Hydrogeochemistry Evidence for Impacts of Chemical Acidic Wastewater on Karst Aquifer in Dawu Water Source Area, Northern China.

The study of the hydrochemical characteristics and the water-rock interaction of karst groundwater is very important for the rational exploitation of karst groundwater and its pollution control. In this paper, the systematic clustering method was used to analyze the hydrochemical characteristics of different types of groundwater, combined with hydrochemical graphic analysis and correlation analysis to explore the impact of chemical acidic wastewater on the evolution of karst aquifer in the Dawu water source area, northern China. The results show that the chemical acid wastewater, sourcing from discharges/spillages from the local chemical industries, has different degrees of pollution impact on karst groundwater, causing the total hardness of all karst groundwater and the total dissolved solids, Cl- and SO42- in nearly half of the karst groundwater to exceed the quality indexes of class III water in China's standard for groundwater quality (GB/T 14848-2017). Hydrochloric acid and sulfuric acid in the wastewater can be buffered by the dissolution of carbonate rocks, resulting in a nearly neutral pH (pH-buffering effect) and an increase in Ca2+, Mg2+, Sr, Cl- and SO42- concentrations in karst groundwater.

Groundwater environmental risk assessment of abandoned coal mine in each phase of the mine life cycle: a case study of Hongshan coal mine, North China.

Human activities during each phase of coal mine life cycle greatly affect groundwater environment. The groundwater environment destruction is not just only the destruction of underground structure but also the social problems caused by available groundwater resources reduction, as well as the environmental problems affecting ecosystem and human health. Moreover, the groundwater environmental risk of coal mining is complex, dynamic, and long-term. Therefore, a framework and quantitative method for groundwater environmental risk analysis at different phases of the mine life cycle was presented, which is composed of the groundwater system destruction risk (GSDR) and social-economic-ecological vulnerability (SEEV) assessment. The framework was applied in Hongshan abandoned coal mine, North China. Based on the aquifer structure destruction, groundwater flow field evolution, contamination, and social-economic influence analysis, 12 main controlling factors for the GSDR and 7 factors for the SEEV were determined and quantified separately. The results showed that the groundwater contamination of the Hongshan mine mainly occurred after closure, caused by the cross-strata pollution of mine water, which significantly reduced the groundwater available resources, which greatly affected local social-economy sustainable development and residents' health. The Hongshan mine closure increased groundwater environmental risk, with the GSDR high-risk zone being 12.51 km2 larger than that during the mining phase and the SEEV was calculated at a high level. This framework promotes systematic integration of the groundwater environmental risk assessment in mine life cycle.

A new four-step hierarchy method for combined assessment of groundwater quality and pollution.

A new four-step hierarchy method was constructed and applied to evaluate the groundwater quality and pollution of the Dagujia River Basin. The assessment index system is divided into four types: field test indices, common inorganic chemical indices, inorganic toxicology indices, and trace organic indices. Background values of common inorganic chemical indices and inorganic toxicology indices were estimated with the cumulative-probability curve method, and the results showed that the background values of Mg2+ (51.1 mg L-1), total hardness (TH) (509.4 mg L-1), and NO3- (182.4 mg L-1) are all higher than the corresponding grade III values of Quality Standard for Groundwater, indicating that they were poor indicators and therefore were not included in the groundwater quality assessment. The quality assessment results displayed that the field test indices were mainly classified as grade II, accounting for 60.87% of wells sampled. The indices of common inorganic chemical and inorganic toxicology were both mostly in the range of grade III, whereas the trace organic indices were predominantly classified as grade I. The variabilities and excess ratios of the indices were also calculated and evaluated. Spatial distributions showed that the groundwater with poor quality indices was mainly located in the northeast of the basin, which was well-connected with seawater intrusion. Additionally, the pollution assessment revealed that groundwater in well 44 was classified as "moderately polluted," wells 5 and 8 were "lightly polluted," and other wells were classified as "unpolluted."