--- title: "How to read a PFAS lab report: ppt, PFOA, PFOS and limits" description: "A PFAS lab report lists compounds and results in parts per trillion (ppt, also ng/L). Learn which numbers matter and how they compare to EPA's 4.0 ppt limits." url: https://aes.multisites.ai/blog/how-to-read-a-pfas-lab-report publisher: Advanced Environmental Services phone: +1-314-865-2662 quote: https://aes.multisites.ai/contact --- PFAS: 4 min read, published October 30, 2026 # How to read a PFAS lab report: ppt, PFOA, PFOS and limits A PFAS lab report lists each compound it tested for, such as PFOA and PFOS, with a result in parts per trillion (ppt), also written ng/L. Compare PFOA and PFOS to EPA's 4.0 ppt drinking water limits. EPA decides compliance by a running annual average, so one result alone does not prove a violation. [Request a Quote](https://aes.multisites.ai/contact)[(314) 865-2662](tel:+1-314-865-2662) ![Aircraft hangar with a yellow fire truck and equipment during an AES PFAS project](https://aes.multisites.ai/_astro/pfas-2025-06-24-11.09.00.CKLsY786_1Qvvzs.webp) ![Steel roof structure inside a large aircraft hangar on an AES PFAS job](https://aes.multisites.ai/_astro/pfas-hangar1-20250623_105358.BLl5LH1X_Z2wtFbb.webp) ![Large warehouse floor with AES equipment in the distance](https://aes.multisites.ai/_astro/pfas-warehouse-2025-12-03-11.52.27.BVKPsHAu_sbKVc.webp) ## What is on a PFAS lab report? A PFAS lab report lists the compounds the lab tested for, the result for each one, and the unit. Most reports also show the sample ID, the date and place collected, the method used, and a detection or reporting limit. Read the unit first. Almost every drinking water result is in parts per trillion. Names will look like a code: PFOA, PFOS, PFHxS, PFNA, HFPO-DA, PFBS. These are different PFAS compounds. Our glossary defines [PFAS](https://aes.multisites.ai/glossary/pfas), [PFOA](https://aes.multisites.ai/glossary/pfoa) and [PFOS](https://aes.multisites.ai/glossary/pfos). Start with PFOA and PFOS. They are the two with the tightest federal limit. ## What do ppt and ng/L mean? They are the same unit. ppt is parts per trillion, and EPA’s rule table says it is “also expressed as ng/L,” which is nanograms per liter. The glossary entry on [parts per trillion](https://aes.multisites.ai/glossary/parts-per-trillion-ppt) explains the scale. If your report shows µg/L (micrograms per liter), that is a thousand times bigger. One µg/L equals 1,000 ng/L. Check the unit before you compare anything. ## What numbers should you compare your results to? Compare to EPA’s drinking water limits. These are legally enforceable levels, called Maximum Contaminant Levels (MCLs), for public water systems. The table below shows EPA’s final 2024 limits. The [MCL](https://aes.multisites.ai/glossary/mcl-maximum-contaminant-level) entry explains the term. Compound EPA final limit (MCL) PFOA 4.0 ppt PFOS 4.0 ppt PFHxS 10 ppt PFNA 10 ppt HFPO-DA (GenX) 10 ppt Mixtures of two or more of PFHxS, PFNA, HFPO-DA and PFBS Hazard Index of 1 (no unit) These limits apply to public water systems. A result from a private well or a site sample is not a “violation” in the same sense. Use the table as a yardstick and ask a professional what the result means for you. ## Are those limits still in force as of October 30, 2026? For PFOA and PFOS, EPA’s page says it has proposed to keep them. As of October 30, 2026, EPA describes a proposed rule that would “not change” the 4.0 ppt limits while letting some systems request more time to comply, to 2031. EPA also proposes to rescind the rules for PFHxS, PFNA, HFPO-DA and the Hazard Index mixture. Both proposals are not final. Read our post on the [2031 proposal](https://aes.multisites.ai/blog/epa-pfas-drinking-water-rule-2031-proposal) for the details, and check EPA before you rely on a number. ## What does the Hazard Index line mean? It is a way to add up several PFAS at once. EPA uses a Hazard Index, a unitless number, for mixtures of two or more of PFHxS, PFNA, HFPO-DA and PFBS. A lab report will not print a Hazard Index in most cases. A utility or consultant calculates it from the individual results. If your report lists those four compounds, ask someone to run the calculation. ## Does one result tell you if you are over the limit? No. EPA says “compliance with MCLs is determined by running annual averages at the sampling point.” One sample is a snapshot. A high result means retest and ask questions. A low result in one sample does not clear a source. ## What should you ask the lab or your consultant? Ask these questions when you get the report. 1. Which method did you use, and which compounds does it cover? 2. What is the reporting limit for each compound? Is it below 4 ppt for PFOA and PFOS? 3. Did anything flag a quality problem, such as a blank with PFAS in it? 4. How should I compare these results to EPA’s limits? 