King County · System ID 40900 · Community water system
Is Sammamish Plateau Water & Sewer’s water safe? PFAS test results (King County, WA)
PFAS above Washington’s state action level
Sammamish Plateau Water & Sewer detected PFAS in 8 of its 14 tested water sources, with at least one result above Washington’s state action level (latest test June 2026).
Community water system serving King County · 24,792 connections · about 79,362 people.
At least one individual sample measured at or above a federal MCL value (4 ng/L for PFOA/PFOS; 10 ng/L for PFHxS, PFNA, HFPO-DA). Compliance with the federal standard is judged on running annual averages at the tap — a single source sample at that level is a flag, not a violation.
PFAS results on record for Sammamish Plateau Water & Sewer
| Analyte | Highest result | WA action level | Federal MCL | Detected at source |
|---|---|---|---|---|
| PFHxS Perfluorohexanesulfonic acid | 40 ng/L | 65 ng/L | 10 ng/L | AA374C/Cascade Water Alliance (2), WELL #10, WELL #7, WELL #9, Well #8, Well 1R, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFOS Perfluorooctanesulfonic acid | 37 ng/L above SAL | 15 ng/L | 4 ng/L | AA374C/Cascade Water Alliance (2), WELL #10, WELL #7, WELL #9, Well #8, Well 1R, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFBS Perfluorobutanesulfonic acid | 11 ng/L | 345 ng/L | — | AA374C/Cascade Water Alliance (2), WELL #10, WELL #7, WELL #9, Well #8, Well 1R, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFPeS Perfluoropentanesulfonic acid | 9 ng/L | — | — | WELL #10, WELL #7, Well #8, Well 1R, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFNA Perfluorononanoic acid | 8 ng/L | 9 ng/L | 10 ng/L | WELL #7, Well #8 |
| PFPeA Perfluoropentanoic acid | 6 ng/L | — | — | WELL #7, WELL #9, Well #8, Well 1R, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFHxA Perfluorohexanoic acid | 5 ng/L | — | — | WELL #7, WELL #9, Well #8, Well 1R, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFOA Perfluorooctanoic acid | 5 ng/L | 10 ng/L | 4 ng/L | WELL #7, WELL #9, Well #8, Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
| PFBA Perfluorobutanoic acid | 3 ng/L | — | — | Well 2.2 (2R) AAD383, Wells 2.1 & 2.2 |
What this means
A Washington state action level (SAL) is the concentration at which the state requires a water system to notify its customers and take action — typically treating the affected source, blending it, or taking it offline. PFAS was detected in 8 of the 14 sources tested for this system, and at least one result was above a SAL. Ask the utility what it has done with the affected sources since the sample date — the table above shows which sources were affected.
For PFAS at the drinking tap, the fix we plan to offer is under-sink reverse osmosis — manufacturer test data shows RO membranes reduce PFAS. See the planned systems.
These results describe the water system’s sources (wells, intakes), not any individual tap — utilities blend, treat, and rotate sources. Data: Washington State Department of Health public PFAS results and Drinking Water Service Areas, dataset updated 2026-07-22. Latest test on record for this system: 2026-06-08. Informational only — not a certification of water quality and not health advice. If you have concerns about your drinking water, contact your utility or the WA DOH Office of Drinking Water.
Free · takes ten seconds · no signup
Is this actually your water system?
Service areas overlap and addresses sit on boundaries. Enter your street address in our free checker and we’ll match it to the right system in state records — 1,294 Puget Sound systems tested so far, 302 with detections.