Characterization of the Lower Quebrada de Oro, Mayagüez aquifer system using surface geophysical techniques

Abstract

Detailed information on subsurface conditions is essential for the development and management of ground‐water resources and the characterization of sites. The objective of this research project is to compare three geophysical methods, Multi‐Channel Analysis of Surface Waves (MASW), Electrical Resistivity (ER), and Ground‐Penetrating Radar (GPR) to identify near‐surface geological features which control ground water flow. MASW is a seismic refraction method which is effective in estimating the saturated thickness of aquifers and the thickness of beds based on a material's elastic properties and density. ER measures the electrical properties of rocks which depend primarily upon the amount of water retained in the rock and the salinity of the water, which provides more information about the porosity of the material. GPR is an electromagnetic (EM) sounding technique which produces an underground cross‐sectional image of the subsurface features in contrast with the surrounding medium. This will be utilized to establish the depth of the water table and the topography of the bedrock. All three methods present different advantages and disadvantages, which is why a comparative approach is necessary to target individual goals posed by this study. This ongoing study is being performed on an valley adjacent to the Civil Engineering department at the University of Puerto Rico, Mayagüez campus in order to better understand the interactive systems between alluvial deposits, weathered bedrock, and ground water flow in the region. The site is presently used as an Environmental and Water Resources field laboratory with both pumping and observation wells installed. A geologic characterization of this aquifer has created a better understanding of the interactive systems taking place in this drainage basin and generated profile images of the environment from which water is being extracted.