failed biodiffuser leach fields

[Robert Raymond De Luca]

I RECENTLY FINISHED BUILDING 39 HOMES IN CALIFORNIA, ALL WITH THERE OWN SEPTIC SYSTEM. THE SYSTEM CONSISTS OF 1-1500 GALLON TANK WITH TWO 50 FOOT LONG LEACH FIELDS. THE LEACH FIELDS ARE BIODIFFUSER “INFILTRATOR” UNITS SET IN A TRENCH. THE SOIL IS SANDY AND HAS EXCELLENT PERCOLATION RATES. IVE HAD TEN OF THE LEACH FIELDS FAIL WITHIN 4-6 MONTHS OF THE HOMEBUYER MOVING IN. THE FAILURES ARE DUE TO SILTATION BACKFLOWING INTO THE INFILTRATORS THROUGH THE BAFFLES ON THE SIDE OF THE UNITS. THE SAME BAFFLES THAT ARE DESIGNED TO PROHIBIT THIS FROM HAPPENING. THE SAME BAFFLES THAT THE LIQUIDS FLOW OUT OF IN THE FIRST PLACE. HAS ANYONE ELSE OUT THERE HAD THIS PROBLEM? IS IT A BAD DESIGN? ARE THESE DIFFUSERS NOT DESIGNED FOR USE IMN THIS KIND OF SOIL? DOES ANYONE OUT THER HAVE AN ANSWER WHY 25 PERCENT OF MY LEACH FIELDS FAILED? ANY INFO. OR COMMENTS ON THIS MATTER WOULD BE GRATLY APPRECIATED.
THANK YOU

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TIM FLATLEY, FLATLEYHOMES INC.

[Retired plbg1Participant]

Try digging them out and use 3/4″ clean rock to backfill instead of sand, check out this site on Goole. http://www.dep.state.pa.us/dep/subject/advcoun/sewage/InfiltrationchambersSAC.htm

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Art retired plbg

[John Aldrich1Participant]

Tim, the generic name of the leach field material of which you speak is “Chamber.” The Advanced Drainage Systems “Bio-Diffuser” and Infiltrator Inc. “Infiltrator” units are brand names of very similar chamber units. I have had discussions on several occasions with engineers from both companies regarding the problem of siltation through the louvers on the sides of the chamber units. The official position of each company regarding the potential for siltation through the louvers is that it will not occur. The engineers claim that the angle of repose of the backfill soil at the louver is such that the soil will not move laterally and up over the lip of the louver to fill the void created by the chamber. They claim that the angle of the louvers will prevent backfill soil from moving laterally into the void under the chambers.

Well Tim, I “flatly” :>) disagree with the premise held by the engineers of both companies. Nature hates a void and will always succeed in filling a void. The soil fines become suspended when the ponding effluent under the chamber saturates the soil on the sides of the chambers. A growing clogging mat forms rapidly when the nutrient rich septic tank effluent is applied to the soil of the end-loaded chamber leach field. This clogging mat grows to cover the entire surface of the soil under the two 50-foot chamber leach fields. Ponding will occur when the clogging mat is fully formed. The thickness of the clogging mat will determine percolation rate of the applied septic tank effluent. As it gets thicker, the percolation rate of the applied effluent declines. The ponded effluent level under the chamber system fluctuates in depth because of the intermittent sewage flow to the system. When the ponding recedes, the direction of flow in the saturated backfill soil is reversed and suspended soil particles are carried into the void under the chambers. A rainstorm event or heavy irrigation of the soil above the leach field will add to the volume and velocity of water that will be flowing into the void. This effect will carry larger soil particles into the void.

So that is what I think caused the rapid failure of ten systems. I also think that the poor performance of those ten systems is just a preview of coming events.

Read the response that I composed to an inquiry from some guy named “Dumbdad” in regard to the very same problem. If you require further direction or have additional questions specific to your project contact me via personal e-mail. [email protected]

Author: Septic Tank Yank

Dumbdad, sure sounds to me like the septic man is right. If you decide to have the leach field replaced, consider installing 2-half sized leach fields equipped with a 4-inch, NDS brand diversion valve. Cover the valve riser with a 10-inch round irrigation valve box to allow for easy access. The top of the box is set at the final grade elevation. The valve will allow the alternation of flow to the fields. Use half the field for 1-year while the other half rests. Turn the valve annually on the 4th of July, SEWAGE INDEPENDENCE DAY. Celebrate your independence of the sewer grid, and remember that with this independence comes the responsibility of a sewage treatment system operator.

I recommend the use of plastic leach field chambers such as the ADS Bio-Diffuser, or Infiltrator brand. Cover each chamber leach field with a 4-foot wide sheet of geotextile fabric (landscaping fabric). The geotextile will prevent the migration of silt into the void under the chambers. The fabric also acts as a wick, wicking by capillary attraction the effluent up over the chamber units, and then into the soil.

Install 4-inch monitoring and ventilation ports to the ground surface on each end of each field. The tops of the 4-PVC risers are covered with plastic 6-inch round irrigation valve boxes. The tops of the irrigation valve boxes are set at the final grade elevation. The boxes will allow easy location, easy access, and you can run the lawn mower right over them. Typically the covers of the boxes are green.

