A Numerical Simulation Study On In Situ Leaching And Hydraulic Capture Remediation Of A Chromium Contaminated Site

In our country a large quantity of chromium slags produced in the process of chromate production were deposited in the natural environment directly in the past few decades,which had caused quite serious pollution problems to the soils.In situ leaching which is a very efficient and economically feasible remediation technique for contaminated soils has been studied and applied widely all around the world.In this study a actual chromium contaminated site was involved,and both of the transport process of the contaminant during the in situ leaching remediation and the hydraulic capture measures were studied by the means of numerical simulation,which were expected to provide theoretical foundation and technical support for the actual remediation project of in situ leaching.The hydrogeological conceptual model was built based on the material getting from the fieldwork with the utilization of ArcGIS and AutoCAD.According to the research results of the laboratory experiment and the field pilot test,the pollution source concentration was conceptualized,and the process during which the contaminant was leached out consecutively was divided into four stage,quick leaching,slow leaching,slower leaching and steady leaching respectively.The groundwater flow model of the study area was built by the means of parametric inversion based on the hydrogeological conceptual model.During the process of parametric inversion,the means of pilot points was found more efficient than the means of parameter zones,which could avoid the problem that the values in the adjacent zones often changed significantly when the traditional means of parameter zones was used.In addition,the matching result between the simulated and actual flow fields was better by the use of means of pilot points.According to the simulated results of the transport process of the contaminant in the condition of natural precipitation,it was found that the removal process of the contaminant was very slow.The removal rate was only 45.73%,when the simulated time reached 106.6 years.Moreover,current hydraulic capture measures couldn’t control the spread of the contaminant in the groundwater efficiently,and the interception rate was only 28.96%.However,according to the simulated results of the transport process of the contaminant in the condition of in situ leaching,it was found that the contaminant could be removed in a short time intensively.The removal rate could achieve 64.67%,when the simulated time reached 106.6 years.Besides the interception results of the hydraulic capture measures arranged at the contaminant discharge area were better than that arranged at the runoff area.Furthermore the combination of the both hydraulic capture measures could achieve a higher interception rate of 99.33%.With the optimization of the designed hydraulic capture measures,the number of pumping wells was reduced by 50%,and the total quantity of pumpage was reduced by 10%,while the interception rate was still as high as 99.34%.Thus a conclusion can be drawn that efficient optimization of hydraulic capture measures can decrease the project cost and operating cost significantly and guarantees the effect of interception at the same time.It can be found from all of the conclusion above,with a proper design and optimization of hydraulic capture measures,an efficient and reliable in situ leaching remediation could be completely guaranteed.