Buried utilities, 811 and locates

Almost every piece of ground in a town or city, and much of the ground in rural and industrial areas, carries buried utilities: natural gas mains and services, electrical cables, oil and gas pipelines, water mains, sanitary and storm sewers, telephone, cable and fiber optic lines, traffic signal cables, street lighting and steam lines. Striking one can kill, as with a gas line that ignites or a high-voltage cable that arcs through an excavator bucket, or can cause enormous cost and disruption. This lesson covers how buried utilities are found and marked before digging. Lesson 4 covers how to dig safely once the marks are on the ground.

The one-call system

The national 811 number connects excavators to the one-call center for their state. The excavator submits one request, often called a ticket, by phone or online, and the center sends it to every member utility whose facilities may be affected. Each utility then either marks its lines on the ground or responds that it has nothing in the area. Every state requires a call to 811 before digging, with exemptions that vary from state to state for things like hand gardening. The Common Ground Alliance publishes the Best Practices guide that most damage prevention programs follow.

Each state's damage prevention law sets its own rules, so excavators who work across state lines must check each one. Common features include a waiting period of two or three full working days after the request before digging may begin, a ticket life after which the request must be renewed, a requirement to keep marks visible and to request remarks when they are lost, a tolerance zone within which power equipment may not be used without first exposing the utility, and penalties for digging without a valid ticket. Some states require the excavator to outline the proposed dig area in white paint or flags before calling.

What a locate request needs

A good locate request is specific. The person requesting it should give:

• The exact address or legal description, the nearest intersection and, for rural work, GPS coordinates or a land location.
• A clear description of the work area: which side of the road, how far from the building, the length and width of the trench.
• The type of work, such as a water service, fence posts, a sewer replacement or directional drilling.
• The method of excavation, the expected depth and the start date.
• Contact details for someone on site who can answer the locator's questions.

White lining, marking the proposed excavation area on the ground with white paint, flags or stakes, removes most of the guesswork. It tells the locator exactly where the digging will be, so the marks cover the right area and the locator does not waste time marking the whole property.

How locators find buried facilities

A locator is a trained technician who works for the facility owner or a contract locating company. Locators combine records with detection equipment:

• Records: maps and as-built drawings show where a facility was intended to be installed, but are often inaccurate by several feet, especially for older installations.
• Electromagnetic locating: a transmitter puts a signal on a conductive line, either by direct connection or by induction, and a receiver traces the signal along the ground. It works well on metallic pipes and cables, and on plastic pipes only when a tracer wire was installed with them.
• Passive locating: a receiver picks up signals already present on some lines, such as power cables carrying current.
• Ground-penetrating radar: radar pulses reflect off buried objects. It can find non-metallic pipes but struggles in wet clay and gives results that require skilled interpretation.
• Acoustic and other methods: used for specific problems such as plastic water mains.

No method is perfect. Signals can bleed onto adjacent lines, tracer wires break, records are wrong, and depth readings are estimates at best. That is why the marks show the approximate location of a facility and why lesson 4 insists on careful exposure within the tolerance zone.

The marking codes

Locators use a standard set of colors so that anyone on site can read the marks. The American Public Works Association codes, adopted in the CGA Best Practices and ANSI Z535.1, are used nationwide. The color identifies the type of utility, and symbols or letters next to the marks can show the owner, the size, the number of ducts and the direction of the line.

Reading the locate package

The locate is not just paint on the ground. Each owner provides a locate sheet or electronic response describing what was marked, the area covered, any facilities that could not be marked and the expiry date. The excavator must collect a response from every owner on the notification list and check that:

• The locate covers the whole work area, including spoil and equipment areas if those will be disturbed.
• Every listed owner has marked or cleared. A missing response means the excavator cannot dig.
• The marks on the ground match the sheets. If a sheet shows a gas service and there is no yellow paint, stop and call.
• The locates are still valid and the marks still visible. Rain, traffic, snow clearing and earlier digging erase paint and flags.
• Any notes, such as a requirement for the owner to be present when its line is exposed, are understood by the crew.

Private facilities

One-call members mark the facilities they own. They do not usually mark private facilities, which can include a homeowner's buried electrical cable to a garage, site lighting in a parking lot, irrigation lines, private water and sewer services, gas lines beyond the meter, and the extensive buried networks inside industrial plants, campuses, hospitals and airports. On many sites these private lines outnumber the public ones.

Private facilities must be located by a private locating company hired by the property owner or contractor, or by the facility owner's own records and staff. A one-call clearance that says no conflicts does not mean nothing is buried there. It means none of the member owners has anything there.

Abandoned, unknown and unlocatable facilities

Old facilities that are no longer in service are often left in the ground. Some are truly dead; others are still live under a different owner, or have been reconnected. Unless the owner has confirmed in writing that a line is abandoned and safe, treat every uncovered pipe or cable as live. If an excavation uncovers a facility that was not marked, stop work near it, protect it, and contact the one-call center and the likely owners before continuing.

Some facilities cannot be located by electronic means, such as plastic pipes without tracer wire. The owner may mark them from records with a note that the location is approximate, or may require that the excavator expose them by hand or vacuum excavation before mechanical digging. Treat these as higher risk.

Keeping marks alive on a long job

Locate marks are fragile. Paint fades under traffic and sun, flags are pulled up by curious passers-by and lawn mowers, and the excavation itself removes the ground the marks were painted on. On a job that lasts more than a few days, the crew should protect the marks from the start. Useful practices include offsetting marks, where stakes are set a measured distance to one side of each line so its position can be re-established after the original paint is dug away; photographing the marks with a tape measure in the frame before digging begins; recording the positions on the site drawing; and requesting a re-mark as soon as marks become unclear rather than relying on memory.

When the ticket is close to expiry, or the work moves outside the area originally described, a new ticket is needed. Most state laws require marks to be maintained or a remark requested when they are no longer visible. A crew that keeps digging after the marks have vanished has, in effect, no locate at all.

Directional drilling and boring add a special challenge, because the drill head travels underground where nobody can see it cross other facilities. Every crossing along a bore path should be exposed by vacuum excavation so the crew can watch the drill head pass, and the bore path should be planned with clearances agreed with the facility owners.