How Septic Systems Function (And What Causes Them To Fail)

Waste water leaves the house and enters the septic tank. The septic tank performs two functions. First, it acts as a holding tank and allows the solids to settle-out. The heavier solids sink to the bottom forming the sludge layer, the lighter solids, fats, oils, grease, etc…rise to the surface and form the scum layer. The relatively clear layer in the middle is called effluent. Second, naturally occurring anaerobic bacteria begin breaking down the solids in size and destroying the pathogens.

septic systemThis is a standard gravity-fed septic system. The treatment process starts in the septic tank and is completed in and around the drainfield. This simple type of system is best suited for those ideal building lots: well draining soils, no high water tables or nearby bodies of water.

After the treatment process is started in the septic tank the effluent enters the soil treatment phase of the process (baffles prevent the larger floating solids from entering the drainfield). The soil treatment system, more commonly called the drainfield, is comprised of distribution pipe laid in a trench partially filled with gravel and covered with topsoil.

As the effluent enters the drainfield it percolates through the gravel bed where a large portion of the pathogens are destroyed. Pockets of oxygen created by the uneven shape of the gravel allow the more efficient aerobic bacteria to exist. As the effluent exits the drainfield the natural soil completes the treatment process. By the time the effluent has traveled 2-3 feet through the soil all the remaining pathogens have been destroyed and the water is drinking quality. The cleaning process continues as the water migrates through the soil Phosphorus and nitrogen are utilized by the vegetative life covering the drainfield and chemically changed in the soil. A large portion of the moisture is returned to the atmosphere though evaporation (evapotranspiration).

septic system installationObviously not all sites are going to be perfect. When dealing with high water tables, a nearby body of water, little or no soil, extremely slow soils, small lots, etc. and a standard system will not adequately perform the treatment process alternative systems can be designed to ensure the treatment process is performed before the effluent is discharged to the environment. Today the lowly on-site septic system has evolved to the point where they can actually treat wastewater better than a multimillion dollar sewage treatment facility. And although these alternative type systems will cost more they will in most cases still be far cheaper than a treatment facility.

Contrary to what most people and community leaders believe, septic systems are one of the best choices for treating household wastewater, in most cases they are a better option financially and far better for the environment than a sewage treatment facility. But as with anything they must be used correctly and properly maintained.

Septic tanks seldom fail, the soil, or drainfield fails when it becomes plugged and the effluent can no longer migrate through the soil. The drainfield essentially becomes a dead pool of water. In most cases these failures occur when it becomes plugged with solids that were supposed to remain in the tank. These failures are usually a combination of factors and can be avoided and in some cases, damages can even be reversed.Failures can be avoided by learning how a septic system functions, how to properly use it, and what steps you can take to protect it. The basics of protecting a system are really quite simple, once you realize that they work on a bacterial process (good bacteria eating bad bacteria) and bacteria don't eat plastic like polyester and nylon...too many harsh cleaning solution will kill off the good bacteria. Also a septic system can only handle a certain amount of water per day...if you put more water down the drain than it can handle you will overload the system.
The homeowner puts more water down the drain than the system can handle hydraulically over-loading the system.Install water-saving appliances, devices and practice water saving techniques. Repair plumbing leaks. Leaking toilet valves are a major culprit of hydraulic overload putting hundreds of gallons of water through the system every day.
Fine solids from washing machines (lint) and garbage disposals do not have the mass to settle in the tank, instead they remain in suspension until reaching the drainfield where they plug the pores of the soilbed.Install filter for the washing machine to remove the fine solids from the discharge and do not use or minimize the use of garbage disposals.
Larger solids like feminine hygiene products, condoms, cigarette butts, paper towels, toys, etc. get out of the tank and enter the drainfield plugging it up. Have the contractor install an effluent filter in the tank. These are cleanable filters that stop the larger solids from reaching the drainfield.
Chemicals are over-used killing the bacteria in the system stopping the treatment (and breakdown of solids) process.Conserve chemical usage. Automatic toilet bowl cleaners can be very hard on a system because they kill the bad bacteria in the toilet but the killing process continues throughout the system.
Periods of heavy water use do not allow solids to settle in the tank and are flushed out to the drainfield.Water use should be spread out. Do 1 or 2 loads of laundry per day rather than 10-15 loads on Saturday morning.
Baffles in the tank are not of the proper size or fall off allowing solids to float out to the drainfield.Exit baffle should be replaced with effluent filters. These cleanable filters prevent the larger solids from reaching the drainfield and if installed properly are permanent baffles.
Solids are allowed to build-up in the tank leaving little settling room for newly introduced solids and forces solids out of the tank to the drainfield. Have the tank inspected annually and pumped when necessary. Ask your contractor about putting you on an annual (cheaper) inspection program. Tanks should be pumped and inspected through the manhole cover, not the inspection pipe.
Vehicles are allowed to drive over the drainfield compacting the soil and destroying the natural (drainage) structure of the soil.Keep vehicular and heavy foot traffic off the drainfield. Plugged/compacted drainfields can be rejuvenated by having the soil fractured. This fracturing creates thousands of tiny fissures that allow the soil to drain and the aerobic bacterial colonies to re-populate.
Sodium (salt) in wastewater can bind with certain types of clay soils causing the soil to seal.A soil de-flocculent can be used to correct sodium damaged soil. A mini-septic system can be installed to receive the discharge from the water softener to prevent this damage.

