Afteruse development of former landfill sites in Hong Kong

Landfill is one of the major methods in disposing of municipal solid waste (MSW) in Hong Kong. There are now 13 closed landfill sites in Hong Kong, and a restoration program has been launched since 1999 to transform the closed landfill sites back into recreational area. The MSW underneath these closed landfill sites will biodegrade slowly and gradually, releasing toxic gases and leachate. As there have only been a few afteruse development ever completed in Hong Kong, this paper describes the consideration in planning and design of two former landfill sites in Hong Kong – Ngau Chi Wan (NCW) and Jordan Valley (JV) landfills, in particular a discussion on the MSW settlement. Various models in predicting the long-term MSW settlement have been available. This paper reviews the applicability of these models to predict MSW settlement. However, as the predicted settlements can be significantly in error, they need site-specific calibration and validation. This paper therefore presents the settlement monitoring data in these former landfill sites over the last 30 years, and suggests modifying the Bjarngard and Edgers’ method for estimating this long-term settlement as well as the effect of additional surcharge due to afteruse development. Based on the regression of these data, compression indices Cce and Cα at different stages of the settlement in the modified method have been calibrated and validated.