The Study On Self-balance Regulation Scheme Of Groundwater Over-exploitation Area In Guoyang County

Over mining areas with different sizes.In recent ten years,China has issued relevant laws and regulations to manage groundwater over-exploitation areas and promote the rational development and utilization of groundwater.In terms of strict groundwater management and protection,Anhui Province prohibits new deep water intake and consumption in over-exploited areas and reduces exploitation.Due to the massive exploitation of groundwater in Guoyang County,112.2km²over-exploited area was designated in 2015.Due to the long-term large-scale exploitation of groundwater in Guoyang County,the water level in the over-exploited area has become lower and lower.It is particularly important to reasonably regulate the over-exploited area.The methods of regulating the over-exploited area are mainly divided into two schemes:reinjection and pressure mining replacement.There are various problems in the commonly used reinjection water sources in Guoyang County,so it is difficult to implement reinjection,and there is no suitable replacement water source in the pressure mining replacement scheme.In this paper,the groundwater in Guoyang county is numerically simulated by Visual MODFLOW model,and the pressure mining and reinjection scheme is used to regulate the groundwater over-exploitation area.The regulation scheme controls the total mining amount to remain unchanged,the total mining amount in the pressure mining over-exploitation area,and uses the shallow groundwater as the reinjection water source to regulate the over-exploitation area for three consecutive years after pressure mining.In order to regulate the groundwater over-exploitation area and study the influence of single well reinjection on the regulation effect of over-exploitation area,six reinjection schemes are designed.In this paper,the groundwater quality after reinjection is simulated and analyzed by PHREEQC software.The results show that:（1）A 3-year simulation study was conducted on the current mining and pressure mining in the over-exploited area.The simulation results showed that if no pressure mining was carried out in the over-exploited area,the falling funnel in the over-exploited area would expand year by year,and the lowest water level would decrease from-28m to-32m,and the water level area below-24m would increase by8.14km²per year on average.If pressure mining is carried out in the over-exploited area,the falling funnel in the over-exploited area disappears,but the falling funnel outside the over-exploited area expands year by year,the lowest water level drops from-28m to-30m,and the water level area below-24m increases by 1.60km²per year on average.（2）Considering the actual reinjection volume of a single well,the reinjection volume of 8 reinjection wells after pressure production is 16500m³/d,so as to control the falling funnel not to expand into the over-exploited area,and the water level area below-22m and-24m remains unchanged,which are 34.70km²and 10.11km²respectively,which has an obvious regulation effect on the over-exploited area.Through the comparative analysis of schemes,the reinjection amount of single well has a great impact on the regulation effect of over mining area,and the amount of shallow groundwater is the factor affecting the reinjection amount of single well.If the actual reinjection volume of a single well is not considered,three reinjection wells are used for reinjection 16500m³/d after pressure production,which has a better regulation effect on the over-exploited area.The area where the water level is lower than-24m is about6.43km².（3）The groundwater quality after recharge is simulated and analyzed by PHREEQC software.Mixing and water-rock interaction mainly take place during recharge.Water-rock interaction is mainly mineral dissolution and cation reversal exchange.The water quality of mixing action after recharging and water-rock interaction after mixing have some changes,which are mainly caused by mineral dissolution leading to the increase of Ca²⁺,CO₃^2-,Mg²⁺content and cation reversal exchange between K⁺and Ca²⁺,Mg²⁺resulting in the decrease of Na⁺,K⁺content,but the water quality category basically remains unchanged,which all meet the water quality standard of Groundwater Class IV.The groundwater over-exploitation area can be controlled by groundwater recharging with shallow groundwater after pressure mining,and the water level outside the over-exploitation area does not extend to the over-exploitation area.No new water chemical components are produced after recharging.The water quality meets the groundwater quality standard IV.Pressure extraction and recharge schemes can achieve self-balancing regulation and control of over-exploitation area with better effect..