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Seepage Pits

A seepage pit is a big hole in the ground with soil on the vertical walls which will absorb effluent. It is lined with concrete brick, block or rings with loopholes or notches. The joints should be staggered and allow passage of fluid through them into the surrounding soil. The seepage pit follows the septic tank and is used in place of a distribution field where the upper layers of soil are not conducive to the movement of effluent. Typically, new seepage pit systems are not approved by health departments or the local environmental protection agency. Where an existing seepage pit was approved in the past, under proper conditions of adequate amounts of vertical soil in the hole for removal of effluent and the percolation rate is under 30 minutes per inch, then a new seepage pit may be approved. The depth of the pit and the width of the hole plus the percolation rate determine the amount of absorption area available in the seepage pit for appropriate disposal of the effluent. There are numerous problems with seepage pits because of the concentration of the effluent which must be processed through the sidewalls of the unit. If the septic tank is not properly maintained, it becomes more difficult for the unit to work properly. The use of evapotranspiration is virtually eliminated as a means of getting rid of the liquid. The installation of the pit is absolutely crucial and frequently not done as planned. Maintenance of the pit is another factor. The greater concentration of the septic effluent in a small area creates the need to separate the seepage pit by much greater distances from wells and other bodies of water.

Best Practices for Seepage Pits or Dry Wells

  • • Recommended percolation test procedures for seepage pits include dig a test hole 12-48 inches in diameter and at least 10 feet below the proposed bottom of the seepage pit and check after 72 hours to determine the level of groundwater that may be present in the hole; backfill the test hole to 10 feet above the bottom of the hole or groundwater level whichever is shallower; presoak the test hole with at least 5000 gallons of water; fill the pit with water up to the cap and then record at 15-minute intervals the drop in the water level. This will help determine whether or not a seepage pit will work under normal conditions. Also have a professional conduct a soil analysis of the sides of the proposed pit.
  • • The bottom of the pit must be at least 5 feet above the seasonal high water table.
  • • Conduct construction work on seepage pits only in dry soil and after excavation scratch all surfaces to make sure they have not been sealed by the use of the equipment.
  • • The depth of the sidewalls must be at least 10 feet below the cap.
  • • Clean gravel should be backfilled around the porous inner lining of the pit up to the top of the concrete cap.
  • • If more than one pit is used, all pits shall be 20 feet apart from the edge of any other.
  • • A riser with a 9-inch diameter opening with a cap on it should be installed in the pit so that the pit can be cleaned out properly by a professional hauler. Frequent inspection of the pit is necessary.

Aerobic Treatment (See endnote 11)

In an aerobic treatment system, a mechanism is used to inject air throughout the treatment tank thereby helping aerobic bacteria degrade the solids. This helps achieve a superior effluent quality. Typically, a system of this type would be chosen where the regular septic systems are failing. Problems are: the unit is more expensive to operate than a septic tank; electricity is required and a back-up system is mandatory in areas where there is frequent electrical failure; mechanical parts can break down; more frequent routine maintenance is needed than for a septic tank; sudden surges of heavy loads of solids can upset the system; more nitrates may be released to groundwater than from a septic system; and pretreatment steps are needed to remove grease, trash, garbage grindings, or other materials which are not biodegradable.

Best Practices for Aerobic Treatment Systems

  • • Use a manufacturer that carries the NSF International class I certification for its aerobic treatment systems for equipment purchased for the effluent disposal site.
  • • Use a pretreatment device of a trash trap, septic tank, or comminutor to remove grease, trash, garbage, and non-biodegradable materials prior to the settling chamber for primary treatment and settling of sludge. The effluent then goes into the aerated chamber and aerobic decomposition occurs. The amount of effluent flowing must be controlled to prevent overwhelming the system.
  • • Frequent maintenance must be provided to keep the system effectively working.
  • • Provide alternate source of electricity if the area is subject to electrical failure.
  • • Do not diminish the size of the effluent disposal system since the liquid flow is still the same as if it were coming from a septic tank although the effluent is far cleaner.
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