Table 10.
Weighted TPH Reference Concentration and example TPH subslab soil vapor screening levels for soil vapor samples collected in the Hawaii DOH petroleum vapor study.
| Site/Fuel Type | Weighted RfC 1(μg/m3) | Indoor AirScreening Level 2(μg/m3) | Subslab Soil VaporScreening Level 3(µg/m3) | TPH:Benzene Critical Ratio 4 | TPH:Benzene Measured Ratio | Vapor Intrusion Risk Driver 5 |
|---|---|---|---|---|---|---|
| Site A | 510 | 530 | 530,000 | 1,710:1 | 1,513:1 | Benzene |
| Site B | 443 | 460 | 460,000 | 1,484:1 | 4,174:1 | TPH |
| Site C | 251 | 260 | 260,000 | 839:1 | 18,710:1 | TPH |
| Site D | 211 | 220 | 220,000 | 710:1 | 9,135:1 | TPH |
| Site E | 127 | 130 | 130,000 | 410 | 54,236:1 | TPH |
1 Based on average carbon range composition (see Table 9); 2 Residential exposure scenario; see equation and assumptions in text; 3 Assuming an indoor air:subslab soil vapor attenuation factor of 0.001; 4 TPH indoor air screening level divided by benzene screening level (based on target cancer risk of 10−6); Above this ratio, TPH in soil vapor could still pose a vapor intrusion risk even if benzene is at or below target screening levels. 5 Based on comparison to average TPH: Benzene ratio for samples noted in previous table.