Does the regulation really apply to my workshop?
Yes, without exception. In Quebec, the Règlement sur les ouvrages municipaux d'assainissement des eaux usées (ROMAEU, Q-2, r. 34.1) sets the discharge limit at 15 mg/L of total oils and greases for any industrial effluent connected to the municipal network (Government of Quebec, MELCCFP, 2023). This limit applies to body shops, dealerships, quick service centers, and fleet garages.
At the federal level, section 36(3) of the Fisheries Act prohibits the deposit of any deleterious substance into waters frequented by fish. Hydrocarbons are explicitly included in this definition. Fines for a first offense range from $15,000 to $6,000,000 per contravention (Fisheries Act, R.S.C. 1985, c. F-14, s. 40).
The National Plumbing Code 2020 (NPC 2020)
Article 7.4.4.1 of the NPC 2020 requires the installation of an oil interceptor on any floor drain, wash bay, or service area likely to receive water containing mineral oils. This requirement applies to:
- Any service bay with a floor drain
- Vehicle washing areas (even with cold water)
- Oil change pits
- Degreasing tanks
The interceptor must be sized according to the expected peak flow and must be accessible for maintenance. The NPC 2020 has been adopted by Quebec, Ontario, and most Canadian provinces, making it the basic reference for all new construction.
Ontario: Regulation 347 and the ECA
In Ontario, Regulation 347 (waste) of the Environmental Protection Act and standard Environmental Compliance Approval (ECA) conditions impose similar requirements. Ontario workshops must be able to demonstrate, upon request from an MECP inspector, that their effluents comply with the limits set in their operating approval. A certified and maintained oil-water separator is the simplest documentary evidence to present.
[CITATION CAPSULE] In Quebec, the ROMAEU sets the maximum concentration of total oils and greases in industrial effluents at 15 mg/L. A mechanical workshop without a functional oil interceptor may receive a notice of non-compliance from the municipality, followed by a closure order if the situation is not corrected within the prescribed deadlines. (MELCCFP, ROMAEU Q-2 r. 34.1, 2023)
How to size your oil-water separator in 4 steps
Sizing an oil interceptor is not a matter of rough estimation. An undersized device does not protect the network and does not legally protect you. Here is the four-step method used by engineers for automotive workshops.
Step 1: Calculate the peak flow (GPM)
Peak flow corresponds to the maximum wastewater flow that your workshop can generate simultaneously. Add up the flows from each active source at the same time:
| Water Source | Typical Flow |
|---|---|
| Cold pressure washer (commercial) | 2.5 - 4 GPM |
| Hot pressure washer (steam) | 4 - 6 GPM |
| Rinse hose (3/4 in) | 5 - 8 GPM |
| Parts washing tank (gravity) | 1 - 2 GPM |
| Bay floor drain (rain/rinse) | 1 - 2 GPM |
In our experience with Quebec workshops, most owners underestimate their peak flow by forgetting to include passive floor drains that collect runoff during rainy days, especially in garages with open doors to the outside.
Step 2: Apply the safety factor (x 1.25)
Multiply the calculated peak flow by 1.25. This factor accounts for pressure variations, equipment wear, and unforeseen peaks. This is the standard recommended by the Plumbing Engineering Design Handbook (American Society of Plumbing Engineers, 2017).
Formula: Design Flow = Peak Flow × 1.25
Step 3: Evaluate the risk of emulsification
Hot water, soaps, and chemical degreasers create oil-water emulsions that standard gravity separators struggle to treat. If your workshop uses:
- Hot water (above 40 °C)
- Solvent-based degreasers
- Engine maintenance products containing surfactants
In this case, you will need to choose a model with an integrated coalescer or combine the separator with downstream treatment. For a workshop using exclusively cold water and biodegradable soaps with low surfactant content, a standard gravity separator is sufficient in most cases.
Step 4: Check the oil storage volume
The separator must be able to store accumulated hydrocarbons between two drainages. The typical maintenance frequency is quarterly. Estimate the volume of oil retained per week according to your activity and multiply by 13 weeks. This value must be less than the retention capacity of the chosen device.
Concrete example: 4-bay workshop in Laval, Quebec
Here's how to apply this method for a general mechanics workshop located in Laval, connected to the municipal sewer system.
Configuration:
- Bays 1 and 2: cold high-pressure washing, 3 GPM each
- Bays 3 and 4: mechanical service (oil changes, brakes, suspension) with passive floor drains, 1 GPM each
Calculation:
| Step | Calculation | Result |
|---|---|---|
| Step 1 - Peak Flow | (3 + 3 + 1 + 1) GPM | 8 GPM |
| Step 2 - Safety Factor | 8 × 1.25 | 10 GPM |
| Step 3 - Emulsification | Cold water, biodegradable soap | Low risk - standard gravity |
| Step 4 - Storage | ~2 L/week × 13 weeks | ~26 L minimum capacity |
Selection: OlioSep™ 8 GPM (surface or recessed model depending on floor configuration). This model offers a nominal flow of 8 GPM with sufficient oil retention capacity for quarterly maintenance in this type of workshop.
