Water Chemical Analysis of Surface Water Runoff from Iron Ore Mine Void at Tanjung - Bone, South Sulawesi.

The main problem in open-pit mining activities is the remaining mine openings as voids after mining activities end. The interaction between rock, water and air can cause dissolved rock chemical elements to cause polluted water. A study of this phenomenon was carried out in a void in the Tanjung area. An abandoned iron ore mine left a void with a depth of 13 meters. Furthermore, around the void existed two stockpiles of mined ore. Therefore, the void and the stockpiles may act as pollutant sources that can reduce surface water quality. In the rainy season, the water from the void flows out as a runoff downstream through a tributary. This study is intended to analyze the chemical concentration of runoff water from the void. Field observation was done to identify rock formation, and measured pH, turbidity, total dissolved solids (TDS), and electrical conductivity(EC) of water on site, and collected 10 water samples from the river and tributary. Field data was completed with laboratory chemical analysis for water major elements of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, CO₃^2- and HCO₃. The results of the analysis of the TDS test with a minimum value of 4 mg/l and a maximum of 607 mg/l. turbidity value 0 to 21.4 NTU, pH value 2.9 to 8.2, EC value 165.6 ms/cm to 316 ms/cm. Plotting the concentration of the major elements into Trilinear Piper Diagram shows that water is as CaMgSO₄ water type based on their major elements. Changes in water quality at voids, stockpiles and areas around the mine indicate that potential water pollution is generated from existing stockpiles.