AFFORDABLE GEOPHYSICAL INSTRUMENTS FOR USE IN DEVELOPING NATIONS

In developing nations water is often a critical resource. Reliable sources of clean water for small rural villages are limited and usually occur in the form of hand pumps from wells in shallow aquifers. Low-cost drilling methods such as hand digging, auguring or drilling with small drill rigs have limited depth penetration and are unable to penetrate hard rock. Therefore determination of depth to bedrock is critical in siting wells. Geophysical methods, such as resistivity, refraction seismic or time-domain electromagnetics have a long history of success in improving the probability of drilling a successful water well. But these methods require costly equipment, often exceeding $10,000. Although national hydrologists often have access to such instruments the device cost greatly restricts their use in rural regions. We are developing simplified resistivity and seismic instruments that cost less than $200. They have been effective in East Africa, Chad and Nigeria in determining depth to bedrock and the overlying aquifer. Excellent agreement is found when comparing results from our devices to data from expensive commercial instruments. Our latest resistivity device uses an inexpensive Arduino microprocessor to reverse current and to measure and display the current and voltage values. We have developed free software that will run on any PC laptop to invert the apparent resistivity values to give the resistivity depth profile. It is also possible to determine induced polarization though we have not completed development of the interpretation freeware. Our seismic refraction device uses a 24-bit USB stereo sound card for a laptop and a single geophone and our freeware records and displays the seismic signal. We also developed software that uses the USGS freeware (SIPT) to analyze the seismic refraction travel-time curve for a 2-dimensional subsurface profile. Ongoing research involves development of an inexpensive time-domain electromagnetic device. An entire geophysical water prospecting suite with a laptop and auxiliary freeware such as GRASS GIS and Open Office can be assembled for less than $800. We have published our methods in a free open-access online peer-reviewed journal. Thus the methods are readily available throughout the developing world and the response has been exceptional and gratifying.