Gravel less effluent disposal septic system - image of the gravelless chamber system design is courtesy US EPA, originally from National Small Flows Clearinghouse

Chamber type Gravelless Septic System Designs

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Chamber type no-rock septic drainfield design: This article discusses the properties & installation of a chamber type gravelless or "no gravel" or "no rock" septic drainfield systems, offering installation specifications. Drainfields, also called leach fields, absorption beds, soil absorption systems, and leaching beds, perform the functions of septic effluent treatment and disposal in onsite wastewater treatment systems, conventionally called "septic systems"

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Design & Installation of No-Gravel Chamber Systems for Wastewater Treatment and Disposal

Gravelless septic systems or "no gravel" septic system trenches use plastic or other prefabricated wastewater distribution systems which are buried in soil without the use of surrounding gravel.

Gravelless Systems - Gravelless Septic Absorption Systems

There are three typical gravel-less effluent disposal systems in current use and shown in the US EPA sketches below (originally from NSFC) and I describe a fourth variation which is provided by some manufacturers:

This article describes the third type, chamber septic systems for effluent disposal.

Typical gravelless septic systems use a plastic chamber, a geotextile-wrapped pipe, or a polystyrene-wrapped pipe to distribute effluent into the soil. The necessary soil absorption area is provided by the perforated surface of the gravelless septic system components (or by soil at the bottom of a chamber) themselves rather than by the gravel and trench walls of a conventional septic drainfield.

Gravelless or "no rock" septic systems can provide an acceptable effluent disposal system for sites with limited space for a drainfield or where gravel is not available or is quite expensive.

Gravel less effluent disposal septic system - Chamber system - image courtesy US EPA, originally from National Small Flows Clearinghouse3. Chamber systems, using pre-formed plastic chambers buried in an earthen trench. Wastewater is delivered to the top of the chamber by a solid plastic pipe. Effluent seeps into soil across the bottom of the chamber.

The empty chamber also provides effluent storage volume to handle peak wastewater flow loads.

Chambers are available in widths varying from 16" across (at the bottom) to 34" wide and are placed in trenches ranging in width from 18" to 36".

Synonyms for this design include "leaching chambers", "galleys", and "flow diffusers". Illustration courtesy of Infiltrator Systems, Inc., used with permission. (Infiltrator Systems Inc. contact information is listed below).

Use of Vertical Thin Wall Chambers for Wastewater Treatment and Disposal

4. Vertical thin wall chambers: A fourth variation on gravelless effluent disposal systems is similar to the chamber system (#3 above), but uses pre-formed but thin plastic "chambers" which are inserted into a narrow slot cut into the soil; these systems diffuse effluent primarily through their sides into the soil.

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