Paper No. Exposure and Risk Assessment at Petroleum Contamination Site with Multimedia Contaminant Fate, Transport, and Exposure Model (MMSOILS) Jong Soo Cho and John T. Wilson US Environmental Protection Agency, National Risk Management Research Laboratory, Subsurface Protection and Remediation Division, Ada, Oklahoma Prepared for Presentation at AIChE Annual Meeting/November 19,1998/ Copyright 'Not Applicable' August 3,1998 Unpublished AIChE shall not.be responsible for statements or opinions contained in papers or printed in its publications. ------- ABSTRACT A multimedia contaminant fate, transport, and exposure model (MMSOILS) was developed by EPA for the human exposure and health risk assessment associated with release of contaminant from hazardous waste sites. The model addresses the transport of a chemical in groundwater, surface water, soil erosion, atmosphere, and accumulation in the food chain. The human exposure pathways included: soil ingestion, air inhalation of volatiles and particulates, dermal contact, ingestion of drinking water, consumption of fish, consumption of plants grown in contaminated soil, and consumption of animals grazing on contaminated pasture. The risk associated with the total exposure dose was calculated based on chemical-specific toxicity data. An application of the MMSOILS has been conducted at a hydrocarbon contaminated site in a federal facility. Transport modules for non-aqueous phase liquid (NAPL) and gas phase was hardwired in the original model to handle the transport processes of spilled and leaked hydrocarbon in forms of NAPL and gas through unsaturated soil zone. The site was contaminated with JP-4 leaked from underground pipeline in front of the fire station in the Coast Guard air field. At the site, natural attenuation with long-term monitoring was adopted as the alternative contaminant management after two years of active remediation. The multimedia model was applied to assess the health risk to the base personnel during the life-span of the remaining contamination. ------- INTRODUCTION Improved risk assessment and risk management are the major goals of current research in the environmental protection field. Risk assessment is the basis for both policy and technical decisions to determine priorities for risk management and to guide the actual process of managing risks. The objective of the risk management is to reduce the risk to the acceptable level, not to eliminate the risk to the pristine level. Risks can be estimated using a variety of techniques including comparing individual exposure and effects values, comparing the distributions of exposure and effects, or using simulation models. Risk can be expressed as a qualitative or quantitative estimate, depending on the available data. Soils at many hazardous sites, including Superfund sites and others, are contaminated with a variety of chemicals. These contaminated sites pose a potential threat to human health via transport through various environmental media. More than one environmental transport mechanism may contribute to a human exposure pathway. As a result, an exposure assessment for a contaminated site must consider the different environmental transport mechanisms that may contribute to one or more of the human exposure pathways. The process of estimating the environmental concentration at exposure points in various media and examining the coupling between different transport mechanisms and human intake pathways is a complex task. In case of soil contamination, the important environmental transport media include contaminated soil, surface and ground water, air, and bioconcentration and movement in the food chain. Four possible human-exposure pathways exist: ingestion of contaminated air and soil particles, ingestion of contaminated water from surface water or groundwater, ingestion of contaminated meat, fish, dairy products, and crops, dermal contact of contaminated soils and water. To allow evaluation of such a soil contamination, the unsaturated zone component of an integrated model 'must have, at a minimum, the capabilities to account for and balance contaminant mass remaining in soil and contaminant mass loss due to volatilization. leaching, and degradation over time. The need for models with such capabilities has been recognized and recently there have been efforts to develop new models (e.g. MMSOILS (US EPA 1992)). MMSOILS is very comprehensive in number of mass loss processes, exposure routes or contamination scenarios, but very difficult to use without comprehensive knowledge and understanding on the modeling. In this presentation, we briefly introduce the capabilities of the model, MMSOILS, and new modules added to the current version. We applied this model for estimation of exposure levels and human health risk at the hydrocarbon release site, and results and problems related to the application are included in the presentation. MODELING METHODOLOGIES The four basic functions of the methodologies are:l) estimate the chemical release rate from the source into each environmental media based on chemical properties and land use at the site. 2) estimate the chemical concentration at exposure points in each environmental media considered based on the chemical release rate and the proximity to exposed populations. 3) estimate the human exposure through inhalation, ingestion and absorption based on the chemical concentration at exposure points and assumptions regarding human intake levels. 4) estimate the potential health risk based on toxicity data for the specific chemical based on the estimated human exposures at exposure points. The model uses several mathematical modules to represent the important fate and transport processes. The modules are relatively simple analytical or numerical models, which are selected to represent the different chemical release and transport processes in water, air and soil. One module added into the current version of the MMSOILS is the multiphase equilibrium module of multicomponent NAPL in soil matrices. This module is based upon the SOILCALC model which was developed for phase equilibrium calculation among gas, aqueous, non-aqueous, and solid phases in subsurface (Mott, 1995). ------- APPLICATION AT JP-4 CONTAMINATION SITE The MMSOILS has been applied for human health risk assessment at the JP-4 release site in the US Coast Guard base. The site was contaminated with a JP-4 release from the failed underground pipeline. The