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SIMULATING INTEGRATED MULTIMEDIA CHEMICAL FATE AND TRANSPORT FOR NATIONAL RISK ASSESSMENTS
Citation:
Saleem, Z A., R B. Ambrose Jr., D B. Schwede, K. L. Little, D. Guvanasen, AND T. P. Lillys. SIMULATING INTEGRATED MULTIMEDIA CHEMICAL FATE AND TRANSPORT FOR NATIONAL RISK ASSESSMENTS. Presented at Society for Risk Analysis Symposium, Atlanta, GA, December 5-8, 1999.
Description:
The site-based multimedia, multipathway and multireceptor risk assessment (3MRA) approach is comprised of source, fate and transport, exposure and risk modules. The main interconnected multimedia fate and transport modules are: watershed, air, surface water, vadose zone and saturated zone. These modules predict chemical concentrations for use by the exposure and risk modules. The fate and transport modules calculate the chemical fluxes into downstream media which are linked by sharing data and results files. The source modules produce time series of chemical fluxes as input to these modules. Because of the complex interacting nature of the natural systems being simulated and the implementation of the model in a Monte Carlo framework, the aim of model development was to produce computationally efficient and numerically stable model, while maintaining reasonable accuracy. Numerous innovative enhancements to the legacy media modules were made and several new modules were developed for use in 3MRA. For example, modifications to the air model (ISCST3) included a revised plume depletion algorithm and a modified meteorological sampling approach (SCIM) to reduce computational burden in estimating long-term average chemical deposition values. The Watershed Module simulates the dynamic response of the watershed to atmospheric deposition of a chemical based on a semi-analytical implementation of an enhanced Jury-type fate and transport model, coupled to stormwater runoff and erosion processes. A pseudo-three dimensional module was developed to simulate the fate and transport in aquifers of chemicals and their transformation products with MINTEQ providing the speciation of metals in the subsurface environments. The surface-water module was innovatively enhanced to make it more robust and efficient for simulating waterbody networks at the site. Verifications of the modules and results of application also are discussed.