CSO Program (1998 to 2002)

During this period, MSD continued its efforts to better understand how the combined sewer system operated by continuing flow monitoring, refining computer models and sampling overflow and stream quality. Additionally, significant investments in infrastructure were made. Some of the projects include the following:

• Wheeler Basin – a large off-line storage facility that protected several neighborhoods from combined sewer flooding;
• Buchanan Pump Station Improvements – this key pump station, built in the 1940’s, was well beyond its design life. A replacement project was initiated to insure the integrity of the system and to realize water quality benefits.
• Sneads Branch In-Line Storage – an inflatable gate project collects overflow from eleven CSOs and stores this “re-captured” flow in a large diameter outfall. This overflow is then pumped back to the Buchanan Street Pump Station where it then flows to MFWTP for treatment;
• Sewer Separation (CSO 080, 088, 123, 147, 206, 209) – traditional sewer separation was attractive in the areas tributary to these CSOs.
• Upper Dry Run Trunk Sewer Storage Basins – these off-line basins capture stormwater runoff before it enters the combined sewer system.

MSD also made a commitment to Real Time Control as an integral component of their CSOs Long Term Control Plan (LTCP). The purpose of Real Time Control (RTC) for combined sewer operation is precisely to optimize storage capacity. This discussion will focus on the total multi-year program that MSD has undertaken, accomplishments to date and future program efforts.

The initial effort was to conduct a RTC Strategy Study to evaluate the potential benefits and costs associated with the implementation of a RTC Program. The studies were conducted over a two-year period from July 1999 to June 2001. The results of the study recommended eight RTC control sites for Region 1 that would eliminate 475 MG/YR of overflow, increase the existing percent capture from 54 percent to 74 percent for a unit capital cost of approximately $0.021 per gallon of overflow removed. Within Region 1 the addition of five off-line storage basins would increase the percent capture to 85 percent and the unit capital cost to $0.049 per gallon of overflow removed. The study also recommended eight RTC control sites for Regions 2 and 3 that would eliminate 2,400 MG/YR of overflow, increase the percent capture from 41 percent to 62 percent for a unit capital cost of approximately $0.006 per gallon of overflow removed.

Based upon the results of the RTC Strategy studies, MSD made the decision to move forward with the development and implementation of a RTC Program. In the fall of 2001, MSD published a Request for Proposals (RFP) for the selection of a consultant to develop and implement an automated RTC Project. As part of the RFP process, the MSD contacted and made visits to other CSO communities with experience in RTC. The purpose of this effort was to gather information on their successes and failures, what worked well and why, what failed and why. MSD felt very strongly that lessons learned by other communities would help MSD avoid similar issues. The overriding sentiment from the other communities was that a “buy-in” from all departments that will play a role in a RTC program is essential to program success. With this in mind MSD put together a Selection Committee and Technical Advisory committee that represented a cross section of all departments that would contribute to the success or failure of the RTC program. These committees included representatives from upper management, the Wet Weather & Water Quality Team, Operations, Maintenance, Information Technology, Diverse Works, Legal, Financial and the CSO Program Consultant. MSD completed the RFP process with the selection of BPR-CSO from Montreal, Canada. BPR-CSO specializes in RTC and has implemented projects worldwide.

BPR-CSO initiated the 22-month project to develop and implement a RTC Program in January 2002. This project will include the following work efforts: project management and administration, information gathering and review, definition of the initial RTC implementation project control strategy, development and implementation of the RTC control strategy, start-up and training, and system performance verification and maintenance. With the completion of this project, MSD will have a RTC system capable of operating at various levels from simple local control to full global predictive optimization. At the end of this project MSD will have five RTC control points fully operational and a system that can easily incorporate the remainder of the recommended sites at a future date. The initial five control points can be described as follows:

• Southeastern Diversion Structure—for the control of diverted flow from the Beargrass Interceptor (BGI) in Region1 to the Southwestern Outfall in Region 3.
• Nightingale Pump Station—for control of diverted flow from the BGI and the BGI Relief Sewer in Region 1 to the Upper Dry Run Trunk system in Region 3.
• Southwestern Pump Station—to generate in-line storage of excess flow by controlling the gates at the Sluice Gate Chamber. This project is currently under construction.
• Snead’s Branch Relief In-line Storage Inflatable Gate—in-line storage for flow from 11 CSOs. This project is currently fully operational in local control and achieving benefit.
• Brady Lake and Executive Inn Storage Basins—for control of flow at the outlet of the downstream Basin for dewatering into the Upper Dry Run Trunk to reduce overflows at CSO 15.

In concert with the selection of a RTC Consultant, MSD has also selected NEXRAIN Corporation for the development of a rainfall prediction tool. This tool will be essential for the operation of the RTC system in a global predictive optimization mode. The tool will also be a major benefit for emergency response during wet weather events.

MSD is defining the remainder of the RTC control site projects and adding them to the MSD Capital Program for future implementation. Additionally, MSD will be revising their current LTCPs to incorporate the RTC Program. It has been estimated that the development and implementation of the RTC Program as an integral component of MSD’s CSO control strategy will save this community millions of dollars when compared to the original LTCP approach. MSD is extremely excited and committed to RTC as an avenue to manage the existing combined sewer system to minimize CSO discharges while making maximum utilization of available capacity in the most cost effective manner.

Related Links

Prior to 1988 Initial CSO Program Efforts
1988 to 1997 CSO Program Efforts
2002 to July 2003 Holistic Watershed Approach

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