Risk Assessment Methodology for Pit Lakes Instabilities

In this study we present a generic probabilistic risk assessment methodology to evaluate the risk associated with flooding process of a pit. We use the bow-tie analysis to analyze the critical events (we focus on slope failures) and the systemic risk assessment methodology to estimate the risk for the population, for the environment and for the infrastructure. Furthermore, we perform a spatial analysis of the risk by discretizing the affected area into squares, by estimating the risk in each one and finally by creating the risk map. The methodology is implemented by specialized software that has been created in a Matlab environment for the deduction of such risk assessments. The developed methodology was applied in the area of the pit lake Most in Czech Republic.

Preliminary results of investigations related to the ecology of Urdari open-pit lake

Flooding the remaining gaps of lignite open-pits and the formation of so-called open-pit lakes tends to become an increasingly common practice in Romania (in the Oltenia Mining Basin, where the lignite deposit contained in Dacian and Romanian formations was and is extracted through open-pits). This type of ecological reconstruction of former exploitation areas has been applied worldwide for quite a time, and there are many references in this regard in the scientific literature. In this context, the present paper aims to present some preliminary results regarding the ecology of these lakes, being taken as case study the lake formed in the remaining gap of Urdari open-pit, within the Rovinari Mining Basin. However, given the multitude of similar conditions (bioclimate, geological framework, the formation of the remaining gaps, etc.) in which they form, we appreciate that the conclusions of this study can be extrapolated for other lakes in the area (eg. South Peșteana). We point out from the outset that this study presents data on the existing biotope and biocenoses (restricted to species identification), without going into details about populations, ecosystem production, energy and matter flows within it, these investigations being foreseen for a future development stage of the present study.

Isotopic and Chemical Assessment of the Dynamics of Methane Sources and Microbial Cycling during Early Development of an Oil Sands Pit Lake

Water-capped tailings technology (WCTT) is a key component of the reclamation strategies in the Athabasca oil sands region (AOSR) of northeastern Alberta, Canada. The release of microbial methane from tailings emplaced within oil sands pit lakes, and its subsequent microbial oxidation, could inhibit the development of persistent oxygen concentrations within the water column, which are critical to the success of this reclamation approach. Here, we describe the results of a four-year (2015–2018) chemical and isotopic (δ13C) investigation into the dynamics of microbial methane cycling within Base Mine Lake (BML), the first full-scale pit lake commissioned in the AOSR. Overall, the water-column methane concentrations decreased over the course of the study, though this was dynamic both seasonally and annually. Phospholipid fatty acid (PLFA) distributions and δ13C demonstrated that dissolved methane, primarily input via fluid fine tailings (FFT) porewater advection, was oxidized by the water column microbial community at all sampling times. Modeling and under-ice observations indicated that the dissolution of methane from bubbles during ebullition, or when trapped beneath ice, was also an important source of dissolved methane. The addition of alum to BML in the fall of 2016 impacted the microbial cycling in BML, leading to decreased methane oxidation rates, the short-term dominance of a phototrophic community, and longer-term shifts in the microbial community metabolism. Overall, our results highlight a need to understand the dynamic nature of these microbial communities and the impact of perturbations on the associated biogeochemical cycling within oil sands pit lakes.

