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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.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
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
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. Thetwo compartment tanks, or two single compartment tanks in series is now required and provides better settling of the solids.
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.
Most septic tanks used in the Township have one compartment, but some are designed with two compartments. The
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.
The soil absorption area may be an in-ground seepage bed, a set of trenches, or an elevated sand mound. The type of system installed will depend on the slope of the property, the depth of usable soil and the percolation rate.
State law requires that there be at least four feet of usable soil for the effluent to percolate through before it reaches the water table.
The soil absorption area receives the liquid effluent from the septic tanks and distributes it over a specific area. The effluent then filters through the soil under the pipes and is treated chemically and bacterially by the components of the soil. The size of the soil absorption area is based on the size of the house and the percolation rate of the soil.
Equal distribution of the effluent is very important to the proper functioning of the system. Uneven distribution of the effluent could result on one of the areas being overloaded, leading to a failure of the system. Most trenches and in-ground bed systems utilize gravity distribution to the absorption area from the septic tanks.
State law requires that there be at least four feet of usable soil for the effluent to percolate through before it reaches the water table.
How it Works
The soil absorption area receives the liquid effluent from the septic tanks and distributes it over a specific area. The effluent then filters through the soil under the pipes and is treated chemically and bacterially by the components of the soil. The size of the soil absorption area is based on the size of the house and the percolation rate of the soil.
Equal Distribution
Equal distribution of the effluent is very important to the proper functioning of the system. Uneven distribution of the effluent could result on one of the areas being overloaded, leading to a failure of the system. Most trenches and in-ground bed systems utilize gravity distribution to the absorption area from the septic tanks.
Cesspools and septic tanks with seepage pits are no longer permitted for new installations or as corrective measures for malfunctioning systems. However, many older homes with systems installed prior to 1970 may have these systems presently in use.
Cesspools
Cesspools are constructed of open-jointed walls (concrete block or stone) and open bottoms. The solids in the wastewater settle to the bottom of the cesspool, while the effluent seeps through the jointed walls and bottom. If the cesspool is not properly cared for, the sidewalls and bottom tend to plug up with solids. This may result in sewage backing up into the house or being discharged to the ground surface.Septic Tanks With Seepage Pits
The sewage system with a septic tank and seepage pit partially reduces the clogging problems inherent in cesspools. The septic tank provides for the separation of solids from the liquid while storing the accumulated solids. The seepage pit allows the effluent from the septic tank to infiltrate into the soil. The seepage pit is constructed similarly to a cesspool, except that there is a layer of rock or aggregate placed around the concrete blocks or stone and the open bottom.Current Regulations
Current state regulations require better treatment of the effluent than either the cesspool or septic tank with a seepage pit can provide. These older types of systems frequently lead to the contamination of groundwater due to the improper renovation of the sewage effluent prior to reaching the water table. Current methods of sewage disposal have been designed to provide for more effective renovation of the effluent. They utilize more soil area to absorb the-effluent and provide for aerobic (oxygenated) conditions in the soil which are more efficient in treating the waste materials.
The elevated sand mound system is used in areas of the Township with reduced permeability, shallow soils and poor drainage characteristics. Soils in these areas require the addition of sand above the ground to provide for adequate renovation of the sewage prior to reaching the water table.