GEOPHYSICAL SURVEYS TO MAP KARST CONDUITS, THE SALT/FRESHWATER INTERFACE AND WATER TABLE ALONG THE RUTA DE LOS CENOTES, YUCATÁN PENINSULA, MÉXICO

The Yucatán Peninsula (YP) is a vast limestone platform with a surface area of about 165,000 km2 (Bauer-Gottwein et al., 2011), and it contains one of the most developed and complex karst systems in the world. This natural wonder is undergoing an increasing pollution threat due to rapid economic development (Vuilleumier et al., 2012) and heavy groundwater pumping. This research employed various geophysical methods along the Ruta de los Cenotes to assist groundwater scientists addressing this threat. Specific targets included mapping the water table, freshwater/saltwater interface and identifying karst conduits that are contaminant pathways from the land surface to the aquifer (Carpenter et al., 2013). Schlumberger resistivity soundings, calibrated by water-level measurements in wells and cenotes, suggests the water table varies from 1 to 6 m below ground surface along the Ruta. Some Schlumberger soundings underestimated the depth of the saltwater/freshwater interface whereas a Wenner-array profile and time-domain electromagnetic (TEM) soundings accurately estimated the interface depth, which deepens from 2.6 m below ground surface at the coast to as much as 45 m at the wellfield 27 km along the Ruta. SP surveys also revealed karst conduits near Well (Pozo) 55.