the basin does
not contribute to violation of the physical characteristics
- The total residual chlorine (TRC) standard -measure TRC
to establish whether TRC plume will have toxic effects and
prevent fish passage.
- The health of the biological community (as a surrogate
for toxic materials and other pollutants) - measure the health
of the biological community using GLEAS* 51 procedures.
Utilizing the approximately two years of sampling data at each basin,
a detailed evaluation of nine basins was undertaken to examine the
performance of the facilities relative to the three goals summarized
in Table 2. The River Rouge CSO basin did not become operational until
2002. It is currently being evaluated to determine its performance.
Goal 1: Ability to Compare Data for All Basins
The first goal or criteria for success was the ability to compare
data from all Phase I CSO basins. The design approaches and assumptions
used in the design of the basins varied widely among the basin designers.
In order to draw conclusions about the performance of the demonstration
CSO basins, the actual basin detention time at each
facility given the same storm event and conditions needed to be determined.
Knowing the actual detention time versus a design detention
time provides a means of comparing the relative sizes of these facilities
and of comparing their size to the demonstration and presumptive sizing
criteria. Then an evaluation can be made as to the effectiveness of
the residence time on settling and disinfection.
The CSO basin evaluation has resulted in the following findings:
- The amount of runoff that is generated by a storm event is greatly
influenced by antecedent moisture conditions. Antecedent conditions
relate to the amount of rainfall that occurred in the days prior
to the event being evaluated.
- The amount of runoff that is generated by a rainfall event is greatly
influenced by seasonal variation in the infiltration capacity of
the soil and interception by foliage. A greater response is seen
during winter and early spring conditions when infiltration capacity
is lower or non-existent due to frozen ground conditions and due
to lower interception by foliage (tree cover).
- The amount of runoff that is generated by a rainfall event is greatly
influenced by seasonal variation in the peak hour intensity of the
rainfall events, which was also found to vary seasonally, with higher
peak intensities occurring during May through October.
Thus, a design event cannot be adequately defined without specifying
These results illustrate the value of having site-specific monitoring
data to develop the parameters used for sizing the basins. Critical
in this sizing analysis are a consideration of the seasonal variation
in rainfall intensities and the impact of antecedent moisture conditions.
Having sufficient data to estimate flows that would be generated by
a design event is difficult, but it is vital to ensure that the facility
will be sized properly.
Because the actual detention times have been determined to be greater
than the original design intended for three of the four basins analyzed,
it is important to look at the actual detention time versus the design
detention time in making an assessment of how effective a CSO basin
is in meeting the regulatory requirements. The additional detention
time provided by these basins could be providing additional treatment
effectiveness. This benefit needs to be considered in answering the
question of "What is the proper size for a basin to meet regulatory
Goal 2: Protect Public Health and Eliminate Raw Sewage
The objective of Goal 2 is two-fold: a) the protection of public health
and b) elimination of raw sewage. Success in achieving Goal 2 is demonstrated
using measurements and observations of CSO basin effluent.
Protect Public Health
The evaluation of the first part of Goal 2, protection of public health,
is based on disinfection of effluent and determining if the Michigan
fecal coliform limit of 400 cts/100 ml is met by the effluent while
minimizing total residual chlorine (TRC). A higher chlorine dose results
in a greater treatment of the fecal coliform, but it also tends to
result in a higher TRC. At the start of the project, the goal for CSO
basin effluent TRC was 1 mg/L or lower. Individual effluent samples
collected during a range of events were tested for fecal coliform concentrations
and discrete measurements of TRC were also made. For each facility
and storm, an event geometric mean for effluent fecal coliform and
an event mean TRC value were calculated. Success is judged to be achieved
if the event geometric mean fecal coliform across the range of monitored
storm events is in compliance with the limit.
The results of the basin evaluations indicate the facilities can consistently
meet the fecal coliform limit when operated to maintain effluent TRC
concentrations of 1 mg/L or greater. For discharge events with effluent
TRC concentrations less than 1 mg/L, the fecal coliform limit was usually
not met. As a result of the evaluation and a consensus by one of the
Rouge Project work groups, the target range for effluent TRC was revised
from 1.0 to 1.5 mg/L.
Eliminate Raw Sewage
The second part of Goal 2, determining if the basin eliminates raw
sewage, is based on the ability to remove sanitary trash and identifiable
sanitary solids. The basis for this criterion is that the discharge
can only be considered treated and no longer raw if it does not have
the visual appearance of raw sewage (in addition to being disinfected).
Removal of sanitary materials includes three process treatment components:
screening, skimming and settling of the flow. Screens installed at
each facility contribute to the removal of larger debris from the flow.
Baffle walls installed in the vicinity of influent, intermediate or
discharge weirs help to facilitate the removal of floating materials.
These materials are captured in the basin for removal during dewatering
or flushing. Sedimentation allows for the removal of heavier objects
and solids. The ability of the facilities to achieve removal of these
objects is typically related to the surface overflow rate and the weir
Elimination of raw sewage was evaluated by visual observations and
a netting study. Visual observations were performed during daylight
hours at the four CSO basins where it was feasible, and were taken
as representative of the other basins. Mesh nets with small rectangular
openings of 6 mm were placed over a portion of the basin outfall grating
at 4 basins to determine if any sanitary trash were being discharged
from the basin to the river. No evidence of sanitary trash was seen
in the effluent of those basins observed, except for a small amount
on one occasion. This event was not viewed as a concern as it was caused
by abnormal basin operation following a power failure.
