Scoring Methodology
How we calculate the composite pollution score for every US zip code.
Overview
Each zip code receives a score from 1 to 100, where lower is cleaner. The composite score combines three independent signals, each measuring a different dimension of environmental exposure.
Composite Score Formula
Score = (Pollution × 0.35) + (Water × 0.35) + (Air × 0.30)All component scores are on a 1-100 scale (lower = better). The composite is a weighted average, clamped to 1-100.
Signal Breakdown
Toxic Facilities (35% weight)
Based on the count of EPA TRI (Toxic Release Inventory) facilities within the zip code. More facilities = higher exposure risk.
0 facilities → score 5
1-2 facilities → score 10-25
3-5 facilities → score 26-50
6-10 facilities → score 51-75
11+ facilities → score 76-100
Source: EPA Toxic Release Inventory via Envirofacts API
Water Quality (35% weight)
Based on drinking water system violations reported to EPA SDWIS. Health-based violations (exceeding safe contaminant levels) are weighted much more heavily than monitoring/reporting violations.
Health violation component: up to 50 points (12 per violation, capped)
Total violation component: up to 30 points (3 per violation, capped)
Contaminant diversity penalty: up to 20 points (4 per unique contaminant)
Source: EPA Safe Drinking Water Information System (SDWIS)
Air Quality (30% weight)
Based on county-level Air Quality Index (AQI) data. Considers both the median annual AQI and the number of days exceeding unhealthy thresholds.
AQI component: (median AQI / 80) × 60, capped at 60 points
Unhealthy days component: (days / 60) × 40, capped at 40 points
Source: EPA Air Quality System (AQS) annual summaries
Rating Scale
| Score | Rating | Meaning |
|---|---|---|
| 1-20 | Excellent | Minimal environmental exposure |
| 21-40 | Good | Below-average exposure |
| 41-60 | Moderate | Average exposure, some concerns |
| 61-80 | Poor | Above-average exposure |
| 81-100 | Very Poor | High exposure across multiple signals |
Limitations
- • Scores are based on reported data only — unreported pollution is not captured
- • Facility count does not account for release volume or chemical toxicity (planned improvement)
- • Air quality is county-level, not zip-level — neighboring zips share scores
- • Water data covers violations, not all contaminant levels below legal limits
- • Scores should not replace professional environmental site assessments