Life expectancy of gravelless septic designs: this article explains the typical life expectancy and typical installation cost of a gravelless or "no gravel" or "no rock" septic drainfield system.

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.

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."

Life Expectancy of Gravelless Septic Systems

To date we have not received study data comparing the life expectancy of a conventional gravel trench drain field with that of a gravelless drainfield in equivalent soils and usage rates.

In either type of absorption system ultimately the biomat and soils around the absorption system trench become clogged, the rate of clogging depending on usage, soil characteristics, maintenance of the septic tank (frequent pumping extends drain field life), and what is put into the wastewater (salts, grease, other products reduce drainfield life).

Ultimately the capacity of the absorption system is a function of the area of soil being used to dispose of effluent around the effluent distribution system (trench width and depth, and surface area exposed to effluent).

OPINION: I would expect that for two alternative below-ground effluent disposal system designs such as a gravel trench or a chamber system, if installed in the same soils and at identical original capacity, there will be no difference in the length of the service life of the installation.

There may be differing costs, however, in subsequent system repair or replacement. For example, does the failed system need to be excavated and removed in one case but not another?

Installation Cost for Gravelless Septic Systems

The primary waste line, septic tank, and distribution piping costs are unaffected by the use of these septic effluent absorption system alternatives, except that some of the choices such as the chamber system are asserted (by Infiltrator Systems Inc.) to use fewer linear feet of material in the absorption field (about half) - a factor that must be taken into consideration in pricing the installation cost.

The trenches may need to be wider or in some instances deeper, however - which will affect the excavation cost.

Some writers suggest that even if a manufacturer claims that you can use less trench length with a no-gravel system you should instead opt for the larger capacity (and probably longer life) provided by not skimping on total trench lengths. However, for a small site with limited space for an absorption field, the added capacity of a gravelless system may be a solution.

Consumers expecting to save in the installation cost of their drainfield by using a no-gravel or "gravelless" septic effluent disposal system should compare all of the costs involved. The savings in gravel and possibly excavation cost (shorter trenches) needs to be weighed against the added cost for the special products (described above) to distribute the septic effluent to the soil.

OPINION: I expect that in all cases the excavation cost is going to dominate the absorption system total cost. It is possible that option 4 described above will have the smallest excavation cost because it can be installed in a very narrow trench, perhaps cut with a smaller specialized machine such as is used for running buried wires and pipes.

We are polling manufacturers for installation costs for gravel-less drainfield alternatives and will post that data here as it becomes available.

Keep in mind that cost comparisons among onsite wastewater handling systems can be specious. It makes little sense to compare the costs of two different systems when only one of them would actually work at a given site. Therefore I advise that you first determine what your site requires because of its soil, space, and so on. Then you can compare alternatives that would work on that site.

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

Question: would wrong trench depth explain the early failure of our EZflow septic system?

2018/09/06 Trent said:

I have 1000 gallon system, distribution box, and three 90' drain field lines (EZflow material). The system was installed in a new house in July 2013. The original county permit required an average trench depth of 12-14", with 12" of required fill.

The water table depth is 36". The drain field has completely failed and is at an advanced state of deteriorated capacity.

We first noticed problems (during heavy rains) 18 months after we moved in and the problem has worsened to the point of the system failing to work for days on end.

I have received two very different opinions from two different septic installers (including the original installer from five years ago).

An assessment of the drain field trenches reveals that the three trenches range in depth from 20" (at the d-box) to 30" + at the end of the 90' runs.

The original installer told me that the trenches are, in fact, 12-14" deep in the original soil (thus, still the required 24" above the water table) and that additional fill dirt was brought in to bring up the elevation of the lot (to avoid a long mound in the front yard).

He states that this is not a problem from a liability perspective because the trenches are only 12-14" below the original soil line (not the finished elevation).

A second installer has told me that the system was installed incorrectly and that the 12-14" trench depth should be, in essence, below the finished grade).

