On-Lot Sewage Systems

What is an On-lot Sewage System? Unless you have recently been through the process of installing or repairing a septic system, or if you have recently moved from an urban environment, you are probably unfamiliar with the on-lot sewage system.

On-Lot Systems


On-lot sewage systems are composed of two primary parts: a treatment tank and an absorption area.
The treatment tanks remove the settleable and floatable solids from the wastewater. The absorption area then utilizes the soil to filter and treat the remaining effluent before it reaches the water table. By removing the solids, the treatment tanks protect the absorption area from becoming clogged. Proper maintenance of the treatment tanks will prevent more costly problems with the absorption area.

Public Sewage System


In highly developed areas the usual method of sewage disposal is a public sewage system. The wastes from your home move through a pipe out of your house to a common sewer line and ultimately are treated at a municipal sewage treatment plant. In most cases, the treated wastewater is then discharged into a nearby creek or river. In South Middleton Township, less than 40% of the residents are served by such public sewerage facilities. The other 60% are served by on-lot sewage systems.

Household Sewage Composition


Household sewage is a combination of wastewater from:
  • Bathtubs
  • Dishwashers
  • Garbage disposals
  • Showers
  • Sinks
  • Toilets
  • Washing machines
  • Water softeners
The conventional 7 - 8 gallon flush toilet is the largest source of wastewater in most households.

On-Lot System Types


Every homeowner should be aware of what type of sewage disposal system they have. The type of maintenance and care may vary depending on the type of system serving the home. The basic types of on-lot systems in South Middleton Township are:
  • Cesspool
  • Septic tanks or aerobic tank with elevated sand mound
  • Septic tanks or aerobic tank with seepage pits
  • Septic tanks or aerobic tank with standard trenches
  • Septic tanks with seepage pit
  1. Septic Tanks
  2. In-Ground Soil Absorption Area
  3. Cesspools & Seepage Pits
  4. Elevated Sand Mounds
The septic tank is a watertight chamber constructed of a durable material which is not subject to corrosion or decay.

Most septic tanks used in the Township have one compartment, but some are designed with two compartments. The two compartment tanks, or two single compartment tanks in series is now required and provides better settling of the solids.

Baffle Component


One of the most important components of the septic tank is the baffle. The inlet baffle forces the wastewater from the building sewer line down into the tank instead of across the surface of the tank and into the outlet pipe leading to the absorption area.

Down the Drain


South Middleton Township has a limited number of videos on septic systems entitled "Down the Drain." Proper maintenance of your septic system is extremely important to keep it working properly. If you would like to borrow a copy of this 11.5 minute video, please contact the Township office.