Community Water System · PWS IL1631100
O Fallon
Operator location O'Fallon, Illinois - 43% of 102 violations are health-based (upper-third health share (> 23%)); surface water source; 46,603 served per SDWIS.
- 46,603
- People served (this PWS)
- 102
- EPA violations (this PWS)
- 44
- Health-based (this PWS)
- 1 PFAS
- UCMR5 (this PWS)
O Fallon standing, high SDWIS violation third
43% of 102 recorded violations are health-based - upper-third health share (> 23%). Corpus terciles use 29,740 systems serving 500+ (the sitemap cohort). Health-based share 43% is upper-third health share (> 23%). UCMR5: lower-third PFAS panel (≤ 2 compounds). Population rank #1,183 of 29,740 among systems serving 500+.
The verdict
O Fallon sits in the upper third of the sitemap cohort by violation count (102), so the tables below sample a dense compliance trail rather than a near-clean ledger. Population served is large (46,603; larger served population (> 3,309)), so household exposure scale sits behind the violation mix. Health-based share is 43% - most of this ledger is MCL or treatment-technique exceedance. UCMR5 detected 1 PFAS compound (lower-third PFAS panel (≤ 2 compounds)).
- #1,183 of 29,740
- Population · /systems
- #35 of 1,310
- Population · IL
- 102
- Total EPA violations on record
- 43%
- Health-based (MCL / treatment failure)
Population ordinals match the sitemap cohort (systems serving 500+, population_served DESC). See methodology · corpus placement.
1 PFAS "forever chemicals" detected in testing under EPA's UCMR5 monitoring program.
System Details
- System Type
- Community
- Owner Type
- Local
- Connections
- 18,497
- County
- St. Clair
- School/Daycare
- No
- MCL Violations
- 42
- Monitoring Violations
- 24
- Treatment Tech Violations
- 2
Violation History
Contaminant violations recorded by EPA.
| Contaminant | Category | Count | Latest |
|---|---|---|---|
| Coliform (TCR) | MCL | 42 | 1999 |
| Coliform (TCR) | MR | 19 | 1999 |
| Lead and Copper Rule | MR | 5 | 2007 |
| Lead and Copper Rule | TT | 2 | 1993 |
Violation Count vs. the National Corpus
O Fallon has 102 recorded EPA violations, 74% of the 29,740 public water systems serving 500+ people nationwide carry fewer, and 26% carry more. 43% of this system's own violations are health-based (44 of 102), and it ranks #1,183 of 29,740 by population served among that same cohort.
EPA violations vs. the national water-system corpus
Public water systems serving 500+ people (EPA SDWIS)
102 Around the middle fewer violations than 26% of 29,740 water systems
the national water-system corpus, bucketed by value
Each bar is a band; taller bars hold more water systems. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA SDWIS · 2026-05-15
PFAS Testing Results (UCMR5)
Results from EPA's Fifth Unregulated Contaminant Monitoring Rule. 4 of 116 samples detected PFAS.
| Contaminant | Date | Result | MRL | Status |
|---|---|---|---|---|
| PFNA | 8/7/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFMPA | 8/7/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| NMeFOSAA | 8/7/2024 | <6.00 ppt | 6.00 ppt | Not Detected |
| NEtFOSAA | 8/7/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFTrDA | 8/7/2024 | <7.00 ppt | 7.00 ppt | Not Detected |
| PFTA | 8/7/2024 | <8.00 ppt | 8.00 ppt | Not Detected |
| PFHpS | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFPeS | 8/7/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| NFDHA | 8/7/2024 | <20.00 ppt | 20.00 ppt | Not Detected |
| 11Cl-PF3OUdS | 8/7/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFOS | 8/7/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFOA | 8/7/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFDA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDoA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMBA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFUnA | 8/7/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFHxS | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 9Cl-PF3ONS | 8/7/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFEESA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHpA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHxA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFBS | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| ADONA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFPeA | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 8:2 FTS | 8/7/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| 4:2 FTS | 8/7/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 6:2 FTS | 8/7/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFBA | 8/7/2024 | 12.10 ppt | 5.00 ppt | Detected |
| HFPO-DA | 8/7/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| 4:2 FTS | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| NEtFOSAA | 5/8/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFOA | 5/8/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFMPA | 5/8/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFTA | 5/8/2024 | <8.00 ppt | 8.00 ppt | Not Detected |
| HFPO-DA | 5/8/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| ADONA | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 9Cl-PF3ONS | 5/8/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| 11Cl-PF3OUdS | 5/8/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFUnA | 5/8/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFHxA | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDA | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFOS | 5/8/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFBA | 5/8/2024 | 11.90 ppt | 5.00 ppt | Detected |
| 6:2 FTS | 5/8/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFMBA | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFTrDA | 5/8/2024 | <7.00 ppt | 7.00 ppt | Not Detected |
| PFBS | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDoA | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHpA | 5/8/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFNA | 5/8/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
Health-based violations on O Fallon
44 health-based rows in the tables above map to MCL or treatment-technique exceedances, verify each contaminant code on the federal SDWIS report for IL1631100.
Sources: EPA SDWIS · Illinois EPA, Bureau of Water
Nationwide peers
102 violations · 46,603 served: nearest cross-state SDWIS matches.
Cross-state systems with comparable violation load
Nearest cross-state community systems (500+ served) by total SDWIS violations on record.
Cross-state systems with similar served population
Nearest cross-state systems by EPA SDWIS population_served (same 500+ sitemap gate).
What to do with O Fallon
Use this system's EPA-reported record as a starting filter, not a final verdict.
- See how every tracked system in Illinois compares on the same EPA violation measures. Illinois systems
- Check whether PFAS was detected at this system under UCMR5 testing. PFAS guide
- Find and compare another public water system by name or PWSID. Search systems
EPA SDWIS and UCMR5 figures are informational only, not a substitute for a certified lab test of your own tap water.