Call Before You Dig: How 811 Utility Locates Work

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Setting a fence post, planting a tree or trenching for a downspout extension looks harmless until a shovel finds a gas service line or a buried electric cable a few inches below the sod. The call before you dig system exists to prevent exactly that. Across the United States, homeowners and contractors can reach their state’s one-call center by dialing 811 or filing an online request, and the utilities that operate buried lines in the area are notified to come out and mark them. The process is free to the caller in most places, but it has limits that surprise a lot of people: utilities mark their own lines, not the private lines a homeowner owns. This guide explains how 811 works, what the colored paint and flags mean, which lines usually go unmarked, which projects need a ticket and what to do if you hit a gas line. Rules differ by state, so treat the details here as general guidance and confirm current requirements with Colorado 811 or your own state’s one-call center.

Part of our Structure & Exterior guide — start there for the full picture →

Call Before You Dig: How the 811 Process Works

The basic sequence is similar from state to state.

1. Plan the dig area. Decide where you will excavate and, where your one-call center allows it, outline the area with white paint or white flags. White marks tell locators where the proposed work will happen.
2. Submit a locate request. Call 811 or use the state one-call center’s online ticket system. You will typically be asked for the address, the nearest cross street, the type of work, where on the property you will dig and when you plan to start.
3. Wait the required time. Each state sets a waiting period, commonly measured in business days. Weekends and holidays usually do not count, so a request filed on a Friday afternoon may not be complete until the middle of the following week. Colorado 811 publishes the current timing rules for Colorado on its own site; check there rather than relying on a rule of thumb.
4. Utilities mark their lines. Each utility member notified by the one-call center sends a locator, often a contract locating company, to mark the approximate horizontal location of its buried facilities with paint, flags or both. Some utilities may instead report that they have no facilities in the area.
5. Confirm responses before digging. Many one-call systems provide a way to check each notified utility’s response. If a utility has not responded or the marks look incomplete, contact the one-call center rather than assuming the area is clear.
6. Dig carefully and keep the marks visible. Locate tickets typically expire after a set period or once marks are destroyed, so long projects may need a renewed ticket.

For context, federal workplace rules for professional excavation follow the same logic. OSHA’s excavation standard, 29 CFR 1926.651, requires that the estimated location of utility installations such as sewer, telephone, fuel, electric and water lines be determined before an excavation is opened, and that utility companies or owners be contacted within established or customary local response times and asked to establish the location of underground installations before excavation starts. When excavation approaches the estimated location, the exact location must be determined by safe and acceptable means. Those rules apply to employers, not homeowners, but they describe the same care a homeowner project deserves.

What the Paint and Flag Colors Mean

Locators commonly use a uniform color code, widely known as the APWA color code, so anyone on the site can read the marks. Details vary slightly by state and utility, but the colors usually mean the following.

• Red: electric power lines, cables, conduit and lighting cables.
• Yellow: gas, oil, steam, petroleum or other gaseous or flammable material.
• Orange: communication, alarm or signal lines, cables or conduit, including cable TV, phone and fiber.
• Blue: potable (drinking) water.
• Purple: reclaimed water, irrigation and slurry lines.
• Green: sewers and drain lines.
• Pink: temporary survey markings.
• White: proposed excavation limits or route.

Marks often include letters identifying the utility, arrows showing direction, and sometimes the size or material of the facility. A mark shows approximate horizontal position only. It does not tell you how deep the line is, and depth can change over time as grading, landscaping and erosion move soil.

Lines 811 Usually Does Not Mark

This is the part of the process that catches homeowners off guard. One-call centers notify their member utilities, and those utilities mark the facilities they own and operate. In most cases, the utility’s responsibility ends at the meter or at a defined service point, and everything past that is private property owned by the homeowner. Private lines are not marked by the 811 locate in most areas.

