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We have utilized the California Department of Public Health Water Quality Analyses database, with approximately 250000 results for methyl tert-butyl ether (MTBE), to evaluate the extent of MTBE in public water supply wells in California and how these impacts have changed over time. These data show that MTBE has never been detected in >98% of 13183 public water supply wells that have been tested for MTBE. The number of wells with first-time detections of MTBE peaked in 2000 and has decreased by 80% since that time. For the 188 wells in which MTBE has been detected at least once, MTBE was not detected in the most recent analysis of 142 of these wells. Tetrachloroethene, another common groundwater contaminant, has been detected more commonly, and new detections are declining more slowly. These results indicate that the impact of MTBE on public water supply wells has peaked and is declining.

Aquifer restoration in the United States is recognized as a technically challenging objective when dense non-aqueous phase liquids (DNAPLs) are present (1). In fact, only a few aquifers impacted by DNAPLs have been restored. Factors that have typically contributed to the lack of successful aquifer restoration include the chemical properties of the DNAPL, the physical properties of the aquifer, the absence of cost-effective technologies, and an incomplete or inaccurate development of a conceptual hydrogeological model for the site. In Latin America, environmental studies historically have been related to biological quality of surface water and groundwater. Recently, the U.S. and Canada have experienced an increased influx of foreign students and professionals interested in studying specialized courses in environmental engineering, or participating in conferences. This exposure to current topics has strengthened the awareness of these professionals regarding groundwater contamination from gasoline-derived compounds and chlorinated solvents. As a result of this increased awareness, Latin American hydrogeologists and environmental regulators have been able to recognize the potential problems that could result from DNAPL spills that may impact groundwater and have learned to approach them using locally available technology and resources. A case study of such an example is presented below.