Grease Interceptors

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Customized Septic Tanks

Precast Concrete Grease Interceptors

A.J. Foss precast concrete grease interceptors (also commonly referred to as grease traps) are designed to remove grease from the waste stream before water is discharged into a septic system. A grease interceptor/trap is a septic tank customized to settle the water and grease, enabling the water to cool down before it is released into a leach field.

Precast concrete grease interceptors have several advantages over other types of grease removal systems and competing materials.

Advantages of Precast Concrete Grease Separators

Strength: The strength of precast concrete gradually increases over time. The load-carrying capacity of precast concrete is derived from its own structural qualities and does not rely on the strength or quality of the surrounding backfill materials. Also, precast concrete grease interceptors can easily support heavy vehicular loads typically found near food service establishments, allowing for convenient placement under parking lots.

Quality: Since precast concrete products are manufactured in a controlled plant environment, they exhibit high quality and uniformity. Installed with high-quality sealants, precast concrete provides a superior, watertight solution.

Easy to Maintain: With the addition of a monitoring system, information such as oil and solid levels, liquid levels and temperature can be recorded, allowing for development of an optimized maintenance schedule. Monitoring systems can be installed and tested in a controlled plant environment, which adds to overall project cost savings.

Buoyancy Resistance: With a specific gravity of 2.40, precast concrete products resist the buoyant forces associated with underground construction. In comparison, fiberglass has a specific gravity of 1.86 and high-density polyethylene (HDPE) has a specific gravity of 0.97.

Environmentally Friendly: Precast concrete is non-toxic, environmentally safe and made from all-natural materials, making it an ideal material for underground use. Concrete has no proven ill effects on groundwater and surface water quality. Specially-designed sealants and rubber gaskets ensure that all pollutants are contained within the interceptor.

The A.J. Foss team can manufacture any precast concrete grease interceptor as traffic or non-traffic rated, depending on your needs and application.

Traffic-Rated Grease Interceptors

Often a precast concrete septic tank or grease interceptor must be installed below a vehicular traffic area, requiring an H-20 or HS-20 traffic-rated loading. A.J. Foss manufactures precast concrete septic tanks, grease interceptors and oil-water separators designed to handle H-20 and HS-20 loading.

Each traffic-rated precast concrete tank is manufactured with our high-quality 5,000 psi concrete using Type III cement, as well as thicker side walls, bottom and top slabs to meet loading requirements.

For each traffic-rated precast concrete tank that A.J. Foss builds, we provide our clients with a diagram and documentation of the tank’s design and testing to verify that the structure can withstand HS-20 loading. This assures clients that our precast concrete tanks are designed and built to exact specifications, using the proper rebar size, grade, lengths, bends, and placement to ensure successful performance.

About Traffic-Rated H-20 and HS-20 Loading

Septic tanks designed to handle traffic-rated loads have thicker side walls and bottom and top slabs, and require specialized equipment to handle their additional weight.

H-20 Loading is defined by the American Association of Highway and Transportation Officials (AASHTO) as a vehicle load with an 8,000 pound front axle and one rear axle weighing 32,000 pounds representing a 16,000 pound wheel load.

HS-20 loading is defined as a vehicle load with an 8,000 pound front axle and two rear axles weighing 32,000 pounds each representing two 16,000 pound wheel loads.

Delivering More than Products

Our team believes in providing clients with detailed information about the design, installation and care of our A.J. Foss-crafted precast concrete septic tank systems.

With every delivery, we supply clients with a colored folder that includes:

  • A diagram of their new precast concrete septic tank, including the size, structural load design (H-10, H-15, H-20, or HS-20) and the access-cover size and its location on the tank. These details are important for the long term, so if the tank ever needs to be pumped out or if a pump inside the tank ever fails, that information will help to streamline servicing and maintenance.
  • A Septic Smart brochure - A homeowner’s guide to use and care of their septic system.
  • Information about the benefits of concrete, and our A.J. Foss contact information for reference.

Clients can also be assured that we maintain internal records for each size of traffic-rated tank that we sell, including in-depth drawings that detail rebar placement, calculated stress loads, and more.


Contact us to discuss your projects throughout New Hampshire, Maine and northern Massachusetts that require precast concrete septic tanks, custom tanks and cisterns, and discover the A.J. Foss difference for yourself.

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