We have written numerous articles over the years about disinfection and maintaining a proper chlorine residual. Just search the blog for chlorine or disinfection and you will find excellent information and references from simple fixes to profound policy positions on appropriate disinfection residuals. Did you ever wonder how effective chlorination is in preventing drinking water contamination and what happened to disinfection waivers in Colorado?
In Regulation 11 rulemaking in 2010, the Water Quality Control Commission (commission) decided to remove the authority of the department to grant disinfection waivers. So at that time all waivers were evaluated and held static. The rulemaking also established more rigorous regulatory oversight for waivered systems. The rulemaking also required that all disinfecting groundwater systems had to maintain 0.2 mg/L at their entry points (surface water already had that requirement). Then, in the 2015 rulemaking to update the total coliform rule, the commission chose to establish a storage tank inspection regulation and also require that all systems maintain at least 0.2 mg/L chlorine residual throughout the distribution system. All of these rule changes were meant to recognize best practices performed by most water systems and to compel the few systems that were not up-to-speed to better protect their distribution systems. While the yearly data is noisy, it is important to recognize that the overall number of E.coli positive samples reported to us per year went dramatically down around the mid-2010s. See the graph below and table below.
It is also worthwhile to look back further at the trends over a few decades:
It’s apparent that over time E. coli violations dramatically decreased. Since about 2014, the majority of E. coli violations occurred at public drinking water systems that were out of compliance with the state’s disinfection requirements.
As the 2010s progressed, we developed rigorous protocols to evaluate systems that maintain disinfection waivers to make sure public health was being protected without disinfection present. Therefore, over time, the department revoked waivers at systems that could not maintain compliance with the rigorous regulatory requirements for waivered systems. Other waivered systems voluntarily began chlorinating their water systems based on concerns over liability and realization of the relatively low level of effort that chlorination requires.
At present, only two public water systems still maintain disinfection waivers. These two systems are the last disinfection waivers that will be used in Colorado. These communities have shown through regulatory compliance and their track record of water quality that the public in those communities has a measure of protection from waterborne disease even though they do not chlorinate. However, these communities ultimately may choose to chlorinate their water in the long term. The department’s position would be that it is always best to chlorinate when possible. Also, through natural disasters, aging infrastructure, or unforeseen events, the two systems may ultimately end up having their waivers revoked due to failure to maintain compliance.
As discussed in the previous blog postings about the importance of chlorination, Colorado has a proud tradition of protecting our public drinking water supplies to the greatest degree possible.
➽ Tyson Ingels, P.E Lead Drinking Water Engineer
➽ Ron Falco, P.E. Safe Drinking Water Program Manager
