1 Scope
NOTE This standard covers the selection, sizing, materials, construction, installation, testing, and operation of grease interceptors and grease-removal devices that pretreat fats, oils, and grease (FOG) bearing wastewater from food-service establishments before that wastewater enters the sanitary building drain or the public sewer. (1.1)
NOTE The scope encompasses both principal device families: hydromechanical grease interceptors (HGI), including point-of-use units installed under or adjacent to a fixture and larger flow-rated units, automatic grease removal devices (GRD) that mechanically skim and remove accumulated grease, and gravity grease interceptors (GGI), which are large in-ground or exterior precast concrete vaults that separate grease and solids by quiescent retention. (1.2)
NOTE Grease interceptors exist to keep congealed FOG out of the sanitary sewer; FOG discharged from a commercial kitchen cools in the drain and sewer, congeals on pipe walls, and accumulates until it restricts or blocks the line, causing sanitary sewer overflows that are both an environmental violation and a public-health hazard, which is why the local sewer authority or pretreatment program frequently dictates the type, size, location, and maintenance of the interceptor through a FOG control ordinance. (1.4)
1.5 The Contractor and the Engineer of Record shall treat the local FOG ordinance as a governing document that may impose requirements more stringent than the adopted plumbing code.
1.6 The Contractor and the Engineer of Record shall confirm the local FOG ordinance requirements before the interceptor type and size are finalized.
1.7 The Contractor shall coordinate the grease waste and vent piping, traps, and the connection to the sanitary building drain with Sanitary Waste And Vent Piping, and shall coordinate the fixtures and food-service equipment that discharge to the interceptor with Plumbing Fixtures and the food-service equipment scope. 1.8 This standard does not cover oil/water separators for petroleum hydrocarbons, sand or solids interceptors, chemical or acid-neutralization pretreatment, or the exterior building sewer beyond the point of connection.
1.9 Where an interceptor is required to also remove settleable solids, as with a combination grease-and-solids interceptor, the solids-handling requirements of this standard apply only to the extent they support grease separation performance.
2 Referenced Standards
2.1 Materials, equipment, sizing, and installation shall comply with the latest adopted edition of the following standards, codes, and the governing local FOG control ordinance, unless a specific year is cited elsewhere in the contract documents.
| Standard |
Title |
| IPC |
International Plumbing Code (Chapter 10 — Traps, Interceptors, and Separators) |
| UPC |
Uniform Plumbing Code (Chapter 10 — Traps and Interceptors; Appendix H — Recommended Procedures for Sizing Gravity Grease Interceptors) |
| Local FOG ordinance |
Sewer authority / pretreatment program Fats, Oils, and Grease control ordinance for the jurisdiction |
| PDI G101 |
Testing and Rating Procedure for Hydromechanical Grease Interceptors with Appendix of Sizing and Installation Data (Plumbing and Drainage Institute) |
| ASME A112.14.3 |
Grease Interceptors (hydromechanical, Types A through D by flow control and connection method) |
| ASME A112.14.4 |
Grease Removal Devices (automatic grease removal devices, GRD) |
| ASME A112.14.6 |
FOG (Fats, Oils, and Greases) Disposal Systems |
| CSA B481 |
Grease Interceptors (test and rating procedure, harmonized with PDI G101 / ASME A112.14.3) |
| ASTM C1613 |
Standard Specification for Precast Concrete Grease Interceptor Tanks |
| ASTM C890 |
Standard Practice for Minimum Structural Design Loading for Monolithic or Sectional Precast Concrete Water and Wastewater Structures |
| ASTM C913 |
Standard Specification for Precast Concrete Water and Wastewater Structures |
| ASTM C443 |
Standard Specification for Joints for Concrete Pipe and Manholes, Using Rubber Gaskets |
| ASTM A48 |
Standard Specification for Gray Iron Castings (interceptor covers and frames) |
| ASTM A536 |
Standard Specification for Ductile Iron Castings (traffic-rated covers and frames) |
| NSF/ANSI 14 |
Plastics Piping System Components and Related Materials (plastic interceptor bodies and components) |
| ASME A112.6.3 |
Floor and Trench Drains (referenced for floor-set interceptor and drain coordination) |
2.2 Where the contract documents, a referenced standard, the adopted plumbing code, or the local sewer authority impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
2.3 On any matter the local FOG control ordinance addresses directly, the ordinance governs.
2.4 Where the project is located in a jurisdiction that has adopted the Uniform Plumbing Code rather than the International Plumbing Code, references to IPC chapter and section numbers shall be understood to refer to the equivalent UPC provisions.
2.5 The Contractor shall confirm the adopted plumbing code edition and obtain the current FOG control ordinance and any interceptor sizing and installation guidelines published by the sewer authority prior to submitting the plumbing permit application.
