Septic Tank Abandonment

What is a septic tank?

A septic tank is a large holding tank that is designed by an engineer as part of an entire septic system. A septic system manages and breaks-down the sewage, that results from structures with toilets, sinks, showers, tubs, dishwashers and clothes washing facilities. Any effluent that is required to be removed from a structure, into the sanitary line, must be either discharged into a municipal or private sewer system or into a septic system. The septic system was originally designed to allow the development of land that does not have immediate access to a sewer line in the street, or adjacent properties.

The septic tank is designed to accommodate the number of individuals inhabiting a structure, and in residential building, the size is calculated based upon the number of bedrooms. Many individuals, initially assume that the sizing of the septic system will be based upon the number of bathrooms or sewage producing fixtures installed within the structure. This is incorrect, the number of actual inhabitants, and therefore the usage of the sewage producing systems, is the relative factor for septic system design.

The actual septic tanks function, is based on the concept that solids will settle, and liquid will remain on the top of the tank. In this manner, the liquid sewage that emanates from a structure into the septic tank will remain on the top and surface of the tank, while the solids settle out. Based upon this physical property, the tank is designed to allow the liquid to flow out of the top of the tank, into septic fields. The septic fields are designed, based upon the size of the septic tank, to distribute the liquid into the surrounding earth, and allow nature and sunlight to effectively cleanse the bacteria out of the sewage. There is substantially more to the proper design and function of a septic tank, however this webpage is a discussion of abandonment, and further technical information on septic systems and the engineering aspects of them is not necessary for this discussion.

When a septic system is abandoned, it is usually due to the installation of a municipal or private sewage disposal system.

An excellent example of this is the abandonment of all the independent septic systems in the Florida Keys. Due to environmental concerns, the EPA ( Environmental Protection Agency ) required that all residents and businesses within the Florida Keys connect to commercial sewage treatment facilities. Prior to this directive, all the sewage in the Keys was managed by individual septic systems. Due to the soil makeup of the Keys, basically limestone and coral, as well as the lack of elevation, the resultant effluent from these multiple septic systems was leaching into the pristine waters of the Florida Keys. To amplify the situation, the depth of the water surrounding the Florida Keys is very shallow. The old axiom, the solution to pollution is dilution, was not occurring, due to the minimum quantities of sea water surrounding the Florida Keys. Therefore, there was substantial pollution occurring around the shoreline of the Keys promoting the need to connect to modern sewage treatment facilities .

The result was forced abandonment of all of the septic systems and construction of four large, commercial sewage treatment facilities, along the length of the Keys, to process all of the sewage created by inhabitants of the Florida Keys.

Four large sewage treatment plants were constructed, miles of sanitary lines were run down Overseas Highway, and thousands of septic systems abandoned.

Due to the number of septic systems that were abandoned, there resulted in thousands of septic tanks that were not required and were left abandoned without any use.

Proper abandonment of all of these septic tanks was required.

What are some of the processes that are used to abandon an existing septic tank?

1.) Removal / The most complete method of any type of abandonment, is total removal of the system. This method of abandonment is easily performed, if the surrounding material around the system is gravel, sand or common earth. In the Florida Keys, the element surrounding the systems was either limestone or coral. The actual removal of the systems inclusive of the tanks had to be performed in limestone or coral. This removal of the systems was more difficult due to the surrounding makeup of the material that the systems were buried in.

2.) Infill / The filling of the system is another means of abandonment. Whether the system is filled with sand, stone or even light weight concrete, the filling of the system is normally acceptable by the local building officials. The difficulty with this method of abandonment, is the assurance that the entire system is actually filled in. There can be no voids, air pockets, or areas of the system that are left open or hollow. This assurance must be verified by an engineering or testing firm that will certify that the system has been properly filled. In most instances, the tank itself must be perforated or broken to ensure that any water or moisture drains out of the system as it is being filled.

3.) Reuse / There is a provision that will allow the reuse of the septic tank itself for another purpose. Septic tanks are designed for sewage accumulation, and are not designed for any type of fuel, chemicals, etc. Based upon this initial design, the reuse of the tank, must comply with the original design intent. One interesting application for reuse of the existing septic tank, is to accumulate rain water.   This type of reuse was especially popular in the Florida Keys due to their lack of fresh water. The accumulation of rain water as a grey water cistern is an interesting and useful method of finding an alternate means of utilizing an existing septic tank. This accumulated rain water can be used for a grey water application within the home, such as flushing toilets, or for irrigation of the surrounding foliage.

There are two very important safety aspects of abandoning a septic tank or any other tank that has been installed in the earth.

1.) Confined space hazard / A tank, such as a septic tank, should NEVER be entered into, without all of the proper breathing apparatus, as well as emergency harnesses, to immediately pull the person entering the tank out of the access hatch. Confined spaces, such as this, can have poisonous gases built up in the confined space that are undetectable without the proper instrumentation. There have been several instances, where a person entering a confined space has been overcome and has died within the confined space.


2.) Collapse / Any tank, pipe or vessel that is buried underground, poses a possibility of collapse. An abandoned tank or other open space vessel, can deteriorate and create an extremely hazardous situation for an individual or vehicle that exerts any downward pressure on the tank. The deterioration that can occur due to water, moisture, ice, earth pressure, etc. on an underground tank or vessel can weaken its ability to withstand the pressure. If this occurs the failure of the structure and the collapse of the tank or vessel is a strong possibility. Care must be taken to ensure that all underground tanks or vessels are properly maintained or properly abandoned for safety purposes.

The abandonment of a septic tank is a relatively common occurrence, however alternate uses should be considered prior to the loss of an asset that is existing and could have an alternate use.

Normally a small site contractor will be capable of properly and professionally abandoning your existing septic tank.


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