Note that the calculated design flow (10 GPM) slightly exceeds the OlioSep™ 8 GPM model. In this specific case, the mechanical service bays generate a very low passive flow and never operate simultaneously with the wash bays at full load. The 8 GPM model is therefore appropriate, provided this operating scenario is confirmed with your plumbing engineer or municipal inspector.
OlioSep™ selection table by workshop type
| Workshop Type | Number of Bays | Main Activity | Recommended OlioSep™ Model |
|---|---|---|---|
| Residential / DIY Garage | 1-2 | Oil change, light maintenance | 4 GPM - Surface |
| Light Mechanical Workshop | 2-3 | General service, no washing | 6 GPM - Surface or recessed |
| Full Mechanical Workshop | 3-5 | Service + cold water washing | 8 GPM - Recessed |
| Quick Service Center | 4-6 | High-pressure washing, oil changes | 12 GPM - Recessed |
| Body Shop | 3-6 | Priming, degreasing, rinsing | 12-20 GPM + coalescer |
| Fleet Garage (trucks) | 6-10+ | Heavy washing, oil changes | 20 GPM+ - Underground |
| Automobile Dealership | 8-15+ | Multi-activities | On quote - Underground |
OlioSep™ models are available in surface-mounted, recessed (flush mount), underground, and portable versions for sites without permanent infrastructure. Browse the complete collection.
What are the risks of not having an oil-water separator?
The consequences of non-compliance are graduated, but they escalate quickly. The municipality has inspection powers and can conduct effluent sampling without notice in most Quebec jurisdictions.
Level 1 - Notice of non-compliance: Imposed correction period (generally 30 to 90 days). No immediate fine, but the deadline is binding if you need to order and have equipment installed.
Level 2 - Municipal fine: Fines vary according to local regulations. In Montreal, the Règlement sur l'assainissement des eaux provides for fines between $1,000 and $50,000 per offense for legal entities, with fines doubled in case of recidivism.
Level 3 - Fisheries Act: If contaminated effluent reaches a watercourse, federal criminal liability is activated. The Fisheries Act provides for fines of $15,000 to $6,000,000 and up to 3 years imprisonment for company executives found guilty. These sanctions apply even if the discharge was unintentional.
Level 4 - Closure order: In case of persistent non-compliance or serious spillage, the municipality may order the closure of the workshop until compliance is achieved.
[CITATION CAPSULE] Section 36(3) of the Fisheries Act (R.S.C. 1985, c. F-14) prohibits the deposit of any deleterious substance into waters where fish live or into any other place if the deposit may reach those waters. Petroleum hydrocarbons are explicitly recognized as deleterious substances. A first conviction can result in a fine of up to $6,000,000 for a legal entity. (Environment and Climate Change Canada, 2022)
Frequently asked questions about oil separators for workshops
Is an automotive workshop required to have an oil-water separator?
Yes. NPC 2020 (article 7.4.4.1) requires an oil interceptor on any drain likely to receive hydrocarbon-contaminated water. In Quebec, the ROMAEU sets the effluent limit at 15 mg/L of oils and greases. Without a functional separator, no workshop with floor drains can legally discharge its wastewater into the municipal network. (NPC 2020, NRC; ROMAEU Q-2 r. 34.1, 2023)
What size separator is needed for a 3-bay workshop?
It depends on the activity. Three mechanical service bays without high-pressure washing generally require a 6 GPM model. If one bay is equipped with a cold high-pressure washer (3 GPM), add this flow and apply the 1.25 factor: the 8 GPM model is then appropriate. With hot water or degreasers, opt for a model with a coalescer. (ASPE Plumbing Engineering Design Handbook, 2017)
Can I install an oil-water separator myself?
The installation of a plumbing interceptor must be carried out by a master plumber holding a license from the Régie du bâtiment du Québec (RBQ) or the equivalent body in your province. OlioSep™ portable models do not require permanent connection and can be installed without a plumbing permit, but they do not replace a fixed interceptor compliant with the NPC for permanent installations.
Is my current interceptor compliant with NPC 2020 standards?
Not necessarily. NPC 2020 introduced stricter flow and accessibility requirements than previous editions. If your separator is more than 10 years old, if you have added bays or equipment since its installation, or if it has not been regularly maintained (sludge and oil drainage), it may no longer be compliant. Have the device inspected by a qualified plumber or supplier before your next municipal audit.
How often should an oil-water separator be maintained in a workshop?
The maintenance frequency depends on the volume of oil treated. For a general mechanics workshop with 3 to 5 bays, quarterly cleaning is the norm. Some municipalities require keeping a maintenance log demonstrating drainages carried out by an authorized carrier. Plan maintenance with your oily waste management supplier as soon as it is installed.
Need a separator for your workshop?
Tell us the number of service bays, the type of work, and your province. We will recommend the right OlioSep™ model to comply with the municipal code and facilitate your compliance.
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Read this article in English: Oil Water Separator for Auto Shops: Requirements & Sizing
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- Oil interceptor: operation and regulation