The tops of the in-use field monitoring ports are fitted with 4-inch female threaded adapters, and threaded plugs to prevent sewer gas odors from emanating into the yard. The tops of the resting field ventilation ports are fitted with a 4-inch female adapters, and plastic drain grates.

The ventilation ports will allow atmospheric oxygen to enter the leach field, and this will create an aerobic condition in the resting leach field. The oxygen will oxidize the Ferric sulfide (that black slimy crap), a major component of the clogging mat. Also, the aerobic condition will allow the aerobic microbes, present in the surrounding soil, to migrate to the clogging mat and consume the organic matter constituent of the clogging mat, and consume the dead bodies of all their anaerobic microbial cousins. Exchange the solid threaded plugs with the drain grates when the valve is turned on SEWAGE INDEPENDENCE DAY.

While you are involved with the major renovation of your septic system, I recommend that 20-inch plastic risers be installed over the inlet manhole, and the outlet manhole of the septic tank. The covers of the risers should be at the final grade elevation to allow easy access to the tank. Let’s face it, if you must excavate the soil over the septic tank manhole with a shovel, chances are that this chore will be avoided. I use Tuf-Tite brand risers.

I also recommend that the outlet tee of the tank be fitted with a septic tank effluent filter. The brand that I use, a bottle brush type, is manufactured by SIM/TECH FILTERS, although there are several other high quality filters on the market. The filter will reduce the organic matter in the effluent from flowing into the leach field. Clean the filter annually on SEWAGE INDEPENDENCE DAY.

Another chore that should be performed annually is the measurement of the sludge accumulation in the primary chamber of the septic tank. The sludge can be measured with a “SLUDGE JUDGE.” Do an Internet search to obtain this neat device. I recommend the implementation of the “1/3 RULE” of sludge removal. When the level of the sludge is 1/3 the total liquid depth of the septic tank, it is time to remove it.

The final chore to be performed on SEWAGE INDEPENDENCE DAY is to record all of the maintenance performed on the system in a maintenance log. I prepare a SEWERS CAN BE BEAUTIFUL operation manual for each of the septic systems that I install for my clients. The manual contains a description of the system design, photos of the system components, an as-built plan, a description of the required maintenance procedures, a copy of the permit, and the maintenance log. The manual becomes an excellent sales tool when the time comes to sell the home. The manual answers all questions a potential buyer may have regarding the performance of the septic system, and will allay the fears typically encountered when purchasing a home served by a septic system.

Well Dumbdad, I had better end this lengthy diatribe. If all soil absorption type septic systems were designed and constructed to the above standards, then there would be far fewer failed septic systems. Maintenance is the key to successful septic systems. However, if the required maintenance is difficult, or impossible, then chances are it will not be performed. If you would like photos of my typical standard system, send me your e-mail address. My address is [email protected]

John Aldrich (Septic Tank Yank)
Septic System Consultant
Timnath, Colorado

[nicktheplumberParticipant]

John,
I’ve got to tip my hat to you. I don’t do septics in my area (they aren’t allowed in San Francisco and the Oakland Bay Area), but I used to do a few in the more rural areas, so I keep up with the technology. I would guess that you’re absolutely right about the siltation problem and I can’t believe the “engineers” would say such things, except that maybe they think plumbers are just gullible morons.

NtP

[John Aldrich1Participant]

nicktheplumber, Thanks for the compliment. Don’t be too hard on the engineers. They are just real confident that they are right in this issue. I am just as confident that they are wrong. I have not experienced a single failure in the chamber systems that I have installed. I have not installed a single chamber system without covering the side louvers with a geotextile to prevent siltation.

Thanks again!

Septic Tank Yank

[John Aldrich1Participant]

Hey Tim, What is your opinion? Do you think it is wise to place a 4-wide sheet of geotextile over the chambers, covering the louvers and thereby preventing siltation?

[TIMFLATLEYParticipant]

John, When I first started having these systems installed I probably would have said that goetextile wasnt neccessary. At this point however, I cant believe its not required, or at the very least recommended by the manufacturer to be used in all applications of the biodiffuser and or infiltrator chamber systems. The fact that it isnt says a whole lot about what these manufacturers main motivation is. Granted, its a business and businesses cant survive without making a profit but this seems to me to be false advertising.I’ve seen on more than one occasion evidence that siltation has occured and sand and soil has traveled back up through the baffles on the side of the chambers. It is my firm belief that the failure of nine out of the ten failed leach fields are a result of the biodiffuser design and siltation occuring through the baffles that their engineers say are designed to prevent this from happening. So in answer to your question I definately will use geo textile material in the future if I ever use a chamber system again.

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TIM FLATLEY, FLATLEYHOMES INC.

[John Aldrich1Participant]

Tim, I don’t believe that the chamber company’s claims are false advertising. Their engineers are firm in their beliefs. They are just wrong. Don’t be hasty in deciding to avoid the use of plastic chambers in your soil absorption systems. Chamber technology is the cutting edge technology in providing leach fields with a very long service life. Chambers are far superior to stone and pipe leach fields. Just install the geotextile fabric over the louvers and be sure to include a diversion valve (NDS Brand) so that the system owner can alternate the septic tank flow annually. If you try to just place the geotextile fabric on a single full-sized leach field, the clogging mat will form rapidly on the inside of the fabric and the leach field will fail quickly. You must provide for alternating leach fields.

[Author]

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