PFAS

Environmental and human exposure to PFAS is highest where it is manufactured and used. There are comparatively few industrial sources in California, and most of the highly contaminated sites in the state have been confined to airports, military installations, and other locations where firefighting foam was in high use historically. While households and businesses contribute to the presence of PFAS found in the air, soil, and water due to the wide variety of applications in packaging and consumer care products, the amount of PFAS being released to the environment continues to decline as products containing PFAS are phased out.

Due to their long-term and widespread use and persistence in the environment, most people in the United States have been exposed to PFAS. There is growing evidence that long-term exposure above specific levels to certain PFAS can lead to cancer and adverse health effects to fetuses during pregnancy or breastfed infants, the liver, immune system, and thyroid.

According to the U.S. Environmental Protection Agency (U.S. EPA): “Current scientific research suggests that exposure to certain PFAS may lead to adverse health outcomes. However, research is still ongoing to determine how different levels of exposure to different PFAS can lead to a variety of health effects. Research is also underway to better understand the health effects associated with low levels of exposure to PFAS over long periods of time, especially in children.”

Learn More

People are exposed to PFAS by working in occupations such as chemical manufacturing and processing and firefighting; eating food contaminated from cookware, packaging, or containing PFAS due to bioaccumulation (e.g., fish, meat, eggs, and leafy vegetables); drinking water contaminated by PFAS; and using, touching, or breathing products treated with PFAS (e.g., carpets, upholstery, cosmetics, and clothing). PFAS have also been found in soil, household dust, and numerous other recurring routes of exposure as well.

Federal Environmental Protection Agency (EPA) Efforts

In 2024, the U.S. EPA issued national Maximum Contaminant Limits (MCL) for six PFAS chemicals. Public water systems were required to complete initial monitoring for PFAS by 2027. Beginning in 2029, public water systems where PFAS has been detected in drinking water above one or more of these MCLs are required to take action to reduce levels of PFAS and provide notification to the public. However, in May 2025 EPA announced that they intend keep the regulations for PFOA and PFOA, but "rescind" the regulations for four compounds (PFHxS, PFNA, HFPO-DA and PFBS), and extend the deadline for compliance to 2031.

Federal Regulatory Enforceable Levels for PFAS in Drinking Water Sources (nanogram per liter or parts per trillion [ppt])

State of California Division of Drinking Water (DDW) Efforts

The State of California also has adopted advisory levels for four PFAS chemicals – a notification level as well as a response level. Notification level represents the concentration level of a contaminant in drinking water that 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 providing treatment.

Other state-level actions have been taken on PFAS. For example, California has banned the use of PFAS in food packaging and infant and children’s products.

State Regulatory Advisory Levels for PFAS in Drinking Water Sources (nanogram per liter or parts per trillion [ppt])

The federal MCLs and California advisory levels are set at parts per trillion (PPT) ranging from 3 to 5,000, depending on the specific PFAS chemical. Sometimes this measurement of concentration is also expressed as nanograms per liter. For reference, one part per trillion is equivalent to one drop of water in 20 Olympic-sized swimming pools.

According to national water management experts, the most significant action needed to eliminate the presence of PFAS in the environment, animals, and humans is to remove these chemicals from the stream of commerce. Some manufacturers and consumer products companies have begun phasing out the use of PFAS and developing alternatives. Dublin San Ramon Services District (DSRSD) is actively advocating for the removal of PFAS from industrial and consumer products at the state and federal level.

PFAS has been detected in municipal drinking water wells in the Tri-Valley. Zone 7 Water Agency, the Tri-Valley’s water supply wholesaler, has mapped a known area of PFAS (referred to as the “footprint”) in the main groundwater basin where some drinking water wells are located. It’s important to note that the majority of drinking water in the Tri-Valley is imported surface water from major California rivers and the Delta.

More information about the presence of PFAS is available in DSRSD’s Water Quality Report.

Ongoing monitoring is being conducted to further understand the presence and movement of PFAS in the groundwater basin, as well as sources that may be contributing PFAS to groundwater. Where PFAS has been detected over the state’s notification level, notifications have been made to the public.

