The Rouge River Project
Bringing the river back to life!
|Home||Search||Site Index||Using This Site||Contact Us|
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:
Thus, a design event cannot be adequately defined without specifying these items.
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 requirements?"
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 loading rate.
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 being evaluated.
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 following findings:
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 stream.
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:
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 is important.
Evaluation Question 2: What Treatment and Hydraulic Processes Are Most Effective?
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.
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 conditions.
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:
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 discharge.
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 Basins: Getting..."
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 pumps.
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 capacity.
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.
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 removed manually.
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.
Lessons Learned on Evaluation Question 3
Operational lessons learned from the Rouge Phase I CSO basins include the following:
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 basins.
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 captured.
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:
Lessons Learned on Evaluation Question 4
Based on these results, the following items are lessons learned for the proper sizing of CSO basins.
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 utilized.
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.
Control Program for the Remaining CSO Discharge Points to the Rouge River
Phase I of the CSO Control Program
Phase I of the CSO control program covered approximately
40% of the Rouge River watershed. A total of 76
of the 83 Phase 1 CSO outfalls are now under control
(retention/treatment basins) or have been eliminated
(sewer separation). As stated earlier, lessons
learned as part of the Phase I CSO control program
have been critical in developing Phase II and III
of the CSO control program.
Phase I Remaining Issues
There are a few remaining issues associated with the Phase I CSO control program that are currently being resolve by the permittees and MDEQ. The following summarizes those issues.
Total Residual Chlorine
The original NPDES permits issued for the CSO treatment facilities included a requirement to provide chlorination of the effluent and to then dechlorinate if the MDEQ instream chlorine standard was not met. Permittees had the choice to dechlorinate or to do the necessary studies to demonstrate there are no instream problems associated with the chlorine discharge. The following briefly describes the MDEQ standard, the demonstration criteria and some of the findings of the various studies that communities have undertaken to address this issue.
The MDEQ has established aquatic health standards for various species under MDEQ rule R 323.1057. These standards cover macroinvertebrates as well as fish and various plants. Using this rule, MDEQ established the maximum concentration of total residual chlorine instream to be 0.038 mg/l to protect the aquatic community. It has been concluded that effluent TRC must be 1 mg/l to assure adequate reduction of pathogens. The approach being used by the Rouge Project to assess compliance with this requirement is to examine in-stream values of TRC
Using the criteria delineated in the MDEQ rule, the Rouge Project investigated compliance of the basins with Phase III Criteria for Success: Health of the Biological Community. The data showed that the biological community was not significantly lower downstream than from locations upstream of the CSO Basins which would indicate that the TRC was not causing any impacts on the biological community.
An element of the Phase III Criteria for Success in CSO Treatment basin evaluation program discussed above includes conducting a mixing zone demonstration for each CSO facility in order to determine if an approved TRC mixing zone can be established. The demonstration must be conducted in accordance with MDEQ Subrule 7 of the Mixing Zone Rule (R 323.1082). Some of the items to be addressed in any demonstration are: maintaining a zone of passage for aquatic life, not interfering with designated stream uses, and no resulting deleterious effects to populations of aquatic life and wildlife. In order to answer these questions, a mixing zone study is needed.
In late 2002, MDEQ issued new permits for the Oakland County CSO Retention/Treatment Basins. The new permits continues the basic requirement that the permittee must dechlorinate if the above described instream standard is not met. But, additional time was granted to undertake any necessary study to assess whether the standard was met.
The permits include the following modifications to the previously issued permits: a new requirement that the permittee conduct a TRC Mixing/Plume Definition Study; a new requirement for disconnecting of eaves troughs and roof downspouts in the service area tributary to the facility; new requirements regarding notification of discharges for the facility; a new requirement for stream bacteria (i.e., Escherichia coli) testing following discharges from the facility; and the deletion of the monthly average effluent limitation for fecal coliform bacteria based upon the intermittent nature of the discharges.
