Up and Running With Vacuum Excavation

Jan. 1, 2009

Jim Broderick tells a story about a large construction company that was excavating to widen a highway in an Eastern city. The contractor struck and severed a fiber optic cable. It turned out that the fiber optic line supported a banking facility, a hospital, an airport, and a 911 call center. The cable company sued the contractor and won—and the loss bankrupted the contractor.

“It all happened because the contractor wouldn’t pay a couple thousand dollars for vacuum excavation to find any buried utilities,” says Broderick, who is general manager of Rockies Construction LLC in Aztec, NM. Rockies Construction specializes in vacuum excavation, a non-destructive method of excavating to find and identify underground utilities.

Vacuum excavation equipment uses high-pressure air or water to control soft excavation precisely. Spoil is sucked through a vacuum hose and is deposited in a debris tank for later disposal or for backfilling into the hole. Models range from large dedicated truck units to small trailer- or skid-mounted units that gained popularity in the 1990s as support machines for horizontal directional-drilling operations. The smallest units even fit into the back of a pickup truck.

As the awareness of vacuum excavation increases, the market for the method is growing. Many states require visual confirmation of the presence of utilities—through “potholing” or slot trenching—before digging with an excavator or backhoe. Vacuum excavation is cost effective, and it works faster than hand digging. And it avoids tremendous financial liabilities. One vacuum excavation contractor says that when one of his former customers realized how much he was hiring the vacuum excavation rig, that customer bought a machine for himself and became a competitor to his former vendor.

The variety of applications for vacuum excavation equipment is almost endless. Broderick says he works for oil-and-gas companies, telecommunications owners, road contractors, construction companies, power plants, and refineries. He even does slot trenching for irrigation pipes on lawns. He digs utility pole holes, cleans culverts, and digs piling holes for footings. If the soil conditions are acceptable, he can dig precision-cut trenches for house foundations. The trenches can simply be filled with concrete to make footings.

PD Units, or Air?
Vacuum excavation units pull a vacuum by means of a positive displacement blower or by fan-powered air. Positive displacement (PD) machines use lobes that resemble revolving doors to move air. Fan-powered units move incredible amounts of air; the fans can be staged in series so that one fan supercharges the next one.

Pacific Tek Inc. of Santa Ana, CA, builds a range of vacuum excavation units that dig with pressurized air or with water. The units have debris tanks that range in size from 66 gallons to 1,200 gallons. All units use PD blowers. “We can get higher cubic-feet-per-minute rates out of a PD unit than a vacuum pump,” says Dan Skorcz, president of Pacific Tek. He’s referring to the rate of debris product movement as pulled by the vacuum.

Why does he favor PD units? “They’re simple in design, reasonable in cost, they provide high flow rates for the size of package they are, and they are pretty reliable,” says Skorcz. His smallest unit moves 325 cubic feet per minute of product; middle-sized units move 525 cubic feet per minute; and the high output machine pulls 825 cubic feet per minute. “The faster you move the wet, sloppy material, the better chance you have to avoid clogging up the line,” says Skorcz.

Tornado Technologies manufactures truck-mounted, water-powered machines only, says Miles Krowicki, vice president of sales and marketing. “Our trucks are extreme digging machines used in the oil and gas fields, where there is a lot of soil to be moved,” says Krowicki. “The water can be heated, so we can dig in frozen soil. Air is very limited in its abilities.”

All four of Tornado’s trucks, the F1 through the F4, are PD units. “With a fan-powered unit, if you drop your vacuum in the mud, it can’t suck the mud,” says Krowicki. “It requires airflow. But with a PD blower, it’s a very powerful vacuum system. We can lift rocks up to 200 pounds with the PD system. Try that with a fan, and you’d seal off your vacuum and you have no more air flow. Your vacuum drops to nothing.”

A debate has arisen over whether it’s better to use pressurized air or pressurized water. Many vacuum excavation contractors work mostly with pressurized water, in the belief that productivity is higher with water: You can dig faster and cut harder material. But a growing number of contractors are advocating air power. They point out that air won’t cut into the utility lines, which water can do. Plus, the dry fill can be backfilled into the hole. With water, especially in California, special environmental measures are required to dispose of water slurry.