Zone 7 Water Agency – which supplies drinking water to DSRSD – continues to operate its water supply systems to ensure the water supply from PFAS-affected groundwater wells remains below the response levels.  In 2023, Zone 7 opened its first PFAS treatment facility using ion exchange at its Stoneridge Well property in Pleasanton, which was followed by a second PFAS treatment facility at its Chain of Lakes location in 2025. Currently, Zone 7 is in the planning phase for a third PFAS treatment facility at its Mocho Wellfield location, scheduled for completion by 2028. 

These facilities effectively treat water from impacted wells to below any response level for PFAS. Zone 7 has proactively removed drinking water wells from service where PFAS has been detected at the state’s response level, and PFAS treatment has not yet been installed. 

Learn More

Wastewater treatment facilities are not “producers” or users of PFAS and do not utilize PFAS chemicals. Rather, they are “receivers” of PFAS because they receive wastewater from residential and commercial sources containing PFAS. 

Traditional wastewater treatment operations do not eliminate PFAS. Monitoring at DSRSD’s wastewater treatment plant has detected PFAS in incoming water (influent), outgoing water (effluent), and solids that are separated from water during treatment (biosolids). 

A study was conducted to determine if the PFAS detected at the wastewater treatment site were migrating off-site or contributing to the PFAS footprint in the main groundwater basin in the Tri-Valley. Operations that were evaluated were lagoon operations - where biosolids are initially deposited for decomposition - and the underground injection of these decomposed solids for long-term disposal. Treated wastewater effluent was not evaluated, since it is piped directly to San Francisco Bay. 

The study concluded that the wastewater treatment site is not contributing in any significant way to downstream surface water or downgradient groundwater PFAS concentrations. The study also found minimal, if any, potential for future impacts to water sources in the Livermore Valley Groundwater Basin. The occurrence of PFAS detected in monitoring wells at the site is contained in a very small and shallow area and almost exclusively in a low-permeability clay layer that exists between the surface and the underlying upper aquifer (referred to as Aquiclude). This clay layer is approximately 40-50 feet thick beneath the lagoons and disposal site and acts as a natural barrier to restrict vertical and horizontal migration of constituents of concern, including PFAS, to off-site locations. This clay layer is up to 70 feet thick beyond the site boundaries. The estimated travel times for constituents of concern in shallow groundwater at the disposal site to the nearest surface water or aquifer locations down-gradient of the site are multiple decades or even centuries long. 

The study also looked at whether recycled water used to water landscapes could be contributing to PFAS in the groundwater basin. The study concluded that there is only minor overlap between areas irrigated with recycled water and the detected PFAS footprint that has been mapped in the Main Basin, which indicates a lack of any contribution of PFAS from recycled water. 

Why did the Dublin San Ramon Services District (DSRSD) commission a technical study of its wastewater treatment plant operations?

In recent years, there has been increased national attention on a group of man-made chemicals referred to as Perfluoroalkyl and Polyfluoroalkyl substances (PFAS), which can be detected in the air, land, and water. PFAS exposure has been linked to a number of health problems. PFAS are among the many chemicals received at wastewater treatment plants each day from residential, commercial, and industrial customers (wastewater treatment plants are referred to as “passive receivers” of these substances). Traditional wastewater treatment methods do not create or eliminate PFAS, but PFAS have been detected in the water discharged from wastewater treatment plants.

For this reason, DSRSD sought to understand the potential for its wastewater treatment plant operations (including treated water discharges, biosolids and recycled water applications) to contribute to the presence of PFAS detected in the main groundwater basin (Main Basin) of the Livermore Valley Groundwater Basin. The technical study, performed by Luhdorff & Scalmanini Consulting Engineers (LSCE) in 2023 and 2024, adds to previous studies conducted by other agencies to detect the presence of PFAS in drinking water, groundwater, and wastewater in the Tri-Valley.

Where is DSRSD’s wastewater treatment plant located and what does it include?

