If you are planning work near buried gas, electric, fiber, water, or sewer lines, you will run into hydro excavation quickly, and often as a requirement rather than a choice. This guide covers what the method is, how the equipment works, what it costs, what it cannot do, and what a crew needs from you before the truck arrives.
What Is Hydro Excavation?
Hydro excavation is a digging method that uses pressurized water to break up soil and an industrial vacuum to lift the resulting slurry out of the hole, so no blade or bucket ever touches the ground. Because nothing mechanical enters the excavation, it is classified as non-destructive digging, and it is the standard approach for working around buried utilities.
The same method goes by several names. Hydrovac excavation, hydro vacuum excavation, vacuum excavation, and hydro vacing all describe the same process. On site, most crews just say “hydrovac,” using it as both a noun for the truck and a verb for the work.
How Does Hydro Excavation Work?
A hydrovac unit puts four systems on one chassis: a water tank, a high-pressure pump, a vacuum source, and a sealed debris tank.
- Locate and mark. The utility locate is called in and existing lines are marked before anything else happens. In Oregon that means a ticket through the Oregon Utility Notification Center at 811, with a waiting period before ground can be broken.
- Cut the soil. An operator directs a handheld wand delivering water somewhere between roughly 1,500 and 3,000 psi, adjusting pressure and nozzle for the ground. The stream turns soil into slurry. Pressure comes down in soft or sandy material and goes up in hardpan and stiff clay.
- Lift the spoil. A vacuum hose, usually six or eight inches, pulls the slurry into the debris tank. Fan systems move high air volume and suit shallow, fast production work. Positive displacement blowers generate more lift and handle deep holes and long hose runs.
- Dispose or backfill. The tank is emptied at an approved site, or the material is processed and returned where conditions and local rules allow.
A working truck typically carries 500 to 1,300 gallons of water and 8 to 16 cubic yards of debris capacity. Those two numbers set how long a crew runs before it has to stop, and on a busy site they matter more than horsepower.
Why Hydro Excavation Is Often Required Rather Than Optional
This is the part most guides skip, and it is usually the reason the method ends up in a scope of work.
Every state operates a one-call damage prevention system. An excavator has to notify the notification center before digging, wait the required period, and let facility owners mark their lines. In Oregon that notification goes to the Oregon Utility Notification Center, and the standard advance notice is two business days.
Marks are approximate. That is the whole point of the tolerance zone: a defined band on either side of the mark where the facility is presumed to be but its exact position is unknown. Inside that band, mechanical excavation is prohibited. You are required to expose the facility by hand digging or by vacuum excavation. Hydro excavation exists as an industry because it is the fast, safe way to satisfy that requirement.
The liability structure is the other half. When a line is struck, the excavator who was digging generally carries responsibility, and the exposure is not limited to fixing the pipe. It includes the facility owner’s repair billing, service interruption claims from everyone downstream, regulatory penalties, project shutdown, and injury. A gas or high-voltage strike can escalate past all of that immediately. Documented compliance, including the ticket number and evidence that the tolerance zone was potholed properly, is what protects a contractor after an incident.
Hydrovac Trucks, Vac Trucks, and Trailer Units
The equipment vocabulary trips people up, so it is worth separating.
A hydrovac truck is purpose-built, carrying water, pump, boom, vacuum, and debris tank on one chassis. This is the standard rig for utility work.
A vac truck is any truck built around an industrial vacuum. Plenty of vac trucks are dry units used for spoil, sludge, or industrial cleanup with no water system at all. A hydro vac truck is the version that adds pressurized water. When someone requests vac truck work on a utility job, they almost always mean hydrovac.
A hydrovac trailer is a smaller towed unit with less water and debris capacity. Trailers earn their place on tight residential lots, behind gates, and inside courtyards where a full truck physically cannot position, at the cost of shorter run times between dumps.
