GWA Provides Seventh Mitigation Update to Sen. Lujan – Sept. 4, 2026

On September 4, 2026, the Guam Waterworks Authority (GWA) provided its seventh update on the Authority's dieldrin mitigation efforts following the conclusion of a joint oversight hearing held by the 38th Guam Legislature.

In the update to Sen. Jesse A. Lujan, Vice Speaker Tony Ada and Committee on Health Chair Sen. Sabrina Salas Matanane, GWA stated that the Authority "remains firmly committed to our dieldrin mitigation plans, and we appreciate the support from you and your office and all of our stakeholders as we progress in our restorative efforts to provide safe water to the Santa Rosa, Yigo community impacted by the dieldrin interim action level (IAL)."

Point-of-Entry (POE) Program – INSTALLATION PROGRESS:

• American Watertek and SBS Guam began installing POE units on May 19 and May 25 respectively.

• 304 POE installations are completed as of August 27. 59 installations are pending.

• GWA Customer Care, engineers and water distribution crews continue working with our

• contractors to schedule and complete installations and home assessments.

• GWA will discontinue receiving POE applications on Thursday, September 17, 2026.

• Notice is posted on GWA’s microsite guamwatersafety.com and GWA social media

• accounts and has been issued to the Yigo Mayor’s Office.

GAC Treatment System Construction – Y-15 PERMANENT TREATMENT SYSTEM NOW

ONLINE:

On August 18, 2026, the Guam Environmental Protection Agency (GEPA) conditionally approved GWA’s August 15 proposal to commission the permanent treatment system installed at production well Y-15, and to remove and relocate the interim treatment system components from production well Y-15 to production well D-17.

Y-15’s interim GAC treatment system was removed on August 24, 2026. The permanent GAC treatment system was placed online on August 25, 2026. Two trains of GAC vessels (4 vessels total) are configured in a “lead-lag” series to ensure redundant treatment to minimize contaminant breakthrough. Y-15’s treatment system continues increased monitoring pursuant to GWA’s GEPA-approved dieldrin mitigation plan.

GAC vessels are installed at M-4. Plumbing and valving work is in progress. Under our

contractor’s latest schedule, the treatment system is expected to be online by October 3, 2026. A transmission waterline linking well M-3 to M4’s treatment system will provide additional mitigation. The waterline work permits have been received, and work is expected to begin in the coming weeks.

Work to relocate Y-15’s interim GAC vessels to D-17 is scheduled for September 15, 2026. Under our contractor’s latest schedule, the treatment system is expected to be online in late October 2026.

Dieldrin Testing Data from Samples Collected July 28 – August 19, 2026:

Dieldrin Sampling Results - Running Annual Average (RAA) – 124 SAMPLE LOCATIONS
Wells	RAA	Remarks
30	Non-Detect (ND)	• No detections for dieldrin
87	0.01 ppb to 0.09 ppb	• 86 locations are less than 0.1 ppb or 50% of the IAL • D-17 offline since 7/31/25; treatment under construction. Result for samples taken on 3/10/26 is 0.1 ppb. RAA is 0.09 ppb.
4	0.10 ppb to 0.14 ppb	• A-23 & A-25 offline since 2016; treatment under construction • M-2 & D-18 online; RAAs for both are 0.14ppb and below IAL
3	0.15 ppb to 0.19 ppb	• M-4 offline since 10/3/25; RAA is 0.16 ppb; treatment system under construction • M-3 was placed on standby mode on 10/19/25 and will only be placed online intermittently if needed operationally to meet customer demand; Result for samples taken on 8/12/26 is 0.13 ppb; RAA is 0.16 ppb; M-3 was placed offline on 01/26/26 but was temporarily activated from 04/07/26 – 05/18/26 for Super Typhoon Sinlaku recovery. • EX-11 remains online and has not had a RAA over the IAL; Result for samples taken on 8/12/26 is 0.13 ppb; RAA is 0.15 ppb.