Using Equilibrium Based Fugacity Analysis to Predict Site-Specific Risk-Based Target Levels for Low Permeability Soils

Gregory D. Hoffman, Clint L. Thompson, and Richard C. Sims

This presentation focuses on using fugacity principles to evaluate the impact of petroleum contamination to soil and groundwater in low permeability media. Risk Based Corrective Action (RBCA) regulations have been implemented by many state agencies leading to increased use of various modeling techniques. Infiltration based models are typically used to determine site-specific target levels for soils that ensure groundwater is protective of human health and the environment. Kinetic transport mechanisms (i.e. infiltration) are, however, usually negligible in low permeability soils where vapor-phase diffusion is likely to dominate redistribution of volatile organic compounds (VOCs). Fugacity analysis utilizes thermodynamic equilibrium principles to predict the limits of VOC r distribution to groundwater and nearby soils. This presentation discusses the fugacity analysis and appropriate applications for determining site-specific target levels for site closure. Case studies are also presented showing fugacity analysis achieving site closure when other transport models suggested additional investigation or required remediation.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California