What is an oil interceptor and how does it work?
An oil interceptor relies on two simple physical principles: gravitational separation and coalescence. According to the Bureau de normalisation du Québec, over 95% of light industrial facilities treating hydrocarbon-laden runoff use these two mechanisms in combination to meet regulatory thresholds (BNQ, 2019).
Water laden with hydrocarbons enters the first chamber. Because oil is less dense than water (relative density of 0.8 to 0.9), it naturally rises to the surface. This floating layer is retained in the retention chamber while partially treated water moves to the next section. This is gravitational separation.
In the coalescing plate chamber, water flows through a network of inclined corrugated or parallel plates. Suspended oil micro-droplets adhere to the plate surfaces, merge into larger droplets, then rise to the surface to join the retained oil slick. This process captures emulsified oils that gravity alone could not separate.
Treated water flows under a baffle before reaching the outlet drain, physically preventing accumulated oil from escaping into the municipal sewer system. A properly sized interceptor achieves outlet oil concentrations below 15 mg/L at peak design flow.
When is an oil interceptor mandatory in Canada?
The 2020 NPC, in Article 7.4.4.1, requires the installation of an oil interceptor when wastewater likely to contain oils, greases, or petroleum products is discharged into a drainage system. This obligation applies regardless of the province, as most provinces have adopted the NPC or incorporated equivalent provisions into their own plumbing codes (NRC, 2020).
Types of facilities covered include:
- Automotive repair shops and garages - drain bays, parts washing areas, lift pits
- Car washes - all types, whether they recycle water or not
- Gas stations - fueling areas, concrete surfaces under pumps
- Indoor parking lots - floor drains receiving vehicle runoff
- Fleet depots and maintenance yards - maintenance areas, truck washing, refueling
- Car dealerships - vehicle preparation area, service shop
- Airports and aircraft hangars - aircraft fueling and maintenance areas
The obligation is triggered as soon as the drain receives water from an area where hydrocarbons are handled, stored, or likely to spill. The absence of visible oil in the water does not exempt the installation.
What regulatory framework applies in Quebec?
In Quebec, three levels of regulation apply simultaneously. Knowing them avoids surprises during an inspection.
The 2020 NPC (Art. 7.4.4.1) sets the obligation to install an interceptor and defines minimum design parameters. This is the regulatory floor.
Municipal bylaws define discharge limits into the sanitary sewer. The most common limit in Canada is 15 mg/L of total hydrocarbons and greases (H&G), but some municipalities apply stricter thresholds. Always check your municipality's bylaw before sizing a system.
The Regulation respecting municipal wastewater treatment works (ROMAEU), adopted under Quebec's Environment Quality Act, requires municipalities to control industrial discharges to protect their treatment plants. A non-compliant oil interceptor can result in a municipal notice of default sent directly to your facility.
Canada's Fisheries Act serves as the federal safety net. Section 36(3) prohibits the discharge of any deleterious substance into waters frequented by fish – which includes sewer systems that ultimately discharge into a watercourse. Penalties can reach $6 million per offense for repeat offenders (Environment and Climate Change Canada, 2023).
Oil interceptor vs oil-water separator: what's the difference?
In practice, these two terms refer to the same type of equipment. The distinction is terminological, not technical.
The term "oil interceptor" is the term used in the National Plumbing Code and in most Canadian municipal bylaws. It is the regulatory vocabulary and the one plumbers and inspectors use in the context of building permits.
The term "oil-water separator" is more common in industrial and environmental contexts - runoff water treatment, site decontamination, downstream treatment systems. It is also the term used by engineers and environmental consultants in their specifications.
Both products operate on the same principles of gravitational separation and coalescence. The confusion arises from the fact that the two product categories overlap in some ranges, particularly for compact coalescing plate units intended for light commercial facilities.
Grease interceptor vs oil interceptor: do not confuse
This is a common and costly specification error. The two devices are distinct, designed for different contaminants.
A grease interceptor treats wastewater from commercial kitchens - cooking oils, animal fats, washing residues. These substances have different physical properties from petroleum hydrocarbons: they solidify at low temperatures and require a specific cleaning method.
An oil interceptor treats petroleum hydrocarbons from vehicles and motorized equipment - engine oil, diesel fuel, hydraulic oil, brake fluids. These compounds are soluble in solvents and do not have the same solidification properties.
Installing a grease interceptor where the code requires an oil interceptor does not meet regulatory requirements. Ensure that the specification matches the actual contaminant present in your facility's wastewater.
How to size an oil interceptor for your facility?
Sizing is based on the peak flow rate in liters per minute (L/min) entering the drain, calculated according to the drainage area, the type of activity, and the frequency of washing. The 2020 NPC and ASME A112.14.3 / CSA B481 standards govern the calculation method.
