A Spill Risk Assessment of the Enbridge Northern Gateway Project

Spill Return Periods for Medium and Large Spills
Volume 7B of the Enbridge application identifies return periods for a hydrocarbon 37
release that occurs along the pipeline route. Enbridge calculates spill return periods
with liquid pipeline failure frequency data from 1991 to 2009 from the National Energy
Board (NEB). According to Enbridge, NEB data best represent the ENGP because data
are based on hydrocarbon transmission lines under the jurisdiction of the NEB
(Enbridge 2010b Vol. 7B, p. 3-­‐1). Enbridge notes that NEB data include pipelines up to
50 years old that use older technology and building material standards associated with
an increased frequency of failures compared to modern pipelines (Enbridge 2010b Vol.
7B, p. 3-­‐1). Accordingly, Enbridge factored improved design features and mitigation
planning characteristic of modern pipelines into its failure frequency calculations.
Improvement factors are expected to decrease the probability of pipeline failure
relative to NEB failure frequency data (Enbridge 2010b Vol. 7B, p. 3-­‐1). The ENGP
pipeline spill analysis does not provide the original or adjusted NEB spill data that was
used in the analysis, does not document the adjustments made to the NEB data and
provides no evidence to support the downward adjustment of NEB spill rates for the
ENGP.
Enbridge estimates return periods for various spill size categories of hydrocarbon
releases for six regions along the pipeline route. Enbridge bases spill size categories on
NEB classifications whereby a small spill is less than 30 m 3 , a medium spill ranges
between 30 and 1,000 m 3 , and a large spill exceeds 1,000 m 3 (Enbridge 2010b Vol. 7B).
Enbridge identifies the six physiographic regions along the pipeline route as the Eastern
Alberta Plains, the Southern Alberta Uplands, Alberta Plateau, Rocky Mountains,
Interior Plateau, and the Coast Mountains.
Table A-­‐23 presents spill return periods calculated by Enbridge for medium and large
spills in the six regions. Based on the adjusted NEB frequency data, spill return periods
for medium spills range between 118 and 1,082 years for each physiographic region,
while spill return periods for large spills range between 275 and 2,525 years per region.
Enbridge does not combine spill return periods for the six regions nor does it combine
return periods for medium and large spills. Combined, the six regions result in spill
return periods for medium and large spills of 41 and 95 years, respectively, for the
entire pipeline route. Similarly, combining overall return periods for medium and large
spills for the entire length of the pipeline results in a return period of 28 years.
Enbridge neither estimates nor presents spill return periods for small spills, yet simply
states “Smaller releases (less than 30 m 3 ) occur more frequently” (Enbridge 2010b Vol.
7B, p. 3-­‐2).
37 Enbridge (2010b Vol. 7B p. 3-­‐1) refers to pipeline spills as hydrocarbon spills. We interpret hydrocarbon
spills to include both oil and condensate and thus assume spill return periods represent oil or condensate
spills.
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