Findings Concerning the Potential Security Consequences and Risks that should be Considered When Making the Switch from Free Chlorine to Monochloramine Disinfectants

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Abstract:

In recent years, there has been a move away from the utilization of Free Chlorine to maintain a residual level of disinfectant in the distribution system towards the use of Monochloramine. The reason behind this change is to decrease the formation of disinfection byproducts (DBPs), which are created when the Free Chlorine reacts with organic material in the water. The use of Monochloramines as a residual disinfectant has been deemed to be an inexpensive and effective means to meet new stringent EPA limits for DBPs in drinking water. There are a number of well-known advantages and disadvantages entailed in using Monochloramines for this purpose. The fact that many municipalities have made or are making the switch indicates that, to date, the advantages have outweighed the disadvantages. One area of potential concern that has been overlooked in the past dialogue weighing the pros and cons of switching has been the security repercussions entailed in a switch from Free Chlorine to Monochloramine.

That our systems, as they are currently configured, are vulnerable to attack has been widely recognized. While most supply sources are limited in their vulnerability due to the massive volumes of water involved, the distribution system remains a vulnerable and tempting target as was clearly stated in a recent General Accounting Office (GAO) report to Congress that listed the vulnerability of the distribution system to attack as the largest security risk to water supplies. Terrorists could compromise a system through an assault anywhere in the distribution system through the introduction of any one of a large number of possible threat agents through a backflow event. Due to the threat posed to our water supplies by a potential terrorist attack, it behooves us to look at factors that affect our water quality, such as the switching from Free Chlorine to Monochloramine for disinfectant purposes, in a new light. There are several characteristics of Monochloramines that may lead to significant security considerations when it is used to replace Free Chlorine in the distribution system.

As part of a recent development endeavor to design a early warning system for the drinking water distribution system, Hach Homeland Security Scientists, in coordination with experts for the Army Corps of Engineers Research and Engineering Laboratory and the Edgewood Biological and Chemical Command, have had cause to study the interactions of a wide variety of potential water borne threat agents with different levels of either Free Chlorine or Monochloramine present. The experimental design entailed the gathering of bulk parameter monitoring data (pH, TOC, ORP, Turbidity, conductivity and disinfectant residual levels) for a wide variety of agents at different concentrations when they were injected into water sources containing differing amounts and types of disinfectants. This resulted in the accumulation of an extensive database on the reactions of these agents in common drinking water scenarios and their effect on the bulk parameters being monitored. This revealed some highly interesting and significant findings on the security repercussions of the Free Chlorine/Monochloramine debate.

These studies have lead to several significant findings that have security implications.



Monochloramine is less reactive than Free Chlorine with many threat agents. This leads to concerns for both degradation of potential threats and their early detection.


Monochloramine is a less efficient disinfectant than Free Chlorine, especially, in the short contact time that may be encountered in a back flow attack.


Monochloramine use may lead to terrorist alteration of attack strategies making an attack more difficult to detect.


The findings in these studies have significant repercussions as to the safety and security of our Nation's water supplies. Details of the studies are discussed along with recommendations to help alleviate the potential risk.

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/193864707787932531

Publication date: January 1, 2007

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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