Page 42 - Materials Chemistry, Second Edition

Site Assessment and Remedial Investigation 25

Example 2.14: Determine the Amount of Impacted Soil
in the Vadose Zone (in SI units)
After the leaky USTs were removed, five soil borings were installed. Soil
samples were taken every 2 m below ground surface (bgs). However, not all
the samples were analyzed due to budget constraints. The areas of the plume
at a few depths were determined as follows:

Depth (m bgs) Area of the Plume at that Depth (m )
2
6 0
8 35
10 42
14 81
16 0

Determine the volume and mass of the impacted soil left in the vadose zone.
Strategy:
The depth intervals given are not the same; therefore, each plume area
represents a different depth interval. For example, the sample taken
at 10-m depth represents a 3-m interval, from 9 to 12 m.

Solution:
Volume of the impacted soil (using Equation 2.9)
= (2)(35) + (3)(42) + (3)(81) m 3
= 439 m 3
or = (9 − 7)(35) + (12 − 9)(42) + (15 − 12)(81) = 439 m 3
Assuming the total bulk density of soil is 1,800 kg/m , the mass of the
3
impacted soil = (439 m )(1,800 kg/m )
3
3
= 790,200 kg = 790 tons

2.2.4 Mass Fraction and Mole Fraction of Components in Gasoline

Gasoline is a common COC found in subsurfaces, usually the result of
leaky USTs. Gasoline itself is a mixture of various hydrocarbons, and it may
contain more than 200 different compounds. Some of them are lighter and
more volatile than the others (lighter ends vs. heavier ends). Gasoline in
soil samples is usually measured by EPA method 8015 as total petroleum
hydrocarbon (TPH), using gas chromatography (GC). Diesel fuel is often
measured by “modified” EPA method 8015 that takes into account the abun-
dance of heavier ends in diesel fuel as compared to gasoline. Some gasoline