Lindsey, B., J. Ayotte, B. Jurgens, and L. DeSimone.
Science of the Total Environment 579:579-587(2017)

MTBE use in the U.S. peaked in 1999 and was largely discontinued by 2007. Based on a national survey of wells selected to represent ambient conditions, temporal changes in MTBE concentrations in groundwater were evaluated in the northeastern United States, an area of the nation with widespread low-level detections of MTBE. Six well networks, each representing specific areas and well types (monitoring or supply wells), were each sampled at 10-yr intervals between 1996 and 2012. Concentrations were decreasing or unchanged in most wells as of 2012, with the exception of a small number of wells where concentrations continue to increase. Statistically significant increasing concentrations were found in one network sampled for the second time shortly after peak MTBE use, and decreasing concentrations were found in two networks sampled for the second time about 10 yr after peak MTBE use. Modeling and sample results showed that wells with young median ages and narrow age distributions responded more quickly to changes in the contaminant source than wells with older median ages and broad age distributions. Well depth and aquifer type affect these responses. Regardless of the timing of decontamination, all of these aquifers show high susceptibility for contamination by a highly soluble, persistent constituent.