If Your Lab Report Lists Multiple PFAS Compounds, Here's What the Hazard Index Means
Laboratory analyses often report concentrations of individual PFAS—per- and polyfluoroalkyl substances—in nanograms per litre (ng/L), also known as parts per trillion. To assess potential combined effects, agencies have developed hazard indexes that consider mixtures of these fluorinated compounds rather than treating each in isolation. Although this index helps summarize exposure, it is not a direct health assessment but a metric to guide further evaluation and decisions.
If You See PFOA or PFOS Concentrations in Nanograms per Litre With Four Decimal Places, Here’s Why
The substances PFOA and PFOS are commonly monitored forever chemicals due to their persistence in the environment. Measurements at four decimal places (for example, 0.0040 ng/L) indicate highly sensitive laboratory methods capable of detecting extremely low concentrations. These low-level detections provide detailed information but do not alone determine water safety or regulatory compliance because the federal maximum contaminant levels (MCLs) set for 2024 are higher, at 4.0 ng/L for both compounds in Rapid City’s water system.
If You Wonder How the Current UCMR5 Survey Differs from UCMR3 in PFAS Monitoring
The Unregulated Contaminant Monitoring Rule (UCMR) programs are periodic surveys conducted by the EPA to gather data on contaminants like PFAS in public water systems. UCMR5 (2023–2025) differs from UCMR3 mainly in the suite of PFAS compounds tested and the sensitivity levels of detection. UCMR5 covers a broader range of substances, including PFHxS and HFPO-DA, and reports results down to parts per trillion levels. These improvements provide a more comprehensive profile of fluorinated compounds in Rapid City’s surface water supply.
If You Plan to Ask About Treatment Options, Note These Details First
Before seeking any treatment advice, it is important to document the demand of your household water use and have a professional laboratory analysis of your own tap water to understand individual conditions. Since government data represent system-wide samples, your home's water profile might differ. Key information includes the volume of water your household uses daily and the specific PFAS concentrations measured in your water. This information will assist in identifying an appropriate solution tailored to your needs.
If You Are Considering How to Proceed with Testing and Evaluation, Follow This Order from Least to Most Intensive
- Review publicly available data for your water system, such as the EPA UCMR5 reports for Pennington County.
- Check for visual or taste-related water quality changes that might prompt further investigation.
- Obtain a certified laboratory test of your household water for a complete PFAS panel that includes compounds listed in the UCMR5.
- Measure your household water demand to ensure any treatment system matches your usage.
If You Want to Know Which Fluorinated Compounds in Rapid City's Water Have Federal Limits as of 2024
Federal MCLs effective in 2024 apply to some but not all of the per- and polyfluoroalkyl substances detected in Rapid City's water system. Specifically, PFOA and PFOS each have a limit of 4.0 ng/L (4.0 parts per trillion). PFHxS, PFNA, and HFPO-DA have MCLs set at 10 ng/L. Other compounds, such as PFBS, PFHxA, PFPeA, PFBA, and PFHpA, currently have no federal MCLs but are monitored under federal surveys to gather data for future regulatory considerations.
Choosing a Solution That Matches Your Household’s Demand After Testing
Once you have your water demand figures and laboratory results for PFAS, the C-Series PFAS Forever Chemicals Filter offers a documented technology designed to address a broad spectrum of these fluorinated compounds effectively. The system ships ready to configure, allowing for personalized setup to meet your household’s specific treatment requirements.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2025-09-03. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR5 monitoring (2023-2025) for RAPID CITY (SD4600406), SD: 200 results across 10 listed contaminants, 2 detections above the reporting level; compared with the applicable federal MCL, none above