Research On Natural Attenuation Of Oil Contaminant In The Vadose Zone

For the past few years, the leakage of oil has become a severe threat to the soiland groundwater. Currently there’s a growing attention on the soil and groundwatercontamination by oil pollution in China. The transport of pollutants will go through along path in the vadose zone since the groundwater table is deepin northern China.Therefore, natural attenuation is expected to play a more significant role in theremoval of pollutants. Hence the study of natural attenuation in the vadose zone hasimportant application value. This study has carried out a field experiment toinvestigate the natural attenuation rules of oil pollutants in a representative gas stationin Beijing where contamination was found previously, using a set of soil gas samplingand monitoring device designed independently. This study could provide effectivereference to remediation program and measures for contaminated soil.This study has investigated the main causes of the oil pollution and thestate-of-art of oil pollution in China. And a few cases which were reported withtreatments carried out have been analyzed. On this basis, the study proposed suitableprevention and treatment measures.The study has designed a set of soil gas sampling and monitoring deviceindependently based on the mechanism of MNA (monitored natural attenuation). Thesamples of soil gas were collected at contaminated site and were tested to examine thecontent of O2, CO2and VOCs in the unsaturated zone. The results have been used inthe evaluation of the natural attenuation occurrence in the gas station.The test of O2and CO2contents has been proved to be an effective approach to determine if theaerobic degradation happens in this study, while the origin of the contamination hasbeen proved as short-term sources.This study has made a further analysis of the ways of natual attenuation based onthe results of in-situ experiment. This study has conducted multi-phase equilibriumcalculation on the concentrion of VOC to evaluate the level of contamination at thepolluted site and the occurrence of natural attenuation. Further, the ways of natural attenuation were evaluated via oxygen and carbon equilibrium calculation. Moreover,this study has got the rates of the natural attenuation and half-life of the oil pollutantsby using the first-order decay model. Based on the analysis, the capability ofmonitored natural attenuation and environmental quality of the soil in this gas stationhas been evaluated.A confirmatory in-situ experiment was carried out to prove the reliability of thepreliminary field experiments in the same station in Beijing. Both of theconcentration of VOCs and profiles of O2, CO2in the soil presented the same rule asthe preliminary experiment.