The Regulatory Framework
Sewage systems in Ontario are governed by the Ontario Building Code Part 8 and specifically by Ontario Regulation 358/11 — Small Sewage Systems. This regulation defines all approved system types, their siting requirements, design criteria, and inspection requirements. In Renfrew County, the Renfrew County and District Health Unit (RCDHU) is the approval authority — all new systems and major repairs require a permit from RCDHU before work begins.
Which system type is approved for your property is determined by a licensed designer who assesses your site — measuring soil characteristics, water table depth, and available area — and selects the appropriate system type based on what the site can support.
Conventional Septic System (Leaching Bed)
The conventional septic system is the most common system type where site conditions permit, and the lowest-cost option. It consists of:
- A septic tank (typically precast concrete, 3,750–4,500 litres for a standard home) where solids settle and anaerobic digestion begins
- A distribution box that divides effluent flow equally among leaching bed trenches
- A leaching bed of perforated pipes buried in gravel trenches, where clarified effluent disperses into the native soil for final biological treatment
Soil requirement: At least 4 feet (1.2 metres) of suitable native soil above the seasonal high water table and above bedrock. The soil must have adequate permeability — it cannot be dense clay that does not accept water, nor coarse gravel that passes effluent through too rapidly without treatment.
In Renfrew County, conventional systems are common in areas with good soil depth and appropriate texture — much of the central and agricultural parts of the county. However, the shallow bedrock prevalent in many northern and rocky areas, and the seasonally high water tables in lower-lying terrain, frequently make conventional systems unsuitable.
At-Grade System
An at-grade system is used where the existing soil depth above the water table or bedrock is insufficient for a conventional leaching bed. Rather than excavating trenches into inadequate native soil, the leaching component is constructed at the existing ground surface and filled with engineered sand to create the required treatment depth above any constraint.
At-grade systems are more common in Renfrew County than in regions with deeper soils, because shallow bedrock is widespread across the Canadian Shield portions of the county. The system is covered with topsoil and seeded, and from the surface appears as a raised or level area in the yard. Cost is higher than conventional due to the imported sand and additional grading work.
Raised Bed System
A raised bed system is a fully above-grade leaching system built where the native soil is entirely unsuitable and the water table or bedrock is too close to the surface to accommodate even an at-grade approach. The entire treatment bed — including imported fill material meeting specific criteria — is mounded above the existing ground. A raised bed is visible in the landscape as a mound, typically several feet high.
Raised beds are used for the most constrained sites and carry the highest installation cost due to the volume of fill material required and the complexity of construction. O. Reg. 358/11 specifies the fill material requirements and setback distances for raised bed systems.
Holding Tank
A holding tank is a completely sealed, watertight tank with no leaching or treatment component. All sewage from the house is stored in the tank and must be pumped out regularly by a licensed hauler who disposes of the waste at an approved facility.
O. Reg. 358/11 approves holding tanks only where no other system type is feasible — for example, on very small lots near water bodies, or in specific seasonal-use situations. For year-round primary residences, holding tanks are not recommended due to their very high operating cost. A family of four will typically fill a standard holding tank in 2–4 weeks, requiring pump-outs at $200–$400 each — annual costs of several thousand dollars are common.
Tertiary Treatment Units
Advanced or tertiary treatment units are prefabricated systems that provide additional treatment beyond what a septic tank alone achieves — reducing nitrogen, phosphorus, or pathogen levels before effluent reaches the leaching component or receiving environment. These systems are required in environmentally sensitive areas, particularly near water bodies where standard effluent quality is insufficient to protect water quality. They are more common for properties on or near lakes and rivers in Renfrew County's cottage and waterfront zones.
Tertiary systems are more expensive to purchase and install, and require ongoing maintenance contracts. O. Reg. 358/11 specifies when advanced treatment is required and what performance standards must be met.
Which System Is Right for Your Property?
System type selection is not a choice made by the property owner or contractor — it is determined by the licensed SSSTS designer based on the site evaluation. The designer's assessment includes a percolation test (measuring how quickly water drains through the soil), measurements of the water table depth at different times of year, and mapping of available area after setbacks are applied. The designer then selects the system type that meets the regulatory requirements for the specific site conditions found.
If you are planning a new build or replacing a failing system, engage a licensed SSSTS designer early — before finalizing lot purchase, if possible. Site conditions that prevent any approved system from being installed at an affordable cost can significantly affect a property's value and buildability.
See also: Septic Systems overview and Ontario septic regulations and permit requirements.