PFAS Compliance Workflow

LimnaFlow maintains the complete set of federal PFAS standards: EPA MCLs for PFOA (4 ppt) and PFOS (4 ppt), MCLs for PFHxS, PFNA, and HFPO-DA (GenX), and the Hazard Index MCL for PFAS mixtures. These are updated as EPA finalizes or revises values. State PFAS standards are maintained for every state that has adopted independent PFAS limits, including states like Michigan, New Jersey, New Hampshire, Vermont, Massachusetts, and California that regulate additional PFAS compounds or have adopted more stringent limits than the federal MCLs.

Because PFAS regulation is evolving rapidly — new compounds are being regulated, existing limits are being revised, and states are adopting standards on independent timelines — the PFAS standard set is updated more frequently than conventional standards. When any PFAS standard changes, users with active PFAS projects receive in-app notification with specifics on which compounds and jurisdictions are affected.

The EPA PFAS MCL rule includes a Hazard Index (HI) approach for PFAS mixtures. The HI is calculated as the sum of individual PFAS concentrations divided by their respective Health-Based Water Concentrations (HBWCs) for the four HI-regulated compounds: PFHxS, PFNA, HFPO-DA, and PFBS. When the HI exceeds 1.0, the sample exceeds the MCL for PFAS mixtures.

LimnaFlow automatically calculates the PFAS Hazard Index for every sample that includes one or more of the four HI compounds. The output shows the total HI value, flags whether it exceeds 1.0, and breaks down the contribution of each compound — so you can immediately see which PFAS is driving the exceedance. This calculation is straightforward in concept but error-prone in Excel, especially when dealing with non-detects (which must be handled per EPA guidance) and when multiple samples across multiple locations each require their own HI calculation.

PFAS are regulated at parts-per-trillion (ppt) concentrations — nanograms per liter (ng/L). This is three orders of magnitude lower than the parts-per-billion (ppb or ug/L) units used for most conventional contaminants. Incorrect unit conversion between ppt and ppb is one of the most common PFAS screening errors.

LimnaFlow displays PFAS results in ng/L (ppt) by default and handles all unit conversions automatically. If a lab reports in ug/L (which some do for higher-concentration PFAS results), the system converts correctly before comparing against the ppt-level MCLs. Detection limits at the ppt level are tracked and evaluated — when a non-detect reporting limit exceeds the 4 ppt MCL for PFOA or PFOS, the detection limit inadequacy is flagged just as it would be for any conventional parameter.

Different EPA analytical methods detect different suites of PFAS compounds. EPA Method 537.1 covers 29 PFAS compounds and is the most commonly used drinking water method. EPA Method 533 covers 25 PFAS including short-chain compounds that 537.1 misses. EPA Method 1633 covers 40+ PFAS across multiple matrices (water, soil, sediment, biosolids) and is the emerging standard for site assessment work.

LimnaFlow recognizes which analytical method was used — from the EDD metadata or user input — and groups PFAS results accordingly. The system shows which PFAS compounds your analytical method covers and which it does not, so you can identify gaps in your analytical program. If your project requires screening against all EPA-regulated PFAS but your lab only ran Method 537.1, the system flags the compounds that are not covered by your analytical results.

Several states use total measurable PFAS concentration as a regulatory threshold rather than individual compound limits. LimnaFlow calculates total PFAS per sample — the sum of all detected PFAS concentrations — for states that require it. The calculation handles non-detects according to the applicable state's protocol (some states count non-detects as zero, others as half the detection limit).

The PFAS Regulatory Tracker is an in-app reference showing the current state of PFAS regulation across all jurisdictions: which states have adopted PFAS MCLs, what compounds are covered, what the numeric values are, effective dates, and whether limits are proposed or final. The tracker is updated as regulations change and serves as a quick reference when you are setting up a new PFAS project and need to know what standards apply. It replaces the need to independently research each state's PFAS regulatory status — information that changes frequently and is scattered across dozens of state agency websites.