PFAS in California Groundwater: What the GAMA Program's First Samples Found

Sampling groundwater for the GAMA Priority Basin Project. USGS / Elias Tejeda.

What PFAS are

Per- and polyfluoroalkyl substances (PFAS) are a family of more than 4,700 human-made chemicals used for decades in hundreds of products. Many are surfactants: one end mixes with water, the other — carbon bonded to fluorine, the strongest bond in organic chemistry — repels it. That lets PFAS repel oil and water, cut friction and resist breakdown, making them useful in metal plating, carpet, clothing, upholstery, nonstick cookware, food wrappers and firefighting foams — and so persistent that they're called "forever chemicals."

• Sources: PFAS factories and users, landfills, wastewater plants, septic systems, and places where foams were used, such as airports and military fire-training areas.
• Phase-out: PFOA, PFOS and other long-chain PFAS were phased out of U.S. emissions and products under the EPA's PFOA Stewardship program.
• Everywhere: PFAS have been found in soil, rain, surface and groundwater, wildlife, and 97 percent of human blood samples. They're hard to remove from drinking water.
• Health: exposure to some PFAS is linked to higher cholesterol, thyroid disorders, weaker vaccine response and lower birth weight.

California's benchmarks: the State Water Resources Control Board's Division of Drinking Water (SWRCB-DDW) sets levels for three PFAS. Above the notification level, utilities should tell customers; above the response level, the source should be taken out of service.

The program

The Groundwater Ambient Monitoring and Assessment Priority Basin Project (GAMA-PBP), begun in 2004 by USGS and the State Water Resources Control Board, assesses groundwater used for public and domestic supply. In 2019 it added PFAS — 24 long-used compounds, analyzed by SGS Laboratory in Orlando, Florida — and in 2020 four "replacement" PFAS, designed to be less toxic, though whether they are much less harmful isn't known.

First results

From May 2019 to September 2020, GAMA-PBP sampled 107 public-supply and 104 domestic wells statewide.

• Detections: at least one PFAS in 49 of 211 samples (23 percent); totals ranged from 1 to almost 70 ng/L, and 17 of the 49 exceeded 10 ng/L.
• Well type: PFAS were found more often, and generally at higher levels, in public-supply wells (36 percent) than domestic wells (11 percent).
• Compounds: 14 of the 28 PFAS appeared at least once, from 1 to almost 16 ng/L. PFHxS was most common (17 percent of samples); PFOA and PFOS were each in 13 percent, PFBS and PFHxA each in 10 percent.
• Benchmarks: PFOA exceeded its notification level in six samples and PFOS in seven; one public-supply well's PFOA exceeded the response level. PFBS never exceeded its notification level.

Total PFAS concentrations in sampled wells. U.S. Geological Survey.

How often each PFAS was detected, above and below 5 ng/L, in GAMA wells and in the state's own public-supply sampling. U.S. Geological Survey.

PFAS concentrations detected, against California's notification and response levels. U.S. Geological Survey.

Why the state found more

The SWRCB-DDW, sampling more than 1,100 public-supply wells quarterly from April 2019 to March 2020, found PFAS in about half — mostly above 5 ng/L (median about 8.0), against GAMA-PBP's median of about 2.5. The difference is by design: the state targeted "hot spots" near known sources such as landfills and airports, or near earlier detections, while GAMA-PBP spreads its sites to give an unbiased picture. Its early results suggest groundwater from most public and domestic wells in California has no PFAS above this study's detection limits (0.83–4.2 ng/L).

What's next

Sampling continues — re-sampling trend networks and denser sampling of domestic wells. From October 2020 to September 2021, GAMA-PBP planned to sample 130 public-supply and about 120 domestic wells, and by April 2024 to finish all public-supply trend networks, five domestic trend networks and several more domestic areas. Because its wells represent ambient groundwater rather than known contamination, the data show how far PFAS reach into drinking-water supplies, and future work will study what controls them. Data: Kent (2021), a USGS data release; GAMA reports.

GAMA-PBP's PFAS sampling schedule. U.S. Geological Survey.

Sources

Based on Sampling for Per- and Polyfluoroalkyl Substances (PFAS) by the Groundwater Ambient Monitoring and Assessment Priority Basin Project, U.S. Geological Survey Fact Sheet 2021–3028, by Robert Kent, USGS Publications Warehouse; a work of the United States government in the public domain. Supported by the California State Water Resources Control Board. Photograph and figures recovered from the fact sheet's PDF.