How to Size and Install a Grease Trap That Meets Metro Atlanta Standards
Selecting, sizing, and installing a grease trap (more accurately termed a grease interceptor) that meets Metro Atlanta county standards is a critical and highly regulated requirement for all food service establishments (FSEs). The primary objective is to prevent Fats, Oils, and Grease (FOG) from entering the public sanitary sewer system, where they can cause massive blockages and costly system failures.
In jurisdictions like the City of Atlanta, Fulton County, Gwinnett County, and others, the process is governed by the local Department of Watershed Management and the plumbing codes. For any high-volume kitchen, the requirement typically mandates large, exterior, in-ground gravity interceptors (GGIs). Non-compliance results in denial of the Food Service Permit, costly demolition, or fines.
Determining the Required Size and Type
The size and type of grease interceptor required are determined by the local regulatory authority based on the establishment's complexity and wastewater output.
Local Minimum Capacity Mandates
Most counties bypass complex formulas by setting a high minimum capacity based on the type of establishment and its potential FOG discharge.
Gravity Grease Interceptors (GGIs): These are large, exterior, multi-compartment tanks required for high-volume FSEs, especially those with dishwashers and high-temperature wastewater.
Fulton County/City of Atlanta Example: Requires a minimum 1,000-gallon capacity for FSEs. Final sizing is based on seating and cuisine complexity, often requiring 1,500-gallon units or larger for full-service restaurants.
Gwinnett County Example: Often requires a stricter minimum 1,500-gallon exterior interceptor. For capacities exceeding that, Gwinnett typically mandates the use of multiples of 1,500-gallon tanks installed in series (connected end-to-end).
Hydromechanical Grease Interceptors (HGIs): Small, indoor units may only be approved for low-volume or limited-menu facilities (e.g., small coffee shops, pre-packaged food vendors) where the wastewater temperature is low and no dishwashers are used. Approval for an HGI must be granted specifically by the local plumbing official.
The Sizing Formula (Load Calculation)
For establishments not easily classified or when the county requires a precise calculation, sizing is typically based on the seating capacity and operational hours using a standardized formula that determines the required retention time.
The most common method calculates the total wastewater volume and then the required capacity in gallons. If this calculated volume exceeds the capacity of a single tank, multiple units are required to be installed in series.
Mandatory Installation and Plumbing Standards
Grease interceptor installation is strictly governed by the Georgia State Minimum Standard Plumbing Code and local municipal ordinances, particularly concerning site work and pipe routing.
Placement and Flow Segregation
The location and connections of the interceptor are non-negotiable and must be detailed in the plumbing diagrams submitted for the Food Service Plan Review.
Exterior Placement: For GGIs, the unit must be located in an area easily accessible for routine pump-out and inspection, typically near the wastewater discharge point (often a maximum of 50 feet away from the kitchen line in some local codes). Access manholes must be brought up to finished grade and clearly labeled.
Flow Segregation (No Sewage): Only FOG-bearing wastewater (from prep sinks, warewashing sinks, dishwashers, floor drains in food prep areas, and mop sinks) is permitted to flow through the interceptor. Absolutely no sewage, toilet waste, or storm drainage can be routed to the unit.
Installation Inspection: The unit must be installed level, typically on a stable crushed stone or concrete pad base. The installation must be inspected by the county's commercial pretreatment or plumbing division prior to backfilling to verify proper pipe connections, sizing, and depth.
The Effluent Test Manhole
Local codes, particularly in major Metro Atlanta jurisdictions, require a sampling point to monitor the interceptor's performance.
Requirement: A specific sampling manhole (or test manhole) must be installed downstream of the interceptor (typically no more than 6 feet away).
Purpose: This manhole allows municipal inspectors to sample the effluent (the wastewater leaving the interceptor) to ensure the FOG concentration does not exceed the maximum allowable limit (often 100 mg/L).
Post-Installation Compliance and Maintenance
Local oversight of FSEs does not end with installation. The county's requirements for permitting and maintenance are ongoing, designed to ensure the sewer system remains protected.
Required Permitting and Records
Commercial Waste Discharge Permit: Most jurisdictions require the FSE to obtain a specific Commercial Waste Discharge Permit from the local Department of Watershed Management (DWM) or similar county authority and pay an annual fee. This permit dictates the FOG limits and maintenance protocols.
Maintenance Mandate (The 25% Rule): Interceptors must be serviced and pumped out frequently enough to ensure that the volume of accumulated FOG and settled solids does not exceed 25% of the interceptor's operating depth. For example, Fulton County mandates a total pump-out at least every 90 days for smaller traps.
Pumping Records: FSEs are required to maintain detailed, written service records (manifests) of all grease trap cleaning and pumping services for a minimum of three years. These records must be readily available for inspection by county officials during facility check-ups.
Consequences of Maintenance Failure
Failure to properly maintain the grease interceptor, resulting in FOG exceeding the 25% limit or causing a sewer blockage, triggers severe consequences:
Fines and Surcharges: The county can impose substantial fines and maintenance surcharges to recover the cost of clearing blockages caused by the non-compliant FSE.
Mandatory Increase in Pumping Frequency: The local authority may mandate a highly frequent pumping schedule (e.g., weekly or bi-weekly) until compliance is verified, drastically increasing operating costs.
By designing the system to the local code's most stringent requirements and adhering to strict maintenance schedules, FSEs can avoid costly violations and ensure a smooth path to obtaining and maintaining their operating permits.
At Radovic Permits, our residential building permit consultant Atlanta experts guide clients through the specific engineering and installation requirements of each county to ensure flawless compliance.