site was actively cleaned until 99% of the most hazardous components, benzene, toluene, ethyl benzene, and xylene isomers (BTEX) in the subsurface soil have been removed. After the termination of the active remediation, natural attenuation with monitoring was implemented as the alternative remediation strategy (Cho et at,, 1997). Even after 99% of BTEX removal, still 50% of initial total petroleum hydrocarbon (TPH) remained in subsurface and dissolved benzene concentration under the initial source zone still remains above the drinking water standard. Risk assessment was focused on two acceptor points: the fire station which was very adjacent to the site and the river which is in 100 meter down gradient from the site. The major pathway of contaminant into the building was the vapor transport through the unsaturated soil from the NAPL source. Exposure levels and related health risks to the fire fighters who stays at the station was estimated. Even though the base doesn't use the ground and surface water as drinking sources, lots of water activities including swimming, fishing, sailing, and boating were in the river. Exposure level and risk related to those activities with various hypothetical conditions were estimated. Transport with groundwater flow and other pathways such as surface run-off was considered as the contaminant pathway s to the river. At the time of the manuscript preparation, the program is still being tested and data values are being evaluated. Output results are to be presented in the conference. CONCLUSIONS The MMSOILS could be used for estimation of human exposure and health risk related to the activities around the contaminated sites or waste management units. The model was used to estimate the exposure level and health risk to the personnel near a petroleum hydrocarbon contamination site in the Coast Guard base. The major pathway investigated was the soil-air intrusion into the building nearby the contamination and surface water intake during the recreational activities in the river. Many parameters including physical, chemical, geological, and biological properties were not easily obtainable and had to be assumed. Many situations were hypothetical so that the results might vary in the order of magnitude. The purpose of this estimation was to approximate to the most possible and conservative cases so the order of magnitude approximation might be acceptable. Monte Carlo simulation capability in the MMSOILS may provide the valuable insight of uncertainty. NOTICE The authors are very grateful to Dr. Mott who provided the SOILCALC source code. Although the research reported in this paper has been funded wholly by the United States Environmental Protection Agency, it has not been subjected to the agency's peer-review and therefore does not neccssarily reflect the views of the agency. No official endorsement of the system design or trade names should be inferred. REFERENCES Mott, H.V., 1995. "A Model for Determination of the Phase Distribution of Petroleum Hydrocarbons at Release Sites," Ground Water Monitoring and Remediation, 15(3), ppl57-167. US EPA, 1996. "MMSOILS: Multimedia Contaminant Fate, Transport, and. Exposure Model, ------- Documentation and User's Manual, Version 4.0," Office of Research and Development, Washington, DC. Cho, J.S., J.T. Wilson, D.C. DiGiulio, J.A. Vardy, W. Choi, 1997. "Implementation ofNatural Attenuation at a JP-4 Jet Fuel Release after Active Remediation," Biodegradation, 8, pp265-283. ------- TECHNICAL REPORT DATA NRMRL-ADA 98110 1, REPORT NO, 600/A—98/127 2. 3. RECIPIENT'S ACCESSION NO. 4. TITLE AND SUBTITLE Exposure and Risk. Assessment at Petroleum Contamination Site with Multimedia. Contaminant Fate, Transport, arid Exposure Model (MMSOILS) 5. REPORT DATE S. PERFORMING ORGANIZATION CODE 7. AUTHQR(S) Jong Soo Cho and John T. Wilson 8. PERFORMING ORGANIZATION REPORT NO. 9. PERFORMING ORGANIZATION NAME AND ADDRESS US EPA Office of Research and Development Subsurface Protection and Remediation Division National Risk Management Research Laboratory 919 Kerr Research Drive Ada, OK 74820 10. PROGRAM ELEMENT NO. 11. CONTRACT/GRANT NO. In-House 12. SPONSORING AGENCY NAME AND ADDRESS US EPA Office of Research and Development Subsurface Protection and Remediation Division National Risk Management Research Laboratory 919 Kerr Research Drive Ada, OK 74820 13. TYPE OF REPORT AND PERIOD COVERED 14 . SPONSORING AGENCY CODE EPA/600/15 15. SUPPLEMENTARY NOTES To be published in proceedings at: Annual Meeting of American Institute of Chemical Engineers, Miami Beach, FX. November 199S 16. abstract A multimedia contaminant fate, transport, and exposure model (MMSCI1S; was developed by EPA for the human exposure and health risk assessment associated with release of contaminant; from hazardous waste sites. The model addresses the transport of a chemical in groundwater, surface water, soil erosion, atmosphere, and accumulation in the food chain. The human exposure pathways included: soil ingestion, air inhalation of volatiles and particulates, dermal contact, ingestion of drinking water, consumption of fish, consumption of plants grown in contaminated soil, and consumption of animals grazing on contaminated pasture. The risk associated with the total exposure dose was calculated based on chemical-specific toxicity data, An application of the MMSOILS has been conducted at a hydrocarbon contaminated site in a feoeral facility. Transport modules for non-aqueous phase liquid ENAPL) and gas phase was hardwired in the original model to handle the transport processes of spilled and leaked hydrocarbon in forms of NAPL and gas through unsaturated soil zone. The site was contaminated with JP-4 leaked from underground pipeline in front of the fire station in the Coast Guard air field. At the site, natural attenuation with long-term monitoring was adopted as the alternative contaminant management after two years of active remediation. The multimedia model was applied to assess the health risk to the base personnel during the life-span of the remaining contamination. 17. KEY WORDS AND DOCUMENT ANALYSIS A. DESCRIPTORS B. IDENTIFIERS/OPEN ENDED TERMS C. COSATI FIELD, GROUP Multimed! a Risk Assessment Hydrocarbon Exposure IS. DISTRIBUTION STATEMENT Release to the Public 19. SECURITY CLASS [THIS REPORT) Unclassified 21. NO. OF PAGES 5 20, SECURITY CLASS(THIS PAGE) Unclassified 22. PRICE SPA FOBM 2220-1 (REV.4-77) PREVIOUS EDITION IS OBSOLETE ------- |