Spatial distributions of lignite mine spoil properties for simulating 2-D variably saturated flow and transport

Abstract

In open–cast brown coal mine spoils, the effect of heterogeneity on water flow and solute transport is largely unknown. The objective of this study is to analyze the effects of differently generated hydraulic property distributions on transport processes in mine spoil heaps originating from open–cast lignite mining. Spatial distributions of hydraulic properties are generated with two different approaches. A deterministic approach is based on the description of mixing, segregation, and compaction during dumping. Using information on the mining and dumping technology along with geological properties of overburden sediments, we generate spatial distributions of the spoil bulk density and texture for a representative 2-D-vertical cross-section of 22 m depth and 29 m width. Water retention is calculated with the Arya and Paris approach and hydraulic conductivity with the Kozeny–Carman equation. The second approach uses direct geostatistical simulation of relative hydraulic conductivity. Water flow and solute transport is simulated with the numerical finite element code SWMS_2 D. The deterministic approach leads to a two-peaked concentration front with tailing. A significant fraction of the solutes is transported faster as compared with a homogeneous profile. Both approaches induce a spreading of the concentration front. Utilizing available information on the dumping technology and on the overburden geology may help to improve predictions of water flow and solute transport in spoil heaps.