Cafe Tenant: Backflow Assemblies and a Grease Interceptor

Match the device to the hazard and to how the backflow occurs.

• Irrigation with fertilizer injector: health hazard (toxics) plus backpressure when the downstream zone is under pressure and a backsiphonage risk when main pressure drops. Protection must be an air gap or a reduced pressure zone assembly (RPZ) at the service branch feeding the irrigation, not a pressure vacuum breaker - a PVB cannot be used where backpressure exists and cannot be installed below grade.
• Carbonator: the CO2 blanket puts the water line under pressure above main pressure, so this is backpressure with a health hazard (carbonated water and CO2 can be driven back into the potable line). RPZ or air gap. A dual check is not acceptable for a health-hazard, backpressure application.
• Mop sink hose bibb: backsiphonage hazard from a hose dropped into the sink or a bucket. A hose-connection vacuum breaker (ASSE 1052) on the bibb, installed at least 6 inches above the flood-level rim of the fixture, plus no shutoff downstream of the breaker. If the hose is ever left submerged, this alone is not enough - use an air gap or a hose-bibb-rated RPZ.
• Ice machine: typically an integral air gap on the fill line; if not, a listed air gap or a vacuum breaker for the potable supply.
• Document each device on the permit drawings; the AHJ is checking the hazard classification, not just that a device is present.

A below-grade vault is a rejection, and it is the most common RPZ failure in the field.

• An RPZ must not be installed where it can be submerged or where the relief port can be blocked. It must be above grade, or in a drained, protected enclosure that the AHJ approves, with the relief discharge visible.
• Installation requirements:
  • Installed horizontally per the manufacturer, with the relief port freely draining to a safe location.
  • Accessible for testing and repair, with the manufacturer's required clearances.
  • Protected from freezing, which in this climate means freeze protection must be addressed.
  • Test cocks on all four test points, and no strainer omitted upstream.
  • No shutoff valve downstream that would trap pressure without a relief path.
  • The assembly must be on the utility's approved list, and the assembly number recorded.
• Testing: tested at installation and annually by a certified backflow prevention assembly tester, results filed with the water utility and the AHJ within the required time. Test kits must be calibrated.
• Tell the tenant in writing: containment at the service plus isolation at each hazard; the RPZ protects the main, the hose-connection device protects the fixture, and neither substitutes for the other.

Size from the fixture, then let the AHJ and the local sewer-use ordinance govern.

• Compartment volume: 18 x 24 x 12 = 5,184 cubic inches / 231 = 22.4 gallons per compartment.
• With a 1-minute drain-down, the sink discharges on the order of 22 gpm, so the interceptor must be rated at least that flow. Select a hydromechanical interceptor rated at 25 gpm, with a grease capacity that matches the code table or the local ordinance (typically 50 lb or more), and a flow-control fitting on the inlet sized to the interceptor.
• Installation requirements: on the sink's discharge only (not the prep sink or the mop sink unless required), accessible for cleaning, with the flow control device, a vented cover if required, and no dishwasher or other high-temperature discharge that would defeat separation.
• The 'it never clogged' argument is not a code defense. Interceptors are required by the code and by the utility's pretreatment rules regardless of past practice. Confirm whether the local pretreatment program requires a gravity interceptor with a minimum capacity rather than a small hydromechanical unit - many utilities require both a small unit at the sink and an exterior gravity interceptor at the building.
• Put the cleaning frequency and responsibility in the lease; grease interceptor maintenance is the tenant's, and the utility can inspect the manifests.