The“tailing”effect caused by residual non-aqueous phase liquids(NAPLs)in porous aquifers is one of the frontiers in pollution hydrogeology research.Based on the current knowledge that the residual NAPLs is mainly co...The“tailing”effect caused by residual non-aqueous phase liquids(NAPLs)in porous aquifers is one of the frontiers in pollution hydrogeology research.Based on the current knowledge that the residual NAPLs is mainly controlled by the pore structure of soil,this study established a method for evaluating the residual saturation of NAPLs by investigating the fractal dimension of porous media.In this study,the soil column experiments of residual light NAPLs(LNAPLs)in sandy aquifer with different ratios of sands and soil were carried out,and the correlation between the fractal dimension of the medium,the residual of LNAPLs and the soil structure parameters are statistically analyzed,and its formation mechanism and main control factors are discussed.The results show that:Under our experimental condition:(1)the fractal dimension of the medium has a positive correlation with the residual saturation of NAPLs generally,and the optimal fitting function can be described by a quadratic model:S_(R)=192.02 D2-890.73 D+1040.8;(2)the dominant formation mechanism is:Smaller pores in the medium is related to larger fractal dimension,which leads to higher residual saturation of NAPLs;stronger heterogeneity of the medium is related to larger fractal dimension,which also leads to higher residual saturation of NAPLs;(3)the micro capillary pores characterized by fine sand are the main controlling factors of the formation mechanism.It is concluded that both the theory and the method of using fractal dimension of the medium to evaluate the residual saturation of NAPLs are feasible.This study provides a new perspective for the research of“tailing”effect of NAPLs in porous media aquifer.展开更多
Non aqueous phase liquids (NAPLs) pollution are worldwide problems at present. NAPLs which enter the underground through spills or leaks may cause long lasting soil and groundwater contamination problems. Groundwater ...Non aqueous phase liquids (NAPLs) pollution are worldwide problems at present. NAPLs which enter the underground through spills or leaks may cause long lasting soil and groundwater contamination problems. Groundwater can be contaminated by non aqueous phase contaminants that are less dense (LNAPL) or denser (DNAPL) than water. The movement of both types of NAPLs will be influenced by the hydrogeological conditions, such as groundwater level, hydraulic conductivity, and porosity etc., however, LNAPL pollutants tend to concentrate at the water table while DNAPL may migrate further down. Understanding the underground migration mechanisms of NAPLs is of primary importance in pollution prediction and site remediation. Several laboratory simulations for NAPLs’ underground movements in porous media have been done in the past (A.S.Abdul et al., 1988, 1989; C.Tang et al., 1995). In this paper, we try to use STOMP (Subsurface Transport Over Multiple Phases) code to simulate the underground migration of NAPLs. The main purposes are: (1). to understand NAPLs’ underground migration mechanisms; (2). to analyze the sensitivities of model parameters, such as hydraulic conductivity, porosity, etc., and to know what are the most sensitive and important parameters in the model application; and (3). to study NAPLs movements in different hydrogeological conditions. The simulations include: Through the computer simulation, we have found that hydraulic conductivity and porosity are very sensitive in the model simulation, small changes of these parameters will cause big difference of the results, therefore, it is essential to accurately determine these parameters for high quality model simulation; The movements of NAPLs in different geological formation are quite different, two different geological media ( clayey sand and sand ) have been chosen in this paper to simulate NAPLs movement with different combinations ( i.e., moving from clayey sand to sand, and from sand to clayey sand ), the results have been analyzed and discussed; Finally, the influence of groundwater level variation to NAPLs (LNAPL and DNAPL) movement has been simulated by using pumping and injecting wells in the model. The results are compared with laboratory simulations conducted by C.Tang et al.. These results may helpful to understand the behavior of NAPLs during the remediation, such as pumping and treat, and air sparging. It is also important to the design of the remediation plans.展开更多
基金financially supported by projects of the National Natural Science Foundation(No.42007171)the Hebei Natural Science Foundation(No.D2021504034)。
文摘The“tailing”effect caused by residual non-aqueous phase liquids(NAPLs)in porous aquifers is one of the frontiers in pollution hydrogeology research.Based on the current knowledge that the residual NAPLs is mainly controlled by the pore structure of soil,this study established a method for evaluating the residual saturation of NAPLs by investigating the fractal dimension of porous media.In this study,the soil column experiments of residual light NAPLs(LNAPLs)in sandy aquifer with different ratios of sands and soil were carried out,and the correlation between the fractal dimension of the medium,the residual of LNAPLs and the soil structure parameters are statistically analyzed,and its formation mechanism and main control factors are discussed.The results show that:Under our experimental condition:(1)the fractal dimension of the medium has a positive correlation with the residual saturation of NAPLs generally,and the optimal fitting function can be described by a quadratic model:S_(R)=192.02 D2-890.73 D+1040.8;(2)the dominant formation mechanism is:Smaller pores in the medium is related to larger fractal dimension,which leads to higher residual saturation of NAPLs;stronger heterogeneity of the medium is related to larger fractal dimension,which also leads to higher residual saturation of NAPLs;(3)the micro capillary pores characterized by fine sand are the main controlling factors of the formation mechanism.It is concluded that both the theory and the method of using fractal dimension of the medium to evaluate the residual saturation of NAPLs are feasible.This study provides a new perspective for the research of“tailing”effect of NAPLs in porous media aquifer.
文摘Non aqueous phase liquids (NAPLs) pollution are worldwide problems at present. NAPLs which enter the underground through spills or leaks may cause long lasting soil and groundwater contamination problems. Groundwater can be contaminated by non aqueous phase contaminants that are less dense (LNAPL) or denser (DNAPL) than water. The movement of both types of NAPLs will be influenced by the hydrogeological conditions, such as groundwater level, hydraulic conductivity, and porosity etc., however, LNAPL pollutants tend to concentrate at the water table while DNAPL may migrate further down. Understanding the underground migration mechanisms of NAPLs is of primary importance in pollution prediction and site remediation. Several laboratory simulations for NAPLs’ underground movements in porous media have been done in the past (A.S.Abdul et al., 1988, 1989; C.Tang et al., 1995). In this paper, we try to use STOMP (Subsurface Transport Over Multiple Phases) code to simulate the underground migration of NAPLs. The main purposes are: (1). to understand NAPLs’ underground migration mechanisms; (2). to analyze the sensitivities of model parameters, such as hydraulic conductivity, porosity, etc., and to know what are the most sensitive and important parameters in the model application; and (3). to study NAPLs movements in different hydrogeological conditions. The simulations include: Through the computer simulation, we have found that hydraulic conductivity and porosity are very sensitive in the model simulation, small changes of these parameters will cause big difference of the results, therefore, it is essential to accurately determine these parameters for high quality model simulation; The movements of NAPLs in different geological formation are quite different, two different geological media ( clayey sand and sand ) have been chosen in this paper to simulate NAPLs movement with different combinations ( i.e., moving from clayey sand to sand, and from sand to clayey sand ), the results have been analyzed and discussed; Finally, the influence of groundwater level variation to NAPLs (LNAPL and DNAPL) movement has been simulated by using pumping and injecting wells in the model. The results are compared with laboratory simulations conducted by C.Tang et al.. These results may helpful to understand the behavior of NAPLs during the remediation, such as pumping and treat, and air sparging. It is also important to the design of the remediation plans.
