Site-specific aftercare completion criteria for sustainable landfilling in the Netherlands: Geochemical modelling and sensitivity analysis.

A novel, regulatory accepted approach is developed that enables competent authorities to decide whether landfill aftercare can be reduced or terminated. Our previous paper (Brand et al., Waste Management 2016, 56, 255-261, https://doi.org//10.1016/j.wasman.2016.07.038) outlines the general approach, that consists of a 10-year treatment phase (e.g., aeration, leachate recirculation), in combination with site-specific Environmental Protection Criteria (EPC) for contaminant concentrations in the landfill leachate after treatment. The current paper presents the unique modelling approach by which the site-specific EPC are derived. The modelling approach is based on the use of mechanistic multi-surface geochemical models covering the main sorption processes in soils underneath the landfills, and is composed of widely-accepted surface complexation models in combination with published "generic" parameter sets. This approach enables the consideration of the main site-specific soil properties that influence the attenuation of emitted contaminants. In addition, the sensitivity of the EPC is shown for variation of the main physicochemical-assumptions and policy-based decisions. Site-specific soil properties have been found to substantially determine the EPC and include soil-pH, dissolved organic matter, and iron-(hydr)oxide content. Apart from the sorption capacity of the local soil, EPC also depend strongly on the assumed dilution with local groundwater in the saturated zone. An important policy-related decision that influences the calculated EPC is the assessment period during which the groundwater is protected. The transparent setup of the approach using geochemical modelling, the explicit consideration of site-specific properties and the achieved regulatory acceptance may also stimulate application to landfills in other countries.