13.30.070 Requirements for gravity grease interceptors (GGIs)/hydromechanical grease interceptors (HGIs).
A. All commercial and industrial facilities dealing with fats, oils and grease (FOG) shall, at the permittees’ expense and as required by the supervisor:
1. Provide an adequately sized interceptor (GGI/HGI). Requirements for interceptor (GGI/HGI) sizing and the design criteria are set forth in this section.
a. Zero to four DFUs are exempt.
b. Five through nine DFUs must provide adequately sized and approved HGI based on a three-compartment sink with a less than two-inch trap or trap arm.
c. Ten or more DFUs must install adequately sized and approved GGI.
2. Locate the interceptor (GGI/HGI) in a manner that provides ready and easy accessibility for cleaning and inspection.
3. Unless otherwise specified by the supervisor, service will be performed on an individual basis as specified in each individual operational permit. Hydromechanical grease interceptors (HGIs) require weekly maintenance or at a frequency as determined by the supervisor. Maintain backup copies of trip tickets and a service log, on the premises of the facility, for at least three years.
4. Reports must be available to the supervisor, as defined in GHMC 13.30.113.
5. Allow inspection of the facility and of records by inspectors during reasonable hours.
6. If the supervisor determines that there is a need for installation or upgrading of sample ports or grease interceptors (GGIs/HGIs) on an existing facility, he/she shall direct the generator to install necessary improvements to bring existing facility into compliance.
B. Requirements for Gravity Grease Interceptor/Hydromechanical Grease Interceptor Sizing and Design Criteria.
1. Size, type, and location of GGIs/HGIs shall be in accordance with the manufacturers’ instructions, the requirements of city of Gig Harbor Municipal Code and/or public works standards, and Uniform Plumbing Code.
All grease bearing waste streams shall be routed through an approved grease interceptor, including: three-compartment sinks, pot/pan sinks, soup kettles, hand-washing sinks, dishwashers, mop sinks and floor drains.
2. Applicability. These requirements are applicable to all commercial food service establishments, including those that are undergoing the following:
a. New construction;
b. Interior remodeling to accommodate expansion or operational modifications;
c. Changes of ownership/occupancy or use;
d. Facilities which may be experiencing difficulty in achieving compliance with maintenance and/or wastewater discharge limitations.
3. Sizing Requirements.
a. Sizing methods described herein are intended as guidance in determining GGI/HGI sizes that may afford the POTW a minimum degree of protection against grease and other obstructing materials. Sizing determinations are based on operational data provided by business owners or their contractors. In approving a generator’s plumbing or GGI/HGI design, the city does not accept liability for the failure of a system to adequately treat wastewater to achieve effluent quality requirements specified under this chapter. It is the responsibility of the generator and/or contractors to ensure the appropriate level of treatment necessary for compliance with environmental and wastewater regulations.
b. Tables in formulas found in subsection (B)(4) of this section shall be used to determine adequate gravity grease interceptor/ hydromechanical grease interceptor (GGI/HGI) sizing.
4. Gravity Grease Interceptor (GGI)/Hydromechanical Grease Interceptor (HGI) Sizing Tables in Formulas. It is the responsibility of the generator/owner and his/her contractors to ensure that the wastewater discharged from their facility is in compliance with the city’s discharge limitations. For the purpose of plan review, a general assessment of GGI/HGI design and size will be performed using the following tables in formulas. (These formulas have been demonstrated as industry standards capable of achieving the city’s discharge criteria when systems are maintained in proper conditions.)