3 Submittals
3.1 Action Submittals
3.1.1 Contractor shall submit the following for the Engineer's review and comment, and for the sewer authority's approval where the FOG ordinance requires it, prior to fabrication, procurement, or installation.
- Sizing calculations for the interceptor, identifying the sizing method used (IPC fixture/DFU method, UPC fixture or drainage-fixture-unit method, PDI G101 flow-rate method, or the local FOG ordinance method), the fixtures and appliances connected to the interceptor, the computed flow rate or required liquid volume, and the selected unit's rated flow rate and grease capacity
- Product data for the grease interceptor or grease removal device, identifying the manufacturer, model, material, rated flow rate (GPM), rated grease storage capacity (lb), the applicable PDI G101 / ASME A112.14.3 type (A, B, C, or D) or ASME A112.14.4 GRD designation, the certification listing, dimensions, inlet and outlet connection sizes and invert elevations, and weight
- Product data for the external flow control fitting and air intake, including the orifice size matched to the rated flow and the air-intake vent configuration, where a flow-controlled (Type A or Type B) hydromechanical interceptor is used
- Shop drawings for gravity grease interceptors, including the tank dimensions, compartment configuration and baffle arrangement, liquid volume, inlet and outlet invert elevations, access manhole and riser locations, structural design loading per ASTM C890, reinforcement, and the buoyancy / anti-flotation calculation where high groundwater is present
- Product data for access covers and frames, including the load rating (pedestrian, light-duty, or traffic-rated H-20 / HS-20), gasketing, and the gas-tight and odor-tight sealing method
- Product data and location for the sample / monitoring port where required by the FOG ordinance, including the construction that allows the sewer authority to obtain a representative effluent sample downstream of the interceptor
- A maintenance and operations plan describing the proposed pump-out and cleaning frequency, the basis for that frequency (the 25 percent rule or the ordinance-mandated maximum interval), the licensed waste hauler arrangement, and the recordkeeping method
☑ Interceptor sizing calculations with method identified
☐ Grease interceptor / GRD product data with flow and grease-capacity rating
☐ External flow control and air intake product data
☐ Gravity interceptor shop drawings (compartments, baffles, structural loading)
☐ Access cover and frame product data with load rating
☐ Sample / monitoring port product data and location
☐ Maintenance and pump-out operations plan
☐ Sewer authority / FOG program approval of type and size
3.1.2 No interceptor shall be procured or installed until the corresponding submittals have been reviewed and returned, and until the sewer authority has approved the interceptor type and size where local approval is required.
3.2 Closeout Submittals
3.2.1 Contractor shall provide the following at substantial completion before the grease interceptor system is accepted.
- As-built drawings showing the installed interceptor type, model, rated capacity, location, inlet and outlet invert elevations, the fixtures connected, the flow control and venting configuration, and the location of access covers and the sample port
- Operation and maintenance data for the interceptor and, for automatic grease removal devices, the skimmer, heater, timer, and grease-collection container, including manufacturer cleaning and service instructions
- The completed maintenance and pump-out operations plan, with the recommended baseline cleaning frequency and the recordkeeping forms or log to be maintained by the Owner
- Field test reports for the watertightness test of gravity interceptors and the leak test of hydromechanical interceptors
- Manufacturer warranty documentation for the interceptor body and, for GRDs, the mechanical and electrical components
- Sewer authority discharge permit or pretreatment authorization documentation where the FOG ordinance requires the establishment to hold a permit
☑ As-built drawings (type, model, capacity, inverts, fixtures, covers, sample port)
☐ Operation and maintenance data (interceptor and GRD components)
☐ Completed maintenance and pump-out operations plan with recordkeeping log
☐ Field test reports (watertightness and leak tests)
☐ Manufacturer warranty documentation
☐ Sewer authority discharge permit / pretreatment authorization
4 Quality Assurance
4.1 Installer Qualifications
4.1.1 Grease interceptor piping and connections shall be installed by a licensed plumbing contractor and by journeymen or apprentice plumbers working under the direct supervision of a licensed journeyman.
4.1.2 Setting of exterior gravity grease interceptors — excavation, bedding, rigging of the precast tank, joint sealing, and backfill — shall be performed by personnel experienced in precast concrete structure installation, and the precast tank shall be set under the direction of personnel familiar with the manufacturer's rigging and joint-sealing requirements.
4.1.3 Automatic grease removal devices shall be installed and commissioned by personnel trained by the device manufacturer in the specific product line, because the skimmer, heater, and control timer require manufacturer setup.