As evidence, he cites that a new county permit is calling for the same size and pattern of drain field installed over the existing field with 12-14" trenches (due to a water table of 36"). My question is basic, but it has to do with interpreting the permit. If a 12-14" trench depth is required by permit, how deep should the drain field trenches be?

Technically, should they be 12-14" below the finished grade or is the observed 20-30+" trench depth technically acceptable since the top foot or so of soil was brought in as back fill to level out the lot?

The second installer has told me that the water table would no longer be at 36" if 12-18" of fill was brought in to cover the entire lot.

Bottom line is that I have a completely failed septic system, but I am trying to determine whether if the current trench depths are in opposition to the county permit of 12-14" or the extra deep fill is allowable and it is just bad luck. Thank you.

This Q&A were posted originally

at SEPTIC DRAINFIELD SIZE

Reply: common causes of gravelless or chamber-type septic drainfield failure

Thanks for the question, Trent.

Watch out: My most-important comment is that it will not be useful to permit a circle of people to stand around arm-waving, gesticulating, or blaming one another for conditions that are buried and thus can't be seen.

Before undertaking a repair or replacement of the EZflow system you need an accurate diagnosis of what went wrong. Otherwise we're just pouring money uselessly into the ground.

Generally we want the very bottom of a drainfield trench to be at least 24" above the seasonal high water table just as you cited.

And yes the soil cover over the gravelless EZflow chamber system made by Infiltrator Systems needs to be no less than 12" of compacted fill, as I'll detail below.

Of course if somebody fudged on the site data that could mean that seasonally the groundwater is in the septic field, thus preventing it from working.

But in my OPINION the issues, the EZflow failure problem you described is more-likely not due the absolute trench depth - the focus of your question - but rather one or more of the following:

1. Is the seasonal high water table flooding
   
   the trenches
2. Were the trenches improperly installed
   
   such as without proper slope? (EZflow specifies a slope of level to 3" in 100 ft.)
   
   Were the trenches spaced apart with sufficient horizontal distance for your soil properties and site?
   
   Were trench bottoms or sides smeared or compacted such that the soil would resist percolation?
3. Was the backfill cover of adequate depth.
   
   The company recommends 12" of compacted cover over the EZflow chamber trenches and sets a maximum cover thickness of 96". In a bed system the maximum cover depth is 48".
4. Followed specifications?
   
   Were the Infiltrator Water Technology EZ-Flow drainfield lines installed according to the manufacturer's detailed specifications?
   
   For example, if the EZFlow drainfield lines were simply installed upside down that would result in a rapid failure of the system - putting the geotextile soil screen down rather than up.
   
   By excavating at a problem or wet spot you can also check to determine whether or not the chamber lengths were properly connected together.
5. Was sufficient total length of EZflow gravelless drainfield material installed
   
   to accommodate both your building's maximum daily wastewater inflow and in considering the percolation or absorption rate of the soil where the field was placed?
   
   The company literature FAQs (source cited below) include this statement:
   
   System sizing is determined by each local health department. Typically, health departments have approved sizing reductions of 25 to 50 percent when Infiltrator chambers are specified. Check your local health codes for the specifics in your area.
   
   

   The image shown above is from EZflow NO-ROCK DRAINFIELD SPECIFICATIONS [PDF] where you can also read the limited warranty (one year for structural failure), retrieved 2018/09/08, original source: t www.infiltratorsystems.com/images/pdf/CutSheets/EZ01.pdf

   Notice in the EZflow illustration shown here that the surrounding soil looks very sandy. Sandy soils have a great percolation rate.

   If your drainfield was installed in soil with a poor percolation rate - such as dense clay -the system would either have a short life and early failure OR it would have needed a correspondingly larger area to support your designed daily wastewater inflow.

   Also see SEPTIC DRAINFIELD SIZE - table of soil percolation rate vs. generic septic drain field size
6. Was the drainfield damaged
   
   during or after installation? Did some dope drive over the septic fields?
   
   For example depending on cover soil thickness and specifics of the EZflow product chosen, driving over the septic field could damage it by compressing soil or even crushing a chamber.An H-10 loading rate product is available for traffic areas but only where local codes permit.
7. Was there a problem at the septic tank?
   
