INEXPENSIVE GEOPHYSICAL EQUIPMENT FOR WATER EXPLORATION IN DEVELOPING COUNTRIES

Pure water is in short supply in many developing nations especially in rural regions where wells are necessary. Finding reliable groundwater sources will significantly help development of these regions. For example, a Tanzanian national drill team used a small portable mud-rotary drill rig capable of penetrating 35 m in soft sediment to drill 50 wells, but 30% were dry. Commonly a low-permeable clay laterite of variable thickness overlies granite or gneiss bedrock. Often the aquifer is a weathered horizon just above the bedrock. Dry holes typically occurred either where i) the bedrock was so close to the surface that the water table, at least for the driest part of the year, was below the aquifer, or ii) the bedrock and overlying aquifer were deeper than the drill rig depth limit. As another example, in Chad a hand dug 2 m well dries up half-way through the dry season requiring women to walk 1.5 miles to fetch water. The well depth was limited because of bedrock.

Geophysical methods, such as resistivity and seismic refraction, can readily determine depth to bedrock prior to drilling and therefore would significantly improve well success rate. However these instruments are unavailable to grass-roots efforts to provide water because of cost (>$10,000). There is a need for inexpensive geophysical instruments that can determine depth to bedrock quickly and simply, and for supporting software for data interpretation. We are therefore developing geophysical instruments that cost less than $200 and free software. Our resistivity device is powered by a car battery and the seismic refraction instrument uses only one geophone. These instruments are easily constructed and inexpensive allowing widespread use by drillers and NGO's. We have trained workers in Tanzania, Chad and Nigeria to use this equipment. A small $400 laptop computer can use our software to collect and interpret both resistivity and seismic data. It can also use free GIS software to display satellite images for recognition of moist regions, lineaments or fractures as well as to perform essential reporting functions. With this equipment a suite of geophysical groundwater prospecting devices can be assembled for less than the cost of a hand auger. Initial experiences in Tanzania, Chad and Nigeria are positive and the nationals have been effective in use of the equipment.