Environmental Impact Assessment(EIA) Registration for the ...

REVISED PROJECT DESCRIPTION AND ENVIRONMENTAL IMPACT ASSESSMENT (EIA) REGISTRATION
FOR THE NEPISIGUIT FALLS GENERATING STATION MODIFICATION AND REHABILITATION PROJECT
resulting environmental effects could be significant in relation to the identified thresholds of
significance for each VEC (previously identified, as applicable).
It is noted that Accidents, Malfunctions and Unplanned Events are evaluated individually, in
isolation of each other, as the probability of a series of accidental events occurring in
combination with each other is not likely to occur. It is not credible to assess the occurrence of
a series of accidental events occurring in parallel or as a result of each other, nor would it be
possible to predict or prevent such occurrences, even with the best of planning. These possible
events, on their own, generally have a very low probability of occurrence and thus their
environmental effects are of low likelihood. They have an even lower probability or likelihood of
occurring together—thus their combination is not considered credible, nor of any measurable
likelihood of occurrence.
Various credible accidents, malfunctions, and unplanned events have been selected to
complete the assessment. Since it is impossible to review and assess all possible accidents,
malfunctions and upset conditions, scenarios which represent higher consequence events that
would more than adequately address the consequences of less likely or lower consequence
scenarios have been chosen for assessment.
4.4.2 Identification of Accidents, Malfunctions, and Unplanned Events
The credible Accidents, Malfunctions and Unplanned events that have been selected, based on
experience and professional judgement, are described below.
Loss of Containment: Loss of Containment includes a partial or total failure of the NFGS or
any of its components, resulting in temporary or permanent damage to structures and
equipment as well as the unplanned release of water downstream.
Failure of the Coffer Dam: Failure of the Coffer Dam during Construction includes a partial or
total failure of the Coffer Dam resulting in a significant delay in the Project schedule, loss or
damage to equipment, temporary or permanent damage to structures, and/or the release of
sediment and/or debris downstream. In the case where a large sudden breach occurred, failure
of the Coffer Dam could result in significant damage to equipment, serious injury, or even loss of
life. As the Coffer Dam will be removed following Construction, this unplanned event is not
relevant to the subsequent Operation or Decommissioning and Abandonment phases of the
Project.
Hazardous Materials Spill: A spill of petroleum, oil and lubricants (POLs) or other liquid
hazardous materials may occur during refueling of machinery or through breaks or leaks in
hydraulic lines of equipment.
Erosion and Sediment Control Failure: Erosion and sediment control structures (e.g., check
dams, sediment fencing) may fail as a result of improper installation, lack of maintenance, or an
unplanned event
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