It is very important to note that based on the evaluations performed
on the effluent discharge from the basins, MDEQ has concluded that
all nine of the Rouge Phase I CSO basins evaluated are currently
meeting the Goal 2 criteria of the elimination of raw sewage and
the protection of public health. The tenth facility is still
Goal 3: Achieve State Water Quality Standards
The objective of Goal 3 is to achieve state water quality standards
in the receiving stream at times of discharge. Success in achieving
Goal 2 (protect public health and eliminate raw sewage) is demonstrated
using measurements of basin effluent, whereas the success in achieving
Goal 3 is demonstrated using measurements in the receiving stream at
times of discharge. The four criteria of success for Goal 3 as outlined
in Table 3 are 1) the dissolved oxygen (DO) standard, 2) the physical
characteristics standard, 3) the total residual chlorine (TRC) standard,
and 4) the health of the biological community (as a surrogate for toxic
materials and other pollutants).
Dissolved Oxygen Standard
The state's DO standard for the Rouge River is a minimum of 5 mg/L
at all times. To achieve Goal 3 for the DO standard required measuring
DO in the river both upstream and downstream to show that the basin
does not cause the DO to go below the standard of 5 mg/l. This criterion
was evaluated by continuous water quality monitoring stations and predictive
modeling to determine the magnitude and location of transitory dissolved
oxygen sags caused by effluent from the facilities.
All available monitoring data and modeling results have led to the
- The DO standard is being achieved downstream of all three Oakland
County CSO basins at times of discharge, except for DO sags that
were not caused by the basin effluent.
- At times of basin discharge, the DO standard is being achieved
from the Redford basin down to a location where other uncontrolled
CSOs impact the river. DO did sometimes drop below the standard during
wet weather events, but since this pattern was nearly identical upstream
and downstream of the Redford basin, the cause of the violation was
not attributed to the basin.
The state's physical characteristics standard prohibits unnatural
physical properties (turbidity, color, oil films, floating solids,
foams, settable solids, suspended solids, deposits) in quantities which
are, or may become injurious to any designated use of the receiving
The physical characteristics criterion was evaluated by comparing
effluent and instream total suspended solids, and by periodic visual
observations of the effluent plumes, primarily to check for the presence
of oil films or high turbidity. Also, effluent nets on the CSO discharges
were used to determine if any sanitary trash or identifiable sanitary
solids were present in the effluent. The documented data for the physical
properties considered indicate there are no unnatural physical properties
in quantities that are considered injurious to any designated use at
times of basin discharge.
Total Residual Chlorine
As required by the state water quality standards, instream TRC concentrations
must not exceed the final acute value of 0.038 mg/L, unless a mixing
zone demonstration is performed and accepted by the state. This standard
is difficult to meet given that effluent TRC must be at least 1 mg/L
for adequate reduction of fecal coliform bacteria. The TRC standard
was evaluated by measuring instream TRC concentrations downstream of
CSO basin discharges. Due to difficulties in safely accessing the river
during high flow conditions, these measurements were limited to one
facility where a boat could be used to perform instream sampling. While
instream TRC concentrations in excess of 0.038 mg/L were measured near
shore at several downstream transects, the concentrations were below
detection for two-thirds of the river cross-section. While the results
show there is a zone for fish passage, a formal mixing zone demonstration
was not performed for the facility.
In summary, the evaluation performed to date has shown that instream
TRC measurements have exceeded the state standard, but there has been
no conclusion regarding the specific environmental impact caused by
chlorine residuals in the Rouge River. As the next step in the evaluation
process, the NPDES permit for the three Oakland County CSO basins requires
that a TRC Mixing Zone/Plume Definition Study be performed for each
basin. The purpose of the study is to determine the water quality impacts
in the Rouge River from TRC in the treated basin effluent. The permit
required a work plan for the study to be submitted in September 2003
with the study report to be submitted by March 2006. If the study indicates
that effluent limitations or additional controls for the discharge
of TRC are needed to meet water quality standards at times of discharge,
the MDEQ may propose to modify the NPDES permits for these three basins
to include appropriate effluent limitations and/or controls for the
discharge of TRC.
Finally, the health of the biological community was assessed in the
vicinity of several Rouge Phase I CSO basin discharges as a surrogate
for assessing the presence of toxic materials and other pollutants
in the basin effluent. Macroinvertebrate samples were collected upstream
and downstream of the CSO basins in Redford and Oakland County (four
basins total) to investigate the compliance of these basins with Goal
3. Collection of organisms and calculation of community scores followed
the Great Lakes and Environmental Assessment Section (GLEAS) Procedure
51 (MDNR, 1991). As a result of this assessment, it was agreed by MDEQ
that the water quality standards for toxic substances are presumed
to be achieved upstream and downstream of the Oakland County and Redford
CSO basins, even at times of discharge, as there is no measurable effect
of these discharges on the health of the biological community.
It is very important to note that evaluations relative to Goal
3, achieving state water quality standards, have been completed at
three of the Rouge Phase I CSO basins and MDEQ has certified that
these basins are meeting water quality standards at times of discharge,
except for meeting the yet-to-be-evaluated total residual chlorine
standard. This certification is expected for at least another three
basins in the year 2004. Additional details of the in-stream
evaluation process can be found in the paper titled "Evaluation
of In-Stream Impacts of CSO Control Facilities" Trend analysis
results clearly demonstrate that DO concentrations are improving
in the Rouge River Watershed during both wet and dry weather conditions.