Seasonal dynamics of methanotrophic bacteria in a boreal oil sands end-pit lake

Base Mine Lake (BML) is the first full-scale demonstration end pit lake for the oil sands mining industry in Canada. We examined aerobic methanotrophic bacteria over all seasons for five years in this dimictic lake. Methanotrophs comprised up to 58% of all bacterial reads in 16S rRNA gene amplicon sequencing analyses (median 2.8%), and up to 2.7 × 10 4 cells mL −1 of water (median 0.5 × 10 3 ) based on qPCR of pmoA genes. Methanotrophic activity and populations in the lake water were highest during fall turnover, and remained high through the winter ice-covered period into spring turnover. They declined during summer stratification, especially in the epilimnion. Three methanotroph genera ( Methylobacter , Methylovulum , and Methyloparacoccus ) cycled seasonally, based on both relative and absolute abundance measurements. Methylobacter and Methylovulum populations peaked in winter/spring, when methane oxidation activity was psychrophilic. Methyloparacoccus populations increased in the water column through summer and fall, when methane oxidation was mesophilic, and also predominated in the underlying tailings sediment. Other, less abundant genera grew primarily during summer, possibly due to distinct CH 4 /O 2 microniches created during thermal stratification. These data are consistent with temporal and spatial niche differentiation based on temperature, CH 4 and O 2 . This pit lake displays methane cycling and methanotroph population dynamics similar to natural boreal lakes. Importance statement: The study examined methanotrophic bacteria in an industrial end pit lake, combining molecular DNA methods (both quantitative and descriptive) with biogeochemical measurements. The lake was sampled over 5 years, in all four seasons, as often as weekly, and included sub-ice samples. The resulting multi-season and multi-year dataset is unique in its size and intensity, and allowed us to document clear and consistent seasonal patterns of growth and decline of three methanotroph genera ( Methylobacter , Methylovulum , and Methyloparacoccus ). Laboratory experiments suggested that one major control of this succession was niche partitioning based on temperature. The study helps to understand microbial dynamics in engineered end-pit lakes, but we propose that the dynamics are typical of boreal stratified lakes, and widely applicable in microbial ecology and limnology. Methane oxidising bacteria are important model organisms in microbial ecology, and have implications for global climate change.

Water Balance of Pit Lake Development in the Equatorial Region

In recent years, Indonesia has become the largest coal exporter in the world, and most of the coal is being mined by means of open-pit mining. The closure of an open-pit mine will usually leave a pit morphological landform that, in most cases, will be developed into a pit lake. One of the main issues in developing a pit lake is the understanding of the pit lake filling process. This paper discusses the hydrological model in filling the mineout void in a coal mine in Kalimantan which is located close to the equatorial line. The J-void is a mineout coal pit that is 3000 m long and 1000 m wide, with a maximum depth of 145 m. The development of the J-void pit lake after the last load of coal had been mined out experienced a dynamic process, such as backfilling activities with an overburden as well as pumping mine water from the surrounding pits. There are two components in the model, i.e., overland/subsurface and pit area. The overland zone is simulated using the Rainfall-Runoff NRECA Hydrological Model approach to determine the runoff and groundwater components, whereas the pit area is affected by direct rainfall and evaporation. The model is validated with the observation data. The main source of water in the J-void pit lake is rainwater, both from the surrounding catchment area as well as direct rainfall. As this coal mine area is characterized as a multi-pit area and, consequently, several pit lakes will be formed in the future, the result of the hydrological model is very useful in planning the future pit lakes.

Hydrology model establishment of pit lake: Extreme event rainfall data analysis

Analysis of water management in the pit lake is divided into two conditions, namely Continuous Events and Extreme Events. The former is an analysis of pit lake management related to the water filling in a pit lake that takes place continuously. Meanwhile, the later is the analysis of pit lake management related to the possibility of extreme conditions that will occur, including extreme rainfall. This study is focused only on the Extreme Event conditions. The Gumbel method is used to calculate the planned return period rainfall T concerning the prediction of extreme rainfall. Meanwhile, for a certain return period, rainfall intensity can be predicted using the Mononobe formula. Based on the result of calculation the Gumbel method, it shows that the planned rainfall for a return period of 10 years is 132.9 mm / day. Then based on the results of the calculation of rainfall intensity using the Mononobe formula, it is obtained that the intensity of rainfall for a return period of 10 years with a concentration-time of 5 minutes is 241.5 mm/hour, while the amount of rainfall intensity with a concentration-time of 300 minutes or 5 hours is 15.8 mm/hour.