Oil Water Separator for Truck Wash and Fleet Wash Facilities in Canada

Any commercial vehicle wash bay that generates wastewater containing petroleum — diesel engine residue, grease, and wash chemicals — must route that water through an oil/water separator before it reaches the municipal sewer. Canadian plumbing codes and provincial environmental regulations are consistent on this point: surface discharge of oily wash water without pretreatment is an offence under both the Fisheries Act and most municipal sewer-use bylaws. This guide covers the regulatory requirements, how to calculate the right separator size for a truck wash or fleet facility, and which OlioSep™ model fits each application.

Why Truck Wash and Fleet Wash Bays Require an Oil/Water Separator

Heavy trucks accumulate diesel fuel residue, engine oil, hydraulic fluid, and grease from brake components — all of it gets stripped off during a wash and ends up in the floor drain. Unlike a passenger vehicle wash where contamination is relatively light, a commercial truck wash produces wastewater with oil concentrations that can exceed 100–500 mg/L before treatment. Municipal sewer limits across Canada typically cap discharge at 15–20 mg/L hydrocarbons. Without an oil/water separator, your drain is in direct violation.

Three regulatory layers apply in most Canadian jurisdictions:

• National Plumbing Code of Canada (NPC): Section 7 requires grease and oil interceptors on drains that receive commercial vehicle wash wastewater. Most provincial plumbing codes adopt the NPC with minor amendments.
• Municipal sewer-use bylaws: Nearly every major Canadian municipality prohibits discharge of petroleum hydrocarbons above 15–20 mg/L to the sanitary sewer. Surcharge notices and fines are issued to facilities without pretreatment equipment in place.
• Federal Fisheries Act: If your facility discharges to storm drains that ultimately reach a water body, the federal prohibition on depositing deleterious substances applies — with penalties up to $6 million per offence for corporations.

“All commercial vehicle washing operations shall provide a grease/oil interceptor or separator before discharge to a sewer system.” — National Plumbing Code of Canada, Part 7 (Traps and Interceptors)

In Quebec, the Règlement sur les ouvrages municipaux d’assainissement des eaux usées (ROMAEU) sets the regulatory context for industrial discharge to municipal systems. Operators in Ontario must comply with municipal sewer-use bylaws setting 15 mg/L hydrocarbon limits. British Columbia and Alberta follow their respective provincial municipal wastewater regulations, which impose identical thresholds. The requirement is consistent across provinces: treat before you drain.

Understanding Truck Wash Wastewater

Truck wash wastewater is more demanding than a light-vehicle car wash for two reasons: the volume of petroleum contamination per vehicle and the volume of water used. Fleet wash operations often run pressure washing at 2–4 GPM per gun, with multiple guns operating simultaneously across bays. The cumulative peak flow rate determines the separator size.

What Contaminants Are Present

• Diesel engine residue: Unburned hydrocarbons, DPF soot, exhaust deposits on the engine and undercarriage
• Lubricating and hydraulic oils: Differential fluid, brake fluid, power steering fluid — particularly prevalent on older fleets
• Grease: Axle and chassis grease from bearing packs; slow to separate due to high viscosity
• Wash chemicals: Many truck wash detergents contain surfactants that partially emulsify oil — select low-emulsification soaps to improve separator performance

Surfactant and Emulsification Warning

The most common performance problem at truck wash facilities is using high-surfactant degreasers that emulsify oil into fine droplets suspended in the water column. Once emulsified, free-phase gravity separators cannot achieve compliant effluent. Where possible, use low-sudsing truck wash soaps and keep detergent dosing below the manufacturer’s recommended rate. If emulsification is unavoidable in your operation, contact ERE to discuss coalescing plate enhancement or dissolved air flotation (DAF) polishing options.

How to Size an Oil/Water Separator for a Truck Wash Bay

The National Plumbing Code sizing method for interceptors is based on peak instantaneous flow rate entering the separator — not average daily volume. The calculation has three inputs:

1. Number of pressure wash guns operating simultaneously — count all guns that could be running at once during peak wash activity
2. GPM per gun — check the pressure washer specification plate; typical commercial truck wash guns run at 2.5–4 GPM
3. Floor sluice flow — additional drain volume from manually rinsing the floor; typically 1–2 GPM per bay

Formula: Peak GPM = (guns active simultaneously × GPM per gun) + floor sluice flow

Select a separator rated at or above your calculated peak GPM. Do not size to average flow — a separator undersized for peak load will overflow hydraulically and pass oil-contaminated water. When in doubt, size up by one model.

Choosing the Right OlioSep™ Model for Your Wash Facility

The OlioSep™ surface-mount series was designed for applications like truck wash bays: high intermittent flow, heavy petroleum loading, and the need for straightforward pump-out access without confined-space entry. All OlioSep™ models are above-grade — no excavation, no concrete forming, no confined-space pump-out required. For the full range, see the oil/water separator collection.

OlioSep™ 8 GPM — Single-Bay Truck Wash

Ideal for single-bay facilities washing pickup trucks, vans, and light commercial vehicles with one pressure wash gun. Compact footprint fits against a wall in the drain room. The most common model for municipal fleet yards and small transport companies washing 5–15 vehicles per day.

