Total Trihalomethanes (TTHM)
Unresolved Total Trihalomethanes Rule violation cited in 2024 (total trihalomethanes (tthm)).
PWSID CA1910022 · Surface waterState-owned
29,854 people served. 6 health-based SDWIS violations recorded in the past 5 years. 59 remain unresolved. Last cited 2 years ago.
Unresolved Total Trihalomethanes Rule violation cited in 2024 (total trihalomethanes (tthm)).
Unresolved Phase I/II/V Inorganic Chemical Rules violation cited in 2024 (contaminant 5200).
Unresolved Phase I/II/V Inorganic Chemical Rules violation cited in 2024 (contaminant 5200).
Unresolved Lead and Copper Rule violation cited in 2021 (contaminant 2218).
Health-based violations exceed an MCL or treatment-technique standard. Monitoring violations are reporting failures with no measured exceedance — they tell you the system isn't fully transparent, not that the water is unsafe today.
Maximum contaminant level exceeded
Maximum contaminant level exceeded; returned to compliance
Maximum contaminant level exceeded; returned to compliance
Maximum contaminant level exceeded; returned to compliance
Maximum contaminant level exceeded; returned to compliance
Reporting failure
Treatment technique violation
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Pomona, California (Census place; block-group disparity scores aggregated by centroid containment): a service population of 149,831. Local disparity score for pm2.5 (fine particulate) sits severely above the reference burden (227). Why we surface this →
Low-income
People of color
Under age 5
Over age 64
| Indicator | Disparity score | Reading |
|---|---|---|
| PM2.5 (fine particulate) | 227 | severely above the reference burden |
| Ozone | 234 | severely above the reference burden |
| Nitrogen dioxide (NO₂) | 194 | well above the reference burden |
| Diesel particulate | 213 | severely above the reference burden |
| Toxic releases (RSEI) | 116 | moderately above the reference |
| Traffic proximity | 218 | severely above the reference burden |
| Lead-paint risk (pre-1960 housing) | 157 | well above the reference burden |
| Superfund site proximity | 10 | well below the reference |
| RMP-facility proximity | 111 | moderately above the reference |
| Hazardous-waste site proximity | 210 | severely above the reference burden |
| Underground storage tanks | 0 | well below the reference |
| NPDES wastewater proximity | 194 | well above the reference burden |
| Drinking-water non-compliance | 0 | well below the reference |
Source: Census ACS 2018-2022 (5-year) + USEPA-clone EJ blockgroup stats (raw indicators + EJ disparity mirror).
Source. EPA Safe Drinking Water Information System · retrieved 2026-05-07. Reporting period 2020-01-01 → 2026-05-07.
What this is not. SDWIS records compliance against federal MCLs — not a direct readout of tap-water concentrations. Active health-based violations are not the same as a current crisis; we link to the EPA record so you can verify return-to-compliance status before forming a conclusion.