| Class | Igeo | Pollution level |
| 0 | <0 | uncontaminated |
| 1 | [0, 1] | uncontaminated to moderately contaminated |
| 2 | (1, 2] | moderately contaminated |
| 3 | (2, 3] | moderately to heavily contaminated |
| 4 | (3, 4] | heavily contaminated |
| 5 | (4, 5] | heavily to extremely contaminated |
| 6 | >5 | extremely contaminated |