"The Patiño aquifer is described as easily accessible and vulnerable to pollution. It shows moderate productivity, good recharge as well as in tensive exploitation. The main threats to its sustainability include a con tamination risk, which is associated with inadequate sanitary sewerage and other pollution sources as well overexploitation and salinization of the west and north boundaries, which are related to the reduction of the recharge area and intensive use (evident in the depletion of groundwa ter level), related to the accelerated urbanization process. The present work is the first that an alyzes the levels of MTBE and degradation products in South American groundwater wells of any kind. This study fills the gap that no data on MTBE levels in the groundwater is available for this region."CONACYT - Consejo Nacional de Ciencias y TecnologíaPROCIENCIA