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| Wellbore effect and its influence on contamination monitor well-a case study on groundwater monitor well around landfill |
| XU Ya1,2,3, LIU Yu-qiang1,2, HU Li-tang3, LIU Jing-cai1, DONG Lu1, NAI Chang-xin1 |
1. Research Institute of Soil and soliid Waste, Chinese Research Academy of Environment Sciences, Beijing 100012, China;
2. China State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China;
3. Engineering Research Center of Groundwater Pollution Control and Remediation of Ministry of Education, Beijing Normal University, Beijing 100875, China |
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Abstract A representative conceptual model for water flow and contaminant transport in the aquifer-monitoring well system under the condition of leachate leakage was constructed. The Equivalent Hydraulic Conductivity (EHC) method was used to describe the water flow and head distribution in the dual-medium system, while the ADE equation and the 1-D solute transport equation for pipe flow were, respectively, used to simulate pollutants migration and distribution in the aquifer and in the wellbore, and eventually a governing equation describing the distribution of pollutants in the monitoring well-aquifer system under leachate emission conditions was constructed. A finite-difference method for this equation was developed based on the Fortan platform. This program was then used to simulate and analyze the effects of monitor well on the regional flow and solute movement in the interior and around the monitoring well, as well as its influence of the wellbore on the flow and solute transport. The results show that The wellbore effect affects the local groundwater flow field and the concentration field around the hole, which leads to the concentration increase in the inner and lower parts of the borehole, and the decrease of the concentration in the certain area outside the wellbore; the effect of the wellbore effect decreases with the increase of the distance. from well to leakage point. The monitoring error caused by the wellbore effect is not more than 20% when the distance is greater than 2times the thickness of the aquifer. The influence of well diameter on wellbore effect is rather complex, not monotonic. In this case, wellbore effect increases with the increase of well diameter, reaches the maximum at 0.1m, and then decreases. The greater the permeability coefficient of the aquifer and the greater the specific storativity, the smaller the influence of wellbore effect. Therefore, the effect of wellbore is less in the gravel and coarse gravel media aquifers with strong permeability and greater porosity, and the effect of wellbore effect on the monitoring effect is greater for the weakly osmosis or medium permeability sand and sand clay aquifers.
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Received: 26 November 2017
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