   A septic tank without baffles or a septic tank kept in agitation from having been under-sized is at great risk of pushing solids into the drainfield, destroying it.
   
   See SEPTIC DRAINFIELD FAILURE CAUSES

You can contact the company directly with questions at the address we give just below.

Gravelless Septic System Design Life Expectancy & Design Specifications

Illustration of trench dimensions for gravelless septic systems,excerpted from Hygnstrom et als (2008) cited below.

[Click to enlarge any image]

• Hygnstrom, Jan R., Sharon O. Skipton, Wayne E. Woldt, RESIDENTIAL ONSITE WASTEWATER TREATMENT: GRAVELLESS DRAINFIELDS FOR EFFLUENT TREATMENT [PDF] University of Nebraska, University of Nebraska–Lincoln Extension Publications, Home Waste Systems ( 2002, Revised November 2008), - retrieved 2021/03/07, original source: https://extensionpublications.unl.edu/ assets/html/g1480/build/g1480.htm
  
  This NebGuide discusses recommended practices for the design and installation of a residential onsite gravelless drainfield.
• EZflow® DISPOSAL FIELD SIZING CHART [PDF], Southern Nevada Health District, P.O. Box 3902 Las Vegas, NV 89127 USA. Tel: (702) 759-1000 Website: http://www.southernnevadahealthdistrict.org Retrieved 2018/09/08, original source: http://www.southernnevadahealthdistrict.org/download/eh/isds/ezflow-disposal-field.pdf
  
  Watch out: the disposal field sizing requirements for your location may differ from the Nevada area above.
• EZflow® DRAINAGE SYSTEMS [PDF] (2009) specifications for using EZflow as an area drain or foundation drain, retrieved 2018/09/08, original source: https://api.ferguson.com/dar-step-service/Query?USE_TYPE=SPECIFICATION&PRODUCT_ID=3799906
• EZflow® NO-ROCK DRAINFIELD SPECIFICATIONS [PDF], Infiltrator Water Technologies, Op. Cit. retrieved 2018/09/08, Geosynthetic Aggregate Technology, original source: https://tyndallseptic.com/wp-content/uploads/2011/12/Chamber-Systems.pdfwww.infiltratorsystems.com/images/pdf/CutSheets/EZ01.pdf
  
• EZflow® INSTALLATION INSTRUCTIONS for EZflow Systems in New Mexico [PDF], Op. Cit. retrieved 2018/09/08, original source: https://www.infiltratorwater.com/images/pdf/ManualsGuides/EZ28_NewMexico_Sept2017.pdf
• Infiltrator Systems, 4 Business Park Road, P.O. Box 768, Old Saybrook, CT 06475 USA, Tel: 860-577-7000 / 1-800-221-4436 Website: www.infiltratorwater.com
  
  Note: the company was previously Ring Industrial Group, a name that may appear in some approval or specification documents.
• Infiltrator Systems, Lentz, David, P.E., COMMENTS PERTAINING TO PROPRIETARY DRAINFIELD TECHNOLOGIES RE: CHAMBER SEPTIC SYSTEMS [CALIFORNIA] - [PDF] (2011)
  
  The comments provided herein summarize Infiltrator Systems Inc.’s (Infiltrator’s) suggested modifications to Public Comment Draft Water Quality Control Policy for Siting, Design, Operation, and Maintenance of Onsite Wastewater Treatment Systems (draft Policy) (September 30, 2011).
  
  Excerpts: Infiltrator’s primary comments pertain to the use of proprietary drainfield technologies in the draft Policy. The proposed change is a broadening of the allowable drainfield technologies from gravelless chambers to IAPMO-approved dispersal system technologies.
  
