Many American cities have a problem hidden beneath their paved streets. Approximately 860 communities in the U.S. have combined sewers that carry commercial and residential sewage along with storm runoff. On dry days these aged sewer systems, parts of which may date back to the 1800s, route soiled water to treatment facilities. However, rain or melting snow can easily overtax the sewer systems, which causes the waste to spill into a local body of water. These spillages, called combined sewer overflows (CSOs), flood nearby streams, rivers, or lakes with untreated sewage, oil from roadways, and other toxins, similar to the “poonami” recorded in New York’s notoriously contaminated Gowanus Canal. These pollutants can affect the health of the more than 40 million people who live in these affected communities and have a negative impact on the local ecosystem.
The need to better manage our cities’ wastewater is facing two additional challenges: climate change is increasing the number of CSO events as more powerful storms bring higher rainfall totals, and cities on the Eastern seaboard are also facing rising sea levels that create sunny day flooding like in Miami. The EPA has used the Clean Water Act to fine cities for each CSO, but adding new infrastructure and waste treatment plants can easily cost taxpayers tens if not hundreds of millions of dollars.
Necessity—and strained budgets—are the mother of invention.
Many cities are employing time-tested and cost-effective solutions to reduce the amount of runoff that enters the system. One of the challenges that cities face is that almost all of the land is covered in impermeable surfaces; buildings, roadways, and sidewalks. This prevents rainwater from being absorbed into the ground organically. New York City has developed a Green Infrastructure plan, which leverages bioswales (aka rain gardens), green roofs, blue roofs (which capture and temporarily hold rainwater), permeable pavers, and rain barrels. Philadelphia has a similar plan, Green City, Clean Waters which was developed in response to the potentially massive infrastructure cost of upgrading their existing sewer system. These inexpensive solutions save money by reducing the volume of water that needs to be processed at sanitation facilities and limiting the need to build additional facilities, but adding green spaces also helps clear air pollution, reduces the ambient temperature, provides areas for wildlife and pollinators, and has shown health benefits, never mind improves the city’s curb appeal.
As beneficial as green infrastructure can be, there is still a need for “gray” infrastructure. The city of South Bend, Indiana, was faced with an $860 million problem. They had 60-70 CSO events a year, dumping approximately 1 billion gallons of wastewater into the St. Joseph River, which flowed into Lake Michigan. Even after spending $87 million on infrastructure improvements, they were still faced with thousands of dollars in EPA fines or spending approximately $10,000 per resident on additional infrastructure. Instead of crippling the city with enormous debt, they leveraged the internet of things to optimize their upgraded system into a “smart sewer”.
EmNet’s (embedded networks) sensors were installed beneath 150 manhole covers at a comparatively nominal cost. The sensors measure the volume of water passing through that point in the sewer and transmit data every 5 minutes for real time tracking. They can monitor the entire network during rain storms and use the data to open and close values to redirect water from segments that are overtaxed to areas that have additional capacity to store the overflow. While this system can still become overwhelmed, as it did in February of 2018 during a flood, they have estimated that the sensors help prevent more than 1 billion gallons of wastewater from polluting the St. Joseph River every year.
Each city will need to tailor their own approach to wastewater management, but using green infrastructure to reduce runoff in conjunction with well planned gray infrastructure upgrades to existing systems may help reduce budget outlays.
Image Credit: EmNet.net