9    Impacts of Major Storms


9.1    Background


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. 


9.2    Sampling Design


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).