Sean McCarthy CE 421 11/27/2007 Abstract: BTEX is a chemical contaminate found in gasoline. The chemical is a common pollutant found at underground storage tank sites. Due to health concerns caused by high solubility of the compound much effort and energy has gone into developing methods of treating contaminated sites. Several technologies have been studied and tested these include in situ aerobic bioremediation, in situ anaerobic bioremediation, in situ chemical oxidation and ex situ bioremediation. Each technology has its own advantages and disadvantages. This paper will look at some of the technologies and how they are being used to treat sites contaminated with BTEX. This paper will also examine the advantages and disadvantages of each technology. Keywords: BTEX, enhanced aerobic bioremediation, enhanced anaerobic bioremediation, chemical oxidation, Adsorption Introduction: BTEX is the acronym for benzene, toluene, ethylbenzene and xylene. These compounds are volatile organic compounds found in petroleum products such as gasoline and other hydrocarbons. Benzene is used in the production of many synthetic products some examples of these are plastic, rubber, nylon and synthetic paints. Toluene is a solvent used on paint and oils. Ethylbenzene is a fuel additive, it is also used in the production of styrene which is a plastic. Xylene is a solvent used in the printing, leather and rubber production industries. There are many sites across the USA contaminated with BTEX, the majority of these sites are old petroleum production and underground storage sites. The major concerns for BTEX are ground water and soil contamination. There are many different methods of treating contaminated sites. There is in-situ, where the contaminated material is left where it is and treated at that location and ex-situ methods, where the material is moved to another treatment location. Chemical oxidation is where chemicals are used to convert contaminates to less harmful products. Free product recovery, a physical treatment where contaminates that are lighter than water are pumped out of the ground and treated or disposed of. Aerobic and anaerobic treatments can both be used, aerobic requires the presence of oxygen anaerobic is without oxygen. Health risks: BTEX exposure can result from ingestion, inhalation and skin adsorption. Known long term health problems associated with BTEX are respiratory disease, kidney, liver and blood problems. BTEX is also known to cause sensory irrigation and central nervous system depression. Benzene is a known human carcinogen. The majority of people showing signs of illness caused by BTEX were exposed in an occupational setting. Occupational workers that were exposed to BTEX had higher incidences of leukemia. (NIEHS) The maximum contaminant level (MCL) for benzene is 5 parts per billion for drinking water. Properties: BTEX is a volatile organic compound that is soluble in water. Gasoline that contains BTEX has a water solubility of 100-200 mg/L. Benzene has a water solubility of 1780 mg/L. (Zogorski et al., 1997) Becauseof the high solubility of BTEX, cleaning contaminated sites becomes more difficult since the free product can’t simply be sucked up and pumped into a treatment system. Bioremediation is an option for treating contamination at the site of contamination. Many contaminated sites have large plumes that have migrated over time. Because of this it is often too expensive to use ex situ methods of treatment. There are many methods of treating contaminated sites. Most sites use a combination of method to reach a satisfactory level. Any time there is a large plume that contains BTEX it is likely that several methods will be needed to clean the site. If free product is present it will need to be removed first. After the free product is removed the aerobic and anaerobic processes technologies can then be applied to remove the remaining dissolved contaminates. Site conditions will also play a large role in determining which technologies are the best choices for any particular site. Soils that have low permeability are particularly difficult to remediate. However the contaminate plume for UST’s in soils with low soil permeability will not migrate as fast, leaving contaminates relatively localized. These conditions must be taken into account when determining which methods of bioremediation to use. Determining in-situ or ex-situ bioremediation will require a cost analysis. Ex situ bioremediation is capable of achieving better results however it is the more expensive of the two options. Ex situ methods include landfilling contaminated soils. The soil is excavated and transported to a landfill. The method can be very expensive for large sites. Excavation will not be able to effectively treat large contaminations plumes. Pump and treat methods are capable of striping voc’s from contaminated water, this method requires a significant energy input. Pump and treat methods also have a larger capital investment because of the physical nature of the treatment processes. In order to capture contaminates that are lighter than water and depression cone must be created by constantly pumping ground water. The depression cone reverses the flow of the contaminate plume by drawing contaminates to the pumping well. From there contaminates that are lighter than water can be pumped out with a separate pump and the water can be treated. The Pump and treat method is an effective way to remove large amounts of free product. Understanding the different zones of contamination is important so that the best methods of remediation can be selected. The main zones of contamination are the unsaturated zone the saturated zone and the capillary fringe. The unsaturated zone begins at the soil surface and extends to the edge of the capillary zone. In the unsaturated zone both water and air molecules can be found in the soil. (Heath 1983) The saturated zone is below the water table. This zone has only water between soil molecules. The capillary fringe is area above the water table where water seeps upward due to capillary action to fill the area between pores. The capillary fringe includes the tension saturated and unsaturated portions of the zone. The size of the capillary fringe depends on the size and shape of soil particles. If the soil particles are small and roughly the same shape then the capillary zone can extend several feet