GWA Provides Sixth Mitigation Update to Sen. Lujan – Jun. 26, 2026

On June 26, 2026, the Guam Waterworks Authority (GWA) provided a sixth 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.

•  As of June 23, 153 installations have been completed, and 196 installations remain.

• GWA Customer Care representatives, engineers and water distribution continue working with our contractors to schedule and complete installations and home assessments.

•  GWA POE applications will be accepted from now and until 30 days after date of GWA commencing operation of the permanent GAC treatment system at well Y-15 in Yigo.

GAC Treatment System Construction:

• GAC vessels have been mounted to concrete pads at well M-4. Plumbing and valving work is in progress. Final completion is expected on or before September 30, 2026.

•  Four (4) permanent GAC vessels are installed at well Y-15. Technical representatives from GAC supplier Calgon Carbon will meet with GWA engineers and contractors to plan and execute vessel backwashing and media conditioning from June 29 – July 3, 2026. Operation of the system will commence immediately thereafter and Y-15 final completion is expected on or before September 30, 2026.

•  After four (4) consecutive weeks of non-detect levels of dieldrin, the interim treatment GAC vessels originally commissioned on October 12, 2025 at Y-15 will be relocated to well D-17. D-17 final completion is expected on or before December 30, 2026.

Dieldrin Testing Data from Samples Collected June 2, 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 remain 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 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 5/28/26 is 0.14 ppb; RAA is 0.17 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 6/2/26 is 0.13 ppb; RAA is 0.15 ppb.

Since October 2025, GWA has increased the frequency of monitoring wells which show results at the “half-IAL,” or 50% of the IAL as part of our mitigation efforts. The next monthly sampling for dieldrin is scheduled for July 16, 2026.

GWA continues providing mitigation updates through our microsite:guamwatersafety.com.