Table 7.
Average contaminant concentrations, average daily doses (ADDs), hazard quotients (HQs) exceeding 1.0, MCLs, MCL exceedances and average risk quotients (RQs) for each of five principal inorganic contaminants in home well water on the Crow Reservation.
| Well Water Contaminant | n | Avg ADD * (mg/L) | RfD (mg/L) | # HQ ≥ 1.0 | % HQ ≥ 1.0 | Avg HQ | MCL (mg/L) | # > MCL | % > MCL | Avg RQ * |
|---|---|---|---|---|---|---|---|---|---|---|
| Nitrate + Nitrite as N | 164 | 0.05 | 1.6 | 0 | 0 | 0.03 | 10.0 | 7 | 4.3% | 0.16 |
| As | 164 | 3 × 10−5 | 0.0003 | 2 | 1.2% | 0.11 | 0.01 | 2 | 1.2% | 0.12 |
| Mn | 164 | 0.03 | 0.046 | 0 | 0 | 0.06 | 0.3 | 18 | 11.0% | 0.34 |
| Zn | 164 | 0.003 | 0.3 | 0 | 0 | 0.01 | N/A | N/A | N/A | N/A |
| U | 97 | 0.0002 | 0.0002 | 32 | 33.0% | 1.16 | 0.03 | 6 | 6.30% | 0.27 |
* When a contaminant was not detected at the reporting limit (RL), RL/2 was substituted.