5.                  SEDIMENT CONTAMINATION

Introduction

5.1              As presented in Section 6 of the EIA Report, dredging works for pipe laying for the submarine outfall would have some impact on the marine environment. Dredging of seabed can release sediments, hence increasing suspended solids concentrations. Contaminants originally trapped in the sediments, if any, may also be released into the water column during the dredging process.

5.2              It is the Contractor’s responsibility to ensure that the sediment are dredged, transported and disposed of in a manner that minimises the loss of contaminants either into solution or by resuspension. Mitigation measures to minimise potential environmental impacts are recommended below.

Mitigation Measures

5.3              The basic requirements and procedures for dredged mud disposal are specified under the WBTC No. 34/2002.  The management of the dredging, use and disposal of marine mud is monitored by the MFC, while the licensing of marine dumping is the responsibility of the Director of Environmental Protection (DEP).

5.4              The uncontaminated dredged sediment will be loaded onto barges and transported to the designated marine disposal site. Appropriate dredging methods have been incorporated into the recommended water quality mitigation measures including the use of closed-grab dredgers and silt curtains.  Category L sediment would be suitable for disposal at a gazetted open sea disposal ground.

5.5              During transportation and disposal of the dredged marine sediments, the following measures should be taken to minimize potential impacts on water quality:

·        Bottom opening of barges should be fitted with tight fitting seals to prevent leakage of material. Excess material should be cleaned from the decks and exposed fittings of barges and hopper dredgers before the vessel is moved.

 

·        Monitoring of the barge loading should be conducted to ensure that loss of material does not take place during transportation. Transport barges or vessels should be equipped with automatic self-monitoring devices as specified by the DEP.

5.6              The implementation for the recommended sediment contamination mitigation measures is presented in Appendix A.