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Unpublished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.

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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.

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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).

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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,

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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.

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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


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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

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