A Model to Evaluate the Flooding Opportunity and Sustainable Use of Former Open-Pits

Abstract

As a result of open-pit mining exploitations, impressive size gaps occur in the landscape. Their flooding leads to the occurrence of so-called open-pit lakes and represents an interesting way to reclaim and use sustainably the degraded land. In the literature, there are numerous plans, strategies, and guidelines for mine closure and open-pit recovery, but these are usually developed at the regional or national level and offer general suggestions, which must be evaluated and approached case-by-case. Because there is still no way to evaluate the opportunity of flooding the open-pits, a methodology for assessing this opportunity was developed to identify the open-pits that are suitable for flooding, this being the main objective of the paper. The paper is novel because of the multicriteria evaluation of open-pits and their remaining gaps, the logical succession of the criteria, and the proposed concept, methods, models, and equations that allow a complex assessment of the flooding opportunity. The methodology also aims to ensure maximum safety conditions in the former mining perimeter, the socio-economic and cultural requirements of local communities, the harmonization of the land in accordance with adjacent ecosystems, and the sustainable development of the region.

A Suggested Methodology for Assessing the Failure Risk of the Final Slopes of Former Open-Pits in Case of Flooding

“…To identify the remaining gaps that are suitable for flooding in the context of ecological restoration of mining degraded lands, an opportunity assessment was made using the following evaluation criteria: geomorphology, orography, hydrology, hydrogeology of the region, the configuration of the remaining gap and final slope stability conditions, the necessity to restore the aquifer resources and to create body water in the area, accessibility and distance to the areas of interest, investments for the recovery and rehabilitation of the remaining gap, and population requirements. The opportunity assessment consisted of a qualitative assessment, the evaluation criteria being ranked with scores from 0 to 3, with 0 characterizing the inopportunity of flooding and 3 the major flooding opportunity of a remaining gap [16]. Therefore, the method of flooding former open-pits can be applied when there are favorable conditions which allow natural flooding in safe conditions with low investments, also satisfying the requirements of the local communities: development of the open-pit in the meadow areas, inflow of water from precipitation and aquifer formations, stable slopes before, during, and after the flooding process, the necessity of restoration of aquifer resources (restoration of water resources for local communities, maintenance of vegetation, crops, etc.…”

“…The identification of the recovery, flooding, and reuse opportunity of the remaining gaps of former open-pits, by case, are made based on well-defined criteria. The higher the number of evaluation criteria, the more reliable the results [16].…”

“…As a result of the opportunity assessment [16], the remaining gap of the North Pesteana open-pit presents a major flooding opportunity. The major flooding opportunity results due to local conditions specific to the North Pes , teana open-pit which favor this type of recovery.…”

Factors influencing the flooding process of former coal open-pits

“…The aquiferity of the rocks influences the conditions of flow and drainage of groundwater and depends on the hydrogeological characteristics of the rocks [11], [12]. From a granulometric point of view, aquifer rocks can show a significant variation, from dusty or clayey sands to coarse sands or mixtures of sands with gravels and boulders, depending on the tectonic cycle in which marine transgressions and regressions occurred [18], [19].…”

“…Because sulfur enters the elementary chemical composition of coal, it can generate, in contact with water, acidic water as a result of the decrease of water pH. Although this possibility exists, the analyses performed on the water samples taken from Pesteana perimeter, does not confirm this hypothesis [11], [21].…”