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EPA order brings innovative wastewater treatment upgrades in Guam

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Alejandro Diaz (

U.S. EPA order brings innovative wastewater treatment upgrades in Guam

GUAM – On Thursday, Guam Waterworks Authority (GWA) held a ribbon-cutting ceremony to begin operation of the newly upgraded Umatac-Merizo wastewater treatment system. This work is part of a series of wastewater upgrades to meet the terms of the U.S. Environmental Protection Agency’s (EPA) 2011 Court Order with GWA. Under the Order, GWA must address the health and welfare risks from numerous discharges of untreated or inadequately treated wastewater and significant deficiencies in its public drinking water systems. 

“This is an important milestone that represents Guam’s commitment to improving wastewater infrastructure,” said EPA Pacific Southwest Regional Administrator Mike Stoker. “We are pleased to  work with GWA in achieving better drinking water and wastewater systems that will benefit the residents of Guam and their environment.”

Upgrades to the Umatac-Merizo wastewater treatment system, completed in December 2019, greatly improved the system’s treatment process.  Although the system’s capacity remains at 390,000 gallons per day, GWA rehabilitated the waste stabilization pond and six constructed wetland ponds to allow natural processes to treat the wastewater and reduce the frequency of discharge to surface waters. This innovative design is well-suited to Guam's natural environment. Another important upgrade is an ultraviolet disinfection system designed to reduce bacteria in the treated discharge.

This work marks GWA’s second major milestone completed under the Order in the last  year. On June 28, 2019, GWA held a ribbon-cutting ceremony for the completion of the new Agat-Santa Rita wastewater treatment plant, which more than doubled the treatment capacity of the old plant from 750,000 gallons per day to 1.6 million gallons per day. The remaining milestones under the Order focus on improvements to the drinking water storage tanks.

To read the 2011 order, please visit:

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Photo of the Umatac-Merizo Wastewater Treatment System and wetlands area [photo credit: Guam Waterworks]Umatac-Merizo Wastewater Treatment System and wetlands area [photo credit: Guam Waterworks]