An Overview of Hydrovac Excavation

By Denise Sullivan
Published: September 4, 2018 | Last updated: July 5, 2023
Key Takeaways

Excavating soil with high-pressure water and vacuum suction methods is worth a deeper look.

Hydrovac excavation usage developed in Canada to excavate areas to gain access to underground utilities. With Canada’s harsh winter climates, the ground often freezes making it challenging to properly uncover buried utilities without damaging them. Canadian workers were able to remove soil more efficiently using heated water than with other methods. To better understand hydrovac excavation, let’s look at what it is, how it's used, what equipment is necessary, and some key benefits.


What Is Hydrovac Excavation?

Removing soil using pressurized water in conjunction with a vacuum or air conveyance instead of digging tools is the process of hydrovac excavation. (Learn more in Soil Types and How They Affect Trenchless Construction.) It is a non-destructive procedure that is ultimately more accurate than traditional excavation methods. Crews can uncover underground utilities without damaging them.

In some areas, hydrovac excavation is known as soft digging. This name is due to the procedure having a less destructive potential than a traditional pit. However, the term soft digging is also used to describe air excavation which is similar to hydrovac digs.


How Is Hydrovac Excavation Used?

Unlike the counterpart, air excavation, hydrovac excavation uses more than just air to penetrate the ground. The hydrovac process works by injecting water into the ground through a hose. This process liquifies the soil causing it to form a slurry mix. The slurry is excavated by a vacuum system pulling the wet clay into a holding tank. In an area with harsh winters causing the ground to freeze, warm water is used to help loosen the soil. Unlike with air excavation, workers cannot use hydrovac excavation spoils to fill in any trenches made by the process.

A hydrovac excavation project can go up to 70-feet deep. The holding tank and pumping truck don't have to reside next to the work site. Depending on project needs and equipment used, the holding tank and pumping truck may be located several yards away.

Hydrovac excavation uses one of two vacuum options: a fan system or positive displacement blower. A fan unit moves air in vast amounts over a shorter distance. These systems work faster and are easier to control and operate. If the holding tank fills to capacity and begins to overflow, it ejects excess debris into the air.

In comparison, the positive displacement blower moves more air over greater distances. A displacement unit can go to greater depths than a fan-based system. However, it is much slower. Additionally, overfilling a displacement unit can cause damage to the system.

When is Hydrovac Excavation Used?

Hydrovac excavation is a popular choice for any application which may need access to underground utilities or facilities. Any job where there is a risk of damage to subterranean lines can benefit from this type of excavation. (Learn more in An Overview of the Utility Tunneling Method in Trenchless Construction.)


Slot trenching

Hydrovac is ideal when trying to locate subterranean utilities; slot trenching opens a narrow trench without disturbing the surrounding soil too much. It's also useful for installing small diameter pipes.

Tight Spaces

Some areas are not large enough for traditional trenching equipment. Instead, hydrovac is used to navigate these tight spaces and excavate soil. Good examples of these areas are narrow streets, planting strips and back yards.

Cold Weather

Freezing temperatures make it difficult to excavate soil. The cold temperatures are a hazard to workers. Hydrovac uses warm water to loosen the soil faster keeping workers out of the harsh conditions.

Debris Removal

Drainage structures and manholes often need cleaning. Hydrovac removes debris without affecting the infrastructure.

What Equipment Is Involved in Hydrovac Excavation?

Hydrovac excavation equipment if straightforward. This process combines high-pressure water and an air vacuum system. The hydrovac truck contains two hoses, one to deliver the pressurized water stream with a handle much like a pressure washer. Workers spray the soil making a slurry while another uses the vacuum hose to pull up the mixture.

Some companies use a truck with a holding tank. Others have the hydrovac system on a trailer which contains the holding tank, water, and vacuum system. Trailer based systems are best used in smaller projects.

The vacuum system operates using either a fan or a positive displacement system. The project manager determines which unit is best for the job, although both work well for most projects.

What Are the Benefits of Using Hydrovac Excavation?

There are several benefits of using hydrovac excavation. Its efficiency and accuracy in comparison to traditional trenching methods are unmatched.

More projects turn to hydrovac excavation for safety. This method is more accurate and more accessible to control than traditional methods. It reduces the risks for accidents and injuries of workers and others who may wander through the construction site.

In addition to being safer for workers, hydrovac is also more reliable on underground utility lines. When operated properly, there's no risk of damage to underground lines as the soil is removed in smaller increments than with traditional trenching. Workers can see the lines as they begin to uncover them and won’t hit them with anything harder than high-pressure water.

Because of the limited risk of injury to workers and damage to lines, companies using hydrovac excavation may see reduced insurance and liability costs.

Hydrovac excavation is one of the best choices for working around subterranean utility lines. It works well in all climates, even those with the harshest winters. In comparison to traditional trenching methods, it's much safer.

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Written by Denise Sullivan | Technical Writer @ Trenchlesspedia

Denise Sullivan

Denise Sullivan is an accomplished freelance writer from Louisiana, with a Associate's Degree in Journalism from Eastern Oklahoma State College. She also graduated from East Central University with a Bachelor's in Biology. Denise began her writing career writing operations and maintenance manuals and software utility manuals for flight simulators. Since, she has expanded her writing to a broad spectrum of topics.

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