When designing a properly functioning residential wastewater treatment system, most wastewater disposal schemes include some sort of leach field. The wastewater leaving a standard septic tank is considered primary treatment. Many people can find information on residential wastewater treatment with septic tanks and leach fields. The primary wastewater treatment includes the separation of solids (see our previous articles), and some sort of minimum water treatment. The “standard United States septic tank” treats to approximately 50 biological oxygen demand (BOD) and a total suspended solids (TSS) of about 100 (50/100) with a total nitrogen loading of about 45 mg/L.Water from the septic system flows right onto the field. The waste water is absorbed through the soils surrounding the field. The leach field acts as a living biological processing machine, as well as a liquid receptor. These biological processes treat the waste water further; so then it is at an acceptable concentration before it reaches either the groundwater, or potable drinking water sources.

The general structure of the fields are usually a layer of 4 feet to 2-4 inches of leach rock. Then there is a leach line that is put over the top of the rock, and then buried with 3″ of the same rock. A geo-textile type barrier is then put on the leach rock to prohibit dirt and debris from clogging the rock underneath. Usually leach rock is covered with a minimum amount of 12 inches of native soil.

There are generally two types of leach fields; a leach trench or a leach bed. A leach trench ranges from 1-ft in diameter to 3-ft in diameter and has a maximum length of about 100-ft. a leach bed can be up to 20-ft wide and up to 100-ft long. Leach beds are generally used for larger commercial wastewater treatment disposal systems which need higher daily flow rates.

Many fields are supposed to be designed to function for a thirty year life span; which is in the worst of conditions. Leach fields are a biological processing plant that will break down into wastewater over time. When wastewater enters a field, the water has a high BOD, which is considered anoxic. Anoxic means that there is no oxygen present. While the waste water is flowing through the fields and in the soil, the biological oxygen demand dwindles down to the point that there is enough oxygen to move into an aerobic condition. Under this condition is when the bacteria levels are in a safe range.

Another item to mention is the biological activity at the rock and soil boundary continues through the life of the field. When the bacteria life cycle continues, the foreign material from processing lays on the rock and soil boundary. The material combines with clothing fibers that cannot be broken down, such as polyester, and it forms a low permeable layer. People call this layer “matting”. The mat grows as it ages, which is the reason why fields have a 30 year life expectancy.

At the end of the fields life, it is usually expanded by adding more leach area, or it is replaced. This process is costly and very disruptive. There are several products out today that are added to promote the health of the field, as well as rejuvenating the field. A major problem is the septic tank health which has grease and oils to pass through to the field. Greases and oils increases the speed of the mat growth. This results in causing earlier line replacements. There are two types of conditioners for septic tanks: liquid biologically active products, and a dry enzyme product, which is like RIDEX. Wastewater engineers like to use liquid digesters as they work better. One brand that engineers use is NORWECO Bio-germ Organic Digester. When the health of the tank is good, it minimizes the forming of matting, and prolongs the life span of the field.

When dealing with a leach line which has reached or is approaching its end-of-life (excessive matting build up) there are numerous products out there which make a lot of performance claims. Some products claim that they can fracture the soil-matting with high pressure or harsh chemicals. These products attempt to raise the permeability of the soil-rock boundary. These processes are usually temporary and fail when the matting grows back together. I prefer adding enzymes to the waste stream before the water enters the leach field. The best way to do this is to add a tablet feeder to the leach line, between the septic tank and the leach field. In this case the wastewater is directly dosed with an active enzyme just before entering the leach field. The enzyme is engineered to effectively break down the matting and to restore the leach field to its near original condition. Obviously, if there are excessive synthetic fibers in the matting, then break down of the fibers is very hard to accomplish. In most cases, the direct dosing of the water stream is quite effective. In my experience, I have not seen a case where the direct dosing using a NORWECO Bio-Perc or similar product did not work.

In summary, you should try to take care of your complete septic system. Use good septic system conditioners and if you are in a failed leach line scenario, then I would recommend using both a conditioner and a continuous direct dosing approach. The combinations of both approaches should be quite effective and extend your complete septic system life. Also, the cost associated with septic tank pumping has escalated over the last five years or so, so a good septic tank conditioner can greatly reduce septic pumping frequency. I used to have to pump my septic tank every 2 to 3 years. Since I’ve been regularly using a conditioner, I have not pumped my septic tank for over 5 years. It saves you money.

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