Environmental Impacts (# 67)

Managing soil contamination in South Africa

When a source of soil contamination is being turned into an essential nutrient in South Africa, faster really is better.

Because of the location of the source of contamination on a watershed, hexavalent chromium plumes extend in two directions.

In 1999, professionals who are now with Golder's Johannesburg office started work at the site of a former chromium chemicals plant where toxic hexavalent chromium (Cr6+) had leached into the soil. Investigations showed that two plumes of Cr6+ impacted groundwater had migrated some 1.5 to 2 kilometres (0.9 to 1.2 miles) beyond the property boundary. By drilling boreholes and pumping out the groundwater, it was possible to contain the spread of contamination and start shrinking the size of the plumes. Doing this, however, would have taken roughly 40 years to clean up the water to meet South African government standards.

Accordingly, Golder staff looked for ways to speed up the process. By applying clean water at the surface to flush the targeted compounds into the groundwater and drilling more wells to fully capture the impacted water, the treatment time is being reduced from an estimate of 40 years to 10 years.

Golder determined that the hexavalent form of chromium would be converted to trivalent chromium by redirecting the Cr6+-bearing groundwater into the local sewage system. As the municipality processes the sewage sludge into agricultural fertilizer, a hazardous material is being transformed into something beneficial.