Hydroexcavation

Soon to Become a Household Word

By April Hirsch / Published September 2019

Lead made Flint, MI, a well-known city. In turn, the city of Flint made hydroexcavation a household word, or at least a more commonly used word.

We know the story. Significant amounts of lead were detected in the water supply. The detection pointed to the urgent need for Flint to determine the composition of service lines so that those lines containing lead could be identified and replaced.

Those following the story closely know that the method for identifying composition of lines became an issue. The Drinking Water and Municipal Assistance Division of the Michigan Department of Environmental Quality (MDEQ) recommended hydroexcavation. The leaders in Flint favored traditional—mechanical shovels and backhoes—excavation.

Consequently, the city of Flint and the state of Michigan (and other entities) were in conflict not only over who was responsible for lead in the water but also how to detect its source. The testiness resulted in the bandying about of the term hydroexcavation, and the term became better known.

Hydroexcavation is variously written hydro-excavation and hydro excavation. We use the compound word, unhyphenated, because it matches usage in Canada. In Canada, hydroexcavation plays a much bigger role than it does in the United States.

According to a Hydroexcavation Q&A at Vac-Con Inc. (Green Cove Springs, FL) website (Vac-Con.com)—a company that has been making hydroexcavators since 1994—only 10 percent of U.S. contractors use hydroexcavation. In Canada, half of general contractors and 90 percent of industrial contractors do.

Can we expect U.S.-based companies to embrace hydroexcavation as the future unfolds? It’s very likely when contractors, regulators, and government entities realize the array of benefits that the method brings to a setting.

“Accuracy and speed are two of the greatest advantages of hydroexcavation,” says Mike Tonies, industrial sales manager at Hydra-Flex Inc. in Savage, MN. The North Star State company focuses on developing products that save resources, reduce operating costs, and get the job done. It designs heavy-duty, high-impact nozzles specifically for hydroexcavation.

“With the right tools at hand, a hydroexcavation contractor can move a lot of material in a short amount of time to determine the precise location of underground utilities, with minimal disturbance of any landscaping,” explains Tonies. “From the customer’s viewpoint, this saves both time and money compared to traditional mechanical excavation methods.”

As reasons to work below ground increase—just think of the perennial demand after severe storms that all electric lines be buried—and populations grow, expect the interest in hydroexcavation to follow the same upward path. There are already more than two million miles of gas pipelines in the United States. Avoiding them, as well as fiber optic, electrical lines, and so on, is as important as finding them so they can be evaluated.

Then, there’s the very real need to keep adding to underground networks. “I believe the use of hydroexcavation will continue to grow due to the future infrastructure needs in the United States—fiber optics, 5G technology, etc.—as well as growing awareness of the safety benefits versus mechanical excavation,” says Tonies.

Most of us have engaged in home-grown types of hydroexcavation. We may have used the pressure from a garden hose to displace soil around a tree root or a large quartz stone that we wanted to extract. It saved us some effort in digging.

On the industrial scale, hydroexcavators use pressurized water (3000 psi is not uncommon) to dislodge soil. The soil that’s disturbed gets mixed with water and that slurry can be lifted with a vacuum. There are different types of vacuum systems.

Augment hydroexcavation tools with cameras that can transmit images of the lines exposed, and it becomes a very safe way to assess the integrity and composition of pipes. Why did city leaders in Flint dislike the method? They worried it might not expose enough pipe to reveal every bit of lead-composed material that water would pass through. For instance, a lead splice in a copper pipe might be missed.

The MDEQ countered that if a traditional dig went 10 feet and the splice were at 11 feet, it would still be missed. MDEQ was quite concerned about the risks associated with traditional excavation, such as disrupting existing utilities and damaging existing infrastructure. Such disruptions and damage would also contribute to environmental degradation.

Benefits and Uses

The petroleum industry is probably the biggest user of hydroexcavation in the United States, but the method is deployed across sectors.

