THE SEWERAGE OF TWO NEW HAMPSHIRE TOWNS.

BY GEO. E. WARING, JR., M. INST., C. E., NEWPORT, R. I.

It may be of interest to the readers of the report of the Board of Health in New Hampshire to be informed as to the sewerage of Keene and of Laconia, works which have been carried out on a system materially different from what had before been used in this State; this being the same system that was introduced in the city of Memphis, Tennessee, after the yellow fever epidemic of 1878-9.

It is a peculiarity of this system that it is used for the removal of foul sewage only, no rain water being admitted either from the surface of the ground or from the roofs of houses. The sizes of the sewer pipes are proportioned to the limited but uniform work of removing the daily foul waste of houses and manufacturing establishments. The lateral sewers, constituting a very large proportion of the system, are only six inches in diameter. When enough building lots have been passed to make the future maximum flow of sewage 'sufficient to fill a sewer one half full, its size is increased to eight inches, which about doubles the capacity on moderate grades. When the eight-inch sewer would run as much as half full, an increase is made to ten inches, of which the capacity is about 60 per cent more than that of the eight-inch. As no rain water is admitted for the flushing of the sewers, it becomes necessary to substitute other means for keeping them clean. This is done by placing at the head of each sewer, below the surface of the street, a small cistern, called a flushtank, and holding, when full to the level of its discharging point, about 150 gallons of clean water admitted from the water supply in a very small dribbling stream, sufficient to fill it about once in twenty-four hours. When it becomes filled, an automatic siphon is brought into operation, discharging the whole volume suddenly in a strong flushing

stream, flowing freely down the sewer and carrying with it all matter stranded by the normal flow, which, toward the upper end of each line, is not sufficient for the removal of all solids. In addition to its effect in cleansing the sewers, this discharge from the flushtank drives along the air contained above the flow in the sewer, forcing it out at the different ventilators as these are approached, and drawing in air through the ventilators which it has passed. The ventilators of the whole system are the house drains and soil pipes of all the houses connected, there being no trap between the sewer and the open mouth of the soil pipe above the houses. This ensures a free and copious ventilation of the sewers at all times; not only during the flushing from the tanks, but from a constant interchange of current between different soil pipes, influenced by the wind, by changes of temperature, by the discharge of fixtures in houses, etc. If properly cared for in the matter of obstructions, and if regularly flushed as above described, these sewers with their house drains and soil pipes are so constantly and freely ventilated that the accumulation of the gaseous products of decomposition is impossible. What is known as sewer gas" cannot exist in such a system of drainage, if the most ordinary care is taken to prevent deposits of organic matter therein. The general principles under which the system is constructed are substantially the same as those used in other sewerage work. Manholes, inspection holes, facilities for cleaning, etc. being measurably the same.

66

The system has three preponderating advantages: (a) Its cost is, on the average, not more than two fifths of that of a system arranged to remove surface water and house drainage together. (b) As it does not depend on the occasional, and frequently lacking, flushing by rain, nor on precarious and costly flushing by hand, but is, on the contrary, thoroughly washed out by automatic process every day, the accumulation of deposits, at least unperceived and neglected accumulations, cannot occur. It is one great advantage of this system that if a deposit forms which the flushtank cannot remove, it is pretty sure to make itself known by a complete stoppage of