PFAS in St. Mary'S County: Understanding Local Data and Your Water Treatment Options

When concerns about PFAS arise, it's important to understand what publicly available data can and cannot tell you about your water. In St. Mary'S County, the information collected and published by federal agencies pertains to public water systems, representing the water before it reaches your home and not your specific household plumbing or well. This distinction is critical if your current water treatment setup is not fully meeting your needs.

Why PFOA and PFOS Are Measured in Nanograms per Liter with Four Decimal Places

PFAS compounds such as PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid) are monitored in extremely low concentrations, reported in nanograms per liter (ng/L), which equals parts per trillion (ppt). Measuring to four decimal places means detecting minute traces that are far below visual or taste detection. These levels reflect advanced laboratory sensitivity, not a direct indication of harm or safety at those values.

Which Fluorinated Compounds Have Federal Maximum Contaminant Levels (MCLs) as of 2024?

In 2024, federal standards have established MCLs for several PFAS compounds including PFOA and PFOS at 4.0 ng/L, PFHxS and PFNA at 10 ng/L, and HFPO-DA (also known as GenX chemicals) at 10 ng/L. Other related compounds like PFBS, PFHxA, PFPeA, PFBA, and PFHpA do not currently have federal MCLs but are still subject to monitoring for research and future regulatory consideration.

How Public Water System Records Differ from Private Well Testing in What They Establish

Public water system data covers water drawn from shared sources, treated and distributed to multiple households in areas like St. Mary'S County. These records provide a system-wide snapshot, not a direct measurement of individual water taps. For private wells or household-specific concerns, testing your own water through certified laboratories is necessary to ascertain exact contaminant levels and treatment needs.

A Worked Example: Interpreting Median and Range in the Water System Record

The Patuxent Naval Air Station public water system in St. Mary'S County shows zero detections above reporting levels for all tested PFAS compounds in recent federal surveys. This means that among 26 sampling results for each contaminant, none measured concentrations above detection thresholds such as 0.004 µg/L (4.0 ng/L) for PFOA and PFOS. Thus, public data for this system reflects PFAS levels below both detection and regulatory limits but does not confirm individual home water quality.

The Order in Which to Rule Things Out: From Cheapest Check to Laboratory Test

• Review local public water system reports for broad area information.
• Assess your current treatment system’s capacity and age, since older units may underperform.
• Consider simple household water quality indicators like taste or staining (which can suggest other issues, not PFAS).
• Arrange for targeted laboratory testing of your home's water supply to quantify actual PFAS levels and other contaminants.

The Hazard Index for Mixtures of Newer Compounds, Explained Without a Health Claim

Some studies examine combined exposure to multiple PFAS compounds to understand possible cumulative effects, called a hazard index. While the presence of multiple substances is noted, no health claim or safety conclusion is drawn here. This index guides research and regulatory review rather than individual household risk assessment.

What the Reader Should NOT Conclude from Area Data

The absence of PFAS detections above reporting levels in the public water system serving St. Mary'S County does not guarantee that your home’s water is free from these compounds or that existing treatment equipment will fully meet emerging challenges from 'forever chemicals.' Confirming your water’s condition requires specific testing, and upgrading to specialized filters designed for PFAS reduction, such as the Fleck PFAS Forever Chemicals Filter, which ships ready to configure, can support households facing persistent contamination.

Where this information comes from

Source: EPA SDWIS public water system record. Sampled 2025-09-16. These figures describe the public water system's record, not the plumbing inside any individual building.

On record: EPA UCMR5 monitoring (2023-2025) for PATUXENT NAVAL AIR STATION (NAVFAC-WASH) (MD0180022), MD: 260 results across 10 listed contaminants, 0 detections above the reporting level; nothing detected above the method reporting level