Common private lines on a residential lot include:

• Lawn sprinkler and irrigation lines, including the supply line from the house and the valve wiring. Many sit only a few inches deep. If you are planning work around an irrigation system, our guide to sprinkler winterization explains how Front Range systems are typically laid out and drained.
• Private sewer laterals. In many communities, the homeowner owns the sewer lateral from the house to the main or the property line, and the sanitation district marks only its main. Repairs to a damaged lateral can be expensive; see sewer line replacement cost for typical scope.
• Gas lines past the meter, such as lines to a detached garage, shop, pool heater, outdoor kitchen, fire pit or gas lamp. The gas utility generally marks only to the meter. Our gas line installation cost guide covers how these yard lines are typically run.
• Electric lines to outbuildings, landscape lighting circuits, pool and hot tub feeds, and wiring to gate operators or detached EV chargers.
• Low-voltage lines such as invisible pet fences, security cameras, doorbell transformers and some data cables.
• Water lines past the meter to hose bibbs, garden spigots, barns or detached structures.
• Propane lines from a privately owned or leased tank, and septic tanks, leach fields and well lines on rural Colorado properties.

Because 811 does not cover these, homeowners usually rely on as-built drawings from the builder, previous owners’ records, visible clues such as valve boxes and lights, or a private utility locating company. Private locators charge for the service, and the price varies by lot size and the number of lines; it is worth asking what equipment they use and whether they can trace nonmetallic pipe, which is harder to locate.

Projects That Need an 811 Ticket

A practical rule is to request a locate any time you will dig more than a few inches below the surface, use powered equipment or drive anything into the ground. Common homeowner projects include:

• Fence posts. Post holes are deep, narrow and frequently placed along property lines where utility services often run. Planning a new fence or replacing leaning posts? Our fence repair guide covers post replacement and footing depth.
• Decks, pergolas and patio covers. Footings for posts and ledger supports reach below frost depth, which is substantial along the Front Range.
• Tree and shrub planting. Even a single tree can require a hole deep enough to reach shallow service lines. Large tree removal with stump grinding also disturbs soil.
• Drainage work. French drains, dry wells, downspout extensions and regrading all involve trenching close to the house, where service lines enter. See yard drainage for common solutions.
• Mailbox posts, retaining walls, garden beds and edging along the street or driveway.
• Sheds, playsets and basketball hoops that need concrete footings or ground anchors.
• Irrigation installation or repair, including trenching new zones.
• Utility work you are coordinating yourself, such as running a new gas line to a grill or a feeder to a detached garage. Licensed contractors should request their own locate.

If a contractor is doing the work, confirm that they have requested the locate under their own name. In many states the excavator, not the homeowner, is responsible for the ticket, and it should match the actual scope and location of the work.

Digging Near the Marks: The Tolerance Zone

Most states define a tolerance zone on either side of a marked facility, plus the width of the facility itself. A figure of about 18 to 24 inches on each side is common, but the exact distance depends on state law, so check Colorado 811 or your state’s center for the current rule. Within that zone, mechanized digging is generally prohibited or tightly restricted, and the line’s exact position is supposed to be confirmed by careful hand digging or vacuum excavation before work proceeds.

Hand digging in the tolerance zone is not the same as digging normally with a shovel. Common practice includes:

• Using a round-point shovel or digging bar gently, prying soil rather than driving the blade straight down.
• Exposing the line from the side, gradually, until you can see it.
• Never assuming a line runs in a straight line between marks, or that it sits at a standard depth.
• Watching for warning tape, which is sometimes buried above lines but not always.
• Stopping and calling the utility if the marks seem wrong, if you find an unmarked line, or if marks have been washed out or mowed away.

Cave-ins are a separate hazard when trenches get deep. OSHA’s trenching and excavation guidance identifies trench collapses as the greatest risk to workers in excavations and calls for sloping, shoring or shielding trench walls. Most homeowner projects are not deep enough to need protective systems, but a narrow, deep hole beside a foundation or in loose fill is not a place to stand unsupported.

What to Do If You Hit a Gas Line

A damaged gas line is an emergency even if you do not see flames. Signs include a hissing or blowing sound, a rotten-egg or sulfur smell, dirt or dust blowing from the ground, bubbling in standing water, or dead vegetation along a line.

