What is a Shallow Buried Trench (SBT) leaching bed?

An SBT is a pressurized, time-dosed leaching bed installed at shallow depth to distribute effluent evenly and encourage aerobic polishing before percolation. It can be installed in native soils or approved leaching bed fill where OBC Part 8 requirements are met.

When is SBT preferred over a conventional bed?

SBT is often preferred on constrained lots, sites with variable soils, or where controlled dosing and uniform distribution are desired. Conventional beds can be suitable on simple sites with good native soils and space, while raised/mounded beds are common with high groundwater, shallow bedrock or poor drainage.

Does SBT require leaching bed fill?

Leaching bed fill is not always required, but can be used when it meets OBC percolation criteria. Designers may choose well-graded fill to enhance polishing and lateral movement before effluent enters the underlying soil.

Shallow Buried Trench (SBT) Leaching Beds | Design, Time Dosing & Pressurized Distribution

Alpha Ex | Shallow Buried Trench (SBT) Leaching Beds

Shallow Buried Trench (SBT) leaching beds use pressurized distribution and time dosing to load trenches evenly at shallow depth, where oxygen supports aerobic polishing. Under OBC Part 8, SBT can be installed in native soils or approved leaching bed fill when percolation and setbacks are met. The result is a compact, predictable bed that protects groundwater while fitting challenging lots.

Need help deciding if SBT is right for your site?

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What Is a Shallow Buried Trench Leaching Bed?

SBT is an engineered bed that distributes effluent under low pressure through small orifices along each lateral. Time dosing meters flow so the soil absorbs consistent, repeatable volumes, reducing local overloading. The shallow placement keeps the infiltrative surface in a higher-oxygen zone to support aerobic treatment before effluent moves to underlying soil.

Key Properties of SBT Leaching Beds

Pressurized distribution: even loading across the bed; fewer “hot spots.”
Time dosing: controls dose volume/interval for predictable soil acceptance.
Shallow placement: more oxygen for polishing; improved biomat management.
Leaching bed fill: OBC allows fill when it meets percolation requirements. Industry practice often targets T in the ~5–10 range for polishing where appropriate for the design.
Compact footprint: efficient use of constrained or environmentally sensitive sites.

Installation in Soil or Leaching Bed Fill

SBT may be installed in native soils or in leaching bed fill that satisfies OBC percolation criteria (1 < T ≤ 125 for the design scenario). Using a well-graded fill layer can increase polishing and lateral movement before percolation into the underlying native soil—especially valuable on lots with variable native horizons.

Because SBT uses pressure and dosing, it does not rely on a long downstream sand mantle the way some gravity systems do. Instead, design focuses on distribution uniformity, trench sizing, orifice/nozzle hydraulics, and dosing frequency to match the site’s acceptance rate.

Advanced treatment with time dosing feeding a Shallow Buried Trench leaching bed — Advanced treatment + time dosing feeding a shallow buried trench leaching bed.

SBT vs Conventional vs Raised/Mounded Beds

Aspect	SBT (Pressurized)	Conventional (Gravity)	Raised/Mounded
Distribution	Pressurized, even dosing by timer	Variable; follows slope/grade	Can be pressurized or gravity
Oxygen Environment	Shallow; aerobic polishing encouraged	Depth varies; less oxygen as depth increases	Raised; oxygen maintained above native grade
Footprint	Compact for many sites	Larger area	Larger visible profile (mound)
When Preferable	Constrained lots, variable soils	Good soils and space	High water table or shallow bedrock
Design Focus	Dose volume, trench spacing, headloss	Grading, distribution spacing	Fill quality, height, separation

Final selection depends on soil testing, setbacks, groundwater, and lot constraints under OBC Part 8.

Why Choose Alpha Ex for SBT Design & Installation

We design and build systems that meet code and perform in the real world. Our team sizes SBT components based on percolation and hydraulics, coordinates permits/inspections, and stages construction to protect soils during access and backfilling. Where SBT isn’t the best fit, we’ll recommend conventional or raised alternatives with clear trade-offs.

Examples of Our SBT Installations

Shallow buried trench septic bed and advanced treatment technology provide a permanent solution for an urban septic bed - Burlington
Advanced septic treatment with time-dosing and a shallow buried trench leaching bed produces the smallest possible septic bed – Norweco - Burlington
Shallow buried trench septic leaching beds may be installed in imported sand when the native soil is not ideal – Norweco - Burlington
Shallow buried trench septic leaching beds should have an inspection port at the end of each run for flushing and to verify pressure – Waterloo Biofilter - Burlington
A shallow buried trench septic bed offers good layout flexibility and a small footprint – Waterloo Biofilter - Burlington
This urban shallow buried trench leaching bed utilized different lengths of absorption trench, using an alternative solution under the OBC - Burlington
The clearance from a leaching bed distribution line to a structure must be 5 meters as per the OBC – Waterloo Biofilter - Dundas