DSRSD provides wastewater treatment service for approximately 165,000 residents of Dublin, Pleasanton, and the southern portion of San Ramon. Located in Pleasanton near the southeast corner of the intersection of I-680 and I-580, DSRSD’s wastewater treatment plant processes wastewater in accordance with regulatory standards before it is discharged via pipe to San Francisco Bay. This plant also processes biosolids and houses a separate treatment facility that further treats wastewater to produce recycled water used for landscape irrigation.

The wastewater treatment plant is located on two different sites. The main wastewater treatment plant is approximately 20 acres and houses all liquid and recycled water treatment. Located to the north, the second treatment site encompasses 100 total acres where solids that are byproducts of the wastewater treatment plant process are deposited into six lagoons whose total surface area of water covers 27 acres. After four to five years in the lagoons, the solids become biosolids, which are removed and injected 8 to 12 inches beneath ground level for final disposal at a 55-acre dedicated biosolids land disposal site.

What were the objectives of this study?

The study’s objective was to analyze the potential for PFAS detected at the second treatment site to migrate southeast toward the Main Basin lower aquifer (from which drinking water supplies are pumped in the TriValley) and to migrate towards nearby surface water channels. The study also evaluated the relationship between the landscape application of recycled water produced by DSRSD and the known “footprint” of PFAS detected in the Main Basin to determine whether recycled water could be a contributor of PFAS to groundwater.

What area was studied?

In addition to DSRSD’s wastewater treatment plant site, the total study area is approximately 5,940 acres, primarily within the “North Fringe Management Area” of the Livermore Valley Groundwater Basin. The North Fringe Management Area is of interest to DSRSD due to the location of DSRSD facilities in this area and the use of recycled water provided by DSRSD for landscape irrigation in this area. The approximate boundaries of the study area are the basin boundaries in the west and northeast, the county line in the north, Tassajara Creek in the east, and Arroyo Mocho in the south. Relative to the area of the Main Basin where PFAS have been detected, the North Fringe Management Area is located to the northwest and has different geological and groundwater characteristics than the Main Basin in terms of thickness, groundwater flow, and water quality.

What methodology was utilized in conducting this study?

A hydrogeologic conceptual model of the study area was developed to help determine historical groundwater elevation, flow rates, and direction (vertically and horizontally), as well as areas of recharge/discharge and interactions with surface water. Prior assessments and studies of the basin geology were utilized to develop this model. In addition, the study authors drew samples from water quality monitoring wells and surface water on-site and near the wastewater treatment plant, as well as the biosolids lagoons and dedicated land disposal area that make up DSRSD’s second treatment site. Prior groundwater models and pond infiltration studies of the biosolids lagoons were also reviewed. The authors performed analytical calculations and numerical modeling to determine migration rates within these underground layers.

To determine any contribution from landscape application of recycled water, the authors evaluated the areas of application compared to the known PFAS footprint in the Main Basin.

What are the findings of this study?

Available data and hydrogeologic conditions show DSRSD’s wastewater treatment site is not contributing in any significant way to downstream surface water or downgradient groundwater PFAS concentrations. The study also identified minimal potential for future impacts to municipal water sources in the Livermore Valley Groundwater Basin. The occurrence of PFAS detected in monitoring wells at the wastewater treatment site is limited to a very small and shallow area and contained almost exclusively in a low-permeability thick clay layer that exists between the surface and the underlying upper aquifer. This clay layer is approximately 40-50 feet thick beneath the second treatment site and acts as a natural barrier to restrict vertical and horizontal migration of constituents of concern, including PFAS, to off-site locations. Beyond the site boundaries, this clay layer is up to 70 feet thick. The estimated travel times for chemicals or substances of concern moving from shallow groundwater at the site to the nearest surface water or aquifer locations down-gradient of the site are multiple decades or even centuries long.

The study also concluded that there is only minor overlap between areas irrigated with recycled water and the detected PFAS footprint that has been mapped in the Main Basin, which indicates a lack of contribution of PFAS from recycled water.

More Information

For more information on this study, contact Kristy Fournier Laboratory and Environmental Compliance Manager at (925) 875-2322 or fournier@dsrsd.com.