Underground Utility Trenching & Hydrovac

Deep Utility Trenching for Water, Sewer & Storm in Calgary

Water, sanitary and storm service lines in Calgary sit deep for a reason: frost. We dig, shore, bed and backfill the trench for planned service replacements and new connections, working to the City’s cover depths and alongside the utility indemnified contractor who makes the right-of-way connection.

(825) 475-5548 Request an Estimate How the job runs

Inside a steel trench box, a green PVC sewer pipe rests on a bed of sand at the bottom of a deep trench.

The Problem It Solves

A water or sewer service line almost never fails at a convenient depth. In Calgary the City specification calls for at least 2.7 m (9 ft) of cover over a water service in clay, and the City reported frost reaching 2.4 m (8 ft) in the extreme winter of 2019, so a line that has to come out is buried well below anything a shovel reaches. Replacing it means a trench from the foundation wall to the property line, and often on into the boulevard or street, and where that trench is cut through clay, a wall can stand vertical for an hour and then slab off without warning.

Get the trench wrong and the new pipe inherits the problem it was meant to fix. Cover shaved off to save digging leaves a water service exposed to the next hard winter. A sewer laid on lumpy native clay settles into a belly where solids collect and backups start again. A rock left against the pipe becomes a point load that cracks it years later. Backfill dumped in thick, wet or frozen lifts keeps settling, and by spring the driveway or sidewalk over the trench has dropped. And an unshored trench at this depth can collapse onto the person standing in it.

The paperwork trips up owners as often as the digging. The owner is responsible for the service from the property line to the plumbing in the house, but the section inside the City right-of-way is a different matter: the City requires those connections to be installed by a utility indemnified contractor, and breaking into a City road right-of-way needs an Excavation Permit. When a replacement is booked before those pieces are lined up, the result is an open, expensive hole waiting days on a permit or a contractor who was never called.

How It Works

We plan the trench around the cover depth and the pipe grade, not around the machine we happen to have. Before digging, the elevation of the existing service where it leaves the foundation and the depth at the connection point are confirmed, so the new line can hold its slope and still sit under the City’s minimum cover: 2.7 m in clay or 3.3 m in gravel for water, 2.5 m for sanitary and 1.2 m for storm. Where a design cannot reach full cover, the City standard calls for approved insulation, and that decision belongs to the designer and the City, not to the operator in the cab.

The trench is protected the whole time anyone is in it. Past 1.5 m we either cut the walls back to the angle Alberta’s OHS Code sets for the soil type, or work inside a trench box sized to the depth, and beyond 3 m the protective system follows an engineer’s specification. Mixed soils are treated as the least stable layer present. Spoil goes at least 1 m back from the edge, a ladder or ramp stays within 8 m of every worker, and pumps keep groundwater and surface water out of the bottom so the pipe is never laid in mud.

Once the pipe is laid by the plumber or indemnified contractor, we bed and haunch it with the specified embedment material, working it under the sides of the pipe by hand so it is carried along its full length. Backfill goes back in controlled lifts at a moisture content near optimum, compacted to the City’s density targets and tested where the specification calls for it. Heavy compaction stays off the first 600 mm above a water pipe, and frozen material never goes in the trench. The surface is then restored to the condition the permit or the owner requires.

At a Glance

Water service cover (Calgary): 2.7 m (9 ft) in clay and 3.3 m (11 ft) in gravel on looped mains and services; 3.0 m (10 ft) in clay and 3.3 m (11 ft) in gravel on dead ends and hydrant leads
Sewer cover (Calgary): Sanitary mains 2.5 m and storm mains 1.2 m, measured from pipe crown to finished grade
Trench protection: Required once a worker is in a trench deeper than 1.5 m (5 ft) and closer to the wall than its depth; protective structures in trenches deeper than 3 m (10 ft) must be engineer-designed
Typical machine class: Midi excavators (roughly 6–10 t) on tight services, full-size excavators (above roughly 10 t) for depth, reach and trench-box handling
Pipe zone: Bedding and haunching in the specified embedment material, compacted with hand-operated equipment; no heavy compactors within 600 mm above a water pipe
Backfill density (City specs): Pipe zone at least 95% and street zone at least 97% of maximum density; sewer trench final backfill at least 97% Standard Proctor; no frozen material
Permits and connections: Excavation Permit to dig in a City road right-of-way; service connections in the right-of-way made by a utility indemnified contractor
Spoil and egress: Spoil pile leading edge at least 1 m back from the trench, face no steeper than 45°; a safe way out within 8 m of any worker in a trench over 1.5 m deep

