Experimental Study Of Hydrogechemical Action In Inland Shallow Slight Saltwater Region

In Northern Shandong, the original hydrogeological environment is harsh, freshwaterresources are scarce. There are widely distributed in shallow slight saltwater or saltwater whichis more than2g.L-1of TDS. The bottom part of the deep ground freshwater has become a majorsource of water supply. However, with the increasing demand for freshwater resources inindustrial, agricultural production and domestic water demand, causing seriousoverexploitation of freshwater resources and groundwater salinization. So, it has become oneof the major hydrogeological environmental problems, further, exacerbating the contradictionof water supply and demand. How to improve and use scientifically and rationally the potentialresources-salt water has become imperative.In this paper, the study area lies in the inland area, Jiyang Country, Jinan City. On thebasis of systematic analysis of the hydrogeological conditions, physical and chemicalproperties of aqueous medium, ions component characteristics of groundwater of the area. Siltof shallow underground aqueous medium, salt water of shallow groundwater and rainwater oflocal precipitation were took by test materials. And basis on soil soluble salt experiment,saltwater-rainwater mixing test, water-rock interaction test and desplacing saltwater-freshwaterexperiment to explore the hydrogeochemical action in the inland shallow salt groundwaterregion. The change characteristics of conventional ion component of groundwater, the laws ofcation exchange and mineral dissolution or precipitation were studied mainly.Hydrogechemical action being internal relations with parameter variation of aqueousmedium.Thus, it provides a scientific theories for the development and utilization of inland saltwater area resources, management assessment, pollution prevention and control work.There are some new results and opinion in indoor test:(1) Soil soluble salt experiment shown that the main advantage ions of soluble salt wereNa+, Mg2+, SO42-and Cl-. Inland shallow aquifer medium was rich in large number of solublesalt, such as NaCl and Na2SO4, and so exchangeable Na+did. The diversity of soluble salt indifferent depth was caused by concentrated salification in shallow aquifer medium and filteringsalt action in deep clay.(2) Rain-salt water mixing experiment shown that under the closed condition, mixing of saltwater and rainwater was not a simple mechanical mixing process. Ion components ofgroundwater was changed with complexing.(3) Water-rock interaction experiment confirmed that under the closed condition, ionexchange, ion adsorption and dissolution-precipitation of minerals had difference in differentsaltwater-rain ratios. Gypsum and halite were in a dissolved state while dolomite and calciteprecipitate. When the saltwater proportion was over20%, the main cation exchange wasMg/Ca-Na, and SO42-adsorbing capacity of aquifer medium was the biggest while Cl-wasrelatively stable.(4) Change trend of specific conductivity shown type of “Reverse S” during rainwaterdeplacing saltwate and “film effect” from aquifer medium to ions component was remarkable.While Specific conductivity was less than6.22ms/cm, gypsum dissolves; Specificconductivity was more than or equal to6.22ms/cm, it kept balance state. While Specificconductivity was more than1ms/cm, calcite precipitates. In addition, while ion strength variedfrom0.20～0.25mol/L, Mg/Ca-Na exchange action took place mainly. And anions wereadsorpted significantly. Specific conductivity was more than12ms/cm, Ca2+and Mg2+ingroundwater exchange with Na+in stratum. Specific conductivity was more than14.1ms/cm,Mg2+or Ca2+exchange action and adsorption were strong. Specific conductivity was more than9.34ms/cm, adsorption of SO42-from clay mineral was remarkable during ground waterevolution process.During the process of rainwater displacing salt water in saturation column, as a whole,permeability coefficient presented the downward trend. Permeability coefficient by the initial6.49×10-4cm/s, fell to2.28×10-4cm/s, and maintained a relatively stable. Salt water againdisplacing soil column which was saturated by rain water, aquifer medium porosity by the start43.02%fell to38.73%, aquifer medium permeability change was irreversible.During the process of rain water displacing salt water, the clay particle was releasing andswelling, hydrochemical effect and viscosity of displacing fluid were the main contributionfactors to influence on variation of the aquifer medium permeability. While, in different stagesthere were differences in its influencing factors.