Eight of nine locations show a statistically significant improving
trend for the mean DO with the annual average improvement ranging
up to 0.53 mg/L per year. The ninth location is still being evaluated
and is influenced by many uncontrolled CSO outfalls.
Lessons Learned on Evaluation Question 1
Lessons learned relative to evaluating compliance of the Rouge Phase
I CSO basins with regulatory requirements include the following:
- Regulatory requirements can be ambiguous; thus, developing a well
defined, technical evaluation process was critical to determine compliance
with regulatory requirements. Use of collaborative work groups that
involved all the stakeholders provided important consensus on defining
criteria for success.
- The process for evaluating the impacts of the basins has led to
constructive decisions. Working with a large group trying to achieve
consensus has taken more time, but was well worth the effort. MDEQ
agreed that implementation of further controls is dependent on this
- A design event cannot be adequately defined without specifying
antecedent conditions, season, and rainfall intensity. These factors
all impact the amount of wet weather response that will be generated
for the same size storm event. Ideally, continuous simulations that
account for these factors by using rainfall records over a number
of years should be used to predict runoff rates and volumes. These
simulation results would better predict the performance of the basins
in terms of frequency and volumes of CSO captured or overflowed.
- The Rouge Phase I CSO basins provide retention and treatment and
the frequency and magnitude of discharges has been considerably reduced.
Therefore, the basins only discharge treated effluent in large events
when assimilative capacity of the river is the greatest.
- Other sources of water pollution are significant, but the evaluation
of CSO impacts can be reasonably isolated from other non-point source
pollution impacts to draw conclusions on the effectiveness of the
CSO basins in achieving the water quality standards.
- A two-year time frame for monitoring and/or 10 overflow events
at each facility is generally sufficient to characterize effluent
quality, demonstrate ability to meet effluent permit limits, and
demonstrate ability to meet water quality standards at times of discharge.
In some cases, an additional 3 to 6 months of study is being performed
to further examine some issues specific to certain basins.
- Treated effluent from the CSO control facilities studied so far
seems to be relatively good quality. Permit effluent limits for fecal
coliform can be met consistently when effluent TRC is greater than
1 mg/L. Water quality standards are being met at some facilities,
but detailed evaluations are ongoing for the other basins, particularly
8. Instream TRC from basin effluent exceeds state standards at times, but further
evaluation is needed to determine if there is any adverse environmental impact.
Overall, the evaluation of the Phase 1 CSO control facilities is providing
valuable technical information for future phases of CSO control in
the Rouge watershed and for communities embarking on CSO control in
other watersheds. The development of an evaluation process provided
an innovative forum for stakeholders to collaboratively establish objectives
for CSO control within the goals of urban watershed restoration. Since
wet weather control is expensive, having a well defined, technical
evaluation process to determine compliance with regulatory requirements
Evaluation Question 2: What Treatment and Hydraulic Processes Are
Treatment and Hydraulic Processes Used
A variety of design features were employed to explore what treatment
and hydraulic processes are most effective in reducing CSO loads to
the river. The Rouge facilities all included influent or effluent screens,
skimming baffles, storage and settling compartments within the basins
that can capture small events or work in a flow-through mode for large
events, and disinfection using sodium hypochlorite. The facilities
also included a variety of innovative technologies: swirl concentrator,
first flush compartments, compartments in parallel, compartments in
series, decanting outlets and shunt channels
A summary of the basin configuration and size for the nine Rouge Phase
I CSO basins in operation is provided in Table 4. Six of the facilities
have the ability to capture the first flush; that is, to route flows
to a second flow-through tank after the first tank/compartment is full.
This prevents the discharge of any loads that may be captured with
the first flush, which has been found to have higher concentrations
of pollutants. One facility has a swirl concentrator, and three facilities
have a shunt channel to avoid potential for resuspending solids after
the facility is full. For screening, most of the facilities used a
bar spacing of 0.75 inches. Two basins used screen bar spacing of 0.5
inches and one used 1.5 inches.
Rouge Phase I CSO Basin Configuration and Size
Compartment Volumes (MG)
1 first flush compartment followed by 2 detention compartments operating in parallel
186 ft x 60 ft x 11.75 ft each detention compartment
First flush compartment = 1.1 MG
2 detention compartments, each = 1 MG
Total = 3.1 MG
2 parallel compartments preceded by one swirl concentrator
180 ft x 66 ft x 11.2 ft each compartment
Each compartment = 0.95 MG
Total = 1.9 MG
3 detention compartment in parallel with the capability of using the first compartment for a first flush capture
175 ft x 60 ft x 11.6 ft each compartment
Each compartment = 0.9 MG
Total = 2.7 MG
2 compartments in series
160 ft x 80 ft x 20 ft each compartment
Each compartment = 2.0 MG
Total = 4.0 MG
2 compartments in series with 11ft tunnel
140 ft x 120 ft x 20 ft each compartment
Each compartment = 2.75 MG
Total = 5.5 MG
3 compartments filling in series through weirs at different elevations
157.5 ft x 128.5 ft x 20 ft each compartment
Each compartment = 3.3 MG
Total = 10 MG
2 compartment operating in parallel
200 ft x 91.5 ft x 8 ft each compartment
Each compartment = 1.1 MG
Total = 2.2 MG
2 compartment operating in parallel
236 ft x 99.5 ft x 8 ft each compartment
Each compartment = 1.4 MG
Total = 2.8 MG
2 compartment in series with the capability of running the first compartment as a first flush capture compartment
900 ft x 240 ft x 16.5 ft overall each compartment
First compartment = 10 MG
Second compartment = 12 MG
Total = 22 MG
2 compartments filling in series
First compartment = 135 ft diameter x 38 ft high.
