ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS’’, Bangkok, May 23-25, 2001
ISPRS, Vol.
60
systems more complicated to quantify. Thus, effective
reflection of uncertainties, which is essential for generating
reliable and realistic outcomes, has been a major concern for
risk assessment (Lein, 1992)
There have been a lot of studies to date to deal with the
uncertainties within the environmental risk assessment for
Petroleum Hazardous Waste concern. Most of the studies are
employing probability theory (e.g., Monte Carlo simulation). For
instance, Paustenbach (1999) proposed a comprehensive
methodology for assessing the risks to human and wildlife
posed by contaminated soil which involving Dioxin (1989).
Adams and Hanna (1994) processed a health risk assessment
using a Latin Hypercube probabilistic risk assessment of health
risks associated with exposures to contaminated sediment and
biota in an estuary.
Another major approach for uncertainty involved environmental
risk assessment is through fuzzy set theory, which is suitable
for situations when probabilistic information is not available
(uncertainties present as fuzzy membership functions rather
than probability distribution functions) (Bardossy et al., 1991).
For example, Lee and Dahab (1994) et al. developed a rule-
based fuzzy set approach for risk assessment of nitrate-
contaminated groundwater. Kangari and Riggs (1989) used
fuzzy number and natural language to represent the
uncertainty in construction risk assessment process. Huang
(1995) proposed a fuzzy risk assessment method to assess
the natural hazards in the urban area. Huang and Chen et al.
(1999) developed a fuzzy relation approach to analysis the risk
causing by the leachate from the UST.
However, results from evaluations of human health risks
associated with environmental contamination are traditionally
presented non-spatially. Non-spatial tabular reporting of single
value has been well-accepted convention for characterization
of human health risk results, no specific spatial information is
included (William and Daniel, 1996). However, It is also very
clear that risk assessments have an important spatial
component, for the reason that risk evaluations are generated
by reference to specific environmental data collected from
specific locations. Regarding to the above mentioned
problems, GIS components can provide a comprehensive
database of contaminated site conditions, tools for spatial and
customized interface of risk assessment, and visual
presentation of modeling results and site natural and spatial
characterization. Especially, integration of the risk assessment
results with spatial land-use information will be very helpful for
identifying and assessing pollution impacts on specific
receptors through various exposure pathways, maps can be
valuable for risk communication. At present, however, such
integrated GIS and risk assessment applications are relatively
rare and an important reason for this situation appears to be
limited awareness among risk analysts of the full capacities of
GIS knowledge.
As an extension to the previous research, a probabilistic and
possibilistic method for assessing human health risk
associated with petroleum-contaminated site is presented in
this study, and GIS technology is integrated to spatially
represent the risk results.
2. METHODS FOR HUMAN HEALTH RISK ASSESSMENT
Based on the results from BIOF&T simulator outputs, a
detailed probabilistic and possibilistic approach is utilized to
deal with environmental risk assessment concerning the
petroleum-contaminated site.
The process of risk assessment in this research involves the
following steps:
□ A 3D multiphase transport model (BIOF&T), a finite
element model from Resources & Systems
International, Inc., is preliminarily employed for
studying the transport process of hydrocarbon-
derived contaminants in soil and groundwater.
□ Individual health risk characterization through widely
accepted exposure-dose model, in this part Monte
Carlo simulation method and fuzzy relation analysis
are employed to evaluate the health risk posed by
different age group.
□ Site overall health risk assessment using a fuzzy
interval risk assessment approach.
□ Results visualization integrated with GIS.
2.1 Site Characteristics and Contamination Status
The research target, the Hoosier Site, is located at
approximately 50 km northwest of Kindersley, Saskatchewan,
Canada. Up to date, the facilities on site include an adsorption
tower building, an above ground naphtha storage tank, a
heater building, a cooler unit, a truck loading dock, a salt bath
line heater, a flare pit, and above ground pipelines. They had
been in operation as a natural gas processing plant ever since
mid 1960s to early 1990s.
The Hoosier Gas Adsorption Plant (HGAP) was designed and
utilized to clean natural gas through a series of scrubbers,
remove naphtha condensate from the natural gas stream prior
to condensate transporting to a regional transmission line. The
hydrocarbons and condensates originated inevitably from gas
by-product impurities. Throughout the history of the site
operation, naphtha condensate, a waste liquid removed from
the gas by a series of scrubbers, has been disposed of in a
perforated underground storage tank (UST) located
immediately south of the adsorption tower building (Roper
Environmental Engineering Inc., 1992; Clifton Associates Ltd.,
1996).
Several studies have been conducted to evaluate the nature
and extent of any chemical residuals at Hoosier Site. “It is
understood that the UST was perforated to accommodate
naphtha disposal via ground infiltration. More recently, the
naphtha condensate was disposed of in an above ground
storage tank (AST) located approximately 32 m south of the
adsorption tower building. Naphtha was trucked off the site and
used to blend with heavy oil. The natural gas condensate was
believed to spill and leak into soil following the seepage into
the groundwater" (Clifton Associates Ltd., 1994). Two
contaminant-concentrated zones were then formed in the
subsurface capillary zone (at the interface between
unsaturated and saturated zones). Numerous of Environmental
investigations of the Hoosier Site were conducted by
Environmental Consulting Companies. Among them, Including
Roper Environmental Engineering Inc. in 1992, Clifton
Associates Ltd. in 1993, 1995 and 1996, Stanley Consulting
Group Ltd. in 1997, and Clifton Associates Ltd. in 1998. These
investigation works included surface and subsurface sampling
of soil and groundwater, bore hole drilling, and monitoring well
construction.
Results of the investigations identified the existence of free
liquid phase contaminants free phase products in several
monitoring wells (Clifton Associates Ltd., 1994, 1995, 1996;
Stanley Consulting Group Ltd., 1997). Residual phase
hydrocarbons were also encountered from the soil samples in
many monitoring wells. Simultaneously, Benzene, Toluene,
Ethyl-Benzene, Xylenes, were also presented in the AST and
flare pit areas.
2.2 Groundwater Transport Model
Developed by Resources & Systems International, Inc.,
BIOF&T 3-D could be utilized to accurately model
biodegradation, flow and transport process in the saturated
and unsaturated zones in two or three dimensions in
heterogeneous, anisotropic porous media or fractured media.
BIOF&T’s powerful functions allow real world modeling which
are not usually available in similar packages. It could model
convection, dispersion, diffusion, adsorption, desorption, and
microbial pmra
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