Estimating the hydraulic parameters of the Arbuckle-Simpson aquifer by analysis of naturally-induced stresses

Groundwater studies often involve the use of either analytical or numerical models to solve problems. For a groundwater model to produce a reasonable prediction, model parameters should represent the physical aquifer system. Most frequently, aquifer parameters are determined by pumping tests. Pumping tests may be problematic, especially when the aquifer water quality is an issue. As an alternative, this study employed the analyses of water-level fluctuations that are induced by natural stresses (earth tides and atmospheric pressure changes) to characterize an extensively fractured and faulted thick carbonate aquifer. Earth tides are known to influence water levels in wells penetrating confined aquifers while atmospheric pressure changes influence unconfined aquifers. The analyses used data from the Arbuckle-Simpson aquifer which is located in south-central Oklahoma.;In the first part of this study, two types of harmonic analyses were employed to determine aquifer type: (1) signal identification and (2) amplitude and phase angle determination. Portions of the Arbuckle-Simpson aquifer responded as each type of aquifer. The results demonstrate that the technique is an accurate and low-cost approach to determine the aquifer type. The barometric efficiency was commonly determined by the Clark method. The method gave inconsistent and, in many instances, physically unrealizable results in previous research. The second part of this study introduced a new method (the Rahi method) to determine the barometric efficiency. The method was tested using data from the Arbuckle-Simpson aquifer and evaluated against data from other research and produced results that were consistent and within the expected ranges reported in the literature. The average barometric efficiency of the aquifer was 54%. The specific storage was estimated using the amplitude of water-level fluctuations and the amplitude of the tides that produced them. The specific storage and the barometric efficiency results were utilized to determine porosity of the aquifer. The results revealed an average specific storage of 5.6E-8 cm -1 (1.7E-6 ft-1) and an average storage coefficient of 6.3E-3 which is comparable to values obtained by previous research. The resulting porosity was approximately 15 percent.