4.2 Listing and Marking
4.2.1 Hydromechanical grease interceptors shall be tested, rated, and marked in accordance with PDI G101, ASME A112.14.3, or CSA B481, and shall bear a legible permanent marking indicating the rated flow rate in gallons per minute and the rated grease storage capacity in pounds.
4.2.2 Automatic grease removal devices shall be listed and marked to ASME A112.14.4.
4.2.3 Plastic interceptor bodies and components shall bear the NSF/ANSI 14 listing mark.
4.2.4 Precast concrete gravity interceptor tanks shall be manufactured by a plant certified for precast concrete production and shall be marked with the manufacturer's identification, the liquid volume, and the date of manufacture.
4.2.5 Interceptors that do not bear the required certification marking shall be rejected.
4.3 Sewer Authority Coordination
4.3.1 The Contractor shall coordinate with the local sewer authority or pretreatment program throughout the interceptor scope.
4.3.2 Where the FOG ordinance requires the sewer authority to approve the interceptor type and size, to inspect the installation before backfill or concealment, or to issue a discharge permit to the food-service establishment, the Contractor shall schedule those approvals and inspections.
4.3.3 The Contractor shall not conceal or place into service any interceptor before the required authority inspection has been completed and released.
4.3.4 The Contractor shall notify the Engineer of Record if the sewer authority imposes any requirement that differs from the contract documents.
5 Interceptor Type Selection
5.1 General
NOTE The two principal interceptor families serve different scales and installation conditions. (5.1.1)
● Hydromechanical grease interceptor (HGI) — point-of-use or flow-rated, indoor
○ Automatic grease removal device (GRD) — powered skimmer, indoor
○ Gravity grease interceptor (GGI) — exterior in-ground precast vault
NOTE Hydromechanical grease interceptors (HGI) are compact, flow-rated devices that separate grease by buoyancy and baffling at relatively high flow velocity; they install at or near the point of use, indoors, and are rated by flow rate and grease capacity. (5.1.2)
NOTE Gravity grease interceptors (GGI) are large in-ground or exterior vaults that separate grease and solids by quiescent retention over a defined retention time; they are sized by liquid volume and serve an entire kitchen or multiple establishments. (5.1.3)
NOTE Automatic grease removal devices (GRD) are hydromechanical interceptors fitted with a powered skimmer that continuously or periodically removes accumulated grease into a collection container, reducing the manual cleaning burden. (5.1.4)
NOTE The selection between HGI and GGI is driven by the connected load, the available indoor space, the local FOG ordinance, and the sewer authority's preference; many jurisdictions mandate an exterior gravity interceptor of a minimum volume for any establishment with a commercial kitchen, and permit hydromechanical interceptors only for limited fixture counts or for tenant build-outs where an exterior vault is impractical. (5.1.5)
5.1.6 The Contractor shall confirm the permitted interceptor types with the sewer authority before selection.
5.2 Application Guidance
NOTE Hydromechanical interceptors are appropriate for tenant restaurants, coffee shops, single-fixture installations, and kitchens with a modest connected fixture count where an exterior vault is not required by the ordinance and where the unit can be located within reach for regular manual cleaning; they occupy little space and have a low first cost, but require frequent manual cleaning — often weekly — to maintain separation efficiency, because their small grease capacity fills quickly under restaurant loads. (5.2.1)
NOTE Gravity grease interceptors are appropriate for full-service commercial kitchens, cafeterias, institutional food service, commissaries, and any establishment for which the ordinance mandates an exterior vault; their large liquid volume provides long retention time and high grease and solids storage, which extends the cleaning interval to monthly or quarterly, but they require exterior space, are costly to install, and require pump-out by a licensed liquid-waste hauler. (5.2.2)
NOTE Automatic grease removal devices are appropriate where space is limited but a high cleaning frequency is undesirable, such as in high-volume kitchens where manual cleaning of a small hydromechanical unit would otherwise be required several times per week; their higher first cost and the maintenance of the powered skimmer are offset by reduced manual labor and more consistent effluent quality. (5.2.3)
6 Sizing
6.1 General
Local FOG ordinance method (governs where prescribed)
IPC fixture / drainage-fixture-unit method (Chapter 10)
UPC fixture-count or DFU method (Chapter 10)
UPC Appendix H method (gravity interceptor volume)
PDI G101 flow-rate method (hydromechanical)
6.1.1 The interceptor shall be sized by the method required by the local FOG control ordinance.
6.1.2 Where the ordinance does not prescribe a method, the interceptor shall be sized by the method in the adopted plumbing code.
6.1.3 The Contractor shall not reduce the interceptor size below the size the ordinance or code requires, and shall submit the sizing calculation for review.
