Groundwater from Fractured Granite and Metasedimentary Rocks in the West Coast of Peninsular Malaysia

Hard rock formations consisting of granite and metasedimentary rocks in Peninsular Malaysia, have been considered to be of poor aquifers. The map of shows the area underlain by hard rock as having poor to moderate potential for groundwater production (<230m(3)/well/day). This paper presents a finding of productive hard rock aquifers in the west coast of Peninsular Malaysia. Data from tubewell drillings carried out for industrial water supply were analyzed. It was found that the hard rocks could yield fresh water up to a maximum of 890m(3)/well/day. The wells were between 50 m and 200 m deep. High discharge rates of groundwater above 300m(3)/well/day were encountered from wells that penetrate major fracture zones. The hard rocks are generally fractured at various depths. Groundwater in interconnected fractures has a steady flow that sustains production during pumping tests and actual usage of the wells. This phenomenon indicates that the groundwater is being recharged by infiltration of rainwater through the overlying weathered rocks and soils. Tubewells in hardrock of West Coast of Peninsular Malaysia were found to have an average discharge rates of 343m(3)/well/day. However, deep tubewells penetrated only weathered granite, are generally non productive (<70m(3)/well/day). Limited fracture openings and restricted recharge areas are likely to be the reason for the low discharge. Clay particles in fractures were observed to be the factor for the low success rate and poor quality of the water particularly in metasedimentary areas.