  At present, the only IAPMO-certified leachfield technologies that Infiltrator is aware of are gravelless chambers and bundled expanded polystyrene synthetic aggregate systems. N
  
  ote that at least two companies in the United States manufacture products using both technologies, so the proposed changes do not provide an advantage to a single company or product.
  ...
  Sizing of gravelless chamber and bundled expanded polystyrene synthetic aggregate systems at a factor of 0.70 has been demonstrated through numerous research studies conducted by independent third parties.
  
  The third-party studies have demonstrated an increased infiltration efficiency for these technologies.
  
  The infiltration rate efficiency for gravelless technologies fully supports the 0.70 factor, which is a conservative value relative to sizing factors in other states. As compared to the efficiency of gravel and pipe, the increased efficiency of gravelless technologies results from:
  
  the comparatively open bottom area;
  
  lack of stone fines accumulating on the trench bottom restricting hydraulic function; and
  
  absence of embedded mineral aggregate stones blocking effluent flow through the trench bottom.
  
  This research has also shown that the purification of effluent by gravelless technologies is equal or superior to gravel and pipe technology, thus maintaining protection of public health and the environment.
• Keys, J. R., E. J. Tyler, and J. C. Converse. 1998. Predicting Life for Wastewater Absorption Systems. Proceedings of the Eighth National Symposium on Individual and Small Community Sewage Treatment Systems.
• NORTH CAROLINA APPROVAL of EZflow® as an INNOVATIVE WASTEWATER SYSTEM [PDF], (1995 - 2015) North Carolina Deparetment of Health & Human Servicves NCDHHS, Website: https://ehs.ncpublichealth.com/ , retrieved 2018/09/08, original source: https://ehs.ncpublichealth.com/oswp/docs/approvals/ie/IWWS-1995-3-R7-080715.pdf
• NSFC, GRAVELLESS AND CHAMBER SYSTEMS: ALTERNATIVE DRAINFIELD DESIGNS [PDF] Pipeline, West Virginia University WVU, PO Box 6064, Morgantown, WV 26505-6064 USA, Summer 2001 Vol. 12, No. 3 retrieved 2018/09/08, original source: https://tyndallseptic.com/wp-content/uploads/2011/12/Chamber-Systems.pdf
  
  Watch out: Excerpt:
  
  While it is true that gravelless and chamber systems have advantages and can perform at least as well as conventional drainfields, the U.S. Environmental Protection Agency and several state health agencies stop short of endorsing land area reductions for these systems.
  
  This is due to a lack of scientific evidence that less land is needed with these systems under specific site conditions.
• U.S. EPA, DECENTRALIZED SYSTEMS TECHNOLOGY FACT SHEET SEPTIC TANK LEACHING CHAMBER [PDF] U.S. Environmental Protection Agency, EPA, - retrieved 2021/03/07, original source: U.S. EPA, www.epa.gov/sites/production/files/2015-06/documents/septic_tank_leaching_chamber.pdf
  
  Excerpt: Reliability
  
  Leaching chambers are reliable, do not have moving parts, and need little maintenance to function properly.
  
  They are usually made of plastic materials, with a useful life of 20 years or more in contrast to the average useful life of a drainfield of 15 years, with a maximum of 20 to 25 years.
• WA, DOH, GRAVELLESS [SEPTIC SYSTEM] DISTRIBUTION PRODUCTS [PDF] (2013) Washington State Department of Health, Wastewater Management Section, : 243 Israel Road SE, Tumwater, WA 98501 USA, Mailing address: PO Box 47824, Olympia, WA 98504-7824 USA, Phone: 360.236.3330 Webpage: www.doh.wa.gov/wastewater Email: wastewatermgmt@doh.wa.gov retrieved 2021/0307, original source https://www.doh.wa.gov/ Portals/1/Documents/ Pubs/337-005.pdf
• See additional citations atReferences or Citations
  

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: seller's inspection says the 30 year old chamber septic system is perfect, my inspector says it has failed: Who's Right?

Mary said:

We are buying a home in New England and had the septic inspection done.

Tank and baffles were in good shape. Inspector had trouble finding 2 distribution boxes from the “as built,” but used a probe/dipstick to penetrate infiltrators.

