Practical Methods of Sewage Disposal for Residences, Hotels and Institutions

by Henry N. Ogden; H. Burdett Cleveland

Fig. 35.—Double Y-Branch with Valves on Branches of Main Carrier.

These underdrains should be placed at least four feet below the surface, and inspection pipes should be placed over the outlets of the underdrains or at the points where they discharge into a main underdrain, in order to afford opportunity to determine if all portions of the irrigation field are properly caring for the effluent. To provide for the placing of the inspection pipes, a length of vitrified tile with a Tee may be placed on each line of underdrain tiling near its junction with the main underdrain. On this Tee, two or three lengths of vitrified tile may be set, reaching to the ground surface and provided with a removable wooden cover or a vitrified tile cap. This provision for inspection is necessary where underdrains must be laid and where the pollution of a stream is to be prevented, since it is often found that through the activities of burrowing animals direct outlets from the distributing tiling to the underdrains are formed and the final effluent is therefore not sufficiently purified by seepage through the soil. It is desirable for this reason to omit the underdrains when possible, and in some instances a blind ditch may be constructed around two or three sides of the field in order to intercept the ground-water flow and to lower the ground-water level at the field, thus better insuring proper seepage of the effluent distributed by the sub-surface tiling.

Fig. 36.—Sub-surface Tiling System with Underdrains.

The essential features of the sub-surface irrigation system of sewage disposal have been outlined above, and it may be said that this method is especially adapted to the residence or single house. The method may be employed with success to dispose of sewage from country clubs and summer hotels, provided the soil conditions are favorable and proper areas may be utilized. In these cases the comparatively short period during each year in which the system is in use and the resulting long periods of rest give opportunity for a recuperation of the soil and permit the use of this system in comparatively large installations where, under continuous operation, a different method of disposal would be indicated. It should be borne in mind, however, that when any doubt arises as to the suitability of the soil to care for sewage by this method, and especially where considerable expense would be involved in the installation of the system, competent engineering advice should be sought by property owners before the installation is undertaken. In fact, it is advisable in the case of all large plants of this type to employ the services of a sanitary engineer to lay out the system, since the matter of accurate gradients and proper operating arrangements then becomes very essential to the success of the undertaking.

While it is not generally advisable to arrange for the disposal of sewage by sub-surface irrigation when the number of persons served by the sewer exceeds two hundred, this method will be found a most satisfactory one if the general conditions at any point are favorable to its use as heretofore described, and in such cases the adoption of this system is strongly recommended to the owners of residences, summer camps, summer hotels and boarding-houses, and to the managers of moderate-sized institutions and of country clubs who must meet the problem of properly disposing of sewage on their own premises.

CHAPTER V
SEWAGE FILTERS

It has been shown that the selection of the type of plant best suited to solve the sewage-disposal problem at any given place depends on several factors and can be safely made only after a consideration and study of such local conditions as the character of the soil, the area available, the presence and nearness to the surface of ground water, and the local topographical conditions. If sub-surface irrigation is not feasible, when, for instance, the soil is nearly impervious to water or when, in the case of a wet soil, adequate underdrainage is not possible, some form of artificial filter must be constructed to complete the reduction of the sewage where the effluent from the settling tank may not properly be discharged directly into a stream.

If such a filter is to be constructed, the kind most suitable depends, in turn, upon several factors, such as the degree of purification to be attained, the suitability of the available areas or locations for the different types of filters, the operating head or fall available, and the relative cost of the sand, gravel, broken stone, or furnace slag which may be used as material for the filter bed.