Access decides this more often than volume does. A full-size unit needs real width to set up, overhead clearance for the boom, and a path that can carry a loaded truck without tearing up finished surfaces. If any of those is missing, a trailer that runs half as long is still faster than a truck that cannot reach the hole.
What Hydro Excavation Is Used For
- Daylighting. Exposing a buried utility so its position and depth can be visually confirmed before other work proceeds.
- Utility potholing. Cutting a small test hole to verify exact depth and horizontal position. Our guide to utility potholing covers that application in depth.
- Slot trenching. Producing a narrow trench for conduit or cable with far less surface disruption and restoration cost than a full mechanical trench.
- Piling and pole holes. Clean, precise holes for signposts, light standards, and structural piles.
- Vault, catch basin, and tank cleanout. Removing material that has to be lifted rather than dug.
- Digging around root systems. Exposing roots without cutting them, which matters on sites with protected trees or an arborist requirement.
For developers and general contractors, the schedule value is usually larger than the line item. Unknown utility positions are the most common source of change orders on underground packages, because a conflict discovered during trenching stops the crew, triggers a redesign, and requires the utility owner to weigh in before anyone moves again. Potholing the conflicts during preconstruction converts that risk into a known quantity while the schedule still has room to absorb it.
How Deep Can You Hydro Excavate?
Deeper than most people expect. The large majority of utility work sits in the top 10 to 15 feet, comfortably inside the range of any working unit. With hose extensions and a blower-type vacuum, crews regularly work past 20 feet, and some configurations are rated considerably deeper.
The limit is rarely the machine. As depth increases the vacuum lifts slurry farther, production slows, and shoring and confined space rules apply the moment anyone needs to enter the hole. Depth also drives water consumption, which drives refill trips, which is what actually shows up on the invoice.
How Long Does Hydro Excavation Take?
A single pothole exposing one utility at normal depth is generally a matter of minutes to an hour once the truck is set and the locate is verified. A crew working a site with good access commonly completes several holes in a day.
Larger scopes behave differently. Slot trenching, deep excavation, stiff clay, cobble, and restricted access each cut production. In practice the schedule is driven less by the digging than by four things: soil type, depth, hose distance from truck to hole, and the round trip to dump and refill. On a site with a nearby approved dump location, a crew stays productive. On a site where the round trip is 45 minutes, half the day disappears into driving.
Hydro Excavation vs. Air Excavation
Both are non-destructive and both are safe around live utilities. The difference is the medium.
Air excavation uses compressed air to break soil and vacuums the dry spoil. The material stays dry, so it can frequently go straight back into the hole as backfill with no disposal cost. That is a real advantage on clean exposures, and some electrical utility owners prefer it specifically because it introduces no water near energized equipment.
Hydro excavation cuts faster and handles more soil types, especially hardpan, stiff clay, and frozen ground where air struggles. The tradeoff is wet slurry that usually has to be hauled off.
Air also loses ground in wet conditions. Saturated soil does not fluidize under air the way dry soil does, which is a meaningful limitation in a climate with a long rainy season. Hydro excavation is the more common default on general utility work for that reason and for raw production rate.
Hydro Excavation vs. Traditional Mechanical Digging
Against a backhoe or excavator this is a question of risk and precision rather than speed.
Mechanical equipment moves far more material per hour in open ground with no conflicts, and it remains the right tool for bulk excavation. What it cannot legally do is dig inside the tolerance zone around a marked utility. That is the dividing line, and it is regulatory rather than a matter of preference.
The efficient approach on most jobs uses both. Mechanical equipment handles the bulk of the excavation, and the hydrovac handles the crossings, the tie-ins, and the tolerance zones. Paying a hydrovac hourly rate to dig an open field is a waste. Sending an excavator into a marked gas corridor is a much more expensive mistake.
What Are the Disadvantages of Hydro Excavation?
- Spoil disposal. Wet slurry usually cannot be returned to the hole. It has to be hauled to an approved facility, which adds cost and truck time.
- Water logistics. Every unit has a finite supply. On remote sites or high-volume days, refills become a scheduling factor rather than a detail.
