Page 40 - Materials Chemistry, Second Edition

Site Assessment and Remedial Investigation 23

Information needed for this calculation

• The areal and vertical extents of the plume, h and A i
i
• Total bulk density of the soil (in situ), ρ t

To determine the mass and volume of the impacted water contained in a
groundwater plume, the following procedure should be followed:
Step 1: Use Equation (2.9) to determine the size of the plume.
Step 2: Multiply the size from Step 1 by the aquifer porosity to obtain
the volume of the impacted groundwater.
Step 3: Multiply the volume from Step 2 by groundwater density to
obtain the mass of the impacted water.

Example 2.12: Determine the Amount of Impacted
Soil in the Vadose Zone
For the project described in Example 2.9, after the USTs were removed, five
soil borings were installed. Soil samples were taken every 5 ft below ground
surface (bgs). The area of the plume at each soil sampling interval was deter-
mined as follows:

Depth (ft bgs) Area of the Plume at that Depth (ft )
2
15 0
20 350
25 420
30 560
35 810
40 0

Determine the volume and mass of the impacted soil left in the vadose zone.

Strategy:
The soil samples were taken and analyzed every 5 ft; therefore, each
plume area represents the same depth interval. The sample taken at
20-ft depth represents the 5-ft interval from 17.5 to 22.5 ft (the mid-
depth of the first two consecutive intervals to the mid-depth of the
next two consecutive intervals). Similarly, the sample at 25-ft depth
represents the 5-ft interval from 22.5 to 27.5 ft, and so on.