From:  Grading & Excavation Contractor Magazine

Written By:  David Engle

Invented a few decades ago to enable safe mechanical digging near buried utilities and other below-ground fixtures, vacuum excavation, or VE, may not be so quick as digging with backhoes, but the methodology is winning converts among contractors by the truckload.

Instead of attacking dirt in  massive bucket-sized scoops, a scalpel-like VE tool pierces with laser focus  and efficiency—applying air or water—striking the ground with impact and  precision.

In the pneumatic version, air  gets tightly compressed through a controlled aperture; in one such tool the  pressurized air emerges at Mach 2 speed, says Andrew Hartman, who is sales and  marketing manager of the tool’s maker, Supersonic Air Knife Inc., of Allison  Park, PA. Poked into the ground at a steady clips, the AirKnife will pulverize  it, expand it like a small seismic shockwave, kick it up skyward, and keep  excavating all day long. After all, it runs on air.

The resulting hole comes out at  usually 1 or 2 square feet in circumference, or whatever’s needed to expose the  underground element of interest.

Loosened material—whether carved  out by a water jet or air—comes out either as a muddy slurry or dry spoils,  depending on which. In either case, it’s then vacuumed up.

Compared to serious trenching  work, VE is but a limited “boutique” digging niche. As Hartman points out, only  a couple of companies make the high-performance nozzles that Hartman  sells—although venturesome excavators, he notes, have been known to fashion  their own crude ones by simply pounding a tube tip to a narrow edge.

Offering a bit of history: Air  “knives” were first introduced in 1986. The current patent ownership moved to  Hartman’s employer about eighteen years ago. Supersonic makes a half-dozen  variations now; some nozzles can handle either liquid or air.

A vacuum “sister tool” that Hartman  describes, runs from a compressor rather than a vac, and sucks or blows  material out through a discharge tube.

As for the VE market, Hartman  observes: “We’re still really in a kind of educational phase, even after some  thirty years of trying to get the average excavation crew to understand why  they need a tool like this and why they should be using it for the hand-dig  zone… There really are a lot of places where air should be used,” he adds, “but  still isn’t.”

Most commonly applied at the  very start of excavation work to verify utility markups and visually locate  buried lines, pipes, cables, wires, tanks, tree roots, etc., VE will enable  crews “to go in with heavy equipment with more confidence and be fairly certain  that you’re not going to run into trouble,” explains Hartman.

In this role, air- or water-  digging, plus vacuuming, is the alternative to shoveling by hand.

These days, though, as Ben  Schmitt, product manager of Vactor Manufacturing in Streator, IL, points out,  “The utility segment appears to be less than 20% of total vacuum excavation.”  Instead, recent demand for VE work has soared and shifted amidst the nation’s  booming oil and gas production sector.

To obtain VE services, Schmitt  adds, excavation contractors typically turn to VE experts. But larger digging  companies “are starting to purchase their own machines as well, when  justified,” he adds.

Immersion by Water by Pneuma Talk to devotees of air  excavation these days, and you will hear them extol VE virtues with a fervor  that almost sounds reverential. Since virtually all excavators began their  careers with conventional trenching and hoeing, they have comparative  experiences to draw upon. Their switch to specializing on VE reminds one of a  conversion of faith.

First, typically, comes a taste  of hydro digging (apparently, more pervasive than air, at least according to  the sources interviewed here). Afterwards comes the discovery of the aerated  alternative. Everyone likes the latter a lot. The reason? Above all, air  provides a remarkably desirable cleanliness at pneumatic job sites. These are a  triumph over messy, water-soaked, apocalyptic mud pits ensuing from hydro VE.

In a couple of cases, the  affection that air VE inspires is so complete, excavators will revamp their  businesses, virtually to forsake water for it’s sake—although it’s more typical  to hear diggers concede, “Yeah, we still do both.” This comes out a bit  grudgingly, though. Their hearts are with pneuma.

Torry Olive is operations  manager for BBU Environmental and Central States Environmental, two sister  companies that excavate Ohio and surrounding states. Hydro VE was launched by  BBU/CSE there about eight years ago, he recounts: “We played around with it a  bit. Basically, it consisted of using a regular turbo vac and a steamer unit.”

Then, clients started asking  about air. “So we did a little bit of research on it, went out and got an air  spade tool, and started using that with our turbo vac. Things just kind of grew  from there,” he says.

BBU/CSE started renting bigger  trucks for hauling “huge” pneumatic blowers that air VE requires; work managers  had discovered that the minimum practical size for VE with air is probably  around 6,300 cfm. BBU/CSE opted for versatile Guzzler trucks, which could  handle not only the super-sized compressors but be reconfigured, as needed, to  perform other tasks as well.

