PFAS removal in drinking water applications with Leopold® Gravity GAC Contactors

Per- and Polyfluoroalkyl substances (PFAS) are a class of man-made chemicals used in a wide range of industrial processes and consumer products, including food packaging, stain-resistant fabrics, cosmetics, non-stick cookware, and firefighting foams. Their chemical structure, defined by strong carbon-fluorine bonds, makes them highly resistant to heat, water, and degradation. These properties have driven widespread use across industries. 

The same properties that make PFAS useful in manufacturing also make PFAS persistent in the environment. Often referred to as “forever chemicals,” PFAS do not readily breakdown and can accumulate over time in soil, groundwater, and surface water. PFAS are highly mobile in the environment. As a result, contamination has been identified in drinking water sources worldwide, including municipal systems and private wells.    

Scientific research has established links between the ingestion of specific PFAS and potential human health risks resulting from bioaccumulation over time. These health effects include:

• Increased risk of certain types of cancer
• Liver damage 
• Thyroid disease 
• Reproductive impacts 
• Developmental effects in children 

Recent nationwide monitoring underscores the scale of the issue. Under the EPA’s Fifth Unregulated Contaminant Monitoring Rule (UCMR 5), thousands of additional sites have reported detectable PFAS levels—bringing the total number of known impacted locations to nearly 10,000. Current estimates indicate that up to 176 million people in the U.S. may have been exposed to PFAS through drinking water.

In response, regulators are establishing stricter standards to reduce exposure and protect public health. In the United States, the EPA’s National Primary Drinking Water Regulation for PFAS sets enforceable limits for specific compounds. These requirements introduce new expectations for monitoring, reporting, and treatment—placing increased compliance and cost pressures on utilities. Internationally, the European Union is evaluating broad PFAS controls under the REACH framework, which could significantly limit production and use. Many other nations are also beginning to evaluate drinking water PFAS regulations that will require future action and treatment. 

Gravity contactors - Gravity contactors are a highly effective solution for medium-to high-flow PFAS treatment applications. These large open-top steel or concrete systems are typically designed for granular activated carbon (GAC), which is recognized as a best available technology for PFAS removal. They offer a cost-effective approach for long-term treatment where permanent infrastructure is required. Designed for continuous operation, gravity contactors are particularly well suited for municipal drinking water treatment.  

System components supplied: 

• Filter underdrains (Type XA, S, SL)
• Media retainers (I.M.S® 200)
• Media
• Wash water troughs
• Filter controls
• Filter accessories
• Engineering and design support

Cement tank (by others) or above ground steel tank (Xylem) configurations

A contactor designed with Leopold’s Type XA Underdrain and I.M.S 200 media retainer features a low‑profile design that supports deeper media beds and greater hydraulic flexibility. When coupled with Leopold’s Grout‑LINK™ underdrain installation method the result is a robust, long-lasting filtration system engineered for decades of reliable performance. Leopold filtration solutions are highly configurable and scalable to easily address retrofits, facility expansions, and new builds.

For over 100 years, Xylem’s Leopold brand has been an industry leading provider of Municipal drinking water filtration technologies, with over 10,000 global installations. By leveraging these innovative filtration technologies, Leopold enables customers to address their PFAS challenges in an effective, cost-efficient manner. With decades of experience in GAC filtration applications and numerous global GAC contactor installations, Xylem through the Leopold brand is a trusted partner giving municipalities confidence in the effectiveness and longevity of their treatment systems.

Actually, no! While Leopold filtration technologies are traditionally a strong fit for medium to very large sized utilities, we offer open-top steel tank package filters which can be a great choice for some smaller sized utilities, depending on site conditions and details. With several standard sizes, the number of right-sized units can be configured to fit site requirements. Leopold designs filter systems for flowrates of 1MGD and greater, with no upper limit on flowrate.

Yes, Leopold’s filtration components are incredibly strong, durable, and designed to withstand the weight of deep media beds across a range of applications. Leopold has numerous deep bed GAC filter installations in operation around the world, with many exceeding 8 feet in depth and several exceeding 10 feet. 

 

With decades of experience in GAC applications, Xylem’s Leopold brand has numerous global installations addressing various Contaminants of Emerging Concern (CEC's) including PFAS​. Leopold filtration components are directly compatible with GAC, and all products are fully compliant with NSF / ANSI / CAN 61 standards.​

The Leopold I.M.S® 200 media retainer directly retains media down to 0.4mm effective size, making it a natural fit for GAC applications. The I.M.S 200 also eliminates the need for up to 14” of support gravel, and with deep filters typically required for contactors removing PFAS, minimizing tank depth can help save on capital construction costs.

 

While GAC contactors are not backwashed in the same manner or frequency as traditional solids filters, backwash still matters. Even with contactors being located after the primary solids filters, small amounts of solids will still accumulate in contactors over time and lead to a loss of head. To return the contactors to optimal operation and relieve the loss of head, a water-only backwash is performed to gently expand the media and remove these solids while avoiding major disturbance to the mass transfer zone within the carbon. 

Leopold’s filter underdrains are built to enable superior backwash distribution, optimizing backwash efficiency, filter performance and runtime. Properly distributed backwash helps to avoid channeling, eliminate dead zones, preserve the mass transfer zone, and ensure the media is being fully utilized before changeout and regeneration. On the other hand, poor backwash can cause disruption of the mass transfer zone, loss of media, and premature breakthrough, potentially leading to more frequent media changeouts and higher operating costs.  

GAC remains a leading media choice for several reasons and continues to be the most widely adopted PFAS removal method. Beyond carbon, there are a plethora of adsorptive medias that have been developed, but few that are viable alternatives to current proven sorbents.  

Xylem is focused on evaluating promising media candidates, both carbon and non-carbon, to determine performance and economics, benchmarking against current best available medias. Medias must be further tested for compatibility and performance in a gravity configuration, which is done with Leopold’s sophisticated test equipment and filter columns at our Product Development Center (PDC). Important benefits of a new media could include; lower required EBCT, less volume of media required, higher bed volumes/reduced media changeout frequency, and reduced contactor footprint and associated capital and construction costs. As an industry leader in gravity media filtration, Leopold remains committed to evaluating novel medias that have the potential to bring value to customers.

As PFAS regulations continue to evolve, utilities need treatment technologies that are reliable, scalable, and designed for long-term performance.

Leopold Gravity Contactors provide a proven solution for municipal drinking water applications, helping communities meet regulatory compliance while protecting public health. Contact us to discuss your PFAS treatment challenges.