6.1.4 The hydromechanical unit shall be matched to the connected load, not arbitrarily enlarged.
NOTE Oversizing a hydromechanical interceptor degrades performance, because at flows well below the rated flow the unit loses the velocity and baffling action it relies on; gravity interceptors, by contrast, benefit from generous volume because retention time and storage both improve with size. (6.1.5)
6.2 Hydromechanical Interceptor Flow Rate and Grease Capacity
4 GPM (single point-of-use fixture)
7 GPM
10 GPM
15 GPM
20 GPM
25 GPM
35 GPM
50 GPM
75 GPM
100 GPM
Per drawings (deferred by default)
Minimum 2 lb per GPM of rated flow (rating-standard minimum)
Enhanced capacity (greater than 2 lb per GPM, extended cleaning interval)
6.2.1 Hydromechanical interceptors shall be rated by flow rate in gallons per minute (GPM) and by grease storage capacity in pounds (lb), determined by test in accordance with PDI G101 or ASME A112.14.3.
6.2.2 The rated flow shall equal or exceed the computed drainage flow rate from the connected fixtures, determined either from the fixture drain rate or from the drainage fixture unit load converted to GPM by the method in the adopted code.
6.2.3 Where the connected fixtures have no assigned drainage fixture unit value, the flow rate shall be computed from the known fixture discharge rate.
6.2.4 The grease storage capacity rating shall comply with the minimum ratio established by the rating standard, which requires not less than 2 pounds of grease storage capacity for each gallon per minute of rated flow.
NOTE The grease capacity determines how long the unit can operate between cleanings before separation efficiency falls; a 20 GPM unit therefore provides at least 40 lb of grease capacity, a 50 GPM unit at least 100 lb, and a higher grease capacity at a given flow rate extends the maintenance interval and is preferred where the cleaning interval is a concern. (6.2.5)
6.3 Gravity Interceptor Liquid Volume
500 gal
750 gal
1000 gal
1500 gal
2000 gal
3000 gal
Per drawings (deferred by default)
● Two compartments (standard minimum)
○ Three compartments (enhanced separation, where required by ordinance)
6.3.1 Gravity grease interceptors shall be sized by liquid volume to provide the retention time required by the adopted code or FOG ordinance.
6.3.2 The minimum liquid volume and the number of compartments shall not be less than the values required by the governing ordinance.
6.3.3 The minimum liquid volume of a gravity grease interceptor shall be not less than 500 gallons unless the governing ordinance permits a smaller vault.
6.3.4 Gravity interceptors shall have not fewer than two compartments separated by a baffle wall, with the inlet to the first compartment and the outlet from the second.
NOTE The Uniform Plumbing Code recognizes a 30-minute retention time, and the UPC Appendix H method and the National Precast Concrete Association sizing procedure compute the required liquid volume from the drainage fixture units or the known fixture flow rate multiplied by the retention time, with adjustments for the establishment type and operating hours; many ordinances establish a 750-gallon or 1000-gallon minimum for any commercial kitchen. (6.3.5)
NOTE The two-compartment arrangement allows grease to rise and solids to settle in the first compartment while the second compartment provides a quiescent zone that polishes the effluent before discharge. (6.3.6)
7 Hydromechanical Grease Interceptors
7.1 Construction
○ Coated fabricated steel
○ Stainless steel (Type 304)
● Polyethylene / polypropylene (NSF/ANSI 14 listed)
○ Cast iron
On-floor, adjacent to fixture (above-floor)
Partially recessed / semi-recessed in floor
Flush-with-floor (in-floor, traffic-rated cover)
Suspended / under-counter
7.1.1 Hydromechanical grease interceptors shall be of welded or molded one-piece construction with internal baffles that direct the incoming flow downward and force the wastewater to follow a path that promotes grease flotation and solids settling before the effluent leaves through the outlet.
7.1.2 The interceptor shall include a removable cover with a gas-tight and odor-tight seal, an integral or separate flow control, and internal air-relief or anti-siphon features as required by the design type.
7.1.3 The interceptor body shall be corrosion-resistant for the service life of the installation.
7.1.4 Polyethylene and polypropylene interceptors shall be NSF/ANSI 14 listed and rated for the installation location, including for in-floor or on-floor service as applicable.
NOTE Coated fabricated steel interceptors are the traditional under-fixture material and are economical, but the coating is the only corrosion barrier and is vulnerable to abrasion during cleaning; stainless steel resists corrosion and cleans well, and is preferred where the interceptor is exposed in a finished kitchen or where long life is required; polyethylene and polypropylene interceptors are corrosion-proof, lightweight, and dominate the current point-of-use and larger flow-rated market; cast iron is durable and heavy but is the least common modern choice for hydromechanical units. (7.1.5)
7.2 Flow Control Fitting and Air Intake
● Type A — external flow control with air intake (vent), directly connected
○ Type B — external flow control without air intake, directly connected
○ Type C — no external flow control, directly connected
○ Type D — no external flow control, indirectly connected
7.2.1 A flow-controlled hydromechanical interceptor (PDI G101 / ASME A112.14.3 Type A or Type B) shall be installed with an external flow control fitting on the inlet side, sized with an orifice matched to the interceptor's rated flow.