OlioSep™ 16 GPM — Two-Bay or Three-Bay Fleet Wash

Most common choice for mid-size fleet operations: 2-bay facilities washing medium trucks (Classes 4–6), or 3-bay facilities where a maximum of 2 guns run simultaneously. Suitable for transit bus maintenance depots, municipal public works yards, and mid-size rental fleet operations.

OlioSep™ 24 GPM — Large Truck Wash

Covers 4–5 bay operations washing Class 7–8 semi-trucks with 3–4 pressure wash guns active simultaneously. Also suitable for highway transport company depots and large rental fleet operations.

OlioSep™ 50 GPM — High-Volume Fleet Depot

For large-scale truck wash facilities, bus terminals, or high-throughput operations with 6–10 vehicles washing simultaneously. Also appropriate for mining and construction sites where heavy equipment is regularly washed at a central facility.

Canadian Oil Discharge Standards for Truck Wash Wastewater

Most Canadian municipalities set a discharge limit of 15–20 mg/L total petroleum hydrocarbons (TPH) for commercial wastewater entering the sanitary sewer. The OlioSep™ series achieves effluent below 10 mg/L under design flow conditions with non-emulsified wash water — a comfortable compliance margin.

Key thresholds by jurisdiction:

• Quebec (ROMAEU and municipal bylaws): Typically 15 mg/L hydrocarbons to sanitary sewer; zero discharge to storm drains connecting to watercourses
• Ontario (municipal sewer-use bylaws): 15 mg/L in most Ontario municipalities; City of Toronto Sewer Use Bylaw (Chapter 681): 15 mg/L
• British Columbia (Municipal Wastewater Regulation): 15 mg/L combined hydrocarbons to sanitary sewer
• Alberta (EMA and municipal bylaws): 15 mg/L to sanitary sewer in most Alberta municipalities

Important: These limits apply to sanitary sewer discharge only. Discharge to storm sewers or surface water is prohibited entirely under federal and provincial law regardless of treatment level. If your wash bay drains to a storm system, contact ERE or your local environmental compliance office before proceeding.

How Often Does a Truck Wash Separator Need to Be Pumped Out?

An oil/water separator requires regular maintenance to function. Petroleum and solids accumulate in the chamber over time; when capacity is reached, the separator loses efficiency and passes contaminated water downstream. For truck wash applications the maintenance interval is shorter than for passenger car washes because of higher oil loading per vehicle.

Typical pump-out intervals for truck wash OWS:

• High-volume operations (20+ trucks/day): Monthly inspection; full pump-out every 3 months
• Medium operations (5–20 trucks/day): Quarterly inspection; pump-out every 3–6 months
• Light-duty (1–5 trucks/day): Bi-annual inspection; pump-out annually or when the floating oil layer exceeds 25% of chamber depth

Maintain a service log. Most municipal sewer authorities request maintenance records during inspections. For complete OWS maintenance procedures applicable to truck wash facilities, see: Oil Water Separator Maintenance: A Complete Guide for Facility Managers.

Frequently Asked Questions

Is an oil/water separator required by law for a truck wash in Canada?

Yes. The National Plumbing Code of Canada (Part 7) requires oil and grease interceptors on drains receiving commercial vehicle wash wastewater. Provincial plumbing codes adopt this requirement. Municipal sewer-use bylaws across Canada also prohibit discharging petroleum-contaminated water above 15–20 mg/L to the sanitary sewer, which is not achievable without pretreatment.

What GPM separator do I need for a single-bay truck wash?

A single-bay facility with one pressure wash gun running at 3–4 GPM needs a separator rated at a minimum 8 GPM to accommodate peak flow plus incidental floor sluicing. The OlioSep™ 8 GPM surface-mount unit is the standard choice for this configuration.

Can I use a standard oil interceptor instead of an OlioSep™ separator?

Traditional cast-iron oil interceptors (gravity-only, non-coalescing) are generally not adequate for heavy truck wash applications. They are typically undersized for the flow rates involved and do not consistently achieve effluent below 15 mg/L under high petroleum loading. Coalescing-plate separators like the OlioSep™ series provide significantly better separation efficiency at truck wash flow rates.

How does surfactant in truck wash soap affect separator performance?

High-surfactant degreasers emulsify petroleum into fine droplets that resist gravity separation. A properly sized coalescing-plate OWS can handle light surfactant loads, but heavy emulsification will reduce efficiency and may require a coagulant dosing system or DAF polishing unit. Selecting a low-emulsification truck wash soap is the most cost-effective mitigation measure.

Can an OlioSep™ handle both a truck wash bay drain and a vehicle fueling pad drain?

In most cases, yes — both sources contribute petroleum-contaminated water and can share a common separator if the combined peak flow rate stays within the unit’s rated capacity. Calculate the maximum simultaneous flow from both the wash bay and the fueling pad and size accordingly. Verify with ERE engineering if your fueling pad uses a large concrete containment berm, as storm event flows can exceed normal sizing assumptions.

Related articles

• Oil/Water Separators: The Complete Industrial Guide for Canada
• Oil Water Separator for Auto Shops: Requirements and Sizing
• Oil Water Separator Maintenance Guide
• Above-Ground vs Underground Oil/Water Separators

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