Using Airborne And Ground Electromagnetic Data To Map Hydrologic Features In Everglades National Park

Ground-water flow requires the development of a three-dimensional model of aquifer properties<br>and boundaries. This task has been traditionally accomplished through drilling and water-quality<br>sampling in wells. While the data obtained by these means are highly accurate, they represent only a<br>very small fraction of the total model volume. Furthermore, in areas where drill sites are limited due to<br>difficult access, model geometry obtained by interpolating between widely spaced wells may be<br>somewhat inaccurate.<br>Helicopter electromagnetic (HEM) resistivity mapping provides high density data coverage over<br>large areas, including those where access is difficult. Interpretation of these data poses other problems<br>due to noise and errors in the HEM data. However, when combined with ground electromagnetic<br>soundings and limited well information, hydrologic features can be mapped with more certainty than<br>possible by interpolating between widely spaced wells.<br>As an example, we present a study from Everglades National Park, Florida. Data consist of an<br>HEM survey, time-domain electromagnetic soundings, well logs, and water quality samples. The<br>interpretation provides information on the depth to the base of the aquifer, the extent of saltwater<br>intrusion, and a three-dimensional picture of water quality in the aquifer.