Second compartment 135 ft diameter x 14 ft high
First compartment = 1.4 MG
Second compartment = 3.8 MG
Total = 5.2 MG
For achieving disinfection, the basins were designed around dosing
concentrations of 10 to 11.6 mg/L and assuming the sodium hypochlorite
is stored at a 5 to 6 percent solution. Design dosing rates ranged
from 1,400 to 12,600 gal/hr.
Results of Evaluation Question 2
The primary treatment process that is most effective is simply the
size of the overall basin that translates into volume captured by the
basin. The larger the basin, the lower the volume and frequency of
overflow will be.
The evaluation of the different design features and capacities of
the Rouge River CSO basins provide a basis for comparing the respective
operating performances of the different components and different basis
of sizing. As more operating experience is gained, the benefits of
first flush tanks, tanks in series versus tanks in parallel, and shunt
channels will be able to be better quantified.
Decanting of stored and treated CSOs is a potential procedure that
is being considered. Decanting refers to the practice of screening,
chlorinating, and settling CSO in the basin, then releasing a portion
of the treated effluent to the receiving water. Tests are being performed
and submitted to the Michigan Department of Environmental Quality for
review. In one test in January 1999, the treated effluent had Carbonaceous
Biochemical Oxygen Demand (CBOD) and TSS less than 20 mg/L, and the
bacteria and TRC standards were also met. This practice has the advantage
of enhancing flows in the river and avoiding the cost of treating the
flow again at the wastewater treatment plant.
Based on the two years of experience, it is clear that more design
attention should be paid to how the basins can be operated in low flow
conditions. Much of the design effort for any CSO control facility
focuses on performance under peak flow conditions. However, there are
usually dozens of events each year that are smaller events with low
flows. In fact, low flows accounted for over 80 percent of the events
in the Rouge watershed. Supervisory control and data acquisition (SCADA)
and weather radar information is critical to monitoring flows and storms
to know how to initially respond to small events and low flow rates.
Also special operating procedures are required to accurately monitor
low flows. The multi-path ultrasonic flow meters that are used at the
Rouge Phase I CSO basins are good for high flows, but they have not
proven to be accurate under low flow collection conditions, especially
when the water level within the collection system and CSO basin rises.
At low flows, it is particularly difficult to accurately determine
the proper rate of chlorine addition. Continuing operating experience
is required to establish standard operating procedures for low flow
Better estimates of the effectiveness of the mixing of the sodium
hypochlorite with the CSO influent is needed to better assess the impact
of mixing to disinfection effectiveness. A standard methodology for
evaluation of the mixing process would be helpful for evaluation of
this aspect of the basin processes.
At this time, additional investigation is underway to "stress
test" the swirl concentrator in the Redford CSO facility and to
determine the performance of this unit separate from the detention
basins that are also part of the facility. These tests will improve
operating protocols for determining how the swirl concentrator should
be used in conjunction with the basins.
Lessons Learned on Evaluation Question 2
The Rouge Project has evaluated CSO discharge data in the Rouge watershed
and influent and effluent quality data from existing CSO basins in
Michigan. Analysis was performed using results from 390 CSO storm water
runoff events in the Rouge River watershed and from 44 events at CSO
basins outside of the watershed. The following lessons learned were
developed from this analysis:
- Samples collected at CSO discharges confirm that pollutant concentrations
decrease over the course of the discharge event. This phenomenon
has been identified for CSO discharges for years and is referred
to as a first flush phenomenon, with the first flush generally defined
as the first 30 minutes of a storm water runoff event.
- Samples collected of the influent to the facilities indicate that
smaller events have greater pollutant concentrations than larger
events. In addition, the smaller events, which are captured by the
facilities for subsequent discharge back to the collection system
after the storm event, account for over 80 percent of the events.
- Because the facilities can contain the smaller events with the
higher pollutant concentrations, the annual pollutant load captured
is much greater than the annual volume captured. The use of first
flush compartments to capture the first portion of larger events
also contributed to this result.
- The magnitude of CSO pollutant load reduction is related more to
capture of concentrated portions of the flow than removal by settling.
Thus, use of first flush compartments and flow bypass (shunting)
were included in the design of some of the facilities. No significant
removal of BOD, ammonia or phosphorus (other than related to volumetric
capture) was apparent in the facilities.
- CSO pollutant quality during larger wet weather events (those that
would activate a treatment facility) was generally quite dilute for
the following parameters: BOD (series), ammonia and phosphorus.
- Effluent quality was generally low in BOD ( < 30 mg/L).
- Significant reductions in TSS were noted for flow through processes
even with loading rates as high as 7,900 gpd/sf.
- Removal of visible sanitary trash was accomplished through a combination
of settling/baffling system and screens. It was unresolved whether
fine screens were necessary to achieve this performance objective
in facilities where settling and skimming were provided. Moreover,
the following was not determined:
- Maximum screen size that would work when settling and skimming
- Screen size necessary when degree of settling and skimming
is reduced due to either a condition of a smaller basin facility
or use of a flow through facility, such as a tunnel. A tunnel
or a smaller basin that operates in a flow-through mode would
not offer the settling velocity characteristics provided by
the basin facilities evaluated for this document.
