Assessing the Influence of Subwatershed Areal Rainfall on Leachate Characteristics: A Case Study of the Piyungan Landfill

Abstract

Population growth increases waste volume, intensifying landfill burden. This condition contributes to environmental degradation, particularly through the formation of leachate that poses a potential risk of contaminating the surrounding environments. This study aims to characterize the hydrological conditions of the Piyungan Subwatershed and to analyse the relationship between areal rainfall and leachate characteristics, comprising physical (TDS), chemical (pH, COD, BOD) and heavy metals (Fe, Zn, total Cr). Hydrological analysis was carried out using QSWAT to delineate subwatersheds in Opak Watershed, while areal rainfall was calculated using the Thiessen Polygon method based on data from four rainfall stations over the 2002-2023 period. Relationship between rainfall and leachate characteristics was analysed using simple linear regression, with statistical significance assessed through a t-test at a 95% confidence level (α=0.05), based on a dataset from 2020-2023. The results indicate that the Opak Watershed comprises 14 subwatersheds, one of which is the Piyungan Subwatershed, which was used as the basis for areal rainfall estimation, yielding an average value of 1,704 mm/year. Rainfall exhibits a negative relationship with most parameters, except for pH and BOD. Nevertheless, statistically significant relationships are only observed for TDS (p=0.0046<0.05) and Fe (p=0.0036<0.05), while the other parameters are not significant. These findings are consistent with the previous studies, indicating that rainfall is not the primary controlling factor of leachate characteristics; rather, the internal landfill factors play a more dominant role, for instance landfill age and waste composition.