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5.
SELECTION OF A REMEDIATION METHOD
There
are many options available for the remediation of contaminated
sites. However, taking into consideration the characteristics
of contaminated sites of petrol filling stations, boatyards
and vehicle repairing/dismantling workshops in Hong Kong,
the following methods may be the more practical options suitable
for use in these small target sites:
i) recovery trenches or wells;
ii) soil venting/air sparging; and
iii) excavation and disposal.
Detailed
descriptions of these three methods are given in Annexes C,
D and E respectively. Table 5.1 below summarises the applicability
of these methods and their characteristics.
Table
5.1 Comparison of Remediation Methods
| Method |
Principal
Use |
Expertise
Required |
| Recovery
Trenches or Wells |
Removal
of leaked oil that floats on top of groundwater; a prerequisite
if leaked oil is found; used in conjunction with other
remediation methods |
Moderate |
| Soil
Venting/ Air Sparging |
Soil
venting for unsaturated zone soil; air sparging for groundwater;
removes volatile chemicals, also promotes bioremediation |
High |
| Excavation/Disposal |
Shallow
contamination, one-off excavation and contaminant removal,
addresses all contaminants. Pretreatment of excavated
soil prior to disposal may be required |
Little |
The list
of methods above is not intended to be exhaustive. Other methods
such as :
i) in-situ
immobilization of contaminants; and
ii) containment
of contaminants
may be
applicable in certain special cases.
It is
important that experienced professionals are engaged for the
remediation work. In situ remediation methods should be adopted
wherever possible. In order to save valuable landfill space,
excavation and disposal to landfill should always be the last
resort which should be used only when:
i) in-situ
remediation is proved to be not feasible; and
ii) there
is very localized contamination and the quantity of contaminated
soil for landfilling is small.
Acceptance
of disposal of contaminated soil at landfill also depends
on the degree of contamination of the soil and the nature
of the contamination. Special approval has to be obtained
from EPD for disposal to landfill. In some cases, contaminated
soil must be pretreated or stabilized before landfill disposal
(see Annex E).
The following
factors should be considered when evaluating the different
remediation methods and selecting the most suitable one for
a site:
i) degree
and extent of the contamination;
ii) anticipated
future use of the site;
iii)
nature of the contaminants;
iv) soil
characteristics; and
v) time
available for remediation.
Information
on the above factors is usually documented in the Contamination
Assessment Report (CAR) prepared during the site investigation
stage.
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