Local Water Source and Distribution
The Fairfax County Water Authority supplies water to over 1.1 million residents using surface water sources. This treated water travels through a vast system of pipes reaching homes and businesses across the county. Government monitoring provides system-wide data but does not measure water quality inside any individual residence.
Why Are PFOA and PFOS Measured in Nanograms per Liter?
Nanograms per liter (ng/L) equals parts per trillion (ppt)
PFAS compounds like PFOA and PFOS are quantified at extremely low concentrations, often in nanograms per liter or parts per trillion. Four decimal places indicate measurements as precise as a few thousandths of a nanogram, reflecting the sensitivity needed to detect these substances despite their tiny amounts.
Different PFAS Compounds Have Different Reporting Levels
For example, PFOA and PFOS have reporting levels at 0.004 µg/L (4 ng/L), while others like PFHxS have 0.003 µg/L. These levels determine whether a sample is reported as detected but do not indicate a safety threshold by themselves.
How the UCMR5 Survey Differs From UCMR3
Broader Range of Fluorinated Compounds Tested
The UCMR5 survey conducted from 2023 to 2025 includes a wider array of PFAS types than earlier surveys. This expanded testing helps track additional 'forever chemicals' beyond just PFOA and PFOS.
Lower Detection Limits Enable More Sensitive Measurements
Compared to UCMR3, the current survey uses detection limits as low as 0.003 µg/L for some compounds, enhancing the ability to detect very low concentrations across the water system.
Water Use Considerations for Different Household Types
Large Households Use More Water, Increasing Total PFAS Loading
Larger families consume more water daily, potentially increasing the total amount of PFAS passing through household filtration where used. This may affect how you evaluate treatment capacity for your home.
Seasonal or Second Homes Require Different Monitoring
Infrequently used properties may experience water stagnation, which is unrelated to PFAS concentrations but can affect overall water quality. Testing the water specific to your property is recommended.
Reading Fairfax County's PFAS Data: An Example
PFOA and PFOS Detected Above Reporting Levels but Below Health-Based Violations
In the Fairfax County system, some PFOA results reached as high as 0.0074 µg/L (7.4 ng/L), and PFOS up to 0.0057 µg/L (5.7 ng/L). These measurements are part of a federal occurrence survey and are not recorded as violations or unsafe conditions.
Median Concentrations Reflect Typical Detected Levels
The median concentration among detections was 0.0061 µg/L (6.1 ng/L) for PFOA and 0.0052 µg/L (5.2 ng/L) for PFOS, indicating that several samples showed measurable but low amounts present in the system.
Other PFAS Compounds Also Detected at Various Levels
Compounds such as PFBS, PFHxA, PFPeA, PFBA, and PFHpA were also detected occasionally at low concentrations, while PFHxS, PFNA, and HFPO-DA were not detected above reporting levels.
Regional Sources of PFAS in Fairfax County Water
Common PFAS Origins Include Firefighting Foam
Firefighting foam has historically been a source of per- and polyfluoroalkyl substances in many regions, including Fairfax County, as documented by federal monitoring.
Industrial Activities Like Textile and Chemical Finishing
Local industrial activities can contribute fluorinated compounds to the environment, detected at low levels in the county's water supply.
Landfill Leachate May Also Introduce PFAS
Landfill sites in or near the area can leach trace amounts of PFAS into groundwater or surface waters feeding the county's water system.
A Documented Approach to Managing PFAS in the Home
To address PFAS present at low levels throughout the county’s water system, the C-Series PFAS Forever Chemicals Filter ships ready to configure for household use. This system is designed to reduce multiple fluorinated compounds effectively, helping homeowners manage water quality according to their specific water use and concern levels.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2025-02-13. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR5 monitoring (2023-2025) for FAIRFAX COUNTY WATER AUTHORITY (VA6059501), VA: 240 results across 10 listed contaminants, 36 detections above the reporting level; 5 results above a 2024 federal MCL