Characteristics and Genesis of Acid Drainage Contamination from a Rock Tunneling Project Site

While acid mine drainage (AMD) issues have become a topic of global concern, few studies have focused on acid drainage problems of non-mining activities. We conducted field research and a series of laboratory experiments to investigate the characteristics, release processes and formation of acid drainage contamination. Spoil rock samples and adjacent surface water, groundwater, soil and sediment samples were collected at a railway tunnel construction site in central China, and various parameters, such as the pH, mineral ion concentrations, and heavy metal concentrations, were measured. Based on the measured concentrations, surface water and sediments were seriously contaminated by acids, sulfate salts and heavy metals. Contamination in surface water showed a decreasing tendency as the distance from the spoils increased, while that in sediments showed a greater influence of coprecipitation and adsorption processes of heavy metal ions. The eluviation experiments of three rock samples indicated that R2 (silty fine sandstone) was the most likely major acid drainage contributor. Thiobacillus ferrooxidans was cultured and isolated from contaminated water to study the oxidation conditions during the release processes. The significant release of acid drainage when air and bacteria were both in the culture container suggested that oxygen and bacteria were necessary to produce acid drainage from spoils.