Hydrovac excavation

STA 0+120How hydrovac excavation works

The water wand liquefies soil ahead of the vacuum hose, which draws the resulting slurry up into an insulated debris tank on the truck. Two variations are common:

• Hydro excavation uses pressurized water and is gentler on buried assets, the standard choice for daylighting near a pipe, cable or fibre line.
• Air excavation uses high-pressure air instead of water to break up soil, producing a dry spoil pile instead of slurry; it is used where a wet hole is a problem, such as around live electrical equipment or in a confined space.

Neither method replaces mechanical excavation for bulk earthworks; hydrovac is a precision tool for the specific volume of ground close to something that cannot be risked. See earthworks and excavation for how bulk cut and fill is priced and moved instead.

STA 0+240Daylighting: exposing a utility before you dig

"Daylighting" means exposing a buried utility to daylight, by hand or by hydrovac, before mechanical excavation is allowed closer to it. Every province sets a hand-expose or precaution zone around a marked utility, and the number is smaller than most people expect:

Inside that zone, mechanical equipment either cannot be used at all or can only be used under direct supervision of the utility owner's representative, depending on the province. Hydrovac is the practical way to expose the zone quickly without hand-digging the whole area with a shovel. See trench safety and shoring and call before you dig for the wider excavation and locate rules each province applies.

STA 0+360Working near pipelines

Pipelines carry their own, stricter rules on top of the general excavation law. In Alberta, the owner of a pipeline within 30 m of planned ground disturbance must be contacted and asked to locate it before work begins¹. For federally regulated pipelines, the Canadian Energy Regulator's damage prevention rules define a prescribed area of 30 m on each side of the pipeline centreline, inside which anyone planning ground disturbance must submit a locate request through the one-call centre at least three working days before starting⁵⁵. Alberta's own one-call centre, Utility Safety Partners, recommends three to five full working days' notice for a standard locate request, longer during the May-to-September peak season⁶. A hydrovac crew scheduled to daylight a pipeline crossing needs that lead time built into the program up front; showing up with a truck before the locate response has come back just means standing by, at cost, until the marks are on the ground.

STA 0+480Hydrovac in winter

Hydrovac keeps working through a Canadian winter longer than open-cut excavation does, because a heated water system and a wand can break through frozen ground that would otherwise need a hoe-ram or ground-thawing equipment first. It is common on winter utility locates, emergency repairs and pipeline exposure work for exactly that reason. It does not eliminate frost as a factor: colder temperatures slow production, water lines on the truck need to be kept from freezing between uses, and slurry disposal sites may have their own winter access or freezing constraints. See snow and winter works for frozen-ground excavation more broadly.

STA 0+600Slurry disposal

The debris tank fills with a mix of soil, water and whatever was in the hole, and it has to go somewhere once the truck is full. Options include an approved municipal or private disposal facility that accepts hydrovac slurry, on-site dewatering (separating water from solids so each can be handled differently), or, where soil conditions and permits allow it, spreading the material back on site. Disposal is rarely free: facilities charge by volume, and the cost depends on what the slurry contains, since contaminated soil or fluid handled by a hydrovac at an industrial or pipeline site is disposed of differently, and at a higher cost, than clean native soil from a residential utility locate. A crew working several locates a day plans its disposal runs as part of the route, because a full debris tank has to be emptied before the next hole can be started, and the drive to and from an accepting facility is time the truck is not excavating.

STA 0+720How hydrovac work is billed

No government body publishes an official tendered unit price for hydrovac excavation the way Alberta Transportation and Economic Corridors does for highway pay items, because hydrovac is rarely its own line item on a public tender; it is usually a sub-scope of a larger excavation, utility or pipeline contract, or a standalone service billed directly to whoever needs a hole exposed safely. Rather than quote a number that does not exist, the drivers that set the price are:

• Truck and crew time, usually billed hourly with a minimum call-out, since most jobs are measured in hours on site rather than cubic metres produced.
• Slurry disposal, billed by volume and by what the material turns out to be.
• Mobilization and standby, which matter more on remote, industrial or after-hours work than on a routine municipal locate.
• Ground conditions, since frozen, rocky or heavily compacted ground slows production and can call for hot water or air excavation instead of standard cold-water hydro excavation.

See the hydrovac cost guide for how these drivers combine into a typical invoice, and the utility locate cost guide for what a one-call locate itself costs (usually nothing) versus a private hydrovac daylighting service.

STA 0+840What to send for a price

A hydrovac job is priced from the site conditions and the reason for the hole, not a volume alone. A useful brief includes:

• The location and how many holes or how much linear exposure is needed.
• What is believed to be buried there, and whether locates have already been requested.
• Ground conditions: frozen, rocky, previously disturbed, or contaminated.
• Where slurry can be disposed of, or whether the contractor needs to arrange disposal.
• Access for a truck, including any overhead or confined-space restrictions.
• Whether the work is a one-time locate or part of an ongoing program.

Ask how the invoice will be broken down between truck time, disposal and any standby, and whether a minimum call-out charge applies. Those answers predict most disputes on a hydrovac job.