“Today more people like to dig with compressed air than with water, because with air they can put the dirt right back into the hole,” says Skorcz. “But when you dig with water, it creates mud. You have to dump it into a spoils pool and let it dry. But if you have caliche or hard clay, you’re forced to use water to cut the soil.”

Rockies Construction uses vacuum trucks from Tornado Technologies, a company known for its manufacture of extreme-duty machines. Working for a utility company, Rockies dug a deep 8-foot-diameter hole in St. George, UT, for the foundation of a steel power pole. As the contractor dug down, he lowered a corrugated metal caisson to support the excavation. The utility wanted a 61-foot-deep hole, but when Rockies had dug 57 feet deep, it hit groundwater. The utility said that was deep enough.

On another project, Broderick came to the rescue of a directional drilling contractor who had twisted a drill bit off as he was drilling a pilot hole under a highway. Rather than lose the $120,000 cost of that work, Rockies vacuum-excavated down to the lost bit and recovered it. The contractor could use the hole he had dug—and saved the high cost of relocating the directional drilling bore.

Atlas Daylighting of West Lafayette, IN, operates three different types of vacuum truck—including three Tornado units and a Vac-Con unit, all with positive displacement blowers ranging from 3,600 cubic feet per minute to 5,800 cubic feet per minute. The third type is a Vactor truck with a two-stage fan to create the vacuum. “The Vactor cannot pull spoils for more than 50 feet away from the truck,” says Dave Kerper, general manager at Atlas Daylighting. “For distances more than 50 feet, you need a positive displacement machine.”

In June 2008, Atlas Daylighting faced a challenging project in Olivet, MI, working for the Panhandle Eastern pipeline company. The use of backhoes was out of the question, because the project area featured unknown underground utilities. “We were trenching in rocky conditions for the installation of underground pipe,” says Kerper. “We dug about 2,000 lineal feet of slot trench. It ranged from 8 to 18 inches wide and up to 36 inches deep. We also dug pole holes, and we dug the foundation for a pier to support a pipe. That project took about three weeks.

“The challenge was the rocky conditions,” says Kerper. “We used high-pressure water to cut the earth into a slurry. Then the vacuum would suck it up. We started with one Tornado and brought in a second machine to help meet the schedule.”

For another project in South Bend, IN, Atlas excavated more than 70 utility pole holes and pier holes. Utilities in the top 8 feet were unknown, says Kerper. For the 8-foot-diameter foundation holes, Atlas set corrugated metal tubes to support the excavations, which ranged to 15 feet in depth.

Other recent vacuum excavation projects by Atlas include:

  • Excavating a 40-foot-deep wet well for a wastewater treatment plant in Terre Haute, Indiana;
  • Vacuum-cleaning cutouts for asphalt patches in pavement;
  • Cleaning out concrete joints on an I-75 bridge between Indiana and Kentucky

More Potholing
“We’ve all seen the stories about houses getting blown up by utility strikes,” says Dave Gasmovic, chief executive officer of McLaughlin Group, which manufactures vacuum excavation equipment for branding by Vermeer. “Business is growing. More and more, we’re seeing vacuum excavating specified before digging. But we’re not as far ahead as Australia. Most of the states in Australia require vacuum excavation by law before any digging can take place for mass excavation or roadwork.”

Gasmovic says Vermeer currently offers mostly pressurized water units but recently began marketing a vacuum unit that digs with air or water. And McLaughlin is working on an all-air-digging unit, he says. The company makes vacuum units with debris tanks ranging from 100 gallons to 1,200 gallons in size. All units use a PD blower, not fan power.

“The biggest advantage of an air unit is that you can put the spoil back in the hole,” says Gasmovic. “Landfills don’t want the wet spoil from water excavations. It’s a disposal problem. But air doesn’t dig as well. Air takes longer in harder soils.

“When vacuum excavation got started, more units were sold for directional drilling, to clean up the drilling mud,” says Gasmovic. “Now that’s changed, and most vacuum units are sold for potholing [locating utilities].

The Charles Machine Works of Perry, OK, makes three models of Ditch Witch–branded vacuum excavation machines. The three are the FX20, the FX30, and the FX60. Ditch Witch offers debris tanks ranging in size from 150 gallons up to 1,200 gallons. What differentiates the three models is the rated airflow volume, which ranges up to 900 cubic feet per minute under 16 inches of mercury. (Inches of mercury is a way to express suction power of the machine; the really large machines pull 27 inches of mercury.)

