From mining void to resource: Water quality of coal mine pit lakes in South Kalimantan

Abstract

Coal mining in South Kalimantan has created numerous pit lakes that local communities use as water sources, although their quality has not been comprehensively assessed. This study presents an integrated evaluation of pit lake water quality by combining regulatory compliance with STORET standards (STOrage and RETrieval), contamination factor (CF), and pollution load index (PLI), while also examining the effect of water depth on quality variation. Water samples were collected using grab sampling and analysed for temperature, total suspended solids (TSS), total dissolved solids (TDS), pH, biological oxygen demand (BOD), chemical oxygen demand (COD), dissolved oxygen (DO), Fe, Pb, and Mn in accordance with Government Regulation of the Republic of Indonesia Number 22 of 2021. Differences between surface water and 5 m depth were tested using the Independent Samples t-test and Mann–Whitney U test. The results showed that BOD indicated moderate contamination (CF = 2.68), whereas the other parameters were in the low contamination category (CF < 1). The overall PLI was 0.348, indicating that the water had acceptable quality. Water depth up to 5 m did not significantly affect most parameters, although pH at 5 m was slightly lower than at the surface. These findings indicate that pit lake water requires treatment before domestic use and support the need for regular monitoring and sustainable management.