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Gravel less effluent disposal septic system - image of the gravelless chamber system design is courtesy US EPA, originally from National Small Flows ClearinghouseChamber type Gravelless Septic System Designs

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Chamber type no-rock septic drainfield design:

What does a chamber system septic design look-like? What are its properties?

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

Gravel less effluent disposal septic system - Chamber system - image courtesy US EPA, originally from National Small Flows Clearinghouse

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.

3. Chamber septic systems, using pre-formed plastic chambers (shown just above) 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.

Consultants or supplies in this field can be listed at our alternative septic designers page at no charge by contacting me.

 

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: explain "stub out" and “ 34 Arc 24’s 510ft^2. Drainfield" on my septic plans

Infiltrator Systems' Arc 24 no-rock chamber system septic product - cited & discussed at InspectApedia.com

2021/03/17 Jon said:

On my engineered plans it says “ stub out no lower then 99.96’ What does that mean because I’m sure doesn’t mean 99.96 feet underground.

On my engineered plans it says

34 Arc 24’s 510ft^2. Drainfield.

What is this?

Moderator reply:

@Jon, your septic engineer is calling for installation of a "no-rock" or "gravelless" septic drainfield installation - the drainfield is the part of your septic system that disposes of clarified septic effluent by allowing it to leach into the soil where bacterial action processes its pathogens.

The Arc 24 Chamber is a "no-rock" septic product (no rocks or gravel are required in the drainfield trenches) produced by Infiltrator Systems, as we illustrate below. Infiltrator Systems, Inc.provides chamber products

The 510ft^2 is perhaps telling us that the total square feet of drainfield area [or length?] is to be 510 square feet. (though I could not add up the data to amount to either square feet nor total trench length).

And I am guessing that the "34" is the number of 24s sections that will be needed - each Infiltrator Arc 24 section is 22"W x 63"L x 12"H and gives you 7.96 sq ft of leaching area. (Unless your engineer knows of a larger variant of this product.)

But frankly I can't make the numbers add-up. If 34 is the quantity, and as the Arc 24 gives you just under 8 sq.ft. then that would give us 8 x 34 = 272 square feet of area, not 510 sq.ft.

So it makes sense to ask your septic engineer to translate her septic design specifications into lay-person English. Please let me know what you're told as we'll both learn something useful.

---

The statement

stub out no lower then 99.96’

is greek to me, too. I wonder if there was a typo in the plan.

In general "stub out" would probably mean that the builder or plumber installs an initial sewage effluent line or sewer line to the tank and thence to the drainfield area. When the gravelless trenches are installed and connected (via a D-box) they'd be connected to a stub that was instaleld previously.

You can read more about no-rock septics that use a chamber like yours at GRAVELLESS SEPTIC CHAMBER SYSTEMS inspectapedia.com/septic/Gravelless_Septic_Chamber_Systems.php

And you'll find a "cutsheet" giving the specifications for your Infiltrator Arc-24 chambers under our listing for Infiltrator Systems
at

GRAVELLESS NO-ROCK SEPTIC SUPPLIERS

Including these references:

Separately

at GRAVELESS SEPTIC DESIGN CRITERIA you will find the actual design specifications and installation guides for Infiltrator Systems' Arc 24 and other similar products.

This Q&A were posted originally

at SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR FAQs

Question: Chamber Septic Feet to Equivalent Conventional Septic Drainfield Trench?

2019/02/11 Steve Haldeman said:

How many feet of sewer pipe does 1 24x48 chamber equal. Like 1 chamber or 10/20/30feet of sewer pipe? do you use a big chamber for a septic tank?

Reply:

Take a look at GRAVELESS SEPTIC DESIGN CRITERIA

There you'll see that the equivalent feet of perforated rain line (conventional leach field drain trench) for a chamber system varies by manufacturer's specific product and its specifications.

For each specific septic chamber system product and plastic pipe or chamber diameter, the manufacturer will indicate the disposal area provided by the product (per linear foot, for example).

But your engineer and installer need to evaluate your soils and daily wastewater usage to determine the amount of leaching area needed for your site.

Also the equivalent area of conventional field (or length) will depend on the gravel-less pipe size.

Here is an example of equivalent drainfield size to gravelless size from Crumpler Plastic Pipe

The 8” size pipe will equal to 2-foot wide conventional trench; and the 10” size will equal a 2.5-foot wide trench. To determine the required linear footage of either pipe size, first determine the square footage by dividing the design sewage flow by the appropriate soil’s long term application rate. Then divide this total square footage area figure by either 2 feet (for 8”) or 2.5 feet (for 10”) to establish the linear footage amount.

- Source: CPP’S No-Rock ™ Fabric Wrapped Septic Pipe [PDF] (2019) Crumpler Plastic Pipe, .O. Box 2068, Highway 24 West, Roseboro, NC 28382 USA, Tel: 1-800-334-5071
Email: cppsales@cpp-pipe.com retrieved 2019/02/11 original source: www.cpp-pipe.com/no_rock.html


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