Septic System & Field Excavation for Calgary-Area Acreages

The Problem It Solves

Many septic problems start in the ground, not in the tank. A treatment field is a soil-based system: effluent has to soak into and move through natural soil, and the Standard of Practice will not allow a treatment field at all on soils whose loading rate is less than 9.80 litres per square metre per day. A field dug without proper test pits can end up in clay too tight to accept it. A trench cut in wet clay with a bucket that smears the walls can seal the very surface the effluent needs to pass through. A trench bottom that wanders off level can send most of the flow to one end.

The results are expensive and hard to undo. Effluent surfaces in the yard, the house backs up, or partly treated sewage reaches groundwater that a well on the same parcel, or next door, may draw from. That is exactly why the setbacks between fields, wells, watercourses and basements exist. A system that fails its inspection before backfill has to be dug and corrected on the spot, and a treatment field that has failed may not be repairable in place; a replacement may have to go on fresh ground that meets every setback, if the parcel still has any.

Acreage sites add their own traps. A new home on a two-acre parcel has to fit the house, well, driveway, shop, septic tank and treatment field together with every required distance between them, and an excavation sequence that ignores the field area can compact or cut through the only ground that would have worked. Tanks are heavy and arrive on trucks that need firm access. Septic tanks, tile beds and wells are private facilities that the utility locate does not mark, so on an existing acreage the old system has to be found before anyone digs near it.

How It Works

We work as the excavation contractor to the certified installer and designer, not in place of them. The installer holding a current certificate of competency designs the system, obtains the permit and signs for the installation; we dig to that design. That starts with soil test pits dug where the designer wants them and deep enough to see the profile, at least 300 mm below the vertical separation the proposed system needs, so the designer can decide between a treatment field, a mound, a packaged treatment plant or a holding tank based on what the soil can actually take.

Tank excavation is laid out from the setbacks outward. The hole for the septic tank or holding tank is dug to the depth the inlet grade and design require, with room to set the tank and a firm, level base prepared to the installer’s specification. If a holding tank ends up with less than 1.2 m of earth cover, the design has to include insulation equivalent to R-8. Where the hole gets deep, the OHS rules for any excavation apply: protection once a worker is in it past 1.5 m, and spoil kept at least 1 m back from the edge.

Treatment field trenches and mound bases get the most care. Trench bottoms are cut level to the design using a laser, and field work is commonly scheduled for when the soil is not wet enough to smear, with walls roughened where the installer specifies. Machines and trucks are kept off the field and mound areas so the soil is not compacted before it ever receives effluent. Everything stays open until the inspector has checked the lateral lengths, bedding depth, field type and gravel cover, and only then is it backfilled and graded to shed surface water.

What Decides the Specification

The soil decides the system, and the system decides the dig. Test pit results tell the designer how well the soil will accept and treat effluent, where any restrictive layer or high seasonal water sits, and how much vertical separation is available. Good, permeable soil can take a conventional treatment field in trenches; tighter or shallower soils push the design toward a mound built above native ground; some sites need a packaged treatment plant, which the Standard sets back 6 m from a property line, or 1 m where it has odour control and treats less than 5.7 m³ a day; and a holding tank that is pumped out is sometimes the only option.

The parcel decides where it can go. Every setback in the Standard has to fit on the lot at once: a treatment field 15 m from the well and 10 m from a basement, 5 m from a building on a permanent foundation without a basement and 1 m from a building without one, and 1.5 m from the property line; a mound 3 m from the property line; tanks 10 m from the well. Slope, drainage paths, trees, the driveway and future buildings all compete for the same ground, and on an existing acreage the location of the old system and the neighbour’s well matter just as much.

Around Calgary

Springbank and Bearspaw, both country residential communities in Rocky View County, have historically relied on groundwater wells, private water co-operatives and septic fields, and many of their parcels are around two acres. The Bearspaw plan says parcels of about two acres became the common baseline precisely because of the servicing standards for private sewage systems, and it also signals a gradual shift toward piped systems. On an established acreage, a replacement field has to be worked around the old field, the well and mature landscaping, all of which the utility locate will not mark. Harmony, in the Springbank area, is on piped servicing, so septic work does not apply there.

South of the city in Foothills County, De Winton is not on the County’s list of piped water and sewer service areas, and the County’s plan describes traditional acreage lots with individual wells and septic systems as appropriate in some cases, so owners around De Winton should confirm how their own parcel is serviced before planning a system. Heritage Pointe is the opposite case: it is served by communal piped water and wastewater, so a home there connects to service lines rather than a septic field, and the work is service trenching, not field excavation.