“Once we became proficient,”  Olive continues, “we started letting people know we have this technology and  can service this part of the industry.” Word-of-mouth in the Midwestern  petrochemical trenching market spread. “You do a job with one pipeline  inspector,” Olive recounts. “He likes the truck. He likes the technology. He  likes that fact that air material remains dry and there is no muddy mess. You  can dump it on site or back in the hole once you’re done digging. You don’t  have any impaction issues.” Then the duly impressed inspector “moves to another  area and tells everyone there about it. It just kind of spread that way.”

These days, Olive says, out in  the marketplace he finds, “One of biggest misconceptions is that you cannot go  through hard-packed surfaces with air. But you can. It takes you a little  longer, but you can do it,” he says with confidence.

In the wake of success and  growing demand, VE competitors have jumped in. “They’re more than capable of  getting our business,” Olive concedes. “But one of the things in the  environmental industry is loyalty. Once you get in somewhere, people like you  and typically they’ll keep you as long as you don’t make a serious mistake.  It’s not that we have a corner on the market, but with loyal customers, it is  working out really well.”

Ideal for the Sandy Southeast, Far West Christopher Niebuhr, president  and chief operating officer of Thompson Industrial Services LLC, based in  Sumter, SC, does air VE (and other) excavation work for firms like Duke Energy  and for multiple regional nuclear power stations. These days, he says, “We do  air more than any other kind.”

Why so?

“Because [clients] just refuse  to let us use a backhoe anymore,” he says. “They don’t know what’s underground  there.” As nuclear sites seek expansion, “They have 40-year-old drawings, but  don’t trust them.”

They call Thompson to bring out  the air knives. In contrast, for the occasional greenfield project,  conventional excavation is typically preferred, Niebuhr notes.

Thompson’s project manager for  nuclear digging, Jerome L. Lawson, discusses his steady work assignments for  the past several years that have been heavily skewed to air VE. Thompson, he  recalls, first launched pneumatic service in 2001. Since then his crews have  dug hundreds of holes this way. Prior to that, says Lawson, “when digging with  a mini-excavator or big track hoe, you’d ruin things. You’d scrape stuff and  then tear lines away—fiber optic cables,” for example. Those days are over now.  Nuclear site work firmly dictates about a 70% overall preference for  compressed-air power as the tool of choice. “Surveyors come out and mark the  ground for what we call ‘a soft dig,’” says Lawson, meaning either air or water  but no heavy stuff. “They locate where they think the lines are. Point me in  the right direction to dig, and I go to whatever depth or width they need.”

One of the most ardent advocates  of air work we spoke with is John West. He’s vice president of Ultra Engineering  Contractors Inc., of Winchester California and sponsors an informative air VE  website, www.digwithair.com. With over 20 years in the excavation business,  UEC’s service territory reaches all of California south of Sacramento, West  says. The “ultra” part of the company name refers to extremely safety-conscious  digging. “That’s all we do is dig safely,” he says. This accounts for why, for  the past three years straight, UEC has been hauling forth its pneumatic tools  more or less exclusively, 99% of the time. Hydro serves as a rare backup only.  Previously, UEC had paired hand digging with hydro.

Why the radical shift to the  air?

“We saw a need for it. There  weren’t a lot of guys out there offering it. A lot of clients began asking for  it. So we got into it,” he answers.

Ultra has enjoyed steady growth  since, and has added round-the-clock emergency repair services for  utility-related sites. “We’re running our trucks full time every day,” he says.  “We’re booked up typically for months in advance. We’ve got two more trucks on  order. We’re really happy with the way things are going. Our clients are  extremely happy and the air technology, to me, seems to make the most sense.”

Why so?

“First and foremost,” West  continues, “we can use the same soil that we removed from the hole to put back  in. We back-fill and move on. We can do a lot more holes a lot faster, if a  client is asking us to do the backfilling.”

Selling-wise, “It’s a matter of  educating the market on what we’re capable of doing,” he sums up. “Once we get  out there and show them, typically we’ve got a costumer for life.”

Hydro VE Not Drying-Up Yet With such uplifting testimonials  about aeration’s advantages, water-digging would seem to be going down the  drain—but, of course, it’s not that simple. The hydroexcavators are extremely  well-entrenched. They too have passionate defenders. Several notable advantages  are repeatedly touted and seem to be keeping the industry afloat, as it were,  and ensuring that commercial job orders keeps flowing.

