Abstract

Groundwater and soil VOC contamination is a common phenomenon in areas where petroleum refineries are situated. In order to eliminate such problems, several bioremediation techniques have been developed and tested. Air sparging, which is one of the most promising remediation methods, has been modeled for the case of a specific refinery, in an effort to foresee and evaluate its performance on the site. A specific part of the refinery facilities, where high BTEX concentrations where measured and enough hydrogeological data existed, was chosen for the application of air sparging and consequently for the modeling of the whole process. Volatilization and biodegradation were the main removal mechanisms that were simulated, given that they represent the basic effect of air sparging on the contaminants. The results show that air sparging can effectively be applied in the refinery, achieving significant decline in VOCs concentrations in the regional aquifer in a relatively short period of time. Of course, a lot of attention must be given to the choice of the number and the location of the air sparging wells.

Introduction

Air sparging is an innovative, cost-effective and timeefficient system for the remediation of volatile and/or biodegradable contamination which has been widely applied over the last 10 years. It has been proved that it can achieve high clean up goals in a quite short period of time, which can vary from 6 to 24 months. The basic criteria for the application of air sparging are the volatility (mainly express by Henry's constant) and the biodegradability of the contaminant, as well as the type of the aquifer and the soil. Generally, it has been demonstrated that unconfined, sandy and homogeneous aquifers are the most preferable for an effective air sparging application.

Few are the models developed for air sparging simulation. Most of them have some kind of weakness, which can sometimes cause important reduction in the creditability of the results. Depending on the processes that take place on the field and the ones taken into account by the model, as well as the available chemical and hydrogeological data, the simulation can either produce accurate results or fail to realistically estimate the performance of air sparging. In this paper, volatilization of the contaminant is calculated using basic and well known equations (Henry's law), while biodegradation is simulated using BIOPLUME III model.

Study Area

The site of the refinery was first identified as contaminated 20 years ago. Extended leakage of petroleum products caused the formation of a free phase layer, floating above the local aquifer. Bioslurping was applied to limit the extension and thickness of the layer, which nowadays has almost been eliminated, in the biggest part of the refinery. The contaminated site of the refinery is situated near a lake and the sea. Although no contamination of surface water has been noticed, groundwater sampling and analysis has shown significant BTEX contamination. The plume is mainly restricted in a certain area of the refinery, where groundwater flow seems to be rather small.

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