Hydrogeochemistry Characteristics and Formation Mechanismof Shallow Groundwater in Yongcheng City, Henan Province

Groundwater is one of the most important water supply resources in Yongcheng City, but the pollution of shallow groundwater seriously restricts the economic development and the improvement of living standards in the city. On the basis of groundwater investigation and sampling, hydrogeochemical diagram method and multivariate statistics method and geochemical simulation method were comprehensively used to analyze the hydrochemical characteristics and formation mechanism, as well as the pollution source and the main affecting factors. With the change of aquifer medium and the intensity of human activities, the concentrations of K⁺, Ca²⁺, NO₃^-, Cl^-, SO₄^2- and COD (chemical oxygen demand) gradually decreased, while the concentrations of Na⁺, F^-, Mg²⁺, HCO₃^- and TDS (total dissolved solids) gradually increased with the increase of depth, the former comes from human activities, while the latter comes from the original sedimentary environment. The concentration of SO₄^2- in the areas of coal mine and coal chemical industry is higher than 250 mg/L, which is much higher than that in other regions. The concentration of NO₃^- is higher than 30 mg/L in agricultural areas. Integrated analyses implies that wastewater discharge of coal mine and chemical industry, leakage of household waste leachate and discharge of sewage, excessive application of pesticides and fertilizers are the main factors affecting the water quality of shallow groundwater.