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.

Zone 7 Response to April 2024 PFAS Regulations from EPA

On April 10, 2024, the U.S. Environmental Protection Agency (EPA) announced final maximum contaminant levels (MCLs) for six PFAS substances. The new regulations require mandatory reporting in the EPA required annual Consumer Confidence Report or Water Quality Report beginning in 2027, which Zone 7 has been doing voluntarily since 2019. These new regulations provide water systems five years to comply with the new regulations.

Though we do not have to meet these MCLs for five years, because of Zone 7’s commitment to delivering a safe and reliable water supply to our customers, we have voluntarily made changes to our operations to meet the MCLs now.

Actions taken include:

  • We have reduced the production of our Mocho wellfield by nearly two-thirds.
  • We have increased our use of surface water.
  • We are starting a conceptual design for a Mocho PFAS treatment facility with the goal of having the facility online in two to three years, which will be our third PFAS treatment facility.
  • We have installed Ion Exchange PFAS Treatment at the Stoneridge Well facility which is online now.
  • We are currently installing Ion Exchange PFAS Treatment at the Chain of Lakes Facility which will be online by the end of this year.

In the meantime, because of our reduced ability to produce groundwater and the constant possibility of dry years reducing the availability of surface water, we encourage our community to continue to use water efficiently.

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?

On April 10, US EPA announced the final National Primary Drinking Water Regulation (NPDWR) for six PFAS, including individual Maximum Contaminant Levels (MCLs) for PFOA and PFOS at 4 parts per trillion (ppt), individual MCLs for PFHxS, PFNA, and GenX Chemicals at 10 ppt, and an MCL for a mixture of 4 PFAS (PFHxS, PFNA, GenX Chemicals, and PFBS) at no greater than a Hazard Index of 1.0 (see summary below).  EPA also finalized health-based, non-enforceable Maximum Contaminant Level Goals (MCLGs) for these PFAS.  Public water systems must monitor for these PFAS and have three years to complete initial monitoring (by 2027), followed by ongoing compliance monitoring.  Public water systems will have five years (by 2029) to implement solutions that reduce these PFAS if monitoring shows that drinking water levels exceed these MCLs.  Primary agencies such as the State of California will have up to two years to adopt standards that are no less stringent than the federal standards.

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.  

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!