| The Erhua district, including Hua county and Huayin city, is located in the low-lying area between the piedmont of Qinling Mountain and the downstream of Wei River. It’s groundwater is recharged by water from the piedmont of Qinling Mountain and Wei River, so the groundwater quality is not good and the chemical composition is complex. The productsion and domestic water consumption in Erhua district was pumped from10m～30m shallow groundwater without any kind of treatment. Based on the project Water Quality Evolution Characteristic in Riverside Water Source Region Reach of Wei River, The theories and methods of hydrogeochemistry, hydrogeology, isotope chemistry and physical chemistry were applied to study the hydrochemical characteristics of shallow groundwater, water cycle rule, evolution mechanism and the effects of Wei River on groundwater quality. Furthermore, on account of the main exceeded micro-pollutants in shallow groundwater, the ozone-sand, carbon layer-manganese sand layer technological process were applied for the first time for the experiment researches, and the optimal technological condition of this process was gained based on theses experiments. The research results can provide the scientific base for the safe, clean water resource consumption and reasonable water resource exploitation.Therefore, it has a significant theory and practice meaning for local groundwater evaluation, reasonable exploitation and drinking and production water safety to study the shallow groundwater cycle rules, analysis its hydrochemical characteristics and seek an appropriate treatment technological process. The main research conclusions are as follows:(1) The distribution characteristics of hydrochemical types, mineralization and hardness of shallow groundwater in research area are:From south to north, that is from the piedmont of Qinling Mountain to Wei River, the hydrochemical types are from simple to complex, namely, from HCO3·SO4-Ca-Mg to SO4·HCO3-Na-Ca, and then SO4·Cl-Na; from west to east, the changes of hydrochemical types are not significant, the hydrochemical types were HCO4·SO4-Ca-Mg and HCO3·SO4-Ca-Mg-Na near the piedmont of Qinling Mountain, SO4-Na and SO4-HCO3-Na-Ca near Wei River.The total dissolved solids (TDS) were high in Xiamiao Street, Wangsu and Huaying farm along the Wei Rive and the mineralization there were high, too, so there were brackish water distribution areas. On the contrary, the TDS were low near the piedmont of Qinling Mountain and in the central of the research area, where were freshwater distribution areas.The water hardness was generally high in research area, where Xiamiao Street, Huaying farm, Qilian and Fushui were extreme hard water distribution areas. In general, from south to north, water quality changes from hard water to extreme hard water.(2) The ions molar concentration ratio of shallow groundwater, such as γci-/γCa2+, γNa+/γ Mg2+, γCl-/γSO42-and γci-/γHCO3-,showed that the hydrodynamic conditions became weaker and weaker from west to east, but stronger along the Wei River. The variations of the TDS and Na+content are more or less the same, namely where the TDS was high, where the Na+was in dominant. Moreover, the cumulative process of the soluble salt happened from south to north; meanwhile, water salinization had the same trend.(3) The value of δ18O and δD in shallow groundwater and Wei River showed that the main recharge of Wei River and shallow groundwater near the piedmont of Qinling Mountain was precipitation. The distribution regularity of δ18Oã€Î´D in shallow groundwater crosswise (from west to east) and lengthwise (from south to north) reflected the runoff rules, namely the flow run from the piedmont of Qinling Mountain to bank of Wei River. There are groundwater depression cones in Wangsu Xiamiao Street and Huaying farm along the Wei River, to where Wei River recharge. Duancun Street is abundance with surface water, so surface water recharge groundwater.(4) The variable fuzzy set theory was applied to evaluate water quality in research area, according to Groundwater Quality Standards (GB/T14848-1993), class IV water account for64%. From south to north (i.e. from the piedmont of Qinling Mountain to bank of Wei River), the water quality class of shallow groundwater was from II to IV, the water quality became worse and worse. From west to east, the variation of water quality was not significant, the class of water was IV in general. The water quality in Wei River was the same with that of riverside, but worse than shallow groundwater in riverside.(5) The turbidity, chrominance and manganese ion exceeded in research area, the ozone-sand, carbon layer-manganese sand layer technological process wree applied for light polluted water treatment. The result showed that the oxidation on Ozone stage remove 80.0%and17.7%of chrominance and manganese, respectively. The turbidity and chrominance were reduced by sand, carbon layer, resulting class I of drinking water standard. The manganese sand layer which is improved by potassium permanganate can remove manganese to the Class II-III of drinking water standard and its manganese absorption kinetics model matches primary adsorption and Elovich equation, as well as Freundlich and Langmuir isotherm equation.(6) The water from Huaying farm as test water was collected and gained the optimum technological conditions for reducing pollution indicators by means of the ozone-sand, carbon layer-manganese sand layer technological process. The ozone dosage is2.0mg/L for20min, then let the ozonized water go through the plexiglass columns at the speed of0.6m/h and0.3m/h, while the plexiglass columns was100mm in diameter,1000mm in tall and filled with20cm+25cm sand carbon and20cm improved manganese sand. The turbidity, chrominance and manganese content of final filtrate were0.2NTU, degree1and0.060mg/L, respectively. Treated water satisfied Class III of drinking water standards. |
