Abstract

This article describes the results of a statistical analysis on MTBE relative to other gasoline oxygenates based on groundwater monitoring data collected in Los Angeles County, CA. The other gasoline oxygenates in this study include di-isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), and tertiary butyl alcohol (TBA). Correlation coefficients were calculated between MTBE and other oxygenates, and between the gasoline oxygenates and depth to groundwater and geological material type of aquifer. The correlation coefficients indicated poor correlation among all components mentioned. Analysis of variance (ANOVA) was used to compare MTBE concentrations detected in aquifers comprised chiefly of coarse-grained material with those comprised of finegrained material. The ANOVA results indicated that the difference is not statistically significant between MTBE detected in the two types of aquifer materials. Similar results were also reached for TBA. The oxygenate concentration distributions were further studied by grouping the data according to different gasoline brands. There is not an overall statistically clear trend on whether certain brands of gasoline contain MTBE and TBA consistently higher than other brands, or whether TBA is consistently higher than MTBE among all brands of gasoline. However, TBA shows statistically higher than MTBE in the mean, the median, and the 95th percentile in the overall groundwater data studied. Therefore, further studies on the relationship between MTBE and TBA are warranted.

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