Water Balance of Pit Lake Development in the Equatorial Region

Edy Jamal Tuheteru,Ginting Jalu Kusuma,Kris Pranoto,Yosef Palinggi,Arno Adi Kuntoro,Rudy Sayoga Gautama

doi:10.3390/w13213106

Edy Jamal Tuheteru, Ginting Jalu Kusuma + Show 4 more

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https://doi.org/10.3390/w13213106

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Abstract

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.

Highlights

Coal mining activities using the open-pit mining method will leave voids when mining activities end
The catchment area of the pit lake was 21.43 km2, which mostly consisted of the reclamation area (Figure 6)
This study shows that in terms of the water balance during the formation in 2014 to reach equilibrium in 2017 with the addition of the volume of water comes from; 40–47% direct runoff, 17–39% groundwater flow, 3–6% direct precipitation, and 7–34% pumping, while the reduction in the volume of water comes from evaporation which ranges between 2–4%

Summary

Introduction

Coal mining activities using the open-pit mining method will leave voids when mining activities end. Coal production generally comes from mining activities using the surface mining method. Many of those surface coal mines potentially leave voids. According to the mining closure plan prepared by this coal mining company, with the best option of mining sequence optimization available, several mine voids will inevitably exist at the end of the mine’s operation period and will become pit lakes afterward. The company has a liability to make sure that the water quality of these pit lakes meets the government’s water quality standards. The initial characterization step needs to be conducted in order to understand the parameters involved and their influence on the pit lakes’ development, which will significantly determine the final water quality of the pit lakes

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