INTEGRATED MODELING OF DISULFOTON TRANSPORT AT AN ABANDONED LANDFILL SITE

Abstract

Abandoned landfill sites pose an uncertain threat to water quality and environmental health. These sites, oftenlocated in rural areas, historically had little or no regulation for use or maintenance, and it is often unknown whathazardous materials may have been discarded. Evaluation and remediation of these sites can be extremely costly.Numerical models of contaminant fate and transport can be a cost-effective tool for assessing the potential hazards that asite may pose and for evaluating potential remediation measures, but seldom are models available which can simulate allaspects of contaminant fate and transport under complex site conditions. A study is presented describing the siteinvestigation and remediation of an abandoned landfill reported to contain unknown quantities of disulfoton, an acutelytoxic pesticide. Depending upon disulfoton concentration, it may or may not be dissolved in the soil water; thus, it may betransported in the soil either in an aqueous (dissolved) phase solution with soil water or as a non-aqueous phase liquid(NAPL). Because of the complex nature of the site and contaminant, it was necessary to employ three different numericalmodels to analyze different aspects of the problem. The article focuses particular attention on the use of different modelsfor contaminant transport modeling in support of a Remedial Investigation (RI). Model selection was based on thecontaminant phase and soil conditions. Various scenarios were hypothesized due to the uncertainty of input parameters.Procedures are presented for site remediation based on site investigation, numerical modeling and risk assessment.