Development and validation of a low-cost DC resistivity meter for humanitarian geophysics applications

Abstract

One of the most challenging and wide-spread global humanitarian issues is an insufficient access to safe drinking water. While the use of geophysics can improve drilling success rates for safe drinking water as well as provide information about aquifer structure, geophysical surveys themselves can be prohibitively expensive. The recent development of low-cost computer microcontrollers and the widespread availability of cheap electronics components raise the possibility of developing and using do-it-yourself (DIY) low-cost geophysical instrumentation with open-source designs and software solutions to avoid costly geophysical instrumentation. An existing design of a low-cost DC resistivity meter system was altered to improve the reliability and operability. A Raspberry Pi-based data-logging system was developed to improve the functionality and usability of the system, as well as the integrity of the acquired data. Numerical modeling and physical tests at Colorado School of Mines (CSM) demonstrate that the system is more robust than previously published low-cost designs and works in a diverse range of geological environments. The low-cost DC resistivity instrument was used in a Geoscientists Without Borders (GWB) project jointly run between researchers from CSM and Université d'Abomey-Calavi (UAC), Cotonou, Benin. The GWB project involved instructing UAC students in the basics of hydrogeophysical surveying including the use of the DC resistivity method, the construction and validation of two low-cost DC resistivity meters, and the subsequent use of the instruments in fieldwork aimed at better characterizing a local aquifer used as a potable groundwater source for communities in the Cotonou region. The low-cost instrument was successfully used alongside a commercial resistivity meter to acquire a dataset imaging a 2D section in the Ouédo pumping field. An analysis of the redesigned instrument shows that the cost is a fraction of the price of a commercial resistivity meter without a significant impact on data quality. Future design improvements are outlined to expand capabilities for multichannel and time-lapse surveying.