A Study Of Urban Groundwater Sustainable Use In Changchun Metropolitan Area

Water resource shortage and water contamination are one of the most pressing issues faced by many China's cities, and groundwater resources is an very important water supply for the cities. The special urban geomorphology and human's social economic activities within urban areas strongly changed the local groundwater cycle and the groundwater environment, and the increasing pumping and the discharge of waste water and solid wastes lead to and accelerate the unconfined groundwater contamination, which will endangered the confined groundwater. Analyzing the urban groundwater evolution and utilizing the groundwater in a sustainable are very important research issues.Urban groundwater model is one of the most important basis tools for the groundwater sustainable management. Taking the case of Changchun, the storage environment was analyzed and the concept hydrogeological model was generalized. The groundwater cycle was modeled include water quantity and water quality. The top-down aquifer was generalize as unconfined, poorly permeable water and confined. The confined and unconfined aquifer comprised a 3D groundwater flow with the poorly permeable water aquifer. Visual Modflow was used to modeling the groundwater flow, Darcy law and Fick law were applied to the model. The groundwater flow was transient and the aquifer was anisotropism. Recharge of from different land use types was estimated for the model, and the representation of the model was enhanced.The equation of three-dimensional groundwater flow is resolved by finite-difference method, and the equation about the advection-diffusion of the three-dimensional contaminant(Cl-1) transportis resolved by the coalition of finite-difference method and method of characteristics.The model was proved to be valid after the identification and validation. The groundwater resource evaluation, pumping scenario and risk evaluation of groundwater contamination were conducted based on the model.The groundwater resource was evaluated in different aquifer and different district, and the long-term groundwater use was also evaluated. The result of the evaluation indicated that, the groundwater in Changchun was a high level abstraction, and the groundwater quantity in shallow aquifer is modestly increasing, while the groundwater quantity in deep aquifer is decreasing. The groundwater evaluation within the district scale indicated that Luyuan and Kuancheng district have the potential to increasing their pumping quality, while Chaoyang, Erdao and Nanguan district need to adjust the industrial use of groundwater, or reallocate the pumping wells and reduce the total abstraction quantity. The dynamic evaluation showed that the groundwater resource is basically positive balanced under the current abstraction way, but the abstraction is close to the recharge in a long-term, which should be noticed by the local government. Some restoration methods need to be applied to prevent the groundwater exhaust to make a sustainable use of groundwater management.Four pumping scenarios were designed for the groundwater supply management. The first scenario indicated that the exploitation will decrease the groundwater head within the whole study area, and the area of the customary the cone of depression will expanded, the groundwater level within the center of the customary cone of depressions will be decreased, and the contaminants transfer will be accelerated. While the other three scenarios showed that the groundwater abstraction will only decrease the groundwater level within the affect radius of the new added pumping wells, and groundwater level out of the affect radius will not be decreased. All of the four scenarios indicate a modestly increase of the contaminants, but this increase concentration will not exceed the national drinking water standard. A comparison of the four scenarios indicated that, under the current abstraction quality, the second and third scenario will be more reasonable for the groundwater management, and the first and fourth scenario will be unsound and should not be carried out because these two scenarios increase pumping quantity substantively and cause the large range groundwater level decreasing within the whole study area, a lot of cells below the alertness level emergence, which will be a disadvantage for the sustainable use of groundwater. According the calculation result of the four scenarios, pumping quantity can be increased within zones of Anlongquan-Xinglonggou, Jiajiagou.In order to test the potential threat of the contaminants to the aquifer of the study area, sensitivity analysis and a worst-case scenario analysis are applied to estimate this uncertainty and build confidence in the model results. The result indicated that the dispersion coefficient of unconfined aquifer and hydraulic conductivities of poorly permeable water aquifer were sensitive for the solute transfer, and the worst-case scenario showed that the average head within the active cells of unconfined aquifer decreased 0.29m, the vertical across flow increase, large dry cells appeared in the cone of depression areas, the contaminants transferred downwards, the average contaminant concentration in unconfined aquifer decreased 23.82mg/l, the average groundwater head and concentration in confined aquifer increased 1.51m and 23.82mg/l respectively, the concentration in the cement factory cone of depression exceed 250mg/l, and this contamination did not endanger the groundwater in the downtown area due to the block of watershed, the area of the Dacheng cone of depression and downtown cone of depression has the largest expansion, and the concentration within these two cone of depression was increased too, but the value was less than 250mg/l.The strategy of groundwater management was proposed based on the groundwater model. The urban storm blood need to be sufficiently utilized to increase the groundwater recharge. The spatial distributation of groundwater and the contamination need to be investigated in detail, and the contaminated and the over exploitation area need to be controlled, and a more rational planning of groundwater use need to be formulated. For the corne of depression within the urban water supply net, both of the public groundwater exploitation and the private pumping wells need to be suspended and substituted by the urban water supply net. For the unconfined aquifer which was abstracted generally reasonable although the contaminant concentration exceed the national standard in some areas, and contaminant within the unconfined aquifer need to be cleaned up; for the contaminated area, engineer method need to be taken to prevent the over exploitation of unconfined groundwater which has the potential to lead to large dry area and endanger the local ecosystem, for the poorly permeable water aquifer , the vital work is to protect its integrality; for the groundwater contamination control, waterproofing protect need to be taken in the communication area of unconfined and confined area, the pumping wells and their pumping quantity need to be under strictly control to prevent to being over exploitation that will lead to the of cone of depressions and the acceleration of contaminants moving. Economic policy, such as the increase of water price, was recommended to impose the water saving consciousness. The education of water resource sustainable use need to be adopted by the public media. The legislation of groundwater water protection need to be enhanced, especially. The groundwater need to be supplied according to the different demand and the different quality. Technical methods related to the key groundwater issues need to be applied to the urban groundwater management supported by the science and technology progress. The ecological economic need to be developed to reduce the produce of new pollutant to control the pollution discgarge from headstream of the product life cycle. A decision supported system of groundwater management need to be constructed.This thesis analyzed the groundwater storage environment, infiltration rate of urban land use, the evolution of groundwater, and modeled the groundwater flow. The groundwater quantity and contaminant transport were evaluated, and scenarios was designed to evaluate the exploitation potential and the contaminant transport. Policy issues related to the groundwater sustainable use was discussed. The thesis is a useful guide and technical support for the groundwater management of Changchun City.