This study describes the results of a statistical analysis on methyl tertiary butyl ether (MTBE) concentration distributions in soil and groundwater and MTBE relative to other gasoline constituents in soil based on data collected in Los Angeles, California. The MTBE soil concentration data are studied in two aspects. The first aspect involves MTBE concentration in soil as it relates to MTBE groundwater concentration and soil type at individual sites. The second involves the correlation between MTBE and other gasoline constituents (benzene, toluene, ethyl-benzene, xylenes [BTEX], and total petroleum hydrocarbons as gasoline [TPHg]) in soil at individual sites and at particular soil boring locations, respectively. The results of statistical analyses indicate that the MTBE concentration in soil correlated poorly with the underlying groundwater concentration and soil type. There was no statistically significant difference in MTBE soil concentration between types of soils. MTBE soil concentration also correlated poorly with BTEX and TPHg, whereas BTEX and TPHg in soil correlated well with one another. Despite the generally poor correlation between MTBE and other gasoline constituents at individual sites, good correlation was observed between MTBE and BTEX based on data obtained at individual soil borings. In particular, a correlation coefficient of >0.82 was observed between MTBE and BTEX at 13 of the 28 soil borings studied. Uncertainties associated with the data used for analyses are assessed to pinpoint the shortcomings of the data analysis and to enlighten future studies.
Key Words: statistics, correlation coefficient, analysis of variance (ANOVA), benzene, BTEX, groundwater, soil type.