This page summarizes EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR 5, 2023–2025) drinking-water monitoring records linked to ZIP codes in Montana, as processed for the PFAS Estimator national dataset. Data updated: July 2026.
| Compound | Applicable threshold | ZIP codes detected | At/above threshold | Mean detected | Maximum detected |
|---|---|---|---|---|---|
| PFOS | 0.004 µg/L (MCL) | 4 (10.5% of state) | 4 (100.0%) — all detections at/above limit by construction | 0.006 µg/L | 0.0066 µg/L |
| PFHxS | 0.01 µg/L (MCL) | 3 (7.9% of state) | 0 (0.0% of detected) | 0.005 µg/L | 0.005 µg/L |
| PFBS | 2.0 µg/L (HI reference) | 2 (5.3% of state) | not calculated¹ | 0.0031 µg/L | 0.0031 µg/L |
| Lithium | 7.36 µg/L (reference, not a regulatory limit) | 32 (84.2% of state) | 32 (100.0%) at/above reference | 44.1375 µg/L | 85.0 µg/L |
| PFBA | — (no federal limit) | 1 (2.6% of state) | — | 0.007 µg/L | 0.007 µg/L |
38 ZIP codes with at least one recorded PFAS detection. Click a ZIP code to view its full compound-level results.
| ZIP code | Compounds detected | At/above threshold |
|---|---|---|
| 59034 | 1 | No |
| 59044 | 1 | No |
| 59047 | 1 | No |
| 59101 | 1 | No |
| 59102 | 1 | No |
| 59103 | 1 | No |
| 59104 | 1 | No |
| 59105 | 1 | No |
| 59106 | 1 | No |
| 59270 | 1 | No |
| 59301 | 1 | No |
| 59330 | 1 | No |
| 59401 | 1 | No |
| 59403 | 1 | No |
| 59404 | 1 | No |
| 59405 | 2 | No |
| 59436 | 1 | No |
| 59474 | 1 | No |
| 59501 | 1 | No |
| 59601 | 1 | No |
| 59602 | 1 | No |
| 59716 | 1 | No |
| 59725 | 1 | No |
| 59758 | 1 | No |
| 59801 | 1 | No |
| 59802 | 1 | No |
| 59803 | 1 | No |
| 59806 | 1 | No |
| 59807 | 1 | No |
| 59808 | 1 | No |
| 59812 | 1 | No |
| 59840 | 1 | No |
| 59841 | 1 | No |
| 59901 | 2 | Yes (1) |
| 59903 | 2 | Yes (1) |
| 59904 | 2 | Yes (1) |
| 59911 | 1 | No |
| 59937 | 1 | Yes (1) |
Results are based on EPA UCMR 5 monitoring data (2023–2025), linked to ZIP codes via Public Water System Identifier. Non-detections are not present in this analytic dataset. For each compound and ZIP code, the highest observed concentration across the monitoring period is retained; this characterizes the upper bound of observed drinking-water concentrations, not a long-term average or an individual exposure estimate. A single water system may serve multiple ZIP codes, so the same monitoring record can appear for more than one ZIP in this table. ZIP-code assignment reflects water-system service area geography and does not establish individual household exposure. Private wells are not represented unless served by a monitored public water system. PFOA and PFOS are reported by detection prevalence because the UCMR 5 reporting limit equals their federal MCL. A full PFBS Hazard Index is not calculated because co-located, same-event multi-compound readings are not retained in this dataset. Lithium has no federal Maximum Contaminant Level; 7.36 µg/L is an evidence-based reference concentration from a prospective cohort study, not a regulatory threshold.
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