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Author:
Septic Tank Yank (CO)
Rich, you have hit the ?Exact Change Lane.? I have personally designed and installed hundreds of septic systems using plastic tanks and the Advanced Drainage Systems, SB-2 Gravelless leach field tubing. As you may guess, I have developed my own standard design using these products. The regulars on this forum are probably just waiting for me to jump on this one, like a chicken on a bug. So here goes. I will assume that the soils work has been completed, and that you have a design for the system in mind.
ALDRICH?S STANDARD SEPTIC TANK/SOIL ABSORPTION SYSTEM DESIGN
Cleanout Assembly:
Typically, the system starts with the installation of a cleanout in the SDR-35 PVC sewage pipe within 3 feet of the foundation of the house. The cleanout assembly is comprised of a 4-inch Sewer and Drain (S&D) wye fitting, a 45º Street Elbow, a short riser pipe of the appropriate length, a female adapter, a threaded plug, and a 6-inch irrigation valve box with cover. Cut the riser pipe so that the top of the threaded plug is about 2 inches below the final grade. Cover the top of the cleanout riser with the irrigation valve box that is set at the final grade.
Most septic system regulations in the USA recommend a sewer pipe slope of ¼ inch per foot or greater. There is no maximum slope, contrary to popular myth.
Plastic Septic Tank:
I am shocked, but gratified, to hear that someone who owns a concrete business is planning to use a plastic septic tank. Perhaps you are aware of the limitations of concrete septic tanks. Modern Precast concrete septic tanks, constructed of Portland Type II cement, have a service life of about 100 years. The demise of the concrete tank will be prompted by the presence of sulfuric acid on the walls of the tank that are above the water line, and on the bottom side of the tank cover. Hydrogen sulfide gas, created in the digestion process by the anaerobic microbes in the tank, mixes with the water vapor on the walls and sulfuric acid is formed. The acid then slowly etches the cement from around the aggregate and the concrete just crumbles away.
Polyethylene plastic is impervious to attack from sulfuric acid. This means that the plastic tank has the potential for an infinite service life. That is, of course, until someone comes up with a microbe that eats plastic. If and when that happens, we?re all in trouble.
My personal preference in the selection of the septic tank is the RMI-D, 1250-gallon, 2-compartment, rotomolded Polyethylene septic tank. Perhaps I favor this tank because I had a hand in the design of the tank back in 1984, and they are produced locally in Commerce City, Colorado.
Place a 45º Elbow on the inlet pipe inside the tank so that the inlet tee is accessible, and on the side of the 20-inch diameter access hole. Be sure to fill the tank with water prior to backfilling around the tank. Do not follow the ridiculous instructions contained in the installation manual, and written by RMI engineers who have never installed a septic tank. They suggest that you backfill at the same rate that the water is rising inside the tank.
The method that I have found to be most effective is to fill the tank with water, and then backfill the tank with a shovel using selected soil fines. I usually just compact the backfill soil with my feet. Backfill up to about 30 inches by hand, and then carefully backfill the rest of the tank hole with a loader after it has been inspected.
The tank outlet baffle is comprised of a Tuf-Tite brand septic tank effluent filter assembly, and a 45º Street Elbow. Adjust the length of outlet pipe inside the tank so that the filter assembly is centered on the outlet end access hole. Clean the filter annually by pulling it to the top of the sanitary tee and then flush the accumulated debris with the strong stream from a hose back into the tank. There are several other high quality filters on the market, but I prefer the non-brittle, more flexible Tuf-Tite filter. The filter will reduce the suspended solids, and suspended organic matter in the effluent from flowing into the leach field. Clean the filter annually on SEWAGE INDEPENDENCE DAY.
Both access holes are fitted with 20-inch diameter, Tuf-Tite brand plastic risers with gasketed lids. The lids, which are at the surface of the ground, are secured with 8 stainless steel screws. Easy access to the tank will encourage regular maintenance. If you have to excavate the soil above the access hole lids, chances are the important maintenance chores will be ignored.
NDS Brand Diversion Valve:
The NDS Diversion Valve is a plug type valve, and I have found it to be the best valve for the application. A little problem with the valve is that the inlet and two outlets are molded as ?male? fittings to fit ASTM 2729 pipe. It is impossible to insert the male fitting inside the SDR-35 PVC sewer pipe. What to do? Simply place and cement a coupling on the inlet and outlet orifices, and then slip the pipes into the other end of the couplings.
Cover the 6-inch 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 between 2 half-sized leach 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.
SB*2 Tubing or ADS, Bio-Diffuser Chambers?:
With the advent of the plastic chamber technology, I have decided to discontinue the use of SB*2 gravelless leach field tubing, except in certain applications and on certain sites where the use of SB*2 is better suited than ADS Bio-Diffusers. If you would like to know the leach field sizing criteria used with chamber type leach fields, I suggest that you contact the septic system regulator in your jurisdiction.
I recommend the use of ADS Bio-Diffuser plastic leach field chambers, but if you are bound and determined to use SB*2, let me know and I will provide some guidance in the use of that fine product.
Place the required number of chamber units in the level trenches. 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 and 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. Remove the 4-inch knockout in the top center of the chamber units on each end of each field. Place couplings with short nipples through the knockout holes, and then cement another coupling to the short nipple. This will secure the riser pipes to the chambers.
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 4-inch female adapters, and plastic drain grates.
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 for easy location, easy access, and you can run the lawn mower right over them. Typically the covers of the boxes are green.
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. Carefully backfill the trenches with a loader.
Septic Tank Sludge Management:
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.
Record Keeping:
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 installed system components before backfilling, 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 design and performance of the septic system, and will allay the fears typically encountered when purchasing a home served by a septic system.
Well Rich, 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 in the world. Maintenance is the key to successful septic systems. However, if the required maintenance is difficult, or impossible, 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 lmajwa@aol.com
John Aldrich (Septic Tank Yank)
Septic System Consultant
Timnath, Colorado
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