One steadfast advocate of  hydroexcavation is Jason Proctor. He’s product manager for the vacuum  excavation product line at Ditch Witch, a major supplier of hydro vacuum units  as well as conventional trenchers, plows, horizontal drills, back hoes, and  such.

Proctor acknowledges the  rapturous buzz that air has enjoyed, but nevertheless says he’s “just not seen  where air excavation is as productive as hydro.” Given that Ditch Witch’s  product line is currently conventional and hydro-oriented, Proctor also admits  a certain bias on this point. But he strongly hints that pneumatic equipment  may well be forthcoming for Ditch Witch. “Even though we don’t make air [tools]  today…that’s not to say we won’t have them in the future, and we absolutely  see the value of them,” he says.

All in all, water blasting is  simply faster-cutting and more productive than air, Proctor believes.

Another strength of water is the  fact that, against frozen ground “air excavation isn’t going to work that well.  But with hydroexcavation you can use heated water” to dislodge icy sod easily.  Hot water can also hasten the breakup of clay, and is useful for non-excavation  job-site chores like cleanup and scouring.

Lastly, Proctor notes, there’s  another downside with air VE, in that, wherever air is pounding dirt and kicking  it skyward, the work area requires shielding “You’re basically blasting the  ground apart. Surrounding homes, vehicles traffic and passers-by are more at  risk with flying debris” than with hydroexcavation, he says.

How about code and regulatory  status?

As it happens, in mid-year  AirKnife’s Hartman undertook to find out how both modes of VE have been  received in various codes and standards. He was hoping to learn that they’re  being widely recognized and officially adopted. What he actually found, he reports,  is that best-practices clauses still uphold hand-digging near utilities—or  prudent equivalents. The latter generally include a reference to pneumatic  digging, he adds. However, he says of the regulatory industry, “Nobody has  gotten as specific as to say that an air knife or similar tool must be used.  They get as far as mentioning pneumatic digging and then listing it in a  glossary somewhere…” he says with a note of disappointment.

Moreover, all of the locally  adopted best practices for digging ultimately seem to cite a common boilerplate  statement on this subject recently formulated by the utility industry’s Common  Ground Alliance. The latest version came out just this year. CGA’s discussion  on vacuum excavation “still reads pretty much the same” in 2013 as when first  introduced in 2010, Hartman adds. He regularly attends CGA meetings, and he  praises the nonprofit organization for getting the word out that air tools are  faster and safer than hand digging. However, he adds, this endorsement has  taken a remarkably long time to obtain.

A second bit of recognition for  soft digging dates back to 2003. At that time, a forerunner of the present CGA  participated with the US Department of Transportation in a grant to the New  York State Department of Public Service, aimed at defining best practices for  digging around buried utility lines. In those days, “damage to underground  structures” is “significant,” even when lines are properly marked. This  statement appears in a subsequent NYDPS white paper titled the “Vacuum  Excavation Demonstration Project” (VEDP), dated 2006 and published online at  www.digsafelynewyork.com. VE researchers back then also expressed concern that  “advances in vacuum technology…[and] in pneumatic and hydraulic equipment  intended to safely expose underground facilities are not being fully utilized  in the field.”

To remedy this, various  stakeholder from New York utility-marking organizations (e.g., Dig Safely New  York and the Northeast Gas Association) were assembled; the VEDP was the  result.

In the study project, a total of  seven local excavators participated. Results of their 106 VE digging sites were  then analyzed. The study sought to compare “soft” vacuum digging benefits  versus hand digging with shovels, assessing relatives costs, drawbacks, efficiency,  etc.

As the eventual report later put  it, “Perhaps most important question was Would the excavator use this  technology if they had to pay for it themselves, rather than having it  underwritten by grants?”

Results-wise, all but one of the  excavators agreed that “using vacuum excavation to locate utilities made the  task easier and more efficient.”

All reported that VE saved time.

All but one reported that VE  saved money.

How about VE enabling workers to  avoid damage?

Six of seven companies said “yes,”  (again, out of a total of 106 VEs job sites; two minor inadvertent, unavoidable  damage incidents occurred that likely would have happened by hand-digging as  well, the report noted).

Participants also felt that VE  was better suited to some sites and tasks than others. Especially apt roles for  VE include: utility location verification; potholing; directional-bore  projects, especially where routes cross utility or gas lines or where lines are  within roads or paving; locating existing facilities for repair or rerouting;  utility projects with spatial constraints; urban projects; and projects seeking  to limit surface disturbance.

Of seven participating  excavators, all reported they would indeed consider purchasing or renting VE  equipment for themselves in the future.

