Exploration of Hydrogeochemical Characterization and Assessment of Organic Pollution Characteristics of Shallow Groundwater near a Chemical Plant That Discharged Sewage Illegally

Benhua Liu,Guangya Zhou,Qiang Wu,Hao Zhan

doi:10.3390/su14020660

Abstract

Groundwater plays a significant role in domestic use and agricultural irrigation in rural areas of northern China. The untreated wastewater from the chemical plant was directly discharged into a seepage well, resulting in the pollution of groundwater. Assessing characteristics of groundwater organic pollution and identifying evolutionary mechanisms of hydrogeochemistry are beneficial for groundwater protection and sustainable management. Statistical methods (correlation analysis (CA) and principal component analysis (PCA)) combined with hydrogeochemical methods including Piper, Gibbs, Gaillardet, and ions binary diagrams and the chloride alkalinity index were employed to explore hydrogeochemical characteristics and evolutionary mechanisms. The results showed that cations were predominantly located at the Ca2+ end and anions were mostly close to the SO42− and Cl− end. The ion concentrations of groundwater were mainly affected by water–rock interactions. The weathering or dissolution of silicate (i.e., aluminosilicate minerals), evaporite (i.e., halite and gypsum), carbonate minerals (i.e., calcite and dolomite), cation exchange, and anthropogenic activities contribute to the chemical compositions of groundwater. Based on CA and PCA, the dissolution of halide minerals and the use of pesticides and fertilizers were the main factors controlling water chemistry. Additionally, the dissolution of sulfur-bearing minerals and gypsum was the key factor controlling the concentrations of Ca2+ and Mg2+. Application of mathematical statistical methods characterized that the exceedance rate of seven organic compounds with high detection rates were as follows: carbon tetrachloride (39.83%) > 1,1,2-trichloroethane (28.81%) > chloroform (10.17%) > trichloroethene (6.78%) > 1,1,2,2-tetrachloroethane (5.93%) > perchloroethylene (5.08%) > trichlorofluoromethane (0.85%). Simultaneously, pollution under the influence of volatilization and diffusion was significantly less than that in the direction of groundwater runoff.

Highlights

Z6 and Z9 were distributed in where the chemical plant was located, with the high measurement of TDS
Exceeding 1700 mg/L, indicating that chemical plant sewage had a significant impact on the TDS of GW
To clarify the regional differences in the chemical cha characteristics and evolutionary mechanism of GW in the study area, the GW catchment acteristics and evolutionary mechanism of GW in the study area, the GW catchment wa was classified into upstream, midstream, and downstream for analysis

Summary

Introduction

Groundwater (GW), which provides drinking water to billions of people around the world and supplies approximately 40% of the water for global irrigated agriculture, is the world’s largest freshwater resource [1,2,3]. The population of the world is increasing significantly, but the availability of water for all populations is decreasing. GW is a vital guarantee for social and human sustainable development [4,5,6]. Over-exploitation of GW coupled with frequent and intensive anthropogenic activities, such as urban sewage discharge, landfill infiltration, industrial wastewater, and agricultural pollution, have resulted in a decline in GW chemical quality and GW pollution [7,8,9,10].

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Results

Conclusion