The management of contaminated sediment in Hong Kong

Many years of uncontrolled discharge of sewage and industrial effluent have resulted in serious contamination of much of the sediments underlying inla nd and nearshore coastal waters in Hong Kong by potentially toxic heavy met al and trace organic pollutants. Much has been achieved to improve control of this pollution at the source and prevent further deterioration. Neverthe less, comprehensive environmental assessment and management measures are re quired to ensure that any unacceptably contaminated sediment that must be d redged to facilitate intrastructural development is safely handled and disp osed of It is estimated that some 50 Mm(3) Of sediment classified as unacce ptably contaminated may require dredging and special management elsewhere o ver the coming 10-year period. To facilitate improved decision making about the most appropriate disposal options for dredged sediment Hong Kong has r ecently implemented a new sediment quality assessment framework under which information on the biological activity of contaminated material is conside red in addition to data on chemical composition. Dredged sediment classifie d as unacceptably contaminated has been disposed of at a contained disposal facility at East Sha Chau since 1992. To date over 20 Mm(3) of sediment ha s been placed into seabed pits that are subsequently capped with clay. The site is subject to a rigorous monitoring programme that has clearly demonst rated its environmental acceptability.