Study On The Groundwater Pollution Simulation In Yinchuan Region

Groundwater is the most important source of water supply in Yinchuan region when weare in shortage of water source. Surface water and phreatic water are polluted. So we mustpay more attention to the groundwater environment protection of confined aquifer which ispurpose aquifer of water supply. Aiming at the problem of groundwater pollution in Yinchuanregion and on the base of calculation and analysis of groundwater balance, thethree-dimensional groundwater model and solute transport model were set up in this paper.And based on the pollution status of phreatic aquifer, the change of groundwater flow field,the pollution and recovery process of confined aquifer were simulated on the condition ofpresent mining and expanded mining. The following conclusions are obtained.1) Canal seepage and irrigation infiltration are major recharge elements in study area,which accounting for80.89%of total recharge. Evaporation and artificial mining are majordischarge elements, which accounting of81.07%of total discharge. For the first confinedaquifer, leakage from phreatic aquifer to the first confind aquifer is major recharge element,which accounting for70.41%of total recharge.2) Better water, worse water and worst water of phreatic aquifer are distributed in studyarea. And better water is distributed in the west and south, worse and worst water aredistributed in east and north, and the area of Pingji farm. It is connected with groundwaterrecharge, stratigraphic lithology, runoff condition, burial depth and human activities.3) The chlorine ion concentration in phreatic aquifer is higher than that in confinedaquifer. The chloride ion concentration exceed the limit value of drinking water standard atHelan chicken farm–Helan brick factory–Ningcheng village–West lake fame area. And thehighest concentration is531mg/L. The area where chlorine ion concentration exceeds thelimit of drinking water standard in confined water is located in north of Shajia village. Thechange of chlorine ion and TDS are in the similar trends. According to the long-termmonitoring, the chloride ion in phreatic aquifer and confined aquifer shows increasing trend.4) The groundwater flow field simulated by model shows that there are few change on the condition of present mining. But the water stage is lower on the condition of expandmining than that of present mining. And the change is significant at depression cone. On thetwo conditions, the largest water stage deffence in pfreatic aquifer, the first and the secondconfined aquifer is6.28m,8.76m and9.31m, respectively. The water stage difference is lessthan1m at the area which is far away from depression cone.5) On the condition of present mining, for the first confined aquifer, chlorine ionconcentration is in obviously increasing trend in the early80years and the trend becomesslowly between80and150years. The trend becomes stable after150years. The change rateof chlorine ion concentration in second confind aquifer becomes large firstly and thenbecomes small. From the spatial distribution of chlorine ion, the obviously changed area ismainly located in Great wall machine factory–Kongjia village–Tax school–West lake farmarea, Wujia village–Shajia village area, Qianjia village–Lijia village area and Lujia village–Fujia village area. For the first confined aquifer in study area, excessive area is existed in thenorthwest and south of Ningcheng village, which covers about24.75km2.6) In the process of present mining recovery simulation, the decreasing trend is showedin the first confined aquifer. Changes are mainly displayed in the area of high chlorine ionconcentration at the end of200years under the condition of present mining. The area is Westlake–Great wall machine factory–Kongjia village area. Because the concentration of chlorineion in the first confined aquifer is higher than that in the second confined aquifer. It is still apollution process for the second confined aquifer. Until the concentration of chlorine ion inthe first confined aquifer is lower than that in the second confined aquifer at thecorresponding area, the concentration of chlorine ion in the second confined aquifer willdecrease. The second confined aquifer shows obvious hysteresis quality. Finally the affectedwater quality is not completely recovered. The maximum recovery rate reached54%and theminimum recovery rate is only3%. The trend become stable or the decreasing speed is verysmall in the finally decades. In the period of recovery simulation, water quality in confinedaquifer performance for the characteristics of slow process and low recovery degree.7) On the condition of expanding mining, the distribution of chlorine ion in the first confined aquifer and the second confined water are similar to that under present mining. Butthe concentration of chlorine ion is higher than that under present mining at the same time andthe same location. By contrast, to reach the same state of chlorine ion distribution, it needsless than20years on the condition of expanding mining. At the end of simulation, there isabout46.75km2area exceeding the drinking water limit value in the first confined aquifer,which is located in the northwest and south of Ningcheng village.8) The recovery process is faster on the condition of expand mining than that of presentmining. The change of chlorine concentration in the first confind aquifer during the first50years is significant. The trend becomes stable after100years. For the second confind aquifer,the chlorine is in increasing trend in the first26years. And then it is in decreasing trend. Thepolluted confind aquifer is not complete recovery.The research result is helpful to promote the study of groundwater pollution and providedata and theoretical support for groundwater environmental protection.