Community Water System · PWS 010106001
Mashantucket Pequot Water System
Operator location Mashantucket, EPA Region 1 — Tribal Water Systems - 37% of 172 violations are health-based (upper-third health share (> 23%)); surface water source; 26,445 served per SDWIS.
- 26,445
- People served (this PWS)
- 172
- EPA violations (this PWS)
- 63
- Health-based (this PWS)
- 6 PFAS
- UCMR5 (this PWS)
Mashantucket Pequot Water System standing, high SDWIS violation third
37% of 172 recorded violations are health-based - upper-third health share (> 23%). Corpus terciles use 29,740 systems serving 500+ (the sitemap cohort). Health-based share 37% is upper-third health share (> 23%). UCMR5: upper-third PFAS panel (> 4 compounds). Population rank #2,100 of 29,740 among systems serving 500+.
The verdict
Mashantucket Pequot Water System sits in the upper third of the sitemap cohort by violation count (172), so the tables below sample a dense compliance trail rather than a near-clean ledger. Population served is large (26,445; larger served population (> 3,309)), so household exposure scale sits behind the violation mix. Health-based share is 37% - most of this ledger is MCL or treatment-technique exceedance. UCMR5 detected 6 PFAS compounds (upper-third PFAS panel (> 4 compounds)).
- #2,100 of 29,740
- Population · /systems
- #2 of 2
- Population · 01
- 172
- Total EPA violations on record
- 37%
- Health-based (MCL / treatment failure)
Population ordinals match the sitemap cohort (systems serving 500+, population_served DESC). See methodology · corpus placement.
6 PFAS "forever chemicals" detected in testing under EPA's UCMR5 monitoring program.
System Details
- System Type
- Community
- Owner Type
- Native American
- Connections
- 154
- School/Daycare
- No
- MCL Violations
- 63
- Monitoring Violations
- 106
- Treatment Tech Violations
- 0
Violation History
Contaminant violations recorded by EPA.
| Contaminant | Category | Count | Latest |
|---|---|---|---|
| Coliform (TCR) | MCL | 57 | 1993 |
| TTHM | MCL | 6 | 2018 |
| Coliform (TCR) | MR | 6 | 1993 |
| TTHM | MR | 6 | 2018 |
| Lead and Copper Rule | MR | 6 | 1993 |
| BHC-GAMMA | MR | 4 | 2016 |
| Endrin | MR | 3 | 2016 |
| Diquat | MR | 3 | 2016 |
| Endothall | MR | 3 | 2016 |
| OXAMYL | MR | 3 | 2016 |
| Simazine | MR | 3 | 2016 |
| Picloram | MR | 3 | 2016 |
| Dinoseb | MR | 3 | 2016 |
| Carbofuran | MR | 3 | 2016 |
| Atrazine | MR | 3 | 2016 |
| LASSO | MR | 3 | 2016 |
| Heptachlor | MR | 3 | 2016 |
| 2,4-D | MR | 3 | 2016 |
| 2,4,5-TP | MR | 3 | 2016 |
| HEXACHLOROBENZENE | MR | 3 | 2016 |
| Benzo(a)pyrene | MR | 3 | 2016 |
| Total Polychlorinated Biphenyls (PCB) | MR | 3 | 2016 |
| 1,2-DIBROMO-3-CHLOROPROPANE | MR | 3 | 2016 |
| ETHYLENE DIBROMIDE | MR | 3 | 2016 |
| Dalapon | MR | 3 | 2016 |
| Di(2-ethylhexyl) adipate | MR | 3 | 2016 |
| Toxaphene | MR | 3 | 2016 |
| Di(2-ethylhexyl) phthalate | MR | 3 | 2016 |
| Hexachlorocyclopentadiene | MR | 3 | 2016 |
| Pentachlorophenol | MR | 3 | 2016 |
Violation Count vs. the National Corpus
Mashantucket Pequot Water System has 172 recorded EPA violations, 83% of the 29,740 public water systems serving 500+ people nationwide carry fewer, and 17% carry more. 37% of this system's own violations are health-based (63 of 172), and it ranks #2,100 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)
172 Higher than most more violations than 83% 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. 19 of 116 samples detected PFAS.
| Contaminant | Date | Result | MRL | Status |
|---|---|---|---|---|
| 8:2 FTS | 9/27/2023 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFHpA | 9/27/2023 | 3.50 ppt | 3.00 ppt | Detected |
| PFHxS | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFNA | 9/27/2023 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFOS | 9/27/2023 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFOA | 9/27/2023 | 7.40 ppt | 4.00 ppt | Detected |
| PFDA | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHxA | 9/27/2023 | 9.20 ppt | 3.00 ppt | Detected |
| 11Cl-PF3OUdS | 9/27/2023 | <5.00 ppt | 5.00 ppt | Not Detected |
| 9Cl-PF3ONS | 9/27/2023 | <2.00 ppt | 2.00 ppt | Not Detected |
| ADONA | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| HFPO-DA | 9/27/2023 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFBA | 9/27/2023 | 6.30 ppt | 5.00 ppt | Detected |
| PFBS | 9/27/2023 | 3.60 ppt | 3.00 ppt | Detected |
| 4:2 FTS | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDoA | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMPA | 9/27/2023 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFPeA | 9/27/2023 | 18.20 ppt | 3.00 ppt | Detected |
| PFMBA | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFEESA | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| NFDHA | 9/27/2023 | <20.00 ppt | 20.00 ppt | Not Detected |
| PFPeS | 9/27/2023 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFHpS | 9/27/2023 | <3.00 ppt | 3.00 ppt | Not Detected |
| 6:2 FTS | 9/27/2023 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFUnA | 9/27/2023 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFTA | 8/9/2023 | <8.00 ppt | 8.00 ppt | Not Detected |
| PFTrDA | 8/9/2023 | <7.00 ppt | 7.00 ppt | Not Detected |
| NEtFOSAA | 8/9/2023 | <5.00 ppt | 5.00 ppt | Not Detected |
| NMeFOSAA | 8/9/2023 | <6.00 ppt | 6.00 ppt | Not Detected |
| PFMBA | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMPA | 5/13/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| 8:2 FTS | 5/13/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| 4:2 FTS | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFBS | 5/13/2024 | 3.40 ppt | 3.00 ppt | Detected |
| PFHxA | 5/13/2024 | 9.70 ppt | 3.00 ppt | Detected |
| PFPeS | 5/13/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFEESA | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFPeA | 5/13/2024 | 19.10 ppt | 3.00 ppt | Detected |
| 6:2 FTS | 5/13/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFBA | 5/13/2024 | 6.50 ppt | 5.00 ppt | Detected |
| HFPO-DA | 5/13/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFDA | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHpA | 5/13/2024 | 3.30 ppt | 3.00 ppt | Detected |
| 9Cl-PF3ONS | 5/13/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| ADONA | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHpS | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 11Cl-PF3OUdS | 5/13/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFUnA | 5/13/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFDoA | 5/13/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFOA | 5/13/2024 | 6.60 ppt | 4.00 ppt | Detected |
Health-based violations on Mashantucket Pequot Water System
63 health-based rows in the tables above map to MCL or treatment-technique exceedances, verify each contaminant code on the federal SDWIS report for 010106001.
Sources: EPA SDWIS
Nationwide peers
172 violations · 26,445 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 Mashantucket Pequot Water System
Use this system's EPA-reported record as a starting filter, not a final verdict.
- See how every tracked system in EPA Region 1 — Tribal Water Systems compares on the same EPA violation measures. EPA Region 1 — Tribal Water Systems 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.