- Effective disinfection of discharges was accomplished with sodium
hypochlorite. Minimum detention times at peak overflow conditions
rarely fell below 30 minutes. The relationship between detention
time and reduction in bacteria colonies could not be determined;
however, for the events monitored, the results suggested that the
detention time provided was not the controlling factor.
- First flush capture compartments assisted in the effective disinfection
of discharges with less variability in results.
- The wide range of flow rates with various levels of solids though
the facility must be carefully considered in the design of the hydraulics
and mechanics of moving flows. For instance, an underflow pump was
installed without consideration of need to handle solids and grits,
causing problems with the operation of this part of the flow stream
through the facility.
Evaluation Question 3: What is Needed for Operational Effectiveness?
In addition to the effectiveness of the design of the various treatment
and hydraulic processes employed at the Rouge Phase I CSO basins, the
effectiveness of the operation of these processes is also critical
to the successful performance of the basins. The process features of
each facility include retention (storage), screening, and disinfection
of the discharge with sodium hypochlorite. In addition, equipment is
provided to clean the facility following an event, monitor flow rate
and volume, collect samples, and return flow to the interceptor system
(dewatering). The facilities have computer control systems with varying
degrees of sophistication.
Operating data collected since June 1997 provides important information
on design features and on various aspects of operating CSO facilities.
The Rouge CSO control facilities have been activated on average once
or twice per month. The Hubbell-Southfield facility is activated most
frequently, because the overflow point that it serves has the largest
drainage area and smallest relative capacity for transmission of wet
weather flows downstream for treatment. Elsewhere, the storage capacity
and dewatering capacities have been exceeded on average only 2 to 4
times per year, depending on the facility. When storage capacity is
exceeded the basins provide settling, screening, and disinfection of
The success of a facility's operation is dependent on the ability
of the facilities to reliably meet permit and other regulatory performance
measures. Of particular interest is the relationship between the water
quality benefits of certain design features and the practices in operating
these features. The following discusses the operation and performance
of disinfection, screening, dewatering, and flushing. Training of staff,
use of mobile staffing, control systems, and monitoring are additional
aspects of operating a facility effectively that are also discussed.
The 10 Rouge Phase I CSO retention treatment basins include three
operated by the City of Detroit Water and Sewerage Department (DWSD),
three operated by the Oakland County Drain Commissioner, and four operated
by the Wayne County Department of Environment. The local communities
assist Wayne County at two of these basins.
The Wayne County and the DWSD basins have no full-time staff except
for at the Redford basin, which has one full-time staff person. The
Oakland County basins have one full time staff person per basin. All
basins rely on mobile crews and have SCADA technology for operational
control. Existing staff persons with pump station and wastewater sampling
experience were selected to form the core group of CSO basin operating,
sampling and maintenance group.
Each operating agency has a somewhat different staffing plan. The
basins operated by Wayne County use a 3-person team per basin, and
each team is mobile. The basins operated by the Oakland County Drain
Commissioner have a mobile supervisor plus one person stationed full-time
on day shift at each basin. The DWSD facilities use a 3-person team
per basin, and each team is mobile. The basins are within 4 to 13 miles
of home base for all three operating agencies.
In October 2000, the operators participated in an "Operator
Forum" to provide feedback on the equipment and operational
characteristics of their facilities.. A number of their comments
are included in the discussions on the various operations provided
in the following sections. The comments relate to experience at nine
of the basins, as the River Rouge basin was not operational at the
time of the forum.
Detailed plans for performance monitoring were developed in collaboration
between the owners of the facilities, the MDEQ, and representatives
of the Rouge Project. The purpose of the monitoring plan was to assess
the relative effectiveness of the different basin sizes, storage configurations,
treatment technologies and operational practices used in the facilities.
The evaluation program was complex, and it was a significant factor
in the operation and maintenance requirements for the basins in the
first two years of operation. Details of the full monitoring program
can be found in "CSO
Basins: Getting..." Comments received from the operators
on flow monitoring and sampling are detailed in the above report.
All facilities are designed to meet NPDES effluent limits for fecal
coliform of 400 cts / 100 ml and an effluent goal for total residual
chlorine (TRC) of 1 mg/L. Operational control is based on monitoring
the influent flow and effluent TRC.
Disinfection is achieved using liquid sodium hypochlorite. Details
of the disinfection process used can be found in "CSO
There are several operational problems that have arisen with the chlorination
systems. For example, first, there has been more rapid degradation
of the strength of the stored sodium hypochlorite strength between
storm events than anticipated. Second, there is the tendency for the
flow meters to under-record flow rates at low flows as the water level
is rising. As a result, this causes too little hypochlorite to be applied.
Third, there was a problem getting accurate measurements of effluent
TRC. The report "CSO
Basins: Getting..." contains comments received from operators
on the disinfection system and its operation.
All facilities were designed to provide screening of the CSO basin
flows. Successful removal of sanitary material is defined by MDEQ's
criteria as the removal of sanitary trash with a size of 4 mm or greater.
Subsequent studies of the effluent of the facilities have shown that
the sanitary trash removal goals are met for the facilities evaluated.
The size of screenings collected ranged from sanitary trash to tires.
The Wayne County and Detroit facilities rely on influent mechanically
cleaned bar screens with spacing that varies from 0.5-inch to 1.5-inch.
The Oakland County facilities use effluent static upflow screens with
0.75-inch spacing. Following the conclusion of a wet weather event,
the material that has accumulated on the screen is sent to the interceptor
with the dewatered flow. The dewatering wet wells for the Oakland County
facilities also have bar screens. Operators try to force the screenings
through to the interceptor. The retained screenings are scraped and
disposed to a landfill.
