Study On The Hydrochemical Characteristics And Causes Of Pollution Of Groundwater In Red Beds Of Chengdu

Chengdu is an important grain production base for China, and also the most populous, economically developed areas in Sichuan Province. Chengdu covers a total area of 12,121 square kilometers, of which the red beds area covers 4200km2, accounting for nearly one-third of the city area. It covers 94 townships(town) from 11 district(city) county. However, in the red beds region of Chengdu, due to the impact of geological, hydrological and meteorological factors, the soil and water conservation conditions are poor, with water shortage; therefore the groundwater is one of the main water sources in the area. Therefore, there is great significance to carry out in-depth study of the hydrochemical characteristics, groundwater hydrogeochemical causes of underground water in the red beds region in Chengdu area, present condition of pollution and causes of pollution for rational development and sustainable use of groundwater in the red beds region in Chengdu.This study takes Chengdu’s red beds hilly area as the study area, groundwater systems theory as the guide and on-field hydrogeological investigations and water samples collection as basis. With integrated use of hydrogeology, hydrology geochemistry principles, the paper carries out research on hydrochemical characteristics and pollution causes of groundwater in red beds region of Chengdu by using the combination of qualitative analysis and quantitative calculation. The conclusions are as follows:1. The hydrochemical characteristics of shallow groundwater in red beds region of Chengdu is mainly HCO3-Ca and HCO3-Ca ? Mg-type water, and there are two kinds of water samples collected which are HCO3 ? SO4-Ca and HCO3 ? SO4-Na.The hydrochemical characteristics of three types of groundwater, Weathering fissure water, interlayer confined water and erosion holes water, are more similar which are mainly HCO3-Ca or HCO3-Ca ? Mg type water.2. This paper takes the upper zone of the environmental background value and the water quality index of three types of water in "groundwater quality standards" as a reference control, and takes use of single index pollution evaluation method to the status of groundwater contamination in the area. The evaluation results indicate that the groundwater contamination in the study area is mainly focused on Chongzhou City, Dayi County, Pujiang County, Xindu District, Qingbaijiang District and JintangCounty; the remaining counties in Chengdu red beds region are not contaminated areas or slightly polluted areas.3. This paper takes use of PHREEQC software to simulate the groundwater evolution process of Yin Small Watershed, and the simulation results show that the main chemical processes leading to small changes in the chemical composition of the water basin are the precipitation action of calcite, dolomite and gypsum as well as the dissolution of quartz, CO2 overflow and cation exchange reaction.4. Through migration simulation by MODFLOW of contaminants in Yin Small Watershed, this paper finds the migration range of pollution is small and changes in the concentration of pollutants shows cyclical variation.