Spatial Distribution and Controlling Factors of Groundwater Quality Parameters in Yancheng Area on the Lower Reaches of the Huaihe River, Central East China

Groundwater samples that were distributed across the Yancheng area in the lower reaches of the Huaihe River were collected from the phreatic aquifer and first confined water layer during the summer of 2016. Using the water quality index, the suitability of the groundwater for drinking and irrigation purposes was systematically evaluated. The controlling factors of solute formation and the causes of water quality deterioration were discussed using the Chadha diagram and the relationship among ions. The results showed that there was a serious lack of excellent- and good-grade groundwater for drinking purposes in the shallow layer. The groundwater was also found to be unsuitable for irrigation, with only approximately 70% being of good quality. The spatial heterogeneity of the water quality was significant, and poor-quality groundwater was found to be distributed discontinuously. The high concentration of alkali metals in the shallow groundwater was found to be due to the weathering of silicate rocks in clay and subclays and the replacement of Ca 2+ with Na + in the surrounding rocks. Additionally, the leaching of residues from the salt industry and marine sediment in historical periods were identified as key factors leading to the scattering of poor-quality groundwater in inland areas. The study found that the shallow groundwater in the study area was not significantly affected by seawater intrusion and human activities. However, signs of human activity, such as agricultural fertilizer and urban sewage, were found to be affecting the “excellent-” and “good-grade” shallow groundwater intended for irrigation purposes.