PFAS in Drinking Water

Keeping your water safe from PFAS
What are PFAS and how are they regulated? 

Per- and Poly-Fluoroalkyl Substances (PFAS) are a class of chemicals not found naturally in the environment that include PFOS (Perfluorooctanesulfonic acid) and PFOA (Perfluorooctanoic acid). Neither Washington State nor the U.S. Environmental Protection Agency (USEPA) have established enforceable drinking water standards for PFAS. The EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) to collect data for substances that may be present in drinking water but do not yet have health standards set under the Safe Drinking Water Act (SDWA).

Here’s what we know. 

In 2016, minute amounts of PFOS were detected in three of our wells in the Lower Issaquah Valley Aquifer (LIVA). The level of PFOS detected was 19 parts per trillion (ppt), which was far below the USEPA’s health advisory level of 70 ppt. The PFAS found are attributed to the use of firefighting foam and the plume originating within the City of Issaquah. Only the Plateau Zone is affected, not the Cascade View Zone.

How we're proactively protecting your water. 

With the help of expert consultants, the District conducted extensive research and developed a three-dimensional groundwater model to assess how PFAS travels through the water underground. Based on what we learned from the groundwater model, we changed our point of withdrawal to a well that is furthest from the potential plume migration. Shifting water production, while blending groundwater from our wells with water from the Seattle Public Utilities’ south regional water connection is keeping PFAS in water far below the USEPA’s health advisory level.

The District continues to follow our interim Monitoring and Response Plan for Perfluorinated Compounds that contains recommendations on reducing the likelihood of future increases in PFAS levels, and options to protect your water if PFAS concentrations do increase. This includes maintaining a vigorous water testing and analysis protocol that exceeds state and federal requirements.

In addition, the District is evaluating the work from consultants who completed an in-depth PFAS treatment analysis. The analysis included evaluating potential PFAS treatment options, site-specific treatment feasibility, and costs associated with treatment versus the long-term purchase of regional water for continued blending to levels below the USEPA’s health advisory level.

As stewards of your water supply, staff members are also regularly monitoring State and Federal regulatory proposals in order to stay on top of the latest developments related to PFAS and drinking water.