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Machine Learning Reduces Combined Sewer Overflow Volume And Helps Reduce A Consent Decree By $145 Million

Buffalo, New York

United States

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At the turn of the century Buffalo was the 8th largest city in the U.S., a gateway for commerce and manufacturing due to its early embrace of hydroelectric power generated from nearby Niagara Falls. To accommodate its projected growth, Buffalo built a (then) state-of-the-art combined sewer system that collected and transmitted sanitary and storm water flows within a single pipe system to the Buffalo River, Scajaquada Creek, and the Niagara River.

By mid-century, the City added a massive wastewater treatment facility and upgraded its sewer system to accommodate at least 750,000 people. This allowed the City to capture dry weather sewer flows and send them to the plant, but the combined sewer system was still designed to send the vast majority of wet weather flows to the City’s receiving waters.

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Challenge

Due to its mid-20th century sewer design, Buffalo still typically experiences nearly 2 billion gallons of combined sewer overflow (CSO) annually, discharging into its receiving waterways.

As the level of national awareness for the need to protect our nation’s water resources continued to grow, federal and state regulators began pursuing a consent decree in 2006 requiring further improvements to Buffalo’s collection system. Recognizing the generally inadequate stormwater capabilities of their existing combined sewer system, the Buffalo Sewer Authority (BSA) began to prepare a comprehensive watershed improvement plan with grey, green and smart sewer solutions. After years of negotiations, the City and its partners came to an agreement and in 2014 BSA received approval of their Long-Term Control Plan for CSO abatement, which had an earlier estimated budget of $525 million. With the City facing limited funds from a reduced taxpayer base, BSA needed an innovative approach to address CSOs.

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Solution

City officials knew they couldn’t continue operating their collection system the same way they had been since the 1950s, and costly investments in new gray infrastructure like tunnels and storage tanks were equally as infeasible. Xylem, along with BSA’s talented team of engineers and consultants, worked together to begin designing and implementing a real-time decision support system (RT-DSS) across the city.

The RT-DSS strategy focused on building and controlling inline storage vaults to transform Buffalo’s massive gravity sewer system into a managed conveyance and storage system. The goal of the RT-DSS program is to minimize and/or eliminate CSOs by retrofitting the operational behavior of the existing infrastructure using implementing a real-time decision support system (RT-DSS) across the city.

The RT-DSS strategy focused on building and controlling inline storage vaults to transform Buffalo’s massive gravity sewer system into a managed conveyance and storage system. The goal of the RT-DSS program is to minimize and/or eliminate CSOs by retrofitting the operational behavior of the existing infrastructure using Xylem’s BLU-X™ for Collection System Optimization. Sixteen RT-DSS sites were identified for inline storage and optimal conveyance throughout the City. These sites were selected for maximum return of investment, and the first two sites selected for implementation were chosen as a representative sample of all the sites.

“The first three sites alone have reduced Buffalo’s CSO volume more than 100 million gallons more than what was originally anticipated assuming all 16 sites were implemented…meaning that BSA’s RT-DSS program could end up reducing CSOs by 3-4 times as much as originally projected.”

Outcome

As of today, four storage sites are now live and BSA is working to build and commission most of the remaining sites by the end of 2020. But what’s truly exciting is that the first three sites alone have reduced Buffalo’s CSO volume by 450 million gallons over the 12 months ending June 30, 2019. This nominal volume is already 100 million gallons more than what was originally anticipated assuming all 16 sites were implemented using a typical year simulation, meaning that the BSA RT-DSS program could end up reducing CSOs by 3-4 times as much as originally projected.

As each wet weather event provides more data, BSA can expect increasing levels of system intelligence, resulting in additional operations and maintenance cost reductions, as well as further reductions in CSOs. BSA’s RTC program is achieving outcomes unpredicted in the original design with even more sewage than estimated now capable of being safely stored, conveyed, treated and released to receiving waters as clean water effluent in a wider variety of weather conditions. BSA is helping to revolutionize the clean water industry while saving the City tens of millions in avoided capital infrastructure investment and Buffalo is regaining its reputation as a national and international leader.

BSA was able to present a revised LTCP with a $145 million reduction in budget due to its RT-DSS program. The RT-DSS retrofits, and additional minimally invasive green and gray infrastructure improvements will enable critical environmental progress at a far more sustainable cost to residents. In fact, with the success of BSA’s RT-DSS program, there may be even more capital infrastructure savings in its future as it achieves its ongoing environmental, economic and water equity objectives.

That’s the power of decision intelligence.

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