The specific Total Residual Chlorine and Disinfection Requirement states: "The permittee shall operate the two retention treatment facilities to provide consistent, effective disinfection achieving the event geometric mean effluent limitations of 400 cts./100 ml for fecal coliform bacteria, while minimizing the discharge of total residual chlorine (TRC) as much as is possible."
The specific requirement for testing for Escherichia coli states: "Each time a combined sewer overflow discharge occurs, the permittee shall test the affected waters for Escherichia coli to assess the risk to the public health as a result of the discharge and shall provide the test results to the affected local county health departments and to the Department. The testing shall be done at locations specified by each affected local county health department but shall not exceed 10 tests for each separate discharge event. The affected local county health department may waive this testing requirement if it determines that such testing is not needed to assess the risk to the public health as a result of the discharge event."
The specific requirement for Total Residual Chlorine Mixing Zone/Plume Definition Study are as follows: "In order to determine the water quality impacts on the Rouge River from the total residual chlorine in the discharge from Outfall (stated), the permittee shall conduct a Total Residual Chlorine (TRC) Mixing Zone Plume Definition Study (Study). The Study shall be conducted in accordance with the applicable provisions of R 323.1082 (7) based upon an approved Work Plan (see Part I.A.2.a., below).
The results of the Study will be used by the Department to determine whether future controls such as dechlorination facilities are necessary to ensure compliance with Water Quality Standards at times of discharge. The Study shall be conducted in accordance with the following schedule:
If, based upon the results of the Study Report, effluent limitations and/or controls for the discharge of TRC from the Birmingham CSO RTB are necessary to ensure compliance with Water Quality Standards at times of discharge, the Department may, in accordance with applicable laws and rules, propose modification of this NPDES permit to include the appropriate effluent limitations and/or controls for the discharge of TRC. It is recognized that the permittee may pursue a variance from a Water Quality Standard as allowed under R 323.1103, or a modification of the Water Quality Standard(s). "
The Work Plan was submitted in accordance with the permit requirements and the study is underway. It is anticipated that the March 1, 2006 date will be met by Oakland County.
It is anticipated that the other CSO basins in the Rouge River watershed will have similar requirements in any new NPDES permits.
Phase I CSO Control Program Costs
The CSO-related capital expenditures to date were funded by a combination of federal and local funding sources. Capital expenditures for Phase I CSO projects in the watershed totaled about $350 million, with another $5 million spent annually on CSO-related operation and maintenance.
Phase II CSO Control Program
Control programs for all remaining CSO outfalls in the Rouge River Watershed were recently defined by MDEQ in reissued NPDES permits. The following summarizes those permit requirements and schedule.
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 and prevention.
For additional and more detailed information on the performance of the CSO treatment facilities, go to technical papers and professional presentations.
USEPA's National CSO Control Policy
USEPA's 1994 National CSO Control Policy has been fully implemented through the Rouge Project with cost effective CSO controls in conjunction with an innovative watershed protection approach that has resulted in truly outstanding water quality improvements. The National CSO Policy contains four fundamental principles to ensure that CSO controls are cost-effective and meet local environmental objectives:
The Rouge Project has been very successful in accomplishing all of the above principles as it has been implementing its CSO control programs. The best news is the outstanding, documented environmental improvements in water quality and ecosystem health that have occurred to date in the Rouge River.
The Project's CSO control program was summarized in a report and was included as a case study by USEPA in their Report to Congress on the nationwide CSO control efforts.
USEPA's Office of Inspector General Report on CSO Control
During the latter part of 2001, USEPA's Office of Inspector General (OIG) conducted a nationwide audit of the national CSO control program. They interviewed EPA headquarters personnel, three EPA Regions, eight states, 22 communities and some others. The MDEQ, the Rouge Project and several Michigan cities were interviewed as part of the study. The OIG issued their final Evaluation Report on "Wastewater Management - Controlling and Abating Combined Sewer Overflows" in August 2002.
