You are here:
EVALUATION OF VADOSE ZONE AND SOURCE MODELS FOR MULTI-MEDIA, MULTI-PATHWAY, MULTI-RECEPTOR RISK ASSESSMENT USING LARGE SOIL COLUMN EXPERIMENT DATA
Citation:
Schmelling*, S G., K. Liu, AND M. Wang. EVALUATION OF VADOSE ZONE AND SOURCE MODELS FOR MULTI-MEDIA, MULTI-PATHWAY, MULTI-RECEPTOR RISK ASSESSMENT USING LARGE SOIL COLUMN EXPERIMENT DATA. Presented at 2003 RCRA National Meeting, Washington, DC, August 12 - 15, 2003.
Impact/Purpose:
To evaluate vadose zone and
Description:
The U.S. Environmental Protection Agency (EPA) is developing a comprehensive environmental exposure and risk analysis software system for agency-wide application using the methodology of a Multi-media, Multi-pathway, Multi-receptor Risk Assessment (3MRA) model. This software system will have application to the technical assessment of exposures and risks relevant for national waste management rules to protect the health of humans and other living organisms. Evaluation of the suitability and applicability of the component modules used for 3MRA is critical. The Ground Water and Ecosystem Restoration Division (GWERD) of EPA's National Risk Management Research Laboratory previously conducted a large-soil-column study to investigate the behavior of organic pollutants, including halogenated aliphatic hydrocarbons, substituted benzenes, and phenols, during infiltration of municipal wastewater into soil. The data from this study were used to evaluate three modules of 3MRA: (1) the fundamental module for Land Application Units (LAU), Wastepiles, and Landfills; (2) the LAU Source Model; and (3) the VZ (Vadose Zone) Model. Through implementations of those models with subsequent comparison and evaluation, it was found that overall, the volatilization rate modeled by the LAU model is in the right order of magnitude for all categories of compounds involved in the experiment, although the simulated volatilization is consistently lower than the observation for highly volatile organic compounds. Moreover, sensitivity analyses indicated that the model outputs of LAU model are not highly sensitive to the thickness parameter for volatilization of organic constituents, but show minor sensitivity to changes in temperature. Generally the VZ model functions quite well in simulating the fate and transport of organic constituents in vadose zones although noticeable difference between the simulated and observed results could be observed for highly volatile organics. In addition, the overall final output through the combined LAU and VZ models gave a good estimate of leachate concentration for organics undergoing both volatilization and transformation, while it overestimated for organics with high volatility and low transformation rate. Furthermore, several other widely used vadose zone models such as VLEACH and CHEMFLO were also evaluated using the same data. Comparisons between the aforementioned vadose zone models were performed. Finally, suggestions on how to appropriately apply those source and vadose zone models are presented based on the evaluation results.