BIOGEOCHEMICAL CHARACTERISTICS OF SUBSURFACE WATERS IN RECLAIMED SOILS AT PT BUKIT ASAM COAL MINE, SOUTH SUMATRA, INDONESIA

Organic soil amendments such as compost, wood chips, and sewage sludge have been reported to influence soil microbial composition, improve soil quality, and increase nutrient concentrations in surface runoff. A potentially negative consequence of adding compost to soils is that it may increase the solubility of metals in surface and groundwater. During this study, we investigated the effects of age and compost on metal (e.g. Al, Fe, Mn, Ni, Pb, Zn) concentrations in subsurface waters at reclaimed areas of the PT Bukit Asam Coal Mine, located near Tanjung Enim, South Sumatra, Indonesia. The mine relies heavily on the use of compost to improve soil productivity of reclaimed and reforested areas. The compost is aged for fourteen-weeks and mainly composed of materials from oil palms (Elaeis guineensis) and, to a lesser degree, organic municipal solid waste from the local community. In an effort to determine the most effective method for applying compost to reclaimed soil, compost is applied in a five-centimeter-thick layer spread over the reclaimed soil surface, or mixed with the soil placed in the hole where vegetation is planted. Metal concentrations were compared to study plots of varying ages (3 months to 10 years) and soil amendment treatments. Reclaimed soil without the addition of compost was also examined as a control. The aluminum concentration of one sample was above the USEPA aquatic life chronic criteria standard, and several samples had lead concentrations above the USEPA aquatic life chronic criteria and drinking water standards, raising management questions. Concentrations of manganese, iron, nickel, and zinc were all below USEPA aquatic life chronic criteria and drinking water standards for all samples taken among sites with varying ages and soil amendment treatments. Our results show metal concentrations in subsurface waters were not effected by varying age and treatment applications within our study area. Future work should focus on influences on metal mobilization by dissolved organic carbon and organic acids leached from these reclamation areas as well as best management practices in reducing aluminum and lead concentrations in waters on site.