Groundwater in crystalline rocks and climatic conditions

The yield and quality of aquifers of the Precambrian crystalline basement rocks of the states of Sao Paulo (humid climate) Parafba (semi-arid climate) in Brazil and southern Ghana (semi-humid climate) in West Africa were studied, using data on about 2000 wells. These aquifers are discontinuous in character with occurrence of water in fractured rock zones, lithological contacts and horizons of weathered rock masses. The average yield of wells in Parafba is 2.16 m3/h and come mainly from fractured zones. In Sao Paulo and Ghana where water is obtained from both weathered mantle and fresh rock the yields are 15.70 m3/ h and 4.25 m3/h respectively. The average total dissolved solids (TDS) of water in Paraiba wells is 4000 mg/I with 5% less than 500 mg/I, while in Sao Paulo and Ghana more than 90% of the waters have TDS less than 500 mg/I.