A numerical study of soil cover performance

• Published in: Journal of environmental management 2006-10, Vol.81 (1), p.72-92
• Main Authors: Yanful, Ernest K., Morteza Mousavi, S., De Souza, Lin-Pei
• Format: Article
• Language: English
• Subjects: acid rock drainage; Applied sciences; capillarity; Capillary layer; Chemical Precipitation; conservation buffers; design; Diffusion; diffusivity; drainage; Earth sciences; Earth, ocean, space; economic costs; Engineering and environment geology. Geothermics; Environmental management; Environmental Pollution - prevention & control; Exact sciences and technology; Facility Design and Construction; hydraulic conductivity; hydrogeology; hydrologic models; Industrial wastes; Industrial wastewaters; infiltration (hydrology); Infiltration barrier; layered soil cover; mathematical models; mine spoil; Models, Theoretical; optimization; Optimum design; Other industrial wastes. Sewage sludge; Oxygen; Oxygen - chemistry; Oxygen diffusion; Particle Size; Pollution; Pollution, environment geology; porosity; probabilistic models; Refuse Disposal - economics; Refuse Disposal - methods; Sand-bentonite; soil; Soil - analysis; soil conservation; Soil cover; Soil infiltration; Soil Pollutants - analysis; soil types; soil water content; Soils; thickness; Wastes; Wastewaters; Water; Water level; water table; Water treatment and pollution; zone of saturation
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2005.10.006

In the investigation of soil cover design options for final decommissioning of reactive mine waste, it is often necessary to analyze or predict the anticipated cover performance as a function of the cost of implementation, which is governed by the type, number and thickness of the layers in the cover system. An example of such investigation is presented in this study where one-dimensional evaporation from hypothetical moisture-retaining cover systems is simulated to assess the influence of several cover properties and hydrogeologic parameters on performance. The commercially available transient flow model, SoilCover, was used to compute suction and water content profiles for different cover design scenarios. The predicted water content profile and porosity of layers were then used to estimate the oxygen diffusion coefficients of the various layers. The oxygen diffusion coefficients were used to estimate oxygen flux through the cover systems. The oxygen flux was, in turn, related to the maximum acid flux. The studied cover and hydrogeologic parameters included soil type, thickness of barriers, and water table elevation. Two types of infiltration and oxygen barrier and two types of capillary layer with different thicknesses were studied. The water table was either kept constant at the base of the waste (tailings) or dropped by 0.5, 1, 2, and 3 m over 120 days. The results showed that the relationship between water table depression and the thickness of capillary layers, on one hand, and desaturation of the infiltration and oxygen barrier, on the other, is not linear. Relationships between oxygen flux and barrier thickness and between cost increase and performance improvement of the studied cover systems are presented. Finally, a method that outlines steps for site-specific and economically feasible design of multi-layer cover systems is introduced.