Policy #5 is used as a basis for reviewing design applications for drinking water treatment works in Colorado. The division routinely updates the document to maintain industry standards with input from stakeholders. The division is initiating a stakeholder process in 2024 and asking for feedback on portions of the drinking water design criteria to be updated. If you are interested in participating in this process please visit the Drinking Water Design Criteria stakeholder engagement website Drinking Water Design Criteria stakeholder engagement website.
The division is aware that there are drinking water systems in Colorado that are looking to implement PFAS removal prior to the completion of the design criteria update. For those systems there are additional resources available. The EPA has released a guidance document for water systems titled Treatment Options for Removing PFAS in Drinking Water. The EPA has identified best available technologies (BAT) for PFAS removal using six criteria:
- removal efficiency,
- historical full scale operation,
- geographic applicability,
- compatibility with other treatment processes,
- ability to bring the entire water system into compliance,
- and a reasonable cost to large as well as medium sized systems
The technologies identified are granular activated carbon (GAC), ion exchange (IX), and reverse osmosis (RO).
Granular Activated Carbon (GAC) is a process where adsorptive media is contained in pressure vessels or atmospheric filter beds. The PFAS contaminated water passes through the vessel or bed and the dissolved contaminants are pulled from the water and onto the surface of the media. In addition to removing PFAS, GAC can remove other contaminants including taste and odor compounds, volatile organic compounds, disinfection byproduct precursors, and others. For this reason, GAC is great for water systems looking to address multiple concerns at once. GAC will generally not have a significant impact on the corrosivity of the water. After a period of time, the GAC media will not be able to adsorb any more contaminants and will need to be replaced by fresh media and properly disposed of. The EPA has published an Interim Guidance on the Destruction and Disposal of PFAS and Materials Containing PFAS. Disposal methods include landfills and thermal treatment for regeneration or destruction.
Ion exchange (IX) is similar to GAC where contaminated water is passed through a media, but rather than adsorbing contaminants, the PFAS in the feed water are exchanged for an ion, such as chloride, on resin beads contained in a pressure vessel. The IX process continues until the resin is out of chloride exchange sites. Unlike other IX treatment applications like water softening, the spent resin can not be regenerated by backwashing. The resin will need to be periodically disposed of and replaced with fresh media. This treatment process generally targets PFAS only and will not remove additional contaminants. The IX process tends to require a smaller footprint than GAC. Due to the addition of chloride ions into the IX effluent, this treatment process may impact the corrosivity of the finished water. Spent IX resin must either be landfilled or incinerated.
There are other PFAS selective media available on the market today. For any of these newer media, GAC or IX resins, pilot testing is recommended to determine what method works best for a specific water quality. Piloting allows the water system to look at factors like comparative costs, treatment efficacy, and secondary impacts to finished water quality whether beneficial or not.
The third technology that EPA has identified is reverse osmosis (RO). RO is a membrane separation process that physically removes contaminants from drinking water. This process results in two streams of water: the clean effluent and a reject stream that contains concentrated PFAS and other contaminants. The disposal of this continuous waste stream can be a substantial challenge in Colorado. The most common disposal method for land-locked states is deep well injection or evaporation ponds. There are other disposal methods in the research phase.
There are many factors that should be considered as a water system addresses compliance with the PFAS MCLs. For some systems there may be a non-treatment option that is a better fit. Non-treatment options include adjusting source water blending ratios to prioritize sources with lower PFAS levels, an interconnect into a system with existing PFAS treatment, or consolidation into an existing system. If you would like to talk to us more about what available treatment options and grant funding opportunities, please email us at cdphe_pfas@state.co.us.
Thank you,
➽ Chelsea Cotton, P.E. Lead Drinking Water Engineer
