On Site Sewage Systems

by Scott Andress & Cameron Jordan

Fall 1996

What is an On-Lot Sewage System?

Landscaping the Absorption Area

Maintenance of the On-Lot Sewage System

What is an On-Lot Sewage System?

Septic systems are a means of disposal of hosehold wastewater for homes that are connected to a public sewer system. On-lot sewage systems are composed of two primary parts: (1) a septic tank, and (2) an absorption area. The septic tank removes the settleable and floatable solids from the wastewater. The absorption area then uses the soil to filter and treat the remaining effluent before it reaches the water table.

Household sewage is a combination of wastewater from toilets, showers, tubs, sinks, washing machings, dishwashers and garbage disposals. The toilet is the largest source of wastewater in most households.

Source	Percentage
Sources of Household Sewage
Toilet	40
Bathing	30
Laundry	15
Kitchen	10

SEPTIC TANKS

The septic tank is a water tight chamber constructed of a durable material which is not subject to corrosion or decay. Most septic tanks have one compartment, but some are designed with two. The two compartment tanks are not required but they do provide better settling of the solids. One of the most important components of the septic tank is the baffle. The inlet baffle forces the waste from the building sewer line down into the tank instaed of across the surface to the outlet pipe leading to the absorption area. The outlet baffle prevents the scum layer from moving into the soil absorption area.

ABSORPTION TRENCHES

The soil absorption area recieves the liquid effluent from the septic tank 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 absorption area is based on the size of the house and the permeablity of the soil.

A standard trench absorption area consists of two or more excevated trenches in which perforate pipes distribute the effluent into a layer of crushed stone under the pipes. The effluent is then absorbed into the soil where it is renovated.

LANDSCAPING THE ABSORPTION AREA

After the area has been installed, inspected by the Health Department and covered by the contractor, there should not be any major changes to the grade of the property. The system was installed at a specific depth due to soil conditions, and any changes in the contours of the property could cause problems for the system. Grass should be planted immediately on the absorption area to prevent erosion. Large trees and shrubs must not be planted on or near the area because roots could clog the distribution lines.

MAINTENANCE OF THE ON-LOT SEWAGE SYSTEM

To insure that an on-lot system will function properly, it is important that the homeowner have regular maintenance preformed on the system.

Septic Tank Maintenance

The septic tank is designed to remove solids from the wastewater by holding the materials for atleast 24 hours. This provides time for the solids to settle and the scum and grease to rise to the top. Up to 50% of the solids retained in the tank decompose, with the remaindere accumulating in the bottom of the tank. Biological or chemical additives are not needed to aid or accelerate the decomposition of this material.

As the septic system is used, the solids accumulate on the bottom of the septic tank. As the sludge level increases, more solids are escaping into the absorption area. If the sludge accumulates too long, no settling of the solids will occur, and the solids will be able to directly enter the absorption area. These solids will clog the distribution lines and cause serious and expensive problems for the homeowner. To prevent this, the tank must be pumped out every two to three years.

Absorption Area Maintenance

The absorption area requires very little maintenance as long as the effluent being discharged to it is nearly free of solids. Solids entering the absorption area can cause considerable damage to the system by clogging the theopening in the pipes of by forming an impermeable layer over the stones. To ensure that solids do not enter the absortion area it is essential that the septic tank is pumped and maintained. For further insurance that the absorption area is functioning properly it is suggeted by the Department of Environmental Resources that:

Prevent heavy vehicles from entering the area in which the system is located.
Do not use drain cleaners or other chemical additives that may destroy the biological activity of the system.
Direct rainwater gutters away from the absorption area to avoid placing an added water burden on the system.

Ground Water Pollution Table of Contents