Page 24 - Materials Chemistry, Second Edition

Site Assessment and Remedial Investigation 7

6. Groundwater elevations
7. Drawdown data from aquifer tests

Using these collected data, engineering calculations are then performed to
assist in site remediation. Common engineering calculations include:

1. Mass and volume of soil excavated during tank removal
2. Mass and volume of impacted soil left in the vadose zone
3. Mass of COCs left in the vadose zone
4. Mass and volume of the free product (LNAPLs and DNAPLs)
5. Size of the dissolved plume in the aquifer
6. Mass of COCs present in the aquifer (dissolved and adsorbed)
7. Hydraulic gradient and groundwater flow direction
8. Hydraulic conductivity of the aquifer

This chapter describes all the above-needed engineering calculations
except for the last two, which will be covered in Chapter 3. Discussion
will also be presented with regard to calculations related to site assess-
ment activities, including cuttings from soil borings and purge water
from groundwater sampling. The last part of this chapter describes the
“partitioning” of COCs in different phases. A good understanding of
the partitioning phenomenon of COCs is critical for evaluation of the
fate and transport of COCs in subsurface and for selection of remedial
alternatives.

2.2 Determination of Extent of Contamination
2.2.1 Mass and Concentration Relationship

As mentioned earlier, COCs may be present in different media (i.e., soil,
water, or air) and in different phases (i.e., vapor, dissolved, adsorbed, or
free product). In environmental engineering applications, people commonly
express concentrations of COCs in parts per million (ppm), parts per billion
(ppb), or parts per trillion (ppt).
Although these concentration units are commonly used, some people may
not fully realize that “1 ppm,” for example, does not mean the same for liq-
uid, solid, and air samples. For the liquid and solid phases, the ppm unit is
on a mass-per-mass basis. One ppm stands for one part mass of a compound
per million parts mass of the media containing it. Soil containing 1 ppm ben-
zene means that every gram of soil contains 1 microgram (μg) of benzene,