Page 144 - Environmental Control in Petroleum Engineering

The Impact of Drilling and Production Operations 131

Protection Agency has developed a set of air quality models that can
be used for airborne pollutant transport,

Risk Characterization describes the nature, magnitude, and uncertainty
of the health risks associated with each pollutant. It is the combination
of the dose-response assessment and the exposure assessment. Risk
characterization determines a quantitative estimate for the risk. This
risk level can then be compared to a risk level that is considered to
be insignificant. In humans, risk levels of one in ten thousand and one
in one million are often used by regulatory agencies as benchmarks
for acceptable risk levels.
The risk to the "maximum-exposed individual," i.e., the individual
who receives the worst-case exposure scenario, and the more realistic
risk to the general population should both be determined. Risk charac-
terization should include a discussion of background levels of pollu-
tants and risks associated with other activities, including the risks if
nothing is done. Finally, risk characterization should be flexible and
incorporate an honest evaluation of the uncertainties of the information
used in the analysis.
Acceptable risk for carcinogens is normally determined in one of
two ways. The most common approach is to calculate the maximum
risk for an individual assuming an exposure level at the highest
predicted long-term concentration. The goal of this approach is to limit
excess lifetime cancer risks to a predetermined level. The second
method is to estimate the aggregate incidence of potential excess
cancer cases for the exposed population within the vicinity of the
source. Risk assessment studies have uncertainties, particularly when
conservative data are used. If more realistic data are used with Monte
Carlo simulation, a more realistic estimate of risk can be obtained
(Gordon and Cayias, 1993).

American Petroleum Institute, "Fate and Effects of Polynuclear Aromatic
Hydrocarbons in the Aquatic Environment," API Publication 4297,
Washington, D.C., May 1978.
American Petroleum Institute, "Analysis of Mussel (Mytilus californianus)
Communities in Areas Chronically Exposed to Natural Oil Seepage," API
Publication 4319, Washington, D.C., May 1980.