天津市宁河北奥陶系灰岩水源地的水文地球化学模拟

天津市宁河北水源地属埋藏型地下水源地，其开采层奥陶系灰岩含水层呈北东向的向斜展布，隐伏于石炭系-二叠系砂页岩之下，并被新近系覆盖，仅在东北部与第四系含水层有水力联系，地下水的补给主要来自浅层第四系含水层的越流补给。应用水文地球化学模拟方法，研究从第四系含水层到奥陶系含水层地下水经历的水-岩作用，包括方解石、白云石、萤石和硬石膏的溶解或沉淀、二氧化碳气体的溶解或逸出等，地下水硬度、矿化度总体上有下降趋势，这是由于含Ca²⁺、Mg²⁺和HCO^-₃的矿物相发生溶解，迁入溶液的比率要小于发生沉淀迁出溶液的比率，具体表现在从第四系含水层到奥陶系含水层Ca²⁺、和HCO^-₃浓度的降低幅度较大。通过模拟计算，可以定量确定从补给区到研究区沿水流路径上的水-岩相互作用及质量交换，有助于揭示该区地下水化学环境的演化机制。

Hydrogeochemical Simulation for Ninghebei Ordovician Limestone Wellfield in Tianjin

The Ordovician limestone aquifer,which is tapped by the Ninghebei wellfield,occurs as a NE-trending syncline and is overlain by the Carboniferous-Permian sandstone and shale and the Neogene sediments.(Only) in the northeastern part of the syncline does the limestone aquifer hydraulically connect with the overlying Quaternary aquifer.Groundwater in the limestone aquifer receives recharge mainly through leakage from the shallow Quaternary aquifer.With hydrogeochemical modeling methods,this paper examines water-rock reactions occurring in the flow path from the Quaternary aquifer to the Ordovician aquifer,including dissolution or(precipitation) of fluorite,calcite and dolomite.For CO_(2),it may dissolve or overflow,leading to a decrease in hardness total dissolved solids of groundwater.The reason for this is that the dissolution ratio of minerals which contain Ca~(2 ),Mg~(2 )and HCO~-_(3)is less than the overflow ratio,reflecting that from the Quaternary aquifer to the Ordivician aquifer,the concentrations of Ca~(2 ) and HCO~-_(3)decrease in a great deal.Through simulation,water-rock interactions and mass exchange along the groundwater path can be quantitatively determined,which is helpful in describing the evolution mechanism of geochemical environment in groundwater.