تعيين سطوح پالايشي تركيبات PAHs به منطور حفاظت ابهاي زير زميني در منطقه جنوب پالايشگاه تهران

Assessment of PAHs Compound Clean up Levels Regarding Groundwater Preservation South of Tehran Oil Refinery

Introduction Leakage of petroleum compounds in the area around Tehran Oil Refinery (TOR) causes severe pollution. Leakage from oil transfer pipelines, storage tanks. and evaporation ponds over a long period of time caused these pollutants to spread through different dispersing mechanisms (Gitipour et al., 2008; Yong et al., 2007). These contaminations have been entered in to underground water and cause carcinogenic hazard on inhabitants directly and indirectly (Taheri 2007). Objectives This research determined the clean up level of the contaminants in soil in order to assess underground water preservation. It is also intended to clarify the condition of the area regarding the existing contamination by the dominant dispersing mechanisms. Furthermore planning the feasible methods in order to control the contaminants and treat the area based on geotechnical properties of the soil and also physical properties of the contaminants were objected. Methodology To determine the concentration of contaminants and also the geotechnical properties of the soil, 12 samples (i.c .. Al to A6 and BI to B6) were collected from 3m and 10m lateral distances of the axis of the contaminated stream adjacent to TOR. In addition. seven soil samples (i.e .. Cl , C2, C3, A7, A8. B7 and B8) were accumulated from the center and around the stream. This research is focused on poly aromatic hydrocarbons (PAHs), the main group of petroleum compounds. Gas chromatography (GC) analysis on 19 samples collected in grid sampling from sides and center of the stream are performed. Also regarding the geotechnical properties of the area and considering physical and hazardous quality of the contaminants, clean-up levels due to the groundwater preservation are assessed. Results and Discussion According to the U.S.EPA regulations, the clean-up level for preservation of groundwater is calculated from the following formula (V.S.EPA, 1996): (I) (B+BxK) Leve/(mg / kg) =C,.[Kd + " u H] p" Clean-up where Bu is the air-filled soil porosity (dimensionless), B" is the water- filled soil porosity (dimensionless). K" is the Henryʹs Law Constant (dimensionless), KJ is the soil-water partition coefficient (cmvg), Pb is the Dry soil b Structure and Volatility specifications of four PAHs Compounds density (g/cm"), and C" is the allowable PAHs concentration in water. Among 16 poly aromatic priority pollutants, four compounds with the highest concentrations in the area and also with careinogenic effects are evaluated. These compounds include benzo[a]pyren (BaP), benzo[k] fluoranthene (BaK), benzola] anthracene (BaC), and chrysene (Chr). Structure and Volatility specifications of these PAHs are shown in Table I. These parameters have an important feature in calculation of clean up level and selection of the appropriate treatment method. Based on analysis it has also been recognized that advection is a dominant dispersing mechanism in spreading the contaminants. Figure I shows concentrations of the contaminant in two lateral sample series in north and south of the stream A and B. It is perceived from Fig.I that latitude dispersion plays a key role in the dispersion of the contaminants. Considering Fig.1 and based on the analyses, concentration of BaP, BkF, and BaA were higher than the allowable limit. Also in case of BaP, maximum evaluated concentration (638 ppm) was 50 times higher than allowable concentration (13.2 ppm). Conclusion The area adjacent to the TOR is completely contaminated with PAHs which have carcinogenic effects on humans. In this regard, control of the advection 10 dispersion mechanisms should be considered a priority. In addition, based on geotechnical properties of the soil and considering physical specifications of the contaminants, biologic methods and phyto-remediation VIa phytotransformation and rhizosphere-biorernediation are recommended to clean up the site