Concentrations, sources, and fate of the gasoline oxygenate methyl tert-butyl ether (MTBE) in a multiple use lake

Discovery of the fuel additive methyl tert-butyl ether (MTBE) in drinking w ater supplies is of concern to public health officials, water suppliers, an d the public. Despite recent policy decisions, few published studies exist on the concentrations, sources, and fate of MTBE in surface waters. The pur pose of this study was to determine(1) the relative contribution of motoriz ed watercraft as a source of MTBE, (2) its seasonal distribution, (3) loss from the water column, (4) the extent of Vertical transport, and (5) its pe rsistence between yea rs; this work was done in Donner Lake, California, a multiple-use lake in the Sierra Nevada Mountains. MTBE measurements were ma de at 9 individual depths from surface to bottom on 16 dates. Recreational boating was the most important source of MTBE. Statistically, 86% of the ch ange in MTBE was explained by variation in motorized watercraft use. Neithe r highway runoff nor precipitation contributed significantly. MTBE concentr ation ranged from <0.1 mu g.L-1 to a high of 12 mu g.L-1 Between July 1 and 7, 1997, MTBE content rose dramatically from 115 to 365 kg. By January, le vels had declined to a minimum of 15 kg, suggesting little interannual pers istence. The major loss of MTBE appeared to be volatilization at the air-wa ter interface characterized by two distinct peri ods. During the boating se ason, MTBE decline was 1.2 kg.day(-1) (193 day half-life). At the end of th e boating season, MTBE loss increased to 8.1 kg.day(-1) (14 day half-life). Thermal stratification acted to retard MTBE transport to deeper depths.