Characteristics of water contamination in abandoned coal mines: a case study on Yudong River area, Kaili, Guizhou Province, China

The seasonal and spatial changes in the chemical composition of the water in abandoned mine drainages and rivers in Yudong River area in the years of 2017–2018 were analyzed. The effects of mine water drainage on the seasonality and physicochemical properties of the river water after mine closure were evaluated, and the feasibility of irrigation using river water and the degree of pollution to farmland were assessed using the Water Quality Standard for Farmland Irrigation. The results show that the mine water has low pH value (< 3.5–4) and high levels of total hardness, SO42−, Fe, Al, and Zn. In addition, the pH of the mine water is negatively correlated with the presence of other metal ions. The correlation coefficient between the chemical oxygen demand (COD) and Fe reached 0.989. While the pollution levels of Pinglu and Baishui rivers were low, the confluence region of the two rivers was seriously polluted. However, only the levels of Fe and Cd slightly exceeded the Surface Water Environmental Quality Standard after the confluence of Yudong and Chongan rivers. Overall, the heavy pollution type of the confluent river is consistent with mine water pollution. The water quality is slightly better in the dry season compared than in the high-water period. Sulfate and Fe content decreased by 39 and 16 mg/L, respectively, and Cd content decreased two-fold. Despite these findings, this study shows that from 2017 to 2018, the pH and Cd content of the rivers at the confluence exceeded the irrigation limit and the water quality continued to deteriorate, which may pose a soil contamination risk. Long-term use of the river for irrigation water may cause toxic elements such as Cd, Fe, Mn, SO42−, Al, and F- to enter the food chain, thereby endangering the life and health of villagers in Yudong River area.