|
Inch |
mm |
|---|---|
|
1-1/4 |
32 |
|
1-1/2 |
40 |
|
2 |
50 |
|
2-1/2 |
65 |
|
3 |
80 |
|
Plumbing Appliance, Appurtenance, or Fixture |
Min. Size Trap & Trap Arm7 |
Private |
Public |
Assembly8 |
|
|---|---|---|---|---|---|
|
Bathtub or Combination Bath/Shower |
1-1/2" |
2.0 |
2.0 |
||
|
Bidet |
1-1/4" |
1.0 |
|||
|
Bidet |
1-1/2" |
2.0 |
|||
|
Clothes Washer, Domestic, Standpipe5 |
2" |
3.0 |
3.0 |
3.0 |
|
|
Dental Unit, Cuspidor |
1-1/4" |
1.0 |
1.0 |
||
|
Dishwasher, Domestic, with Independent Drain2 |
1-1/2" |
2.0 |
2.0 |
2.0 |
|
|
Drinking Fountain or Water Cooler |
1-1/4" |
0.5 |
0.5 |
1.0 |
|
|
Food Waste Grinder, Commercial |
2" |
3.0 |
3.0 |
||
|
Floor Drain, Emergency |
2" |
0.0 |
0.0 |
||
|
Floor Drain (for additional sizes see Section 702) |
2" |
2.0 |
2.0 |
2.0 |
|
|
Shower, Single-Head Trap |
2" |
2.0 |
2.0 |
2.0 |
|
|
Multi-Head, Each Additional |
2" |
1.0 |
1.0 |
1.0 |
|
|
Lavatory, Single |
1-1/4" |
1.0 |
1.0 |
1.0 |
|
|
Lavatory, in Sets of Two or Three |
1-1/2" |
2.0 |
2.0 |
2.0 |
|
|
Washfountain |
1-1/2" |
2.0 |
2.0 |
||
|
Washfountain |
2" |
3.0 |
3.0 |
||
|
Mobile Home, Trap |
3" |
12.0 |
|||
|
Receptor, Indirect Waste1,3 |
1-1/2" |
See footnote 1,3 |
|||
|
Receptor, Indirect Waste1,4 |
2" |
See footnote 1,4 |
|||
|
Receptor, Indirect Waste1 |
3" |
See footnote 1 |
|||
|
Sinks |
|||||
|
Bar |
1-1/2" |
1.0 |
|||
|
Bar2 |
1-1/2" |
2.0 |
2.0 |
||
|
Clinical |
3" |
6.0 |
6.0 |
||
|
Commercial with Food Waste2 |
1-1/2" |
3.0 |
3.0 |
||
|
Special Purpose2 |
1-1/2" |
2.0 |
3.0 |
3.0 |
|
|
Special Purpose |
2" |
3.0 |
4.0 |
4.0 |
|
|
Special Purpose |
3" |
6.0 |
6.0 |
||
|
Kitchen, Domestic2 (with or without food waste grinder and/or dishwasher) |
1-1/2" |
2.0 |
2.0 |
||
|
Laundry2 (with or without discharge from a clothes washer) |
1-1/2" |
2.0 |
2.0 |
2.0 |
|
|
Service or Mop Basin |
2" |
3.0 |
3.0 |
||
|
Service or Mop Basin |
3" |
3.0 |
3.0 |
||
|
Service, Flushing Rim |
3" |
6.0 |
6.0 |
||
|
Wash, Each Set of Faucets |
2.0 |
2.0 |
|||
|
Urinal, Integral Trap 1.0 GPF2 |
2" |
2.0 |
2.0 |
2.0 |
|
|
Urinal, Integral Trap Greater than 1.0 GPF |
2" |
2.0 |
2.0 |
2.0 |
|
|
Urinal, Exposed Trap2 |
1-1/2" |
2.0 |
2.0 |
2.0 |
|
|
Water Closet, 1.6 GPF Gravity Tank6 |
3" |
3.0 |
4.0 |
6.0 |
|
|
Water Closet, 1.6 GPF Flushometer Tank6 |
3" |
3.0 |
4.0 |
6.0 |
|
|
Water Closet, 1.6 GPF Flushometer Valve6 |
3" |
3.0 |
4.0 |
6.0 |
|
|
Water Closet, Greater than 1.6 GPF Gravity Tank6 |
3" |
4.0 |
6.0 |
8.0 |
|
|
Water Closet, Greater than 1.6 GPF Flushometer Valve6 |
3" |
4.0 |
6.0 |
8.0 |
|
|
1 Indirect waste receptors shall be sized based on the total drainage capacity of the fixtures that drain therein to, in accordance with Table 7-4. |
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2 Provide a two-inch (51 mm) minimum drain. |
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3 For refrigerators, coffee urns, water stations, and similar low demands. |
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4 For commercial sinks, dishwashers, and similar moderate or heavy demands. |
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5 Buildings having a clothes-washing area with clothes washers in a battery of three or more clothes washers shall be rated at six fixture units each for purposes of sizing common horizontal and vertical drainage piping. |
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6 Water closets shall be computed as six fixture units when determining septic tank sizes based on Appendix K of this code. |
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7 Trap sizes shall not be increased to the point where the fixture discharge may be inadequate to maintain their self-scouring properties. |
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8 Assembly (Public Use (See Table 4-1)). |
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|
Size of Grease Interceptor |
|||
|---|---|---|---|
|
Diameter of Grease Waste Pipe |
Maximum Full Pipe Flow (gpm)2 |
One-Minute Drainage Period (gpm) |
Two-Minute Drainage Period (gpm) |
|
2" |
20 |
20 |
10 |
|
3" |
60 |
75 |
35 |
|
4" |
125 |
150 |
75 |
|
5" |
230 |
250 |
125 |
|
6" |
375 |
500 |
250 |
1For interceptor sizing by fixture capacity see the example below.
2One-quarter-inch (0.250) slope per foot based on Manning’s formula with friction factor N = 0.012.
EXAMPLE FOR SIZING HYDROMECHANICAL INTERCEPTOR(S) USING FIXTURE CAPACITY
Step 1: Determine the flow rate from each fixture.
[Length] X [Width] X [Depth] / [231] = Gallons X [.75 fill factor] / [Drain Period (1 min. or 2 min.)]
