Page 35 - Materials Chemistry, Second Edition

18 Practical Design Calculations for Groundwater and Soil Remediation

Discussion:
1. One m of soil was used as the “basis” in this example. Other
3
volumes (e.g., 1 ft ) can also be used, and the results should be the
3
same.
2. Although mass and weight are different, these two terms are often
used interchangeably in this book (and in many other engineer-
ing articles).
3. Many equations that relate these parameters can be found in
technical articles. However, the procedure used in this example,
without using any of those equations, was to develop a better
understanding of the concepts and definitions.
4. As expected, the value of the total bulk density (1.78 g/cm or
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111.1 lb/ft ) is larger than that of the (dry) bulk density (1.59 g/
3
cm or 99.2 lb/ft ).
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3
5. In civil engineering practices, water content is usually on a grav-
imetric basis. However, in environmental engineering applica-
tions, volumetric water content and degree of water saturation
are more commonly used. In this example, for a water content
of 0.12, water occupies 19% of the total soil volume and 47.5% of
the pore volume (air occupies the balance, i.e., 52.5% of the pore
volume).

2.2.2 Amount of Soil from Tank Removal or from
Excavation of the Impacted Area
Removal of USTs typically involves soil excavation. If the excavated soil is
clean (i.e., free of COCs or below the permissible levels), it may be reused as
backfill materials or disposed of in a sanitary landfill. On the other hand,
if it is impacted, it needs to be treated or disposed of in a hazardous waste
landfill. For either case, a good estimate of soil volume and/or mass is neces-
sary. If feasible, we should separate the apparently impacted soil from the
clean soil by putting them into separate piles to save the subsequent treat-
ment/disposal costs. Using a portable instrument, such as a photo-ionization
detector (PID), flame-ionization detector (FID), or organic vapor analyzer
(OVA), would help us to make the decision.
The excavated soil is typically stored on site first in stockpiles. The amount
of excavated soil from tank removal can be determined from measurement
of the volumes of the stockpiles. However, the shapes of these piles are irreg-
ular, and this makes the measurement and subsequent calculations difficult.
An easier and more accurate alternative is

Step 1: Measure the dimensions of the tank pit.
Step 2: Calculate the volume of the tank pit from the measured dimensions.