Groundwater Quality Vulnerability Assessment In Central City Of Huaxian

Huaxian is located in the alluvial plain of the Yellow River in the northern part of Henan province.The terrain is flat,the elevation is between 50 and 65 m,and the precipitation is moderate.The exposed strata are Quaternary deposits,with yellow and light grey loose silt and silty clay,good permeability.The buried depth of groundwater is shallow between 10~20m and is closely related to the surface water system.The river flow in the evaluation area,such as Wei River and the Cultural Revolution River,is the main discharge channel of industrial wastewater and domestic wastewater in Huaxian,and the general water quality is poor,most of which are V or even bad V.Because the thickness of the soil layer is thin and permeable,the surface water also brings various pollutants into the aquifer,which pollute the groundwater.Since Huaxian was directly listed in Henan Province in 2014,various industries in Henan province have been developing rapidly.The heavily polluted groundwater system has been further damaged.Therefore,it is urgent to evaluate the vulnerability of groundwater in this area.This paper collects and analyzes the geological and hydrogeological data of the loose layer pore water in the central city of Huaxian,selects the typical landform points to collect the groundwater samples,and evaluates the groundwater quality status of Huaxian city by the single factor standard index method.Based on the above work,combined with the DRASTIC evaluation model,this paper selects the study area groundwater level depth,net recharge,aquifer lithology,soil type,vadose zone,aquifer medium permeability coefficient of six natural factors and ammonia flux,the drawdown of two individual impact indicators,and using the AHP to calculate the weight,on the ArcGIS platform of Huaxian City Center for groundwater vulnerability assessment and special vulnerability.The result shows:(1)The evaluation results show that the groundwater quality evaluation area of underground water in the overall total dissolved solids,total hardness,ammonia nitrogen and nitrite nitrogen,iron and manganese have exceed the standard in different degree,river pollution and agricultural activities is the main reason of groundwater pollution on groundwater recharge.(2)The evaluation result of intrinsic vulnerability shows that the vulnerability of groundwater in the evaluation area was regular,and the vulnerability of the groundwater increased gradually from south to north as a whole.The water level evaluation area northwest of the Wei River in the depth of 8~10m,the Wei River recharge,groundwater vulnerability is the highest level,8.5% of the total area;high level of vulnerability zoning is widely distributed in the Northern Wei River,the river segment in the area during the cultural revolution,the groundwater is 10~15m,the partition area of the total area of 11.5% level of vulnerability;secondary partition is mainly of the plant and the distribution area along the river,the region accounted for 17.9% of urban area;although the shallow groundwater,but the urban surface drainage facilities more perfect,with the majority of the surface anti-seepage treatment,the lower level of vulnerability in the region area of 15.8%;low level of vulnerability zoning in the southeast area of evaluation area,with agriculture,the total area of 46.4%.(3)The evaluation result of special vulnerability shows that due to the influence of human factors,the high level of vulnerability zoning area increased,mainly located in the assessment area north and Chengguan Town,the total area of 21.2%;high level of vulnerability zoning in the region accounted for 10.5% of the area,in the evaluation area in northern sporadic distribution;degree of vulnerability zoning in the middle medium farming land,accounting for the whole area of 13.7%;the vulnerability level is low,low partition accounted for the whole area of 17.6% and 37%,located in the Southern District evaluation of farming areas.