7.2.2 The flow control orifice shall match the rated flow of the interceptor.
NOTE The flow control limits the rate at which wastewater enters the interceptor so that the unit is never overwhelmed by a slug discharge that would carry grease through before it can separate; an unmatched or omitted flow control causes the interceptor to fail under peak fixture discharge. (7.2.3)
7.2.4 The air intake of a Type A flow control shall be vented to atmosphere or to the vent system, shall terminate above the flood-level rim of the highest connected fixture, and shall not be capped, plugged, or omitted.
7.2.5 The flow control type shall be the type the interceptor manufacturer specifies for the rated flow and the connection method used.
NOTE As wastewater accelerates through the flow-control orifice of a Type A interceptor it creates a negative pressure that draws air through the air intake, and that entrained air mixes with the wastewater and improves grease separation as the flow enters the interceptor; a Type A interceptor with a sealed or missing air intake does not perform to its rating. (7.2.6)
7.3 Automatic Grease Removal Devices
● Programmable timer-initiated skimming cycle
○ Sensor-initiated skimming (grease-layer thickness sensing)
7.3.1 Where an automatic grease removal device (GRD) is specified, the device shall conform to ASME A112.14.4 and shall automatically remove free-floating grease from the interceptor into a collection container without user intervention except for periodic emptying of the container and routine service.
7.3.2 The GRD shall include a heating element to liquefy the accumulated grease layer, a powered skimmer or draw-off mechanism, a control timer that initiates the skimming cycle on a programmable schedule, and a removable grease-collection container.
7.3.3 The control system shall be supplied from a dedicated circuit coordinated with the electrical scope.
7.3.4 The grease-collection container shall be sized for the establishment's grease load and the desired emptying interval, and shall be readily accessible for removal and emptying by kitchen staff.
7.3.5 The Contractor shall set the skimming schedule during commissioning to match the establishment's operating hours so that skimming occurs after peak meal-service periods when the grease layer is thickest.
8 Gravity Grease Interceptors
8.1 Tank Construction
● Precast concrete (ASTM C1613)
○ Fiberglass-reinforced plastic (FRP)
○ High-density polyethylene (HDPE)
8.1.1 Gravity grease interceptors shall be precast concrete tanks conforming to ASTM C1613, designed for the imposed structural loads in accordance with ASTM C890 and manufactured in accordance with ASTM C913.
8.1.2 The tank shall be watertight, with monolithic or sectional construction.
8.1.3 Sectional joints between the base, mid-section, and top shall be sealed with a preformed flexible joint sealant or a rubber gasket conforming to ASTM C443 to achieve a watertight, gas-tight joint.
8.1.4 The tank shall have a structural design rating appropriate to its location, accounting for the depth of cover, the groundwater condition, and any vehicular loading above the tank.
NOTE Precast concrete is the standard material for exterior in-ground gravity interceptors because of its mass, structural strength, resistance to flotation, and long service life; fiberglass-reinforced plastic and high-density polyethylene tanks are lighter, corrosion-proof, and may be selected where site access limits the weight that can be set or where soil chemistry is aggressive to concrete, but a lightweight tank requires an engineered anti-flotation design where groundwater can rise to the tank, because an empty lightweight tank will float. (8.1.5)
8.2 Structural Loading and Anti-Flotation
● Non-traffic (landscaped or pedestrian area)
○ Traffic-rated H-20 / HS-20 (driveway, parking, or drive lane)
8.2.1 The tank and its access risers and covers shall be designed for the loads imposed by the depth of burial, the soil, the groundwater, and any traffic above the tank.
8.2.2 Where the interceptor is located under a driveway, parking area, or other area subject to vehicle traffic, the tank, risers, and covers shall be traffic-rated for AASHTO H-20 / HS-20 loading.
8.2.3 Where groundwater can rise above the tank base, the Contractor shall provide anti-flotation restraint — an extended base slab, anti-flotation ballast, or tie-downs — designed so that the empty tank does not float, in accordance with the shop drawing buoyancy calculation reviewed by the structural engineer of record.
8.3 Inlet and Outlet Configuration
8.3.1 The inlet and outlet of a gravity interceptor shall be fitted with sanitary tees or submerged elbows that direct the inlet flow downward below the floating grease layer and draw the outlet flow from below the grease layer, so that the floating grease is retained in the tank and only the clarified middle layer of wastewater discharges.
