Table 8.
Example critical ratios over which TPH in soil vapor will drive vapor intrusion risk over individual compound.
| Chemical | Critical Ratio 1,2 | |
|---|---|---|
| TPH Gasoline Vapors | TPH Middle Distillate Vapors | |
| Benzene | 935 | 452 |
| Ethylbenzene | 299 | 144 |
| Toluene | 0.06 | 0.03 |
| Xylenes | 2.9 | 1.4 |
| Naphthalene | 4,028 | 1,944 |
1 TPH vapor intrusion screening level (Table 7) divided by individual compound screening level (Table 6); 2 Ratio at which TPH will exceed vapor intrusion screening level when individual compound is at or below its respective screening level (based on a target cancer risk of 10−6 or a noncancer Hazard Quotient of 1.0).