Rehabilitation of abandoned non-hazardous tailings ponds

Sand quarrying left behind more than 400 tailings ponds in Bedok, Tampines and Pasir Ris in Singapore. A large quantity of non-hazardous tailings consisting mostly of clays from the quarrying activities over decades was present in these abandoned ponds. Because of the high proportion of montmorillonite, the clay in the tailings ponds remained in suspension for years and did not settle. A large area of land meant for housing development was sterilised as a result. Before any development could take place, the sterilised land had to be rehabilitated and the tailings had to be disposed of. Studies were carried out to understand the characteristics of the tailings ponds and their contents. Various alternatives were investigated for the rehabilitation with the purpose to arrive at an environmentally acceptable and the most economical solution to this huge problem. The development of Tampines new town was substantially completed in the 1990s, housing half a million people. To date, after 30 years, there are no reported foundation and settlement problems related to the rehabilitation works. There is also no adverse environmental impact reported for disposing of the tailings. Valuable lessons and experience has been gathered in the process of a successful rehabilitation and are presented herein.