In general, the operators have been relatively satisfied with the
screening equipment and operation of the screens. The report "CSO
Basins: Getting..." contains comments received from operators
on the screening system and its operation.
The basins are dewatered after an event, when capacity is available
in the receiving interceptor. The Wayne County facilities dewater by
gravity, with the rate controlled by a control valve. A meter provides
information in the downstream interceptor. The Oakland County basins
are dewatered by pumping. A SCADA system is used to monitor levels
in the receiving interceptors as well as total discharge rate at their
point of connection to the DWSD system to ensure that peak contract
capacity is not exceeded. The Detroit basins are pumped, though the
top 9-feet of the Hubbell-Southfield facility is dewatered by gravity.
Level indicators are provided in the downstream interceptor. Significant
maintenance issues include the need to visit sites regularly, reliability
of the SCADA system, and maintaining the dewatering pumps and the sump
The time required for basin dewatering ranges from 5 to 45 hours.
The time required depends on the volume stored, the interceptor capacity
available and in some cases also depends on the dewatering pumping
Eight of the Rouge Phase I CSO basins use tipping buckets to remove
settled debris after an event. The ninth and largest facility, Hubbell
Southfield Basin, uses flushing nozzles. In some locations, there are
auxiliary hoses to clean debris from wet wells and channels.
In general the tipping buckets are proving to be adequate. In some cases, where
there is a long flushing length to clean, the process needs to be repeated several
times and manual cleaning of some corners and walls is required.
The flushing nozzle system installed in the one facility has been
a disappointment. The pressure maintained in the system has not been
adequate to scour deposited solids from the floor. These nozzles are
located near the ceiling of the facility. Older CSO facilities operated
by Wayne County and Oakland County also use flushing nozzle systems.
Both of these agencies are satisfied with the performance of these
systems. The Wayne County facility has the nozzles mounted near the
floor, and the Oakland County system has jets that are intended to
flush debris to a center trough, where the bulk of the material is
The report "CSO
Basins: Getting..." contains comments received from
operators on the flushing process and its operation.
The CSO facilities have varying degrees of control systems. The control
systems help to determine the status of various components of the facility
and the adjacent collection system, as well as various degrees of remote
monitoring and operation.
The ability to remotely monitor the facilities is critical as this helps to determine
when staff needs to be mobilized. At this time, remote operation of the facilities
during an event is not considered feasible, regardless of the sophistication of
the control system. Experience to date demonstrates that staff must be present
during events for proper operation.
The report "CSO Basins:
Getting..." contains comments received from operators on the control
system and its operation.
Lessons Learned on Evaluation Question 3
Operational lessons learned from the Rouge Phase I CSO basins include
- 1. Protocols for items such as chemical feed, flow monitoring and
sampling are often different for smaller wet weather events. As the
vast majority of events will be small, the facility design should
also recognize the operational differences for small storms.
- Sodium hypochlorite disinfection systems need to address proper
materials for long life, system flushing, testing of stored solution,
and flow pacing of chemical addition.
- Complex hydraulics, intermittent events and highly variable flow
rates made the use of high tech flow metering equipment problematic.
The best flow measurement results were achieved by metering with
Parshall flumes and by calculating flows from pump capacity and run
- Process flow control needs to be able to respond to highly variable
flow rates. For example, a static weir for flow splitting is preferable
to meter/ valve arrangements. Additionally, gate-closing action may
not be quick enough for wet weather flow variations.
- Regardless of level of automation, facilities generally require
staff presence during wet weather events.
- Start-up and testing of any CSO basin will likely take at least
two years to fine tune, depending on the frequency of overflow events.
Because most overflows from the combined sewer system were contained
in the basins, there were very few events (e.g., 2 to 4) each year
through which operators were able to develop experience with the
flow-through operation of the facility.
Evaluation Question 4: What is the Proper Size for CSO Basins To
Comply With Regulatory Requirements?
The Rouge Project was initiated in part to answer this very question.
Since wet weather control is so expensive, having good evaluation data
and analysis to determine appropriate CSO basin size is important.
As mentioned in the introduction, the CSO basins were sized for different
design storms and incorporate a variety of additional features or variations
in compartment sizing and flow sequencing. The performance of the demonstration
basins constructed under Phase I have been evaluated over a two-year
period to determine if the level of control provided under the demonstration
criteria have achieved the regulatory objectives established for these
The existing Rouge Phase I CSO basins, with the hydrologic sizing
and treatment/hydraulic processes as provided, have demonstrated that
they can meet the Phase I goal of eliminating raw sewage and protecting
public health. Effective operational protocol needs to be maintained
to consistently meet this goal, as described in the previous section.
This section discusses what is the proper size for CSO basins to be
effective in meeting the Phase I and II goal of eliminating raw sewage
and protecting public health and the Phase III goal of achieving state
water quality standards in the receiving stream.
CSO data from nine of the facilities have been evaluated. Flow and
sampling data for over 180 CSO events were collected. An objective
of the Rouge Project data collection effort was to quantify volume
and load reductions, and the relative performance of the facilities
with variable design sizing and process configurations. As part of
this monitoring and evaluation effort, a number of design and operational
considerations have been identified. These results indicate ways in
which facility design and operation results in the conveyance of additional
pollutant loads to a wastewater treatment plant (WWTP) for an equivalent
capital outlay. The findings and results summarized below also help
answer the question of what is the proper size for the CSO basins to
achieve the goals of the demonstration project. The report "CSO
Basins: Getting..." contains much greater information
on these topics.
