Modifications of volatilization factors in risk based corrective action

'Full text:' Risk Based Corrective Action (RBCA) is a scientific tool used to evaluate extent of contamination and associated risk at contaminated sites. It is a simple, structured and scientifically sound methodology. RBCA integrates a chemical database with exposure assessment and fate and transport modeling to estimate the concentration of contaminants and associated risk in multimedia environments. Fate and transport of contaminants from one medium to another and concentration levels are estimated using cross media transfer factors and natural attenuation factors. One of the cross media transfer factors is volatilization that is used to predict volatilization of contaminants from soil and water to air. In this paper, an in-depth evaluation of volatilization factors used in RBCA was made and an improved formulation is proposed to estimate volatilization of chemicals from soil to air without introducing any computational complexity and also without additional input data requirements. The proposed model was evaluated and compared with the original RBCA model as well as with a more complex but accurate model. It is concluded that the proposed modifications are simple but reliable. The analysis shows that the modifications proposed in the surface soil volatilization factor will reduce carcinogenic risk prediction by 125% while the modified subsurface to enclosed space volatilization factor will reduce carcinogenic risk prediction by 24% compared to the volatilization factors used in RBCA. It is believed that risk predicted using these modified volatilization factors would be more reliable because the modified volatilization factors are based on better conceptual approach and incorporate more parameters in comparison to earlier factors. (author)