How the Job Runs, Step by Step

Locates, crossings and elevations

Locate requests go in well ahead, and every utility the trench will cross, such as gas, power or telecom running across the service route, is exposed by hand or hydrovac inside its hand-expose zone before a bucket gets near it. Locate marks show where a line runs, not how deep it is, so crossing depths are measured, not assumed. The existing service is exposed at the foundation and at the connection end to fix both elevations. Private lines the utility will not mark, such as power to a detached garage, are identified with the owner first.

Permit, connection contractor and traffic

If the work breaks into a City road right-of-way, the Excavation Permit is applied for online, which the City accepts up to two weeks in advance, with processing of up to two business days, or up to ten on pavement laid within the last two years. The utility indemnified contractor responsible for the right-of-way connection is booked into the same window. Where the trench touches a sidewalk, lane or lane of traffic, the setup is arranged before the day of the dig.

Open the trench in protected lengths

We open only as much trench as can be protected, worked and closed in a practical span, moving the trench box forward as each length is finished rather than leaving a long open cut. Spoil is piled at least 1 m back with its face no steeper than 45°, or loaded straight to trucks on a tight lot. Topsoil and sod are kept separate from clay. Pumps go in as soon as water shows, so the trench bottom stays firm enough to carry bedding.

Bedding, haunching and inspection

A layer of the specified embedment material is placed and levelled to grade before the pipe goes down, so the pipe rests on a uniform bed instead of on clods or rock. After the plumber or indemnified contractor lays and joins the pipe, embedment is worked under the haunches by hand and brought up around and over the pipe in thin layers. The trench stays open for whatever inspection or testing the permit holder has arranged before anything covers the pipe.

Backfill, density testing and restoration

Backfill returns in lifts with rammers or plates, and heavier compaction only once there is at least 600 mm of cover over a water pipe. On City work the sewer specification calls for a density test on each 0.5 m of trench depth (to a maximum of 75 m), and two tests on each service trench, which only works if the lifts were placed properly. Surplus clay is hauled out, and the surface is rebuilt to grade. Under the City Roads specification, winter trench settlement has to be reworked to 97% by the following May 31.

Equipment on This Job

Full-size or midi excavator

Cuts the trench to design depth with a bucket width matched to the pipe and the box, lifts and advances the trench box, and places bedding into the trench without anyone standing under the load. On a narrow city lot a midi machine, roughly 6–10 t, can often do the whole job; open acreage or deep mains call for a full-size excavator above roughly 10 t.

Trench box or engineered shoring

A modular steel or aluminium box, sized to the trench depth and width, that workers stand inside while the pipe is laid and bedded. It moves forward as each length is backfilled. Past 3 m of depth the system used follows a professional engineer’s specification.

Dewatering pumps

Submersible or trash pumps set in a sump at the low end of the trench keep groundwater and rain out of the pipe zone. A trench bottom that stays dry holds grade and compacts properly; one that turns to slurry lets the pipe sink out of line.

Rammer and vibratory plate compactor

The rammer, or jumping jack, drives clay backfill down in the confined width of a service trench; the vibratory plate compacts granular bedding and road base. Both work in thin lifts, and both keep heavy impact off the pipe while its cover is still shallow.

See every machine class we work with

What Decides the Specification

Soil decides more of this job than anything else. Calgary’s water cover depth itself changes with it: 2.7 m in clay but 3.3 m in gravel on looped services, and 3.0 m in clay or 3.3 m in gravel on dead-end services and hydrant leads. Soil type also sets the cut-back angle if the trench walls are sloped instead of boxed: at least 30° from vertical for hard, compact soil, 45° for soil likely to crack or crumble, and 45° from the very bottom for soft, sandy or loose ground. Groundwater, old fill and buried debris from earlier construction all change how wide the trench gets and how much of the dug material can go back in.