Findings and Results
An evaluation of the quality of the influent is important in assessing
the proper size of the CSO basins and their treatment effectiveness.
Influent quality was found to vary from site to site, even though these
basins are located in predominately residential areas. The variation
for the Redford facility in particular is thought to be due to the
fact that the tributary area includes a significant number of gravel
streets. In addition, the area tributary to the regulator structure
includes a separated sewer area approximately three times the size
of the tributary combined sewer area.
Treatment effectiveness can be measured by the percent reduction of
CSO volumes and percent reduction of pollutant loads that are discharged
to the river. Because of the first flush phenomenon as discussed earlier,
the percent reduction of pollutants is greater than the percent reduction
of the CSO volume. For instance, the Inkster Basin reduced the volume
of flow discharged to the river by 55 percent, but the CBOD load was
reduced by 76 percent, TSS was reduced by 74 percent, and Ammonia was
reduced by 84 percent. A number of small events are contained within
the CSO basins, accounting for additional pollutant load reduction.
Treatment of that portion of the flow stream that is discharged from
the CSO basins to the receiving streams accounts for a further reduction
in pollutant loading. The overall impact is that the pollutant load
reduction is higher than what can be accounted for by the flow volume
Overall, the effluent quality from the Rouge Phase I CSO basins is
much better than the quality of uncontrolled conditions. Typical CBOD
values have been less than 30 mg/L for most events. This result has
been due both to the observed decrease in CSO concentration as an event
proceeds, as well as additional removal which occurs during flow through
conditions in the facilities.
The primary operational issue related to proper sizing of the basins
that has been discovered during the operation of the facilities has
been the management of system flows reaching the CSO basins. A significant
number of the rainfall events that formerly caused discharge to the
river can now be contained within the CSO retention treatment basins.
This operational capability is improved by monitoring systems within
the downstream interceptor, which allow the facility operator to pump
back to the interceptor system when capacity is available. Approximately
one half of the CSO events can be contained in this manner.
Other operational lessons learned are associated with the wide range
in flow rates that enter the CSO basins and the irregular frequency
of operation of the basins due to variable rainfall events. For example,
flow monitoring and sampling needs to be designed for both minimal
flow rates as well as peak flow rates. Further, a consequence of infrequent
operation is the reduction in the potency of sodium hypochlorite. The
concentration of the solution deteriorates over time, as it is stored.
Use of a lower concentration than what is specified for operation results
in inadequate disinfection during some discharge events.
Assessment of CSO Basin Sizing
The sizes of the Rouge Phase I CSO basins ranged from 1.9 MG to 22
MG in total storage volume (previously provided in Table 1). In terms
of inches over the drainage area, the volumes range from 0.06 inches
to 0.28 inches, with a majority of the CSO facilities having volumes
between 0.10 inches to 0.18 inches (See Table 1).
Based on the results of the two plus years of evaluations, nine of
the 10 facilities are of sufficient size to be effective in meeting
the regulatory requirements imposed for the Rouge River. The tenth
CSO basin, River Rouge, is still being evaluated. Of the nine basins,
the smallest basin (based on an estimate of the basins actual detention
times) is the Inkster CSO basin. This basin provides a detention time
of 20-minutes for the peak flow resulting from a 1-year, 1-hour design
event under wet antecedent conditions. The volume of this basin relates
to 0.14 inches over the contributing drainage area.
These results do not preclude that a basin could be designed for an
even smaller detention time and still meet the regulatory requirements.
The exact threshold of how small a basin can be and still be effective
in meeting the project objectives has not been determined as no basin
in this project was found to be too small.
However, the program does show that the proper size of the basins
can be smaller than what would be required by the presumptive criteria
and still meet Michigan regulatory requirements for Phase I and II
goal of protecting human health and eliminating raw sewage. Meeting
the requirements of the Phase III goal of achieving water quality
standards is also anticipated, though the issue of total residual
chlorine is still outstanding. Through the Rouge Project, the permittees
have managed to substantiate the sufficiency of the demonstration
criteria used in the design of the Phase I Rouge River CSO basins.
Some additional factors that should be considered in these findings
are as follows:
- The success of the basins in meeting the program objectives are
dependent not only on the proper sizing of the storage volume, but
also on other factors, such as innovative design features and how
the facilities are operated.
- The basins are meeting the criteria for success goals based on
the regulatory requirements for the Rouge River. The Rouge River
is a DO limited stream. If DO is not the critical parameter in a
waterway that receives treated CSO discharges, a lower detention
time or screening and disinfection only may be sufficient to meet
water quality standards.
- The effluent from the Rouge CSO basins' includes oxidizable nitrogen,
which can exert an oxygen demand after several days. Currently, during
storm events that result in overflows, the travel time from the CSO
basins to the mouth of the Rouge River, and into much larger waterbodys,
the Detroit River and then Lake Erie, is less than the time for this
demand to be exerted. If the river had a much longer travel time
before this dilution came into play, the ability to show that the
basins meet the DO standard at times of discharge would have to consider
the impacts of nitrogenous BOD.
Lessons Learned on Evaluation Question 4
Based on these results, the following items are lessons learned for
the proper sizing of CSO basins.
- It is very likely that CSO basins can be smaller than what would
be required by the presumptive criteria and still meet regulatory
requirements for effluent requirements and for in-stream requirements
- Because of the first flush phenomenon and because 80 percent of
the events in the Rouge watershed are small events (any event smaller
than the design event), the impact of the basins on the percent reduction
of the pollutant load is greater than the volume reduction.