The report cites a number of examples of the successes of the Rouge Project's CSO control program. The following is a quote from the report about the program and the watershed approach being utilized:
Environmental Results To Date
The Long-Term Monitoring Network of the Rouge Project includes continuous measurement of Rouge River dissolved oxygen (DO) content at five key locations. Adequate dissolved oxygen content is one key element of a healthy river ecosystem. The DO measurements are made from mid-April through mid-November each year, and most sites have been monitored since 1994. Since the measurements are continuous, they show the combined effect of dry and wet weather conditions in the river. A review of the 2003 data from these long-term monitoring locations is summarized below.
The water quality in the Rouge River continued to show the very encouraging trend of continuous improvement because of the CSO control efforts and other watershed efforts. The MDEQ water quality standard for DO is 5 mg/l. The mean DO in the lower reaches of the Rouge River has increased from 4.5 mg/l in 1994 to over 7.0 mg/l in 2003. The percent of DO readings that violated the DO standard of 5 mg/l dropped from 61 percent in 1994 to less than 4 percent in 2003. Similar improvements occurred at all stations in the watershed where those stations met the standard 100% of the time. The water quality improvements that are occurring clearly reflect the benefits of the watershed management strategies that have been implemented to address and control both dry and wet weather pollution sources in the watershed.
Ecosystem Health Improvements
Coupled with the water quality improvements, the ecosystem health continues to improve as well. This improvement is demonstrated by the results of the annual Frog and Toad Survey which is conducted by volunteers surveying various locations in the watershed. Frogs and toads are sensitive indicators of ecosystem health because they require clean water and good quality habitat to survive. The volunteers heard a greater number of green frogs, bullfrogs, and northern leopard frogs during the 2003 survey than they did in the previous year. Leopard frogs have been undergoing a nationwide and statewide decline in recent years so it was very good news that they continue to survive in the Rouge watershed. Green frogs were also heard in a higher percentage of blocks and were calling in every subwatershed. The possible statewide decline of green frogs reported by the Michigan statewide survey may not be happening in the Rouge River Watershed. Bullfrogs, while never numerous in the Rouge River Watershed, were reported from more urban areas this year than in past years.
Assembly of Rouge Communities
In August 2003, the Rouge River Watershed Local Management Assembly (Assembly of Rouge Communities) was formed to continue the restoration of the Rouge River Watershed. The Assembly of Rouge Communities is a voluntary organization of the local municipal governments (i.e., cities, townships, and villages) and the three counties (i.e., Wayne, Oakland and Washtenaw) located in part or totally within the Rouge River watershed. It was formed following nearly two years of discussion between the communities and the three counties who are part of the Rouge River National Wet Weather Demonstration Project. The new organization will continue to support collaborative local governmental efforts to restore the water quality of the Rouge River and meet federal and state water quality requirements through more effective and efficient cooperative use of limited local resources. Membership in the Assembly of Rouge Communities, under the terms of the Memorandum of Agreement, is limited to cities, townships, villages and counties in the watershed that have storm water management responsibilities under a state issued discharge permit. In addition, membership requires the payment of assessments based upon equal weight given to community's population and land area within the watershed. The three counties were initially allowed to join based upon in-kind services provided communities.
The total budget for the Assembly of Rouge Communities during 2003 and 2004 was approximately $1.2 million which will be used to fund:
In addition, the funds will be used to provide
technical guidance and facilitation for the
The Rouge River National Wet Weather Demonstration Project is an unqualified success, using any of several measures of achievement. Major progress has been made in the control of pollution being discharged to the Rouge River. The combined sewer overflow pollutant loads to the river have cut by 90 to 100 percent during most rainfall events. In previous years certain water quality standards were violated most of the time at many places in the watershed. Now, the majority of the waters in the Rouge River watershed meet most standards. Coupled with the water quality improvements, the ecosystem health continues to improve as well. The United States Environmental Protection Agency's Inspector General called the Rouge Project, "A blueprint for success".
Last Updated: 8/2/2005
Please address all comments and suggestions about the contents of this Web page to email@example.com.
The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -08 and C-264000-01.