A Spill Risk Assessment of the Enbridge Northern Gateway Project

there will be one spill every 200 years, more effectively communicates the
likelihood of a spill to decision-­‐makers 10 .
2. Failure to combine estimates for tanker, terminal, and pipeline spills to present a
single spill estimate for the entire project
A second major deficiency is Enbridge’s failure to estimate spills for the entire
ENGP. The risk assessment for marine transportation in Volume 8C, the risk
assessment for pipelines in Volume 7B, the marine shipping QRA prepared by DNV,
and the Bercha Group (2012a; 2012b; 2012c) and WorleyParsons studies all
present separate spill estimates. Enbridge does not combine separate estimates
for tanker, terminal, and pipeline spills, as well as their component parts including
pumps, storage tanks, and pump stations to demonstrate the collective likelihood
of a spill from all potential spill sources. By presenting separate spill return
periods for individual components of the project instead of the entire project,
Enbridge underestimates spill likelihood and fails to provide decision makers with
the overall spill risk information necessary for applying the CEAA decision
criterion.
To address the lack of clarity in the ENGP application, we restate spill return
periods estimated by Enbridge and their consultants by converting return periods
to annual spill probabilities and estimate spill probabilities over the life of the
project rather than on an annual basis 11 . Based on Enbridge’s analysis, the
restated probability of any size oil or condensate tanker spill over the life of the
ENGP ranges from 11.3% to 47.5% (Table 19). The probability of a spill increases
significantly to 99.9% when spill probability is evaluated for the entire ENGP
inclusive of tanker, terminal and pipeline spills 12 . Our revised estimates in Table 19
likely underestimate spill probabilities because they are based on estimates in the
ENGP regulatory application that understate risk due to data limitations and
undocumented mitigation adjustments 13 . Therefore actual spill probabilities are
likely higher.
10 To estimate the chance of a 5,000 m 3 oil spill over a 50-­‐year operating period, we calculate the inverse of
the return period for a 5,000 m 3 spill (200 years) to estimate the annual probability of a spill (0.005 or 0.5%)
and use the formula in footnote 11 to obtain a 22.2% probability over 50 years.
11 We use the following formula to convert annual probabilities to probabilities over a 30-­‐ and 50-­‐year
period: 1 -­‐ ((1 -­‐ P) n), where P is the annual probability and n is the number of years.
12 Return period calculated based on the following spill probabilities: (1) any size tanker spill; (2) any size
terminal spill, and; (3) pipeline leaks. We note that Enbridge’s consultants estimated an overall probability of
70.9% over 50 years during the hearings (Enbridge 2012b Vol. 78 p. 53). However, this lower probability is
based on any size oil/condensate tanker spill (18.2%), any size oil/condensate terminal spill (56.2%), and an
oil pipeline rupture (18.8%). This approach is not representative of overall spill probability for the ENGP
because it relies on the likelihood of a pipeline rupture, which is less likely to occur than a leak, and omits
condensate pipeline spills.
13 Data limitations in the ENGP application include estimating spill likelihood for tankers with LRFP data that
potentially underreport actual tanker spills, omitting the majority of the distance travelled by tankers to
export markets, potential double-­‐counting of mitigation measures, and failing to consider characteristics of
the project that could increase risk such as the corrosiveness of diluted bitumen and maneuverability
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