A deep palaeovalley (ranging between 150 and 170m in depth) extends along the length of the LSOP area, infilled with predominantly lacustrine clays and sand interbeds of Tertiary age. Seven hydrostratigraphic units have been identified comprising:
• An extensive surficial unit of mixed alluvial/lacustrine sediments comprising:
- Approximately 15m of sandy loam, including local laterite and evaporite deposits, overlying the entire lake area.
- An upper, low permeability, clay-rich unit with minor sand horizons extending across the entire lake area.
- Local areas of permeable calcrete and / or silcrete.
• An upper sand aquifer unit at the base of the surficial unit, occurring at depths ranging between 35 and 70m, with thicknesses varying between 1 and 12m and anticipated to be continuous both along the length and across the width of the palaeochannel.
• A lower clay aquitard comprising puggy lacustrine clay with minor sandy interbeds. Adopted permeability ranging between 0.07 and 0.8 m/d
• A mixed aquifer unit comprising interbedded sand and clay.
• A basal sand aquifer located along the length of the paleochannel and encountered in 25 drill holes. Although predominantly of Tertiary age, in places, there are thin remnants of Permian glacial deposits (conglomerates and diamictites) overlying the Archean basement, which have also been included in this hydrogeological unit.
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