Study On The Evolution Characteristics And Prediction Of Groundwater Quantity And Quality Of Longkeng Water Source In Songyuan City

Songyuan City located in the arid and semi-arid area of China with poor precipitation and high evaporation. It is an ecological fragile region of Jilin Province. The local development of society and economy has been affected by water sources shortage. Longkeng Water Source is one of the most important water sources in Songyuan City. With the increase of groundwater explotation water supply of Longkeng Water Source decreased year by year. In additioin, sacles of fertilization has caused non-point pollution in groundwater.In order to protect the water source to confirm the sustainable utilization of groundwater, the characteristics of groundwater circulation and its evolution regulation has been study in this thesis. The appraise system of groundwater quantity and quality evolution is built and applied in the study area. It is of great significance for social stability and sustainable development in Songyuan City.Based on the collection of geologic and hydrogeologic data, quantitave and qualitative analysis are combined. Field investigation and indoor experiments are applied in the study and predication of groundwater quantity and quality evolutioin characteristics. Which include the next five parts.1. According to field investigation and collection of numbers of drilling data, pumping test data and groundwater dynamic data, the aquifer of study area is confirmed to be the late Pleistocene sand-gravel prous aquifer. The hydrogeological cross sections are ploted according to the drill to analysis the distribution of aquifer in space. Connected with the groundwater flow field the water sheld is confirmed correctly. It is a unclosed basin. The watersheld of groundwater is about six to ten kilometers south to the landsurface.2. based on the analysis of corresponded data, pumping tests, spring discharge inverse method, groundwater dynamic method, indoor experiment are applied to confirm hydrologic and hydrogeologic parameters. Isotope and groundwater dynamic method are applied to calculate the renewability of groundwater. The results of isotope method show that the test result along the direction of groundwater flow is steady. There is no obvious difference of 8D between groundwater and precipitation. The value of theδ18 increase from recharge area to discharge area. It shows that the recharge of groundwater is alomt from precipitation. Groundwater discharge in the north boundary of bench terrace. The rate of ciculation is 0.1466km/a.On the other hand, the outcome of hydrogeochemistry and hydrochemical dynamics along three flow lines show that the deposit and solution of calcite, dolomite, gypsum and halite are the main factors of chemical constitution in groundwater. It will spend 112 years for groundwater move from recharge area to discharge area. The results the two methods are generally the same.3. Cumulative water balance method is proposed to get the quantity of groundwater resource and exploitable amount. According to this method, the mean annual groundwater recharge source is 88.305 million m3. the exploitable amount is 75.059 million m3. and the amount of spring discharge is 27.23 million m3. Groundwater system is in the burden equilibrium status on average condition. It is high flow year in 2008. The amount of groundwater recharge is 120.65 million m3. The exploitation amount is 55.65 million m3. The discharge of springs is 26.66 million m3. The amount of groundwater flow from the boundary is 16.32 million m3. The amount of recharge is large than discharge. So it was in the positive balance in 2008.Based on the appraise of groundwater resource the numerical model of groundwater quantity is built to forecast the evolution of groundwater quantity. The results of cumulative water balance method and groundwater model shows that it is in the burden equilibrium for groundwater in this area.As groundwater are mostly exploited for irrigation, it is in low demand of quality. After Hadashan hydro-junction being put into service. The scheme of exchange groundwater exploitation by surface water is proposed. According to groundwater quantity model, five different exploitation schemes are palyed and the fifth scheme is confirmed to be the best one.4. Nemerow index method, Projection Pursuit Method and Matter-Element Extension Method are applied in the appraise of groundwater quality type. The results show that the water quality type is generally the first class. The chemical types of groundwater in study area are generally HCO3-Ca and HCO3-Na·Ca. The specific pollutant is 3-nitrogen.The transfer rule of specific pollutant is studied by indoor experiments. The results show that the adsorption of NH4+in soil balanced in 60 minutes. The maxmuim adsorb quantity of NH4- is 19.58mg/kg which takes 39.2% to 78.3%NH4- in the solution. The adsorb rate is fast at first. After 30 minutes the rate slow down to less than 00.1mg/kg. The adsorption stops after 90 minutes. The desorption rate of NH4+is fast at first. It became steady in 10 hours. The desorption of NO3- vary fast in the first 7 hours. The desorption bacome equilibuim in 10 hours. The maximum desorption quantity is from 77.34 mg/kg to 175.64mg/kg. the leaching experiments show the adsorption quantity of NH4+takes 82.21%of the total in solution. NO2- is 45.82%and NO3- 45.82%. As N4+can be easily adsorbed by soil. So the adsorption ratio is the largest. NO2+ is the intermediate which can be easily transformed. So the adsorption ratios of NH4+and NO2-are correspondly more.Based on groundwater quantity numerical model, groundwater quality numerical model is built. The 3-nitrogen and TDS are chosen to be the simulation factors. The predicting result shows the slow increase of them in groundwater in future.5. the appraise system of groundwater quantity and quality is proposed. And the main factors of groundwater quantity and quality evolution are confirmed. Take Longkeng Water Source as an example, the main factors of groundwater quantity and quality in this area are filtered. And the weight of each factors are confirmed too. The evolution of groundwater quantity and quality in typical year 2000,2008 and 2015 are appraised by fuzzy comprehensive evaluation method. The result shows that the tendency of groundwater evolution by time is "poor"→"good"→"poor". The main reason is that the precipitation in 2000 is little (353.20mm) and large in 2008 (621.8mm). So it is well recharged by infiltration of rainfall in 2008. But with the increase of groundwater exploitation in future, the main trendency of groundwater quantity and quality evolution is still poor.According to the appraise result, groundwater quantity and quality will generally maintain the status quo in terrace in 2015. Groundwater level decrease in Wangfu Terrace section (Ⅲ-4 and I1) in the east of terrace. Groundwater quality will develop in the poor direction. With scales of groundwater exploitation for irrigation and fertilizer utilization, groundwater level will decline and the spring will decrease. The chemical elements in groundwater will increase further. In the slightly inclined plain in the west groundwater will keep the status quo in future.