“Most states in the US require you to do a physical [visual] locate of the utilities in an area before you do directional drilling,” says Greg Adkins, product manager for Ditch Witch vacuum machines.

VacStar Inc. of Kalona, IA, manufactures six models of vacuum excavation machines, all trailer-mounted with debris tanks ranging from 350 gallons up to 800 gallons. All use PD blowers and dig with pressurized water.

VacStar’s machines can move 350 cubic feet per minute at 22 inches of mercury. “Our machines pull at deeper inches of mercury,” says Lance Slabach, a vice president at VacStar. “With a PD pump, you can get a greater pull in inches of mercury.

“Recently we were able to dig 26 feet deep with the PD unit, and the fan-powered unit hit a dead end at 15 or 16 feet,” he says. “We’re also able to reach out to greater horizontal distances. We have pulled from 200 feet out from the machine.”

Glenview, IL–based Sewer Equipment of America offers three trailer-mounted vacuum excavation units and four truck units. All units feature PD blowers, which enable the vacuum units to dig deeper and at further distances from the base machine, says Brandon Shelton, marketing manager.

“With a PD blower, you create between two and three times the vacuum power that you get with a fan-powered unit,” says Shelton.

“Our 3,000-cubic-feet-per-minute machines pull about 16 inches of mercury—and the HX 1227, our largest truck-mounted unit, pulls 27 inches of mercury,” he says. “We do both air and water digging, but we recommend water over air. You’ll be more productive with water. Air does all right if you can’t add water to the material, like when you’re cleaning up an oil spill.”

Slabach says trailer units cost less than vacuum trucks, and notes that trailer units can gain access to difficult places, like parking ramps.

As awareness of vacuum excavation builds, its use is sure to grow. The financial risk and dangers are simply too great to avoid this exciting, relatively new technology. And as more competitors enter the field, it’s entirely possible that costs will come down or at least level out.

Pressurized Air Excavation: Wave of the Future?

“We find that more and more clients request the air knife,” says Larry Deutsch, manager of operations for Terra Testing Inc., a vacuum excavator from Washington, PA. “And we prefer air-driven excavation for potholing instead of water. With air you have less chance of breaking the utilities. Plus, with water you can change the composition of the spoil and create a material that is environmentally sensitive.”

Deutsch says the water slurry often requires separating the soil cuttings from the host water. Plus the resulting water slurry risks polluting the surrounding soil.

To be sure, the air versus water discussion is a debate. Atlas Daylighting has operated air-powered units, and has found that pressurized water is much more productive, according to Dave Kerper, general manager. Atlas Daylighting carefully limits water pressure to below 2,500 psi and Kerper says that pressure is safe to use on any underground utility, including fiber optic cable. Kerper says you can cut fiber with 2,500 psi water, but that with skilled operators, it won’t happen.

Terra Testing has one Vacmasters 4000 air excavation unit. How far can he work from the truck? “Right now we have two, 30-foot hoses, each 4 inches in diameter,” says Deutsch. “So we can go 60 feet away. I am told it can work four city blocks away.”

“We love our Vacmasters,” says Deutsch. “It’s been a good piece of equipment for us. We don’t find it necessary to use water and our clients don’t request water.” Typical clients are environmental engineers, he says, looking to “pothole” an area (i.e., to search for utilities) because they want to install a monitoring well.

For many of the same reasons, Underground Solutions Inc. (USI) also prefers air, says business development manager Dave Munson. The company has been in business for five years, and specializes in potholing for utilities. USI runs five Vacmasters 4000 machines.

Currently the company is working on air excavation of 85 to 100 potholes on a project called the North Embarcadero Visionary Plan in San Diego. In some cases, there are buried utility vaults, like manholes, and USI must find the depth and direction of utilities running out of the vault.

Two-man crews are assigned to each Vacmasters 4000 excavation rig. After utility mark-outs are completed, the crews typically break out the surface pavement and air excavate and vacuum the soil from the location until the subject utility is found and identified, and the total depth has been determined. When excavating over gas, HP gas, electric, and fiber optic lines, USI and/or the owner arrange for “standby” personnel from the subject utility. Typically, most potholes are excavated in as small an area as possible, such as 12 inches by 12 inches, and as deep as necessary to determine the depth of the subject utility.