8.3.2 The inlet invert shall be set above the outlet invert by the amount the tank manufacturer specifies to establish the flow gradient through the tank.
9 Connection of Fixtures
9.1 Permitted Connections
☑ Three-compartment / scullery sink
☐ Pot and pan sink
☐ Pre-rinse station
☐ Wok range / kettle drains
☐ Mop sink (kitchen cleanup)
☐ Kitchen floor drains and floor sinks
☐ Food-preparation equipment indirect drains
Per drawings
9.1.1 Only fixtures and appliances that discharge grease-laden wastewater shall be connected to the grease interceptor; these typically include pot and pan sinks, three-compartment scullery sinks, pre-rinse stations, wok ranges and kettle drains, mop sinks used for kitchen cleanup, floor drains and floor sinks in food-preparation and dishwashing areas, and the indirect drains from food-preparation equipment.
9.2 Prohibited Connections
● No food-waste grinder discharges to the interceptor
○ Grinder permitted by ordinance — discharges to interceptor with separate solids handling
● Dishwasher bypasses interceptor (discharges to sanitary building drain)
○ Dishwasher discharges to interceptor (where required by ordinance)
9.2.1 Sanitary waste from water closets, urinals, and other plumbing fixtures that carry human waste shall never be connected to a grease interceptor; sanitary sewage must bypass the interceptor and discharge directly to the building drain.
9.2.2 Stormwater, condensate, and other non-grease wastewater shall not be connected to the interceptor, because diluting flows reduce retention time and degrade separation.
9.2.3 Food-waste grinders (garbage disposers) shall not discharge to a grease interceptor unless the governing FOG ordinance and the adopted code specifically permit it.
9.2.4 Commercial dishwasher discharge shall be connected to the grease interceptor only where the governing ordinance permits it.
9.2.5 The Contractor shall confirm the treatment of food-waste grinders and dishwasher discharge with the sewer authority before connecting either to the interceptor.
NOTE Connecting sanitary waste to a grease interceptor is a code violation and renders the interceptor effluent septic; macerated food solids from a grinder overload the interceptor and many jurisdictions prohibit grinders ahead of an interceptor or require a separately sized solids interceptor, and some jurisdictions exclude dishwasher discharge because the high temperature and detergent emulsify grease and carry it through the interceptor, while others require it to be connected. (9.2.6)
10 Trapping and Venting
10.1 Fixture Trapping
10.1.1 Each fixture discharging to the grease interceptor shall be individually trapped and vented in accordance with the adopted plumbing code and Sanitary Waste And Vent Piping. 10.1.2 The interceptor is not a trap and shall not be relied upon to provide the trap seal for the connected fixtures.
10.1.3 Where a hydromechanical interceptor has an integral trap on its outlet, no additional trap shall be installed downstream that would create a double trap.
10.1.4 Where the interceptor does not have an integral trap, a trap shall be provided on the interceptor outlet as required by code.
10.2 Interceptor Venting
Flow-control air intake vent plus downstream outlet vent (hydromechanical Type A)
Downstream outlet vent only (hydromechanical Type B / C)
Vented access risers (gravity interceptor)
Dedicated vent connection (gravity interceptor)
Per drawings (deferred by default)
10.2.1 The grease interceptor shall be vented in accordance with the adopted plumbing code.
10.2.2 A flow-controlled hydromechanical interceptor of Type A shall have its flow-control air intake vented as described in the flow control section.
10.2.3 The interceptor outlet shall be vented downstream so that the discharge does not siphon the interceptor or the connected fixture traps, and so that air can move freely through the interceptor as wastewater flows.
10.2.4 Gravity interceptors shall be vented through the access risers or a dedicated vent connection as the code and the tank manufacturer require, so that gases generated within the tank are relieved and the tank does not become pressurized or develop a vacuum during flow.
11 Access and Monitoring
11.1 Access Covers
○ Gray iron (ASTM A48) — non-traffic
● Ductile iron (ASTM A536) — traffic-rated
○ Coated steel
1836
1820243036
Default: 24 in
11.1.1 Every grease interceptor shall be provided with access covers that permit complete inspection, cleaning, and pump-out of every compartment without removing permanent construction.
11.1.2 Hydromechanical interceptor covers shall seal gas-tight and odor-tight and shall be removable by hand or with simple tools for routine cleaning.
11.1.3 Gravity interceptor access manholes shall extend to finished grade with risers, shall be located over the inlet, the outlet, and each compartment, and shall be fitted with gas-tight, odor-tight covers.
11.1.4 Covers in traffic areas shall be traffic-rated to match the tank loading.
11.1.5 Access manholes and risers shall be sized to permit a cleaning hose and pump-out equipment to reach the bottom of each compartment.
