Geoscience Reference
In-Depth Information
concentrations in groundwater following the intrusion of contaminated ''seawater''
are given not only by the amount of petroleum hydrocarbon dissolved but also by
the presence of dispersed organic droplets (Yaron-Marcovich et al.
2007
). More
details on this phenomenon are provided at the end of
Sect. 8.3.4
.
Petroleum plume breakthrough associated with seawater intrusion along the
coast of southwestern Nigeria was reported by Ojuri and Ola (
2010
). Also, the
effect of seawater intrusion on petroleum hydrocarbon plumes in the Mediterra-
nean coastal area of Southern Italy was studied by Mastrocicco et al. (
2012
), who
examined the influence of the density contrast between fresh groundwater and
seawater on the transport of petroleum contaminants within an unconfined coastal
aquifer. The monitoring site was a petrochemical plant, located on a polluted
unconfined sandy and sandy loam aquifer of 10-30 m thickness, which becomes
semiconfined in silty clay sediment. Local confined aquifers separated from the
polluted unconfined aquifers were also defined. Seawater reaches the polluted site
through a canal used permanently for plant cooling purposes. An unknown volume
of light nonaqueous phase liquid (LNAPL) contaminating the aquifer in the past
decades came into contact with a plume of seawater originating from the cooling
canal. Mastrocicco et al. (
2012
) show that as a result of the density contrast, the
effect of the total petroleum hydrocarbon (TPH) plume is to force flow in the
bottom part of the aquifer.
Partial attenuation: Natural attenuation of the petroleum hydrocarbon com-
ponents may be the result of volatilization, adsorption on the aquifer solid phase,
or microbial activity. Volatilization leads to removal of a fraction of the com-
pounds, while adsorption of some compounds may be irreversible on specific
mineral or organic solid phases; microbial activity may enhance TPH degradation
and formation of various metabolites. However, despite the complete eradication
of some petroleum product components, TPH residues will remain and lead to
irreversible changes in groundwater chemistry at least on the human lifetime scale.
Kerosene is a heavily used petroleum product formed by a mixture of about 100
components. The pathway of kerosene dissolution and volatilization in and from a
water solution confirms potential residual kerosene presence in groundwater.
Excess aqueous solubility of aromatic constituents is explained by cosolvency due
to the presence of polar compounds in TPH mixtures. This cosolvent effect
potentially increases aqueous concentration in hydrocarbons (Lee et al.
1992a
,
b
).
An extended discussion of kerosene behavior in the soil-subsurface environment is
presented in
Sect. 16.1.5
.
Petroleum hydrocarbon concentrations in groundwater may be also altered by
irreversible adsorption on the aquifer solid phase, which contains clays and sands
as major constituents. Cosultchi et al. (
2004
) found that most organic species of
petroleum organic compounds remain adsorbed on layered clays after aging. This
retention is conditioned by the petroleum paraffinic content and by molecules
containing alkane chains, which easy intercalate within the clay interlayers.
Petroleum hydrocarbon adsorption may lead to irreversible modification of the
clay structure. The partial dissolution of clay matrix is indicated by X-ray dif-
fraction (XRD) as an irreversible modification of the clay structure. Figure
17.23