All in all, the study proved VE  to be a resounding success. VE demonstrated “clear and distinct advantages over  hand digging to locate utilities.” VE “…saves design, excavation, and  construction time and…money, minimizes damages, while complying with  construction codes,” the VEDP report states.

At the time of its publication,  the study was so eye-opening for New York excavators that the NYDPS decided to  thump the results in a promotional booklet.

Naturally, the study steered  clear of endorsing either hydro or air against each other. Nor did it tout  equipment brands. But there was frank discussion of several key differences,  including statements such as these:

  • “… water…at high pressures can damage underground  utilities, and there are documented cases of this occurring.”
  • Water is also “a very good conductor of electricity” which  means it presents a hazard of electrocution.
  • “In cold or freezing temperatures, working with water can  be difficult,” as “equipment can freeze, and there may be sloppy, difficult  conditions at the discharge points. Environmentally friendly antifreeze  solutions are often required,” the report says. More favorably, the report  notes that hot water easily cuts frozen ground.
  •     Air excavation is superb for locating lines, being  nonconductive and carrying the lowest hazard. “When air hits a utility line, it  will flow around without damaging it,” the report states. Air also won’t damage  road base or tree roots

The report took note of the  perception that a water excavator’s cannon-like force cuts holes much faster  than air. Thus, it conceded, water “works best in moderate temperatures for big  jobs, especially if a convenient dump and water refill source” are present.

As for comparative market  reception of air versus water in New York, the report stated: “Until recently  [as of 2006], compressed-air vacuum excavation equipment was the most commonly  used. Now, with the advent of less expensive water systems, those have become  more prevalent.”

On the other hand, the report  noted that air offers easier use, and this would seem to portend a boost in its  market share. Air equipment is also typically “smaller, lighter and more  economical” than hydro support tools, the report notes.

Air can cut all soil types,  including clay or densely packed soils, but works best with sandy soil or loose  loam, the report adds.

In contrast, hydro digging  requires larger trucks and trailers to carry water—in fact, two tanks often are  needed, one to haul the fresh water supply and another to cart away the muddy waste.  When fresh water is exhausted, an excavation gets put on hold until the tank  can be refilled. Contrast this with air VE in which “On-board compressors  generate a limitless supply of air,” the report concludes approvingly.

When it comes to cleanup and  restoration, air again seems to present a big advantage. Getting rid of hydro  VE mud is comparatively difficult. It’s usually not suitable for back fill  after the underground utility elements have been laid bare. So, the excavation  contractor must come up with dry fill. Conversely, with pneumatic excavation  the dry spoils of the dig sit handily nearby, ready for reuse in the same hole.

Market Opinion Update, 2013 A quick survey of our excavators  interviewed here adds a few further insights, essentially confirming the  determinations in New York. Following is a sampling of quotes and observations.

Comparing Water VE to Air…

DitchWitch’s Proctor: A  lot of the customers insist that productivity with water “outweighs the ability  to put dry spoils back in the ground.” This preference is confirmed by the  sheer numbers of customers “who still continue to do hydro versus air  excavation,” he adds.

Thompson LLC’s Lawson: “I  used water on a trench about 100 feet long, 11 feet wide and 9 feet deep. It  took me about a month…with two water guns.” The same job with air would have  taken six months, he estimates.

UEC’s West describes how  much faster air is than water, when you factor-in the comparative time needed  for backfill/mud removal/restoration. “A lot of places won’t even take mud  anymore,” he begins. And here’s one head-to-head comparison: Working against  one of Ultra’s competitors in Southern California, “using the exact same trucks  as they did and working exactly the same delineation, we outperformed them,  digging eleven holes [with air] in the same time frame it took them to dig  three. … Air makes so much more sense,” he concludes. “One truck can typically  do 15 holes a day from start to finish. That includes backfilling and putting  in the cold patch.”

On VE Messiness in Environmentally Sensitive Areas…

Lawson: “Sometimes,  inside a nuclear site you especially don’t want to splash water everywhere…”

Olive, on digging near  petrochemical or gas facilities: “Our [air digging] crews can work  three day straight and not have a waste lagoon full of oily water that’s got to  be solidified or pumped out or hauled to a landfill,” he says. “With air, at  the end of day you just basically have got a big, dry pile of dirt.” Clients  are ecstatic. “That seems to be the big kicker.”

On Avoiding Damage to Underground Lines…

Proctor, rebutting the  negative claim in the New York VEDP that hydro work can damage utility lines:  “CGI advises that water [VE] is ‘very safe,’ so long as the pressure does not  exceed 3,000 psi and the nozzle producing the linear stream of pressurized  water is not aimed directly at the utility lines.”

