In Situ Remediation Technologies - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 963

microbial sulphate reduction, leading to precipitation of ZnS in a relatively small
volume to concentrate the waste stream.
A similar immobilization was performed with the Zn 2+ contaminated ground-
water at a zinc smelter in Budel, the Netherlands. Here, the controlled process
of sulphate reduction was used to concentrate the heavy metal as ZnS in a small
volume that could be taken up in the zinc melting process thereafter (Janssen and
Temminghoff 2004 ).
21.2.2.2 Path Oriented In Situ Technologies
Between the source of contamination and the receptor, the plume or path of the
contaminants is found. In this area, which can have dimensions varying from meters
to kilometres, several treatment methods have been developed.
“Early path” In Situ technologies include the funnel and gate system (Starr and
Cherry 1994 ). Here, emphasis was on the physical phenomena related to the ground-
water flow, making use of the natural groundwater flow instead of the pump & treat
methods that were popular at the start of In Situ treatment. The installation of cut-off
walls in combination with In Situ bioreactors in the gate of the system led to a less
energy consuming treatment.
In later years the concept was extended to all types of biological active screens
or bioscreens (Fig. 21.4 ) in which attention was mainly focused on the biological
Legend
CAH's
cDCE
VC
Ethene
Ethane
Contaminant
Plume
soil
Sand
Silt
peat
Concentrations ( μ M)
1000
100
10
Fig. 21.4 An effective In Situ bioscreen at a site contaminated with chlorinated solvents in the
Netherlands