Application of QUAL2K for Water Quality Impact Assessment of Mining-Impacted River: A Case Study of Sungai Rui, Perak

Abstract

Tin mining activities pose significant environmental risks, particularly to adjacent water bodies, by releasing pollutants that degrade water quality and disrupt aquatic ecosystems. This study investigates the water quality impacts of tin mining in the upstream region of Sungai Rui, Perak, a tropical river system that supports the endemic Thynnichthys thynnoides. Using the QUAL2K water quality model, five scenarios were simulated to assess the effects of mining phases and management practices on key water quality parameters, with a focus on total suspended solids (TSS), biochemical oxygen demand (BOD), pH, and ammoniacal nitrogen (NH3N). Results revealed that during construction without mitigation, TSS levels at the project site (WQ9) increased from a baseline of 49.84 mg/L (NWQS Class II) to 3,979.86 mg/L (Class V). Under tailing pond outburst conditions, BOD at WQ3 (Sg. Rui–Perak confluence) rose from 3.19 mg/L (Class II) to 23.73 mg/L (Class V), and NH3-N spiked from 0.155 mg/L to 11.39 mg/L (Class V). pH levels also dropped from 7.65 to 6.08, indicating increased acidity. The application of best management practices (BMPs) during construction significantly reduced TSS to 47.97 mg/L, showing near-baseline recovery. These findings underscore the severe impact of unmitigated mining activities on river water quality and highlight the importance of BMPs and regulatory enforcement. The model also illustrates the limited dilution capacity of downstream rivers under high pollution loads, reinforcing the need for preventive measures at the source.