AirKnife’s Hartman: “If  you’re talking about pipelines that have a protective coating on them or a  fiber optic cable that is buried directly…you can still cause damage to it,  even with a hand shovel or with a pick.”

Vactor’s Schmitt: “Hydroexcavation does not produce the sandblasting effect the way air does.  This reduces the potential for damage to underground utilities.”

On Worker Safety…

Olive: “If we’re going  down to find a utility line or a pipe, somebody has to get in the hole and work  on it. Water in the hole—sometimes mixed with oil—will loosen up the wall of  your excavation. I don’t like putting anyone in a hazard like that.”

West: “Out of the 15,000  holes we’ve dug, we haven’t had an electric line break once. But if we were  ever to crack [one]… with air, you’re a lot safer, especially with the fact  that we use a Fiberglas air lance. So we’re insulated from the tip…”

Hartman: “The person  going into the trench will be digging with a shovel, a piece of steel that  usually has a fairly sharp edge on it. Or somebody will go down with a 20-pound  steel digging bar with a chisel point that you kind of hurl into the ground  like a spear. And, to be honest, who is the one you’re going to send down into  the hole? It’s usually the enthusiastic 18-year-old who just joined the crew.  And you’re saying, ‘Okay, now somebody has to dig by hand. Here you go. Go down  that hole and do it. Good luck.’ Using air excavation…air is coming out at only  90 psi. It is easily deflected… It’ll break up soil. It will blow it away. But  anything solid and nonporous, the air just goes around it.”

Schmitt: Operator safety  training is of course critical, which Vactor provides. “The biggest safety  concern with VE is… the larger units operate at 28-inches Hg of vacuum, which  is capable of pulling almost 800 pounds through an 8-inch diameter hole. If an  operator is not careful, a significant injury or fatality can occur… Vactor  provides many standard safety features to quickly and safely disable the vacuum  should an emergency occur.”

Hydro VE water pressure can  range up to 3,000 psi, he says. “This can severely injure the operator or  damage underground utilities.”

Air VE can also produce static  electricity so tools must be properly grounded, he adds.

On market trends, client preferences…

Olive: When first  introducing “soft digging” to clients, hydro is more intuitive and  understandable, “and hydro has been around for many years,” he notes.

In comparison, if you say  “pneumatic excavation,” lay-people “don’t really grab the concept of what  you’re talking about. Pneumatic is the new kid on the block. A lot of people  still just haven’t been exposed to it.” Both water and air, he finds, “are  still not widely accepted.”

Proctor: “The vast  majority of [VE] contractors” are using hydro vacuum excavation.” Unofficially,  he puts the figure at 70% or more, “just because hydroexcavation is much more  effective and productive.”

Schmitt: “Some utility  companies, departments of transportation or power plants can specify pneumatic  excavation for a given job for a number of reasons….”

Work, Equipment, “Parting Tips”…

Olive: One challenge for  men excavating at distances away from the truck, “whether for pneumatic or  hydro, is coping with the boom limited to 20 to 25 feet,” which all of them  have. “Once you get away from using that boom [i.e., excavating where the boom  isn’t available for hose support], that is where it gets tricky. Basically,  excavation is not efficient out there.” The worker winds up man-handling a  6-inch-diameter hose. This usually happens if the truck boom can’t get close  enough. So, he advises, try to arrange the job site to overcome this.

West, on trucks: “We like  having everything on one truck, having one equipped with every piece of  equipment we can think of that would possibly be needed to get the job done.”  Olive also buys trucks through a custom shop that builds to his design specs,  so the $400,000 vehicle with a turbo vac can be used for work besides pneumatic  excavation. GapVax and Badger are two preferred equipment suppliers for  pneumatic and hydro.

Lawson on compressors: “Make sure you find out what psi to cut with,” as newcomers to vacuum  excavation usually lack the necessary field experience to know which power  combinations can cut what.

The water standard is 2,000 psi,  he adds.

“If you want to go with air,  you’ve got to make sure your application tips are right and know something  about how they cut. Some people come in there and they don’t know how to use  the application right. Make sure you run tests on how much material you can  move over time,” in order to give the customer an accurate job quote.

Lawson on air against clay: “Clay is no problem. If you give me a 375 psi air compressor I can cut that  clay just as good with air as water,” he says. An under-powered 185 psi will  take much longer. And a very high-powered 750 “is definitely going to cut the  [expletive] out of it. I’ve’ gone as far down as 18 feet and [trenching] 200  feet long,” in clay, with 750 psi, he reports. Compressors require adequate  horsepower as well—60 to 100 horsepower, he advises.

Author’s Bio: Writer David Engle specializes  in topics related to excavation and environment.