Ground disturbance, pipelines and buried hazards

Under the surface of most oil and gas leases is a web of buried lines: flowlines from wells to the battery, gathering lines to other facilities, fuel gas lines, water and chemical lines, electrical and communication cables, cathodic protection cables, and old lines that may or may not be abandoned. Beyond the lease, transmission pipelines carry gas and liquids at high pressure across farmland and forest. Striking any of these with a shovel, auger, excavator or post driver can release gas or liquid under pressure, start a fire or explosion, expose workers to hydrogen sulfide or electrocute the operator. This lesson explains how oil and gas sites control ground disturbance near buried facilities.

HSE-217, Ground Disturbance and Excavation Safety, is the full course on locates, hand exposure, soil classification, sloping, shoring and trench rescue. Its Lessons 3 and 4 cover locate requests, marks, tolerance zones and hand exposure in detail. This lesson does not repeat that material; it focuses on what is particular to oil and gas leases and pipeline rights-of-way. HSE-332 covers pipeline operations and maintenance.

Why oil and gas sites are different

Three features make ground disturbance on oil and gas sites especially hazardous. First, the density of buried lines is high: a multi-well pad and battery can have dozens of lines running in several directions, added over many years by different companies. Second, many of those lines are private facilities owned by the operator, which may not be registered with the provincial or state one-call center, so a one-call request alone may not find them; the operator's own records and locators are needed as well. Third, the contents are hazardous: sour gas, condensate, produced water, high-pressure gas and chemicals, rather than the water and low-pressure gas found under most city streets.

Old and abandoned lines add uncertainty. Records from decades ago may be incomplete or wrong, lines may have been abandoned in place without being purged, and some old wells and lines have no solvent owner. Alberta's Orphan Well Association and similar programs in other jurisdictions deal with such sites, and reclamation crews regularly find unexpected lines. Treat every unexpected line as live and hazardous until proven otherwise.

What counts as ground disturbance

In the United States, state one-call laws require anyone who will excavate to notify the one-call center, by calling or clicking 811, a few working days before digging, so that underground facility owners can mark their lines. Excavation is defined broadly in most states to include trenching, augering, boring, grading, plowing, driving posts and demolition. Federal pipeline safety rules administered by PHMSA require pipeline operators to run damage prevention programs, and PHMSA can enforce against excavators in states without adequate enforcement. Rules on gathering lines and on lines that are not members of the one-call system vary from state to state, so oil and gas operators must locate their own private lines on leases. Many operators require competent person and excavation supervisor training for anyone who supervises ground disturbance on their sites, and pipeline companies often require their own representative on site for any work within a set distance of their lines.

Locating buried facilities on a lease

Finding buried lines on an oil and gas site takes several sources together:

• A locate request through 811, the national call-before-you-dig number, which routes the request to the state one-call center and on to member facility owners.
• The operator's records: plot plans, pipeline maps, as-built drawings and the state regulator's permit records for the site.
• A private locate by a qualified locator for lines the one-call system does not cover, including flowlines, gathering lines that are not members, fuel gas lines, cables and abandoned lines.
• A site walk to look for evidence of buried lines: pipeline markers, risers, valve sets, test posts, warning signs, scars and depressions in the ground.
• Contact with each line owner to obtain their crossing or proximity requirements, which may include a representative on site.

Locate marks show the approximate horizontal position of a line, not its depth, and the line may lie anywhere within a tolerance zone on either side of the marks. Depth can vary because of grading, erosion and the way the line was laid. Inside the zone, lines must be exposed by hand digging or hydrovac (vacuum excavation) before mechanical equipment is used, and the exposed line must be protected and supported. HSE-217 explains the hand exposure rules and their distances.

Pipeline rights-of-way and markers

Pipelines outside the lease run in rights-of-way, strips of land where the pipeline company has rights to operate and maintain the line. Markers stand where pipelines cross roads, railways, fences and watercourses and at intervals along the right-of-way. They show the product, the company and an emergency telephone number. A marker shows that a pipeline is nearby, not exactly where it is or how deep; several lines may share a right-of-way, and lines do not always run straight between markers. Never remove or damage a marker, and report any that are missing.

