Table 3.

Summary of vertical screening distances for TPH, hexane and naphthalene associated with LNAPL sources at petroleum UST sites

AnalyteVertical screening distance in feet (m)US EPA (2013)
Minimum (RBSL)Median (RBSL)Maximum (RBSL)
C5–C8 aliphatics4 (1.2)
(4100 µg m−3)
2 (0.61)
(90 000 µg m−3)
0
(3.72 × 108 µg m−3)
Five vapour concentrations > RBSL (20 000 µg m−3) for separation distance up to 3 ft (0.91 m)
C9–C12 aliphatics4 (1.2)
(3300 µg m−3)
3 (0.91)
(4800 µg m−3)
0
(2.04 × 107 µg m−3)
Eight vapour concentrations > RBSL (20 000 µg m−3) for separation distance up to 2 ft (0.61 m)
C9–C10 aromatics7 (2.1)
(100 µg m−3)
1 (0.30)
(6000 µg m−3)
0
(2.04 × 107 µg m−3)
Four vapour concentrations > RBSL (5000 µg m−3) for separation distance up to 2 ft (0.61 m)
n-hexane16 (4.9)
(2400 µg m−3)
14 (4.3)
(22 000 µg m−3)
12 (3.7)
(70 000 µg m−3)
Five vapour concentrations > RBSL (70 000 µg m−3) for separation distance up to 3 ft (0.91 m)
n-hexane (US data)11 (3.4)
(2400 µg m−3)
5 (1.5)
(22 000 µg m−3)
5 (1.5)
(70 000 µg m−3)
n-hexane (Australia data)—*
(2400 µg m−3)
15 (4.6)
(22 000 µg m−3)
12 (3.7)
(70 000 µg m−3)
naphthalene—*
(2.45 µg m−3)
3 (0.91)
(26 µg m−3)
0
(42 600 µg m−3)
Zero vapour concentrations > RBSL (300 µg m−3) for separation distance up to 3 ft (0.91 m)
total (bulk) TPH—*
(22 000 µg m−3)
—*
(79 000 µg m−3)
0
(3.97 × 108 µg m−3)
none reported
  • * Soil-gas concentrations are below the RBSL in <95% of cases at a vertical screening distance of 15 ft (4.6 m).