11.1.6 The Contractor shall confirm that the access provided allows a liquid-waste hauler to fully evacuate and clean the tank.
NOTE Risers that are too small or covers that cannot be opened without special equipment defeat the maintenance program. (11.1.7)
11.2 Sample and Monitoring Port
● Required by FOG ordinance — provided downstream of interceptor outlet
○ Not required by ordinance
11.2.1 Where the FOG control ordinance requires the sewer authority to obtain effluent samples, a sample port or monitoring structure shall be provided on the interceptor outlet, downstream of the interceptor and upstream of the connection to the building drain or sewer, so that a representative sample of the treated effluent can be drawn.
12 Installation
12.1 Hydromechanical Interceptor Installation
12.1.1 Hydromechanical interceptors shall be installed level on a firm, supporting surface in the location shown on the drawings, with adequate clearance around and above the unit for cover removal and manual cleaning.
12.1.2 The interceptor shall be installed so that the inlet and outlet inverts establish the correct flow direction and so that the flow control fitting is upstream of the inlet at the elevation the manufacturer specifies.
12.1.3 Under-fixture and on-floor units shall be located where the floor can be cleaned around them and where staff can reach the cover for the frequent cleaning these units require.
12.1.4 In-floor flush units shall be set with the cover flush with the finished floor and shall be sealed to the floor so that floor washdown does not enter the cover seam.
12.2 Gravity Interceptor Installation
● Compacted granular bedding on prepared subgrade
○ Concrete leveling slab beneath tank
Per drawings — structural / geotechnical drawings
12.2.1 Exterior gravity interceptors shall be set on a compacted, level bedding of granular material prepared to the dimensions and bearing capacity required by the tank shop drawings and the geotechnical recommendations.
12.2.2 The excavation shall be dewatered as required so that the tank is set on dry, stable bedding.
12.2.3 The tank shall be rigged and set in accordance with the manufacturer's lifting instructions, and sectional joints shall be sealed before the inlet and outlet piping is connected.
12.2.4 Backfill shall be placed and compacted uniformly around the tank in lifts so that the tank is not displaced, and anti-flotation restraint shall be in place before backfilling where groundwater is a concern.
12.2.5 The interceptor shall be located the minimum distance from the building required by the code and the ordinance, accessible to a pump-out truck, and clear of building footings, other utilities, and the water service.
12.3 Piping Slope and Connection
12.3.1 The grease waste piping from the connected fixtures to the interceptor, and from the interceptor outlet to the building drain or sewer, shall be sloped and installed in accordance with Sanitary Waste And Vent Piping. 12.3.2 The Contractor shall maintain uniform slope without sags, because grease waste piping is especially sensitive to inadequate slope as cooling grease deposits in any low spot or flat run.
12.3.3 The piping material between the fixtures and the interceptor, and downstream of the interceptor, shall be as indicated on the drawings and compatible with grease-laden waste at the temperatures discharged by the connected fixtures.
13 Testing and Commissioning
13.1 Watertightness and Leak Testing
● Fill-and-observe water test to outlet invert (per manufacturer / authority)
○ Vacuum test (where specified for the tank type)
13.1.1 Gravity grease interceptor tanks shall be tested for watertightness before being placed in service and before backfill conceals the tank joints, by filling the tank with water to the outlet invert and observing for leakage over the test period required by the tank manufacturer and the sewer authority.
13.1.2 Any leakage at joints, penetrations, or the tank body shall be repaired and the tank re-tested.
13.1.3 Hydromechanical interceptors and grease removal devices shall be checked for leak-free connections at the inlet, outlet, cover, and flow control after installation.
13.2 Commissioning and Initial Fill
13.2.1 Before the establishment is placed into service, the interceptor shall be filled with clean water to the operating level so that the grease-flotation and effluent-draw geometry functions from the first discharge.
13.2.2 For automatic grease removal devices, the Contractor shall verify operation of the heater, skimmer, timer, and grease-collection mechanism, and shall set the skimming schedule for the establishment's operating hours during commissioning.
NOTE An empty interceptor placed into service passes grease straight through until it fills. (13.2.3)
13.3 Functional Verification
13.3.1 After installation, the Contractor shall verify that the interceptor receives flow only from the permitted grease-bearing fixtures and that no sanitary waste, stormwater, or prohibited connection has been made.
13.3.2 The Contractor shall verify that the flow control fitting and air intake are installed and unobstructed on flow-controlled hydromechanical units, that the venting is connected, and that all access covers seal and open as intended.
