septic tank connected to city sewer line

[Celeste&Mike]

We just bought an old house (turn of the century) in a rural area. The house has an old septic tank. A few years ago the previous owner was told that the pipe from the septic tank which went into a drainage ditch was illegal and had to be removed. So instead of bypassing the septic tank and running a new sewer line, he simply connected the septic tank pipe to the city sewer drainage line. What problems could this cause in the future?? Does anybody have any idea??

[LazyPup]

In order to answer your question let us first begin by examining how a septic tank waste treatment system actually works.

Although there are some variations, primarily a septic tank waste treatment system can the thought of as having three sections. The actual septic tank is usually divided into two chambers by an internal baffle.

The house sewer line is connected to the first chamber which is called the sediment chamber". As the effluent enters the sediment chamber any non-digestible solids normally settle to the bottom of the chamber. These may be such things as metals, plastics or bits of bone which may be present in the waste. During this phase solid wastes such as fecal material are broken down into a thick watery sludge that passes through the baffle into the digester chamber.

In the digester chamber anaerobic bacteria break down the waste primarily by consuming the organic materials which then leaves gray water which is then passed through an overflow pipe into the leach field system. The leach field pipes are buried relatively close to the surface of the soil and a small amount of air can penetrate to soil into the leachfield pipes. This provides an oxygen supply that will support aerobic bacteria which perform the final stages of digesting the effluent. The remaining water, which does contain some organic nutrients is then passed through the holes in the leach field piping and is absorbed into the soil where the water and organic nutrients are primarily consumed by grass or vegetation covering the leach field.

By the time the liquid enters the leachfield it is no longer toxic and primarily presents no health risks, howerever it does contain a very heavy concentration of organic nutrients, basically it is a liquid fertilizer. If that liquid were to be indescriminately discharged into the surface watershed those nutrients promote the growth of fibracious algae in the watershed. The algae appears like a thick mat of hair and in a worst case scenario it will blockup the gills of fish or choke out aquatic plants that live in that water resulting in the death of the fish or the stagnation of the watershed.

They are now building a variation of the septic tank which has a third chamber called the aeration chamber. These are normally installed in areas where the soil will not perk for a regular leachbed. With the addition of the aeration chamber the final digesting that would nomally take place by the aerobic bacteria in the leach bed is done in the aereation chamber, which is supplied with air by an external air compressor and small air nozzles built into the tank. Most of these units are also equiped with a chlorinator that requires weekly maintenance to put the large swimming pool type chlorine pucks in a dispenser. The output from these tanks can then be discharged directly into the watershed.

In most communities as the public sewer infrastructure is expanded into the rural areas that formerly only had septic systems the homeowner is permitted to continue using their septic system until such time as there is a problem with the septic system. When a problem is noted the homeowner is denied the opportunity to repair the septic system and must at that time make final connection into the public sewer. Normally a septic tank is located behind the structure while the public sewer is in an easement beside the roadway in front of the structure so the normal method of changing over is to run a house sewer line from the structure to the municipal sewer and abandone the use of the septic tank.

There are specific codes governing the methods used to abandone a septic tank, however those codes change dramatically from one community to another.

Fudamentally when a septic tank is abandoned it must be disconnected from the house sewer line then it must be pumped out. Some jurisdictions will then require the tank to be steam cleaned while others may require it to be pressure washed and in some localities no cleaning is required. Normally we are then required to punch a large hole through the bottom of the tank and the tank is then filled with sand and everything is backfilled.

In the above post the original descrepancy was in regard to the leach field, but there is no mention of any problems with the septic tank itself so the cheapest solution at the time may well have been to just run the leach field line to the municipal sewer.

On the down side, if the septic tank itself were to suffer a catastrophic failure you would most likely be required to route the house sewer line directly to the municipal sewer then take the appropriate steps to abandone the exisiting tank.

On the upside, a septic tank is primarily just a large fiberglass or concrete tank and there are no internal parts to fail. Depending upon the amount of non-digestible wastes that go into your DWV system it may be necessary to have the tank pumped periodically to remove the non-digestible sludge, but even that would most likely only occur about once every 10 to 15 yrs. The only other thing that you should be concerned about is to make sure no one drives a heavy vehicle over the tank which could break the tank top and would then require immediate abandonment procedures.