Results of pumping tests in the Deccan Trap Basalts of Central India

Abstract

The Satpura Hills Region of Central India is characterized by hilly to mountainous terrain, plateaus, and gently undulating country. The area is underlain by basalt, crystalline rocks and sandstone. Basalt rocks of Cretaceous age outcrop over about 60% of the area. During the past 14 years the authors, through their association with the Evangelical Lutheran Church (ELC) Water Development Project, have been involved in the development of groundwater resources for village, town, agricultural, and industrial uses. To date, over 700 wells have been drilled in the basalt rocks and aquifer pumping tests have been run on more than 200 wells. As a result of the controlled testing and detailed analysis of these pumping tests, it was possible to evaluate the applicability of standard analytical models for the analysis of pumping tests in basalt-rock aquifers. Step-drawdown pumping tests were run to determine the components of drawdown due to aquifer loss and well loss. Step-test data were analyzed by Rorabaugh's (1953) method and by a graphical method. The results indicate that well losses comprise a significant component of drawdown in most wells and these losses are probably a result of non-Darcian flow in the aquifer adjacent to a pumped well. Constant-rate pumping tests were run to determine aquifer transmissivity and specific capacity. Time-drawdown data were analyzed by the Cooper-Jacob (1946) approximation to the Theis (1935) equation and recovery data were analyzed by the residual-drawdown method. Aquifer transmissivity ranged over two to three orders of magnitude from less than 10m 2 day −1 to more than 300m 2 day −1. Pumping test results often enabled the prediction of aquifer conditions such as limited aquifers, recharge boundaries and aquifer dewatering.