ASSESSING THE VULNERABILITY OF DRINKING WATER WELLS TO PATHOGENS IN TULUM, QUINTANA ROO, MEXICO

Little is known about the extent of pollution in groundwater that occurs in the Yucatan Peninsula, however with rampant growth in many areas throughout the peninsula there is a potential to release from wastewater a large number of contaminants including pathogens. Disposal of wastewater has been a major concern with the current practice to dispose of wastewater directly in the ocean with little or no treatment. While done in communities close to the ocean, much of the rural population without access to the ocean dispose of wastewater in open pits above the fresh groundwater or inject it into the saline water below the freshwater lens. Studies have shown that rural waters in this area can have high fecal coliform concentration but research has not been done on the sources of this fecal contamination (human or livestock). Persistence of pathogens in groundwater is common and can be particularly acute in tropical karstic environments where high permeability of the rocks and the lack of top soil permit the rapid transport and perseverance of these compounds and organisms. The objective of this research project is to sample a series of wells that range from protected to impacted in the Tulum region to determine the occurrence and persistence of pathogens then link this information to hydrogeological and geochemical (sulfur cycle) setting. Three wells were tested near Tulum, Quintana Roo, Mexico for possible pathogens: a municipal well that has been shut down by the city of Tulum (TLMP1), a rural well (CCRP), and a private commercial well (BPPT4) that has also been shut down. Membrane filtration method and the IDEXX technique were used for the quantification of total and fecal coliforms along with E. coli. Qualitative isolation in reference to the source of the coliforms (bovine, swine, or human) is assessed by means of bacteriodes testing. In comparison to each other, CCRP and BPPT4 were moderately to heavily contaminated while TLMP1 exhibited nearly non-existent levels of E. coli or fecal coliforms. Further testing of wells within and surrounding Tulum will be conducted in the summer of 2009 to receive a more accurate assessment of the region's hydrogeology and how bacteria related to intestinal disease moves through the area's groundwater supply.