Evaluation of the Heterogeneity of Constructed Landforms for Rehabilitation Using Lysimeters

Abstract

Rainfall ingress into sulfi dic rocks or tailings from metalliferous mining opera ons can result in acid mine drainage. Waste rock cover systems in semiarid areas are commonly designed to retain all precipitated water within benign material, from where it is removed by evapotranspira on. The long-term eff ec veness of covers is o en predicted from models that are based on data obtained from single trial plots assuming that the trials are homogeneous and representa ve of large areas. Two cover designs were tested in semiarid monsoonal northwest Queensland: (i) 1.5 m of unconsolidated waste rock overlying 0.5 m of consolidated waste rock; and (ii) 2.0 m of unconsolidated benign waste rock. Three idencal plots comprised each treatment in which water balance equa on parameters were es mated from meteorological measurements and ver cal arrays of soil suc on and moisture sensors and seepage collec on using a 3-m-deep lysimeter inserted in the waste rock. In a wet season with 900 mm of precipita on, water movement through the covers was followed through changes in moisture content, suc on, and seepage. Greater diff erences in these parameters occurred within than between cover treatments. Water reten on and water movement varied substan ally and seepage ranged from 2 to 80% of total rainfall. The internal heterogeneity of hydraulic proper es had more eff ect on cover performance than did the ini al cover design. Therefore, it is important to include internal heterogeneity in mine waste cover water balance models to improve their applicability.Abbrevia ons: ET, evapotranspira ve; NAF, non-acid-forming; PAF, poten ally acid forming; PSD, par cle size distribu on; WRC, water reten on curve.Mining can oft en result in hazardous or potentially hazardous byproducts such as waste rock from the extraction of the ore and fi ne-grained residues (tailings) from the processing of the ore. Th e exposure of potentially acid-forming (PAF) sulfi dic waste rock to O 2 and water can result in acidic or metal-contaminated drainage waters. Tailings can contain high concentrations of heavy metals or sulfi des and seepage from these systems can also be highly contaminated (Lottermoser, 2007). Infi ltration of precipitation into the waste material can result in the leaching of hazardous substances into adjacent environments. For mine lease relinquishment, mining companies are required to prevent any potential contamination of the surrounding environment.In semiarid environments, evapotranspirative covers (ET covers) have been proposed to prevent the ingress of water to hazardous mine wastes (Hauser et al., 2001; Mine Environment Neutral Drainage Program, 2004; Fourie and Tibbett, 2007). Th e aim of an ET cover system is to retain precipitation within the benign cover material, thus preventing it from either running off the surface or percolating through the base of the cover by deep drainage and reacting with the underlying hazardous waste. Stored rainwater is then removed from the cover through evaporation and transpiration (Mine Environme...

Transpiration and water relations of evergreen shrub species on an artificial landform for mine waste storage versus an adjacent natural site in semi‐arid Western Australia

“…In addition, material segregation and self-filtration, which are common phenomena on coarse-textured and highly heterogeneous tailings and mine rock wastes [ Figure 1(a,b)] could have enhanced the transport of fines into deeper layers, resulting in increased soil moisture retention at that depth (e.g. Webb et al, 2008;Dikinya et al, 2008;Shuniak and O'Kane, 2009;Schneider et al, 2010;Gwenzi et al, 2011a).…”

Exploration of the Interaction between Hydraulic and Physicochemical Properties of Syrian Soils

“…Negative correlation coefficients were found for soil carbonate and gravel with soil water content at all matric potentials. Generally, the presence of gravel will increase the macroporosity and therefore decrease the soil water retention (van Wesemael et al, 1996; Schneider et al, 2010). According to Baetens et al (2009), the soil water retention usually decreases when the rock fragments content increases.…”

The limited impact of vegetation on the water balance of mine waste cover systems in semi‐arid Australia

“…However, the initial re-establishment of these ecosystems might be challenging because intensive water users with elevated initial biomass production may outcompete extensive water users if both species show similar drought adaptations (Zea-Cabrera et al, 2006;Smesrud et al, 2012). Nevertheless, the coexistence of species with contrasting water use patterns is favoured by the irregular spatial distribution of soil moisture (Zea-Cabrera et al, 2006), which is likely to occur on reconstructed ecosystems because of the high likelihood of spatial heterogeneity of soil physical properties (Krümmelbein et al, 2010;Schneider et al, 2010;Gwenzi et al, 2011;Mazur et al, 2011). Moreover, given the purpose of engineered cover systems (i.e.…”