Integrated Hydrological and Geophysical Characterisation of Surface and Subsurface Water Contamination at Abandoned Metal Mines

Abstract

The mining and processing of metal ores in the UK has left a legacy of environmental degradation, and abandoned metal mines still pose a significant threat to terrestrial and fluvial environments. Flow gauging, water quality and geophysics were combined in an integrated assessment of surface and subsurface hydrological contamination at Esgair Mwyn, an abandoned mine in Ceredigion, Wales. Heavy metals discharged from the site are polluting downstream watercourses, leading to widespread Environmental Quality Standards (EQS) compliance failures. Through salt water dilution gauging and water quality sampling, a daily efflux of 876 g of heavy metals was calculated, with contaminant mobilisation occurring mainly in two primary surface streams draining an exposed tailings heap. Electrical resistivity tomography subsurface imaging found a seepage plane within the tailings lagoon wall, whilst the main tailings heap became increasingly saturated with depth. A large adjacent field also had a high potential to convey pollutants in solution, yet its morphological characteristics have limited transmission, as the area acts as a passive treatment type system. With remediation of already polluted water both difficult and expensive, this approach provides a cost-effective way to identify the origins and pathways of contaminants, informing mitigation strategies focussed on containment. Esgair Mwyn is not an isolated case, as abandoned metal mines release at least 860 t of heavy metals annually into UK water bodies. These techniques could reduce or prevent abandoned metal mine hydrological pollution for decades to come, and enable associated UK water bodies to comply with future water quality standards.

Microwave Sensors for In Situ Monitoring of Trace Metals in Polluted Water

“…The ability to detect an unexpected change in freshwater and then return to the baseline level could not be investigated by injecting trace metals into natural water, so it was evaluated using slug injections of sodium chloride (NaCl) as a tracer, usually used for flow measurement evaluations. The tracer is injected into the stream as a near-instantaneous slug [ 97 ], named slug injection [ 98 , 99 ] or salt gulp injection dilution gauging [ 19 , 27 ]. A certain amount of salt (e.g., 100–500 g depending on the flow) is mixed in a specific water volume (e.g., 10 L of the same surveyed stream water) in a bucket and injected in a point along the stream.…”

“…Recently, the Department for Environment, Food and Rural Affairs (DEFRA) has reconsidered standard values by evaluating the pollution above the baseline metal concentration, especially for Zn, recognising the importance of local baseline variability [ 18 , 19 ].…”

Shallow geophysical and hydrological investigations to identify groundwater contamination in Wadi Bani Malik dam area Jeddah, Saudi Arabia

“…Geophysical techniques and hydrogeological studies are the pivotal tools to detect and study the different environmental problems caused by the drinking and waste water, and the integrated geophysical methods with a hydrogeological investigation can impeccably delineate the contaminated, partly affected, and virgin area. The integration also provides insight into the future potential and venerable subsurface areas to be affected by lateral and vertically downward movement of contaminants [1][2][3][4].…”

Detection of land degradation caused by historical Zn‐Pb mining using electrical resistivity tomography

“…Many authors have described the importance and impact of individual soil properties that is soil type, water content, porosity, electrical resistivity of fluids, mineralogy, cation exchange capacity, and particle size distribution on electrical conductivities (Brevik et al, 2006; Robinson & Friedman, 2005; Tabbagh & Cosenza, 2007; Yoon et al, 2002; Yoon & Park, 2001), in order to validate field studies (Caselle et al, 2019; Mainali et al, 2015; Sreedeep et al, 2005). All this research, however, has focused largely on the pollution of groundwater and surface watercourses with heavy metals (Abudeif, 2015; Hudson et al, 2018; Jarvis & Mayes, 2012; Pierwoła et al, 2020; Wynn, 2000) rather than on soil contamination. Such an approach has, moreover, been applied only rarely in industrial areas (Martin‐Crespo et al, 2011), especially with respect to studies of post‐metal mining wastes (Hudson et al, 2018; Mendecki et al, 2020; Warchulski et al, 2019).…”