Based on the previous experience with the development and
approval for CMP IV at East of Sha Chau for use as a confined disposal facility
for contaminated mud, monitoring of the dispersion of uncapped sediments during
major storm events, such as typhoons of signal 8 or higher, is considered as an
important objective of the study.
It is therefore considered necessary to include this post-storm
monitoring as part of the EM&A programme for the mud disposal facility.
The main design objective of the post-storm monitoring
programme is to determine whether there are any detectable changes in sediment
quality in the active pit area after a major storm. The post-storm monitoring programme will be mobilized within
one week of a major storm event (ie a minimum Typhoon Signal of No 8) and will
consist of regional sediment sampling as described in Section 4. However, in
order to be cost-effective, only the inorganic contaminants will be
analysed. Should any sediments
have eroded from the pits during a storm then the inorganic
"fingerprint" will be detected.
This therefore, removes the need for extra testing of the organic
contaminants. As it is unlikely
that water column effects associated with any dispersion of sediments from the
pit during the storm could be observed, water column monitoring is not
proposed. Similarly, trawl
sampling and tissue collection is not proposed due to the length of time
required for community structure or body burden effects to manifest themselves
after the storm event.
The regional sediment sampling programme (Section 4.7.2) has several key features
which are particularly applicable to addressing concerns associated with major
storms. The regional programme
contains stations on previously capped pits for the purpose of attributing whether
any identified contaminants are emanating from the previously capped pits. As the regional programme will be
routinely conducted twice in the wet and dry seasons, pre-storm (ie pre-impact)
data is likely to be available for all of the sampling stations. This will allow a statistical
comparison of pre- and post-storm datasets for the contaminants of concern
using statistical methods described in Section
4.5 and an assessment of the effects of the storm on ambient sediment
quality. In addition, through
analysis of pre-storm near field sediment datasets, it may prove possible to
derive a "fingerprint" or profile of sediment contamination
originating from the active pits.
If so, using information on the magnitude and direction of the storm,
examination on whether patterns of sediment contamination after the storm can
be attributed to the active pits should be conducted.
The field, laboratory and QA/QC procedures for sediment
sample collection after major storm events will be identical to those used for the
Regional Monitoring of Sediment Quality (Section
4).