- Hourly cost. The rate is higher than conventional equipment. It only makes economic sense applied to the portion of work that genuinely requires it.
- Poor fit for bulk excavation. For large volumes of open ground with no conflicts, mechanical equipment wins decisively.
- Rock and cobble. Water cuts soil, not stone. Cobbles have to be vacuumed whole or worked around, and a cobble larger than the hose will stop production while the crew clears it.
- Operator skill is the safety variable. Water at pressure can damage pipe coating or direct-buried cable if the wand sits too close or the pressure is set wrong. The method’s safety record belongs to trained operators, not to the equipment.
How Much Does Hydro Excavation Cost Per Hour?
Hydro excavation is normally billed as an hourly rate for truck and crew, with a minimum charge covering mobilization and a set number of hours. Published rates across the United States commonly land somewhere in the range of roughly $150 to $400 per hour, with debris disposal either included or billed separately.
What actually moves a quote:
- Crew size. A two-person crew is standard. Traffic control or confined space requirements add people.
- Travel and mobilization. Distance to the site, and whether the truck can stay on site across multiple days instead of remobilizing.
- Dump distance. The round trip to an approved disposal facility is billable time on most contracts.
- Depth and soil. Deep holes in stiff clay or cobble produce a fraction of the holes per day that shallow work in silt does.
- Water access. An on-site hydrant meter or fill point removes refill trips from the bill.
- Disposal classification. Material from a site with known contamination requires different handling and different disposal pricing.
- Schedule. Night work, weekend work, and emergency response carry a premium.
The number that matters is not the hourly rate in isolation. It is holes per day. A crew at a higher rate with good access, a nearby dump, and on-site water frequently costs less per completed pothole than a cheaper crew losing half the shift to driving.
What to Have Ready Before the Truck Arrives
Sites that are ready run at close to double the production of sites that are not. Before the crew mobilizes, confirm:
- A valid, unexpired locate ticket with marks still visible on the ground. An expired ticket stops the job on arrival.
- Access. Width for the truck, overhead clearance for the boom, and a route that will support a loaded vehicle. Note any weight-restricted surfaces.
- A water source, or advance notice that the crew needs to arrive full and plan refills.
- A dump plan. Either an approved disposal facility identified in advance, or written permission and a location for on-site spoil containment.
- Marked dig locations, with stationing or coordinates rather than a verbal description. Guessing at locations on arrival burns paid time.
- Traffic control, if any hole sits in a right of way. Confirm who is providing it and whether a permit is required.
- Known contamination history. If the site has any, say so before the crew starts filling a tank, because it changes disposal entirely.
How to Scope Hydro Excavation in a Bid or Spec
If you are writing hydro excavation into a bid package, specify:
- Unit of measure. Per pothole, per hour, or day rate. Per-hole pricing shifts production risk to the contractor and works when depths are predictable. Hourly works better when conditions are unknown.
- Assumed depth and hole dimensions, with a stated procedure for anything deeper.
- Who provides water, traffic control, and permits.
- Disposal responsibility, including whether contaminated material is included or excluded.
- Deliverables. This is the one most commonly left out. A pothole is only worth what gets recorded: measured depth to top of facility, facility size and material, horizontal offset from a fixed reference, surface elevation, and a photograph. Ask for a pothole data sheet or a survey-grade tie. Without it, the crew fills the hole and the information leaves with them.
- Restoration standard, especially for holes in asphalt, concrete, or finished landscape.
Ground Conditions in the Pacific Northwest
Generic guides describe hydro excavation as if the ground were the same everywhere. It is not, and the Portland metro area has three conditions worth planning around.
Cobble. Much of the Willamette Valley floor sits on Missoula Flood deposits, which means silt over sand and gravel with cobble in places, particularly along river terraces. Water does not cut rock. In cobbly ground, production drops and the crew spends time removing stones individually. This is the single most common reason a local hydrovac day underperforms the estimate, and it is worth expecting near the Columbia and Willamette corridors.
