MODELING AND RISK ASSESSMENT OF A 30-YEAR-OLD SUBSURFACE RADIOACTIVE-LIQUID DRAIN FIELD

The contamination from a 30-year-old radioactive liquid drain field wa s assessed for movement in the subsurface and potential risks to human s. This assessment included determining field concentrations of cesium 137 (Cs-137) and other inorganic contaminants and modeling of the flo w and transport of the liquid waste that was sent to the drain field. The field investigation detected no contamination deeper than 15 feet (4.6 m) from the bottom of the drain field. Prediction of the water co ntent of the vadose zone showed no saturated conditions for times grea ter than 10 years after the known infiltration. Sensitivity analysis o f the modeling parameters showed the equilibrium sorption coefficient to be the most important factor in predicting the contaminant plumes. Calibration of modeling results with field data gave a Cs-137 sorption coefficient that is within the range of values found in the literatur e. The risk assessment for the site showed that the contamination pose s no significant risk to human health.