How do Excavation Tolerance Zones Protect Utilities?

How do Excavation Tolerance Zones Protect Utilities?

Failing to maintain sufficient clearance between digging equipment and underground utilities causes 13.46% of damages to buried infrastructure every year in the U.S., according to the Common Ground Alliance 2022 DIRT Report.

In every state, you must abide by federal, state, and local laws and regulations that require anyone planning to excavate near underground utilities to contact 811 or a utility locating company to have the utilities located and marked before digging begins.

Construction Safety Week (CSW) aims to connect workers and their employers with the resources they need. This annual safety initiative is May 6-10, 2024, where sponsor companies such as GPRS send their safety experts across the country to hold free presentations about a variety of safety-related topics, including tolerance zones for digging around utilities.  Click here to schedule a CSW Toolbox Talk / Lunch & Learn with GPRS.

What is a Tolerance Zone?

A tolerance zone refers to the area surrounding underground utility lines where excavation work should be approached with caution to avoid damage to the utilities. A utility locating company will place markings and flags to indicate the approximate location of a buried line. The tolerance zone typically extends a certain distance from the marked location of the utility line and may vary depending on factors such as the type of utility, soil conditions, and local regulations.

Is the Tolerance Zone Different in Each State?

The size or width of the tolerance zone for digging around utilities can differ by state and may even vary within a state based on local regulations and utility company guidelines. According to the Excavation Safety Guide, states are evenly split between using 18 inches or 24 inches in their tolerance zone definitions.

To determine the total size of the tolerance zone area, contractors must know the state’s guidelines and the size of the line or pipe. For example, the total size of the tolerance zone area for a two-inch pipe in a state with a defined tolerance zone size of 18 inches would be 38 inches: 18 inches on either side of the pipe, plus the two-inch diameter of the pipe itself.

Tolerance Zone Map

Are there Excavation Guidelines Per State?

The state also has guidelines for the methods and equipment allowed for excavation within these zones to ensure the safety of underground infrastructure and prevent damage during excavation work.

Excavators are usually required to exercise caution and use hand tools or non-destructive excavation methods within the tolerance zone to avoid accidentally damaging the utility lines, which can lead to service disruptions, safety hazards, and costly repairs. Some states only allow contractors to employ hand digging, soft digging, potholing, and vacuum excavation in the tolerance zone. They state that instruments such as pick axes, digging bars, and pointed spades should never be used.

It's essential for anyone planning to excavate near underground utilities to familiarize themselves with the relevant laws, regulations, and guidelines in their state and locality, as well as to contact a utility locating company prior to excavation. This helps to minimize the risk of damage to utility lines and ensures compliance with safety regulations.

Also, emphasizing safe digging practices, specifically within the tolerance zone, would reduce excavator errors in the field. Careful planning and adherence to safety protocols will prevent damage to underground infrastructure and ensure the safety of workers.

Many companies have comprehensive ground disturbance policies in place that helps mitigate the risk of utility strikes and damages. Ground disturbance policies typically include requirements for in-depth review and locating of utility information, and notification of community members whenever construction is going to take place. GPRS offers free ground disturbance policy reviews to help you ensure you have the procedures in place to guarantee success. Click here to request a ground disturbance policy review.

Tolerance Zone by State

How Would a Contractor Excavate Around Utilities?

Before any excavation work begins, the contractor must contact the relevant utility locating company to request utility locating services. These services involve using ground penetrating radar equipment to detect and mark the location of underground utilities, such as gas lines, water pipes, electrical cables, and telecommunications lines.

Here are the main elements that must be considered when creating or following a dig policy.

Utility Locating: Calling 811 before you dig is the law, and One Call will connect you with public utility contractors who will provide you with the location of all public utilities near your excavation. One Call cannot provide locates for the private utility lines on site, nor do they provide depths for public utility lines. GPRS professional private utility locating can locate both public and private utilities, provide accurate field markings, including depths, and give you complimentary digital and PDF utility maps of your utility infrastructure.

Review Utility Maps: The contractor will review utility maps or as-built drawings to get an idea of the location and depth of underground utilities in the area.

Define Tolerance Zone: Once the utilities are located and marked, the contractor identifies the tolerance zone.

Non-Destructive Excavation: Within the tolerance zone, the contractor may use hand tools or non-destructive excavation methods, such as hydro excavation or vacuum excavation, to carefully expose the utilities. These methods minimize the risk of accidental damage to underground infrastructure.

Visual Inspection: As the excavation progresses, the contractor visually inspects the exposed utilities to verify their type, condition, and depth. This information helps ensure that excavation activities proceed safely without causing damage to the utilities.

Temporary Support: The contractor may provide temporary support or protection for exposed utilities to prevent damage during the excavation process. This could involve shoring, bracing, or other protective measures.

Excavation Equipment and Techniques: Depending on the nature of the project and the size of the excavation, the contractor may use a variety of excavation equipment and techniques, such as backhoes, excavators, trenchers, or hand digging tools. Care must be taken to avoid striking or damaging the marked utilities during excavation.

Monitoring and Compliance: Throughout the excavation process, the contractor monitors the work area for any signs of utility damage or safety hazards. Compliance with safety regulations and best practices is essential to minimize the risk of accidents and ensure the integrity of underground infrastructure.

By following these steps and exercising caution and diligence, contractors can safely excavate around utilities while minimizing the risk of damage and ensuring the success of the project.

Why Choose GPRS? The GPRS Difference.

When it comes to construction and facility management, every decision you make can cost time, money, and even lives. GPRS is in pursuit of a world with 100% subsurface damage prevention. Our 99.8% accuracy rate for ground penetrating radar services (GPR), utility locating services, and utility mapping services will locate critical underground utilities to help keep your project on time, on budget, and safe.

GPRS has an extensive nationwide network of highly trained and experienced Project Managers in every major U.S. market. When clients hire GPRS, they have the peace of mind of knowing that they have the most reliable ground penetrating radar and electromagnetic locating technology on their job site, and they'll receive the assistance of a Project Manager who can provide them with the most accurate data. For over two decades, GPRS has been the industry leader by providing outstanding service and cutting-edge technology, keeping projects on time, on budget, and safe.

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Frequently Asked Questions

Are all underground utility lines buried at the same depth?

The depth of utility lines can vary depending on the type of utility on site. For example, cable and telephone lines in a conduit are typically buried one foot or less underground.

What is the dig alert tolerance zone?

If you are digging within 18-24 inches of the outside diameter of the utility (or tolerance zone), you are required to utilize hand tools only. Any underground facilities that are in conflict with your excavation must be located with hand tools and protected before power equipment is used. GPRS offers free ground disturbance policy reviews to help you ensure you have the procedures in place to guarantee success.

What is a vacuum excavation?

Vacuum excavation is a non-mechanical and less invasive method of excavation. A blast of air or water is first directed into the dig site to loosen soil and break up any large materials. It is categorized as air or hydro vacuum excavation depending on how the soil is broken down.

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