1. Stop work immediately. Turn off any engine-powered equipment if it is safe to do so, and leave it where it is.
2. Leave the area on foot. Move people well away from the strike site, upwind if possible.
3. Avoid ignition sources. Do not start vehicles, use lighters, operate electrical switches or use a phone near the leak.
4. Call 911 and the gas utility from a safe distance. Let emergency responders and the utility manage shut-off.
5. Do not try to stop the leak, cover it or bury it. Do not attempt to operate utility valves yourself.
6. Notify the one-call center about the damage once everyone is safe. Even a small nick or scrape in a gas line or its coating should be reported, because damage can lead to a leak later.

Our guide to gas line leak detection covers warning signs inside and around the home and how professionals test for leaks after repairs.

For electric lines, the advice is similar: stay away from exposed or damaged cable, keep others back and call 911 and the electric utility. For water and sewer strikes, shut off the water at the main if you can do so safely and call the utility or a plumber. Communication and fiber lines are not life-safety hazards, but damage still needs to be reported.

What a Home Inspection Does and Does Not Cover

Buyers sometimes assume a home inspection will identify buried lines on the lot. It does not. The ASHI Standard of Practice states that inspectors are not required to inspect underground items, including underground storage tanks and other underground indications of their presence, whether abandoned or active. An inspector may note the visible ends of systems, such as the gas meter, the electric service entrance, a cleanout or a sprinkler backflow device, but the routes between them are outside the scope.

If you are buying a property where you already plan to build a fence, add a deck or install drainage, it can be useful to ask the seller for any as-built site plans or records of private lines, and to schedule a sewer camera inspection of the lateral. Our structure and exterior inspections section and the main guide to hiring a home inspector explain which add-on services help with exterior and site concerns.

Situations That Need Extra Care on Front Range Lots

A few site conditions make locating and digging harder than usual, and they come up often in Colorado.

Snow, frozen ground and short seasons

Paint marks can disappear under snow or get scraped off by a plow, and flags get knocked over. If marks are no longer visible when you are ready to dig, request a re-mark rather than guessing. Frozen soil also makes careful hand digging much harder, which tempts people to reach for power equipment exactly when they should not.

Rural and acreage properties

Properties outside city limits may have wells, septic systems, propane tanks, buried electric runs to barns and long private water lines. Most of these belong to the owner and will not be marked by 811, so records from the seller, a septic permit file and a private locator are more important here.

Townhomes and HOA communities

In attached-home communities, shared service lines and common-area irrigation may belong to the association. Check with the HOA before digging in a shared yard or along a common boundary, because it may have its own approval process and records of where lines run.

Older neighborhoods

Homes built decades ago may have abandoned lines, old clay sewer laterals, retired gas services or replaced water lines that no longer match any record. Unexpected pipe or cable in a hole should be treated as live until someone qualified confirms otherwise.

Common Myths About Calling 811

• “It’s only a small hole.” Many service lines are shallow, and a single post hole is enough to cut one.
• “We already know where the lines are.” Previous owners, utilities and landscapers may have rerouted lines over the years.
• “The marks from last year are still there.” Old paint is not a valid locate. Tickets expire and new work needs a new request.
• “The contractor will handle it.” Often true, but confirm the ticket number and date before work starts.
• “811 marks everything.” It does not mark private lines on your side of the meter in most areas.

When to Call a Professional

Hire a private utility locator when your project crosses areas where private lines likely run, such as between the house and a detached garage, near a pool, or across an irrigated lawn. Bring in a licensed plumber or electrician for any work on gas lines, water services or electrical feeders. And if a utility line is damaged, let the utility and emergency responders handle it rather than attempting a repair.

References

• 29 CFR 1926.651 Specific Excavation Requirements — Occupational Safety and Health Administration
• Trenching and Excavation — Occupational Safety and Health Administration
• ASHI Standard of Practice for Home Inspections — American Society of Home Inspectors

Planning a fence, deck or drainage project on a home you are buying? Send us a note and we can help you line up a Front Range inspector and the add-on services that look at the yard, sewer lateral and exterior before you commit.