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1 <br /> CONTENTS <br /> Page <br /> *Abstract 1 <br /> Introduction 1 <br /> Study methods 5 <br /> Study results 7 <br /> Occurrence of MTBE in shallow ground water 7 <br /> Relation of MTBE in shallow urban ground water to historical use 9 <br /> Occurrence of MTBE in deeper ground water 9 <br /> Possible sources of MTBE in ground water 9 <br /> Conclusions and discussion 12 <br /> References cited 13 <br /> ILLUSTRATIONS <br /> Figure 1 Map showing location of areas using oxygenated or reformulated gasoline, <br /> U S Geological Survey National Water-Quality Assessment(NAWQA) Study Units, <br /> and Urban and Agricultural Land-Use Studies 3 <br /> 2 Graph showing concentrations of MTBE versus total concentrations of BTEX compounds <br /> in shallow ground-water samples from Urban Land-Use Study areas, 1993-94 7 <br /> 3 Graph showing frequency of detection of MTBE in shallow ground water from Urban <br /> Land-Use Study areas, 1993-94 g <br /> 4 Graph showing concentrations of MTBE in shallow ground water from Urban Land-Use <br /> Study areas, 1993-94 8 <br /> . 5 Graph showing concentrations of MTBE in atmosphere and precipitation at <br /> various temperatures I 1 <br /> TABLE <br /> Table 1 Components and attributes of the National Water-Quality Assessment ground-water <br /> sampling design 5 <br /> • <br />