Decision Analysis for Storage for Reclaimed Asphalt

Abstract

Hydrogeological decision analysis was used to compare five alternative designs for temporary storage of reclaimed asphalt pavement (RAP) with respect to the environmental economical risks to groundwater and the construction costs. The study was generic in scope and directed at RAP storage in gravel pits in glacio-fluvial deposits. This hydrogeological setting constitute the major aquifers for public water supply in Sweden, and storing RAP in this setting may therefore impose conflicts with groundwater protection and supply interests. The decision analysis considered the contaminant load on the hydrogeological system, the subsurface contaminant transport conditions, the environmental economical risks of contamination above existing compliance levels, and the construction costs of the facility. A sensitivity analysis was done with regard to the costs, the cover efficiency, and the model uncertainty. Risk was defined as the expected costs of failure to meet existing compliance levels, and the objective of the study was to identify the alternative that minimizes the sum of investment and risk costs at a typical RAP site. Field measurements identified chloride, lead, and butylated hydroxytoluene (BHT) as major contaminants. Stochastic transport simulation for a typical glacio-fluvial sand and gravel aquifer indicated that lead and BHT pose little risk to this hydrogeological setting, but that chloride has a stronger impact. The decision analysis showed that a simple cover to prevent leachate production is the most cost-effective design for small- to medium-sized glacio-fluvial aquifers. It further showed that unmonitored RAP storage should be avoided for large aquifers.