Smart sewers: Smart technology for water utilities

The Clean Water Act (CWA) was passed in 1972 to protect the nation’s waterways. To further bolster the CWA’s authority, the Combined Sewer Overflow (CSO) Control Policy was published in 1994, introducing nine minimum controls required for any municipality with CSOs. These controls included maximizing collection system storage, prohibition of CSOs during dry weather, public notification, and monitoring CSO impacts and controls. Municipalities across the country, especially the 772 with combined sewer systems, were now faced with new water quality requirements and little increase in funding.

Rising demand, aging infrastructure, limited resources

Billions of gallons of untreated sewage flows from cities across the country into local rivers and waterways. Over the past few decades, as the population has shifted to urban centers, a greater demand has been placed on city’s infrastructure. This trend is expected to continue as the most recent Infrastructure Report Card published by the American Society of Civil Engineers projects an increase in sewer system demand of 23% by 2032. This rise in demand, along with aging infrastructure and limited resources, are increasing the number of municipalities found to be in violation of the Clean Water Act. The pressure on the system is not only causing environmental issues; sewage flowing into rivers and backing up onto private property is also creating massive financial burdens on communities.

The report card also estimates the country’s sewer infrastructure requires a $271 billion investment to meet current and increasing needs. Additionally, as municipalities are found to have violated the Clean Water Act, settlements are reached in the form of consent decrees. These signed agreements between the EPA, Justice Department, and the offending municipality typically dictate the implementation of a Long-Term Control Plan (LTCP) as well as a civil penalty or fine. Although set up for the benefit of the environment and community, these plans can cost hundreds of millions, and occasionally billions, to implement.

While the federal government has funding programs in place designated for water infrastructure improvement projects, 95% of the investment comes at the local level. These municipalities are faced with the task of bringing the sewer system into compliance while minimizing the investment that will be passed on to their customers.

An emerging way to solve compliance issues 

Traditionally, an investment in gray infrastructure including new sewer lines, storage tanks and tunnels has been used to reach compliance. More recently, green infrastructure has been incorporated into the solution, used to slow the flow of storm water into the wastewater system. Both gray and green options can involve high capital investment and large construction undertakings. 
Smart sewers are a combination of hardware (sensors and meters installed at manholes, pump stations, and control valves) and data management software to help optimize operations at much lower cost than the alternatives.

In their basic form, smart sewers continuously monitor flow and wastewater levels throughout the system while measuring rainfall across the service territory. This data is collected and analyzed to shed light on current operations.

Sewer systems are built with a factor of safety such that inadequate system capacity is rarely the cause of an overflow event. However, flow is not uniform throughout, which can lead to one portion of the system to overflow while leaving another with excess capacity. Smart sewers address this problem by utilizing pumps and valves that are connected into the network of sensors to move the wastewater towards open capacity for storage and eventual treatment. 

What success can look like

Faced with a LTCP that would cost the city of South Bend, Ind., and its 100,000 residents $700 million, a new innovative approach was necessary. The first step was to install sensors and monitors throughout the system to understand current operating conditions. This data led to the discovery of excess capacity in the system that had been cut off due to grit and blockage. Smart control valves were than installed, providing real time flow adjustments throughout the system. 

In its current state, the city’s 165 sensors and 13 control valves collect a data point every five minutes. This helped maximize O&M efforts while the introduction of the “Sewer Watch Dog” notification application allowed the utility to take preemptive actions when the operators are informed of abnormal conditions. Additionally, the digital transformation led to the creation of a digital model which the utility can rely on when sizing and locating capital improvement projects. These steps led to a reduction of annual CSOs of 1-2B gallons to 40M gallons per year, sending 99.8% of wastewater flow to a treatment plant. 

With the implementation of smart sewers, the city was able to reduce the LTCP cost to below $200M. However, the value created goes beyond the financial impact. With this system, the E. coli levels in the river are significantly down and the community disruptions of large-scale constructions projects that can affect local neighborhoods and businesses are minimized. 

Conclusion

The EPA has stated that it is willing to consider a request to modify existing plans to incorporate cost-effective innovative approaches that achieve comparable and measurable results. For water utilities looking for an innovative way forward, smart sewers can be the answer. Successful utility programs have utilized the following approach:

The thought of undergoing this digital transformation can be overwhelming. However, for communities with consent decrees due to violation of the Clean Water Act, smart sewers are an option that can help reach compliance and alleviate the financial burden while setting the utility up for success into future.