Using compound-specific isotope analysis for assessing biodegradation of gasoline products in groundwater below a gas station above Israel's costal aquifer

Fuel leakage from underground storage tanks (UST) is a worldwide problem. Gasoline spills containing benzene, toluene, ethyl benzene and xylene (BTEX) as well as methyl-tert-butyl-ether (MTBE). In the groundwater, these... [ view full abstract ]

Fuel leakage from underground storage tanks (UST) is a worldwide problem. Gasoline spills containing benzene, toluene, ethyl benzene and xylene (BTEX) as well as methyl-tert-butyl-ether (MTBE). In the groundwater, these pollutants undergo processes of natural attenuation (NA) including volatilization, dilution, sorption, and microbial degradation. The latter is the most important process since it is the only one that breaks down or transforms the pollutants. Monitored Natural Attenuation (MNA) was selected as alternative for a spill below gas station situated in the southern part of Israel coastal aquifer. The aim of the study was to answer the question: Does biodegradation of BTEX and MTBE occur and if so can we determine the rate of degradation? To address the question, groundwater samples were analysed for biogeochemical and isotopic indicators for in-situ microbial activity. These parameters included changes in water geochemistry, isotopic fractionation of carbon in the target pollutants. The results indicated that manganese, iron, nitrate and sulphate reduction took place in the two most contaminated wells with concurrent reduction in BTEX. In addition significan changes in carbon isotope composition of MTBE has been detected in the groundwater sampled from the contaminated site. The results proved natural biodegradation occurence at the contaminated site; the rate of the biodegradtion was estimated as 0.5 /year.