Step 2: Calculate the total load from all fixtures that discharge into the interceptor.
|
Size of Grease Interceptor |
||||
|---|---|---|---|---|
|
Fixtures |
Compartments |
Load (gallons) |
One-Minute Drainage Period (gpm) |
Two-Minute Drainage Period (gpm) |
|
Compartment size |
||||
|
24'' x 24'' x 12'' |
2 |
44.9 |
||
|
Hydrant |
3 |
|||
|
Rated Appliance |
2 |
|||
|
Total |
49.9 |
50 |
25 |
|
5. Gravity Grease Interceptor. Where sizing formulas result in determination of an exterior grease interceptor (GGI) less than 750 gallons in capacity, minimum size shall be 750 gallons.
The size of a grease interceptor shall be determined by the following formula:
|
DFUs (1, 3) |
Interceptor Volume (2) |
|---|---|
|
10 |
750 gallons |
|
21 |
750 gallons |
|
35 |
1,000 gallons |
|
90 |
1,250 gallons |
|
172 |
1,500 gallons |
|
216 |
2,000 gallons |
|
307 |
2,500 gallons |
|
342 |
3,000 gallons |
|
428 |
4,000 gallons |
|
576 |
5,000 gallons |
|
720 |
7,500 gallons |
|
2,112 |
10,000 gallons |
|
2,640 |
15,000 gallons |
|
* DFUs are calculated using Uniform Plumbing Code Table 7-3 |
|
|
Notes: |
|
|
(1) |
The maximum allowable DFUs plumbed to the kitchen drain lines that will be connected to the grease interceptor. |
|
(2) |
This size is based on: DFUs, the pipe size from this code; Table 7-5; Useful Tables for Flow in Half-full Pipes (ref: Mohinder Nayyar Piping Handbook, 3rd Edition 1992). Based on 30-minute retention time (ref.: George Tchobanoglous and Metcalf & Eddy. Wastewater Engineering Treatment, Disposal and Reuse, 3rd Ed. 1991 and Ronald Crites and George Tchobanoglous. Small and Decentralized Wastewater Management Systems, 1998). Rounded up to nominal interceptor volume. |
|
(3) |
When the flow rate of directly connected fixture(s) or appliances(s) have no assigned DFU values, the additional grease interceptor volume shall be based on the known flow rate (gpm) multiplied by 30 minutes. |
Additional information and assistance about sizing and installation can be obtained through the building and fire safety department and/or the public works operations/engineering divisions of the city of Gig Harbor.
6. Alternate Sizing Formulas/Proposals. Facilities that propose the use of alternate sizing techniques and/or procedures that result in specifications that differ from calculated requirements (or are less than the minimum 750-gallon requirement) must submit formulas and other bases to the supervisor to support proposed grease interceptor (GGI/HGI) size/installation. Submission should also provide documentation of the generator’s ability to meet effluent quality requirements. The generator’s proposal must be signed by an engineer licensed in the state of Washington. The supervisor shall make the final decision on any installation.
Notable Exceptions: Drains that receive “clear waste” only, such as from ice machines, condensate from coils and drink stations, may be plumbed to the sanitary system without passing through the grease interceptor.
7. Generator/Owner Responsibilities. It is the responsibility of the generator to ensure compliance with the city of Gig Harbor’s discharge limitations.
Hazardous wastes, such as acids, bases, grease emulsifying agents, strong cleaners, pesticides, herbicides, heavy metals, paint, solvents, gasoline or other hydrocarbons shall not be disposed of where they would go through GGIs/HGIs. If commercial dishwashers are discharged through a GGI, care must be taken in system design. Dishwashers use detergents and elevated water temperatures that will melt grease. If the GGI is either too small or too close to the commercial dishwasher, grease may pass through the GGI/HGI and into the collection system. Relocation and upsizing may be required to comply with city discharge requirements. (Dishwashers may not discharge through a hydromechanical grease interceptor (HGI) without the supervisor’s approval as per UPC Section 1014.1.3).
Generators/owners are responsible for maintaining GGIs/HGIs in continuous proper working condition. Further, generators are responsible for inspecting, repairing, replacing, or installing apparatus and equipment as necessary to ensure proper operation and function of GGIs/HGIs and compliance with discharge limitations at all times.
GGIs/HGIs shall be maintained with a minimum frequency as specified in the individual operational permit to ensure proper function. (Maintenance frequency assumes proper sizing and installation consistent with this requirement.) The GGI/HGI shall be maintained more frequently if needed to meet the city’s discharge criteria. If, in cooperation with the supervisor, frequency of cleaning can be extended, without degradation of GGI/HGI effluent, an alternative schedule can be approved. Records of maintenance are required to be maintained on site for three years.
Enzymes, solvents, and emulsifiers are not permitted, as they will only change the form of grease, allowing it to be carried out of the GGI/HGI with the wastewater and deposited in the collection system (POTW). Biological treatment systems must be pre-approved by the supervisor. These systems will not alleviate the necessity for inspection and proper maintenance. (Ord. 1185 § 4, 2010; Ord. 1107 § 7, 2007; Ord. 1087 § 6, 2007).