- Sizing the basins using the demonstration criteria will reduce
the costs of the Phase II controls scheduled for the remaining CSOs
within the watershed. The resulting smaller basins will also reduce
the potential for the need to increase the capacity of the transport
sewers downstream and increase the treatment capacity at the WWTP.
- Using a phased approach allows lessons learned in one phase to
result in cost savings for the subsequent phases.
- The impact of seasonal variation in rainfall events, that is, what
types of storms occur and at what times of the year, should be evaluated
in defining a design event. The runoff potential is higher during
the winter in Michigan, but the higher intensity rainfall events
tend to occur during the summer.
- The impact of seasonal variation in infiltration capacity and interception
on runoff potential should also be considered in formulating a design
event. Preferably, continuous simulations would be used to project
the performance of the basins (frequency and volume of overflow events)
for a long-term precipitation record.
- Flows should be monitored, ideally during critical seasons, as
determined from the above items, to calibrate design parameters used
for sizing the basins. If a mathematical model is used for the design
calculations, it needs to be calibrated for local conditions to properly
account for the routing characteristics within the contributing sewer
network. It also must consider antecedent rainfall events.
- CSO basin design should consider operations during low flow conditions,
because the vast majority of events will produce flows that are only
a small fraction of the peak design flows. The use of a variety of
influent pump capacities, installing flow meters to handle low flow
regimes, smaller and larger screen channels, and multiple basins
are approaches that should be considered for providing the flexibility
to handle low flows.
Conclusions of the CSO Basin Evaluation Program
The Rouge River Wet Weather Demonstration Program has been successful
in identifying efficient and cost effective CSO basins for control
of combined sewer overflows. The wisdom of controlling CSOs at remote
locations versus trying to convey all of the combined sewage at one
time to the central treatment plant was confirmed. Demonstration basins,
built to a smaller size than what would have been required by presumptive
criteria, have reduced release of pollution to the river with excellent
environmental protection results. Protection of human health, elimination
of the discharge of raw sewage, and meeting water quality standards
have been achieved, with the exception of TRC, which is still being
investigated. Phased implementation has allowed lessons learned to
be used in subsequent phases, affording greater efficiencies in developing
and implementing controls for the remaining CSOs with a very large
savings in capital expenditures. The completed basins are controlling
overflows at a rate of approximately 4 billion gallons per year with
water quality and aesthetic improvements and increased recreational
usage in the Rouge River. It is very important to note that the MDEQ
has certified that the nine operating basins meet the Phase II Criteria
for Success in CSO Treatment for the elimination of raw sewage discharges
and protection of public health. Also, three basins have been certified
as achieving the Phase III goal of meeting water quality standards
at times of discharge.
Standard operation and maintenance (O&M) procedures are ensuring
that the basins are meeting effluent limits and keeping the basins
as good neighbors to surrounding land uses, which include nature centers,
a golf course, and recreational facilities. Overall, the operating
experience with the Rouge River CSO control facilities has provided
valuable information for designing future phases of CSO control in
the Rouge River watershed and for communities engaged in CSO control
in other watersheds. The experience has also been helpful in identifying
operational problems and strategies for dealing with them.
The evaluations have provided a number of insights into the nature
of CSOs as well as their treatment. Some of the lessons learned were
related to those items previously believed to be well understood, such
as the hydrology of combined drainage areas and the quality of CSO
discharges. Other lessons learned were more subtle, and relate to the
interrelationship of CSO discharges on the receiving stream, management
options for the reduction of discharges consideration of the small
storms as well as the large ones, and others. These issues are difficult
to predict and quantify during a planning and design mode, but may
have dramatic impacts on the effectiveness of the control measures
A key factor to the success of the CSO control program in improving
the water quality of the Rouge River was the expansion of the program
into a comprehensive watershed management approach to identifying and
addressing other major sources of pollutants to the river. Early investigations
identified other major sources of pollution such as stormwater runoff
and illicit sewer connections that needed to be addressed if restoration
of the river was to be successful. The watershed approach fostered
a cooperative effort between federal, state and local agencies to address
all sources of pollution. This cooperative effort led to the development
of watershed-based general permits for municipal storm water discharges
issued under the NPDES program. These permits foster participation
in developing watershed management plans that will result in achieving
water quality standards.
The Rouge Project has enough preliminary data to make a rough cost
comparison between utilizing a watershed approach to achieve desired
water quality objectives as compared to the historical approach of
addressing the causes of water quality degradation individually and
in the sizing of CSO basins. This preliminary data indicates a cost
savings for the Rouge River Watershed citizens could easily approach
several hundred million dollars.
CSO Overflow Reductions
Untreated overflows in excess of 50 times per year have been reduced
to treated overflows occurring one to seven times per year where retention
treatment basins have been implemented. There are approximately 127
miles of the larger streams and tributaries (stream order 3, 4 and
5) in the Rouge River watershed. Approximately 89 of those miles are
now free of the adverse impacts of CSO discharges. That means that
only about 38 stream miles currently are negatively impacted by CSO
discharges. This is a 51% reduction in the past 6 years. In addition
to the CSO controls, the improvements to the River can be attributed
to the multitude of other Rouge Project programs including illicit
connection elimination, storm water management activities, and developing
better public, industry and community awareness of pollution control
For additional and more detailed information on the performance of
the CSO treatment facilities, go to technical
papers and professional presentations.