Renewable energy is increasingly being viewed as one possible answer, particularly where existing road and electricity infrastructure already exists. Liefferink said renewable energy had considerable potential to become one of the most valuable post-mining land uses in the country. She noted that there are thousands of hectares of disturbed mining land, particularly in the Northern Cape, Mpumalanga, Limpopo, Gauteng and North West. At Sishen, the biggest challenge was establishing confidence in the stability of the 80m-high rehabilitated waste rock dump, where differential settlement was an inherent consideration. Mason said the biggest challenge was establishing confidence in the stability of the 80m-high rehabilitated waste rock dump, where differential settlement was an inherent consideration.