PFAS Information

Keeping Your Water Safe


All water supplied to our customers meets the regulatory standards set by the state and federal governments and, in almost all cases, the quality was significantly better than required. We are committed to delivering a safe and reliable water supply to our customers. Zone 7 continues to deliver all water below the California Division of Drinking Water’s response levels for PFOA and PFOS.

Know the Facts – PFAS 101

What are PFAS?

PFAS (Per- and Polyfluoroalkyl Substances) are a large group of synthetic chemicals designed to resist heat, water and oil. PFAS are used in a wide range of industrial and consumer products such as fire-fighting foams, stain- and water-resistant clothing, carpets, cleaning products, non-stick cookware and food packaging.

PFAS have been found in air, soil and water around the world, and are persistent in the environment. They can accumulate in the human body over time, and are toxic at relatively low concentrations. Scientific studies have shown that exposure to some PFAS in the environment may be linked to harmful health effects in humans and animals. Although certain PFAS are no longer manufactured in the U.S., these chemicals are still produced internationally and imported into the U.S. in consumer goods.

How do PFAS get into the drinking water?

Since PFAS are used in array of industrial and consumer products, there could be many sources of contamination in water supplies. Common sources of PFAS include industrial facilities where PFAS are manufactured or used, wastewater, landfills and areas where fire-fighting foam was used. There are areas across the nation where PFAS have seeped into groundwater, lakes and rivers. These chemicals travel easily through the ground and may make their way into groundwater basins that supply drinking water.

How are PFAS removed from water?

There are several available treatment technologies with demonstrated effectiveness in removing PFAS from drinking water. These include:

  • ion exchange treatment 
  • granular activated carbon filters
  • high-pressure membranes such as
    • nanofiltration 
    • reverse osmosis (RO) filtration

In addition, point-of-use water filters with similar technologies are available on the market for purchase by consumers directly.

What is Zone 7 doing about PFAS?

Zone 7 has been actively monitoring for PFAS since late 2018.  No PFAS has been detected above any Consumer Confidence Report Detection Level (CCRDL) in its treated surface water which made up the majority of the total water delivered to its customers. Although PFAS have been detected in some Zone 7 groundwater wells, these wells are either below the response levels or are treated to levels below the response levels prior to entry into the distribution system. Typically, Zone 7 supplies approximately 60-80% treated surface water and 20-40% groundwater per year. The ratio of surface water to groundwater varies depending upon the season, hydrologic conditions and customer’s location in the Tri-Valley.  

Zone 7 recently installed Ion Exchange (IX) PFAS Removal Treatment at the Stoneridge Well, one of two well sites where PFAS was detected above the State Water Resources Control Board’s drinking water response levels that did not have existing treatment options. The second site at Chain of Lakes will also have IX treatment installed; construction on the Chain of Lakes facility is currently underway and expected to be complete in summer of 2024. 

How does Ion Exchange (IX) PFAS Removal Treatment work?

The new tanks at Stoneridge Well are filled with small IX resins designed to attract the type of PFAS detected in the local groundwater basin. The PFAS are removed from the water as they stay attached to the resins, allowing delivery of clean, safe water for homes and businesses.

What are the regulatory limits for PFAS?

Over the past several years, the science on PFAS and its impacts to the environment and public health have prompted regulatory actions.  In March 2023, the U.S. Environmental Protection Agency (EPA) released its proposed PFAS regulations which includes maximum contaminant levels (MCLs) for six PFAS.  The proposed MCL for PFOA and PFOS is at 4 parts per trillion (ppt) for each compound due to its carcinogenic health effects. The proposed MCL for a mixture of 4 PFAS (PFHxS, GenX chemicals, PFNA, and PFBS) is a Hazard Index at 1.0 due to their toxicological endpoints.  The Hazard Index is calculated as the sum of the four individual health-based water concentrations.  EPA anticipates finalizing the regulations by the end of 2023.  Once the rule is finalized, water systems would have three years to be in compliance with the MCLs. 

Setting limits for PFAS is also a high priority for California.  The State has already issued drinking water notification and response levels for four PFAS so far and is evaluating other PFAS found throughout the state.  Notification and response levels are nonregulatory-health based advisory levels established by the State for contaminants in drinking water for which MCLs have not been established. When a contaminant is found at concentrations greater than its advisory level, certain notification requirements and recommendations apply.  In addition, the State is currently developing Public Health Goals (PHGs) for PFOA and PFOS, which is the first step in establishing MCLs for these PFAS. 

Notification level represents the concentration level of a contaminant in drinking water that does not pose a significant health risk but warrants notification.

Response level represents the concentration level of a contaminant in drinking water at which water systems should take additional actions such as taking a water source out of service or provide treatment.

Zone 7’s Commitment to Transparency:

At Zone 7, transparency is one of our core values. Zone 7 has posted all sampling data, reports and presentations to the Board on its website where the public can access it anytime. We have also included this data in our annual Consumer Confidence Reports. In addition to that, we have a PFAS Information Sheet and Quarterly Monitoring Update that are regularly updated to help our customers better understand this issue. We have also compiled local, state and federal resources for our consumers to easily access. All of this information can be found in the links below. Should you have any additional questions, please send a message to our Water Quality Team.

Zone 7 PFAS Reports & Presentations:

Local retailer PFAS Information:

additional State and Federal resources on PFAS:

Have additional questions about Water Quality? Send us a message!