Identifying And Assessing Ground Water In The Lower Rio Grande Valley, Texas, Using Airborne Electromagnetic Induction

We are applying airborne and ground-based geophysical methods to identify potential groundwater<br>resources and assess their quality in two 260-km2 areas in the Lower Rio Grande Valley,<br>Texas. In this drought-prone and rapidly growing region, heavy agricultural, municipal, and industrial<br>demand for fresh water overburdens limited surface water supplied by the Rio Grande. Primary<br>data for this study are two electromagnetic induction surveys flown using time-domain instruments<br>carried by fixed-wing aircraft. Supporting data used to help interpret the geophysical<br>data include ground-based geophysical measurements, water quality data from existing wells, geophysical<br>well logs, and geologic maps and cross sections showing the lateral and vertical distribution<br>of hydrologic and stratigraphic units in this coastal plain setting. We are analyzing these data<br>within a geographic information system to interpret late Cenozoic geologic environments, analyze<br>the relationship between water quality and ground conductivity, and display subsurface images<br>showing likely availability and suitability of ground water at various depths. If successful, state and<br>local agencies will use results from this study to guide development of supplemental ground-water<br>resources.