Framework for site specific leachate limits in MSW dumpsites: Integration of high-resolution site characterization and contaminant transport modeling

The establishment of site-specific target limits (SSTLs) for old municipal solid waste (MSW) dumpsites is essential for defining remediation goals in a scientifically rigorous manner. However, a standardized framework for achieving this is currently lacking. This study proposes a comprehensive framework that integrates high-resolution site characterization (HRSC) tools, targeted sampling, and contaminant transport modeling to derive SSTLs. The framework was applied to a case study at a MSW dumpsite in Delhi, India, with a focus on contaminant transport within the unsaturated zone. HRSC was performed using a cone penetrometer (CPTu) and a hydraulic profiling tool (HPT). Ammonium (NH₄⁺) and nickel (Ni) were identified as contaminants of concern based on pore water analysis from the unsaturated zone, which comprised of clay and silty sand. Sorption isotherms and soil-water characteristic curves (SWCC) were developed for different soil types to derive contaminant transport parameters. These parameters were validated by comparing model results with observed concentration profiles, yielding a satisfactory correlation. A 50-year forward modeling exercise determined an SSTL of 100 mg/L for NH₄⁺. For Ni, the modeling indicated no breakthrough from the unsaturated zone over the 50-year period due to the high sorption on clays, suggesting that remediation for Ni is not required. A sensitivity analysis was also conducted to identify key parameters influencing contaminant migration. This framework provides a rapid, robust, and scientifically sound approach for setting remediation goals at un-engineered landfills, supporting the implementation of dynamic remediation strategies.