9706203 Perry This is a proposal to study the complex but largely unconfined carbonate karst aquifer system of the northern Yucatan Peninsula, Mexico. Over much of its extent this aquifer system is extremely permeable with the result that a saline intrusion penetrates at least 100 km inland. The resulting dispersion zone produces important rock-water interaction and affects water quality in the overlying fresh water lens. A principal activity under this grant will be measure water levels (with respect to mean sea level) and seasonal water level changes throughout the northwest Yucatan Peninsula. These measurements are difficult because of the high permeability and extremely low water table gradients on the peninsula. At the time, they are necessary inputs to any meaningful aquifer models. Approximately six water level gages will be installed for long-term water level measurements. Water samples will be taken for radium, barium, and stable isotope analysis. Radium and barium analyses will lead to a better understanding of groundwater discharge into the Gulf of Mexico, and stable isotope measurements will help determine evapotranspiration. The ultimate objective of this work is to compile the information necessary for a complete water budget for the northern Yucatan Peninsula.
