Environmental Engineering Reference
In-Depth Information
Figure 12.3. Aerial photograph of the Rhinelands case study site, a large BTEX
contaminated paint factory site in Germany, with co-contamination from chlorinated
hydrocarbons and metals.
manufacturing plant for more than 100 years, was characterised by deep
(30mplus) Rhine sediments with groundwater flowing towards the Rhine
and was found in the 1990s to be contaminated predominantly by monoaro-
matic hydrocarbons (benzene, ethyl-benzene, toluene and xylene the 'BTEX').
These compounds were used in the manufacture of paints and were spilled into
the soil and groundwater over decades of storage and use. Also present were
some chlorinated hydrocarbons (e.g., trichloroethylene, TCE) and heavy metals
such as lead, copper and zinc. The metals were used to pigment the paint and
were primarily introduced as metal oxides. The chlorinated solvents were used
as paint thinners and, like the non-chlorinated aromatics, were introduced to
the environment over many years. The BTEX contaminants are partly soluble in
groundwater and were transported across the site, while the remainder of the
BTEX compounds float on the groundwater, being less dense than water. The
latter are examples of Light, Non Aqueous Phase Liquids (LNAPLs). In contrast,
the chlorinated solvents are denser than the water and so sink deeper into the
system. They are examples of Dense, Non Aqueous Phase Liquids (DNAPLs).
The extent of the contamination in the deep sediments and the associated
groundwater and the presence of high copy numbers of BTEX catabolic genes
led to the conclusion that the best way to tackle the site was to exploit the
indigenous microbial community in the sediment to attenuate the main
organic contaminants, in a process referred to as in situ bioremediation.
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