Distribution of heavy metals influenced by pumped storage hydropower in abandoned mines: Leaching test and modelling simulation.

Renewable energy generation varies frequently, making it difficult to match electricity demand. Pumped storage hydropower plants can alleviate this problem by reducing the unevenness of renewable energy generation. It is a new exploration of energy storage methods to construct pumped storage hydropower plants by using underground goaf of abandoned mines and mining subsidence water area. However, the construction of lower reservoirs using underground goaf areas of abandoned mines can lead to potential heavy metal pollution. To assess the impact of using abandoned mines for pumped storage hydropower on the downstream surface water environment, this work first analyzed the release characteristics of heavy metals from underground goaf and surface dump through field sampling and leaching tests, then constructed a water-environment model of the downstream surface water based on the experimental results and water environment theory, and finally simulated and analyzed the impact of underground pollutants pumped to the surface on downstream surface water-quality in typical hydrological years. The maximum error between the simulated values and measured values of the hydrodynamic model was 0.1, and the overall error was within a reasonable range (±0.2 m). The comparison between simulated values and measured values of heavy metal concentration in water quality model showed RMSE values ranged from 0.003 to 0.81, with an average of 0.4; the SI ranged from 0.84 to 0.95, with an average of 0.89. During the simulation of low, normal, and high flow years, pollution downstream was concentrated near the drainage outlet, and the underground pollutants pumped to the surface influenced the concentration of heavy metals there. After a period of drainage, the concentration of heavy metals decreased. Drainage volume was an important factor affecting the concentration of heavy metals downstream surface water. These results prove that the water environment model established based on MIKE21 is reliable and can provide guidance for the simulation and control of heavy metal pollution in the utilization of abandoned mines for pumped storage hydropower. This work provides a reproducible idea and method to assess the impact of using abandoned mines and mining subsidence water area for pumped storage hydropower on downstream surface water and ensure the safety of the ecological environment.