PNNL-11080
UC-602, 630

 
 
 
 
 
 
 
 
 

 
 
 

THE MULTIMEDIA ENVIRONMENTAL POLLUTANT
 ASSESSMENT SYSTEM (MEPAS):
 ATMOSPHERIC PATHWAY FORMULATIONS

 J. G. Droppo
 J. W. Buck
 

March 1996
 

Prepare for
the U.S. Department of Energy
under Contract DE-AC06-76RLO 1830
 
 
 
 

Pacific Northwest National Laboratory
Richland, Washington 99352
Copyright 1989-1996 Battelle Memorial Institute












PREFACE

    This report is one of a series of reports that document the mathematical models in the Multimedia Environmental Pollutant Assessment System (MEPAS). Developed by Pacific Northwest National Laboratory(a) for the U.S. Department of Energy, MEPAS is an integrated impact assessment software implementation of physics-based fate and transport models in air, soil, and water media. Outputs are estimates of exposures and health risk assessments for radioactive and hazardous pollutants.

    Each of the MEPAS formulation documents covers a major MEPAS component such as atmospheric, vadose zone, groundwater, surface water, overland, and exposure/health impact assessment. Other MEPAS documentation reports cover the sensitivity/uncertainty formulations and the database parameter constituent property estimation methods. The MEPAS atmospheric component is documented in this report.

    MEPAS simulates the release of contaminants from a source, transport through the air, groundwater, surface water, or overland pathways, and transfer through food chains and exposure pathways to the exposed individual or population. For human health impacts, risks are computed for carcinogens and hazard quotients for noncarcinogens. MEPAS is implemented on a desktop computer with a user-friendly interface that allows the user to define the problem, input the required data, and execute the appropriate models for both deterministic and probabilistic analyses.

(a) Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract     DE-AC06-76RLO 1830.






SUMMARY

    The Multimedia Environmental Pollutant Assessment System (MEPAS) is an integrated software implementation of physics-based fate and transport models for health and environmental risk assessments of both radioactive and hazardous pollutants. This atmospheric component report is one of a series of formulation reports that document the MEPAS mathematical models.

    MEPAS is a "multimedia" model; pollutant transport is modeled within, through, and between multiple media (air, soil, groundwater, and surface water). The estimated concentrations in the various media are used to compute exposures and impacts to the environment, to maximum individuals, and to populations.

    The MEPAS atmospheric component for the air media documented in this report includes models for emission from a source to the air, initial plume rise and dispersion, airborne pollutant transport and dispersion, and deposition to soils and crops. The material in this report is documentation for MEPAS Versions 3.0 and 3.1 and the MEPAS version used in the Remedial Action Assessment System (RAAS) Version 1.0.

    The atmospheric component of MEPAS uses a series of climatological models for modeling the releases from point and area sources. In MEPAS, emission estimation models are provided as an alternative method for cases where the emission rates are unknown or cannot be back-calculated from environmental monitoring data. MEPAS has seven volatilization models for estimating gaseous vapor emissions from various types of sources and a particle suspension model for estimating soil-bound pollutant emissions. Plume rise models are included for stack releases. A sector-average Gaussian model using standard dispersion rates is used for the atmospheric transport. Both wet and dry deposition are computed. An important enhancement is that the wind speed, dispersion, and deposition models account for the influence of local surface roughness. This feature allows the model to account for local roughness influences along a wind trajectory ranging from smooth over-water to rough forest cover. A complex-terrain nocturnal flow option allows for the near-source channeling of airborne releases.

    The major products from these atmospheric component models include 1) contaminant emission rates, 2) regional patterns of long-term air concentrations and deposition rates normalized by emission rates, 3) near-release short-term acute air concentrations normalized by emission rates, 4) long-term deposition rates for selected types of surfaces, and 5) regional patterns of ambient pollutant concentrations. These output products from the atmospheric component are linked as input to other components as part of the integrated MEPAS exposure and impact evaluation software.






ACKNOWLEDGMENTS

    The development of this multimedia contaminant environmental exposure and risk assessment methodology over the past decade required input from a wide spectrum of engineering and scientific technologies. The original MEPAS concept was developed by G. Whelan and B. L. Steelman. They were joined by K. A. Higley, D. L. Strenge, B. L. Hoopes, and the authors of this volume to form the initial MEPAS development team.

    The development of the air component of MEPAS involved a number of staff. D. L. Strenge, and B. L. Hoopes helped in the initial design and integration with other components. C. D. Whiteman provided input on processes in complex terrain. S. Hwang, J. L. Stroh, and G. P. Streile provided inputs on volatilization models. C. J. Fosmire helped in the implementation of the formulations presented in this document.

    We also wish to acknowledge L. J. Thibodeaux for his helpful suggestions and lecture notes relative to the modeling of volatilization from ponds.

    We also acknowledge valuable inputs from the following review efforts: U.S. Department of Energy's (DOE) Environment Survey MEPAS External Peer Review Panel, U.S. Environmental Protection Agency's Review of Hazard Ranking Systems, Health and Welfare Canada's Review of Multimedia Models, Hanford Single Shell Tanks Review Panel conducted by the National Academy of Sciences, DOE's Environmental Restoration Priority System External Review Panel, the DOE Programmatic Environmental Impact Statement External Review Panel, and U.S. Department of Defense's Review of Risk Prioritization Methodologies conducted by the National Academy of Sciences.

    Thanks go to R. J. Aiken of the DOE's Office of Environment, Safety, and Health for his support in the early stages of development. Special thanks also go to T. P. Longo, F. W. Baxter, P. V. Strider, K. J. Kelkenburg, P. M. Beam, and W. Wisenbaker Jr. of the DOE Office of Environmental Management for their long-term vision in supporting continued development and application efforts. These efforts were conducted for the DOE under contract DE-AC06-76RLO 1830.

    Special thanks also go to the Pacific Northwest National Laboratory's editing and word processing staff who made the many review drafts and this final document possible. Their hard work, patience, and professionalism in producing versions on very tight schedules is particularity appreciated.