ABSTRACT
As an important water supply source in Beijingï¼ karst groundwater has played an irreplaceable role in the security of urban water supply and ecological environment protection in the past 70 years. The Xishan karst groundwater systemï¼ located in the upper reaches of western Beijingï¼ belongs to ecological conservation areas. There are several centralized water supply fields in this area. In this studyï¼ the Xishan karst groundwater system was taken as the research object. A total of 120 karst groundwater samples in this area were investigated by using statistical analysisï¼ ion ratioï¼ and principal component analysis ï¼PCAï¼ methods to explore the spatial distribution characteristics and formation mechanism of groundwater hydrochemistry. The research results showed thatï¼ â the groundwater quality of the Xishan system was generally goodï¼ with the characteristics of neutral pH and low salinity. A total of 84.17% of the water samples were classified as hard water. The chemical type of groundwater was mainly HCO3-Ca·Mg. â¡ The chemical composition of groundwater was mainly affected by the water-rock interactionï¼ and the weathering source of rock was mainly the dissolution of carbonate. ⢠The results of principal component analysis showed that 34.41% of the chemistry formation of groundwater could be explained by carbonate dissolutionï¼ 27.33% by rock salt and evaporate dissolutionï¼ 11.76% by aquifer sediment dissolutionï¼ and 10.30% by domestic sewage discharge. From the recharge area to the runoff area and then to the discharge areaï¼ the TH and TDS gradually increased. Coal mining drainage and human activities were the main factors that caused groundwater degradation and variable hydrochemical types in the piedmont. In the futureï¼ it is necessary to further strengthen environmental governanceï¼ control point and non-point source pollutionï¼ and continuously monitor key areas to provide scientific support for ecological and environmental protection.
ABSTRACT
Investigation and numerical simulation, based on RT3D (reactive transport in 3-dimensions)were used to identify the source of tetrachloroethylene (PCE) and trichloroethylene (TCE) in the groundwater of a city in the north of China and reverse the input intensity. Multiple regressions were applied to analyze the influenced factors of input intensity of PCE and TCE using Stepwise function in Matlab. The results indicate that the factories and industries are the source of the PCE and TCE in groundwater. Natural attenuation was identified and the natural attenuation rates are 93.15%, 61.70% and 61.00% for PCE, and 70.05%, 73.66% and 63.66% for TCE in 173 days. The 4 source points identified by the simulation have released 0.910 6 kg PCE and 95.693 8 kg TCE during the simulation period. The regression analysis results indicate that local precipitation and the thickness of vadose zone are the main factors influencing organic solution transporting from surface to groundwater. The PCE and TCE concentration are found to be 0 and 5 mg x kg(-1) from surface to 35 cm in vadose zone. All above results suggest that PCE and TCE in groundwater are from the source in the surface. Natural attenuation occurred when PCE and TCE transporting from the surface to groundwater, and the rest was transported to groundwater through vadose zone. Local precipitation was one of the critical factors influencing the transportation of PCE and TCE to aquifer through sand, pebble and gravel of the Quaternary.