The following table indicates the recommended OlioSep™ models based on typical facility type:
| Facility Type | Typical Peak Flow | Recommended OlioSep™ Model |
|---|---|---|
| 1-2 service bays, no active washing | 0.5–2 GPM | OlioSep™ 0.5 or 2 GPM |
| 2-3 bays, light workshop | 2–4 GPM | OlioSep™ 2 or 4 GPM |
| 3-4 bays, garage with cold water wash | 6–8 GPM | OlioSep™ 8 GPM |
| 5-6 bays, active garage with washing | 10–16 GPM | OlioSep™ 16 GPM |
| Large fleet workshop / 6+ bays | 20–30 GPM | OlioSep™ 24 or 30 GPM |
| Commercial car wash (2 lanes) | 30–50 GPM | OlioSep™ 50 GPM |
These values are indicative. Final sizing must be performed by a licensed plumber or engineer, taking into account the actual drain configuration, working pressure, and local municipal requirements.
For facilities where flow is difficult to assess, ERE offers a sizing analysis upon request. Tell us the type of facility, the number of bays, and your washing activity.
What are the maintenance requirements?
An unmaintained oil interceptor quickly loses its effectiveness. When the retention chamber is saturated, accumulated oil begins to circulate back into the sewer - a situation called "bypass" - which nullifies any regulatory benefit and exposes the operator to prosecution.
The minimum recommended maintenance program includes:
- Monthly visual inspection - check oil slick level, absence of obstructions, condition of cover and ventilation.
- Quarterly or semi-annual draining - depending on activity volume. A high-flow facility (high-frequency car wash) may require monthly draining.
- Annual inspection of coalescing plates - clean or replace coalescing media according to manufacturer's recommendations. Fouled plates reduce separation efficiency.
- Maintenance log keeping - several municipalities require a dated log of drainages and inspections, signed by the operator or service provider.
Sludge and oils removed from the interceptor are hazardous waste. Their disposal must be entrusted to an authorized collector according to applicable provincial regulations.
What are the risks of not having a compliant oil interceptor?
The consequences of non-compliance are concrete and progressive.
A municipal inspection can trigger a compliance order with a deadline - usually 30 to 90 days. If the facility does not comply, municipal fines vary by jurisdiction but commonly reach several thousand dollars per day of infraction (City of Montreal, By-law 2008-47).
Proven contamination reaching a watercourse can trigger the application of the Fisheries Act. Penalties for corporations reach $6 million for a first serious offense. Criminal charges are possible.
Beyond legal risk, an oil spill into the sewer engages the operator's civil liability towards the municipality for cleanup costs and damage to treatment infrastructure.
Frequently Asked Questions
Is an oil interceptor the same as a grease interceptor?
No. They are two distinct pieces of equipment designed for different contaminants. A grease interceptor treats food oils and animal fats from commercial kitchens. An oil interceptor treats petroleum hydrocarbons from workshops and garages. Substituting one for the other does not meet the requirements of the 2020 NPC. Always check the specification according to the type of facility and the contaminant present.
Can I install an oil interceptor myself?
In Quebec, the connection of an interceptor to the plumbing system must be carried out by a plumber holding a certificate of qualification issued by the Régie du bâtiment du Québec (RBQ). The work must be subject to a plumbing permit and an inspection by the municipality. Unauthorized installation exposes the owner to fines and invalidates certain insurance coverages.
How do I know what size oil interceptor to choose?
Sizing is based on the peak flow rate in liters per minute, calculated according to the drainage area, the type of activity, and the frequency of washing. ASME A112.14.3 and CSA B481 standards provide the calculation method. For simple installations (1 to 3 bays), ERE can help you evaluate the correct OlioSep™ model based on some basic information. Contact us before ordering.
Does my current interceptor meet the requirements of the 2020 NPC?
An interceptor compliant with the 2020 NPC must be sized for the facility's peak flow, equipped with certified coalescing plates, and maintained according to a documented program. If your unit is more than 15 years old or has never been inspected by a professional, a conformity assessment is necessary, especially if your municipality has updated its discharge regulations since the original installation.
How much does an oil interceptor cost in Canada?
The cost varies depending on capacity and configuration. Compact units for 1 to 2 service bays start at around $1,500 to $3,000 CAD, supply only. Medium-capacity systems for car washes or garages with 6 to 10 bays generally range from $5,000 to $15,000 CAD. Custom systems for large fleet depots or parking lots are priced upon request based on flow rates and installation constraints. These amounts exclude plumbing labor and permits.
Ready to specify an oil interceptor for your facility?
Tell us the type of facility (service bays, car wash, parking), your province, and your washing activity. We will recommend the correct OlioSep™ model and confirm that it meets your municipal requirements.
→ Request a Quote | 1-888-287-EREC | Browse OlioSep™ Interceptors | sales@ereinc.com
Read this article in English: Oil Interceptors: How They Work and When You Need One
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