Activities that seem minor can damage pipelines: driving heavy equipment across a right-of-way where the cover is shallow, storing materials or soil on it, deep tillage, installing fence posts and drainage tile, and blasting nearby. Pipeline companies and regulators usually require permission for crossings with heavy equipment and for any ground disturbance on or near the right-of-way.

Zones around buried facilities

The program below checks a list of proposed dig points against the nearest located line and classifies each as inside or outside the hand exposure or tolerance zone and, where relevant, the regulated area around a pipeline. The distances used are illustrative examples consistent with HSE-217; actual distances come from the applicable rules and the line owner's requirements.

# Proposed dig points: (name, inches from nearest located line, line type)
points = [("anchor A", 12, "flowline"), ("anchor B", 36, "flowline"),
          ("fence post", 20, "HP pipeline"), ("sump", 40, "HP pipeline"),
          ("sign post", 600, "HP pipeline")]
TOL = 24          # tolerance zone each side in inches (illustrative; 18 to 24 in common)
OWNER_REP = 300   # inches: owner requires a representative within 25 ft (illustrative)
for name, d, kind in points:
    if d <= TOL:
        rule = "inside tolerance zone: hand dig or vacuum excavation only"
    elif kind == "HP pipeline" and d <= OWNER_REP:
        rule = "within owner's set distance: pipeline representative on site"
    else:
        rule = "outside zones: valid 811 ticket and normal care"
    print(f"{name:10} {d:4d} in from {kind:11} -> {rule}")

anchor A     12 in from flowline    -> inside tolerance zone: hand dig or vacuum excavation only
anchor B     36 in from flowline    -> outside zones: valid 811 ticket and normal care
fence post   20 in from HP pipeline -> inside tolerance zone: hand dig or vacuum excavation only
sump         40 in from HP pipeline -> within owner's set distance: pipeline representative on site
sign post   600 in from HP pipeline -> outside zones: valid 811 ticket and normal care

Two of the five points need hand digging or vacuum excavation before any machine is used, and one more needs the pipeline owner's involvement even though it is outside the hand exposure zone. Only the last point can proceed with locates and normal care. A tool like this helps planning, but it does not replace the locate, the owner's requirements and careful exposure on the day.

Planning the work

Ground disturbance near buried lines should be planned in writing before the crew arrives. The plan pulls together the locate information, the owners' requirements and the method of exposure, and it is reviewed with the crew at the start of the job and whenever conditions change.

Hydrovac excavation is the safest way to expose lines, but it has its own hazards. The high-pressure water wand can cut skin and inject water under it, and it can damage pipe coating or cables if held too close or too long. The truck's boom must be kept clear of overhead lines. The debris tank and the excavation can collect gas, including hydrogen sulfide when digging near sour lines or contaminated soil, so the crew should monitor the air at the hole and at the truck. Hydrovac slurry from contaminated sites may need special disposal. Exposed lines must be supported along their length so that they do not sag or crack when the soil beneath them is removed.

If a line is hit

Any contact with a buried line, even a scrape or dent that does not leak, must be reported to the line owner, because damage to the pipe or its coating can lead to corrosion and failure later. If a line is struck and is leaking:

• Stop work immediately and shut off equipment engines if you can do so safely; do not try to move the equipment if gas is escaping.
• Get everyone away, upwind and uphill, and keep others out, including vehicles and the public.
• Do not try to stop or plug the leak, and do not operate valves unless you are the owner's authorized person.
• Eliminate ignition sources from a safe position: no starting vehicles, smoking or phones near the release.
• Call 911 or the local emergency number if there is any danger to people, and call the line owner's emergency number on the nearest marker or in the site plan.
• On sour sites, treat any release as an H2S release: monitors on, upwind, follow the site emergency plan (Lesson 11).
• Report to the regulators as required, and preserve the scene for investigation.