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​​Hello Joe,
Thank you for the conversation today.  In response to your email below, I will provide some background into why any form of chlorine dioxide is already allowed for use at public water systems within Colorado.
Public Water Systems are regulated by Regulation 11, Colorado Primary Drinking Water Regulations.  Section 11.2(6) defines disinfectant as follows:
According to both the surface water rule (Section 11.8) and the groundwater rule (Section 11.11), suppliers of water must disinfect the water and provide a minimum disinfectant residual concentration at Entry Point of 0.2 mg/L and a disinfectant residual of 0.2 mg/L throughout distribution.  
Therefore, because chlorine dioxide is a disinfectant by definition, it can be used to comply with the above rules. 
Furthermore, new water treatment must be designed in accordance with our Department's Design Criteria for Potable Water Systems (Policy 5, DCPWS). Our DCPWS already contains sections outlining the requirements for chlorine dioxide feed systems.   Section 4.4.8 and Section 5.4 specifically.  
With regard to the TwinOxide Product, the product is allowed as a form of chlorine dioxide because it is NSF 60 certified (Section 2.21), and it is by definition allowed in the regulations as chlorine dioxide.  
While TwinOxide (mixing solid sodium chlorite and solid sodium bisulfate) is not listed specifically as a known type of chlorine dioxide generation in section 4.4.8 of the DCPWS; the Department is willing to allow for deviations from the specific design criteria laid out in Section 4.4.8 (Deviation process is discussed in Section 1.4 Site Specific Deviations).  
Therefore, while TwinOxide is not listed specifically as an alternative treatment technology, it is permissible to be used by public water systems in the treatment of their water.  Should a system decide to convert chemicals, they will be subject to design review and approval.  Also, chlorine dioxide specifically requires compliance with Regulation 11.23(2) for maximum chlorine dioxide residual and Regulation 11.25(2) for chlorite.
Thanks and please let me know if you have other questions.
Tyson Ingels
Lead Drinking Water Engineer

Engineering Section