Evaluation Of Groundwater Quality And Simulation Of The Freshwater/saltwater Interface In Longdian Township,hengshui,hebei

The study area is located in the water scarcity area of the Heilonggang River Basin in the central and eastern Hebei Plain.The groundwater is the main source of industrial,agricultural and domestic water.A series of geological environmental problems have been caused for the excessive exploitation of groundwater in the area.In particular,local shallow saline water invades into deep fresh water,which threatens the safety of water supply in this area,makes the contradiction between supply and demand of groundwater more prominent,and restricts the rapid development of local social economy.Combined the collection of natural geography,geology and hydrogeology,the methods of ground investigation,drilling,groundwater level surveys,and indoor and outdoor tests,and the principles of sedimentary science,geology and hydrogeology were used to deeply analyze the stratigraphic structure,groundwater quality characteristics,and hydrogeological conditions within the 350m depth range,for studing saltwater intrusion in the study area.At the same time,according to the“Groundwater Overexploitation Treatment in Hengshui”?GOTH?and“The 13th Five Year Plan for Hengshui's Economic and Social Development”(13^thFYP),two different groundwater development and utilization programs were set up,and the groundwater flow model of the study area was constructed.The groundwater flow model and the solute transport model were used to analyze the TDS changes of groundwater in the next ten years,the mechanisms and influences of the saltwater intrusion under different schemes,which can provide important scientific evidences for the development,utilization and protection of groundwater in the area.At present,the main conclusions of this study were as follows:?1?Combining the geological and hydrogeological conditions of the study area,the correlation analysis of the main ions in the groundwater show that Na⁺,Mg²⁺,SO₄^2-,and Cl^-in the first aquifer are closely related to TDS;Na⁺,Ca²⁺and Mg²⁺in the second and third aquifer are closely related to TDS.By comparing and analyzing the values of?_{N a}/?_Cll and?_Na/(?_Na+?_Cl),it can be known that the sodium in the groundwater in the study area is not only derived from the leaching of salt rocks,but also from the alternating cation adsorption of Ca⁺,Mg⁺in the groundwater and Na⁺in rock minerals.?2?The relevant geological and hydrogeological data and the previous research results were used to analyze the water-bearing rock group structure and boundary conditions to construct the three-dimensional unsteady flow model and the solute transport model in the study area.Two different groundwater development and utilization plans were set up by the current scale exploitation and reduce exploitation based on GOTH and 13^thFYP.The calculation results of the numerical model showed that:The salt water body would continue to move downwards under the current exploitation situation,and the rate was 0.3m/a.But the rate under reduce exploitation would be significantly weakened from 2019 to 2020,and be maintained from 2021 to 2030.?3?Through comprehensive analysis of hydrogeological conditions and calculation results,the following conclusions were summarized.?1?Sodium in groundwater is mainly affected by the dissolution and the cation exchange and adsorption.?2?The freshwater/saltwater interfaces were mainly affected by the hydrodynamic field.?3?The salt water mainly enters the deep fresh water through three ways:the weak permeable layer,the wells and"natural skylight".