The Vanderbijlpark plant is one of the world’s largest inland steel mills, the largest producer of flat steel products in sub-Saharan Africa and has been operational for over 40 years. Back then, environmental concerns were not as strong a concern for either industry or the public as they are today and there was also no appropriate legislation to effectively safeguard the environment. One consequence of this was the gradual accumulation of 40 million m3 of metallurgical waste in a slag heap that extended over 170 hectares, which impacted on groundwater resources.
By the end of the last decade the remediation of the old waste disposal site was a key priority for ArcelorMittal South Africa, mainly because it was the right thing to do and because new environmental legislation meant that the site was only licensed for waste disposal until the end of 2010. Remedial work would have to be done to regenerate the area and mitigate environmental contamination.
The first phase of remediation work began in September 2009, and covered about a third of the total old waste disposal site area. Over the next 18 months this area was cleaned up and shaped, and a number of storm-water canals dug to ensure rainwater ran off the site in a managed way. At the same time, remediation of a facility comprising a number of wastewater dams covering an 80 hectare area, commenced. Organic and inorganic waste was safely removed and remediated wherever possible, and the slope of the site re-shaped to ensure that storm water did not collect in stagnant pools. The final phase involved enriching the earth and remediated soil with compost and seeding the area with indigenous grass species.
This project used a number of innovative techniques. For remediation of the Dam 10 facility, historically used for the storage and evaporation of waste water, heavy-duty machines resembling compost turners were used for mixing the compost and moisture with contaminated soil in order to promote bacterial activity to assist in the decomposition of harmful substances, whilst simultaneously breaking agglomerations.
These techniques represented a steep learning curve for the newly-established Environmental Management Team at the site. A lot of useful knowledge is being accumulated for the next phase of work which entails the remediation of other legacy dams on site, once used as evaporation facilities for surplus waste water, as well as initiating the remediation process of Phase 2 and 3 of the old waste disposal site, which is now underway.
Capping of the old waste site marked the end of an era for the unsightly disposal facility. Apart from the aesthetic benefit of this remediation option, capping of the site has mitigated the advancement of the historic groundwater contaminant plume. The leachate generation rate from the disposal site has been substantially reduced. This is attributable to the capping system which inhibits the seepage of rain water through the waste body. The capping and storm water management interventions direct any rain water off the disposal site, thereby averting contact with the waste and generation of additional leachate. The final layer of the capping system comprises a carefully selected palette of grass species which provides a habitat for numerous insects and small animals.