The National Pollutant Discharge Elimination System (NPDES) is a permit program established as part of the Clean Water Act. Facilities dumping into a body of water are required to have a permit and to periodically submit discharge water reports. A "violation" on the map means a facility exceeded the limits in its own permit or failed to submit a report.

Some specifics:

Data comes from EPA's ICIS-NPDES bulk exports, synced every 2 weeks.

There's ~550k facilities registered nationally.

We built a detailed view showing each facility's violation history (allowed limit vs. actual amounts for each pollutant, by quarter)