- This topic has 1 reply, 2 voices, and was last updated 21 years, 1 month ago by John Aldrich1.
22 Mar 2000 at 3:50 pm #278486Anonymous
I own a 30 year old home with the origianl septic system in place. I belive that the leaching field, while still working, may be failing. I do not have any odors or surface water, but the area above the leaching field has sunk somewhat. I have several questions. First, do any of the septic system additives such as “Septic Helper” really work? They claim to work to open up clogged lines and, if that were true, it might solve my problem. (There are only 2 of us in the house, my wife and I, so the load on the system is not great.) Second, can I put down about 6″ of topsoil over the leaching field so that I can get a lawn going again or will that cause me more problems?
Any advice would be greatly apprecicated.
22 Mar 2000 at 6:52 pm #298599John Aldrich1
Will Brien, from what you describe about the condition of your leach field, it appears that the soil above the leach field gravel has migrated by siltation to the voids between the gravel pieces, effectively reducing the reservoir capacity of the leach field. Nature hates a void, and will always fill it. The reservoir capacity is important because the percolation rate of the effluent through the clogging mat, and soil is slower than the application rate from your septic tank. The water level rises and falls depending on the differential of the two rates. When the reservoir capcity is reduced, the water backs up, and flows in the path of least resistance. This sometimes results in surfacing sewage effluent at the leach field, and sometimes results in backing up the flow into the home. As siltation progresses, one of these conditions will occur. Placing soil in the depression over your leach field will allow you to have a nice lawn, but will not solve the inevitable problem. Septic tank additives will do nothing to solve this problem, and in my opinion, are a waste of money.
I recommend that you install a new leach field. The design should include the use of a gravelless leach field material such as Advanced Drainage Systems, Inc. (ADS), SB*2 tubing, or the ADS “Bio-Diffuser” chamber material. The Bio-Diffuser is similar to the “Infiltrator” chamber system.
The SB*2 tubing comes with a geotextile sock called “Drain Guard”, which prevents siltation of the reservoir provided by the interior of the 10 inch diameter polyethylene tubing. The Drain Guard also acts as a wick, drawing the applied effluent completely around the tubing, and wicking it into the soil.
If you decide to use a chamber leach field material, place a 4 foot wide sheet of geotextile over the chambers to prevent siltation of the void provided by the chambers. Siltation appears to be a significant problem on your particular site, so the use of a geotextile to prevent this natural process is important to create a leach field which will have a very long service life.
Another design feature of this new leach field is to install two separate leach fields, 50% of the required area in each field, and put a diversion valve in the effluent pipe line between the septic tank, and the two leach fields. This will allow you to alternate the effluent flow, annually, to the leach field. Alternately using, and resting the leach field will allow for the control of the clogging mat that will form on the surface of the soil where the effluent is applied.
This clogging mat is what controls the percolation rate of the effluent into the soil. As the thickness of the clogging mat increases, the percolation rate of the effluent through it decreases. When the application rate exceeds the percolation rate, the effluent will either surface, or back up into the home. The clogging mat is composed of organic material which has escaped the septic tank, microbial slimes, and an iron compound, Ferrous sulfide.
Ferrous sulfide is created in the disgestion process by the anaerobic microbes in the septic tank. It leaves the tank as a liquid, and when it is applied to the soil, it changes state, and becomes a solid, which is that black slimey crap on the bottom of the leach field. The only pracical method to eliminate the Ferrous sulfide is through oxidation.
The environment in the leach field is anaerobic (no oxygen present), so in order to oxidize the Ferrous sulfide in the soil below the leach field, the effluent flow must be diverted to the alternate field. The ponded effluent will slowly percolate through the clogging mat, and will be replaced by air when it becomes unsaturated. The oxygen in the air will then provide an aerobic environment, and the Ferrous sulfide will be oxidized. The aerobic environment will also allow aerobic microbes to exist, and they will consume the organic material in the clogging mat.
Monitoring, and ventilation ports should be installed on each end of each field to provide for positive ventilation of the field. Atmospheric air contains about 21% oxygen, while the air 2 feet below the surface of the ground is less than 10% oxygen.
I use 4 inch PVC pipe for these ports which rise to within 3 inches of the surface of the ground. Place a S&D female adaptor on the pipe, and a treaded plug on the “in-use” field, and a 4 inch drain grate on the resting field. All risers are then covered with round 6 inch irrigation valve boxes which are set so that they are level with the final grade. Exchange the plugs, and grates when the flow to the fields is alternated.
I use a plug type diversion valve manufactured by National Diversified Sales, and cover the lid of the valve with a round 10 inch irrigation valve box.
While you are about it, I recommend that you place risers from both the inlet, and outlet access holes of the septic tank to the ground surface. I use a cast aluminum meter pit bonnet, which has a rubber inner lid, and a cast iron, lockable lid for the top of the risers. I also recommend that you install a septic tank effluent filter in the outlet tee of the tank. I use the “Zabel” brand which fits into the 4 inch outlet baffle. Clean the filter annually by removing it, and flushing the accummulated debris with a strong stream from a hose, back into the septic tank.
The annual maintenance duties should be performed on July 4th, “Sewage Independence Day”. Celebrate your independence of the “Sewer Grid”, but remember, with this independence comes the responsiblity of a sewage treatment system operator.
An old friend of mine observed that I am the kind of guy, that if you asked me the time, I would explain the procedure to build a clock. However, I feel that the above lengthy, detailed description of the solution to your problem is necessary.
Good luck, and if you would like to discuss this issue further, contact me via e-mail. JWA
Septic System Consultant
P.O. Box 205
Timnath, Colorado 80547
(970) 482 7460
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