Inspections, Permits & Work Requests

In the City of Monona, any person who is required by the department to install a grease interceptor, oil interceptor or sand interceptor shall, at all times, maintain the interceptor in proper working order. The interceptor shall be readily accessible for cleaning and inspection at all times. Additionally, No interceptor, catch basin or similar device shall contain greater than 25% combined grease, oil or solids at any one time based on industry standards. The owner of a grease interceptor shall keep a log describing the cleaning and repairs performed on the grease interceptor and the dates of such activity. The log shall be kept on site for 3 years.

Each year City of Monona Public Works staff play a pivotal role in inspecting grease traps and preventing blockages and sanitary sewer overflows.                                                       

Sanitary Sewer Overflow (SSO)

An SSO is a release of raw sewage from a sanitary collection system prior to treatment. These releases spill out of manholes, into homes, business property or waters of the state. What causes SSO? Inadequate flow capacity, power failures, excess inflow and infiltration, and blockages. The largest contributor of SSO is blockages. Why are SSOs prohibited? To protect public health, prevent property damages, protect resource damage and protect waters of the state. 

Grease Traps - Basic Operation 

Most grease traps are "passive" which means they operate without any moving or mechanical devises. The grease traps or interceptors work by separation the grease from the water. Greasy wastewater entering the interceptor passes through a vented flow control that regulates the flow of the wastewater. The wastewater passes over a series of baffles separating the grease and oil from the water by slowing the flow to allow enough detention time for separation.

Frequency of Maintenance

Interior grease traps should be evaluated for cleaning needs on a weekly basis. Depending on the size and volume it may need to be cleaned more or less. If heavy grease is accumulating in the outlet baffle of the trap it needs to be cleaned more often. Proper and frequency of maintenance is the only sure way to know if your trap is operating properly.

Dip accumulated grease out from the top and place it in a watertight container such as a plastic bag. Bail out any water and place it in a watertight container. Scrape the sides, baffles, and lid and place in watertight container and place in the garbage. Smaller interior traps can be cleaned by using a shop vac. A 100% of the contents must be removed and may not be introduced into the trap or any drains. DO NOT FLUSH WITH HOT WATER OR USE DRAIN CLEANERS, ENZYMES OR BACTERIA AGENTS. This just removes the problem into the sanitary sewer and is a violation of the Wisconsin Plumbing Code SPS 382.34(5)(e).

DO Not Discharge Hot into the Grease Interceptor

Using hot water, 120 degrees F or higher to rinse the dishes or if a dishwasher is connected, keeps the grease in suspension and does not allow for separation. If the trap does not have sufficient capacity to allow for cooling grease will again be discharged into the sewer. Many treatment facilities requiring cooling jets that are activated to cool the water as it enters the interceptor. Even if the grease amount isn’t a lot as it cools it accumulates on the interceptor pipe walls and causes a plug. Hot grease cools quickly in a sanitary sewer.

Best Management Practices 

1. Train kitchen staff and other employees about proper maintenance of your grease trap. 

2. Post “No Grease Down the Drain” signs above sinks and on the front of dishwashers.

3. “Dry wipe” pots, pans, and dishware prior to dishwashing.

4. Dispose of food waste by recycling and/or solid waste removal.

5. Recycle waste cooking oil.

6. Do not pour grease down the sinks or into the toilet. Remember that only the  four P's (Pee, Puke, Poop, and Toilet Paper) down the drain!

7. Avoid or limit the use of garbage disposals.

8. Use a 3-sink compartment dishwashing system, including sinks for washing, rinsing and sanitizing.

9. Use strainers in sinks to catch food scraps and other solids.

10. Keep up with maintenance log on grease interceptor/trap maintenance.

Sizing

It is extremely difficult to formulate an exact criteria for sizing grease interceptors because of so many variables that exist. Size is often evaluated on the following criteria:

• Type of restaurant (drive through, walk in)
• Type of food being served (fried, baked, broiled)
• Seating capacity or quantity of flow
• Retention time required for efficient separation of water and grease
• Frequency and type of maintenance

The general rule the City uses to determine capacity is that the grease holding capacity in pounds shall not be less than double the value of the maximum flow rate which the interceptor can accommodate. For exterior interceptors the minimum liquid capacity is 750 gallons by plumbing code. However, it is best to install exterior interceptors of no less than 1,500 gallons. Most traps are not sized to allow enough detention time for the water and grease to separate. Therefore, grease is being discharged into the sewer with the water.

1.  Flow Check and Capacity

Check the manufacturer’s specifications. Clean the interceptor. Fill to normal level with water. Place food coloring in the interceptor. Fill sinks with some measurement of water such as using 5-gallon pails. Place about 30-40 gallons of water in the sink. Allow the water in the sink to drain into the interceptor. As the water is entering the interceptor check the amount of color left in the trap. Also note if the flow enters the trap evenly. You may use food coloring or dye tablets to check which if any appliance are connected to the unit.

Why Following the Plumbing Code May Not be Good Enough

The Wisconsin Plumbing Code Comm 82 requires that all nonresidential establishments who prepare food must have a grease interceptor. Comm 82 also provide guidelines for choosing an appropriate grease interceptor for installation. HOWEVER, following the plumbing code will not assure that you will not violate prohibited discharges standards under the sewer use ordinance. The SUO may be more restrictive than the plumbing code when it comes to installing pretreatment equipment. Pretreatment equipment is any piece or pieces of equipment used to treat wastewater to meet pretreatment regulations.