This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
Having thus far dealt with the general question of the disposal of sewage, it is neccessary to say a few words upon that very difficult problem of the disposal of sewage from isolated houses, which have not the advantage of being con-nected with any genera] system of sewerage. A number of the previous remarks will apply in considering this question, but, of course, unless the isolated house is a large establishment, such as an asylum, hospital, gaol, hotel, school, large mansion, or something of the kind, it would be an expensive if not an altogether unwarrantable proceeding to adopt a chemical precipitation or other process for dealing with the sewage; nor might it be possible, on the other hand, to find sufficient land to take the sewage on the irrigation or filtration system, although in some cases, even where there is but little available land, this latter method might be advantageously adopted, and the remarks in the preceding pages on these systems are worthy of attention in connection with this question. Let us, however, deal with the problem of the disposal of the sewage from an isolated cottage or small residence.
Hitherto the methods mostly adopted in connection with such houses have been either privy-middens or cesspools, as being the most convenient and least expensive methods for getting rid of the sewage-matters. With regard to the former method, all the necessary remarks have been made in the chapter dealing with "Interception" or dry systems, so that the cesspool only remains to be considered.
The cesspool has been found - and is still found - to be the most convenient method for disposing of the sewage from isolated establishments, but it is almost unnecessary to state that such an arrangement is barbarous and insanitary, especially where, as in the majority of cases, the cesspool is badly situated and wretchedly constructed. Other books have dealt at length with the evils arising from ill designed and badly-situated cesspools, especially that delightful book on Dangers to Health, by T. Pridgin Tealc. M.A, BO that it is unnecessary to say more upon the subject, but rather to point out what considerations are necessary to mitigate as much as possible this, at present, requisite adjunct to many houses; and it will be the object of these pages to endeavour to point out some of the more modern methods for effecting this purpose.
The choice of position must be guided by the available land, the position of the house, the gradient of the land, and above all by the "dip" of the subsoilstrata and the position of the well or water-supply. One of the questions often given to the candidates at the examinations held by the Sanitary Institute for pass certificates for fitness as a Sanitary Inspector, is as follows: - A sketch, similar to that which is here given, is laid before the candidate, and he is asked, "Where would you put the well, and where the cesspool in this case, where there is no sewage-system and no water-supply?" In giving the answer, the candidate must consider the question of the fall of the ground, which is obviously from the road towards the river, and the flow of the river, which is in an easterly direction. The correct answer is purposely not given, but is left to the ingenuity of the readers of these pages.
Fig. 440.- Plan of Country-house and Grounds.
Having settled the position, it is necessary to consider the size of the cesspool. This will, of course, be governed by the daily quantity of the flow of the sewage, and the interval of time to be allowed between each cleansing of the cesspool. The quantity of the daily flow depends upon the number of persons inhabiting the house, and the water-supply. That great sanitarian, Dr. Edmund A. Parkes, in his Manual of Practical Hygiene, states that "in poor families who draw water from wells, I have found the amount to vary from 2 to 4 gallons per head, but then there was certainly not perfect cleanliness"; and further on he states, after quoting various authorities, " I believe we may safely estimate that for personal and domestic use, without baths, 12 gallons per head daily should be given as an usual minimum supply, and with baths and perfect cleanliness 16 gallons should be used. This makes no allowance for water-closets or for unavoidable waste."
It is probable that these observations of Dr. Parkes hold good to the present day. so that, as 6 ¼ gallons of sewage equal a cubic foot, the dimensions of the cesspool can be easily calculated, when we know the exact amount of daily flow from a given number of persons, and have decided how often the cesspool should be emptied. If any part of the rainfall enters the drains, the calculations will be somewhat more complicated.1 Authorities on this subject state that a cesspool should be emptied at least once a week, but it is much to be feared that, owing to the nuisance and expense of this operation, much longer intervals are allowed to elapse between the cleansings, and this is specially the case where there is an overflow from the cesspool into an adjoining ditch or stream, or where, as in the majority of cases, the cesspool is steined with open brick or stonework so as to allow the liquid contents to soak into and pollute the surrounding soil, the solid matter remaining behind in a terribly decomposing condition.
Having then settled the dimensions, it is necessary to design the shape of the cesspool. It is found geometrically that the largest area is obtained, with a given amount of material, by a circular chamber, and in addition to this such a shape has considerable resisting power, and, if properly designed, is more easily cleansed. Thus, for a simple cesspool, the design shown in Fig. 441 meets most of the requirements.
The construction of the cesspool is a matter of great importance. In order to make the cesspool water-tight, it is a good plan to excavate the ground sufficiently wide that the cesspool can be surrounded with at least 6 inches of well-puddled clay. It is almost unnecessary to say that it should be built of good hard bricks (better lined throughout with Suflfordshire blue bricks), set in Portland-cement mortar. It should be covered with a hermetically-closed door for access for cleansing, and be well ventilated.