Application of Hagedoorn’s Plus-Minus Method to Hydrology Study

Abstract

The Memphis aquifer has been the major source of water for the City of Memphis municipal, industrial, and commercial uses for the past 100 years, and is considered to be among the highest quality water reservoirs in the nation. Above the Memphis aquifer are the confining unit (aquitard) of the Memphis aquifer and the surficial aquifer (Figure 1). The surficial aquifer is exposed to the surface and is prone to pollution due to industrial and human activities. The potential for contamination of the Memphis aquifer is exacerbated in areas where the aquitard is missing or thin. Recent studies indicated that the drinking aquifer might be at risk for contamination due to aquitard breaches existing in the confining unit of the Memphis aquifer. Aquitard breaches in the Memphis area have been identified through the correlation of stratigraphic picks from borehole data (Parks and Mirecki, 1992). The lack of uniform data coverage has restricted the study of breaches in Shelby County to areas proximal to the well fields. Although accurate, direct and reliable, the study does not provide crucial information about aquitard breaches, such as their extent, orientation, origination, and matrix characterization. Indirect methods (e.g. shallow seismic methods) can provide critical information that can help identify the possible causes responsible for the formation of the breaches (Ge et al., 2010, Part II). In this paper, the Hagedoorn’s (1959) plusminus method was applied to the seismic refraction data acquired in a walkaway test to map the top of the confining unit and identify possible aquitard breaches.