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 (NH) 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 NH. 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.