Some remarks on ground water conditions and use of geophysical instruments in hard rock (Crystalline Rock) areas based on findings from the WHO/UNICEF assisted village water supply programme in India

Some states in India such as Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, Mysore and Tamil Nadu are located in hard rock areas where intensive drilling is necessary to provide wells. In 1970 the Government of India, assisted by UNICEF and WHO, initiated a programme for the provision of potable water to 12,000 villages in these hard rock, water scarce areas. Some 18,000 wells were to be drilled under this programme and the majority fitted with handpumps. As of January 1973, 9,000 wells had been drilled. In this paper, aimed at geologists and engineers working in the programme, some of the findings and conclusions regarding the use and usefulness of the geophysical surveying equipment provided by UNICEF is discussed as well as some of the various groundwater conditions found during the drilling activities. An assessment of geophysical instruments is made including resistivity methods and instruments, considered the most useful for locating good well sites in this programme; magnetometer methods and instruments, most useful in granite areas; seismic methods and instruments, with limited use due to cost and untrained staff; and electrial well loggers, considered a versatile instrument for the evaluation of geological and hydrogeological parameters. The paper also comments on ground-water hydrogeology based on findings from drilling activities and data collected during field trips. A comparison of the yield from open wells and bore wells is made based on variations in yield due to depth and type of rock. Finally, the paper evaluates the efficiency of the various drill rigs used considering such factors as penetration rate of various drill bits and hammers contra various rock materials and running costs per depth drilled. The paper is supported by a series of graphs.