Improving water quality with operations research

Edelman: Louisville Sewers

To combat increasingly frequent and intense rainfall that can overwhelm urban wastewater collection and treatment systems and threaten local water environments, Louisville and Jefferson County Metropolitan Sewer District (MSD) in Kentucky uses operations research and analytics to optimize its sewer management. This smart approach allows MSD to have fewer overflows during rainfalls while reducing the storage facilities required and saving the community over $200 million to date.

MSD protects the community’s overall health and safety by providing clean waterways and managing flood and drainage issues across the 376 square miles of the Louisville Metro area. MSD operates and maintains extensive and very complex sewer, storm and floodwall systems, with more than 3,200 miles of sewer lines, five regional wastewater treatment plants, over 280 pump stations, 27 long-term stream water quality monitoring stations, as well as the Ohio River Flood Protection System.

With increasingly intense and more frequent rainfall, urban wastewater collection and treatment systems are often inundated during large rainfall events and generate overflows of untreated sewerage and stormwater. To address the many challenges of reducing overflows to improve water quality and considering the financial limitations of a nonprofit regional utility service, MSD has a progressive vision for total wastewater system optimization that requires innovative operation approach and analytics.

Louisville MSD was one of the early adopters of real time control (RTC) in the nation, applying inline storage since the 1990s. In partnership with Tetra Tech, MSD pioneered the application of model predictive RTC using Csoft®, Tetra Tech’s innovative software solution to provide system-wide optimization, which has been in operation since 2006. Initial RTC feasibility studies identified a relatively low unit cost for overflow reduction that is 4–10 times lower than the cost of constructing traditional storage solution alternatives.  

Tetra Tech started the development of the RTC software solution in the mid-1990s, to efficiently manage sewer networks in real time based on rain forecasts, model predictions, and sensor readings. It is applied as a more adaptable and robust solution complementary to the traditional engineering methods to address the various challenges in urban water management, such as sewer overflows, stormwater runoff, water quality, flooding, and drought, exacerbated by climate change in recent years.

The solution uses a hydrologic and hydraulic model and mixed-integer linear programming, allowing the full use of system capacity, while reducing additional infrastructures required to achieve multiple operational and environmental objectives. This unique solution has been successfully implemented in other communities in the United States, Canada, and France, saving each client between 25 and 75 percent in capital expenditures to address pollution and flood control objectives.

The Louisville RTC system with Csoft® to automate decisions for storing or routing flows in the sewer has been implemented in phases. Current reductions show it stores or mitigates more than two billion gallons per 2001 Typical Year of combined sewer overflows. Incorporating RTC into the MSD’s Integrated Overflow Abatement Plan has resulted in approximately $200 million in savings to date, compared to traditional methods.

Once all planned storage projects are constructed, RTC will allow MSD to eliminate or capture and treat 98 percent of combined system flow, up from approximately 60 percent prior to RTC and the implementation of the overflow abatement plan. RTC is an important component of Louisville MSD’s long-term plan to mitigate untreated combined sewer overflows into Beargrass Creek and the Ohio River. It provides an innovative, cost-effective and sustainable management strategy that helps to satisfy regulatory requirements while also improving overall sewer system operability.