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The Impact of Drilling and Production Operations 129

hazards. It identifies what the potential hazards may be, their potential
impact, how many humans could be impacted, and what the overall
impact might be.
Risk assessment can be used to identify and rank the substances
that have the greatest potential environmental impact. This helps
companies identify and prioritize efforts to ensure environmentally safe
operations. Risk assessment studies also document environmentally
responsible actions and can be used as a scientifically defensible study
if litigation occurs. Risk assessment studies are expensive, however,
and may not be feasible for small operations. They are normally
required only for new emission sources or modified stationary sources.
The calculations are complex and based on various exposure pathways.
Sullivan (1991) provides a discussion of risk assessment for crude oil
contamination.
Risk assessment consists of four steps: hazard identification, dose-
response assessment, exposure assessment, and risk characterization.

Hazard Identification determines the nature and amount of toxic
pollutants that could potentially be emitted. It identifies the potential
adverse health effects associated with those pollutants. Hazard identifi-
cation includes a qualitative review of the available information of
each substance to determine which substances should be included in
a detailed assessment. It also determines the potential exposure path-
ways for the spread of the pollutant following a release e.g., ground-
water or airborne transport, and the affected populations. Information
for hazard identification can be obtained from relevant federal, state,
and local regulations, risk assessment studies from similar facilities,
Material Safety Data Sheets, and technical journals.

Dose-Response Assessment determines the relationship between the
magnitude of an exposure to a substance and the occurrence of specific
health effects. It involves determining the actual toxicity of each
substance identified in the hazard identification. Dose-response assess-
ment includes obtaining a description of the toxic properties of the
substances, including acute (short term) effects, noncarcinogenic
chronic (long-term) effects, and the carcinogenic potential for different
dose levels. The result of this assessment is a probability estimate of
the incidence of the adverse effect as a function of human exposure
level to the substance.