Page 58 - Materials Chemistry, Second Edition

Site Assessment and Remedial Investigation 41

(c) Number of 55-gal drums needed for each well
= [(11.8 ft )(7.48 gal/ft )] ÷ (55 gal/drum) = 1.6 drums
3
3
(d) Total number of 55-gal drums needed
= (1.6)(4) = 6.4 drums

Answer: Seven 55-gallon drums are needed.

2.4 Mass of COCs Present in Different Phases
Once an NAPL enters a vadose zone, it may end up in four different phases.
COCs may leave the free product and enter the void space. The COCs in the
void and in the free product, in contact with the soil moisture, may get dis-
solved or absorbed in the liquid. Those COCs that enter the soil moisture
may adsorb onto the soil grains. In other words, the NAPL can partition into
four phases: (1) free product, (2) vapor in the void, (3) dissolved constituent
in the soil moisture, and (4) adsorbed onto the soil grains. The concentrations
of the COCs in the air void, in the soil moisture, and on the soil grains are
interrelated and are affected greatly by the presence or absence of the free
product. The partition of the COCs in these four phases has a great impact on
the fate and transport of the COCs and the required site-remediation effort.
A good understanding of this partition phenomenon is necessary to imple-
ment cost-effective alternatives for the site cleanup.
In this section, we first discuss the vapor concentration resulting from the
presence of free product in the pores (Section 2.4.1). We then describe the
relationship between the COC concentration in the liquid and that in the air
(Section 2.4.2). The relationship between the COC concentration in the liquid
and that on the soil grains is covered in Section 2.4.3. The relationship among
the liquid, vapor, and solid concentrations is discussed in Section 2.4.4. The
procedure to determine the partition of COC in these phases is discussed in
Section 2.4.5.

2.4.1 Equilibrium between Free Product and Vapor
When a liquid is in contact with air, molecules in the liquid will tend to enter
the air space as vapor, via volatilization. The vapor pressure of a liquid is
the pressure exerted by its vapor at equilibrium. It is often reported in mil-
limeters of mercury. (Note: 760 mm-Hg = 760 torr = 1 atm = 1.013 × 10 N/m
2
5
= 1.013 × 10 Pascal = 1.013 bar = 14.696 psi.) and varies greatly with tempera-
5
ture. In general, the higher the temperature is, the higher the vapor pres-
sure will be. Several equations have been established to correlate the vapor