Identification and Prioritisation of Mine Pollution Sources in a Temperate Watershed Using Tracer Injection and Synoptic Sampling

Identifying and prioritising mine sites for remediation is challenging due to inherently complex hydrological systems and multiple potential sources of mine pollution dispersed across watersheds. Understanding mine pollution dynamics in wet temperate watersheds is particularly challenging due to substantial variability in precipitation and streamflows, which increase the importance of diffuse sources. A tracer dilution and synoptic sampling experiment was conducted in a mined watershed in Scotland to identify the main sources of mine pollution, the relative importance of point and diffuse sources of pollution, and the potential benefits of mine site remediation to stream water quality. Using high spatial resolution metal loading datasets, the major Zn and Cd source areas were identified as point sources of mine water predominantly located in the upper part of the watershed. In contrast, the main sources of Pb were diffuse sources of mine tailings and wastes located in the lower part of the watershed. In the latter case, mobilisation of Pb occurred primarily from a section of braided wetland and an uncapped tailings area. Importantly, diffuse sources of mine pollution were found to be the dominant source of Pb, and an important source of Zn and Cd, even under steady-state streamflow conditions. Mass balance calculations suggest that treatment of the main mine water sources in the upper watershed and capping of the tailings deposit in the lower watershed could reduce stream trace metal concentrations by approximately 70%. These data support the development of conceptual models of mine pollution dynamics in wet temperate watersheds. These conceptual models are important as they: (1) help prioritise those mine sites and features for remediation that will deliver the most environmental and socio-economic benefit, and; (2) provide a means to quantify the importance of diffuse pollution sources that may increase in importance in the future as a result of changes in precipitation patterns in temperate watersheds.

Chemical and Statistical Studies on Water and Stream Sediments Around the Coal Mine Area in Dazhu, China

Coal mine pollution has become one of the most serious environmental problems in China and elsewhere. Water, in the form of groundwater and streams, as well as stream sediment samples, were collected from the coal mine area in Dazhu, Southwestern China. Different analyses, including the hydro-geochemical, multivariate analyses and X-ray analyses, were conducted to examine the coal mine pollution effect. The study results show that the groundwater and stream samples are slightly acidic to alkaline with pH values of 6.36 to 7.17 and 6.51 to 7.39, respectively. With the dissolution of carbonate and sulfate, a large amount of Ca2+, Mg2+, and SO42- is found in the groundwater and stream samples, which is higher than the environmental background value. Typically, the water samples are dominated by Ca2++Mg2+-HCO3- and Ca2++Mg2+-Cl-. According to Chinese standard and the World Health Organization’s guidelines, the water in the coal mine area is of good quality in terms of its physical and chemical properties, except for the concentrations of Fe and Mn (1925.14 and 12872.882 μg/L, respectively). Principal component analysis reveal two groups that explained the variance in the data consisting of SO42−, Ca2+, Mg2+, and low pH as well as HCO3−, Na+, and Cl−, which can reflect the acid mine drainage effects as well as different human activities or the evaporation found in low mountains and hills, respectively. Hence, the concentrations of metals and metalloids in the stream sediments are affected by the coal mine drainage, which are generally enriched in Cr, Mn, Zn, Sr, Co, Ni, Cu, Al, Ca, Fe, and Mg. Mn and Fe average concentrations are higher in the downstream Kongjiagou drain stream sediment samples were 2035.03 ppm and 6%, respectively, relative to the Mn and Fe average concentrations in Xiaojiagou of 453.04 ppm and 2.96%, respectively. Both Mn and Fe concentrations are higher than the background values. Ultimately, mine closures can help with the process of ecological and environmental recovery.

Historical mine pollution and environmental resilience: biomineralization processes and biogeochemical barriers

Three streams in SW Sardinia were studied to evaluate the transport of metals in the environment, and to characterize the natural processes that lead to decreased metal loads. Here we focus on Zn. Although the metal load varies by 2-3 orders of magnitude, we have observed natural biologically mediated attenuation processes, including uptake by vegetation and biomineralization. In this paper, we review the chemical and physical processes that lead to natural Zn attenuation, and discuss the merits of mimicking those processes when designing remediation schemes.