![]() When that happens, the biomat completely clogs the soil and does not allow the sewage effluent to flow out of the trench. If the solids accumulating in the septic tank are never pumped out, however, they can flow into the trenches and accumulate into an intensive biomat that becomes too thick. It helps remove many of the germs and chemical pollutants. The soil can also retain certain chemicals, including phosphorus and some forms of nitrogen.Ī special zone, called a biomat, forms in the upper 1 to 6 inches of the soil at the soil/trench interface just below the trench bottom. The soil adsorbs some of the smaller germs, such as viruses, until they are destroyed. As sewage effluent enters and flows through the ground, soil particles filter out many of the bacteria that can cause diseases. These materials provide a void space in the trench to allow distribution of the effluent to the trench bottom. There are also “gravel-less” trenches used where plastic louvered chambers, polystyrene aggregate, tire chip aggregate, or large diameter pipes are used in place of the gravel aggregate. Effluent flows into the perforated pipe in the trenches, passes through the holes in the pipe, and then trickles down through the gravel to the soil ( Figure 3). Sewage effluent flows out of the tank as a cloudy liquid that still contains many disease-causing germs and environmental pollutants. ![]() The real treatment of the wastewater occurs in the soil beneath the drainfield. The purpose of the drainfield is to deliver the liquid sewage effluent to the soil. What Happens in the Drainfield and the Soil? Skip to What Happens in the Drainfield and the Soil? These are installed in place of the sanitary tee at the outlet end of the septic tank (in the second compartment shown in Figure 2). Newer septic systems installed since 1999, however, include an effluent filter in the septic tank. The retention time is necessary for separation of the solids from the liquid and for anaerobic digestion of the solids to begin in the septic tank.Īn outlet baffle (or a sanitary tee at the outlet end) prevents solids from flowing out with the liquids. After a retention time of about two days, the liquid portion (the sewage effluent) flows out of the tank through the outlet pipe. The tank’s primary purpose is to retain the solids. As wastewater flows into the tank, the heavier solid materials settle to the bottom (forming a sludge layer), and the lighter greases and fats float to the top (forming a scum layer). Even waters from the shower, bathtub, and washing machine can contain disease-causing germs or environmental pollutants. SepticSmart – EPA offers advice on proper septic care and brochures and factsheets for homeowners.Ĭraft3's Clean Water Loans - Craft3 offers financing for replacement of septic systems in many areas of Washington.What Takes Place in the Septic Tank? Skip to What Takes Place in the Septic Tank?Īll of the wastewaters from the home should flow into the septic tank. ![]() Local Health Department – Your local health agency can help you locate your septic system, provide a list of certified septic pumpers, and if available, certify you to do your own septic system inspections. Protects Your Property Value – An unusable septic system or one in disrepair will lower your property value and poses a potentially costly legal liability. The pollutants harm local ecosystems by killing native plants, fish, and shellfish. ![]() Protects the Environment – Malfunctioning septic systems release bacteria, viruses, and chemicals that eventually enter streams, rivers, lakes, Puget Sound, and the ocean. A properly functioning septic system helps remove these pollutants so well water and nearby surface water doesn't get contaminated. Keeps You and Your Neighbors Healthy – Household wastewater is loaded with disease-causing bacteria and viruses, as well as high levels of nitrogen and phosphorus. Saves You Money – Regular maintenance fees of a few hundred dollars every few years is a bargain compared to the cost of repairing or replacing a malfunctioning septic system, which can cost thousands. Septic systems use a combination of nature and time-tested technology to treat wastewater from household plumbing produced by bathrooms, kitchen drains, and laundry. Do-It-Yourself Septic System Inspection VideoĬommon in rural areas without centralized sewer systems, septic systems are underground wastewater treatment structures that you own and operate.
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