Chapter 7.30


7.30.010    General.

7.30.020    Vault.

7.30.030    Construction.

7.30.010 General.

Whenever a commercial and/or retail food preparation operation, regardless of size, generates animal/vegetable fats, oils or grease (FOG) waste, which causes a visible sheen or accumulations in the effluent, to be discharged to the sanitary sewer, pretreatment is required. A grease interception device, if required, shall be installed by the property owner as specified herein. Selection and sizing of the grease interceptor shall be subject to the approval of the district. Effluent discharged from any grease interceptor shall not contain a visible sheen or accumulations of FOG, and shall be in compliance with Cross Valley Water District and King County/Metro regulations for discharge to the sanitary sewer.

(1) Before a grease interceptor is installed, the property owner shall submit all plans to Cross Valley Water District for review and approval. The property owner will need a letter approving the design and allowing discharge of wastewater from the properly installed tank. When submitting plans, include the following information:

(a) Name and address of the facility, and the phone number and mailing address of the person legally responsible for operation and maintenance.

(b) Drawing of the grease interceptor with capacities and dimensions. See standard details.

(c) Site map detailing all drains and the interceptor location.

(d) Location of the water sources and maximum water flows (in gallons per minute) from all potential service areas and equipment discharging to the grease interceptor.

(2) Size and design of the grease interceptor shall conform to the Uniform Plumbing Code, Appendix H, Standards, and shall be subject to approval by the district. Minimum capacity shall be 600 gallons and the minimum criteria for sizing shall be as follows:

Interceptor Capacity (gallons)


Waste Flow Rate × Retention Time × Storage Factor

Waste Flow Rate (GPM)


Provided by developer, with approved supporting documentation

Retention Time


150 minutes minimum

Storage Factor


1 for 8-hour operation



2 for 16-hour operation



3 for 24-hour operation

(3) Fixtures in the kitchen area which discharge wastewater containing grease are to be connected to the grease interceptor. Such fixtures include, but may not be limited to, dishwashers, pot sinks, range woks, janitor’s sinks, floor sinks, and rotoclones. Toilets, urinals, and wash basins shall not flow through the interceptor.

(4) The interceptor shall be located outside the building within 20 feet of drive for access by maintenance vehicles.

(5) The interceptor shall be filled with clean water prior to startup of system.

(6) Allowable materials for construction are as follows:

(a) Tank: concrete.

(b) Baffles: concrete, plastic.

(7) Access to the interceptor shall be maintained free for inspection and compliance determination sampling at all times.

(8) When pretreatment is no longer required, the inlet and outlet pipes shall be permanently plugged, the separation chambers pumped out, and the vault removed, or filled with compacted crushed rock or controlled density fill. [Res. 2015-6-1.]

7.30.020 Vault.

Grease interceptor vaults shall be of precast concrete construction. Cement concrete shall have a minimum 28-day compressive strength of 4,500 psi.

Deformed bars for steel reinforcement shall be in accordance with ASTM A615, grade 60. Welded-wire fabric reinforcement shall be in accordance with ASTM A185, grade 65. All interior piping shall be PVC sized to match side sewer line size.

Interior baffle shall be precast reinforced concrete, four inches thick. Concrete baffle shall be secured in place by slotted vault walls or with stainless steel angles as shown in the standard detail.

Vault cover shall include 24-inch-diameter bolt-locking manhole covers and frames located over inspection tees. Manhole covers shall not allow passage of air or gases. Vault cover shall be designed for AASHTO H-20 load with 30 percent impact factor. See the standard details for vault sizes and miscellaneous details. [Res. 2015-6-1.]

7.30.030 Construction.

Grease interceptors shall be constructed as shown in the standard details. Excavation for precast vault shall be sufficient to provide a minimum of 12 inches between the vault and the side of the excavation.

Twenty-four-inch-diameter manhole frame and cover shall be adjusted to the elevation required by the engineer prior to final acceptance of the work. Adjusting rings shall be manufactured from precast reinforced concrete. Total height of rings shall be from eight inches minimum to 20 inches maximum.

The grease interceptor shall be placed on firm soil. If the foundation material is inadequate, the contractor shall use foundation gravel or bedding concrete under the normal base to support the interceptor.

Vault shall be placed and set plumb so as to provide vertical sides. The completed interceptor shall be rigid and watertight.

The outside and inside of manhole adjusting rings, joints of precast concrete sections and the perimeter of precast baffle shall be thoroughly wetted and completely filled with mortar, plastered and troweled smooth with three-quarters inch of mortar in order to attain a watertight surface.

All lift holes, if any, on precast items shall be completely filled with expanding mortar, smoothed both inside and out, to ensure watertightness. All steel loops, if any, on precast section must be removed flush with the vault wall.

The stubs shall be covered with mortar and smoothed. Rough, uneven surfaces will not be permitted.

Precast vault and baffle shall be provided with eight-inch-diameter knockouts at all pipe openings or have openings core-drilled prior to installation.

All rigid pipe entering or leaving the structure shall be provided with flexible joints within 12 inches of the manhole structure and shall be placed on firmly compacted bedding. Special care shall be taken to see that the openings through which pipes enter the structure are completely and firmly filled with mortar from the outside to ensure water-tightness. All PVC pipe connections to vault and baffle shall be made with gasketed coupling as approved by the district. [Res. 2015-6-1.]