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Post-Filter GAC Contactor Facility for PFAS Control

To reduce PFAS in the primary drinking water source, Hazen and Sawyer provided design services for a Post-filter Granular Activated Carbon (GAC) Contactor Facility at Gadsden Water Works and Sewer Board’s C.B. Collier Water Treatment Plant. The project was implemented on a fast-track, with design, bidding, and construction completed in 15 months.

The Collier WTP relies on the Coosa River for its drinking water supply. The U.S. Environmental Protection Agency (EPA) issued health advisory levels (HALs) for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in May 2016 at a level of 70 ppt. Both compounds occur in the Coosa River and PFOA and PFOS levels have been increasing above the HAL. The primary goal for this project was to implement a Post-filter GAC Contactor Facility – Phase 1 for PFOA and PFOS removal to maintain potable drinking water within the EPA HALs. The initial capacity of the GAC Contactor Facility is less than the full WTP capacity and relies on blending of GAC treated water with filtered water from the C.B. Collier WTP to meet the HALs. The initial capacity of the GAC Facility is 6 mgd with an empty bed contact time of 20 minutes.

The project also includes two new intermediate 150 hp pumps, 24 Inch influent pipe, 36 Inch discharge pipe, and instrumentation and controls.

Long-term solutions that consider other PFAS (including short chain compounds) are being assessed to provide the most optimal treatment for managing PFAS compounds in the drinking water. The objective is expedited implementation of the Phase 1 GAC Facility to provide a tool for control of PFOA and PFOS below the HALs.

New intermediate pumps were installed in an existing pump station to convey filtered water to the new GAC Facility. The GAC Facility consists of pressure vessel type GAC contactors. Space on the site was reserved for future expansion of the ultimate PFAS treatment solution (GAC, IX, both) up to the full WTP capacity of 24 mgd, including construction of a new intermediate pump station. This project was delivered using the traditional design-bid-build approach, and was completed within 15 months, including design, bidding, and construction.

Gadsden timeline
Design was completed in 4 months, with the facility online in just 8 months.

Project Outcomes and Benefits

  • Post-filter GAC contactors for PFOS/PFOA control were implemented on a fast-track, with design, bidding, and construction completed in 15 months
  • GAC effectiveness for removal of short chain PFCs is being evaluated