The pipe and the surface above it decide the rest. City sewer specifications set pipe embedment by installation type, from 95% Standard Proctor with Class 1A or 1B material for a Type 1 installation down to 90% and 85% for Types 2 and 3, and the road specification sets 95% of maximum density in the pipe zone, 97% in the street zone and 90% in the boundary area near the property line. A trench under a lawn and a trench under a driveway or public road are not built to the same finish, and the pipe material, size and connection details come from the designer, the plumber and the City standard, not from us.

Code, Safety and Permit Notes

Alberta’s OHS Code governs the hole itself. Once a worker is in an excavation more than 1.5 m deep and closer to the wall than its depth, the walls must be cut back, supported by a temporary protective structure, or both, unless the trench is in solid rock or a professional engineer certifies that the ground is and will remain stable. Temporary protective structures in trenches deeper than 3 m must be engineer-designed, and if a trench runs close enough to a building foundation to affect it, that foundation must be supported by an engineer-designed structure before digging starts. Natural frost in the trench walls does not count as shoring.

The City of Calgary adds its own layer. Breaking or digging into a City road right-of-way needs an Excavation Permit under the Streets Bylaw. Water, sanitary and storm service connections in City rights-of-way must be installed by a utility indemnified contractor, and the owner carries the service from the property line to the building plumbing. New service connections, including replacements and required disconnections, public and private portions alike, are at the lot owner’s expense. Foundation drainage from weeping tile or a sump cannot be connected to the sanitary sewer; it must go to the surface or to the storm system.

General guidance only. The municipality, Alberta’s safety codes and the engineer of record, where there is one, decide what applies to your job.

Around Calgary

In communities the City classes as 1950s-era, such as Killarney/Glengarry in the SW and Capitol Hill in the NW, a house may still be on a service line that is many decades old, and an infill rebuild needs its old services disconnected and new connections made, at the lot owner’s expense. The City says lead water services were used only briefly, mainly between 1939 and 1947, and that most services, including those in pre-1950 homes, are copper, though galvanized steel services also exist. If the age or material of a service is unknown, the City is the place to ask before anyone assumes the line needs replacing. On narrow inner-city lots the trench also has to thread past fences, trees and the neighbour’s foundation.

Outside the city the rules change with the municipality. In Chestermere, the City of Chestermere runs a Quick Trench programme that starts automatically when a building permit application is submitted, and its building permits page says the excavation contractor must be vetted by completing five installations, with qualification lasting four years. Owners building there should confirm the contractor’s standing under that programme with the City before booking the service trench. The trenching method, cover and compaction discipline stay the same wherever the pipe goes; what changes is who approves the connection and who inspects it.

Common Mistakes to Avoid

Cutting cover to save digging: A service laid a half-metre shallow is cheaper for one day and a frozen line in the next hard winter. Calgary’s cover depths are minimums, and reduced cover needs approved insulation, not a shrug.
Laying pipe on the clay that came out: Native clay with clods and rock is not bedding. A sewer that settles unevenly develops a belly that holds solids, and a rock against the pipe wall becomes a crack years later.
Trusting a clay wall or frozen ground: Clay can stand straight for a while and then slab off in one piece. Alberta’s OHS Code does not accept natural frost as shoring, and a trench past 1.5 m needs protection whether it looks stable or not.
Digging before the right-of-way side is arranged: Opening a trench to the property line before the Excavation Permit is issued and the utility indemnified contractor is booked leaves a deep open hole on the lot while the paperwork catches up.

When to Choose Something Else

This is planned replacement and new-service work. If water is surfacing in the yard or sewage is backing up right now, the priority is an emergency dig-out, not a scheduled trench, and if water or sewage is surfacing in the street, boulevard or sidewalk, report it to the City through 311 because the public side of the line is the City’s. If you are not yet sure what is wrong with the line, a plumber’s camera inspection comes first, since a partial blockage or root intrusion near the house may be cleared or spot-repaired without a full-length trench. Some plumbing contractors also offer trenchless relining or pipe replacement that can avoid digging up a finished driveway; it is worth asking before paying to open one.

Every Dig Starts With a Locate

Before any ground is disturbed, buried utilities are located and marked. In Alberta, locate requests go through Utility Safety Partners, the province’s one-call service, using Click Before You Dig. We request locates for the dig area and keep the paperwork on site.

