The Environmental Protection Agency estimates that more than 40 million Americans living in 770 communities, mostly in the Northeast, Great Lakes, and Pacific Northwest, still rely on combined sewers.
Why is this a problem? These Victorian-era water management systems collect sewage and stormwater runoff in the same network of pipes. During heavy storms, overwhelmed systems flood streets and basements and discharge a variety of bacteria and toxic chemicals.
In 1994, the EPA required these municipalities to make improvements to reduce overflows and health concerns. Six years later, Congress required municipalities to comply as part of the Clean Water Act. Many major cities have since begun planning for hundred-million-dollar fixes, addressing failing pipes and networks as well as system overflows.
In an effort to develop more affordable and effective methods of compliance, one Midwestern group thinks it has a superior solution: EmNet’s Combined Sewer Overflow Network relies on wireless sensors installed on the underside of manhole covers to monitor water levels at various points across a city. The sensors broadcast data via simple radio waves to a central monitoring facility, and can send messages telling smart valves to open or shut during times of peak water flow.
When EmNet was formed in May 2004, scientists estimated that combined sewer overflows result in the release of 850 billion gallons untreated wastewater each year, leading to contaminated drinking water and human and animal sickness.
Their decentralized system provides real-time information on developing bottlenecks or blockages, helping crews act quickly. It also ensures optimal water conveyance and storage across the system, helps cities meet compliance requirements and improves billing accuracy for local water users.
EmNet began testing the system in South Bend in 2005, receiving a $1 million grant from a state research fund in 2007. For the past two years, some 115 sensors have been monitoring the system across the city. Gary Gilot, South Bend's public works director, says his system has not yet achieved the forecast 23 percent reduction in storm-related overflows because the city is expanding its water storage capacity. Once that's complete, he expects to reduce storm flooding by about one quarter.
Meanwhile, South Bend has traditionally experienced 25 or so dry-weather overflows each year, due to debris or other blockages. That's all changed with EmNet's system. “We had one such incident each of the last two years, and both were related to a contractor digging into the system,” says Gilot.
He estimates that the $6 million the city spent on the system has knocked as much as $120 million off the half billion dollars it plans to spend to bring its aging water infrastructure up to state and federal standards. These savings will show up in local water bills. “We don't want to just throw money at this problem so we're trying to use smarter technology,” says Gilot.
Several nearby cities – including Elkhart and Evansville, Indiana, and Joliet, Illinois – have since implemented the EmNet system, at least partially. Last March, Hoboken, New Jersey, installed monitors at 15 locations across the city to collect data and develop an effective long-term flood control system. A spokesperson from the mayor's office says the city is satisfied with the results thus far.
The technology seems likely to proliferate. Buffalo has begun a feasibility study with EmNet, while Washington, D.C., is currently installing EmNet's flooding alert system, and New York City water officials visited South Bend last year for a firsthand look.