A sampling port is a tee, box or vault on a grease interceptor's outlet where an inspector can draw a sample of what's leaving. Peoria requires a sample vault on every outdoor interceptor. Phoenix, Mesa, Scottsdale, Glendale and Tempe require a sampling point or control manhole when the city calls for one.
What is a sampling port?
It's a fitting or small structure on the outlet line. Someone can reach the flowing wastewater there and fill a sample bottle. It can be a sample tee with a cap, a small box, a vault, or a full manhole.
Pima County's code describes it as "A sampling port/box/T, which will accommodate the collection of a valid oil and grease sample." Flagstaff's FOG manual gives a broader definition. It says sampling facilities are paid for by the user and let the city take a sample. They can also "provide access to plug/terminate the discharge." That last part matters. The same opening can let a city block a discharge that's out of compliance.
Oil and grease samples are taken as grab samples, not collected over hours. Phoenix's pretreatment code says "Samples for oil and grease, temperature, pH, cyanide, total phenols, sulfides, and volatile organic compounds must be obtained using grab collection techniques." Gilbert's code defines a grab sample as "an individual sample of effluent collected in less than 15 minutes." So the port has to let someone reach the flow directly and quickly.
Which Valley cities require one?
The codes we read split into two groups. Peoria writes a sample vault into its interceptor rules. The others require a sampling point or control manhole only when the city decides a property needs one.
| Jurisdiction | What the code requires | When |
|---|---|---|
| Peoria | Sample vault on external interceptors; control manholes for new source interceptors | Always |
| Phoenix | Compliance sampling point in the building sewer | When the Director requires it, for potentially harmful or industrial wastes |
| Mesa | Control manhole in the building sewer | When required, for industrial or manufacturing process wastewater |
| Scottsdale | Monitoring manhole or monitoring vault | When required, for industrial wastes |
| Glendale | Control manhole in the building sewer | When required, for potentially harmful or industrial wastes |
| Tempe | Control manhole or compliance sampling point | When the Public Works Director requires it, for industrial wastes |
| Pima County (Tucson area) | Sampling port, box or tee | On every pretreatment device |
Peoria. Peoria's interceptor code says "All external interceptors must include a sample vault," and they must be built to the city's standard detail drawing. Peoria's code also says "Control manholes shall be required for all New Source interceptors." If you're putting an outdoor interceptor in Peoria, plan the vault from the start. For Peoria's pump-out and records rules, see grease rules for Glendale, Peoria, Gilbert and Surprise.
Phoenix. Phoenix's pretreatment code applies "When required by the Director." It covers a building sewer that carries "potentially harmful or industrial wastes." In that case, the user must put a "suitable compliance sampling point" in the building sewer.
Mesa, Scottsdale, Glendale and Tempe. Their codes use nearly the same "when required" wording. Scottsdale's monitoring manhole rule covers a building sewer "discharging any industrial wastes or that has the potential to discharge industrial wastes." Scottsdale defines industrial waste broadly. It includes waste from a "trade, or business as distinguished from domestic wastewater." So a business's kitchen waste can fall under it.
### Does Phoenix sample restaurant grease interceptors?
Rarely, by its own account. In the list of rights an inspector reads to a business, the Phoenix FOG manual notes that "The Commercial Inspection Section rarely takes samples." Phoenix's grease inspections lean on the interceptor's condition and your pumping records instead. See what city inspectors check on a grease trap. A city can still require a sampling point on a specific site, especially after violations, so a FOG violation notice is worth reading closely for that kind of requirement.
What does the sample get tested for?
Mostly oil and grease, and sometimes pH. Nationally, the EPA found that cities set local oil and grease limits in a wide band. Its fact sheet (EPA-833-F-12-003) says it "identified typical numeric local limits controlling oil and grease in the range of 50 mg/L to 450 mg/L with 100 mg/L as the most commonly reported numeric pretreatment limit." We did not find a numeric oil and grease limit in the Valley city codes we read, so ask your city's pretreatment program what number applies to you, if any.
pH matters too. Scottsdale's plumbing code amendments require interceptor cleaning when the "pH of a sample taken from the interceptor effluent is below 5.0," which is a sign of acidic, decaying waste. That same acid is what attacks concrete tanks; see why concrete grease interceptors corrode. For a primer on what the tests are measuring, see what FOG means.
Where does the port go, and what should it look like?
On the outlet side, where the city says. The codes leave the design to plans the city approves, and they agree on a few points:
- Accessible and safe. Glendale says the manhole must be "accessible and safely located." Phoenix, Mesa, Scottsdale and Tempe use similar wording.
- Built to approved plans. Each "when required" rule says the structure is built in accordance with plans the city approves. Peoria points to its own standard detail.
- At the owner's expense. Mesa says the manhole "shall be installed by the owner at the owner's expense."
- Maintained. Phoenix says the sampling point "must be maintained by the user so as to be safe and accessible at all times." A cracked lid, a missing cap or a box full of dirt can count against you at an inspection.
- Kept clear. Phoenix's pretreatment code says "Any temporary or permanent obstruction to safe and easy access to the facility to be inspected and sampled must be promptly removed by the user at the request of the Director and must not be replaced." Don't park dumpsters, pallets or equipment on it.
Outdoor ports and vaults in a drive lane need a lid rated for the traffic over them; see traffic-rated grease interceptor lids. For where the interceptor itself can go, see grease interceptor location and access rules.
### Can a port be added to an existing interceptor?
Usually, yes. When a city requires a sampling point on an older site, the usual fix is a sample tee or box on the outlet line. It goes between the interceptor and the building sewer. The codes tie these to approved plans, so expect a permit and a drawing, not just a fitting. The steps look much like other interceptor work; see grease interceptor permits for a replacement in the Valley and how a grease interceptor is installed. The Valley grease trap and interceptor rules by city collects each city's code in one place.
If you're adding a new interceptor, build the port in from the start. It's simpler than cutting one in later.
HQ Plumbing & Air installs and repairs grease interceptors and their outlet piping for restaurants across the Phoenix area, including sample tees and vaults when a city calls for them. We're licensed and insured, with free estimates.