Pressurized water cuts the soil. A vacuum lifts it away. Nothing hard ever touches the pipe. Scroll down and we'll take the machine apart, one layer at a time.
Buried utilities sit inches apart, and a bucket can't feel them.
Under almost every street sit gas lines, fiber, water mains, power cables and sewers, often stacked within a few feet of each other.
Marking paint and flags follow the APWA uniform color code: yellow for gas, orange for communications, blue for water, red for power, green for sewer.
A backhoe bucket feels the same resistance from a gas main as from a rock. Hit the wrong one and the result can be an outage, a fire, or worse.
The Common Ground Alliance's 2025 cost study modeled about 669,000 damages to buried utilities in a single year, counting repairs, lost business and response costs.
Source: Common Ground Alliance, 2025 cost-of-damage studyTo dig right beside a live line, you need a tool that can't cut a pipe. Swap steel for two things: water and air.
Two systems run at once: one cuts, one lifts.
Hydro excavation, usually called hydrovac or soft digging, is what NG crews do every day. The whole method fits in one sentence: water loosens the ground, and suction carries it away.
A high-pressure jet breaks the soil apart and mixes it into a thick mud called slurry. The water does the digging, so there's no blade and no bucket in the hole.
At the same time, a powerful vacuum pulls the slurry up a wide hose and into a sealed debris tank on the truck. The hole stays clear, so the operator can see what they're uncovering.
The utility is exposed by washing soil away from it, not by scraping it. That's the whole safety case for hydrovac.
Six systems on one chassis. Tap a part on the truck to jump to it.
Tanks along the frame carry the digging water. Capacity sets how long a crew can work before refilling.
The pump feeds the hand-held digging wand at high pressure but a modest flow.
Many trucks carry a diesel-fired heater so crews can cut frozen ground and dense clay. More on that in chapter 7.
The sealed tank at the rear holds everything the hose picks up, until it's dumped at an approved site.
The blower pulls air out of the debris tank. That pressure drop is what powers the suction at the end of the hose.
The boom swings the heavy suction hose over the hole, so the truck can stay parked clear of the work.
Cutting power, not volume.
That's enough pressure to break up packed soil quickly. For scale, a household tap runs at roughly 40–60 psi.
Dedicated hydrovac units often run under 10 gpm. The goal is cutting power, not flooding the hole, which also keeps the tank from filling with water.
NSC specification: 4–10 gpm for hydro excavation rigsA straight tip fires one concentrated needle of water. A rotating, or oscillating, nozzle sweeps the jet into a cone, so the energy spreads out. It's the nozzle preferred for exposing utilities.
Done right, the spray breaks the soil apart while keeping concentrated force off the pipe.
Ditch Witch vacuum-excavation best practices; GTI Vacuum Excavation Best Practice & GuidelineThe blower removes air. The atmosphere does the pushing.
The blower draws air out of the sealed debris tank, dropping its pressure well below the atmosphere outside.
Outside air rushes toward the low pressure through the only opening: the end of the hose. That fast-moving air carries the slurry with it.
CFM measures how much air moves. More airflow means material moves faster up the hose.
Inches of mercury measure how hard the system pulls. A perfect vacuum at sea level is about 29.92 inHg.
Fan systems move lots of air but top out around 16 inHg, so they fade on deep holes and long hose runs. Positive displacement blowers reach roughly 15–27 inHg and keep pulling.
Illustrative trend, not measured data for any specific truck.
A big, slow room for air, and a chain of guards in front of the blower.
The fast air stream from the hose suddenly enters a big open tank and slows down. Rock, soil and water can't stay airborne, so they fall to the floor.
If the tank overfills, rising liquid lifts a float ball that seals the outlet and stops flow to the blower.
A backup trap catches carry-over, and filters or cyclones strip out fine dust.
Chandler VAC: primary and secondary shutoffs and final filtersWhat's left is clean air. It passes through the blower and out through a silencer.
When the tank is full, the rear door opens and the body tilts to empty it at an approved disposal or decant site.
Heat makes hydrovac a year-round tool.
A large onboard heater can deliver very hot water. One commercial unit is rated at 420,000 BTU, about 175°F at 5 gpm.
Dig Different: hydrovac water heater specificationsThat's how hydrovac keeps digging through a Denver or Boise winter, cutting through frost that would stop a shovel.
Hydrovac News cold-weather guideNear buried lines, crews dial temperature and pressure back down. One gas-industry guideline caps water at 115°F and 2,500 psi around facilities.
GTI Vacuum Excavation Best Practice & Guideline (2012)From test holes to tree roots.
The most common job is a small test hole that shows a utility's exact depth and position before anyone drills or trenches nearby.
Calling 811 gets public utilities marked. Private lines, like power to a parking-lot light or a building's own water service, often go unmarked.
NG pairs hydrovac with private utility locating through its partner, Safe Site. Ground-penetrating radar and locators find the unmarked lines, then the hydrovac exposes them.
| Factor | Hydro excavation | Air excavation |
|---|---|---|
| Speed | Generally faster | Slower |
| Clay and frozen ground | Handles well, especially with hot water | Struggles |
| Spoil | Wet slurry, hauled to a disposal site | Dry soil, reusable as backfill |
| Water supply | Required | Not needed |
Wet spoil and a powerful jet both need a plan.
Slurry goes to approved disposal or dewatering sites, where solids are separated from water, tested, then landfilled or recycled. It never goes down a storm drain.
Hydrovac News: slurry handling and disposal guideWater at thousands of psi can cause injection injuries. Never point the wand at anyone.
National Safety Council: hydro and pneumatic vacuum excavation specificationNational reach. Local crews.
NG crews work from Nashville, Dallas–Fort Worth, Tampa, Charlotte, Boise and Denver, and travel to projects across the country.
Hydrovac is one of five NG services, alongside utility locating, video pipe inspection, hydro jetting and trenchless pipe repair.
NG has handled potholing, coring and full excavation for a downtown Kansas City water main replacement, and complex excavation for Tampa International Airport's new terminal.
Large contractor or small, NG brings the same commitment and the same grit, across industrial, education, residential, manufacturing, commercial, public infrastructure, healthcare, energy and heavy civil work.
The result is a hole dug exactly where you need it, with the buried lines around it still intact.
2,000–3,000 psi through a moving, rotating nozzle loosens soil into slurry.
Low pressure in the tank lets the atmosphere push slurry up the hose.
Air slows in the big tank and the heavy material drops out.
Shutoffs and filters make sure only clean air reaches it.