Heritage Cases

The Duvha Power Station produces wet ash that gets pumped into an Ash Dam. The settled water is then decanted to a Low Level Ash Water Return Dam (LLAWRD), before it is pumped back to the station for reuse. A groundwater study revealed that the Ash Dam is experiencing water seepage towards the Witbank Dam, leading to groundwater contamination and possible contamination of the Witbank Dam in future. Polluted seepage is also emanating from the LLAWRD and High Level Ash Water Return Dam (HLAWRD). A solution is required to prevent the groundwater seepage as Duvha Power Station’s WUL states that “Any water containing waste or any substance which causes or is likely to cause pollution of a water resource must be prevented from entering any water resource, either by seepage or natural flow.” The Department of Water and Sanitation (now the Department of Human Settlements, Water and Sanitation (DHSWS) thus instructed Eskom to mitigate and prevent groundwater pollution. The construction of subsoil groundwater seepage interception drains at the Ash Dam, LLAWRD and HLAWRD, as well as a Raw Water Dam, is proposed to mitigate seepage from the Ash Dam and prevent contamination of the Witbank Dam. Seepage interception drains are deemed to be the only possible solution to prevent contamination of Witbank Dam. The advantage of the system is that the seepage water will be pumped and re-used by the power station, and thus polluting of the Witbank Dam will be avoided. In order to limit groundwater seepage from the existing Ash Dam, as well as the HLAWRD and LLAWRD, it is proposed to construct cut-off interceptor drains along sections of the perimeter of each of these dams and to convey the intercepted water to designated discharge points. The seepage interception drains will be constructed with manholes and perforated pipes. A float level switch to pump the water back to the dam will have to be installed and the process will continue as a cycle. This same system will be used for the LLAWRD and HLAWRD.