Hydroexcavation requires less backfill than mechanical digging, and it causes less disturbance to the landscapes. Treading as lightly as possible on the land—protecting the environment—is always a plus when undertaking a project.

Safety is also enhanced with hydroexcavation. Equipment operators are not near or in trenches. Keeping workers out of trenches (a very risky place to be) promotes well-being. (It also reduces liability for employers.)

Practitioners of hydroexcavation promote the speed that it offers over conventional mechanical digging. One side benefit of speed is that the noise associated with the construction project occurs over the shortest possible interval. Hydroexcavation can be very friendly to those living and working around the site of a project. Instead of listening to the beeping of a backhoe that keeps backing up and reorienting itself, they know what they hear is associated with a project going as fast as possible. Also, they have less fear a gas line will be ruptured by construction equipment.

Combining heat and water in winter allows hydroexcavation to be used when the ground is frozen. When a utility pole snaps in a winter storm, digging a hole for a new pole may be easier with hydroexcavation to start the process and an auger to finish it.

The Pipeline and Hazardous Materials Safety Administration (PHMSA), which is part of the U.S. Department of Transportation, has a keen interest in hydroexcavation—and related methods, such as vacuum excavation. With millions of miles of pipelines to safeguard, it makes perfect sense.

PHMSA has funded research and held symposiums regarding best practices in accessing pipelines for maintenance and installing new lines. One line of inquiry has to do with whether vacuum excavation with compressed air (or an air-water mix) may be able to equal the productivity of hydroexcavation. As part of the evaluation, comparisons of volumetric excavation rates were made, including rates from mechanical digging.

If hydroexcavation works so well, why is there a need for vacuum excavation? For one thing, the wet soils from hydroexcavation cannot immediately be used for backfill in some settings. The delay increases costs for disposal and fuel and adds to downtime. PHMSA is looking at what it anticipates will be a system of tools to recommend for best practices in excavation.

On a parallel track of complexity, OSHA has been trying to sort out what constitutes “acceptable means” and “other acceptable means” of locating underground utilities. It’s quite murky, and the best guidance for any company planning to use hydroexcavation will likely come from state OSHA offices.

One source of difficulty in rule setting—standards—for hydro-excavation is mingling of terminology. PHMSA uses hydro-vacuum exca-vation to designate what we—and most practitioners—label hydro-excavation. It compares it to vacuum excavation (with very little or no water).

Two terms that PHMSA uses and that are in general use under the hydroexcavation umbrella are potholing and daylighting—or safely exposing buried utility lines to daylight. PHMSA sees hydro-vacuum excavation (our hydroexcavation) as a viable method for verifying depths, verifying top-side markings, verifying actual existence of a line, and verifying location of a line (markings on maps cannot simply be trusted).

Where there is a problem, there is the search for a solution. Because the wet soil from hydroexcavation cannot generally be used immediately for backfill, reuse technologies have emerged that make it possible to dry (PHMSA labels it “de-water”) the soil, so that it can be used as backfill sooner. The successful methods to date are limited to smaller excavations (the more soil, the longer it takes to get the water out).

The push to de-water and reuse soil on site will certainly continue. Carrying slurry away for off-site disposal is expensive and time consuming.

What’s feasible for the depth and length of a hydroexcavation? PHMSA puts the safe and efficient vertical distance at more than 45 feet and the safe and efficient horizontal distance at more than 400 feet. It puts the maximum diameter of debris removal at 24 inches.

It’s not just the use of variable water pressure but also oscillating nozzles that allow a combination to be struck that exposes sensitive lines in different kinds of soil. What about the sensitivity of fiber optic cables and pipeline
coatings? PHMSA cites the use of neoprene covered debris hose and wand tips to provide extra protection.

OSHA does not try to soften the harsh reality of the dangers of mechanical digging and trenches. It reminds us that one cubic yard of soil can weigh as much as a car.

With the safety it enhances and the speed and versatility it possesses, hydroexcavation will soon become a household word.