Practical Solutions for Pumping Tests in Carbonate‐Rock Aquifers

Abstract

ABSTRACT The validity of standard methods of aquifer test analysis as applied to wells in consolidated‐rock aquifers has long been a subject of debate. In a recent investigation of the carbonate‐rock aquifer in northwestern Ohio, 76 wells were drilled and tested. Control and detailed analysis of such a large number of pumping tests afforded an excellent opportunity to evaluate various techniques. The data from each test were analyzed by the standard analytical methods. The results were viewed with varying degrees of confidence, but realistic values for hydraulic properties usually were obtained. Step‐test data were analyzed by three methods of which a graphical solution is preferred. It was believed in most instances that the CQ 2 . relationship gave an adequate approximation of well loss for the practical range of pumping rates. Once dewatering occurs, the hydraulic response of a given well may change drastically and well‐loss computations may give meaningless values. However, the analysis reveals the depth of major water‐yielding zones. Step‐test data can also be used to predict well yields when drawdown relationships are distorted by dewatering effects. Time‐drawdown data are preferred for the determination of hydraulic properties of carbonate‐rock aquifers. Data from the pumped well are considered valid for calculating aquifer transmissivity unless dewatering has occurred. Realistic values of transmissivity can be determined by using recovery data wherein distorted relationships caused by dewatering are minimized. The analysis of time‐drawdown data from a fully‐penetrating observation well provides what are believed to be the most reliable values for aquifer transmissivity and storage coefficient. It is best to employ regional concepts where possible and not become bogged down with minor inconsistencies in the test data.