On the lookout

By Dan Kroll

The vulnerability of our water supplies to intentional attack, not to mention accidental contamination, has been well documented. Due to its nature, the distribution system that delivers water from the treatment plant to the end user is the primary focus of this vulnerability. The distribution system’s widespread nature and easy accessibility makes the task of physical hardening impractical. The only solution to address this weakness is the use of monitoring to rapidly detect and respond to any anomalies.

The distribution system represents the last analytical frontier in the water quality industry. Once the water reaches our aging distribution systems, our knowledge as to its continued integrity is limited. Historically, most monitoring in the distribution system has been relegated to the occasional snapshot provided by grab sampling for a few limited parameters. The development of water security monitoring based on the use of multi-parameter sensor packages coupled with interpretive algorithms in the years since 9/11 has begun to change this paradigm.

Monitoring in the distribution system is a difficult proposition. The sheer number and diversity of potential threat agents that could be utilized in an attack against the system makes monitoring for them on an individual basis an effort that is doomed to failure. To counter and detect the unprecedented number of compounds that may be encountered, what is needed is a broad-spectrum analyzer that can respond to any likely threat and even unknown or unanticipated events.

Rather than attempting to develop individual sensors to detect contaminants, the Hach Homeland Security Technologies approach was to utilize a sensor suite of commonly available off-the-shelf water quality monitors such as pH, electrolytic conductivity, turbidity, chlorine residual and total organic carbon (TOC) linked together in an intelligent network. One of the difficulties encountered when designing such a device is that the normal fluctuations in these parameters found within the water can be quite pronounced.

The problem then becomes how we differentiate between the changes that are seen as a result of the introduction of a contaminant or anomalous condition and those that are a result of normal everyday system perturbation. The secret to success, in a situation such as this, is to have a robust and workable baseline estimator to facilitate event detection.

In the system as it is designed, signals from five separate measurements of water quality (pH, Conductivity, Turbidity, Chlorine Residual, TOC) are processed from a  five parameter measure into a single trigger signal that indicates if water quality has changed in a meaningful way. This signal is easy for operators to interpret and recognize when an intrusion occurs

The deviation vector that is derived from the trigger algorithm is then used for further classification of the cause of the trigger. The direction of the deviation vector relates to the agent's characteristics. A deviation vector from the monitor can be compared to agent vectors in the threat agent library to see if there is a match within a tolerance indicating the potential cause. This system can also be very useful in developing a learning-based system for classifying normal operational events that is a useful process control tool.

Such systems have been deployed in a number of locations. These deployments include both municipal water systems and major projects at military and government facilities. While at the time of this writing no actual intentional attacks have been recorded, detected events have included pressure problems, rain events, main breaks, chlorine over and underfeeds, ammonia feed problems and other operational events. More serious problems that could have caused health effects if they had not been detected have included fluoride overfeeds, caustic soda overfeeds and a contamination of a well with jet fuel on a military base. The systems ability to detect such events and theories of response and operation when anomalous events in the distribution system are detected will be of paramount importance as we endeavour to secure our water supplies from not only terrorist activity but also a variety of other hazards.

Biography

Dan Kroll is Chief Scientist at Hach Homeland Security Technologies and Principal Investigator for the Hach Advanced Technology Group.  Kroll has developed both advanced and simplified methods for a variety of crucial water quality parameters and is the author of Securing Our Water Supplies; Protecting a Vulnerable Resource.