In multiple places, probe showed dripping liquid and determination was made that drain field was saturated. 29 year old, gravel-less infiltrator system.

No pooling, odor or other evidence of failure.

Seller next had drain field inspection with backhoe to dig out distribution boxes. Camera showed pipes clear and exam of d-boxes showed very little effluent. Determination: drain field is perfect.

We now have dueling inspection reports. Is there any way to reconcile them? Can infiltrators be full, yet distribution boxes and surrounding soil fine? - 2021/03/07

This Q&A were posted originally

at SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR

Moderator reply: plan to pay for a new septic effluent disposal system

@Mary,

Thanks for an interesting, if also frustrating problem and question about conflicting septic inspection reports.

OPINION: Review this matter first with your attorney: my understanding is that in a real estate transaction a buyer is expected to perform her own due-diligence, and that if she relies on a seller's representation and later finds that the representation was incorrect she has no recourse.

In other words, rely on the seller's representation at your own risk - unless the seller is also willing to post bond equivalent to the cost of septic field replacement.

It would be a nice surprise to find a nearly 30 year old gravel-less septic system that is both still working and that had any further expected life.

The typical predicted life of a "no-rock" septic system is 20-25 years.

Bottom line: even if the system appears to be "working" by a report given by a party who was hired by the seller who is by no means a neutral to the transaction, you or any buyer would be prudent to buy the property with the assumption that you are very likely to face a significant septic field replacement cost at any moment.

Details:

If you can find out the brand of system installed we can probably find specfific "failure criteria" described by the manufacturer.

You should also review the two reports with an independent septic design engineer who thus has no conflicts of interest, and who has experience in specifying and installing no-rock or gravelless septic systems.

I agree that a camera finding no backup of effluent in the system is encouraging, but, then, we have not one iota of data on exactly how that test was performed - under what conditions: was the system under load, had it been un-used for some period of time, what was recent weather like, how wet have conditions been, etc.

If a septic system seems to be "working" "sometimes" but during wet weather or under times of normal loading it is not working then it's a failed system.

Take a look at NO ROCK SEPTIC SYSTEM LIFE inspectapedia.com/septic/Gravelless_Septic_Life.php

where we will move this discussion to invite comment.

Above in this article we provide sources for gravelless system design and life expectancy data.

Watch out: although the property owner has had some exploration of the chamber septic using a backhoe (by your report), in general one should keep heavy equipment off of the septic field as there is risk that driving over it with backhoes or anything else that's heavy can cause costly damage.

On 2020-04-22 by (mod)

Rex

Take a look at GRAVELLESS SEPTIC SYSTEM SOURCES https://inspectapedia.com/septic/Gravelless_Septic_Buyers_Guide.php

On 2020-04-21 by Rex

Trying to locate a place to purchase 100’ of reckless 4” septic drain field pipe that is wrapped and uses polystyrene inside the wrap near Tyler texas

On 2018-07-16 by Anonymous

Also, what is the approx. Depth of the dome for cold region?

On 2018-07-16 by Mark

Would infiltrator domes work with clay soil on bottom and black soil on top?

On 2017-09-26 by Phil - The infiltrator domes, or tunnels, should NOT be full of solid effluent.

@Greg Weber,
No Greg. The infiltrator domes, or tunnels, should NOT be full of solid effluent. They shouldn't even be full very often of liquid. Maybe an inch or two during a heavy load of liquids added to the system, which then dissipate quickly as they leach into the ground.

Watch out: A tunnel FULL of liquid that is not being absorbed into the ground relatively quickly has failed.

On 2017-07-29 by Randy

We bought this place five years ago the first year we was here we had to have the septic tank pumped out after that I thought it was good until a year are toilets was backing up into the sink and into the tub and we have pumped out again but I don't see no water puddle in the yard it backs up in the house I think it's the feline

On 2016-04-08 by Greg Weber

Should my infiltrator domes be full of effluent

...

Continue reading  at GRAVELLESS NO-ROCK SEPTIC SUPPLIERS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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