Geoscience Reference
In-Depth Information
concentration of Zn and Ni at values greater than those expected from the dis-
solution of metal-bearing Mn oxides are due to exchangeable trace elements.
These elements can be released due to changes in the electrolyte concentration, for
example, as a result of the reduction process.
8.3.3 Dissolution from Mixtures of Organic Contaminants
Dissolution of volatile organic mixtures was observed by studying the behavior of
kerosene. Dror et al. (
2002
) compared the gas chromatographs of neat kerosene to
those of the fraction of kerosene dissolved in an aqueous electrolyte solution of
0.01 M NaCl, at an ambient temperature of 22 C (Fig.
8.18
). Aliphatic and
branched aliphatic hydrocarbons in the range C
9
-C
16
constitute the major group of
components in neat kerosene, with only a minor set of aromatic components. In
aqueous electrolyte solutions, on the other hand, aromatic compounds, especially
branched benzene and naphthalene, make up the majority of compounds. The
C
9
-C
16
aliphatic and branched aliphatic components do not appear in the gas
chromatograph of the aqueous electrolyte solution. The reason for the difference
between the neat and aqueous dissolved kerosene is the wide range of aqueous
solubility typical of the different kerosene components. Aromatic compounds
usually are much more soluble than aliphatic components. Therefore, aromatic
components, which are minor constituents of neat kerosene, dissolve in a water
solution much more readily than the major group of aliphatic compounds.
Gasoline commonly contains appreciable amounts of aniline, phenol, and their
alkyl substituted homologs as well as many other polar compounds. Schmidt et al.
(
2002
) measured the fuel-water partitioning coefficients, K
fw
, of several polar
compounds during a batch experiment. The K
fw
values for the investigated phe-
nols, anilines, benzotriazoles, and S-heterocycles ranged from 0.2 to 1,700; these
values are up to three orders of magnitude lower than the K
fw
of benzene. The
nonaqueous-phase liquid (NAPL)-water partitioning of anilines and phenols
depends strongly on the structure of the compound as well as on the pH of the
gasoline composition. Due to their polarity, anilines and phenols associated with
the gasoline, after a spill on the land surface, may reach groundwater ahead of the
benzene and may be used as a marker to predict groundwater contamination.
8.3.4 Apparent Solubility
The ''apparent solubility'' of contaminants can be defined when the theoretical
solubility deviates from the initial value, as a result of a number of factors
encountered in the subsurface environment. Waste and sludge disposal sites usu-
ally contain a mixture of salts, toxic trace metals, and organic contaminants. When
the disposal site is leached by rain or irrigation water, a solution containing soil
