MTBE Soil Concentrations Relative to Other Gasoline Constituents at Contaminated Sites

Abstract

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. Dr. Yue Rong has his Ph.D. in Environmental Health Sciences from the University of California at Los Angeles, and his M.S. degree in Environmental Sciences from the University of Wisconsin. He is the chief of the Underground Storage Tank Unit at the California Regional Water Quality Control Board, Los Angeles Region. Dr. Rong has more than 11 years experience with the Board in dealing with the problems of groundwater contamination by volatile organic compounds and petroleum hydrocarbons in the Los Angeles Region. Currently, he is a staff member of a multidisciplinary team in dealing with MTBE groundwater contamination problems in the Charnock and Arcadia well fields in Santa Monica, California. Dr. Rong is also the Associate Editor for the Journal of Soil Contamination and is an editorial board member for Environmental Geosciences .