Clay and silt in the hills. West side sites in the Portland Hills work through loess and weathered basalt. Stiff clay cuts fine at higher pressure, but it comes out as heavy slurry that fills a debris tank faster than sandy material does, which means more dump trips per cubic yard.
Saturated ground. From roughly October through May the soil column stays wet. Saturated soil actually cuts easily, so digging speed holds up. The problem lands in the debris tank, which fills with a thinner, wetter slurry carrying less soil per load. The same number of holes takes more dump cycles in February than in August. Budget accordingly.
Frozen ground, which nearly every national guide highlights as the headline advantage of heated hydro excavation, is rarely the operative issue here. It matters at elevation and during a hard freeze, and it is otherwise a non-factor in the valley.
Utility Owner Requirements
Beyond state law, individual facility owners set their own contractor requirements. Portland General Electric maintains a certified contractor program, and work in or near their facilities is expected to be performed by contractors who have gone through it. Municipalities, water districts, and ODOT each carry their own prequalification, inspection, and documentation standards.
This matters at the bidding stage rather than the digging stage. A crew that is not on the approved list cannot perform the work regardless of equipment or price, and discovering that after award costs schedule.
Frequently Asked Questions About Hydro Excavation
Is hydro excavation the same as hydrovac?
Yes. Hydro excavation, hydrovac excavation, hydro vacuum excavation, and hydro vacing all refer to digging with pressurized water and an industrial vacuum. “Hydrovac” is the shorter term used on site.
Is hydro excavation required by law?
Not universally, but effectively yes inside the tolerance zone. One-call damage prevention rules prohibit mechanical excavation within a defined band around a marked utility and require the facility to be exposed by hand digging or vacuum excavation. Hydro excavation is the practical way most contractors meet that requirement.
Who is liable if a utility line is struck?
Generally the excavator performing the work, and the exposure extends well past the cost of the repair to include service interruption claims, penalties, project delay, and injury. Documented compliance, including the locate ticket and proof the tolerance zone was potholed, is what limits that exposure.
Is hydro excavation safe around live utilities?
It is the safest widely available method, because no mechanical blade enters the ground. Damage prevention rules point to vacuum excavation for exactly this reason.
What is daylighting excavation?
Daylighting means exposing a buried utility to visible daylight so its exact position and depth can be confirmed. It is one of the most common applications, and daylighting and potholing are frequently used interchangeably.
Does hydro excavation damage pipes or cables?
Performed correctly, no. Pressure and nozzle are matched to conditions and the stream is kept moving rather than held on one spot. Poor technique can damage pipe coating or direct-buried cable, which makes operator training the variable that matters.
How much does hydro excavation cost per hour?
Rates commonly fall in the range of roughly $150 to $400 per hour for truck and crew, usually with a minimum charge. Crew size, travel, dump distance, depth, soil conditions, water access, and schedule all move the figure.
What happens to the material that gets vacuumed out?
It goes into a sealed debris tank and is emptied at an approved disposal facility. Where conditions and local rules permit, some material can be processed and returned to the excavation.
Can hydro excavation work in cobble or rock?
Water cuts soil, not stone. Cobble slows production because stones have to be vacuumed whole or worked around, and anything larger than the hose has to be cleared by hand. It remains workable, just slower, which is worth accounting for in Willamette Valley river terrace soils.
Working With a Hydro Excavation Crew
Angelo Underground performs hydrovac and potholing work and utility trenching across the Portland metro area and Southwest Washington. We are a PGE certified contractor, CCB# 243015, DBE/MBE/ESB# 13892, and certified for public works and ODOT projects.
Recent work includes the Multnomah County B425 electrical infrastructure project with Christenson Electric, where trenching, hydrovac excavation, and generator pad and light pole base work were phased around an active county facility that could not lose service, and potholing for Tualatin Valley Water District in Beaverton.
Call (503) 828-9663 or request a proposal to discuss your project.
