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Gravelless Septic Systems - Geotextile-Wrapped Designs InspectAPedia®  -

• Design manual for gravelless or no rock septic fields
• No-rock or chamber septic drainfield product descriptions, sources
• Septic leaching field product cost comparisons
• Septic absorption field capacity & life comparisons
• Septic Systems - Design, Inspection, Testing, & Maintenance

This chapter discusses determination of a 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".

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. 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. These 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.

Advanced septic treatment methods are discussed in separate chapters. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at "References." This document is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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:

Here we describe the second type - Geotextile-wrapped designs.

Use of Geotextile-Wrapped Perforated Pipe for Onsite Wastewater Treatment and Disposal

CPP informs us that because the square foot equivalent leaching area when this system is used is not a foot-for-foot ratio based on a 36" trench, the 8" & 10" CPP Filter Wrapped systems are typically longer than the traditional septic drainfield trenches. Although the individual line length may be longer, the CPP system may actually require less total square footage of lot space if the on-center line spacing is controlled by the excavated trench width treatment plume & not an "arbitrary CODE stipulation".

According to CPP, this added length achieves superior distribution to the trench sidewall where the bulk of the septic liquid enters the soil for treatment. [One reason for wider trench on-center spacing advanced by some health departments is to assure that the site affords space for future trench line replacement .--DF].

Most sanitary or health department codes size 8" diameter Geotextile-Wrapped Perforated Pipe to equal a 2 Foot wide conventional septic drainfield trench, and similarly size 10" diameter Geotextile-Wrapped Perforated Pipe to be equal to a 2.5 foot wide conventional drainfield trench.

In determining how much leach field area shall be provided when using Geotextile-Wrapped Perforated Pipe, most state codes (where they have them) will require that the cubic footage that would have been required if a conventional 3-foot wide conventional perforated pipe & gravel leach field system had been installed will be used to determine the size 2 Foot or 2.5 Foot wide gravelless systems as well. Thus if 100 feet of a conventional gravel system in 3 Foot wide trenches is required for one bedroom (or 300 Cubic Ft), then 150 feet of 8" Geotextile-Wrapped Perforated Pipe will be required or 120 feet of 10" diameter Geotextile-Wrapped Perforated Pipe. Sketch of geotextile-wrapped pipe in plan view, courtesy of Crumpler Plastic Pipe - CPP - links below.

For OC (On-Center) spacing of parallel lines treating sewage from a 2 bedroom home, a conventional gravel system of 100 foot length would require 1200 square feet of lot surface area if 3 times the actual 'excavated' trench width is used for OC separation. In comparison, for an 8" Geotextile-Wrapped Perforated Pipe system, which can be placed in a 1.5 Ft(18") wide trench, 1,125 square feet of lot surface area would be required. For a 10" diameter Geotextile-Wrapped Perforated Pipe, which can be placed in a 1.5 Ft (18") wide trench, 900 square feet of lot space is needed.

If a different or as CPP puts it "arbitrary" OC trench width spacing is mandated (ie: 5 ft or 7 Ft OC required regardless of 'excavated' trench width) by a state code, then the lot surface area calculations will of course be different. [Thanks again to Crumpler Plastic Pipe, Inc. for this added detail. Links to this company's website and products are provided below.]

What all this means is that for a given building usage and set of soil conditions, whether or not the Geotextile-Wrapped Perforated Pipe system is going to provide the necessary effluent handling capacity in a smaller total square feet than a conventional drain field would require depends on the on-center spacing requirements set by the local authorities.

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• Additional technical contributors & reference sources for this article are listed below.
• Crumpler Plastic Pipe, Inc. Crumpler provides fabric-wrapped drainage piping 800-334-5071 Roseboro NC USA - "No-Rock TM Septic-Leachate drainpipe systems" are available in 8" and 10" systems.
• Jeff Pildis, Technical Service & Support, Infiltrator Systems, Inc. 800-718-2754
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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

SEPTIC DESIGN ALTERNATIVES
  AEROBIC SEPTIC SYSTEMS
  ALTERNATING BED SEPTIC SYSTEMS
  CESSPOOLS
  DRYWELLS
  SEPTIC EFFLUENT DISINFECTION SYSTEMS
  EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS
  FIXED-FILM PROCESS SEPTIC SYSTEMS

  GRAVELLESS SYSTEMS
  Polystyrene-wrapped perforated pipe
  Geotextile-Wrapped Perforated Pipe
  Chamber Systems
  Site Requirements / Design Criteria
  Construction Details
  Life Expectancy of No Rock Septic Designs
  Installation Cost of No Rock Septics
  Gravelless Septic Product Sources

  LAGOON SEPTIC SYSTEMS
  MEDIA FILTER SEPTIC SYSTEMS
  SEPTIC & GREYWATER FILTERS
  SEQUENCING BATCH SEPTIC SYSTEMS
  MOUND SEPTIC SYSTEMS
  RAISED BED SEPTIC SYSTEMS
  SAND BED SEPTIC SYSTEMS
  SEWAGE TREATMENT SYSTEMS
  TOILET ALTERNATIVES
  VEGETATED SUBMERGED SEPTIC BEDS
  WETLAND SEPTIC SYSTEMS
  ALTERNATIVE SEPTIC DESIGNERS
  ALTERNATIVE SEPTIC PRODUCTS

More Reading:

SEPTIC SYSTEM DESIGN BASICS
How Big Should the Leach Field Be? includes a practical example using sample calculations and a table of soil percolation rate vs. field size
Design Basics for Septic Systems: Choosing Septic Tank Size, Leach Field Size - basic septic system volume and absorption system design guides.
Components of a Septic System- the Basic Parts of a Conventional Septic Tank and Leachfield, a chapter in the Home Buyers Guide to Septic Systems
Sketches of the Septic System Components Private Sewage Disposal Systems - Septic Drawing Library
Cesspools for more in-depth information about those systems.
Drywells for more in-depth information about those systems.]
SEPTIC SYSTEM DESIGN ALTERNATIVES
(1) (2) (3) (4) APPENDIX 75-A to Public Health Law, 201(1)(1) NEW YORK STATE WASTEWATER TREATMENT STANDARDS - INDIVIDUAL HOUSEHOLD SEPTIC SYSTEMS. Portions of the text of this web page (using paragraphs identified by parenthetical numbers (1)-(4)) are quoted from this document, expanded with edits and additions by this author
"Gravelless Drainfields, Recommended Standards and Guidance for Performance, Application, Design and Operation & Maintenance", Washington State Department of Health, an MS Word .doc file available at: www.doh.wa.gov/ehp/ts/WW/Gravelless2004.doc

More Information on Building Diagnostic Inspections and Repairs

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include

• Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
• Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
• Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)

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