AS PREVIOUSLY PUBLISHED IN THE RURAL VOICE:
At one time, oil and
gas pipelines in Canada were installed with as little as two feet of depth of cover
– maybe less. Although the minimum depth
of cover required over new pipelines as set out in the applicable CSA Standard
Z662 remains two feet, companies today routinely install pipelines with four
feet depth of cover or more. However, a major
deficiency in the depth of cover standard has been the absence of a requirement
to maintain depth of cover over pipelines to any specified minimum. A pipeline may be sufficiently deep at
installation to ensure the safety of those using the land above the line, but
what if depth of cover erodes over time?
Thousands of kilometres
of oil and gas pipelines run beneath agricultural land across Canada with ever
larger and larger farm equipment tilling, planting, spraying, fertilizing and
harvesting above. Pipelines lying four
feet or more beneath the surface may be unlikely to pose a risk of danger to
agricultural operations above, but what of pipelines only two feet beneath the
surface? What if the ground above a
pipeline installed long ago with two feet depth of cover has eroded by water or
wind or been displaced by decades of tillage?
In Ontario, the CSA
standard for depth of cover has been modified by regulation to include the
following requirements:
10.6.5.5
Operating
companies shall develop written procedures for periodically determining the
depth of cover for pipelines operated over 30% of SMYS of the pipe at MOP. Such
written procedures shall include a rationale for the frequency selected for
such depth determinations. Where the depth of cover is found to be less than 60
cm in lands being used for agriculture, an engineering assessment shall be done
in accordance with clause 3.3 and a suitable mitigation plan shall be developed
and implemented to ensure the pipeline is adequately protected from hazards.
Where a pipeline
company determines that the current depth of cover over a pipeline is less than
60 cm (2 feet), the company must perform an engineering assessment and develop
a “suitable” mitigation plan to ensure the pipeline is adequately
protected. The company is required to
have written procedures for “periodically” determining the depth of cover over
its pipelines. What passes for
“suitable” in a mitigation plan or “periodically” in monitoring depth of cover
over pipelines is not prescribed by the CSA standard or the Ontario regulation.
Are the current
requirements for monitoring depth of cover and addressing instances of
insufficient depth of cover enough to protect those carrying out agricultural
operations and other activities above pipelines? A recent incident suggests pipeline
landowners may have cause for concern.
The Transportation
Safety Board of Canada (“TSB”) has released a report of its investigation of an
October, 2021 natural gas pipeline rupture in Manitoba caused when a farmer
struck the line with a ground-scraping blade.
The strike happened in an agricultural field in a rural area in
southwestern Manitoba near the Saskatchewan border. To the east of the pipeline that runs through
the field, there is a drainage channel running almost perpendicularly to the
pipeline. The channel crosses over the
line and drains into a small marsh area.
At the time of the strike, the farmer was pulling an 18-foot-wide
landleveller/scraper with a large articulated four-wheel-drive tractor to
scrape weeds and silt from the bottom of the drainage ditch. The blade was in a “flat position”, which has
a maximum blade depth of just 26 cm (less than 2 feet) according to the
manufacturer of the implement. The
farmer had carried out the same scraping process periodically for several
decades prior to the pipeline strike. It
was determined that, at the time of the strike, the ground-scraping blade was
penetrating the ground less than 12 cm (less than 5 inches).
The regulation in place
at the time the pipeline was installed in 1960 required that it be buried to a
depth of at least 61 cm. Obviously, the
depth over the line had diminished considerably since the time of construction
at least in the location of the strike.
The company responsible for the pipeline conducts annual right-of-way
inspections, but had not noted any unsafe conditions at the occurrence
location. The last depth of cover survey
conducted by the company was in 2009, with the closest identified issue being
about 700 metres upstream of the occurrence location. The 2009 survey involved taking depth
measurements at 25 m spacing generally, at 3 m spacing across sloughs,
depressions or abrupt changes in elevation, and at all key features such as the
bottom of ditches, drains and streams.
The measurement taken closest to the site of the 2021 pipeline strike
was 4.5 metres downstream of the site.
As depth of cover at that location was 88 cm (approximately 2.9 feet), a
more detailed assessment of the area was not triggered.
The TSB concluded that the October, 2021
pipeline strike and rupture was caused in part because the pipeline company did
not identify that the depth of cover over its pipeline had been gradually
reduced through the removal of weeds and silt from the drainage ditch over
time. The TSB warned that: “If a
pipeline company’s damage prevention program does not consider variations in a
pipeline’s depth of cover over time, depth of cover reductions may go
unmitigated, increasing the risk of pipe damage due to agricultural
activities.”
Read the TSB Report at: P21H0143.