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On-Site Wastewater Systems Septic Tanks and Distribution Boxes

A septic system includes the septic tank, drain field, and soil beneath the drain field. A pipe coming from the house carrying the contents of the toilets and sinks goes into a watertight container in the ground outside of the house. It is made of a durable material which is resistant to corrosion or decay. The material of the tank may be concrete, some form of reinforced fiber, polyethylene, or coated metal. There should be inspection ports which are secure in the top of the tank to be able to determine what is occurring within the tank and to allow the removal of accumulated sludge and scum. The length to width ratio of the tank and the liquid depth are very important considerations in the construction of the septic tank. (In the 1950s, the minimum size septic tank for a three-bedroom home was 500 gallons and for four-bedroom home was 750 gallons. By today’s standards these are far too small, since one of the main purposes of the tank is to allow for as much retention time as possible to allow the separation and movement of the oil and grease upward and the settleable solids to the bottom of the tank.) The tank may have two or three sections which are used to better remove suspended solids from the liquid. Inlet baffles force the incoming wastewater downward and the outlet baffles, unless they are overwhelmed by the amount of liquid flow, should keep the scum and solids from leaving the tank thereby not allowing these substances to move out into the disposal field along with the effluent. The settle- able solids typically settle to the bottom of the tank while the grease and scum rises to the surface. The biological process has begun and there is decomposition of the material by the bacteria which are using anaerobic digestion on the solids to create liquids and gases.

A solid pipe leads from the septic tank to the header which then sends the effluent to perforated pipes within the field, or the septic tank is connected to a distribution box which has several openings leading out to the effluent disposal areas, which may consist of various types of systems, all with the purpose of using the surrounding soil for dispersal of the liquid.

The effluent in the soil is further treated by microorganisms in an aerobic manner. (See below for different types of effluent disposal systems.) This is typically a gravity flow system from the house to the effluent disposal area. Problems related to septic tanks and distribution boxes are usually caused by improperly installing them causing them to malfunction, not enough depth in the ground to place the septic tank because of bedrock or high seasonal water tables, and lack of proper maintenance on a regular basis. Other problems are related to dumping unnecessary items into the toilets including grease, wash water from floors, unwanted chemicals, cleaners, disposable diapers, sand and grit, old pharmaceuticals, remnants of garbage, cigarettes, etc. Garbage grinders cause substantial problems because the remaining ground material helps fill up the septic tank. The worst problem of all is the overuse of water by the residents of the property, whether this occurs through extended shower time, plumbing leaks, or running the water unnecessarily in various parts of the house into the sinks and drains.

Sewage system failure can be easily seen in sewage backup on the ground, and sewage backflow into the drains of showers, sinks, and toilets. Odors coming from the drain field or from the water supply of the properties downhill or the well on this property may indicate system failure.

Best Practices in Installation and Maintenance of Septic Tanks and Distribution Boxes

  • • Obtain information about the seasonal high water table and how close bedrock is to the surface on the housing site to predetermine where the house and septic tank system can be placed to avoid problems of design and installation of the system.
  • • Make sure that all regulations are observed concerning appropriate setbacks from water supply, bodies of water, property lines, houses, and drainage lines in planning the septic tank system including the location of the septic tank and distribution box or header.
  • • Provide a properly sized, minimum two-compartment septic tank, based on the usage of the system and the projected volume of liquid entering the unit at peak times. Hydraulic residence time should be between 6 and 24 hours. Typically, the minimum size is 1000 gallons or more.
  • • In order to protect groundwater, it is necessary to have a sufficiently large lot exceeding one half acre per house for a large subdivision utilizing septic tank systems.
  • • Do not install the septic tank or effluent distribution system when the soil is wet.
  • • Provide immediate access to the septic tank.
  • • Determine if all of the pipes leading from the house to the septic tank to the distribution box and the effluent disposal system are downhill in an appropriate slope in a gravity system.
  • • Determine if the septic tank, header, or distribution box is on level original ground and not fill material.
  • • Use effluent screens, which are a physical device placed on the outlet pipe of the septic tank to help remove solids from the effluent before it goes on to the distribution box, to assist in preventing solids and non-biodegradable material from entering the drain field and clogging it. (See endnote 4.)
  • • Never enter a septic tank or cesspool that has been used or work alone on these units because of the many dangers which can cause illness or death.
  • • Check tank covers and make sure they are safe and put on securely.
  • • Do not bend or lean over septic tanks or cesspools.
  • • Determine if there are sewage backups, odors, or seepage onto the ground or into nearby water sources when inspecting the septic tank system.
  • • Determine if the sludge is accumulating rapidly and have the tank cleaned out by a licensed sewage hauler on a periodic basis.
  • • If a system does fail, have the septic tank and distribution box pumped out by a licensed hauler and allow the system to rest for several days before use again.
  • • Do not wear contaminated clothing from working with the septic tank system in the home and make sure that the individual’s tetanus inoculations are current.
  • • If the septic tank is no longer being used, the material inside called septage, which consists of an odorous slurry of organic and inorganic material containing hair, nutrients, pathogenic microorganisms, oil, grease, chemicals, and whatever else has been thrown down the toilet over the years, should be pumped out by a licensed individual who will dispose of the contents in an appropriate manner. Then crush the tank in place and backfill the area. Grade the area and plant grass over it.
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