Implementing early warning of toxic chemical intrusion into a WWTP by using remote toxic chemical sensors communicating over cellular wireless telemetry into a central SCADA system with advanced alarming and voice notification.

Problem: The District of Columbia Water and Sewer Authority (DCWASA) has experienced in the past sudden influx of high concentrations of organic chemicals into their main pumping station and the Blue Plains Wastewater Treatment Plant. Many DCWASA staff members were affected by the presence of the toxic gas in the main pump station. There was no early warning system in place to warn the staff of the pending intrusion.The environmental impact of a major system disruption could be extreme. Flooding has proven to cause major local community and regional impacts. Introduction of toxic substances into the system will impact all facilities along the path to the treatment plant.Solution: DCWASA has installed an MSA remote toxic chemical sensor upstream of the main pumping station to provide an early warning of the pending threat. It is currently monitoring volatile organic compounds (VOCs). The VOC sensor had to be installed in an underground location in a public area with high pedestrian use in a park setting. The use of antenna masts for communications was not feasible. Cellular communications with a low profile hidden antenna was the selected as the method of transmitting data to a central SCADA system. An Allen-Bradley CompactLogix PLC was connected to the VOC detector at the remote site. The PLC monitored the status of the VOC detector plus also performed other functions such as communications logic and also provides unauthorized intrusion logic. A Rockwell RSView SE SCADA system provides monitoring and alarming to a touch screen located in the main control room. Since the operators are not always in the control room, a voice annunciation system was also installed. In the event of an alarm, a pre-recorded voice (WAVE file) is sent to speakers in the control room and outdoor bullhorn type speakers outside the control room.