Assessing fecal contamination in groundwater from the Tulum region, Quintana Roo, Mexico

Underlying the Yucatan Peninsula in Mexico is a highly permeable fractured karst limestone that increases the potential for rapid transport of microbial and chemical contaminants from the surface to underlying aquifers. With rampant growth in many areas throughout the peninsula there is a potential to release from wastewater a large number of contaminants including pathogens. The objective of this research project was to test multiple groundwater samples near Tulum, Quintana Roo that ranged from protected to impacted to determine the occurrence and source of fecal contamination and link this information to the hydrogeologic setting. The membrane filtration and most probable number (MPN) methods were used for the quantification of total coliforms and E. coli. Testing for Bacteroides indicated that fecal contamination was indeed occurring in the region's groundwater. Bacteroides levels were highest in water samples with known human impact, averaging 1.0 x 106 and 4.4 x 103 molecular markers/100 mL across impacted and non-impacted source waters, respectively. Geochemical data indicates a saline water intrusion with possible seasonal trends of meteoric water influx and increased microbial metabolism. We determined that the fate and transport of fecal indicators within the karstic system of the Yucatan Peninsula will aid in identifying point sources of groundwater pollution which is knowledge that is vital to the design of remediation strategies for this seriously degraded aquifer.