Subsurface contamination at petroleum-contaminated sites is posing a serious threat to the environment and the publicand is acquiring more and more attention by governments and industries. This paper proposed a fuzzy risk assessment method and its application to a petroleum-contaminated site. The method consists of three parts:

  • calculation of fury steady-state contaminant concentrations in the aquifer based on an analytical solute transport model,

  • possibilistic analysis of fuzzy criteria for different risk levels, and

  • environmental risk assessment based on the Euclidean method.

The method can effectively reflect fuzzy natures of environmental quality at a site and evaluation criteria for different risk levels. Results of an illustrative case study indicate that environmental risks at a petroleum contaminated site can be effectively evaluated through the developed methodology. The assessment results are useful for the related site remediation and management decision.


Development of the petroleum industry is currently associated with a number of environmental concerns. Among them, soil and groundwater contamination is acquiring more and more attention by the public, governments, and petroleum industries themselves 1, 2, 3. This situation is especially true in western Canada where petroleum production, processing, upgrading, and utilization are active. Generally, the major sources of soil and groundwater contamination are leaking storage tanks used by commercial, industrial and residential sectors. Similar contamination can also occur during landfarming, petroleum sludge disposal, heavy oil upgrading, and others 4.

Soil and groundwater contamination has lead to a variety of impacts, risks, and liabilities to the communities and for the industries themselves 5. For example, it is proved that one gallon of gasoline can render one million gallons of water unsuitable for drinking. In Canada, about 10% of the 200,000 underground storage tanks are leaking and contaminating the surrounding environment, causing losses of thousands of dollars yearly to petroleum industries. In Alberta, there are over 130,000 abandoned drilling sumps that are associated with a number of subsurface contamination problems. It is estimated that rendering all these abandoned drilling sumps will require a minimum expenditure of 10 billion dollars. Therefore, in-depth and effective environmental risk assessment of groundwater contamination due to leaking petroleum contaminants is important and desired for evaluating the need for site remediation actions and providing support for decisions related to prevention, detection, and correction of the leakage and contamination problems 6.

In recent years, risk assessment techniques have become widely used as aids in the decision-making process related to contaminated soil and groundwater. Risk assessment could give managers a more rational basis on which to make decisions 7. The general formulation of the environmental risk problem captures the entire process of identifying the source term of the risk agent, its fate and transport through porous media, estimation of human exposure, and conversion of such exposure into the risk level. This process involves a number of chemical, physical, biological, geological, and socioeconomic factors due to their direct or indirect relations to the environmental impacts/risks.

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