Predicting the Benefits of Mine Water Treatment under Varying Hydrological Conditions using a Synoptic Mass Balance Approach

Abstract

Geochemical and hydrological data from abandoned mine watersheds demonstrated that (1) point sources of pollution fail to account for total receiving watercourse metal load at higher flows and (2) an inverse relationship exists between river flow and pH due to peatland runoff. Quantifying the varying importance of point and diffuse pollution sources enabled prediction of treatment benefits for a major point source of pollution in one watershed. Instream zinc load increases with river flow (∼3 to 14 kg Zn/d) due to diffuse groundwater and surface runoff pollution sources at higher flows. Lab tests demonstrated that metal release from the streambed, driven by pH decreases at higher flows, also contribute to increased downstream metal loads. Predicting point source treatment benefits demonstrates major instream improvements at low flow (zinc decreases from >800 to 120 μg Zn/L). At higher flows treatment benefits diminish (Zn decreases from 240 to only 200 μg Zn/L) due to the greater influence of diffuse sources. A quantitative understanding of the variable importance of point and diffuse sources of pollution, and instream processes of metal attenuation and release, is crucial to evaluating the benefits of treatment to downstream water quality.

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

“…Diffuse sources identified in the study area included erosion of mine tailings/waste, remobilisation of mine waste deposited in the wetland area, and subsurface drainage of tailings/waste (as demonstrated by effective inflow concentrations of Zn and Cd for the stream segments next to the Queensbury tailings ponds). These findings are important as they demonstrate that diffuse sources, typically thought to be related to rainfall runoff events (Byrne et al 2013;Jarvis et al 2019), can also be important sources at the watershed-scale under steady flow conditions in a temperate watershed. Other potential diffuse sources in our study reach include the hyporheic zone, where remobilisation of sediment-bound metals to dissolved phases has been established in other studies (Palumbo-Roe et al 2012).…”

“…Diffuse sources can be both persistent and episodic in nature and can vary in importance in response to rainfall and streamflow. For example, drainage from the Queensbury tailings ponds might be expected to increase in importance as a source during periods of high rainfall, when erosion and runoff rates may be greatest (Gozzard et al 2011;Jarvis et al 2019;Onnis et al 2018). The mode of entry to the stream channel could be via a complex combination of episodic point and diffuse source inflows.…”

“…surface mine waste drainage, groundwater efflux, hyporheic zone mobilisation) or for discriminating the relative importance of point and diffuse sources at the river watershed scale (Mayes et al 2009). Diffuse sources of mine pollution are particularly problematic in the UK due to the temperate-oceanic climate, which drives substantial variability in precipitation and river and stream flows (Jarvis et al 2019). Recognising the limitations of existing methodologies, a major recommendation of the UK's Department for Environment, Food and Rural Affairs (Defra) Prioritisation of abandoned non-coal mine impacts on the environment project was to develop methodologies for systematic scoping of river watersheds affected by mine pollution for more informed decision-making (Jarvis and Mayes 2012).…”

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.…”

Characterization and Modeling Study on Softening and Seepage Behavior of Weakly Cemented Sandy Mudstone After Water Injection

“…Shendong coal mining area spanning three provinces of shaanxi, Mongolia and Shanxi, is now the largest mining area of coal mine in China, among which Buertai coal mine is the largest mining area in the world. The host rock of Shendong coal mining area mainly consists of sandstone and sandy mudstone (Gu et al 2015;Jarvis et al 2018;Song et al 2020). In general, these rocks are weakly cemented and the softening effects under water saturation are significant (Li et al 2016;Du et al 2019).…”