Sasol groundwater remediation.
Fifteen boreholes were drilled over a period of two years to delineate the free phase product (FPP) and dissolved plumes and to sink FPP recovery points. The FPP recovery also took place over two years. Due to the fractured nature of the bedrock, the FPP recovery proved slow and inefficient, but the contamination could also not be physically removed, due to the depth at which the FPP occurred. The FPP plume typically migrated down to the groundwater table and then migrated laterally, only affecting a zone of c. 1 m above and below the water table. The risk drivers included the receptors (river and groundwater), gradient (if it rains the gradient changes and contamination migrates), and on-going contamination (new contamination linking up with existing contamination). The site cannot be remediated whilst operational and therefore the risks must be managed as best possible. This is being done by reducing the volume of the FPP plume to make it less mobile. A risk-based corrective action (RBCA) Tier 2 assessment was done on the dissolved contamination and it suggested that, at current conditions, the river is not at risk. The area is zoned as commercial and there are no groundwater users. On-going monitoring of FPP thicknesses and water quality is required, coupled with occasional FPP recovery when the plume starts to migrate.
