The use of radioisotope tracers to identify the location of seepage areas in a dam

A novel radioisotope tracer technique has been used to locate seepage areas in the Pedu Dam, Malaysia, a 61 m high rock-filled dam with an upstream asphalt/bitumen membrane. The radioisotopes were 198Au (2 GBq) and tritiated water (200 GBq). The seepage areas were located using 198Au adsorbed onto a fine powder with a particle size selected to control the rate of sedimentation in water to 1 m/h. A submerged injection device was constructed to allow the tracers to be injected at a constant height of 5 m above the bitumen membrane. The device was towed at a constant speed with a constant rate of injection of the mixed tracers to give an even distribution of the tracers over the ∼ 15,000 m2 of dam face. Because of operational difficulties it took three days to inject the tracers. The distribution of the 198Au labelled sediment over the bitumen membrane was measured in one day and the data were used to build up a picture from which potential seepage areas were identified. Subsequent brine testing confirmed the presence of all but one of the seepage areas by identified 198Au. The use of this tracer technique for dam seepage location was a significant improvement over previous methods. All the seepage points were located in under one week whereas brine testing of this area would have taken two years. (author). 15 refs, 4 figs