What does Surprise require for a grease interceptor under its 2024 plumbing code?

Surprise changed three pieces of the plumbing code that touch grease.

The gravity interceptor definition. The model code calls a gravity grease interceptor a unit of not less than 500 gallons where separation happens "during a retention time of not less than 30 minutes." Surprise struck "of not less than 30 minutes" and wrote in "approved by the City of Surprise." The 500 gallon floor in the definition stays. The retention time is now whatever the City approves.

The automatic grease removal device. The model definition of a GRD, a unit that skims grease on a timer or an event without anyone touching it, stays as written. Surprise added one sentence: "These devices must perform as a gravity interceptor if mechanical or electrical power is lost and provide continuous separation." A GRD that stops separating when its motor or heater loses power does not meet the definition in Surprise.

Section 1003.2, Approval. The model code says each interceptor's size, type and location follow the manufacturer's instructions and "the requirements of this section based on the anticipated conditions of use." Surprise struck that phrase and replaced it with "the requirements of the City of Surprise." The code's own sizing rules no longer decide on their own; the City's requirements do.

• Gravity grease interceptor: a large tank, usually buried outside, where grease floats and solids settle while wastewater sits in it.
• Hydromechanical grease interceptor (HGI): a smaller unit that uses baffles and air to separate grease as water flows through. Kitchens often call it a grease trap.
• GRD (automatic grease removal device): a unit that removes the grease it collects on its own, on a schedule or when it senses grease. Our GRD page explains how they work.
• Retention time: how long wastewater stays in the tank. Longer retention gives grease more time to rise.

Food businesses in Surprise that put in, replace or move a grease interceptor, trap or GRD: restaurants of every kind, fast food, pizza delivery, sandwich shops and bakeries, which the City's page lists as needing an interceptor. It also reaches the landlords and property managers whose buildings serve them. Homes are not covered. Service stations, car washes, salons, pet groomers and laundries have their own oil, sand, lint and hair interceptor rules on the same City page.

Because the code points to the City's requirements, the Commercial Pretreatment page is where the numbers live. It says grease interceptors in Surprise shall be:

• installed outside;
• accessible for cleaning and inspections;
• a minimum of 750 gallons and a maximum of 2,500 gallons;
• installed and maintained per the manufacturer's specifications;
• fitted with traffic rated covers.

Its guidance section adds three more rules: 750 gallons or larger for a three compartment interceptor, no more than two restaurants on one interceptor (with under sink trap units installed), and two smaller interceptors once the size passes 2,500 gallons. The City gives its reason: large interceptors let odor and gases build up in the sewer, where crews lifting manhole covers downstream are exposed.

For a hydromechanical unit, the page says the City accepts the sizing and selection method developed by IW Consulting Service, LLC. The full fixture unit formula and the City's 828 to 1,050 gallon example are on our sizing worksheet page.

One thing to settle early: the same page lists a 750 gallon minimum in its rules but says "minimum 500 gallons" in its rounding step. Ask the plan reviewer which applies before you order a tank.

• A taco shop moving into a former retail suite. The plans show a three compartment sink, a mop sink, two floor sinks and four floor drains. That is the City's own example: the formula lands at 828 gallons, the City rounds it up to a 1,050 gallon tank, and the tank goes outside where it can be pumped and inspected.
• A drive-through coffee shop. No fryer and no Type I hood, so it is on the City's list of shops that may use a trap. An Arizona professional engineer seals the calculation, and the trap goes on the plans.
• A kitchen that wants a GRD to save space. The model chosen has to keep separating grease during a power outage. If the maker cannot show that, the unit does not fit Surprise's definition.

1. 1Count every grease-bearing fixture: three compartment sinks, pre-rinse sinks, mop and floor sinks, dishwasher floor drains and floor drains that can carry grease. Leave hand sinks, ice machines and restroom fixtures off the grease line.
2. 2Run the City's formula and round up to a size the manufacturer makes, between the City's minimum and 2,500 gallons.
3. 3Plan the tank outdoors where a pump truck can reach it, with traffic rated lids if it sits in a drive or parking area.
4. 4For a GRD or HGI, get the maker's data showing how it meets Surprise's definition or the IW Consulting sizing method.
5. 5Submit the plumbing plans through the City's permit process before any work starts.

• "The code says 30 minutes, so that is the design." Surprise removed that number. The City approves the retention time.
• "500 gallons is the floor everywhere." Surprise's pretreatment rules list 750 gallons.
• "One big tank is better than two." Over 2,500 gallons, Surprise wants two smaller interceptors.

A grease interceptor touches the kitchen drains, the building sewer and the City's plan review at once. A plumber who works on commercial kitchens counts the fixtures the way the City does, sizes the tank, routes the lines so restroom waste and hot liquids stay out of it, and draws the work so it can pass plan review. HQ Plumbing & Air services grease traps and interceptors of all sizes. After the pumper empties a unit, our three-person crew enters it under OSHA confined-space rules to replace broken baffles, then hydro jets and camera inspects the lines in and out. See our grease trap service, commercial plumbing and Surprise plumbing pages.