Chlorine
Unresolved Disinfectants and Disinfection Byproducts (Stage 2) violation cited in 2025 (chlorine).
PWSID AZ0412305 · GroundwaterMixed
153 people served. 1 health-based SDWIS violation recorded in the past 5 years. 12 remain unresolved. Last cited 1 year ago.
Unresolved Disinfectants and Disinfection Byproducts (Stage 2) violation cited in 2025 (chlorine).
Unresolved Disinfectants and Disinfection Byproducts (Stage 2) violation cited in 2025 (chlorine).
Unresolved Disinfectants and Disinfection Byproducts (Stage 2) violation cited in 2025 (chlorine).
Unresolved Disinfectants and Disinfection Byproducts (Stage 2) violation cited in 2025 (chlorine).
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.
Failure to monitor as scheduled
Failure to monitor as scheduled
Failure to monitor as scheduled
Failure to monitor as scheduled
Failure to monitor as scheduled
Reporting failure
Treatment technique violation
OTHER; returned to compliance
Failure to monitor as scheduled; returned to compliance
Failure to monitor as scheduled; returned to compliance
Failure to monitor as scheduled
Failure to monitor as scheduled; returned to compliance
Failure to monitor as scheduled; returned to compliance
Failure to monitor as scheduled
Failure to monitor as scheduled
Failure to monitor as scheduled; returned to compliance
Failure to monitor as scheduled
Failure to monitor as scheduled
Failure to monitor as scheduled; returned to compliance
OTHER; returned to compliance
OTHER; returned to compliance
Nogales, Arizona (Census place; block-group disparity scores aggregated by centroid containment): a service population of 19,761. Local disparity score for pm2.5 (fine particulate) sits moderately above the reference (111). Why we surface this →
Low-income
People of color
Under age 5
Over age 64
| Indicator | Disparity score | Reading |
|---|---|---|
| PM2.5 (fine particulate) | 111 | moderately above the reference |
| Ozone | 253 | severely above the reference burden |
| Nitrogen dioxide (NO₂) | 214 | severely above the reference burden |
| Diesel particulate | 41 | well below the reference |
| Toxic releases (RSEI) | 0 | well below the reference |
| Traffic proximity | 81 | below the reference |
| Lead-paint risk (pre-1960 housing) | 116 | moderately above the reference |
| Superfund site proximity | 0 | well below the reference |
| RMP-facility proximity | 0 | well below the reference |
| Hazardous-waste site proximity | 0 | well below the reference |
| Underground storage tanks | 174 | well above the reference burden |
| NPDES wastewater proximity | 147 | moderately above the reference |
| Drinking-water non-compliance | 225 | severely above the reference burden |
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.