When coal fly ash is added to soils for physical stabilization, questions arise as to the environmental risk. Fly ash that is high in CaO is an inexpensive material for treating clayey soils to enhance engineering characteristics. When 10 to 20% ash is added, as is common in engineering applications, the concentration of some potential toxic elementals will be increased, which in the long-term could increase the risk of pollution of ground water and could have negative human health consequences from direct contact with the ash mix. We developed a computer program that determines allowable upper limits of ash using spreadsheet-based worksheets of the Minnesota Pollution Control Agency. These worksheets set clean-up goals for polluted soils and they are used when a responsible party does not want to pay for a site-based risk assessment. Twenty-one elements of concern are evaluated with respect to the health risk of direct contact based on several human contact scenarios and with respect to the potential of leaching to ground water with possible violation of the drinking water human health risk limits. The computer program uses soil properties, and chemical data from fly ash and soil to calculate the concentrations of elements of concern in a soil mix and indicates pass or fail. We also developed a chemical database of ash fly ash sources and soils in Minnesota.
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