Early Warning

A real-time wireless system in manholes monitors sewer levels and helps prevent overflows in a northeast Florida city

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Sanitary sewer overflows (SSO) in Jacksonville, Fla., were a problem for JEA, the municipal utilities provider.

The authority had invested in a SCADA system to control and monitor 1,240 lift stations. It also had paid a company to monitor manholes with known deficiencies and report them to a Web site, but the program was expensive and ineffective. JEA considered installing power and control circuits to monitor sewer levels in certain manholes, but digging up the roads was expensive and would cause traffic congestion and delays.

In 2007, the authority asked its water and wastewater reliability specialist, Rodney Williams, to explore ways to monitor sewer levels at manholes, then transmit the information to the SCADA system. The remote transmitter Williams and JEA personnel developed prevented 100 percent of SSOs from happening at 17 monitored locations.

Compatible and portable

“We wanted to transmit a radio signal from within the manhole to the nearest lift station, thereby gaining access to our network,” says Williams. “Additionally, JEA wanted to monitor the transmitters for high level, battery strength and communication failure.” The system also had to be portable, Division I, Class I compliant and have no recurring costs.

The team searched for transmitters powerful enough to send analog and digital signals through the ground and through steel manhole covers, yet able to run on batteries. “We went through many different scenarios and transmitters before selecting a WI-I/O 9-K transmitter with matching battery pack from Weidmuller,” says Williams. “The WI-I/O 9-4 transceiver collects the data from each transmitter and forwards it via a wired connection to our SCADA application.”

The included programming software made it simple for JEA to map the signals and control transmit schedules, thereby prolonging battery life. “Based on the system’s power consumption, we could replace the standard AA alkaline batteries once a year,” says Williams.

Boosting the signal

To protect all voltage, the team constructed an explosion-proof enclosure with cradle from 3/16-inch stainless steel. The cradle mounts in the manhole. A small external antenna on the enclosure boosts the signal past manhole covers. The addition of a Yagi directional antenna system at the lift stations made long-range transmissions possible.

“The start of a backup trips a float, which triggers the signal,” says Williams. “When we receive the alarm, we immediately send a vacuum truck to that location to remove the blockage. The beauty of the equipment is that once the infrastructure is repaired, crews can move the device to a new manhole with no recurring cost.”

Based on the success of the 2009 pilot program, the authority budgeted for 15 more manhole monitoring devices, bringing the total to 32. “JEA is pleased with the success of the wireless manhole monitoring system and its ability to protect public health and the environment,” says Williams.



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