Requested ahead of the dig.Utility Safety Partners asks for at least three full working days’ notice, and busy seasons can take longer, so locates are requested well before the machine is booked, not on the morning of the job.
Exposed before a bucket goes near.Within 1 metre either side of a locate mark, or 5 metres for a high-pressure pipeline, the line is exposed by hand or by a non-destructive method the line owner accepts, such as hydrovac, before any machine digs there.
Private lines are not marked.Utility locates stop at the utility’s own equipment. Power to a garage or shop, a gas line to a barbecue or heater, yard lights, irrigation, well lines and septic pipes belong to the owner, so tell us where they run.

Often Done Alongside

Hydrovac & Non-Destructive Daylighting

Non-destructive digging to expose buried lines before any machine gets close.

Emergency Utility Leak Dig-Outs

Priority dig-outs that expose broken water and sewer lines for the repair crew.

Infill Lot Digging & Tight-Access Excavation

Mini and midi excavator digs on narrow infill lots beside neighbouring homes.

Where We Do This Work

Calgary, quadrant by quadrant

Acreage country

Neighbouring cities and towns

A narrow service trench runs across the front lawn of an older bungalow from the sidewalk, with the soil piled in a row set back from the edge and plywood protecting the sidewalk. — Trenching a service from the street

Water, Sewer & Storm Trenching: Questions We Get

Do I need an excavation permit to replace my sewer or water line in Calgary?

If any digging breaks into a City of Calgary road right-of-way, yes. The City requires an Excavation Permit under the Streets Bylaw for that work, applied for online through a myID business account, and applications can be made up to two weeks in advance; processing can take up to two business days, or up to ten on recently paved roads. That permit covers the road right-of-way itself; separately, the service connection inside the right-of-way must be installed by a utility indemnified contractor, so both are arranged before the trench is opened.

Why does a water service in Calgary have to be buried so deep?

Because frost goes deep here. The City reported frost reaching 2.4 m (8 ft) during the extreme winter of 2019, and City specifications require at least 2.7 m (9 ft) of cover over water mains and services in clay, 3.3 m (11 ft) in gravel, and 3.0 m (10 ft) in clay on dead ends and hydrant leads. Sanitary sewer mains need 2.5 m and storm mains 1.2 m of cover. Shallower cover needs approved insulation.

Can you connect my new service to the City main?

The City requires water, sanitary and storm service connections in its rights-of-way to be installed by a utility indemnified contractor, so that part of the work is done by a contractor on that list. We dig, shore, dewater, bed and backfill the trench, and coordinate the schedule so the indemnified contractor is on site when the trench reaches the right-of-way. Everything from the property line to your plumbing is the owner’s responsibility and is typically installed by your plumber.

How do you stop the trench from sinking under my driveway later?

By controlling what goes back in and how. Bedding and haunching are worked under the pipe by hand, then backfill goes in thin lifts near optimum moisture, never frozen, and is compacted rather than dumped. City specifications set 95% of maximum density in the pipe zone and 97% in the street zone, and on City sewer work density is tested on each 0.5 m of trench depth. Heavy compaction waits until there is 600 mm of cover over a water pipe.

How do you scope and quote an excavation job?

From the site or the drawings, not a guess over the phone. We look at access for machines and trucks, overhead lines, what is likely buried, the soil and any sign of groundwater, and how deep the dig goes, because work in excavations deeper than 1.5 m brings sloping or shoring under Alberta’s OHS Code. We work out how much material comes out, whether it is stockpiled or hauled away, and what backfill or gravel comes in. The written quote says what we dig and haul, which locates and permits apply, what engineers or other trades do, and the assumptions, such as soil conditions, that could change it.

Get a Written Estimate for Water, Sewer & Storm Trenching

Send the basics and we will come back with questions or a time to look at the site. Drawings, a geotechnical report or photos of the access all help.

Type of work Property type Community or area When does it need to happen? Site access

Where are you with drawings and permits?

Engineered or architectural drawings Permit applied for or issued Geotechnical report None yet

Describe the job Your name Phone Email

Or call (825) 475-5548

Sending opens your email app with these details filled in, addressed to us. Nothing is sent until you press send there.

Considering Water, Sewer & Storm Trenching?

Call Aspen Excavating or send the details. We will look at the site, tell you whether water, sewer & storm trenching is the right scope, and price it in writing.

(825) 475-5548 Send the Details