Chicago Grease Trap Requirements

Grease trap requirements in Chicago apply to food service establishments, commercial kitchens, and any facility that discharges fats, oils, and grease (FOG) into the municipal sewer system. These requirements are enforced through a combination of Chicago municipal code, Illinois Environmental Protection Agency (IEPA) regulations, and inspection programs administered by the Chicago Department of Buildings and the Metropolitan Water Reclamation District of Greater Chicago (MWRD). Non-compliance carries direct consequences for sewer infrastructure and public health, making this one of the more closely regulated aspects of commercial plumbing in Chicago.

Definition and scope

A grease trap — also referred to as a grease interceptor — is a plumbing device designed to intercept and retain fats, oils, and grease before they enter the sanitary sewer system. Under Chicago's regulatory framework for plumbing, grease traps are classified by their installation context and flow capacity into two primary categories:

Passive grease traps (under-sink units): Small-volume devices typically rated between 20 and 50 gallons per minute (GPM), installed beneath a single fixture or a small cluster of fixtures. These are commonly found in smaller food service operations with limited cooking volume.
Gravity grease interceptors (in-ground units): Large-capacity systems, typically ranging from 500 to 2,000 gallons, installed underground outside the facility. These handle the aggregate FOG load from multiple fixtures in high-volume establishments such as institutional cafeterias, restaurant chains, and catering facilities.

Chicago Municipal Code Chapter 11-4 governs discharges into the sewer system and establishes prohibitions on grease disposal. The MWRD's Pretreatment Program, operating under authority delegated from the U.S. Environmental Protection Agency (EPA) under the Clean Water Act (33 U.S.C. § 1317), sets enforceable pretreatment standards for FOG discharge concentrations.

Scope coverage and limitations: This page addresses requirements applicable within the City of Chicago's municipal jurisdiction. Suburban Cook County municipalities, DuPage County, and other jurisdictions within the broader metro area operate under separate ordinances and are not covered here. Industrial facilities classified as Significant Industrial Users (SIUs) under EPA definitions are subject to additional federal pretreatment requirements beyond the scope of this page.

How it works

Grease interception functions on a principle of differential density. FOG is less dense than water and rises to the surface when wastewater is slowed in a baffled chamber. Solids settle to the bottom, and the clarified effluent exits through an outlet baffle into the sewer lateral.

The operational cycle for a properly sized and maintained gravity interceptor involves three zones:

Inlet zone: Wastewater from kitchen fixtures enters the interceptor and velocity is reduced by the inlet baffle.
Separation zone: FOG accumulates at the surface; settled solids form a sludge layer at the base.
Outlet zone: Clarified water exits below the grease accumulation layer, then flows to the sanitary sewer.

The Chicago Plumbing Code, which adopts and modifies provisions from the Illinois Plumbing Code (77 Ill. Adm. Code 890), specifies minimum retention times and flow ratings for interceptors based on fixture count and peak flow calculations. Sizing calculations typically use the fixture unit method described in ASPE (American Society of Plumbing Engineers) standards, with adjustments for Chicago's specific wastewater concentration limits set by the MWRD.

A grease trap loses effectiveness when the combined volume of accumulated grease and solids exceeds 25% of the total interceptor capacity — a threshold referenced in MWRD educational materials and consistent with guidance from the Water Environment Federation (WEF).

Common scenarios

Grease trap requirements apply across a predictable range of facility types in Chicago. The following breakdown reflects the installation contexts most commonly encountered by licensed plumbers and building inspectors:

Full-service restaurants: Required to install gravity interceptors if daily FOG discharge volume exceeds the capacity threshold for passive under-sink units. Pumping frequency is typically every 30 to 90 days depending on volume.
Fast food and quick service: In-ground interceptors are standard due to high-volume fryer use. Some facilities require automatic grease removal units (AGRUs) that mechanically skim collected grease on a programmed cycle.
Ghost kitchens and shared commissaries: Each tenant may be individually regulated, requiring sub-metering and separate interceptor assignment or proportional capacity allocation.
Hotels and institutional food service: Large interceptors are common; MWRD may require sampling manholes and flow measurement as part of the permit.
Bakeries and coffee shops: Passive under-sink traps may be acceptable depending on product mix; chocolate production and bulk butter operations often trigger interceptor requirements regardless of facility size.
Food trucks with commissary hookups: The commissary facility is the point of FOG discharge regulation; the commissary must have adequate interceptor capacity to cover all users.

Permit documentation for new installations or interceptor replacements is processed through the Chicago Department of Buildings plumbing permitting process. Inspections may be conducted by DOB plumbing inspectors and, for facilities classified as industrial users, by MWRD compliance staff.

Decision boundaries

Determining whether a passive trap or a gravity interceptor is required — and what capacity applies — depends on a structured analysis rather than a single rule:

Facility type classification: Chicago Municipal Code and MWRD pretreatment standards distinguish between food service establishments, food processing facilities, and other commercial users. Classification determines the applicable pretreatment standard.
Fixture count and flow rate: The number of FOG-generating fixtures (fryers, pot sinks, floor drains in cooking areas, dishwashers) determines peak GPM load. A facility with a calculated peak flow exceeding 50 GPM will typically require an in-ground interceptor rather than a passive unit.
Available installation space: Passive traps are physically limited by under-sink dimensions. Where in-ground interceptors cannot be installed due to site constraints, an alternative compliance path may require approval from the MWRD and the DOB.
Discharge concentration compliance: MWRD Local Limit 7 governs FOG concentration in effluent. Facilities that cannot achieve compliance through passive trapping must install larger-capacity or mechanically assisted systems.
Maintenance and recordkeeping obligations: Permitted facilities are required to maintain service records — including pump-out manifests from licensed liquid waste haulers — for a minimum period specified in the MWRD permit. Failure to produce these records during inspection is treated as a compliance violation.
Change of use triggers: A building converted from retail to food service, or a kitchen expanding its cooking capacity, triggers a new grease trap sizing review. This intersects with broader Chicago plumbing code requirements for permit-triggering alterations.

The overall Chicago plumbing regulatory landscape situates grease trap requirements within a multi-agency framework where both DOB and MWRD have enforcement authority, and where federal Clean Water Act obligations flow down through the MWRD's delegated pretreatment program.

References

📜 2 regulatory citations referenced · 🔍 Monitored by ANA Regulatory Watch · View update log

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