| PAHs is widely distributed in the atmosphere, water, soil and other environmental media. Its content exceeds the naturally occurring levels so much due to the impact of natural events and human activities. It is difficult for PAHs which has four benzene rings or even more to be degraded by microorganisms ,PAHs contaminations do harm to human health eventually by drinking water and the transmission through food chain, so it is necessary to study the pollution of PAHs.Long term irrigation using the sewage water in the Xi River and the recharge of the Xi River to groundwater cause serious groundwater contamination in our study area---ZhangShi irrigation District in Shen Yang City, the analysis result of soil samples from the study area showed the highest phenanthrene level up to 410μg/kg, in the same time groundwater was also in different concentration levels of phenanthrene. On the basis of reading many papers, we do research in migrating rule of phenanthrene in aquifer .It has practical significance in mastering the migration rule of pollutions in the Xi River and in providing the feasible proposal for The old Industrial Bases in northeast China contaminated sites remediation .On the bases of the practical hydrological and geological data in ZhangShi irrigation District and sample analysis, our study is divided into two parts :experimental simulation and software simulation using GMS.The lithologic constitution of aquifer in research area is sandy gravel and conglomerate, the coefficient of rainy infiltration is up to 0.00023m/d,and permeability coefficient varies between 40m/d to 80 m/d, even higher than 100m/d in some mountainous area. During the experimental simulation , thesandy gravel has pH value of 7.18, the bulk density of 1.70 g/cm3, porosity of 0.3, K(level) =82.49m/d,the simulating conditions coincide with the local hydrological and geological data. The part of software simulation uses MODFLOW, MODPATH which are parts of the popularly used groundwater simulation software GMS, getting the flow field and migration of contaminants in the groundwater. Through experiment and simulation we draw the following conclusions :1. Static experiments. Firstly do sandy gravel adsorption kinetics experiment about four different kinds of particle size, the adsorption rate is higher in the first 2 hours than other time, after 6 hours the adsorption achieves stability; The adsorption process of the four kinds of sandy gravel has been proved to follow the first-order Lagergren equation, and also can be described by the second-order kinetic model, which describes the adsorption process to phenanthrene on the four kinds of sandy gravel more appropriate. The sandy gravel contains less organic matter, little amount of clay minerals which can only do the adsorption, so the adsorption is universal result of clay minerals and effective surface area. The experiments indicate that the adsorption isotherms of all of the sandy gravel fit the Langmuir equation respectively, and the correlation coefficient R2 are all higher than 0.9. Generally speaking, the adsorption capacity of phenanthrene is very low for the four kinds of sandy gravel, it varies between 8.46% and 11.44%. Simultaneously the adsorption capacity has depressed trend of n×0.01 by increasing ionic strength and increased trend of n×0.01 by decreasing pH value.2. Dynamic experiments. There is a certain relationship between the transferring velocity of pollutions v' in the aquifer and the groundwater migration velocity v, which is as follows: v' =v/Rd. Pollutants enter thedynamic environment in aquifer, then it occurs that the migration of pollution is behind the groundwater due to various physical, chemical and biological reactions. Experimental aquifer media is with effective porosity of 0.3, bulk density of 1.70 g/cm3, and K of 0.0008 cm3/g which is got by fitting Henry adsorption isotherm. The calculated retardation factor Rd is 1.045, and the migration rate of phenanthrene in aquifer comes up to 0.038m/h. The simulation shows that the migration of phenanthrene in groundwater is mainly longitudinal , in partial strict obviously longitudinal and lateral, the concentration of phenanthrene achieves stability for short time which is near the inlet. Through the monitoring of pH, Eh, the result means that pH Eh is stable at 7.8 and 15 respectively. Purificated degradation bacteria plays an obvious role in degradation of phenanthrene, after 16 days microbial degradation rate comes up to 43.42%-55.31% in every monitering point, the coefficient of degradation is 0.48; During the microorganism degradation ,pH varies a little ,usually keeps stable at 7. The conductivity in the second monitoring wells keeps stable, but in the first monitoring wells the conductivity increases corresponding the cyclic input of nutrients needed by microorganisms ,and reduces following microbial metabolic process.3. Software simulation. On the basis of water level contour map simulated by MODFLOW, the groundwater level rises from south to north continually, the lowest water level is 20.7m, and two different water levels has a difference of 0.3m . Contrasted with the actual water level contour map of the contaminated sites, the direction of groundwater flow and the water level contour are similar to the actual one. Regarding to experience and actual situations, we think that the simulation can reflect the actual situation of study region objectively. In MODPATH simulation, we establish particles streamtracing capture area at w2-11 and w1-8 two monitoring wells, the monitoring cycle of the two monitoring wells is 300 days,3000 days and 6000 days respectively. At the same time , we establish line source pollution capture area of The Xi River , the monitoring cycle is between 300days and 6000 days, the contamination will affect the groundwater quality in the area between two rivers. Through calculation ,particle transferring distance and area is respectively 168m,840m and 62300 m 2 ,218050 m 2 ,when the monitoring time of well W1-8 is 300days and 3000days( pollution area enlarges by 3.5 times);As well as the monitoring time of well W2-11 is 300 days and 3000 days , particle distance and area is respectively170m,735m and 74760 m 2 ,186900 m 2 ( pollution area enlarges by 2.5 times).When transferring time is 6000 days , particles will transfer from Xi River polluting source to two monitoring wells. At the same time , regarding as phenanthrene front transferring rate got in physical models, we can simulate pollution plume variation curve of one year, five years and ten years. |
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