Intercepting sewers may rightly be called collecting sewers. They are constructed of poured concrete and are placed at depths in the ground varying from 15 to 100 feet, depending entirely on the natural contour of the soil. These are the sewers that connect directly to your own bathtubs and other bathroom fixtures; bathroom faucets and the like.



The intercepting sewer does not have, as a rule, any connections to it other than the smaller tributary arrangement. These sewers vary in size from 2 to 10 feet in diameter and serve as a direct run to the disposal plant.

The more recent installations of intercepting sewers are constructed in the shape of an inverted egg to assure a deeper and naturally a more self-cleansing flow. There are also sewers of oval and round design in common use.

The older type of intercepting sewers was constructed of brick and the interior was plastered with a rich cement mortar to make it water-tight. Some of the first public sewers were constructed of wood. Both of these early types of sewer installations are now obsolete.

As society gets more complicated, so do the jobs of our plumbers and contractors. Now they have a plethora of different projects to undertake, from indoor hot tubs to an individual swim spa for aqua therapy.

Before the contractor is invited to submit a figure for the construction of an intercepting sewer, he is given a very concise specification calling for certain kinds of materials, type of sewer, grades, data of soil test drillings and construction procedure, as well as many other important phases involved in the installation. Once the contract has been awarded, the procedure involved in construction is somewhat standard.

Because the intercepting sewer usually is many feet below the surface of the street it would be impractical to attempt to lay it by the open trench method, hence it must be installed in a tunnel.

Shafts are dug at intervals of 750 to 1,500 feet or more to the depth specified by the engineering authority responsible for the work. Where the soil is of a substantial nature, lateral tunnels may be dug from the bottom of each shaft to meet at some point between them, or they may be dug from one shaft to the other.

This is often referred to as the mining process. The tunnel is dug accurately, for its walls may serve as the outside surface of the finished concrete sewer. The tunnel may be made in the form of an octagon or, where unstable soil is encountered, it may be made rectangular in shape. Construction specifications are exact and require perfect grading and alignment.

These types of sewers are where all domestic drains converge. So everybody's wash tub and bathtub water, even Jacuzzi tub water will end up here.

The sewer proper usually is poured in sections. The length of the section which may be poured is determined by the stability of the soil. The bottom half of the sewer is framed first and concrete is then poured into it. A 4x4 timber is pressed into the soft concrete to form a depression, thus providing a more substantial bond for the top half of the sewer, which is poured later.