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Environmental evaluation and assessment of some important factors of oil contamination in soil around sarkhoun gas refinery of ar abbas

Ebrahimi, S ; Sharif University of Technology

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  1. Type of Document: Article
  2. Abstract:
  3. Hydrocarbon contaminations due to their volatility, solubility and biodegradability properties can enter the vadose zone and adversely influence the soil properties. Recently, some deep and superficial signs of oil pollution have emerged in the soils around the refinery of Sarkhoun. In order to assess the exact type and behavior of pollutants, evaluate the environmental attributes and measure some important factors of oil contamination in this region, and also to see how pollution transfer in the underground environment, this study has been done. Materials & methods Sarkhoun refinery is located 50 kilometers away from ar Abbas in the northeast direction. The area is mostly composed of Marne and sandstone. Investigations on the sources of pollution show that the refinery is fed by 13 wells controlled by South Zagros Company with a capacity of 500 million cf per day. All effluents discharge to two reservoirs of wet and dry swage, going to burning pits discontinuously afterwards. In the next stage, in order to evaluate the characteristic of the main source feeding the burning pits, some experiments were done including: TSS, TDS, BOD, COD and Oil. In the sampling stage, in order to recognize the initial scale of the pollution, Wells were dug up to hardpans (80 cm to 2 m deep) based on the basic information. Samples were taken from different layers and the amount of TOG and TPH contaminations were determined according to the standard methods. Soil pollution extent was determined on the basis of standard methods, extracting with solvent, absorption by IR at 2940 cm-1 frequency, and using TOG/TPH Analyzer. Hydrocarbon extraction was done by tetrachloroethylene by three replications. Separation of polar and nonpolar pollutants was done by silica-gel powder. It can absorb the polar compounds such as grease and water and just pass the non-polar hydrocarbon compounds. The parameters read before and after the addition of silica gel were TOG and TPH respectively. Plotting the Pollution map of the site was done with geo statistic techniques. The samples were analyzed by Surfer and Arc GIS software. Then the suitable models with the least error were chosen. Results and Discussion The results of some experiments showed that hydrocarbon pollution spread in un-saturated upper parts of bedrock, because the bed rock is located in various depths between 80 and 200 cm. Investigations on the type of pollutants and sewage emission properties and also gasses fluidal analysis entering the burning pits were done. The results were determined for different types of hydrocarbon pollutants. In next stage, experiments such as TSS, TDS, BOD, COD and Oil were done. Important factors to evaluate the intensity of wastewater pollution were BOD and COD indicators. High COD values indicated high oxidation capability. If leakage occurs, COD can be eliminated from the environment by the oxidation potential. Large amounts of BOD indicated high removal capability of the pollutants by microorganisms. The value of oil index was a suitable indicator of oil initial value input to the burning pits. If it leaks or impacts the environment, causes a source of hydrocarbon contamination in soil around the refinery. TSS and TDS indicators, in addition to the effluent quality, are appropriate indices for the predicted re-use. TDS results indicate a very high amount of soluble solids and the possibility of its being reused. These results were beneficial guides for wastewater management decisions, strategies for the refinery conduction and also an appropriate indicator to determine the best cleaning up system. TABLE PRESENTED Conceptual model of pollutants fate in soils was complex and several processes occurred. The results showed that due to the existence of groundwater in the depth of 24 meters and the existence of hardpans near the soil surface, the pollution spread through vapor and hydrocarbon is condensed in the surrounding soil above the hardpan. In practical stage, according to the site condition, wells were dug manually up to the hardpans and samples were taken from different layers. After gathering the quantitative results of TOG/TPH experiments, GeoStatistic studies were done. Having normalized the data by Arc GIS software, it was found out that Gaussian model was the best model for both TOG and TPH pollutions. Then the best interpolation was determined with the Mean Biases Error. The best model in order to fit the data was Kriging method for TOG and TPH data. Results of the level lines maps showed that a high amount of pollution have been absorbed by the soil in the north area around the refinery. Whereas in the west and central points of the studied site, the long distance of the level lines shows less pollution amount. This result may prove burning pits as the pollution sources. Furthermore, these maps showed that pollution spreading toward east of the refinery was more than that of the west part. The 3-dimension maps of TOG and TPH pollution are shown in figure 1 on the longitudinal and latitudina basis and with the consideration of the level line maps and the situation of samp ing places. FIGURE PRESENTED In both pollution spreading maps, in the east parts of the refinery, pollution amount increased abruptly. Investugations showed that this is related to a pipe damage, which occurred a few years ago. For more investigations on how pollution spreads and its quantity, sampling places were located around the broken pipe and the amount of pollutant was analyzed. Next step was providing deep-seated profiles of TOG and TPH pollutions, by collecting data from various layers and Geo-Statistical maps of the whole site. FIGURE PRESENTED As you see, most of the seepage was in dimensionless depth of 0.2. The amount of the obtained pollution decreases noticeably as the depth is increased. It shows that the highest hydrocarbon pollutant concentration is in the surface layer of the soil around Sarkhoun refinery. Conclusions The confined area of pollution spread is located above the hardpan and mostly consists of gas condensations. COD and BOD Parameters in both of the wastewater basins demonstrated the ability of oxidation and elimination of hydrocarbon compounds by microorganisms from the system. The amount of oil entering the reservoirs represents the initial oil input to burning pits. These parameters are beneficial guides for making decisions about the management of the refinery wastewater and to determine the best system. The results of the Geo statistical survey indicated that the main source of TOG and TPH pollutions were the burning pits. Pollution spread horizontally in the direction of soil layers gradient towards Salt River, which is located in the east side of the refinery. The geo-statistical results indicated a sudden increase in east part of the refinery. Because of the low quantity of the recent pollution and it's spreading towards Salt River, elimination of the source of pollution by passing a long time and fewer amounts of pollution against main pollution sources, in quantified investigations and simulations burning pits designated to be the main source of pollutions. Furthermore, TOG and TPH pollution maps had similar trends but the amount of TOG pollution was more than that of TPH. The result gained considering the pollution transport mechanisms indicated that the risk of pollution spreading would increase by increasing the amount of water entering to the burning pits,. Thus, appropriate considerations would be necessary to block spreading. The results of TOG and TPH deep emission pollutions showed that the most spread pollutions were infiltrated before reaching to 0.2 dimensionless depths and by increasing distance from the surface, the amount of pollution will be decreased extremely. Furthermore, the results of this research can estimate the pollution emission in any part of the study area at any time, and can be used for planning and monitoring to choosing the best cleaning method. On the other hand, given the lack of personnel consistent with the climate of Iran, this study provides a valuable tool in future similar research guideline
  4. Keywords:
  5. Hydrocarbon ; Pollution ; Refinery ; Vados zone ; Vapour condensations
  6. Source: Journal of Environmental Studies ; Volume 37, Issue 57 , 2011 , Pages 9-18 ; 10258620 (ISSN)