DEVELOPMENT OF SITE-WIDE DILUTION ATTENUATION FACTORS FOR RISK-BASED CORRECTIVE ACTION (RBCA) MANUAL AND PROTOCOL MIAMI INTERNATIONAL AIRPORT

KHAN, A., alauddin.khan@cpmx.saic.com; and PACK, S., samantha.pack@cpmx.saic.com, Science Applications International Corporation, 800 Oak Ridge Turnpike, P.O. Box 2502, Oak Ridge, TN 37831.

Dilution Attenuation Factors (DAFs) were developed to create Airport-specific Tier 2 cleanup levels for the Miami International Airport (Airport) Risk-Based Corrective Action (RBCA) process. The Airport spans over 3,000 acres and contains many historical contaminant releases. The Tier 2 cleanup levels have been proposed to the State of Florida to be used in all RBCA decisions at the Airport.

Hydrologic and geologic information collected at the Airport was conceptualized to form the basis for developing the DAFs. AT123D was selected as the fate and transport model. AT123D can simulate the migration of a contaminant through the subsurface and account for the relevant mechanisms and processes affecting migration to off-Airport receptors. Site-specific data used in the model indicated the following: 1) there are four distinct groundwater flow paths at the Airport; 2) groundwater gradients are very transient due to multiple anthropogenic structures in the region, and; 3) widespread fuel releases have resulted in methanogenic conditions, which speed up the degradation of chlorinated releases. DAFs were developed for seven primary chemical groups identified at the Airport. A surrogate chemical was selected from each of the seven chemical groups so that the DAF developed for the surrogate could apply to all chemicals in the group. The proposed DAF approach requires that individual RBCA sites use DAFs that are dependent on the site’s distance from the Airport boundary.