Mannum Limestone outcrops along 300m on the left bank of a proposed artificial lake at Rocky Gully, Monarto. A seismic refraction survey and eight rotary drill holes tested the extent of the limestone and the possibility of leakage from the lake. The base of the limestone was close to lake top water level, with Kanmantoo Group schists underlying the limestone. Leakage from the lake would thus be minor.