14 Operation and Maintenance
14.1 Maintenance Program
○ 25 percent rule — clean when grease plus solids reach 25 percent of liquid depth
○ Fixed maximum interval per FOG ordinance
● Whichever of the 25 percent rule or the ordinance interval occurs first
Weekly (small hydromechanical point-of-use unit)
Monthly (larger hydromechanical unit)
Quarterly / every 90 days (gravity interceptor)
Per FOG ordinance and 25 percent rule (verify in service)
14.1.1 The Owner shall maintain the grease interceptor on a schedule that keeps it functioning within its rated separation efficiency and that complies with the FOG control ordinance.
14.1.2 Under the 25 percent rule, the interceptor shall be fully pumped out and cleaned whenever the combined thickness of the floating grease layer and the settled solids layer reaches 25 percent of the total liquid depth.
14.1.3 Where the ordinance imposes a maximum interval, that interval applies regardless of the measured accumulation, and whichever trigger occurs first governs.
NOTE The ordinance maximum interval is commonly 90 days for a gravity interceptor at a food-service establishment, and as frequently as weekly for a small hydromechanical unit. (14.1.4)
14.2 Full Pump-Out and Cleaning
14.2.1 Gravity grease interceptors shall be fully pumped out — all liquid, floating grease, and settled solids removed — by a licensed liquid-waste hauler, not merely skimmed of the surface grease.
14.2.2 The hauled waste shall be disposed of at a permitted facility and disposal records retained.
14.2.3 Hydromechanical interceptors shall be fully emptied and the baffles and interior cleaned at each service.
14.2.4 Automatic grease removal devices require periodic emptying of the grease-collection container and periodic full cleaning of the interceptor body in addition to the automatic skimming.
NOTE Partial skimming that leaves the wastewater and solids in the tank is not compliant cleaning and allows solids to accumulate and reduce capacity. (14.2.5)
14.3 Prohibited Additives
14.3.1 Chemical, enzyme, solvent, and bacterial additives intended to dissolve, emulsify, or digest grease shall not be used.
14.3.2 Maintenance shall consist of physical removal of the accumulated grease and solids, not chemical treatment.
NOTE Additives do not remove grease from the waste stream; they liquefy or suspend it so that it passes through the interceptor and congeals downstream in the sewer, defeating the purpose of the interceptor, and most FOG ordinances prohibit additives outright. (14.3.3)
14.4 Recordkeeping
14.4.1 The Owner shall maintain a maintenance log recording the date of each cleaning, the measured grease and solids accumulation at the time of cleaning, the volume of waste removed, the name of the licensed hauler, and the disposal location, and shall retain the records and manifests for the period the FOG ordinance requires.
14.4.2 The maintenance log shall be available for inspection by the sewer authority.
14.4.3 The Contractor shall furnish the initial log forms and the recommended baseline cleaning interval as part of the closeout documentation.
15 Identification and Labeling
● Cover cast or permanently marked 'GREASE INTERCEPTOR'
○ Surface-applied marker / tag
15.1 The grease interceptor and its access covers shall be identified so that maintenance personnel and the sewer authority can locate and identify the unit.
15.2 Exterior gravity interceptor covers shall be marked to indicate that the structure is a grease interceptor.
15.3 Interior grease waste piping shall be identified in accordance with Sanitary Waste And Vent Piping and distinguished from sanitary waste piping so that the grease waste system is not inadvertently cross-connected to sanitary waste during future work. 16 Delivery, Storage, and Handling
16.1 Interceptors and grease removal devices shall be delivered in the manufacturer's packaging with rating and listing markings intact, and shall be inspected on delivery for damage to the body, covers, flow control, and connections.
16.2 Damaged units shall not be installed.
16.3 Plastic interceptors shall be stored out of direct sunlight, because ultraviolet exposure degrades the material.
16.4 Precast concrete tanks shall be handled with the manufacturer's lifting points and shall not be rolled, dropped, or set on point loads that could crack the tank.
16.5 Automatic grease removal devices contain electrical and mechanical components and shall be stored dry and protected from impact until installed.
17 Warranty
1 year from substantial completion
2 years from substantial completion
17.1 The Contractor shall warrant all materials and installation covered by this standard against defects in workmanship and against leakage for the project warranty period following substantial completion.
17.2 The warranty shall cover the interceptor body, covers, flow control, connections, and, for gravity interceptors, the watertightness of the tank and joints.
17.3 Manufacturer warranties for the interceptor body and, for automatic grease removal devices, the heater, skimmer, motor, and controls shall be passed through to the Owner as part of the closeout documentation.
17.4 Where a manufacturer warranty extends beyond the Contractor's installation warranty period, the Contractor shall assign and transfer the manufacturer warranty to the Owner at closeout.
17.5 The warranty shall not limit or replace the Contractor's obligation to comply with all applicable code and FOG ordinance requirements and the requirements of this standard.