A handy graph.
We’ve seen full grease traps, usually after they start to backflow into kitchens and parking lots. These grease traps and interceptors haven’t seen maintenance or pumping for months when we’re called in for an emergency consultation. Once we are done, we try and get these clients on a regular schedule, depending on how much FOGS (Fats, Oils, Grease, and Solids) they produce, their best practices, and what capacity they have. Read more about that in our blog, How Often Should My Grease Trap Be Cleaned? for some rules of thumb.
The 1/4th Rule of Thumb
Speaking of rules of thumb, the biggest is the “25% Rule” also known as the One-Quarter or 1/4th rule. This rule (which in many states and counties is an actual rule enforced by health inspectors) states that the total depth of the “brown grease” layer in an inceptor – which is usually floating on the top and a combination of food matter, grease, and oil – including any solids that have settled to the bottom should not be more than one-quarter of the total depth of the inceptor.
The Possible Origins of the 25% Rule: Hawaii
While grease traps have been around for a long time (seeing a rise in popularity in WWII), the first instance found of the one-quarter rule appeared in Honolulu in the 1990s by the head of the Regulatory Control Branch Head or the Department of Environmental Services, James Baginski. All the Hawaiian Islands have slim margins when it comes to FOGS in wastewater, and James did multiple tests to see what the total volume of grease traps in those days could hold before FOGS started leaking out with the wastewater. 25 to 35 percent is what he found, and so he placed his recommendations for cleaning at the lower number.
Support from the PDI and Orange County, CA
The findings of Baginski seemed to provide a basis for other organizations to provide that number. In the Plumbing and Drainage Institute’s (PDI) 1998 paper, Guide to Grease Interceptors – Eliminating the Mystery, they also pointed to 25% as the point where grease traps needed maintenance to avoid a drop-off in performance. Studies like the 2003 Orange County FOG Control Study came to similar results from surveys for FOG control programs around the US, which many pointed to using the one-quarter rule. Learn more about this history in Ken Loucks’ excellent article, Where Did the 25% Rule Come From? from his blog.
To determine how much FOGS has built up in your system requires a special core sample mechanism for sludge and sediment sampling like a “Sludge Judge” and the know-how to use it. Combining that alongside your model, type of restaurant, and practices can help figure out how often your grease trap or interceptor needs to be serviced. Here at Food Grease Trappers, we provide free consultations to help you figure out the best maintenance cycle for your businesses and budget. Contact us if you have any questions, or to get started.
