Geoscience Reference
In-Depth Information
Fig. 17.22 Rate of intrusion of organic compounds from freshwater (FF) and seawater (SF)
source cells into freshwater collector cells, expressed as concentrations of selected compounds (in
mg/L) (Dror et al.
2003
)
from 0.4 to 86 %. These data confirm potential contamination of groundwater by
petroleum hydrocarbons below service stations, but also underline differences in
concentration values as a function of the distance from the solid phase pollutant
within the aquifer. The impact of NAPLs on groundwater chemistry is more
evident in the ''smear zone'' of the aquifer, where the presence of undissolved
compounds was higher than that predicted from theoretical solubilities.
Petroleum hydrocarbon contamination under lateral flow: Contamination of
seawater by petroleum hydrocarbons raises the possibility of intrusion of organic
contaminants into coastal aquifers. Such behavior was observed in a study of
intrusion into a freshwater cell of low density (benzene and toluene) and high
density (trichloroethylene) petroleum hydrocarbons dissolved in freshwater (FF)
and in simulated seawater (SF). From Fig.
17.22
, it may be seen that a much
higher rate of intrusion and much large amounts of petroleum hydrocarbon were
found in the SF system than in FF system (Dror et al.
2003
).
The intrusion of petroleum hydrocarbons from seawater into fresh groundwater
may occur in response to chemical gradients that are enhanced by the ''salting-out
effect.'' This process, which reduces the aqueous solubility of petroleum hydro-
carbon in seawater, acts to force petroleum hydrocarbons across the interface
between seawater and fresh coastal groundwater. The total petroleum hydrocarbon