5. Do I need a second sample or a site assessment? Our guide to [PFAS testing for property owners](https://aes.multisites.ai/guides/pfas-testing-for-property-owners) shows what to do after a result, and our [PFAS sampling](https://aes.multisites.ai/pfas-sampling) page explains how samples are collected. ## What can a lab report not tell you? It cannot tell you where the PFAS came from, how far it spread, or whether your cleanup is done. A water result is one point in time at one tap or well. Soil and groundwater at a site need a plan for where and how to sample. The result also does not tell you about health effects for your household. For that, see our [health effects of PFAS](https://aes.multisites.ai/health-effects-of-pfas) page and talk to your doctor. If a result is above 4.0 ppt for PFOA or PFOS, three things are reasonable: retest, ask your water utility for its own results, and read EPA’s page on steps to reduce your risk. If the sample came from a property you own or manage and a source is possible, a [PFAS assessment](https://aes.multisites.ai/pfas-assessment) is the next step. ## Next step Advanced Environmental Services offers [PFAS testing](https://aes.multisites.ai/pfas-testing) and [PFAS assessment](https://aes.multisites.ai/pfas-assessment). Call (314) 865-2662 or use the quote form at [/contact](https://aes.multisites.ai/contact) to talk about your testing needs. Our team is available 24/7 for urgent cleanup needs. ## Frequently asked questions ### What does ppt mean on a PFAS lab report? ppt means parts per trillion. EPA's rule table also writes it as ng/L, nanograms per liter. A 4.0 ppt result means four parts of the compound in a trillion parts of water. It is a very small amount, which is why PFAS labs use special methods. ### What is EPA's limit for PFOA and PFOS in drinking water? EPA's 2024 rule sets a limit of 4.0 ppt each for PFOA and PFOS. As of October 30, 2026, EPA has proposed to keep those limits and let some water systems request more time to comply, to 2031. The proposal is not final. ### Does one high result mean my water breaks the rule? Not by itself. EPA's footnote says compliance with the limits is determined by running annual averages at the sampling point. A single high sample is still a reason to retest and to ask your water utility or a professional what to do. ## Terms on this page - [MCL (maximum contaminant level)](https://aes.multisites.ai/glossary/mcl-maximum-contaminant-level) - [Parts per trillion (ppt)](https://aes.multisites.ai/glossary/parts-per-trillion-ppt) - [PFAS](https://aes.multisites.ai/glossary/pfas) - [PFOA](https://aes.multisites.ai/glossary/pfoa) - [PFOS](https://aes.multisites.ai/glossary/pfos) ## Sources 1. [U.S. EPA: Per- and Polyfluoroalkyl Substances (PFAS), final rule table](https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas) 2. [U.S. EPA: Per- and Polyfluoroalkyl Substances (PFAS), averaging](https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas) 3. [U.S. EPA: Per- and Polyfluoroalkyl Substances (PFAS), six regulated PFAS](https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas) 4. [U.S. EPA: Proposed PFOA and PFOS Compliance Extension Rule](https://www.epa.gov/sdwa/proposed-pfoa-and-pfos-compliance-extension-rule) Written by Advanced Environmental Services and checked against the sources above on October 30, 2026. Rules change, so check the linked page before you act. ## Keep reading - [PFAS testing for property owners: when to test, how sampling works and what results meanTest for PFAS if your property sits near an airport, military base, landfill or industrial site, used firefighting foam, or draws from a private well. A site assessment picks sample points, trained staff collect clean samples, and an accredited lab reports results in parts per trillion. AES says most results arrive in two to four weeks.](https://aes.multisites.ai/guides/pfas-testing-for-property-owners) - [EPA keeps PFOA and PFOS limits, proposes a 2031 deadline optionAs of October 30, 2026, EPA's page describes a proposed rule, not a final one. It would keep the PFOA and PFOS limits at 4.0 parts per trillion each and let water systems request two more years, to 2031, to comply. EPA announced it May 18, 2026. The comment period closed July 20, 2026.](https://aes.multisites.ai/blog/epa-pfas-drinking-water-rule-2031-proposal) - [The EPA PFAS drinking water rule explained: limits, deadlines and what is proposedEPA's 2024 rule sets legally enforceable limits for six PFAS in public drinking water, including 4.0 parts per trillion each for PFOA and PFOS. Compliance is due in 2029. As of October 30, 2026, EPA has proposed, but not finalized, an optional extension to 2031 and the removal of four other limits.](https://aes.multisites.ai/guides/pfas-drinking-water-rule-explained) - [Asbestos in older St. Louis homes: where it hides and what to doAsbestos can hide in floor tile, floor adhesive, siding, roof shingles, textured walls, pipe wrap, furnace parts and attic insulation. About 87% of St. Louis city housing units and 68% of St. Louis County units were built before 1980. The only way to know is a lab test from a certified inspector.](https://aes.multisites.ai/guides/asbestos-in-older-st-louis-homes) - [Lead paint in pre-1978 homes: when to test, renovate safely or abateAny home built before 1978 may have lead-based paint. In Missouri, an estimated 60% of homes built 1960 to 1978 do, rising to 90% before 1949. Intact paint is a lower risk. Peeling paint and renovation dust are the problem. Missouri requires licensed lead professionals for abatement and for paint chip sampling.](https://aes.multisites.ai/guides/lead-paint-in-pre-1978-homes) - [Mold after water damage: how to inspect, remediate and verify the fixDry water-damaged areas and items within 24 to 48 hours, because mold needs moisture to grow. If mold already shows, or covers more than 10 square feet, EPA says to treat it as a larger job. Find the water source, contain the area, remove damaged material, dry everything, then confirm the moisture is gone.](https://aes.multisites.ai/guides/mold-after-water-damage) ## Request your custom environmental remediation estimate Contact us for a free environmental remediation or restoration estimate and a personalized solution to your problems. [Request a Quote](https://aes.multisites.ai/contact)[(314) 865-2662](tel:+1-314-865-2662)