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Site Requirements, Design Criteria, & Construction Details for Gravelless Septic Systems InspectAPedia®  -

• Design manual for gravelless or no rock septic fields
• No-rock or chamber septic drainfield site requirements

This chapter discusses the site requirements, design criteria, and construction details 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".

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.

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.

Site Requirements & Design Criteria for Gravelless Septic Absorption Systems

Site Requirements: These systems shall be used on sites that have been classified as having a design percolation rate of one to 45 minutes per inch, and meet the vertical and horizontal separation distances in Table 2 (of the New York State Standard - for example) shown in 75-A.4 Soil and site appraisal for Septic Systems.(2)

Chamber systems provided by Infiltrator Inc. (links below) have been approved for use in some states, including New York, at perc rates up to 60 minutes/inch, and in some other states, at percs up to 120 minutes/inch. Approval letters are available from that company.

Design criteria: The local health department having jurisdiction shall be contacted prior to construction regarding the acceptability of specific products for use as a gravelless distribution system. (3)

As we described above when discussing Geotextile-Wrapped Perforated Pipe systems for onsite wastewater treatment and disposal, the total lot area in square feet which is required for a given alternative treatment system will vary not only depending on the anticipated daily flow, flow rates, soil and site conditions, but also on what spacing requirements the local or state code officials will require.

Construction of gravelless septic absorption systems

Gravelless distribution systems shall be installed in conformance with the manufacturer's instructions because of the proprietary design of some products.(4) The length, width, and depth of the required excavation will vary by individual product.

The essential difference between a gravelless wastewater treatment system and a conventional perforated-pipe and gravel-trench drainfield is the use of a special product to distribute and release effluent (sketches above) and the absence of gravel in the trench where the distribution system is buried.

The special gravelless products used are designed to avoid soil-clogging right at their surface or they would have a short life. This concern is addressed by use of special materials (such as geotextiles) which resist soil clogging, and by a design that provides an adequate total area in square feet for soil contact.

Each product manufacturer should be expected to provide an installation manual for the product that you are going to use. The list below is generic and incomplete as site specific and product specific details can't be provided here.

• Perform a site survey to determine the size, layout, and materials needed. The manufacturer 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. (Tables of field sizing and soil percolation test procedures are provided at this website).
• Obtain local building code or board of health requirements
• As with any wastewater disposal field, never drive equipment in or over the trenches. Compacting the soil (or after installation, damaging the drainage components) will reduce the absorption system capacity or may destroy it completely.
  
  Some systems such as Infiltrator Inc. chambers, have been tested to meet an H-10 engineering rating (16,000 lbs / axle), so occasionally if a system built using some chamber products are driven over it won't necessarily be an issue. But Infiltrator Inc. 's technical experts do not recommend constant vehicle traffic over anything but their heavier duty H-20 chambers.
  
  These disclaimers notwithstanding, it remains a better practice to keep all traffic off of septic fields. And even where septic equipment has been described as rated for vehicle traffic, heavy equipment traffic can cause some surprising collapses that can be costly to repair as shown in this photo.
• Some sites may need a curtain drain or other special measures to redirect surface or subsurface runoff away from the effluent/wastewater absorption area.

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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
• Daniel Friedman - principal author/editor of the InspectAPedia ^TM Website

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 SEPTIC 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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