Tip for Buying a Home: If you are buying a home with a septic system, do not overlook the status of the septic system!!! The codes have changed dramatically over the last decade rendering more than half of all systems technically illegal. Up to this point most regulatory agencies have been content to ignore these old systems. However as the environmental damage from these old noncompliant systems becomes evident, some states states/counties are starting to require the systems be brought up to current codes before the property can be sold. However this is not a perfect process and what is starting to happen more frequently is people are told by the health depts. after they buy the home and move in that the system needs to be replaced and they as the new owners will be held responsible…an unforeseen cost that few can afford.

More and more realtors are now beginning to realize it is their responsibility to represent BOTH the buyers and the sellers when it comes to the septic system. An educated agent will strongly suggest the sellers have the system inspected for code compliancy and upgraded if necessary before deciding on a selling price and factor those costs into the final selling price before listing the property. When representing a buyer they will again suggest a full compliance inspection be done before making an offer and if the system comes up short factor those costs to upgrade/replace the system into the counter offer.

If you are shopping on your own and find a house you are serious about, hire your own independent septic contractor to perform a full compliance inspection. I stress septic contractors and compliance inspection because most home inspectors inspect homes, not septic systems and a good home inspector will tell you that. And even many contractors when asked to inspect a septic system will often assume you just want to know if it is failing or slow. Often those inspections are nothing more than flushing a dye down the toilet, running some water down the drain and look in the yard for surface discharge, that only tells you if the system is having problems, not what is in the ground. Believe it or not there are many septic systems that are nothing more than pipe out to a cesspool (illegal for years in most of the country…click on the animated history lesson in red at the top of the page to see why), a ditch or a lake or a stream.

Grandfathered in…fuggedaboudit. Even some government agencies don’t realize it but you can not grandfather in a health or environmental issue. If that were the case you could still smoke in airplanes, restaurants and public buildings, as long as you smoked before those policies kicked in. Industry could still dump their toxic waste anywhere they wanted as long as they were doing it before the environmental protection laws were passed.

Unfortunately once you buy the house the problem is yours and there have been cases where the people have been kicked out of their home weeks after moving in because the failed system is an immanent health risk to the public.

A full compliance inspection should include:

  • Tank pumped and inspected for cracks/crumbling concrete, missing/inadequate baffles, excessive drain back from the drainfield (indicating a failing system).
  • Size of tank.
  • Size and depth of drainfield.
  • Depth of seasonal water tables should be determined and the amount of separation from the trench/bed bottom to the water table.
  • Perk rate of the soil and if the [size of] the drainfield will handle the daily flows from the house (usually 150 gallons per bedroom per day. A 3 bedroom home should have a drainfield that will handle up to 450 gallons per day).
  • Any non-complying parts of the system should be noted. Any future code changes that would put the system in non-compliance should be reported. Example: Even if the system meets code requirements today, the system should be assessed if it will meet any proposed changes in the septic code requirements in the near future (and a good septic contractor will be aware of pending changes).
  • Dollar estimates for any suggested up-grades should be provided.
  • This inspection assessment should be provided to the sellers and buyers in writing and these costs should be incorporated into the selling price.

This inspection will cost $200-$600 but it is worth every penny if you find any problems. Any up-grades can/should be negotiated into the selling price of the home. If no problems are found then you know you are starting with a good system and it is up to you to take care [of the system] from the beginning. Buying a home is the biggest investment most will ever make…that septic inspection is part of your due diligence.

If the seller refuses an inspection you should take this as a sign of potential problems and walk away or plan $ accordingly (if you are getting a good buy on the property and you really like it, then paying for these upgrades out of your own pocket would be worth it).

Tip for selling a home: Before you list the home, have the system inspected to see if it meets current code, if not have the system upgraded and factor those costs into the selling price and use that new system as a selling point. Warning: do not try slipping a noncompliant system past the buyers…many sellers are getting sued by the buyers when they learn you sold them a house with a pre-existing problem.

Tip for building a home: If you are having a house built, make sure the contractor that designs and installs your system is a certified professional (most developers go with the cheapest subcontractors they can find…insist they use a qualified septic contractor). If you are your own general (hiring the subs) try to find a contractor that does both septic and foundations to do all of your “dirt” work. Also have them out to the lot to to design the system first and build the house according to the septic…in some cases moving the house 10 feet in one direction or eliminating that basement bathroom can make a difference between a $5,000 system and a $15,000 system.

Also don’t make the mistake of hiring someone because they are the cheapest. Go with the contractor with the best track record. Many people have saved a few bucks on the first installation only to have the system fail 1, 2, 3 years later and by that time the original contractor is out of business or refuses to correct the problem. Now the second system can be even more expensive because the yard is landscaped and the choices for a replacement are narrowed down.